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Davek0974
01-11-2014, 11:20 AM
Hi all,

Thinking of a project for the shop. I have a small plasma cutter, up to 12mm cut.

What would I be looking at to build an x-y table and CNC control system for it?

I have looked at plasmacam but while it is pretty superb, I don't have 10k for the project, I'm looking at home build, low cost, speed is not a requirement.

Manual height control should be ok and I'm guessing it's a. Pretty basic system as micron precision is not really required.

Looking to cut shapes and designs in steel sheet etc.

Bear in mind I have never used anything CNC before but and pretty good with electronics and welding etc. I have built an attachment for a machine at work that used a 4 axis card for a PC, but that was used only for linear feed and I wrote the program in VB.

This would need software etc that I have no idea of.

I have a massive amount of Flexlink structural aluminium which would be good for the chassis and table support frame and maybe a few stepper motors soon but not sure if it needs feedback or not?

Any ideas or links?

lakeside53
01-11-2014, 12:19 PM
Ignoring the cnc part for the moment (there are MANY reasonably simple and cost effective options...), one thing to watch out for with the plasma cutter is duty cycle. While you may be able to cut continuously in 16 gauge, at 1/2 inch it's probably quite limited. Recently I've been running into this with my small welder.

You won't need "feedback". The stepper counts are maintained by the system so it "knows" where it is. As there are no tool pressures, with the correct sized sized motors skipping counts due to overload isn't a problem.

duckman
01-11-2014, 12:35 PM
Make a down draft table, if you can do a wet bed all the better, there is a lot of fumes and dust from a plasma cutter. For what it's worth a friend of mine bought a system and after getting it assembled and building a table and wet bed with a suction fan found it was VERY SLOPPY, so he went about fixing it, he now has less than .001 backlash in both X & Y. He was one of my better employees.

JoeFin
01-11-2014, 01:02 PM
I think CNC forums has links for CNC Plasma Table kits using Mach III and Gecko Drives and a whole forum dedicated towards them

Davek0974
01-11-2014, 01:21 PM
Thanks for that, just checked and it's a smallish unit but well built, 35% at 30A and will easily cut 7-8mm steel. I am only looking to cut 1-5mm on it.

Good regarding the feedback, much cheaper.

I'm only looking to make the table around 1m square, guessing so far would say I could get away with a one sided drive on the gantry?

Davek0974
01-11-2014, 01:25 PM
Downdraft would be easy, I have a large extract duct system that I can connect into, will look into water bed as well, thanks.

What sort of software am I looking at to generate paths from pictures etc?

EddyCurr
01-11-2014, 01:26 PM
I second duckman's advice about provisions for ventilation.

I was on the sidelines nearly 3 decades ago when a local firm installed
a Linde plasma machine. This had a downdraft table and for it to be
effective at exhausting cutting smoke, not only was a fairly substantial
fan required, it was also necessary to beef up the provision for make-up
air to supply and heat air to replace what the plasma's exhaust fan was
pulling out of the building. Not a trivial consideration where winter
temperatures drop to -40F and below as they regularly do here.

That first unit had no provision for filtration. Whatever particulate matter
was light enough to remain in suspension went up the spout and into the
sky. The machine was used for HR, CR, SS and lots of galv. The following
machine had a filtration system that trapped a lot more material.

I believe the firm is on its third or fourth machine these days but I don't think
they are using a waterbed system. I looked at a small one of those on display
at Praxair a few years ago. IIRC, the water eliminated or at least greatly
reduced the ventilation/filtration requirements. However, there were some
downsides.

Incidently. Back in the 80's, the Linde used proprietary control systems. Users
could cut basic patterns provided with the machine, buy additional canned functionality
from Linde or set about piecing together their own patterns very laboriously using
G-Code (and a lot of trial/error). It was a hair-pulling time for tradesmen who
had taken the vocational route through school and then found themselves being
called upon by mgmnt to learn to operate computers so that the big new investment
would begin to pay for itself. (That wasn't my role but it happens that I played a
prominent part in freeing that first Linde machine from the shackles of its
proprietary patterns.)

Anyway, consider how fumes will be dealt with.

.

EddyCurr
01-11-2014, 01:33 PM
About the intended table size.

My vote is that if the room is available, larger is better from
the perspective of being able to start with bigger, preferably
full-sized sheets. More economic to purchase, less handling,
the potential for a lower scrap-to-finished part ratio.

Mind, handling larger sheets brings its own considerations.

.

Davek0974
01-11-2014, 01:48 PM
Hi, sorry but space is tight and intended ideas don't call for a massive table, cost is most important factor here.

John Stevenson
01-11-2014, 02:00 PM
What sort of software am I looking at to generate paths from pictures etc?

Sheetcam from Les Newell was designed from day 1 for plasma cutters.

www.sheetcam.com

Davek0974
01-11-2014, 04:56 PM
Ok thanks, what other software would be needed?

I guess there is something to control the driver boards, is that mach3 or similar?

The software part seems harder to grasp than the hardware

Dave

Mtw fdu
01-11-2014, 05:58 PM
I am doing the exact same thing. I already have an oxy/plasma table which I made and use a magnetic tracer. Now I am in the process of changing it to cnc plasma only. I have purchased BobCAD/CAM software for the drawing package and also Mach 3 the the plasma setup. I have just received a quote from Camcutcnc on a price and kit for my table including all controllers etc. They have quoted me $1100 US (I live in Australia) and have asked for more details. Maybe give them a try.

Mtw fdu.

lost_cause
01-11-2014, 06:16 PM
these can literally be as cheap or expensive as you want to make them. i've looked into it myself a few times, but space, time, and necessity aren't high enough on the priority list to even think about the cost factor. for one looking to make it as cheap as possible, there are linux based software packages (open source = free) that can save you $1000+. there are numerous builds to be found on the internet based on many types of track systems, so you can go with what is easiest or cheapest. i think you are pretty much in line as far as my knowledge goes, but here's what i think of your ideas so far:

table size of 1m x 1m: probably reasonable if size dictates. i'm sure you considered this already, but i'd also see what size sheets i can get the cheapest from my local supplier that suit the parts i would cut, and work around that. since things here are in feet, i can't say what you are likely to have available there.

one drive for each axis: probably ok for a smaller table like you are planning. since there is no resistance with a plasma or fuel torch system you don't have the forces to deal with that you would with a cutter (router, mill, etc). i'd do some research to see what people think is acceptable for a single drive unit, then figure out how heavy you are. considering aluminum for the gantry material might be good.

manual height control: this is a way to cut costs, but it might not be a good idea. sheet steel isn't perfectly flat, especially thinner materials, and especially after a thermal cut has heated part of it. the digital height controls will take feedback from your plasma unit and adjust the height of the torch to match any curve in the metal as it moves along. if you do decide to go manual, see if there are any contingencies you would want to plan for if you were to want to add height control later.

material thickness: with a plasma table you are dealing with a pierce operation to initiate your cut. most all plasma units are rated to pierce at 1/2 the normal rated cut, so if you have a 12mm rated machine, 6mm is the rated pierce thickness. this will vary by brand, but it sounds like you are ok if you want to do 6mm and under. i have a 1/2" rated machine and there are numerous videos of that machine cutting 1" plus, so it could probably pierce 1/2" if i were trying to push it.

Davek0974
01-12-2014, 03:49 AM
Thanks for that, very helpful.

I have been scanning eBay and where there once was very little of any good, I am now seeing thousands of control boards, motor drivers, hand controllers, motors etc, brilliant.

I have seen a combined 3axis board that connects to a PC via parallel port, drives 3.5A steppers directly, will take a manual jog unit and will talk to mach3 all for about 70, it also has a demo version of mach3 but I'm not sure what the demo version does.

I think I can create DXF files in Photoshop which I use a lot, so maybe the only missing link I have is DXF file - mach3??? As I said, CNC is pretty new to me so maybe I am oversimplifying things?

Stuff like limit stops, home stops, e-stops, power supplies etc are easy, it's mostly the control side that is difficult it seems. I have found a UK CNC forum and will register today, but reading so far seems to be that tool height control is an ultimate luxury and not generally needed, so something else to consider.

This project is partly for fun and education and partly for a small money making idea I have so I'm not too worried about chucking a couple of hundred quid at it either way. I have a PC waiting, tons of aluminium structural beams, and itchy fingers :)

John Stevenson
01-12-2014, 05:40 AM
Keep away from those cheap 3 axis combined boards, they are utter rubbish, one chip goes, and they do very regularly, and the whole board is toast.

Demo version of Mach will only run a file 500 lines long then bails out.

Sheet cam will import a DXF from Photoshop and convert it into code for mach3 to understand will also send signals to fire the plasma when needed. It can also handle torch hight control [ THC ] but you will need an addon board for this. As you say you don't need THC from day one

http://www.candcnc.com/

I run my plasma by bolting a length of 40mm box section to the bed of the mill sticking out one side and the torch clamps to this.
I use a spare set on contacts on the coolant pump rely to switch the plasma on and off. That bit needs manually editing but for the limited amount I do, it's a get John out the $hit setup, it works.
material is supported on a metal milk crate at the side.

Black Forest
01-12-2014, 08:40 AM
One thing to keep in mind is acceleration and deceleration of your gantry. The lighter gauge (thinner) the material you are cutting the faster your torch has to move. This is when a two motor drive on your X axis comes into play. Not a must but definitely a big help. You can use smaller steppers that will accelerate faster than bigger ones to a point.

The thinner the material the more critical your torch height control becomes. Thin material warps and if you don't have Automatic torch height control your cuts won't be as clean and dross free. It is a situation of , pay me now or pay me later. Without Automatic torch height control you will go through consumables much faster. It doesn't take long to add up. Also your time to clean up the workpiece if it is not cut at optimal height. Piercing is what tears up the consumables if not at the correct height. Normally your torch raises to pierce and comes down to cut height when the torch motion on X and Y starts.

Davek0974
01-12-2014, 09:37 AM
Interesting stuff, my torch likes to pierce at an angle, would it need some sort of tilting head rather than lifted?

As said, it will pierce at 90deg but can sometimes blowback crap into the nozzle.

I will steer clear of the one-board items then, there is not much difference than two or three boards plus the breakout board anyway.

This is pretty much going to be a learning bed I feel anyway, chances of success on the first build seem slim but has to be worth a punt. As space is very tight, I might even make it tabletop as I have a build-bench in the shop that's about 1.2m x 750mm and I could overhang that a bit if needed.

The other job I did do was for three drive feeds on a printing press, it was re-using the existing 500w servo motors with encoders and replacing all the defunct drive side with a four-axis PC board plus three servo amplifier boards and I wrote the interface in Visual Basic. The fourth axis was set for 0-10v to drive the motor VFD. The job worked very well and is still running at our factory, very enjoyable.

So I need mach3 to control the breakout board via the parallel port then something like sheetcam to feed mach3 with the path?

Dave

wmgeorge
01-12-2014, 09:44 AM
I had a PlasmaCAM for 2 or 3 years. It was fun but generated lots and lots of plasma cut metal dust and it goes everywhere. Not any money maker that's for sure, had some income but by the time you purchase and then have to store and handle the sheets of steel for a while it stops being fun. Art work via CNC? Once you get your machine up and running you will find out your not the only one around. Lots of people doing it, and selling cheap. Problem is the folks from India and China are also doing the same thing for 1/10 your selling price.
I did not think Photoshop did scaled drawings? Any CAD program and free ones like Draftsight will generate a DXF file most CAM machine control programs can use. Bob CAD is expensive and once you download the demo they never leave you alone. I used an old version of AutoCAD LT and it worked fine.

Have fun with your building project, but don't expect to pay the mortgage off.

jimcolt
01-12-2014, 10:27 AM
I have had "low cost" cnc plasma cutting machines in my home hobby shop for over 16 years. I also have worked for Hypertherm, the worlds largest plasma cutter manufacturer...for over 36 years.

Fume control is important, but can be acomplished rather easily with either a water tray (with water level right at the bottom of the plate), with a water table (with simple pneumatic water level control, or with the base of the cutting table enclosed with sheet metal and a blower to pull the fumes outside. I prefer the downdraft as there is no water spashing on the plate and the machine....and water does have a cut quality (roughness and dross).

Be careful with many of the extremely low cost table offerings that are not from a known supplier. Undersized drive motors, and no means of a height control system will produce very poor cut quality, the need to babysit the machine continuously, and extremely short plasma consumable life (which leads to poor cut quality and higher cutting costs). Software makes a big difference in efficiency and learning curves for plasma cutting as well. Some of the CAD / CAM packages are difficult to learn and clunky to use, some are very easy and efficient. Those of us that have been cnc cutting for years certainly have our preferences, and they are generally not the lowest cost packages, rather they become the lowest cost as you use them much more efficiently! Many of the software packages are designed around milling and routing.....and are far different than those designed specifically for plasma cutting, these can be used for plasma but are extremely clunky in my opinion.

Currently I have two PlasmaCam and one Torchmate machines in my home shop. Between PlasmaCam and Torchmate....they are the largest suppliers with about 15,000 to 20,000 small cnc machines in the field. There are dozens of other companies building these types of machines as well, some are developing excellent reputations, some not so good!

If you are looking at building your own machine.....take a look at www.candcnc.com . They are the leader in supplying electronics, drives, motors, torch height control systems, software, as well as good advice for the do it yourself guys. Check out their website!

Also, there is one company that specializes in building the mechanical parts of the machines, and thay are cleverly designed to bolt up to the equipment from CandCNC listed above. They are www.precisionplasmallc.com Check them out...they produce a variety of well built and affordable machines including x, y and z moving mechanics for 2' x 2' cutting areas to larger machines.

I am happy with my shop machines, I'd be glad to discuss their capabilities performance, and my perceptions of what has worked for me. By the way, my first PlasmaCam from over 16 years ago paid for itself in less than 6 months with nights and weekend work for local welding shops and construction companies. It as about a $12k investment. The PlasmaCam I have today is about the same price, yet is of a much better design. Excellent height control, very nice software.

Jim Colt Hypertherm

Davek0974
01-12-2014, 11:31 AM
Thanks Jim,

The precision plasma stuff is excellent, very simple designs, US only unfortunately though.

My priorities for this project are maybe education, home shop use, fun, possibly make some cash in that order. If I wanted to make decent money I would guess I would need to be looking at laser cutting anyway. I think the mechanical side is pretty easy to grasp, basic linear motion, no precision needed so guide rails/bearings etc.

The electronics looks like some stepper motors (big enough of course), drive boards for each motor, a breakout board to connect the drives to the PC, and a psu.

Am I right in guessing that if I want dual drive motors on the gantry that I just need two drive boards and feed the same signal to each one?

Software looks like mach3 to control the hardware and sheetcam etc to feed mach3?

Fume extraction is ok, I have a large extract line I can connect to, below the table can be boxed in and downdraught achieved.

Noitoen
01-12-2014, 11:43 AM
I've been thinking myself on building a small cutting rig. I was also thinking about a meter square but a kind of portable unit that you can setup on top of the plate you need to cut. If it's portable, you can take the cutter outside to do the job.

jimcolt
01-12-2014, 11:50 AM
There are more plasma cnc's in the world making money than there are laser cnc's making money, by far! A laser that can cut 1/2" steel with 5 x 10 plate cutting capability would set you back at least $400k (US), an entry level plasma cnc of the same capability could be bout for under $20k (US). A high definition plasma on a more precise machine perhaps $100k (US). For hobbyist use the entry level plasma cnc is generally the only choice from a budget perspective.

Most low cost plasma cnc's use steppers because they are simpler and lower in cost. Some of the better performing entry level machines use servo's. Virtually all industrial machines use servo's. Servo's have a better torque / RPM curve that can provide better acceleration over a wide speed range. Plasma cuts extremely fast on thin materials, and slow on thick materials.....acceleration is a key to best cut quality. Two of my machines use servos, the third uses steppers.....I see a big difference in quality on materials thinner than 1/4" (6mm).

Mechanically, better precision with less mechanical backlash produces better cuts. Put a plasma on a machine with lesser guideways, then the same plasma on a better built machine with linear bearings and precision gearboxes, racks, etc.....and you will see and be able to measure better cut quality.

Jim Colt Hypertherm


Thanks Jim,

The precision plasma stuff is excellent, very simple designs, US only unfortunately though.

My priorities for this project are maybe education, home shop use, fun, possibly make some cash in that order. If I wanted to make decent money I would guess I would need to be looking at laser cutting anyway. I think the mechanical side is pretty easy to grasp, basic linear motion, no precision needed so guide rails/bearings etc.

The electronics looks like some stepper motors (big enough of course), drive boards for each motor, a breakout board to connect the drives to the PC, and a psu.

Am I right in guessing that if I want dual drive motors on the gantry that I just need two drive boards and feed the same signal to each one?

Software looks like mach3 to control the hardware and sheetcam etc to feed mach3?

Fume extraction is ok, I have a large extract line I can connect to, below the table can be boxed in and downdraught achieved.

jimcolt
01-12-2014, 11:52 AM
Look at www.gotorch.com (division of PlasmaCam) for this type of machine. Torchmate makes one as well....as do a few others. You can also buy a kit from Precision Plasma.

jim Colt



I've been thinking myself on building a small cutting rig. I was also thinking about a meter square but a kind of portable unit that you can setup on top of the plate you need to cut. If it's portable, you can take the cutter outside to do the job.

Davek0974
01-12-2014, 02:26 PM
Thanks, the GoTorch stuff is very nice, shipping could be an issue though :)

Portable would be good, nice idea. It will have to be stepper motors though for cost at least, strictly budget stuff until I see what it can do at least.

wmgeorge
01-12-2014, 02:58 PM
Thanks, the GoTorch stuff is very nice, shipping could be an issue though :)

Portable would be good, nice idea. It will have to be stepper motors though for cost at least, strictly budget stuff until I see what it can do at least.

If its like the PlasmaCAM I had a few years ago it comes knocked down and with all the parts in a box. Some assy required. You would have the advantage of a system that works "out of the box" and with a warranty. Servo motors are better. Don't fool yourself thinking you can build one much cheaper, Maybe. But if you get the factory designed and made machine it has re-sale value, homebrew/homemade has none. Ask me how I know.... sure its fun to design build, but if you want to make and sell products this will do the job.

jimcolt
01-12-2014, 03:38 PM
I have a Go Torch, I also have the 4 x 4 PlasmaCam. Both reliable, very capable machines. Mine are both upgraded with advanced height control and software.

Jim Colt

peter76
01-12-2014, 03:40 PM
I built my own plasma cnc which can cut upto to 800 by 1000 mm. I bought a motor package from www.impulsecnc.nl . That included three motors, three drivers and a power supply. From the same guy I bought a parallel port interface board which I had to solder myself.
I use two motors on the x an one motor on the y, z is manual at the moment; thc is on the list, but it works good without it.
All axes are controlled through 16mm trapezium threaded rod using evanuts ( search this forum ). IMO they are a very good diy solution!
The machine is controlled through Linuxcnc, Sheetcam for the cad cam conversion and qcad for most of the drawing; very cheap and good working.
All very doable:-)

Good luck with yours.

jimcolt
01-12-2014, 04:25 PM
Here is the link to a video of my 2' x 2' (610 mm x 610mm) Go Torch. My son is showing how easy the software works....no GCode necessary, draw the part in CAD and convert it to cut path (1 second) then cut it. This shows cutting with auto height that locates the surface of the plate before each cut, retracts to pierce height, pierces, indexes to cut height then controls height via arc voltage feedback. Watch carefully and you will see the torch moving up and down to maintain accurate height while driving over the bumps on some treadplate. Proper height controls nozzle life (cut cost) and cut edge quality.

Link to youtube: http://www.youtube.com/watch?v=kw5ED_YLM9M

Jim Colt

Mtw fdu
01-12-2014, 04:54 PM
Just out of curiosity, what is the reputation like about Camcutcnc? I am from Australia and looking at a controller, motor package from them. The units are similar to the Go Torch setup. I will be adding it to my existing oxy/plasma table setup.

Mtw fdu.

wmgeorge
01-12-2014, 05:42 PM
Jim I don't know how you could have one work without some sort of automatic height control? I think the Go Torch is a great idea, good for portable take to the job and cut out shapes on the jobsite work.

jimcolt
01-12-2014, 05:49 PM
The Camcut motors are steppers, PlasmaCam are servos. Software for CamCut is Machine Code based, PlasmaCam is not. Other than the fact that both are designed to cut metal with a plasma torch there are few similarities.

CamCut seems to be a good, low cost do it yourself project. I'm sure it can produce great cuts on most materials. The PlasmaCam is an engineered unit (they have over 15,000 in the field) that is pretty well proven, and has some very easy to learn software, and and easy to operate system. You will spend more for the PlasmaCam, but I'm pretty sure you be cutting much faster.

I have built a couple of machines in my years...they take more time than I usually expect, and almost always need a level of re-engineering. Now that I have purchased a few well proven machines I realize a great time savings and enjoy much better cut quality, easier to use software, and much more productivity when I need it. I can program 100 parts on a sheet and walk away...the height control controls cut quality and minimizes the chance of collisions.

Jim



Just out of curiosity, what is the reputation like about Camcutcnc? I am from Australia and looking at a controller, motor package from them. The units are similar to the Go Torch setup. I will be adding it to my existing oxy/plasma table setup.

Mtw fdu.

lakeside53
01-12-2014, 08:38 PM
How does the height get sensed?

Davek0974
01-13-2014, 04:20 AM
Hmm, it looks like my low budget idea may be a non-starter after a chat with the plasma makers, it has a contact-start system and I really need an HF-Pilot arc system instead. He did say it "might" works some of the time but if the arc does not strike immediately the work will be spoilt.

So its either sell my unit and upgrade, this would use a large chunk of my budget, or give up as a non-starter.

Shame as most of my queries were slowly getting answered.:(

jimcolt
01-13-2014, 08:31 AM
There are two important heights that need to be controlled with cnc plasma cutting for best performance;

-Initial height or pierce height. This function has to occur before the plasma arc fires, essentially the machine needs to locate the surface of the material, then retract to a pierce height as suggested by the plasma torch manuafcturer. There are many different torch designs and they have different piercing capabilities, and piercing height and duration needs to be handled differently depending on material type and thickness.

-The most common method of sensing the surface is with torque sensing, the z axis drive essentially collides the torch with the material....increased motor torque is sensed, and then the direction is reversed (up) until the correct pierce height is achieved. This is a good process except on thinner materials the force of the sensing often deflects the material, then sensing occurs, but the spring of the material often follws the torch in its upward motion rendering the pierce height incorrect.
-A very popular method also is with "ohmic sensing", or using the metalic shield (not all plasma torches have a shield) that is the frontmost part of the torch to contact the material, which is sensed with a low voltage, low current ohmic sensing circuit. This can be very sensitive and generally causes no material deflection, and an accurate pierce height. This process can be problematic if there is water on the surface of the material (water table fume controls) or if the surface is painted, extremely rusty or dirty.
-There are many systems as well that use a limit switch on the torch mounting assembly (often called a "floating head") that senses collision with the material, then retracts to pierce height. This process, like torque sensing, also can cause plate deflection and requires a hysteresis setting to account for limit switch movement.

Once the surface of the plate is detected and the torch indexes upward to the pierce height, the plasma sytart command is issued, the torch fires and a pierce delat timer activates. This timer disallows any x, y or z axis motion until the pierce is complete. The pierce time is suggested by most plasma torch manufacturers, and it varies depending on material thickness, power levels, etc.

Once the pierce times out, the torch then should index quickly to the cut height....this height is recommended by the torch manuafcturer for best cut quality, and should be maintained throughout the cutting process.

Arc Voltage feedback is then activated once the x and y axis achieve the programmed cut speed. An electronic comparator circuit measures the plasma arc voltage (between the torch electrode (negative) and the plate (positive)) and compares it to a known arc voltage setting, which is normally supplied by the torch manuafcturer for the material and thickness being cut. Arc voltage is proportional to arc length, so when the circuit sees the voltage increase to a level higher than the correct voltage, the z axis drive activates and lowers the torch until the voltage is correct. This technology has the ability to maintain proper torch to work distance within a few thousandths of an inch, necessary for best cut quality. This is complex and requires interaction with the cnc motion control in order to freeze the height during slowdaons in x and y motion, during kerf crossings, and at the beginning and ending of each cut cycle.

On most of the good quality, well engineered cnc plasma machines these height control functions are engineered to work quite well. Some of the "kit" do it yourself equipment manufacturer offer height control electronics as well.......some are well integrated and work very well, some do not. It is very difficult to develop and implement the height control functions for plasma by an independant experimenter, trust me....many have tried, few have succeeded!

Can you cut without height control? Yes. Expect shorter consumable life with the plasma torch...usually caused by piercing too close to the material, or by material collisions.

Can I just use really flat metal? That helps, but there is no metal flat enough for bet plasma cutting performance. A Hypertherm air plasma used on a cnc machine cuts at .060" (1.5mm) off the plate. A variation of .010" (too high or too low) affects cut edge angularity, dross and material warpage. You could stert with perfectly flat plate, but as heat is inputed and parts are cut, expect internal stresses and thermal input to affect flatness.

Hope this lengthy explanation helps with understanding!

Best regards, Jim Colt Hypertherm



How does the height get sensed?

Davek0974
01-13-2014, 08:53 AM
My little plasma (which i was going to use originally) has a drag-head and is pretty happy cutting at 0mm height, it only has a 9mm clean-cut depth @30A

Would this not function if the X/Y table was fitted with a lightly spring loaded torch holder?

Obviously all cuts would need to start inside the plate edges.

For piercing it likes to be tipped over at about 40-45deg from square, this sounds pretty easy to accomplish.

Please bear in mind that my target metal is around 4-5mm steel and 1-2mm brass etc.


Dave

wmgeorge
01-13-2014, 10:11 AM
As soon as you start cutting the metal heats and moves or warps a bit. Drag cutting and CNC would not work, you need to go someplace to see one working to understand.

If your serious about this, sell off your plasma cutter and purchase one that will work. Jim knows his stuff. I also ran a PlasmaCAM for 2 or 3 years with a Hypertherm plasma cutter so I can't tell you how a Chinese made PC would work with a CNC table.

Davek0974
01-13-2014, 10:47 AM
As soon as you start cutting the metal heats and moves or warps a bit. Drag cutting and CNC would not work, you need to go someplace to see one working to understand.

If your serious about this, sell off your plasma cutter and purchase one that will work. Jim knows his stuff. I also ran a PlasmaCAM for 2 or 3 years with a Hypertherm plasma cutter so I can't tell you how a Chinese made PC would work with a CNC table.

Thanks for that, as it stands I just don't have the funds to go for anything shop-made, would love one but it's just not going to happen.

I have already thought of building the table first then when the time comes, sell and upgrade my torch, it's not much more cash and could be done.

It seems THC is generally needed but again adds a large amount of cost to the build if its not 100% essential.

I can't find anyone local that has CNC plasma so a visit is looking tricky at present, would be good though.

I might just shelve the project as it's not looking like the budget idea I first had, a basic X/Y table with mach3 + sheetcam is do-able but throw in THC as well and it goes way over budget ;)

jimcolt
01-13-2014, 10:57 AM
A lot of the older tech, or the low cost Chinese plasma's use a high frequency discharge for starting the plasma arc. These are generally not recommended for a cnc plasma (entry level) that uses a standard PC or Laptop as the cnc control. If your plasma must touch the plate to start...then it likely is a high frequency start. There are also many pilot arc start plasma's (again, older tech, or low cost new copies of older tech) that use high frequency or capacitive discharge to start. Stay away from these!

The latest technology for low cost air plasma is with the blowback start torches that use a moving electrode to create a short circuit internal arc, which ionizes the air (instead of using a high frequency/high voltage discharge). These torches will fire a pilot arc in the air, and if close enough (.25", 6mm) will transfer to a cutting arc easily. These torches are designed to pierce metal from the vertical (perpendicular) position at a fixed pierce height.

In theory you could build something to pierce at an angle.....and you could clamp the material and drag cut. Just is not really what cnc machines are all about!

Jim Colt




My little plasma (which i was going to use originally) has a drag-head and is pretty happy cutting at 0mm height, it only has a 9mm clean-cut depth @30A

Would this not function if the X/Y table was fitted with a lightly spring loaded torch holder?

Obviously all cuts would need to start inside the plate edges.

For piercing it likes to be tipped over at about 40-45deg from square, this sounds pretty easy to accomplish.

Please bear in mind that my target metal is around 4-5mm steel and 1-2mm brass etc.


Dave

Davek0974
01-13-2014, 01:04 PM
Thanks,

The upgrade plasma was a HF pilot arc one, and while it will start in free air, switch to full power when near metal and back to pilot when away from metal, it certainly has no moving electrode arc start.

I think the project is pretty much dead in the water, seems to be too much negative feedback coming in from various sources, not a bad thing and is one outcome of asking questions ;)

Now to find a different project :)

wmgeorge
01-13-2014, 02:55 PM
Well if your only drawback is the plasma cutter then I would skip that for now and go about exploring table and control designs. I've looked at your website and you seem to be a pretty talented person design metal working wise.
My Longevity 40 plasma cutter is non-contact, non-high frequency start pilot arc but not sure if it would work on a CNC plasma table?

lakeside53
01-13-2014, 03:15 PM
Jim Colt - great write up. Thanks.

I have a Hypertherm 1000 That I was hoping to use as part of a Home brew cnc cutting table. I can see how the initial pierce control could be implemented without too much trouble, but the "active" height control seems a little daunting without some form of interface to the plasma cutter. Does Hypertherm offer any such interface?

Davek0974
01-13-2014, 04:18 PM
Well if your only drawback is the plasma cutter then I would skip that for now and go about exploring table and control designs. I've looked at your website and you seem to be a pretty talented person design metal working wise.
My Longevity 40 plasma cutter is non-contact, non-high frequency start pilot arc but not sure if it would work on a CNC plasma table?

It's not so much the plasma itself, just the torch height control. It's an expensive lump and would likely double the cost of the build, something I don't want to do;) My little plasma should fetch a good price on eBay etc so I'm not overly concerned about that aspect.


Jim Colt - great write up. Thanks.

I have a Hypertherm 1000 That I was hoping to use as part of a Home brew cnc cutting table. I can see how the initial pierce control could be implemented without too much trouble, but the "active" height control seems a little daunting without some form of interface to the plasma cutter. Does Hypertherm offer any such interface?

That's my concern too. THC for a hobbyist seems extremely costly, but I have no idea other than replies here as to whether it is essential or not. The torch being a non-contact type I can understand now, but not quite there on THC yet.

gdavis2265
01-13-2014, 04:35 PM
You can get an exact copy (pert near) of AutoCAD Lite by downloading a free copy of "Draftsight" (made by the good folks who sell Solidworks) They offer this free of charge. I've been using AutoCAD from their beginning and Draftsight is great.

Also, download "Inkscape" - this will convert graphics and text into a vector file. In Inkscape, the vectors can be saved as a .dxf file.

This file can be opened by Draftsight for fine tuning and tweeking. I essentially trace over the lines with the "Polyline" command to make sure the lines are closed and continuous.

This file is saved again as a .dxf.

I then open the file in SheetCAM for the tool paths - very simple, very easy. Hit the post process button and it automatically writes the g-code file.

I open the G-Code file in MACH III and cut away.

It's really very simple, the hardest part is determining what speed and amperage to cut for different materials.

I bought a complete gantry off of e-bay (very poor quality), so I did not have to learn the electronics. I just wanted to get busy making some money. I'm currently building a better gantry of my design and will copy the electrics.

BTW, the electrics are dirt cheap and can all be had on e-bay (all china stuff, but most stuff is these days)

For instance, stepper motors are about $25 each, driver board for all motors cost $65 - power supply another $30 - Seriously, there might be $200 in total electronics. I even bought a brand new computer with a parallel port for around $100. (you'll want a dedicated computer with just this software on it)

I built my own water table and it has over 1000 lbs of steel in it, so that was a fair amount of money.

The best thing I ever did was to buy the Hypertherm 45 with machine torch. This thing will literally cut 1-1/2" plate starting on the edge of the material and using only 45 amps! It really is amazing. (I only have a 50 amp breaker in my shop, It needs updating)

Jim Colt can get you an adapter that provides pigtails out of the back of the machine for easy hook-up. Oh, and it's a blowback start torch, so no high frequency to mess things up. No grounding, no shielding to fool with.

Here is a photo of my table:

http://www.flickr.com/photos/100586259@N06/10967658595/

http://www.flickr.com/photos/100586259@N06/10967851234/

http://www.flickr.com/photos/100586259@N06/10967832274/

http://www.flickr.com/photos/100586259@N06/

wmgeorge
01-13-2014, 06:39 PM
Jim Will jump in here with the "real" info but when I purchased my PlasmaCam I think the torch interface was either part of the deal or a purchase from PlasmaCam. It had two parts, one you tied the hand torch trigger back with a wire tie and the interface provided the on-off for the torch. Part two was a connection inside to pick up the voltage sensing part of the circuit that told the DHC how far away from the set point the torch tip was by reading the voltage. Sounds simple but it was not.

Davek0974
01-14-2014, 03:39 AM
Thanks, I can see how the system works, its the electronics behind the scenes that seems to cost. I found a listing on ebay for a unit that looked ideal and only 150 but sadly not listed any more :(

Nearest units seem to be 400-500 each.

Davek0974
01-14-2014, 06:46 AM
Upon doing some more web searching, I found a couple of excellent pages...

http://www.lesnewell.co.uk/Plasma/Plasma_index.html

And

http://forums.bit-tech.net/showthread.php?t=255937

Both show budget builds and the last one is so amazing that it practically says "Just bung it together and it will work".

The first thread uses a drag-torch as well although he does mention it's limitations.

So in light of these discoveries I think I will proceed to the fag-packet stage and start drawing up some ideas of frame and motion methods. Im using 44mm structural aluminium for the chassis as i have tons of it, might run the carriage bearings direct onto the frame rails or possibly fit some plate to each side and use V-rollers top and bottom.

My criteria so far are...
Cheap,
Small,
Light,
Table-top.

I'm looking at T5 belt drive to both sides of the gantry via a main drive shaft with one stepper driving it via a reduction system. Again the X axis will be T5 belt drive as i have a box full of useful T5 pulleys :)

Probably 3Nm Nema23 motors, drive gear from ebay, mach3, sheetcam etc

Anyone wants to throw ideas in please feel free.

John Stevenson
01-14-2014, 07:24 AM
Upon doing some more web searching, I found a couple of excellent pages...

http://www.lesnewell.co.uk/Plasma/Plasma_index.html

And

http://forums.bit-tech.net/showthread.php?t=255937



The first one is Les Newalls page who writes Sheetcam that I pointed you to umpteen posts ago..............

Davek0974
01-14-2014, 07:54 AM
The first one is Les Newalls page who writes Sheetcam that I pointed you to umpteen posts ago..............

Yes, but, I never said it wasn't did I?

I looked at sheetcam, saw it would do what i need, if there was a link to his build then i missed it.

Its still a nice build and uses a drag-head torch.

jimcolt
01-14-2014, 12:54 PM
Cutting without height control can certainly be done, but it is a one part at a time operation. With a properly designed height control (not all of them are!) you can program hundreds of parts and then go do something else in your shop. So, for a small shop there is still value.....the ability to cut farly precise, repetitive parts with a low cost cnc that is not equipped with height control. If you are looking to make money, or do production work....then I say a good height control is necessary, and will pay for itself in a short period of time.

Jim Colt Hypertherm

Davek0974
01-14-2014, 01:00 PM
Ok so I've lashed together some of my aluminium buts to get a feel for the size of table I can build, poor pic, sorry.
http://www.davekearley.co.uk/LinkPics/CNC1.JPG

It's 4'6" x 2'6" so I should end up with nearly a 4x6 cut area.

Thinking of mounting some 75x6mm mild along the long sides to use as carriage rails, gantry carriage can be quite slim as I'm driving it from both sides using T5 belt and sprockets.

Davek0974
01-14-2014, 01:04 PM
Cutting without height control can certainly be done, but it is a one part at a time operation. With a properly designed height control (not all of them are!) you can program hundreds of parts and then go do something else in your shop. So, for a small shop there is still value.....the ability to cut farly precise, repetitive parts with a low cost cnc that is not equipped with height control. If you are looking to make money, or do production work....then I say a good height control is necessary, and will pay for itself in a short period of time.

Jim Colt Hypertherm

Thanks Jim, your advice is much appreciated.

This is for a home shop/micro business, I'm definately not thinking of advertising as CNC plasma cutters :)

Apart form the learning side of it, I want to cut some arty stuff to complement or expand my scrollwork that I sell.

I popped out to the shed tonight and played with my plasma torch, it seems it will happily strike an arc at around 0.5 to 1mm clear of the work, once pierced, it can happily drag along the surface or run clear at a small height.

Davek0974
01-15-2014, 04:11 AM
I contacted the seller on ebay that listed the affordable THC units and he has re-listed some more, so it looks like i can easily add THC later on for about 200 which is much better (obviously i will still need to upgrade my torch)

Its slowly coming together as a plan now.

Could a Mach3 user tell me where the cut starts? I.e. does it start running the code from wherever you plonk the carriage on the sheet of steel or is it referenced from the home point or something else?

Is there any reading material on mach3 anywhere?

Thanks

Davek0974
01-15-2014, 10:36 AM
Rough calculations, with a 3:1 reduction on my gantry drive motor, 1 step of the motor will give me 0.16mm of travel, if using micro-stepping as recommended, then 8 micro-steps will give me 0.02mm which seems very fine for a plasma cutter??

If I can reach 500rpm on the shaft, I should get around 16m/min of speed but that's a guess as I have no idea of acceleration curve yet, I'm looking to keep the gantry light by mounting the drive motor on the main chassis and driving through the belt along the side-frames, I think that makes more sense than mounting the motor on the gantry and using to "rack" its way along a fixed belt.

I have two 3.1Nm motors, 5A drive boards a breakout board and a 36v PSU coming.

Have also reloaded XP onto my target PC and have been playing around with the demo mach3 plasma install, downloaded a manual too.

Just waiting for material to arrive now.

BTW, I have had to reduce the size of my intended machine as it wouldn't fit in my workshop :( so it's now got a cutting area of 2' x 2', not as good but easy to expand later on.

Jaakko Fagerlund
01-15-2014, 01:28 PM
You are off to a good start, but one thing I noticed - your power supply voltage. It might not be enough to get proper acceleration or top speed, but this is just a guesstimate. But just a caution, if you happen to run in to performance issues in these two aspects.

John Stevenson
01-15-2014, 02:18 PM
If I can reach 500rpm on the shaft, I should get around 16m/min of speed but that's a guess as I have no idea of acceleration curve yet,

In your dreams. At 2' x 2' it will never get up to speed unless you hit it with about 400 volts.

Davek0974
01-15-2014, 03:30 PM
In your dreams. At 2' x 2' it will never get up to speed unless you hit it with about 400 volts.

LOL, I can see that now, especially having just read the mach3 manual :)

The psu came as a set with the drive boards and breakout board so I guessed would be ok, as a starter at least, I think they can go to 48v if needed.

It's all educational, but at least I've met g-code now :) albeit in blind demo mode, still good though, downloading sheetcam demo tomorrow, see how that runs.

At least scaling the machine up is just a matter of lengthening some metal parts, all the control gear will still function.

camdigger
01-16-2014, 02:07 AM
Unless I missed it, I see no reference to a breakaway system for the torch head. From what I understand, tip ups and torch crashes are inevitable, and can cause expensive damage to the torch head.

Breakaway head designs are available from various sources including some forums, and would be well worth the time invested.

Davek0974
01-16-2014, 03:03 AM
Unless I missed it, I see no reference to a breakaway system for the torch head. From what I understand, tip ups and torch crashes are inevitable, and can cause expensive damage to the torch head.

Breakaway head designs are available from various sources including some forums, and would be well worth the time invested.

Excellent point, thanks.
I did see a professional system with magnetic torch mount, just need to devise a simple way for trials first.

At the moment I'm looking to build a gantry with a plain carriage mounting plate on it, no Z axis or tool mount at all. Then get that moving with mach3 and look at the Z afterwards as its own entity that can be mounted onto my plain carriage.

If I'm building without THC, would a manual Z adjustment be workable? Bear in mind that I realise I will have to jog into the work, set the height then ref-home before starting the cut. I'm not looking at mass production.

My torch will happily strike and pierce at 0.5 - 1mm clear and will cut well at 0 - 1mm on thicknesses up to 6mm where it needs to be dragged up to 9mm thick.

So, question is, what is the minimum Z-axis required????

jimcolt
01-16-2014, 02:42 PM
Magnetic breakaway torch mount: www.snapncut.com 1 saved torch will pay for this unit! I have been using one for over 3 years on both of my cnc plasma's.

Jim Colt



Unless I missed it, I see no reference to a breakaway system for the torch head. From what I understand, tip ups and torch crashes are inevitable, and can cause expensive damage to the torch head.

Breakaway head designs are available from various sources including some forums, and would be well worth the time invested.

Davek0974
01-16-2014, 03:03 PM
Interesting and simple.

If I'm building without THC, would a manual Z adjustment be workable? Bear in mind that I realise I will have to jog into the work, set the height then ref-home before starting the cut. I'm not looking at mass production.

My torch will happily strike and pierce at 0.5 - 1mm clear and will cut well at 0 - 1mm on thicknesses up to 6mm where it needs to be dragged up to 9mm thick.

So, question is, what is the minimum Z-axis required????

jimcolt
01-17-2014, 09:39 AM
Well, the z axis travel obviously needs to cover the thickness range that you need to cut. Most commercial machines have adequate z axis travel so that during traverse to the next part the torch is lifted high enough to avoid collision with already cut parts that may have tipped up in the slat bed. There are some CAM nesting softwares with collision avoidance features that apply the start/stop points on each individual cut part so that the next move avoids traversing over previous cuts, and in the case where it cannot do this the z axis lifts higher to avoid the potential collision.

On most small entry level cnc plasma's the z axis full stroke is in the 3 to 6 inch range (75 to 150 mm) and on most industrial machines it is in the 6 to 9 inch (150 to 225mm) range.

Jim Colt Hypertherm

Davek0974
01-17-2014, 10:00 AM
Well, the z axis travel obviously needs to cover the thickness range that you need to cut. Most commercial machines have adequate z axis travel so that during traverse to the next part the torch is lifted high enough to avoid collision with already cut parts that may have tipped up in the slat bed. There are some CAM nesting softwares with collision avoidance features that apply the start/stop points on each individual cut part so that the next move avoids traversing over previous cuts, and in the case where it cannot do this the z axis lifts higher to avoid the potential collision.

On most small entry level cnc plasma's the z axis full stroke is in the 3 to 6 inch range (75 to 150 mm) and on most industrial machines it is in the 6 to 9 inch (150 to 225mm) range.

Jim Colt Hypertherm

Thanks again Jim,

After seeing sheetcam and mach3 in action now, I am planning on a motorised Z-axis with, as you say, a travel of around 75mm, hopefully allied with a magnetic break-away torch mount.

I have the driver and motor for this, just need to come up with a cost effective slide mechanism. There are some nice units on ebay that are probably not much more than the materials would cost me so i might go for a ready-made option and just mount my motor.

Dave

Black Forest
01-17-2014, 11:41 AM
Well, the z axis travel obviously needs to cover the thickness range that you need to cut. Most commercial machines have adequate z axis travel so that during traverse to the next part the torch is lifted high enough to avoid collision with already cut parts that may have tipped up in the slat bed. There are some CAM nesting softwares with collision avoidance features that apply the start/stop points on each individual cut part so that the next move avoids traversing over previous cuts, and in the case where it cannot do this the z axis lifts higher to avoid the potential collision.

On most small entry level cnc plasma's the z axis full stroke is in the 3 to 6 inch range (75 to 150 mm) and on most industrial machines it is in the 6 to 9 inch (150 to 225mm) range.

Jim Colt Hypertherm

Hey Jim, Don't you need to change your signature to Jim Colt, Owner Hypertherm! Now that it is a completely employee owned company! I bet your sitting quite pretty seeing as how long you have been with the company. I am happy for all of you at Hypertherm.

jimcolt
01-17-2014, 12:16 PM
We are all very happy with this weeks 100% employee ownership announcement. It however has no affect on our pay.....the stock ownership is only turned into cash after you leave the company. There are complex rules that delay the payment for stock depending on age and reasons for leaving....so it truly is designed as a retirement plan (and a very lucrative one) for longe term employees. I actually am the longest term Hypertherm employee with the exception of the founder. I have no plans to retire....but when I do I will be in good shape!

Jim Colt Hypertherm


Hey Jim, Don't you need to change your signature to Jim Colt, Owner Hypertherm! Now that it is a completely employee owned company! I bet your sitting quite pretty seeing as how long you have been with the company. I am happy for all of you at Hypertherm.

Davek0974
01-18-2014, 02:12 PM
Made the frame a bit smaller, now 2'-6" square, plus a bit more on the y axis.

http://www.davekearley.co.uk/LinkPics/CNC2.JPG

And made the carriages for the gantry that run on the steel plates each side of the table...
http://www.davekearley.co.uk/LinkPics/CNC3.JPG

Coming along.

Davek0974
01-26-2014, 03:25 AM
Got the carriage for the z-axis made today...
http://www.davekearley.co.uk/LinkPics/CNC4.jpg
http://www.davekearley.co.uk/LinkPics/CNC5.jpg

I know it's running on aluminium beam but it's a mk1 educational model, so we'll see how it goes, it does run very smoothly though.

I have the z-axis waiting to mount, cheated on that one as the price was not worth making it tbh.

John Stevenson
01-26-2014, 07:04 AM
Dave,

If it's not too late on other parts of the design use smaller bolts inside the bearing and fit an eccentric sleeve so you can tune to fit.

If you make the sleeve out of a bit of hex bar cut off about 5 mm longer that the width of the bearing and turn down to fit the bearing for the same length [ does that make sense ? ] then you have 5mm of hex on top you can get a thin spanner on to turn it.
Obviously the centre hole has to be off set.
I usually put a bit of shim under one jaw of the 3 jaw to get this, it's not a critical dimension.

Davek0974
01-26-2014, 07:18 AM
Thanks john,

It's not quite clear in the pics but the two rear bearings are on slotted holes with a pressure screw against the bolt where it passes through the main plate, all the other screws are positioned accurately so they are all square to each other etc. it seems to work well, but your idea would be equally as good.

Dave

John Stevenson
01-26-2014, 07:31 AM
OK not spotted that. Hope you don't think anything I offer is a criticism of your design as it isn't.
Often people see solutions to problems in different ways.

boslab
01-26-2014, 07:39 AM
I do like eccentric adjustors, my concentric bushings usually end up being eccentric anyway! Lol
Nicely documented so far, cant wait to see sparks
Mark

Stern
01-26-2014, 10:33 AM
If you are building this from scratch (which it looks you are) you can do what I am doing (Im a total CNC newbe, and building a CNC PCB router), go to

http://www.cnczone.com/forums

These guys have thousands of posts on anything CNC, with a whole section on plasma. This site have been extremely helpfull on learning CNC stuff as well as a lot of "dont do it" advise thats helped me "zero in" on the proper way for me to make this thing (and my budget is really low, has to be way under $1000.00)

Davek0974
01-26-2014, 11:48 AM
I'll check that link tonight, looks good.

Don't worry about the comments and tips, it's all good, there's always more than one way to do something :)

Davek0974
01-28-2014, 03:43 PM
Just found a very interesting thread where another builder improved matters with his cheap HF start plasma by adding a ground wire from the tip to the plasma ground lead connector.

This tricked the unit into starting instantly and with full power plasma arc, even in free air, pretty much like a souped up pilot arc torch. It also cut down the HF interference massively.

Now thinking this through, it's a harmless idea as the torch is meant to be grounded anyway when dragging so no harm there. Thinking further, would this now mean that I could set a reasonable height for piercing as I would have a full power arc immediately and then drop to cutting height, thus getting the piercing dross out of the way safely????

I will certainly be trying this idea.

jimcolt
01-28-2014, 04:42 PM
Not to mention that it dramatically shortened the (already short) nozzle orifice life! A full power pilot arc in air is the fastest way to destroy the nozzle orifice. Older pilot arc plasma systems used this type of circuit but limited current with a pilot arc resistor, and limited time on with a pilot arc relay....crude by todays standard....but it added to the nozzle life significantly. Todays major brand systems use a pilot arc control circuit that ramps power up to enough to maintain the pilot arc, but not enough to cause nozzle damage.....different ramping depending on the nozzle design (orifice diameter and length).

Jim Colt



Just found a very interesting thread where another builder improved matters with his cheap HF start plasma by adding a ground wire from the tip to the plasma ground lead connector.

This tricked the unit into starting instantly and with full power plasma arc, even in free air, pretty much like a souped up pilot arc torch. It also cut down the HF interference massively.

Now thinking this through, it's a harmless idea as the torch is meant to be grounded anyway when dragging so no harm there. Thinking further, would this now mean that I could set a reasonable height for piercing as I would have a full power arc immediately and then drop to cutting height, thus getting the piercing dross out of the way safely????

I will certainly be trying this idea.

Davek0974
01-28-2014, 04:58 PM
Yes but I'm thinking that improving piercing height from practically zero to a couple of mm is better for the tip ??

Naturally I'm not going to fire the torch until it's at a suitable height so although not ideal it's possibly better than nothing?

jimcolt
01-28-2014, 05:10 PM
It may work.....just remember the plasma energy is all going to the nozzle with the work lead attached to the nozzle. The same energy that cuts the plate. If it was that simple....then all the circuitry we have developed over the years to maintain the integrity of the nozzle orifice (which controls the shape of the arc.....which of course controls the shape of the cut) would be for nought!

Those older contact start torches have pretty short nozzle life anyway, and you can get the nozzle's online for cheap....so its worth a try! May want to try about a 3 ohm, 400 watt resistor (large ceramic type) in the line between the nozzle and the work ground...that may give the nozzle a better chance of survival, and forces the arc to transfer more quickly to the plate (path of least resistance). Some of the old Hypertherm systems used a current sensor that sensed current on the work ground cable.....which then opened a pilot arc relay in series with the resistor.....this takes the nozzle out of the circuit. The relay needs to be rated for the DC current and voltage...they used to have a magnet to create a field right between the two big open contacts. In fact the Hypertherm part number for that relay is 003021 (not sure how I remembered that from 20+ years ago!)

Jim Colt

boslab
01-28-2014, 07:09 PM
Mow does nozzle material influence the plasma stream, they seem to need to be conductive so copper is used, what would happen if the orifice was say, tungsten or even platinum? Just thinking out loud if you know what i mean, i know the rare earth doped Tungstens stabilise the electron flow?
Mark
I have plasma Learner plates on my shed, large blue P

Davek0974
01-29-2014, 01:25 AM
Yes the nozzles are cheap, very cheap so definitely worth trying, I like the resistance idea too.

I find the whole plasma cutting thing fascinating, after years of using a saw, being able to rip through 1/2" of steel plate without effort is totally amazing.

Dave

wmgeorge
01-29-2014, 11:45 AM
Jims trick may save some of the nozzle life on your plan, but as the nozzle wears the flame pattern changes and your not going to like what it does to your cut! Sell your machine and purchase the correct pilot arc plasma that will work with a CNC table.

Davek0974
01-29-2014, 01:08 PM
Yes I know it's not ideal, but while I'm accumulating knowledge and experience, it will need to do for a while until I can scrape up the cash for a pilot arc model.

It's definitely on the cards though, the next model up has the feature so will likely be the one I get.

jimcolt
01-29-2014, 03:44 PM
The nozzle is made from copper because it transfers heat very efficiently. The arc is in excess of 25,000F, so anything found on earth will melt. Tungsten has a higher melting temp, but a far lower ability to conduct heat....so would wear much faster than copper. Platinum or gold would last better than copper, as long as you wouldn't mind paying the price!

Jim Colt Hypertherm


Mow does nozzle material influence the plasma stream, they seem to need to be conductive so copper is used, what would happen if the orifice was say, tungsten or even platinum? Just thinking out loud if you know what i mean, i know the rare earth doped Tungstens stabilise the electron flow?
Mark
I have plasma Learner plates on my shed, large blue P

boslab
01-29-2014, 06:01 PM
Thanks jim, learning all the time!, just thinking aloud is good for that, i do have a stock of platinum rods, and tungsten curtesy of sylvania tungsten as i used to make electrodes for spectrometers, think the best bet is to sell the stuff and buy a ****load of nozzles!
The whole concept of the 4th state of matter is rather exciting, its only a shortbwhile ago that new forms of carbon were found, mostly by accident, it will be interesting to see where plasma leads us.
Regards
Mark

Davek0974
01-31-2014, 12:43 PM
A short vid of my first foray into the world of CNC...
http://www.davekearley.co.uk/LinkPics/CNCVID1.mp4

Hopefully it works ok.

Certainly fun to play with.

boslab
01-31-2014, 04:07 PM
Brilliant, like the z axis, but torch height is a worrying complexity at the moment, myself got the plasma, x, and y linear thingys (toothed belt inside an aluminium extrusion off a sample robot for an old XRF spec that was being scrapped) no z axis yet, but my garage/shop is about 100m from my house so i had to buy a 100m coil of 10mm 3 core SWA cable to stand the 7kw pull off the plasma plus everything else
Bloody rain stopped play im afraid, not going down the seafront tomorrow to watch the spring tide waves plus forcast 70mph wind, get washed away!
Well done
Mark

Davek0974
01-31-2014, 04:48 PM
I cheated on the z axis and bought it ready made off eBay, special offer 98 plus I had the motor already, probably couldn't get the parts for that much and it's nicely made too, marchantDice was the seller.

I have electric worries too, only got 30a in my garage, I have a 30a plasma plus it has to run the compressor, I was hoping to get a bigger plasma but will need to rewire which means digging up the driveway and the back garden :(

Once the axes were calibrated, I ran a few files over and over again and it didn't lose a step, I'm most pleased with that, got it set for 15m/min max at the moment but it would go much more if pushed.

It's addictive to play with :)

boslab
01-31-2014, 04:57 PM
Run a second cable rather than dig, use the two!
Mark

Davek0974
01-31-2014, 04:59 PM
Yeah but it would still need burying.

;)

Davek0974
02-03-2014, 01:56 PM
Picture of the whole contraption, still temporarily wired....
http://www.davekearley.co.uk/LinkPics/CNC7.jpg

And one of my first attempt at a floating head that I knocked together today...
http://www.davekearley.co.uk/LinkPics/CNC8.jpg

Seems to be working ok so far at sensing material height.

vpt
02-03-2014, 05:14 PM
Awesome!

boslab
02-03-2014, 06:36 PM
Might be a stupid question but how does it sense height?, nice job btw
Mark

John Stevenson
02-03-2014, 06:43 PM
Can't answer directly for Dave but I'm guessing it doesn't, Z over feeds down and the front carriage gets pushed backup by the torch, pen in this case is always in contact with the work.
If you look on the test lettering there are two lines from the corner to the e where it doesn't lift z high enough. Post pro probably need tuning a bit.

Drag engravers work the same way but the carriage on them is spring loaded to keep pressure on the diamond.
In this case it's a non force operation so just dragging it will work.
Still an impressive build

wmgeorge
02-03-2014, 06:47 PM
Yes, beautiful job of fabrication and building.

Davek0974
02-04-2014, 02:18 AM
Got it in one John, but the "Test" word was written before i fitted the floating head.

It uses a command to drop the torch onto the plate then over feeds until the switch trips, this distance is a known amount and programmed in, it then resets its ref point, lifts up by the known amount and proceeds to lift to pierce height ready for the cut.

Its very simple and very clever.

This was fitted as a way around (partially) of fitting THC or torch height control which is fully automatic and adjusts the torch on the fly, but it costs and personally is a bit overkill on a small machine. On the other hand it would allow it to cut on slopes and corrugations, there are vids on youtube and again is very impressive.

Hopefully i will have it running again today as i blew a motor drive last week and am waiting for the replacement not sure if it was my fault or just poor cheap components.

John Stevenson
02-04-2014, 04:22 AM
Your fault ;)

Seriously motors today are vitually bomb proof, really hard to take a motor out without taking the driver out.
Drivers are the weakest link in a CNC operation that's why I don't like the all on one board operations, one goes the whole lot is toast.

The seperate Leadshine type driver like the 542 and it higher voltage cousin are very good. They have done a lot of work on these and are always working forward. Things have certainly moved on from the early days. 5 years in electronics is a lifetime.

Davek0974
02-04-2014, 04:39 AM
Yeah I'm pretty certain it was my fault, they have built in heat-sinks so I cleverly thought I could get away with bench-testing them as stand-alone units, seems I was wrong :)

They get very hot, very quickly, and one unit let the smoke out, so I am guessing these cheapy units have no over-temperature shutdown in them. I have now bolted the remaining good ones to some big lumps of aluminium with some thermal paste at the joint, should help, I also have some small PC CPU fans I might slap on them as well.

I'm running 36v at 4.2A on each motor and the drives are rated 5A.

I too didn't like the all-in-one board, looks tidy but only one point of failure, I like smaller, cheaper to replace items.

It's addictive stuff :)

Davek0974
02-04-2014, 01:57 PM
Having said it was my fault, I'm not so sure now.

I stripped the blown drive down today looking for the hole where the magic smoke escaped :)

They use a TB6600 single chip and was amazed to see that there was no thermal paste or sheet between the chip and the heat sink, not a drop. Now, even my minimal electronics knowledge tells me that's a long way from a good idea!

I think I'll strip them and remount the chips on some heat sink paste.

lakeside53
02-04-2014, 08:37 PM
I've never had any luck with those drivers other than at mediocre step rates. Replacing them with gecko drivers was like night and day, but of course more $.

Davek0974
02-05-2014, 01:11 PM
Well, the replacement driver came today, didn't work, appears it's not compatible with my breakout board or just dead-in-the-box :( of course no support as the guy is in china. That will be going back for a refund.

So the only option was to bin the whole lot and try and get some cash back due to the failed drive board, then I ordered some decent gear from cnc4you which is a uk supplier and have excellent phone support.

Three new drivers and a breakout board on the way for tomorrow, loads more but at least they will be compatible with each other and I have support.

I guess you get what you pay for, as usual, lesson learnt.

Davek0974
02-07-2014, 02:22 PM
New drives are much better, only just get warm and seem stable so far.

Here's another video of her running a g-code file created from a file intended for a laser etching machine that makes cutting dies I use in the day job. It's an evil file and would not work with plasma due to the kerf width but it's a great test job.

http://www.davekearley.co.uk/LinkPics/CNCVID2.mp4

The image shown has been overdrawn two or three times already and shows zero step error or loss. The more I play with it the more impressed I am.

This was also shot before I fixed the CV code issue I had spotted today that's why it seems a little jerky.

I'm work-hardening the electronics now, until that's done I dare not light the torch near it, bound to bugger something up with the radiated HF ;)

Davek0974
02-09-2014, 12:07 PM
Thinking of using angle iron as the sheet support area, I have a qty of 20x20*3 hot rolled angle on the floor, was thinking of using it with the ^ upwards, laying on some angles bolted inside the frames. That way I could move them around as needed and replace easy?

I gather the work is directly grounded to the plasma as normal, you don't just ground the table supports and hope for the best???

wierdscience
02-09-2014, 02:39 PM
The angle would probably work for testing,but a plasma even at a low power setting will butcher up that small angle fairly quick.

Some of the lite commercial tables use vertical slats made from 1/16"(1.5m) thick x 3"OR 4"(75/100m) wide sheetmetal strips.That way even if a cut goes half way through the vertical it's still strong enough to keep using.Cheap and sacrificial is what you need for the task.

Davek0974
02-09-2014, 03:29 PM
Ok thanks, will look into devising ways to install strip supports.

I like the idea of running the slats wavy or at angle to minimise coincidence with straight cuts.

John Stevenson
02-09-2014, 04:28 PM
You want a sheet of 19mm ply and 7lbs of 4" nails
Belt them into the sheet all the way in 1" grid squares, turn over and stand the ply in a inch of water and you have a nail bed.
Supports but is hard to hit with the torch. Easy to replace.

Davek0974
02-09-2014, 04:38 PM
I quite like that idea, thanks ;)

lakeside53
02-09-2014, 05:07 PM
You want a sheet of 19mm ply and 7lbs of 4" nails
Belt them into the sheet all the way in 1" grid squares, turn over and stand the ply in a inch of water and you have a nail bed.
Supports but is hard to hit with the torch. Easy to replace.

Ah.. and with a little practice you can lie on it to impress the ladies.

John Stevenson
02-09-2014, 05:16 PM
Certainly will if you lie on it face down....................

Davek0974
02-10-2014, 01:43 PM
Got the panel wired today...
http://www.davekearley.co.uk/LinkPics/CNC9.jpg

Need to figure out a slat support system for the bed, then I can get her cutting.

wmgeorge
02-10-2014, 04:37 PM
You want a sheet of 19mm ply and 7lbs of 4" nails
Belt them into the sheet all the way in 1" grid squares, turn over and stand the ply in a inch of water and you have a nail bed.
Supports but is hard to hit with the torch. Easy to replace.

John, assuming you have pegboard over there, its pretty much worldwide. That would automatically get him the 1 inch grid he needed. If you used the thin stuff and ringed shank nails...

lakeside53
02-10-2014, 08:28 PM
pegboard? Not going to last underwater at all.

boslab
02-10-2014, 09:12 PM
Well extending the pegboard idea i saw punched steel sheet at my local metal stockist, or should i say perforated, think it may be for baffles or filters not sure, there was stainless too, perhaps that sort of thing would work?
Mark

wmgeorge
02-11-2014, 08:38 AM
pegboard? Not going to last underwater at all.

For the pattern, and isn't 19mm ply, plywood?

lakeside53
02-11-2014, 01:18 PM
Yes, it's 3/4. But there many types. You'd be using a marine ply around here as typical sheathing plyood (doug fir outers, hemlock and cotton wood cores) delaminate and buckle in short order. You might get away with exterior ply for a few months, maybe. Cabinet ply would be a joke.

Davek0974
02-11-2014, 02:31 PM
I think wood is a non starter in this application, I was aiming for a down draught design eventually and there would be a pretty good fire hazard with wood under a plasma cutter surely?

I have a large stock of black steel 3mm x 20mm so if I could use that it would be handy, just need some sort of support system that would allow me to bow the strips, I think that would work for a while.

The width is only about 700mm so I guess three supports and strips every 40-50mm?

RichR
02-11-2014, 03:36 PM
Hi Davek0974

I have a large stock of black steel 3mm x 20mm so if I could use that it would be handy, just need some sort of support system
If you can cut 1.5mm x 10mm notches in them you can interlock them into a grid.

Davek0974
02-11-2014, 03:59 PM
That's the current thought, just need to find a painless way to cut 3mm slots 10mm deep in something like 20x20 angle etc, don't want to invest much effort in this bit as I have a feeling it will need changing.

Of course, indeed it's running I guess I can get it to cut it's own support slats, might just fit on the diagonal ;)

wmgeorge
02-11-2014, 07:32 PM
That's the current thought, just need to find a painless way to cut 3mm slots 10mm deep in something like 20x20 angle etc, don't want to invest much effort in this bit as I have a feeling it will need changing.

Of course, indeed it's running I guess I can get it to cut it's own support slats, might just fit on the diagonal ;)

I think Johns idea was submerging the nail studded plywood in water.

Davek0974
02-12-2014, 01:27 AM
Sounds like a recipe for wood soup, even marine ply wouldn't live long under water, even with varnish.


Quick question, can plasma cut a one sided path?

I.e. If I have a drawing with a slot 5mm wide and try to cut it with a tool having a 3mm kerf, would the second, one-sided cut work or fail?

vpt
02-12-2014, 08:18 AM
Our bait tanks that are filled with water all the time are made out of marine plywood.

http://img593.imageshack.us/img593/874/mj7r.jpg

lakeside53
02-12-2014, 11:58 AM
Sounds like a recipe for wood soup, even marine ply wouldn't live long under water, even with varnish.




Well... I've had some underwater in my lake for 15 years. All it got was a Penofin oil finish, (which is long gone).

alha
02-12-2014, 02:23 PM
Davek0974, very attractive build. I am new to the forum, have to say there is a Lot of VG information here. I do have one question about your build, and it isn't a criticism. If you look at factory built pieces like the Plasmacam and such, the table legs seem to be a little more beefy, and the tables just seem to have a bit more mass. Since you have now had it running with a pen, and soon with a torch, how has it responded to rapid changes in lateral movements with the extruded AU legs? Is it pretty stable so far? I see a little triangle bracing where the legs meet the table, which should stiffen it up a bit, but how does it perform in action? That was the first thing I thought of once I saw the table assembled. And please don't take it as a criticism, I am thinking of possibly adding one to my shop, and if I can build one using reasonably priced materials and my knowledge of computers and electronics, that works as good or better than a factory built one, I may just follow in your footsteps! Thanks for the great documentation, keep us informed how it's going, both the successes and challenges, we appreciate both.

Davek0974
02-12-2014, 02:27 PM
I'm impressed, some good wood :)

Did some tidying up today, hardened the electronics as much as possible against the plasma torch..
http://www.davekearley.co.uk/LinkPics/CNC11.jpg
http://www.davekearley.co.uk/LinkPics/CNC10.jpg

I also went scrounging round a metal fab shop nearby, looking for flat scraps to practice on, while there I explained what I was doing and what I needed and he is now punching some slots in steel strips for me to make a bed unit. He's fitting it in on the cheap so I could hardly refuse, also walked away with a pile of scrap steel plate :)

Davek0974
02-12-2014, 02:33 PM
Davek0974, very attractive build. I am new to the forum, have to say there is a Lot of VG information here. I do have one question about your build, and it isn't a criticism. If you look at factory built pieces like the Plasmacam and such, the table legs seem to be a little more beefy, and the tables just seem to have a bit more mass. Since you have now had it running with a pen, and soon with a torch, how has it responded to rapid changes in lateral movements with the extruded AU legs? Is it pretty stable so far? I see a little triangle bracing where the legs meet the table, which should stiffen it up a bit, but how does it perform in action? That was the first thing I thought of once I saw the table assembled. And please don't take it as a criticism, I am thinking of possibly adding one to my shop, and if I can build one using reasonably priced materials and my knowledge of computers and electronics, that works as good or better than a factory built one, I may just follow in your footsteps! Thanks for the great documentation, keep us informed how it's going, both the successes and challenges, we appreciate both.

Yes, the legs were a bit flimsy, the idea is that the back two legs will be removed when I fit it into my shop and then be bolted to one end of my bench, something like that anyway ;)

As you can see above, I've fitted some bracing straps now, the moving mass is pretty low due to the aluminium and small size and I've managed to tune the drive to some pretty spectacular and impractical speeds without losing steps so I'm pretty confident.

So far it's been a very educational project.

Davek0974
02-17-2014, 02:54 AM
Some questions for the advanced plasma guru's :) ....

Thinking more about the possible damage caused by running my HF touch-start torch with a grounded tip so it starts with full plasma flame, I keep coming up with questions.

In my limited knowledge, the arc is formed between the electrode and the tip with round orifice, the air then forces the arc gases or plasma out of the orifice into a flame shaped gas stream at very high temperature, very similar in shape to a fine tip on an O/A torch?

The flame is wider at its base and thinner at its tip, this shape is what gives plasma cuts a bevel depending on the cut height, normal cut is made at the fattest part of the 'flame'?

So, if my little torch is designed to be started and run with the tip grounded (its a drag torch), how can running it with the tip grounded in free air do it damage? Surely the arc current is still passing between the electrode and the tip inside the head and the flame and gas stream does the cutting, the gas (air) keeps the tip from melting?

I'm not trying to justify the modification of permanently grounding the tip as I do believe the manufacturers know best but I really am fascinated by the whole plasma thing (I also build and mess about with Tesla coils etc:)) so just want to know more about this simple modification and its possible ramifications in use, I have been told it will wreck the tip in short order but is that it? Will it damage the PSU or does the flame just go out and the tips go in the bin?

Interesting stuff.

jimcolt
02-17-2014, 02:03 PM
The plasma arc is started by ionizing gas (air) between an electrode (negative) and a nozzle (positive). To ionize the air often a high frequency, high voltage AC discharge is created between the electrode and the nozzle, the plasma gas (air) passes through this discharge, converting the air to an ionized gas , which is electrically conductive....this electrically conductive air then creates a path from the negative electrode to the positive nozzle, which creates a DC pilot arc.

In a plasma system that is designed to fire a pilot arc, the nozzle is connected to positive through a relay (that can handle the voltage and DC current), and then through a current limiting circuit (resistor in older technology plasma....a current control circuit (chopper) in a more modern plasma system) that limits the amount of current that flows from electrode to nozzle. Too much current (on a small plasma generally more than about 12 to 15 amps) and the noozle orifice will be altered (melted) by the plasma arc. In this type of plasma the pilot arc relay opens as soon as the arc attaches to the positive plate.....sensed by current flow on the work ground cable.

In a plasma system that is designed to start by touching the nozzle to the plate (which is also positive)...the nozzle is not connected to the positive output of the power supply, rather, it becomes at positive potential whenthe operator makes the copper nozzle touch the positive plate...thus allowing the HF a path, as well as ionizing the DC so that a more intense DC arc is started. If the nozzle remains in contact with the plate, some of the DC energy will exit through the plasma stream through the nozzle orifice, the remaining energy will short from the nozzle to the plate, two paths of current flow....this is known as double arcing. Because some current bleeds through the nozzle body to the plate...the cutting process has less power. By lifting the nozzle off the plate (1/16" to 1/8" typically), the shorting from nozzle to plate stops, and all of the DC power goes directly through the ionized plasma stream and improves cutting power and speed.

If you wired the nozzle directly to the positive power supply output....current splitting between the arc and the path back to the power supply would continu, the nozle would be overheated (very quickly) and would not last long. Trust me.

A couple of other things....there is no flame. It is an arc that is shaped by the nozzle orifice. If the orifice is properly designed and there is no orifice damage, and the gas pressure and current are correct the arc is actually a column. Once the nozzle orifice is damaged, the arc will "extrude" at whatever shape the nozzle orifice has taken, often producing wildly varying bevel angles around the perimeter of a cut. Some think this is normal for plasma....and it is with some older technology as well as some improperly operated plasma systems.

There is a most efficient area of the arc where it produces its best energy density. Some torch designs work best very close to the material (.060", 1.5mm) and some work a bit further away. Height control during cutting is critical to ensure that the highest energy density area is doing the cutting. To high and edge angularity gets worse.

Jim Colt Hypertherm




Some questions for the advanced plasma guru's :) ....

Thinking more about the possible damage caused by running my HF touch-start torch with a grounded tip so it starts with full plasma flame, I keep coming up with questions.

In my limited knowledge, the arc is formed between the electrode and the tip with round orifice, the air then forces the arc gases or plasma out of the orifice into a flame shaped gas stream at very high temperature, very similar in shape to a fine tip on an O/A torch?

The flame is wider at its base and thinner at its tip, this shape is what gives plasma cuts a bevel depending on the cut height, normal cut is made at the fattest part of the 'flame'?

So, if my little torch is designed to be started and run with the tip grounded (its a drag torch), how can running it with the tip grounded in free air do it damage? Surely the arc current is still passing between the electrode and the tip inside the head and the flame and gas stream does the cutting, the gas (air) keeps the tip from melting?

I'm not trying to justify the modification of permanently grounding the tip as I do believe the manufacturers know best but I really am fascinated by the whole plasma thing (I also build and mess about with Tesla coils etc:)) so just want to know more about this simple modification and its possible ramifications in use, I have been told it will wreck the tip in short order but is that it? Will it damage the PSU or does the flame just go out and the tips go in the bin?

Interesting stuff.

jimcolt
02-17-2014, 02:04 PM
The plasma arc is started by ionizing gas (air) between an electrode (negative) and a nozzle (positive). To ionize the air often a high frequency, high voltage AC discharge is created between the electrode and the nozzle, the plasma gas (air) passes through this discharge, converting the air to an ionized gas , which is electrically conductive....this electrically conductive air then creates a path from the negative electrode to the positive nozzle, which creates a DC pilot arc.

In a plasma system that is designed to fire a pilot arc, the nozzle is connected to positive through a relay (that can handle the voltage and DC current), and then through a current limiting circuit (resistor in older technology plasma....a current control circuit (chopper) in a more modern plasma system) that limits the amount of current that flows from electrode to nozzle. Too much current (on a small plasma generally more than about 12 to 15 amps) and the noozle orifice will be altered (melted) by the plasma arc. In this type of plasma the pilot arc relay opens as soon as the arc attaches to the positive plate.....sensed by current flow on the work ground cable.

In a plasma system that is designed to start by touching the nozzle to the plate (which is also positive)...the nozzle is not connected to the positive output of the power supply, rather, it becomes at positive potential whenthe operator makes the copper nozzle touch the positive plate...thus allowing the HF a path, as well as ionizing the DC so that a more intense DC arc is started. If the nozzle remains in contact with the plate, some of the DC energy will exit through the plasma stream through the nozzle orifice, the remaining energy will short from the nozzle to the plate, two paths of current flow....this is known as double arcing. Because some current bleeds through the nozzle body to the plate...the cutting process has less power. By lifting the nozzle off the plate (1/16" to 1/8" typically), the shorting from nozzle to plate stops, and all of the DC power goes directly through the ionized plasma stream and improves cutting power and speed.

If you wired the nozzle directly to the positive power supply output....current splitting between the arc and the path back to the power supply would continu, the nozle would be overheated (very quickly) and would not last long. Trust me.

A couple of other things....there is no flame. It is an arc that is shaped by the nozzle orifice. If the orifice is properly designed and there is no orifice damage, and the gas pressure and current are correct the arc is actually a column. Once the nozzle orifice is damaged, the arc will "extrude" at whatever shape the nozzle orifice has taken, often producing wildly varying bevel angles around the perimeter of a cut. Some think this is normal for plasma....and it is with some older technology as well as some improperly operated plasma systems.

There is a most efficient area of the arc where it produces its best energy density. Some torch designs work best very close to the material (.060", 1.5mm) and some work a bit further away. Height control during cutting is critical to ensure that the highest energy density area is doing the cutting. To high and edge angularity gets worse.

Jim Colt Hypertherm




Some questions for the advanced plasma guru's :) ....

Thinking more about the possible damage caused by running my HF touch-start torch with a grounded tip so it starts with full plasma flame, I keep coming up with questions.

In my limited knowledge, the arc is formed between the electrode and the tip with round orifice, the air then forces the arc gases or plasma out of the orifice into a flame shaped gas stream at very high temperature, very similar in shape to a fine tip on an O/A torch?

The flame is wider at its base and thinner at its tip, this shape is what gives plasma cuts a bevel depending on the cut height, normal cut is made at the fattest part of the 'flame'?

So, if my little torch is designed to be started and run with the tip grounded (its a drag torch), how can running it with the tip grounded in free air do it damage? Surely the arc current is still passing between the electrode and the tip inside the head and the flame and gas stream does the cutting, the gas (air) keeps the tip from melting?

I'm not trying to justify the modification of permanently grounding the tip as I do believe the manufacturers know best but I really am fascinated by the whole plasma thing (I also build and mess about with Tesla coils etc:)) so just want to know more about this simple modification and its possible ramifications in use, I have been told it will wreck the tip in short order but is that it? Will it damage the PSU or does the flame just go out and the tips go in the bin?

Interesting stuff.

Davek0974
02-17-2014, 02:44 PM
Excellent reading, thanks

So, once the arc is established, the current path is from the electrode with its little hafnium insert, through the hole in the tip and to the metal being cut via the plasma stream?

My little torch does cut better with a little gap, around 1 to 2mm maybe from the work but the manual does say it can be fully dragged as well. It will actually start on its own if held about 1mm away from the work as well.

I can see an upgrade to a larger machine with pilot arc on the way, can't afford a hypertherm unfortunately though :(

Davek0974
02-17-2014, 02:52 PM
Jim, I tried emailing you regarding the cut charts but it bounced straight back??

Anyway I'll send a PM.

jimcolt
02-17-2014, 03:01 PM
The swirling of the gas creates a magnetic vortex....which is supposed to force the arc attachment point dead center on the hafnium insert. It nrmally starts off to the side.

If you ever really start using your torch, then you can afford a Hypertherm! Cheaper to operate, cheaper cost of ownership. Yes they do cost more to purchase, thats why I suggest looking for a used Hypertherm.

Best regards, Jim Colt


Excellent reading, thanks

So, once the arc is established, the current path is from the electrode with its little hafnium insert, through the hole in the tip and to the metal being cut via the plasma stream?

My little torch does cut better with a little gap, around 1 to 2mm maybe from the work but the manual does say it can be fully dragged as well. It will actually start on its own if held about 1mm away from the work as well.

I can see an upgrade to a larger machine with pilot arc on the way, can't afford a hypertherm unfortunately though :(

jimcolt
02-17-2014, 03:03 PM
Recently some people reported having trouble with my email, has to do with whatever browser you are using doesn't get along with mine......I sent you a direct copy of the cut charts for 30 amp air cutting with a Hypertherm.


Jim, I tried emailing you regarding the cut charts but it bounced straight back??

Anyway I'll send a PM.

Davek0974
02-17-2014, 03:07 PM
Many thanks and yes, I'll look out for used hypertherm.

Dave

Davek0974
02-18-2014, 09:48 AM
Had a chat with R-Tech today, they are my favoured supplier for mig and plasma stuff, I did check for used Hypertherm kit but even on ebay the prices are just silly at present.

It turns out they will do me a good deal on an upgrade package for my little 30A plasma as they are in high demand at present, naturally I agreed :)

So, some time next week I should have a nice new 50A Pilot arc plasma coming with a machine torch and CNC connection lead, that should alleviate a few possible issues and give me some comfortable headroom in capacity, plus it has a respectable 60% duty cycle at full power which likely means that at my thinner material settings will give practically non-stop cutting.

Its one of these babies...
http://www.r-techwelding.co.uk/welding_equipment/Plasma_Cutter/Plasma_Cutter_R-Tech_P50HF

wmgeorge
02-18-2014, 09:54 AM
It looks to be HF pilot start which might cause a problem with your electronics.

Davek0974
02-18-2014, 10:06 AM
Well, yes but it's built for CNC and I have taken every precaution I can as regards isolation between the outside and inside of my control cabinet.

There are no low power signal lines outside, it's all star earthed, housed in a grounded metal cabinet, all controls are 24v relay isolated and so on.

Plus, as mentioned, it's made for CNC.

jimcolt
02-18-2014, 10:13 AM
If you are shopping for a plasma for a cnc , you really should consider a non high frequency start (known as blowback start). The one you have spec'd is high frequency.....which is always problematic on cnc machines that use a PC or laptop as the cnc control (as opposed to using an industrial cnc control that is designed for noise electrical environments). There are plenty available....Hypertherm's patent for the blowback start invention expired years ago! Often these systems are less expensive as compared to HF start.

The difference: The electrode and nozzle are in contact when the torch is off. When you trigger the system for the torch to fire, the DC pilot arc power (lower than cut current) activates and is dead shorted from electrode to nozzle. A few miliseconds later the air flow builds at the torch head...the increasing pressure in the torch pushes the (spring loaded) electrode back away from the nozzle.....the release of the electrical short between the two creates a high intensity spark (takes the place of high frequency spark) and ionizes the plasma gas (air) to create a DC plasma pilot arc.

High frequency starting circuits in a plasma are in the 15 kv, 2 megahertz range. This type of energy easily couples (inductively) through cables on a cnc system, and often will affect or damage the PC, the height control or sensitive drive electronics.

Another thing I note with the new plasma system is the 60% duty cycle rating. I find that most of the Chinese built machines have a rating...but with no data regarding how the 60% is calculated. For a duty cycle number to be valid...it needs an ambient temperature, it needs a load voltage and an amperage....with these three items a duty cycle percentage can be calculated. All plasma systems are 100% duty cycle at full output amperages......if it is a cool day (low ambient temperature) and you are cutting very thin material (low load voltage, the voltage is determined by the length of the arc....thicker material requires a longer arc). The major manufacturers include this data in their specifications, and duty cycle is rated at 40C ambient, at full rated output amperage, and at the voltage required to cut the maximum rated production thickness. Manufacturing a power supply with a lower output load voltage and ambient temp rating is far less costly.

Jim Colt

Davek0974
02-18-2014, 10:28 AM
I have just been talking to them again, they do have a cartridge-start system but I would have to go to a 100A system which I cannot power at home so that's out of the question, the 100A unit also has the 7pin torch plug etc.

He also agreed with my concerns regarding the HF but reassured me that many CNC machines both DIY and small professional are running ok on this PSU so I have little choice but to give it a go.

There have to be limits in any system and power supply, air supply and cash supply are three of mine, I just can not run to a Hypertherm unit, even used as I would not get such a good buy-back deal for my old unit.

Don't forget that this is hobby stuff, so I'm already way beyond hobby-style with a 50A cutter! :)

BTW, R-Tech build their kit in the UK.;)

jimcolt
02-18-2014, 10:42 AM
Looks exactly like the Chinese power supplies under a variety of different brand names that we see in the U.S.! I understand budget, just offering advice from my 36 years of plasma cutting, as well as building my own machines over the years! Yes you can make it work, but, yes you will have some issues that will need to be sorted out. The blowback start eliminates these electrical noise issues.

Jim Colt



I have just been talking to them again, they do have a cartridge-start system but I would have to go to a 100A system which I cannot power at home so that's out of the question, the 100A unit also has the 7pin torch plug etc.

He also agreed with my concerns regarding the HF but reassured me that many CNC machines both DIY and small professional are running ok on this PSU so I have little choice but to give it a go.

There have to be limits in any system and power supply, air supply and cash supply are three of mine, I just can not run to a Hypertherm unit, even used as I would not get such a good buy-back deal for my old unit.

Don't forget that this is hobby stuff, so I'm already way beyond hobby-style with a 50A cutter! :)

BTW, R-Tech build their kit in the UK.;)

Davek0974
02-18-2014, 10:59 AM
No worries Jim, advice is good and always welcomed, don't take any offence if it seems I ignore it :)

Yes R-Tech uses many imported parts but they pick and choose what goes in, and the rest is upgraded as they see fit to produce what are pretty much bomb-proof units, I've checked inside both my little plasma and the mig welder I have and the stuff looks top quality and well made. The mig wire-drive is a massive unit with a motor twice as big as my old hobby machine, the wire feed is rock-steady. It's just good kit basically backed up with the best tech support I've seen in a long time.

I'm sure there will be issues but there should be a lot less of them compared to me trying to use my small unit on the CNC.

wmgeorge
02-18-2014, 01:05 PM
I guess what Jim is trying to tell you, look for a used Hypertherm or other blow back start machine instead of HF. I paid for a new Hypertherm 380 in USD close to or within 300 in what you are going to pay for the HF start unit.

Davek0974
02-18-2014, 02:14 PM
I guess what Jim is trying to tell you, look for a used Hypertherm or other blow back start machine instead of HF. I paid for a new Hypertherm 380 in USD close to or within 300 in what you are going to pay for the HF start unit.

The nearest I can find is a used powermax 45 currently running on eBay at 200 more than I paid for a new 50a unit, it has a few days to run yet and I would be surprised if it didn't end at around 1000 pr so.
Just too rich for me at present, who knows what the future will bring ;)

wmgeorge
02-18-2014, 05:12 PM
Do you have to pay VAT on eBay purchases? I see the one you are buying is over 700 with the VAT added.

Davek0974
02-19-2014, 01:26 AM
I'm paying around 400 with my buy-back deal, that's why it's a bargain.

The eBay stuff is vat inclusive over here, that one will likely hit 1000 at the end.

wmgeorge
02-19-2014, 11:35 AM
In searching for a laser control system for a China made laser engraver I came across this Dave> http://www.candcnc.com/ They have controls for torch height and more.

jimcolt
02-19-2014, 12:12 PM
www.candcnc.com is the largest supplier of low cost electronics (CNC and height control) as well as drive packages (morors and drives) and software (CAD and CAM) for do it yourself cnc plasma cutting machines. Great company, great products, excellent support.

Jim


In searching for a laser control system for a China made laser engraver I came across this Dave> http://www.candcnc.com/ They have controls for torch height and more.

Davek0974
02-19-2014, 12:56 PM
I'll check that site, looks useful, thanks.

I got the bed slats fitted today...
http://www.davekearley.co.uk/LinkPics/CNC12.JPG

Also ordered some shielded cable for the rewire.

Davek0974
02-19-2014, 01:13 PM
Yes, and the price of the LTHC kit is great, but America only it seems :(

Black Forest
02-19-2014, 01:50 PM
Yes, and the price of the LTHC kit is great, but America only it seems :(

The last time I talked to Tom he said they will ship to anyone that speaks fluent English. Support was a problem in non English speaking customes.

Email them and ask.

Davek0974
02-19-2014, 02:00 PM
Ok thanks

Davek0974
02-20-2014, 07:59 AM
Grounding...

Having been informed about the risks of interference from a plasma cutter affecting the Pc controlling it, I am doing some work prior to the cutter arriving next week. There is an excellent thread here as well..http://www.cnc-arena.com/en/forum/grounding-cnc-plasma-question--176941.html

So far, I have fitted screening braid to the stepper motor leads up to the point where they connect to the (now) shielded 4-core cables, this shield is connected at one end only to machine ground. The motor cable shields are connected at one end only, inside the steel control cabinet directly to my cabinet star earth stud.

I have connected the Z-axis to the gantry carriage at the steel terminal box, this point is the run back to the cabinet star point with its own ground cable. Next I have connected the gantry back to the star point with it's own ground cable. The steel cabinet is bolted directly to the chassis so I can't see much point in connecting another ground lead there??

The travel limit, e-stop and probing switch circuits are all relay isolated from the BOB and run on a separate 24v PSU, cables are just standard 2-core flex.

The e-stop relay also kills the torch control signal in case the board locks up with the torch on.

I have fitted several ferrite clamp-ons to supply cables etc.

The case of the PC is connected back to the control star point with a ground lead.

The keyboard and mouse have ferrite clamp-ons fitted at the PC end.


Now for the unknown bits....

The case of the plasma PSU has a bolt lug for grounding, I intend to connect this to a ground spike, the chassis of the machine also, as well as the slat bed with its own ground lead. Is this a good idea or should I just connect the slat bed ??

The torch lead will be suspended from above and not run in the cable-track.

How long can the ground leads be to the earth spike??
Where the machine will likely be going is about 15' from the ground outside, I could drill through the concrete floor but I have no idea how far down actual 'soil' is underneath the shop.

I could possibly drill through the wall and sink the spike there, that would be about 4' away.

Is it best to remove the ground clamp from the plasma and bolt the lead directly to the slat bed or just clamp it on??


I want to give myself the best chances of success before actually firing up the torch:)

John Stevenson
02-20-2014, 08:29 AM
Dave,
i have run one of these Cut40 plasma cutters by bolting a 3' length of box section to the bed of the mill and putting the torch on that. Work is supported on an old metal milk crate.
A really crude get John out the Sheite situation but it works and the CNC isn't hardened at all, in fact it's messy as it's been modified much over the years and frankly if i was keeping it , it needs a rewire. No shielded cables, cables hanging in loops from the wall mounted driver box back to the machine.

but as I say it works and has never fallen over

Davek0974
02-20-2014, 08:43 AM
Dave,
i have run one of these Cut40 plasma cutters by bolting a 3' length of box section to the bed of the mill and putting the torch on that. Work is supported on an old metal milk crate.
A really crude get John out the Sheite situation but it works and the CNC isn't hardened at all, in fact it's messy as it's been modified much over the years and frankly if i was keeping it , it needs a rewire. No shielded cables, cables hanging in loops from the wall mounted driver box back to the machine.

but as I say it works and has never fallen over

That is the kind of response I like to hear, down and dirty and it still worked, gives me great confidence that what I am doing will actually work when I finally push the button :)


I like the idea of multi-tasking the mill too ;)

Davek0974
03-05-2014, 02:42 AM
The new 50A plasma cutter arrived today, this thing is beast, there must be half a pound of copper in the torch tip at least :o

Found out some more about the internals of the PSU, seems they come from the US or Germany, no China parts.

Hopefully get it cutting this week some time.

Davek0974
03-06-2014, 10:43 AM
Well, my feeling of positive "yes it will work" didnt last long....


As many of you will know I have been eagerly awaiting the delivery of my new plasma torch, while waiting I have been extensively testing and debugging my new DIY CNC table and it was all going very nicely.

The torch came yesterday so I moved the table into my test area, connected up the ground clamp to the slat bed and powered the system up.

All went ok, Mach3 was happy, so I placed a bit of test metal on the table, moved to position for a test fire and triggered a quick pierce signal, no cut just a quick pierce at half power.

That went ok so I went to move the torch back to start position for a cut test, the torch would not move so I pressed the e-stop and re-enabled Mach3, z axis started moving and partial x axis but not Y.

Killed the plasma supply and restarted Mach.

Now it was jumping about randomly as i turned the MPG knob on the pendant and kept throwing "e-stop requested" errors.

Thinking it might be my cheapo crap pendant, i unplugged it, turned off "run macro-pump" and disabled support for modbus/mpg, I think that was all that is needed to return to normal?

Then i restarted Mach and tried again, now it sort of moves but the DRO's are moving like 20mm for every physical mm moved, its moving very jerky too.

Pressing home-all, would bring the axes to home but then back off at 1% speed or very slow at least.

It would also still throw the e-stop requested errors.



Now, having spent a lot of effort hardening the table against RF, I really can't believe I have fried it with a two second pierce?

No other PC's in the area showed any sign of problem and there was no radio interference.
This was just a quick pierce at half power.

Any suggestions at all?
I'm desperate.

lakeside53
03-06-2014, 11:21 AM
If it's doing these weird things with the table unplugged, then I'd reinstall Mach or whatever.

Was your interface buffer board optically isolated (with separate power supplies for each side), all signal lines?

Davek0974
03-06-2014, 02:40 PM
If it's doing these weird things with the table unplugged, then I'd reinstall Mach or whatever.

Was your interface buffer board optically isolated (with separate power supplies for each side), all signal lines?

Hi, yes it's optically isolated, I have one psu which runs the bob and motors, and one for the control circuits/relays.

All controls are 24v relay isolated, no PC signals are taken outside the enclosure.

The software loads fine and still passes the mach driver test ok, I can reload it in the morning.

wierdscience
03-06-2014, 03:01 PM
I would try grounding to the workpiece itself,though you may have already toasted something from the sound of it.

Davek0974
03-06-2014, 03:47 PM
I did check with a meter before firing that there was a good continuity from the work to the ground clamp lead.

Hopefully it's just a loose wire as I have no budget left to replace toasted parts, and in any case I would not know why it toasted so quickly, with the extra work I did rewiring in shielded cable etc, I presumed it was pretty much bomb proof.

Davek0974
03-07-2014, 03:08 AM
No loose wires :(

I'm going to order a new parallel cable and try that, might be able to get another PC but if it works I can't risk testing it until I have removed the point of destruction.

Davek0974
03-07-2014, 07:38 AM
Scrub that, had a chat with the suppliers and the BOB is toast.

I had it wired to the supply for the z-axis motor and it seems this is a big no-no so i now have another supply for it but too late of course. New board on the way.

Here's how its wired currently...

1 - I have a 36v 11A smps connected to the three motor drives,

2 - a smaller 24v smps connected to the BOB,

3 - The BOB is a cnc4you.co.uk HG07 unit - http://www.cnc4you.co.uk/index.php?route=product/product&path=81&product_id=160

4 - Another small 24v psu is running the relays for e-stop and limits / torch trigger.

5 - I have used screened cable for all motor leads, this is connected at one end only inside the cabinet to a star ground.

6 - I have connected the Z-axis to the X-axis carriage and then back to the star point.

7 - I have connected the Y-axis gantry to the star point.

8 - The case of the PC is connected to the star point.

9 - All PC leads are fitted with ferrite chokes.

10 - The mains is now filtered at the plug.

11 - The plasma ground lead is clamped to the cutting bed.

12 - The frame of the table (and therefore the cutting bed) is not connected to my star point, I am guessing this is catered for by having the cabinet bolted direct?

The whole lot is mounted in a steel cabinet bolted to the machine frame.

Any obvious issues here ???

MrSleepy
03-07-2014, 08:35 AM
5 - I have used screened cable for all motor leads, this is connected at one end only inside the cabinet to a star ground.


I dont like that....thats an Audio solution for ground loops...which can easily be avoided by a full encloseure designed in a double insulated fashion....unfortunately HF has a habit of getting into everything through capacative coupling if not dealt with.

If you go to the UKs Compliance Club website archive , and download issue 65 of the EMC Journal... Page 25 onward has an article by Keith Armstrong on Design Techniques for cables and connectors ,and how to design full enclosures and avoid ground loops etc.

http://www.compliance-club.com/archive.aspx (you may have to register , but the archive is an incredible resource)


Rob

Davek0974
03-07-2014, 08:43 AM
I dont like that....thats an Audio solution for ground loops...
Rob

It's also a bone of contention for the whole of the internet it seems :(

Will look into that link, thanks

Davek0974
03-07-2014, 09:10 AM
I have just tested it again with a different 24v PSU connected to the BOB, this one is a PLC supply so pretty good quality.

It worked ok with the torch off, ran a cut program 10 times in succession and all worked ok.

Connected up the plasma and did a quick test pierce and down it goes again, no movement on the motors.

This now confuses me as it seems the BOB is OK still but i have serious issues elsewhere, trouble is i dont where or how to test them????

Following a reboot, normal control is returned.

The PC showed no signs of a crash, no lock-up or BSOD etc.

Not sure which way to go now but clearly i have issues.

Davek0974
03-07-2014, 09:41 AM
Its random, tried a reboot again, this time no control is regained.

As soon as i triggered the torch, the power led on the bob went out, the y-axis jumps 5mm and that's it, no more action.

Its also holding the motors locked despite being told to disable the drives, this point indicates the fried BOB but I cant risk another BOB until I know what went wrong or it can get expensive quickly.

RichR
03-07-2014, 11:29 AM
Did you keep your wiring separated or bundle all together to make it look pretty? Wiring that connects to one side of the opto-isolators
should be kept away from the wiring on the other side.

lakeside53
03-07-2014, 12:00 PM
If your BOB has socketed interface circuits, buy some replacements and try changing them. If you have access to an oscilloscope (and if you can't, someone that can drive it), it's a few minutes work to figure out what's wring.

Also.. check your BOB - even though you have two separate supplies, sometime you need to cut a link to isolate both grounds or common returns.

Davek0974
03-07-2014, 02:02 PM
i had a chat with the plasma supplier, told them of my woes and the only suggestion they had was to rive an earth rod, connect the terminal on the cutter to that and then connect the CNC table likewise. Unfortunately I couldn't drill a hole through the factory floor so I just connected the terminal to the table frame.

I tried that and managed three pierce tests this time but then locked up again.

Then I disconnected the earth from star point to PC case and it worked! Passed repeated pierce tests, then I run a simple cut-line test of six 70mm lines at reducing speeds, table was still responding so I ran another test pass followed by a more detailed test and it still responded afterwards!

here's the results...
http://www.davekearley.co.uk/LinkPics/CNC13.jpg
numbers are mm/min at 30A.

i like the result at 4000mm/min, it's very fine and about 0.75mm kerf, this is 1.5mm sheet so very thin.

i gather the point where it closes up at the end is due to deceleration?

anyway, it was getting late so I quickly dialled in 4000mm to my next test in sheetcam and compiled the g-code.
http://www.davekearley.co.uk/LinkPics/CNC14.jpg

It looked ok, showed up some signs of serious axis wobble but ok. However on turning it over it appears not to be cut very well. ...
http://www.davekearley.co.uk/LinkPics/CNC15.jpg

Now, I'm not too worried as I did rush the test and the changes to sheetcam so I may have bodged it up. The main thing for this thread is that it's working and surviving extended cuts.

many thanks to all for the helpful suggestions, much appreciated.

John Stevenson
03-07-2014, 02:57 PM
dave.
Looking good Think I can help but have to wait a couple of hours gotta shoot out

John Stevenson
03-07-2014, 04:49 PM
Dave.
Clues are on the back side in the corners like the T.
For something this thin, 1.5mm 30A sounds an awful lot.
Try running at less amps and less speed.

Also go into mach and in Config > general Config > second row from the right second box down is LookAhead xx lines, I think the default is 20, try stepping this up a biy so it doesm't slow into corners.

Also and I don't really know what I'm talking about but first row right hand side second block from the bottom is some controlas for plasma with again a look ahead command called distanvce tolerance.

try playing with these settings, as i say never run a plasma in anger so it's only a suggestion.

vpt
03-07-2014, 08:34 PM
I cut some 16 gauge (close to 1.5mm) just yesterday with 45 amps but at 350 ipm (8890mmpm). Cut beautifully!

wierdscience
03-07-2014, 08:49 PM
This chart might help-
http://www.victortechnologies.com/IM_Uploads/Literature/lit_233_CS_CM_81_A.pdf

Your optimum performance should have been at the 6000 mm travel rate.Looks like maybe you had a bit too much stand off.

The Comet trails look like accel/decel to me as well.

Looking good though,you are getting mighty close!

Davek0974
03-08-2014, 04:36 AM
Thanks, the chart is useful.

These were cut at around 2mm height.

I was rushing though as it was near closing time for the factory I work at, I should have more time this week, once I'm satisfied, I will bring it home and and squeeze it into my shop;)

Looks like I need to up my speeds as well, it's faster than I anticipated, but I'm confident it will handle it, probably have to drop the acceleration a little to cope though.

Davek0974
03-10-2014, 07:41 AM
Tried again this morning in my tea break :)

I cut repeated test lines at various speeds and settled on the one that gave me seemingly acceptable results, this turned out to be 20A at 1275mm/min. I am trying to keep speed down as my machine is happier at lower speeds (this will be looked at later) hence the lowest power possible, 1.5mm steel again, pierce height 4mm, cut height lowered to 1.5mm.

This setting gave me a 1mm kerf width, picture to follow as I need to upload it first then link.

One point I noticed was that I had plenty of dross on the good (job) side and almost none on the scrap (cutoff) side, does this indicate my cut direction is wrong???

System is behaving itself though which is good.

http://www.davekearley.co.uk/LinkPics/CNC16.JPG

Davek0974
03-12-2014, 11:06 AM
Well, all is still not as well as i thought it was...

I had some more play time today, tried some 30A test cuts and it's messing about, stopping the cut motion midway, throwing e-stops, losing co-ordination etc. the whole gamut of errors really.

It will be even worse if I plug the PC into the same extension as the system, I have to run two extension leads back to the wall socket just to get a partial success.

If it was 100% because I have no ground rod then I would stop testing until I take the machine home where I can fit one, but I'm not totally convinced it is that.

The system has a filtered plug fitted and the pc has an in-line mains filter fitted.

Not sure where to focus my efforts now????

boslab
03-12-2014, 07:14 PM
I recently read somewhere that a plasma torch should be treated as a rotating cutter due to the swirly thingy!, ie clockwise puts the dross on one side, and anticlockwise puts it on the stock, i have no idea as to the truth of this as my cutter is a pile of parts and i still have no power in the shop!, too busy laying bricks, only another 29000 to go
Mark

wmgeorge
03-12-2014, 08:04 PM
Thanks, the chart is useful.

These were cut at around 2mm height.

I was rushing though as it was near closing time for the factory I work at, I should have more time this week, once I'm satisfied, I will bring it home and and squeeze it into my shop;)

Looks like I need to up my speeds as well, it's faster than I anticipated, but I'm confident it will handle it, probably have to drop the acceleration a little to cope though.

FYI I ran my PlasmaCam table for over two years using a Hypertherm 380, max cut 3/8 steel max output as I recall 27 amps. Cut everything up to 1/4 inch but most was under like 16 gauge or 14 gauge. None of it looked as bad as what you are showing.

Davek0974
03-13-2014, 03:20 AM
FYI I ran my PlasmaCam table for over two years using a Hypertherm 380, max cut 3/8 steel max output as I recall 27 amps. Cut everything up to 1/4 inch but most was under like 16 gauge or 14 gauge. None of it looked as bad as what you are showing.

That is something I have noticed too from looking at many internet pictures of cut parts, must be something wrong somewhere.

The air although running on a long 3/4" run down the building is put through a filter and refridgerated dryer so it *should* be ok, don't think its water anyway.

Will be trying again today with some different mains filtering on the pc, if i can get it cutting i will try some thicker metal, but if i can only cut 1.5mm at half the recommended speed then something must be wrong. Yesterdays short tests short that 1.5mm at 30A would only cut at 3750mm/min, that still seems way off-chart.

Getting a bit concerned now.

Black Forest
03-13-2014, 05:11 AM
What pierce height and cut height are you running? Maybe you should pay closer attention to what Jim Colt has told you!!!!!!!

Davek0974
03-13-2014, 05:41 AM
What pierce height and cut height are you running? Maybe you should pay closer attention to what Jim Colt has told you!!!!!!!

I am using the plasma suppliers chart which lists 4mm pierce height for all metal up to 6mm thick and a cut height of 1.5 - 2.0mm across the board.

And which information from Jim do you feel I need to pay more attention too??

I can't find a blowback start system with less than 100A and I can't run more than 50A due to the supply. Its not strictly a start fault anyway as the cut will stop mid-way and not just as the torch fires.

Hypertherm is way out of budget.

As I said, I do not have any way to drive a grounding rod in its current location but if that is a definite solution then I will move it to it's final home where I can fit one.

Black Forest
03-13-2014, 07:16 AM
cut your pierce height in half and you cut height and see what happens. I don't know your plasma cutter but those distances you are using are very extreme.

Davek0974
03-13-2014, 07:35 AM
cut your pierce height in half and you cut height and see what happens. I don't know your plasma cutter but those distances you are using are very extreme.

Ok will have a go.

wmgeorge
03-13-2014, 10:10 AM
Never used a ground rod on the PlasmaCam table I was using. I made sure the ground clamp was on the grid and then made a short jumper cable from the Hypertherm ground clamp wire to the work piece using a heavy duty battery charger clamp.

Davek0974
03-13-2014, 10:35 AM
Hmm, I'm just going to do a test with the clamp direct to the work.

Will post back in a minute.

Davek0974
03-13-2014, 10:57 AM
Well, I'm not getting anywhere here, clamp direct to work, 30A on the display, 2mm pierce, 1.25mm cut at 3750mm/min pierce was ok but it barely made it halfway through 1.5mm sheet.

Something is desperately wrong I feel.

Of course, the PC crapped out at the end of the cut as well.

Davek0974
03-13-2014, 11:23 AM
Just had a chat with the suppliers and they feel the generator is not switching to full power i.e. I am cutting (or trying to) with pilot arc power which is about 20A on this model :(

They are sending me a new (tested good) hand-held torch for test purposes and while waiting they have advised me to try upping the air pressure to 75psi just for a test.

But basically at 30A and 1.5mm sheet, it should practically vaporise the damn thing at the slow speeds I have been trying!!

Will know more tomorrow.

wmgeorge
03-13-2014, 12:30 PM
What can you cut and what settings just using the PC on some sheet steel?

On my cheap Chinese Longevity 40D it will cut up to 1/2" (13mm) steel without a problem and it is pilot arc or blow back start not HF like some of the others on the market. It does a nice job with the hand torch. BUT I had a problem with it after I set the air pressure higher thinking it would be better for the heavier material. Wrong, it has a set air pressure range, too high too low it would not cut or even start.

Davek0974
03-13-2014, 03:07 PM
What can you cut and what settings just using the PC on some sheet steel?

On my cheap Chinese Longevity 40D it will cut up to 1/2" (13mm) steel without a problem and it is pilot arc or blow back start not HF like some of the others on the market. It does a nice job with the hand torch. BUT I had a problem with it after I set the air pressure higher thinking it would be better for the heavier material. Wrong, it has a set air pressure range, too high too low it would not cut or even start.

As it stands, I can just about cut 1.5mm steel, at 1750mm/min, any faster and it just about marks the surface. According to the supplier tech guy at that speed and 30A it should be repeatedly flicking from pilot to main arc due to the slow speed causing the metal to move from the arc and cause intermittent open circuit, it should be going pop-pop-pop quite loudly and is not a good situation to be in for the torch.

He tested another unit and at 45A it will rip through 18mm steel with a clean cut so something is definitely off.

All I see is the one arc and no power switching, that's what makes him think the pilot HF board is foobarred and just running on pilot only, this would also cause massive HF as it's permanently running in HF mode and not switching to pure DC mode.

If the new torch does not prove fruitful then it's a new unit, see what happens tomorrow.

wmgeorge
03-13-2014, 03:23 PM
None of my 3 plasma cutters I have owned did any switching at all when cutting thick or thin material. Except the Eastwood which was HF start, but only on rusted metal. You have a defective unit.

Davek0974
03-13-2014, 03:37 PM
This is HF pilot arc torch, the pilot arc is supposed to be around 15-20A and as soon as the arc transfers to the metal it's meant to kick the power up to cutting power and kill the HF. If the arc is lost due to running across a gap or cutting mesh etc it's meant to go straight back to low power and start the HF again.

Mine is stuck in HF low power it seems.

Davek0974
03-14-2014, 05:43 AM
Its the torch!

The new hand-torch cuts perfectly, 10mm steel, 45A, nice clean cut, dross falls of easy. 20A on 1.5mm steel cut very well, couldn't move the torch fast enough really!

They are looking into what is wrong with the machine torch now.

vpt
03-14-2014, 07:37 AM
Good deal!

Have you opened up the machine torch and checked it out ever? With bad pierces and cuts you get lots of blowback on the torch and up into the tip which can block air holes, cause internal arcing, and other bad things.

Davek0974
03-14-2014, 07:54 AM
Yes, its clean inside.

Major difference is that the hand torch has a 1mm orifice and as it came, the machine torch had a 1.3mm orifice, the spares were 1.1mm so i popped one of them in and it improved matters but its still got no penetration, 50A @ 750mm/min would only make it to 6mm in a 100 plate whereas the hand torch just ripped through it.

John Stevenson
03-14-2014, 08:39 AM
Must admit i was a bit amused when driving a grounding spike came into play, this after Dave has got every thing earthed.

Had to wonder if I was reading a plasma cutting post or one about Dracula ?

Davek0974
03-14-2014, 08:40 PM
Have a new, tested machine torch coming out Monday, plus they said I could keep the new hand torch FOC, nice touch I thought :)

boslab
03-14-2014, 11:27 PM
Must admit i was a bit amused when driving a grounding spike came into play, this after Dave has got every thing earthed.

Had to wonder if I was reading a plasma cutting post or one about Dracula ?
I had heared that the only way to kill a shift electrician was a copper stake through the wallet
Spectrometers are funny like that, theres a lot of arc, high voltage, high frequency and stuff with the arc generator to spark the metal to be analysed, they can get quite touchy if not earthed properly and used to drive the mitsibushi robot bonkers if the earth on the robot wasnt fixed properly, it used to loose positions on its program and crash, replaced with ABB and all was well, the robots were used to load the samples and standards onto the spectrometer table, then unload them after
Mark

Davek0974
03-15-2014, 04:37 AM
While I'm waiting for my new torch, can someone explain or point me to a document that explains the relationship between nozzle size, amperage and air pressure on a plasma torch?

wmgeorge
03-15-2014, 09:41 AM
While I'm waiting for my new torch, can someone explain or point me to a document that explains the relationship between nozzle size, amperage and air pressure on a plasma torch?

Once again with my HyperTherm just used what came with it from the factory worked fine. This was just a hand torch in the standard holder that came with the table from PlasmaCam. Ampere settings for the metal, you would need to get from the plasma mfg. If this is indeed their machine CNC model they should have them available.

Davek0974
03-15-2014, 10:26 AM
Thanks wmgeorge, I do have mfg chart but the point I was asking was for educational reasons, there must be a correlation between orifice size, current and air pressure?

Davek0974
03-17-2014, 09:28 AM
Well, i'm getting baffled again, the new torch arrived this morning and results seem to be better but something is still wrong.

In this picture...
http://www.landyzone.co.uk/lz/members/davek0974-albums-problems-picture15119-photo-1.jpg

The long cut is made at 20A @ 4000mm/min, its a nice fine cut about 0.5mm kerf with zero dross front and back.

After that success I thought I'd load up a little test file i've been messing around with and try that after editing the sheetcam settings to suit the new parameters...
http://www.landyzone.co.uk/lz/members/davek0974-albums-problems-picture15120-photo-2.jpg

Now, this was the second run as the first one at 4000mm/min was worse so i dropped to 3750mm/min but all i got was a pile of dross and partial cuts.

Both tests were pierced at 4mm (mfg recommendation) and cut at 1.75mm (mfg says 1.5 - 2.0mm)

Now this tells me that something is badly wrong but my lack of experience does not tell me what.

Any pointers here???

Also, I have set a pierce delay of 0.1 sec in sheetcam but mach3 seems to stay for at least a second or so.???

vpt
03-17-2014, 09:34 AM
It sounds strange to me that you are using such low amps. I have never ever dropped my machine below 45 amps yet even cutting sheet metal. But like I figured out before and posted in metric terms I would be cutting 45amps at around 8000mmpm.

Davek0974
03-17-2014, 09:39 AM
My main reason was to get the speed down while i'm setting my table up.

The main point was that the straight line was also at 20A so why the massive difference in finishes??

I will try higher power now.

Davek0974
03-17-2014, 10:24 AM
Well it seems you were right, this was run at 30A...
http://www.landyzone.co.uk/lz/members/davek0974-albums-problems-picture15121-photo.jpg

Its pretty good I think, I have axis wobble to fix but the cut is clean there is no dross front or back apart from a small amount where it slowed down for the corners.

Still 100% better than the first go.

Although I am happier now, I still fail to see why 20A will cut an excellent straight line but produce so much dross and crap on a simple shape at similar speeds??

Oh, and I still need to fix the pierce delay issue, I have 0.1s set but its holding so long that the torch starts popping before moving due to lack of metal in front of it.

Davek0974
03-17-2014, 11:11 AM
This is 10mm steel at 50A and 470mm/min
http://www.landyzone.co.uk/lz/members/davek0974-albums-problems-picture15122-photo.jpg

It's an excellent cut, square on this edge, clean and no hard dross but seems a little below spec as the mfg sheet seems to feel 10mm should be up around 900-1000mm/min?

Is 470mm/min reasonable, bear in mind that this machine should edge-start upto 18mm @50A and 150mm/min.??

Need a voice of experience here ;)