CNC- the new religion?

[beanbag]

Ever since I started using the CNC, I think that they are the greatest thing ever, and only use the manual mill for the most menial and imprecise tasks.

[dp]

Ever since I started using the CNC, I think that they are the greatest thing ever, and only use the manual mill for the most menial and imprecise tasks.

How has that affected job turn-around time? I've wondered if CNC can keep up with non-trivial but low yield jobs - say less than 10 parts in a one-off batch, vs manual.

[macona]

With a machine that has decent conversational programming its way faster than a mill. For example the base plate on my vacuum system. Put it in the VMC, had it mill out a hole 5.5" in diameter through 1.25" thick aluminum then drill 8 holes concentric to the hole on a 5" radius and then tap those holes. Took about 1/2 hr. There is no way I could have done this on a manual mill in one setting. Even drawing the part in cam real quick would have only added 20 to 30 minutes to the job. Still faster than doing it manually.

Even for one off parts I have found the CNC mill to be faster. You can operate it like a standard mill with power feeds if you use the handwheel. Lathes are a different story. I prefer to use a manual machine for most ops. Maybe its just because I really havnt used my CNC lathe much.

[beanbag]

How has that affected job turn-around time? I've wondered if CNC can keep up with non-trivial but low yield jobs - say less than 10 parts in a one-off batch, vs manual.

Unless it's a one-off of a menial and imprecise task, the CNC is generally faster. There are a bunch of other benefits too, like:

If you get the first part right, you WILL NOT screw up on any of the rest. This is very helpful if you've been working continuously for 6 hrs and are starting to get pretty tired.

Your tools last longer because you can do things like climb cut, don't dwell while you are alternating between the x and y axis, have more efficient and expeditious toolpaths, etc

You can be busy doing other things like planning for the next part while the machine is busy churning on the current batch

Even for doing something rote like drilling a series of holes in 1/2" steel, I prefer to do on the CNC because you can just turn on the flood coolant and let it go. It will use a continuous feed rate and won't work harden the material.

The only tool I haven't used on the CNC is the slitting saw, because I can't turn it off fast enough if something goes wrong.

[John Stevenson]

You have to differentiate here between home shop and work, then split that up into one off's and production, so basically you have four different groups all requiring a different method of doing a job.

Then throw into the equation that two people, doing the same job, with the same machinery won't do it the same way.

That gives you the correct answer

I'm a big believer in CNC as many know but my main machine often stands idle for a couple of weeks at a time or just ticks over making division plates for Gert to sell.

Guy up the road, one man band, lives on his Hurco and would be lost without it.

.

[Mark Hockett]

there is an attitude about it these days that it is superior to all other types of machining.

They are superior or they wouldn't be the machine of choice for the majority of machine shops world wide. I have a shop full of CNC and manual machines. There is rarely anything I do that can't be done faster and more accurate on a CNC machine. Who says you need a program for every little move you make. I use the MPG wheel for facing and edge cuts all the time. One of my machines has a tool changer but who says I can't just hand load a tool if needed, I just push a button and its in, which is much faster than unscrewing a draw-bar.

Many old timers that haven't seen or used modern conversational CNC machines have no concept of how fast and easy they are to program. My CNC lathe is way faster than using a manual lathe. You just answer a few questions and hit the start button. It will create complex parts with radii or chamfered edges and roughing and finishing cycles with just a handful of questions answered. I can have a finished part before a manual lathe would make the first step and be within a few tenths. I have a CNC mill that is the same way, answer questions and hit start.

Setting up tools is no different on CNC than a manual machine. On a manual mill don't you still have to put the tools in a holder? no different on a CNC. On a manual mill don't you locate your position and zero you micrometer dial or DRO? it's no different on a CNC. My VMC has features for set up that allow you to find the center of a circle by touching the edge finder to 3 points (no co-ax or DTI needed), find the center of a part by touching two points and it finds a corner by touching two edges. It will do the math and with the push of a button will input the info into the work offset. It also automatically compensates for the radius of the edge finder. I will be making chips before the average guy is done zeroing his dials on a manual mill.

One thing I really like about my CNC lathe is I can do things that to do on a manual lathe require extra expensive tooling. I can cut tapers without a taper attachment, I can cut radii without a radius attachment, I can thread to within .001" of a shoulder on an outside or inside thread at 1500 RPM and I can use the lathe as a CNC shaper to cut key ways or automatically index the spindle and cut splines with a form tool. My lathe also has a feature to remove taper called taper compensation. Guys complain here all the time that they get a taper when cutting between centers or with the part sticking too far out of the chuck. On my lathe you just measure each end of the part, divide the difference by the length and enter that number into the taper comp offset and the lathe will cut straight. How many hours do some guys spend shimming and dialing in their tail stocks? I doesn't matter if my tail stock is off.

What if your tolerance was such that you didn't require that kind of precision? I am thinking set ups with mill stops, that you could drill holes or make quick bores or tap holes. You can run a pile of parts with all the same hole size/ location, then change position, drill, tap, etc. and run them all back through. To me, your accuracy is there, and you save the time of programming. In addition, your CNC cycle time would probably be greater because it (assuming a machining center) has to stop for tool changes and so forth. Not talking willy nilly careless set ups here, just some old time common sense stuff.

I think what you are talking about here is a drill press not a mill. But there is no reason you can't run your CNC this way too. I do lots of second operations on my CNC knee mill where there is no tool change and the spindle never turns off between parts.

Here is a simple part I make on my CNC knee mill, how long would this take on a manual mill,
http://www.youtube.com/watch?v=NpbN1UDwtQM

That mill cost me less than the average Bridgeport, I payed $1250 and it was in perfect working order. Two of my friends just bought identical mills for not much more than I payed,

http://cgi.ebay.com/ws/eBayISAPI.dll...=STRK:MEWAX:IT

http://cgi.ebay.com/ws/eBayISAPI.dll...=STRK:MEWAX:IT

Have had a couple of situations recently where the attitude is that it can't be done right without CNC! My point is precise is precise, no matter how it is achieved, but that is getting hard to sell!

There is a post on the Chaski board that is a great example of the advantage of CNC. Gary needed a very tiny handle made for an elevation screw on a model cannon. There were many opinions offered on how to make them. Resin molds, radius attachments, free hand turning, hydraulic tracer and form tools. I had 12 of them done accurate to his drawing in less than an hour with programming and machining, each part took 1 minute 37 seconds. He sent me a drawing and I programmed the part on my lap top with my CAM system while eating dinner at the dinner table, it was that easy. Here is the part,


Here is a link to the post,
http://www.chaski.org/homemachinist/...er=asc&start=0

and here is a video of the lathe cutting one. It would have been faster but the smallest diameter 1144 stock I had was 5/8 and this was with my old slow tool turret, I now have a high speed turret with 2 second tool changes on that lathe.
http://www.youtube.com/watch?v=5ZcEmkvdp-g

[.RC.]

All very good and well, but what does a decent CNC machine with good conversational programming cost??

Certainly a lot more then a manual machine... Well that is the situation in this country.. I saw a Haas TL1 second hand sell for $30 000..That was probably the sort of money you will spend on a good industrial CNC machine..

[DR]

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I have to admit that there are things they can do easier than a manual machine but they are not the end all to machining. There is plenty of things the manual machines outshine CNC at. Making a one off complicated part is one thing for sure.

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Several posters have expressed the same thing. That a one -off of a complicated part is easier on a manual machine.

Actually, that's totally backward, a complicated one-off is far, far easier on a CNC.

[DR]

All very good and well, but what does a decent CNC machine with good conversational programming cost??

Certainly a lot more then a manual machine... Well that is the situation in this country.. I saw a Haas TL1 second hand sell for $30 000..That was probably the sort of money you will spend on a good industrial CNC machine..

The good news is "modern" style CNC's have been around long enough that good used "industrial" grade machines are available for well under $10K.

A TL1 for $30K? It would depend what options it had. It's entirely possible that wasn't a bad price although it does seem high. Those Haas machines tend to bring top dollar on the used market.

[.RC.]

The good news is "modern" style CNC's have been around long enough that good used "industrial" grade machines are available for well under $10K.

Maybe in the US.. Not here...

Don't get me wrong, I love CNC and it's capabilities, but it is expensive... A bit like how in the pre-CNC era industrial manual machines were expensive items and hobbyists simply could not afford them and could only afford little machines like South Bends and Myfords...

I have a near new Chinese round column geared head Mill Drill here that one day I hope to convert to CNC..