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woodnerd
05-21-2012, 11:46 AM
I bought a used Thermal Dynamic Cutmaster 151 a few months ago. I replaced the consumables in the torch and made a test cut, it fired up just fine and worked perfectly.

This morning I finally needed it for an actual job. I got a bit of an arc for a split second, then nothing. Now the torch will not start an arc, after a second or so of normal flow the airflow starts pulsing, 2-3 pulses per second.

I thought maybe my test cut clogged the tip somehow, so I put another one it. No real change, except that perhaps the airflow is pulsing a bit faster.

I've checked all the settings (which should not have changed from the successful test cut). Mode is set to "run" (I also tried Rapid Restart), air pressure is set to 70psi. Lights that should be on are on, lights that should be off are off.

Any ideas on what's going on?

firbikrhd1
05-21-2012, 12:02 PM
I too have a Thermal Dynamics plasma cutter, the Cutmaster 81. I'm no expert by any means so take what I say as a suggestion more than a definite solution.
I had a similar problem when using my machine and found that it was related to the ground. The clamp was fine, connection to the cable etc., but there was a black coating (scale) that is often seen on the steel plate I planned to cut. Apparently it doesn't conduct electricity as well as might be assumed. I ground that coating off where the ground clamp was to be attached and the torch worked perfectly after that.

From my experience I believe that any interference with a good ground will inhibit proper operation of your plasma cutter.

Also be certain you have dry air supplying your machine. Moisture in the lines can cause significant issues. I am using a desiccant air dryer from HF that was reasonably priced to dry my air and I drain my compressor prior to using it for the plasma cutter. I also have a filter/separator in the system before the dryer.

davidh
05-21-2012, 12:04 PM
i have had similar problems. i found that the conection of little parts in the tip of the gun must be CLEAN and totally free of toasty marks. i use a small pc. of steel wool and polish the parts that contact each other. . . . thats all i got.

PTSideshow
05-21-2012, 12:23 PM
GROUND, Ground, Ground is probably the biggest problem with non start and non continuous arcing if all things are good to go and it worked the last time.
You need a clean and shinny connection point, It is after basic electricity! I know a lot of the legends say you can hook it up and go. But what they don't say is they clamp it and rock the clamp to get a good ground. Or they use a modified C clamp as a ground. No paint, dirt and heavy rust! Works a whole lot better :D
By the way if you are using it at full capacity you might get lucky and it will work as in cutting up scrap, lower the juice the clean the material the easier the start.
And make sure the ground isn't clamped to the side that will fall away and keep it close to cut line. and it works great

winchman
05-21-2012, 01:34 PM
That torch uses an air start, and the part that moves sometimes gets bound up. I've had it happen a few times, and it's always started working again after I took it apart and put it back together. Of course, you need to replace any of the consumables which are obviously bad, but that's almost never the case, in my experience.

woodnerd
05-21-2012, 03:38 PM
I've made sure the work clamp is grounding to completely bare, clean metal. I also wire-brushed the starting point for the cut.

My total experience with plasma cutters was that one test cut. As I recall, the torch starts out arcing to itself, does it not? Which I would think it would do regardless of whether the work was grounded correctly or not. A bad ground would just prevent the arc from transferring to the workpiece?

Why does the airflow start pulsing? Is that normal?

aboard_epsilon
05-21-2012, 04:11 PM
i havnt got your machine ...but on mine there is a little jumper on the torch ..safety device that you can take off and put in your top pocket ..if i take this device off i get nothing ..

maybe because its new ..you misslaid this device forgot about it .

mine was basically a curved insulted peice of metal that curved around and connected two buts of exposed brass each side of the torch head.

mine got lost a long time ago ..now have improvised one on it .

all the best..markj

winchman
05-21-2012, 04:57 PM
Whenever I've had a grounding issue, the torch would start but not cut through the workpiece. It makes a shallow trough with lots of blowback instead.

This is the start cartridge I was talking about earlier:

https://lh4.googleusercontent.com/public/2eJSyTuJLjWFK11ClnyZCVsT8Lgvo9fCv80rrt7qPaCup8NEj_-dxd6iXYEhMNkIVONRQ-2Tfl6fjNKYeGHi_s2CZdruX2ucCPladeGcVJd5mYjl3k8oKE7m FasdkeuDlq9sy1FtitQ9KQrWCtF_ruuR9aJAplUjRjkhwg=s90-c

If it can't move into the position where it makes contact, the torch will not start. Apparently, the sensing system built into the torch will not detect this problem, so all the lights remain normal.

Some other things....

The torch usually doesn't start immediately when you pull the trigger. You need to pull it and wait several seconds for anything to happen.

If you get the tip too far away from the work, the torch will go out. If this happens, you have to wait for the airflow to stop before you can resume the cut, and wait several seconds after pulling the trigger, too.

Tamper84
05-21-2012, 05:01 PM
You said the air is pulsing. Is the air filter (assuming it has one) clogged? Had one do that to me at work one time.

PTSideshow
05-21-2012, 05:06 PM
Is the set/run switch in the run mode and note set.

Don't know if it came with the manual or not, http://www.thermadyne.com/IM_Uploads/Literature/lit_452_300X4668.pdf is a a PDF of the manual.
here is their web pagehttp://www.thermadyne.com/thermaldynamics/component/option,com_doclib/task,/id,/Itemid,237/categoryID,4/
I have a Hyperthrem so other then general I know if the consumables are not seat properly the torches will not work. or if they are loose. Drove me crazy first time I had to change them.
:D

mf205i
05-21-2012, 05:07 PM
The unit has a safety that needs to see backpressure at the torch to energize. Check for leaks and replace the old hard O ring at the air cap. Thatís why I got mine for $50!
Mike

lazlo
05-21-2012, 05:28 PM
Macona helped me debug my Thermadyne that had the exact same issue. 90% of the time it's the start cartridge, but in my case it was the pilot arc relay.

But if your air is pulsing, that sounds like a likely issue -- you need a consistent, dry air source to maintain the arc.

woodnerd
05-21-2012, 06:42 PM
You said the air is pulsing. Is the air filter (assuming it has one) clogged? Had one do that to me at work one time.

The air flows fine for the first second or so, then starts pulsing. Releasing the trigger makes the pulsing stop immediately. So no, I don't believe the air filter is an issue.

woodnerd
05-22-2012, 03:10 AM
I pulled the entire tip assembly apart, replaced both O-rings and cleaned the current start cartridge with some steel wool. The cartridge seems to be working smoothly, no binding at all. However, the arc still will not start.

I noticed that when the air is pulsing, the rapid restart light is blinking at the same time (and rate). Could the pulsing air actually be the rapid restart trying to work?

I guess I'm at the point of taking it into a service center, which means a 50-75 mile trip :(

oldtiffie
05-22-2012, 03:26 AM
I bought a used Thermal Dynamic Cutmaster 151 a few months ago. I replaced the consumables in the torch and made a test cut, it fired up just fine and worked perfectly.

This morning I finally needed it for an actual job. I got a bit of an arc for a split second, then nothing. Now the torch will not start an arc, after a second or so of normal flow the airflow starts pulsing, 2-3 pulses per second.

I thought maybe my test cut clogged the tip somehow, so I put another one it. No real change, except that perhaps the airflow is pulsing a bit faster.

I've checked all the settings (which should not have changed from the successful test cut). Mode is set to "run" (I also tried Rapid Restart), air pressure is set to 70psi. Lights that should be on are on, lights that should be off are off.

Any ideas on what's going on?

My plasma cutter amd mig sets are sensitive to poor earthing circuits - from the machine outward. I grind all earth surfaces - work and clamps - as well as checking all leads and fasteners. I keep my leads as short as possible.

I haven't run my plasma cutter for a while - I must remember to try it again soon. Mine is a 3/8" x 10" per minute machine.

It is sensitive to both air pressure and free air delivery at the "gun".

Trying to cut stuff that is beyond the cutter capacity and running the cutter speed too high (or too low sometines) doesn't help much either. Cleaning off scale and rust in the line of cuts assists as well - as does correct nozzle to job distance.

If mine packs it in, I think I'd get a newer better one as repairs are doubtful and expensive and a new machine may well be viable.

https://www.machineryhouse.com.au/C422

macona
05-22-2012, 04:09 AM
The air pulsing is very, very odd.

You need to put a meter on the air solenoid inside the machine. If that is pulsing then it is something electrical. Check the trigger switch to make sure it has good continuity. You can measure that inside the machine. It should not read more than a few ohms.

Thermadyne has pretty darn good tech support. Call them and talk to the techs.

macona
05-22-2012, 04:10 AM
Oh, and those start carts, they may seem like they move freely, but I have replaced many that seemed ok. Always keep a spare on hand.