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Plasma conversion
« on: September 21, 2012, 02:39:34 AM »
Hi everyone I'm looking for advice on adding a plasma torch to my benchtop CNC milling machine running on Mach 3. I cut six small copper shape I 0.7mm copper plate for a friend using a 3mm cutter, being copper it was a nightmare as cutters kept breaking. I finally did the job for him thinking that was that. Unfortunately I did a good job, he was well pleased and proceeded to ask for another 100. I pointed out the cost of tooling and the time it took me saying if you were paying industry prices it would be cheaper to cast them in gold, but said I would think about it. I'm a hobbyist and don't do contract work however I had a thought that retro fitting a cheap plasma cutter might be cost effective method of doing the job, indeed if i did the 100 pieces for him it would pay for the plasma cutter. Just for reference the component is 100mm x 75mm x 0.7mm with rads and internal corners that should be sharp, so I have to file out the 3mm rads caused by the cutter.
Here's the question(s).
Can you use a hand held torch, fitted to the z axis to cut components.
Will the plasma unit cause problems with the machines electronics
What other equipment will I need, I have a standard compressor.
The cut can start on or off the job, but looking on the forum cutter height and arc contact seem to be important how do I achieve this

I'm not looking for a pucker units, just one for this job, although I do make model steam trains and might find other uses for plasma cutting.

OK I can hear some of you saying where is this bloke coming from, but being a retired tight fisted mechanical engineer I ain't got a clue about plasma cutting, its all science fiction to me. I thought to cut material as long a the cutter was harder than the material to be cut I was OK.
Advice and suggestions welcome, Cheers fellow CNCers.
 

Offline Hood

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Re: Plasma conversion
« Reply #1 on: September 21, 2012, 03:13:09 AM »
Never used plasma or indeed any experience with it but I am wondering how suited it is to cutting copper? My thinking is it will be similar  (and worse) than Aluminium. I do a lot of Mig and Tig welding of Alu and you need a lot of current compared to ferrous metals, may be similar for plasma and copper, thus your normal cheapo plasma may not be much use.

Milling copper is not usually a problem for me but the important thing is flood coolant or a good mist coolant, might be a better idea to rig up something along these lines to try it out.

Hood
Re: Plasma conversion
« Reply #2 on: September 21, 2012, 03:40:22 AM »
Hi Hood, looked at the plasma cutters on the net at around £300 they all seem to be suited to cut copper. I used parafin to cut the copper components however the chips get clogged in the cut, I do 4 at a time and go round with 1.5mm depth each pass. Thought about flood coolant but unfortunately all the electronics on the Denford Triac are immediately under the machine table. Could move them but such a lot to move and this machine was built in 1988 so the term hard wire might come into the equation. Will have a think. Nice to hear from you Hood. Jim

Offline Hood

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Re: Plasma conversion
« Reply #3 on: September 21, 2012, 04:20:25 AM »
Just watch what you are buying when getting the cheap machines, some are ok because they have been imported from China then checked over and dodgy wiring and components sorted/replaced. However a lot are just punted straight out the crate and are seriously dangerous. I have direct experience of this and ended up losing all my money on a tig that I bought from eBay seller 160572carol    also known as LOCAL TOOL SALES from Blackburn. First one I got caught fire after about 10 mins of trying to get it working, second one lasted about 10hrs of welding before again catching fire. Sent it back at my expense but made the mistake of saying I wanted a refund before they had accepted delivery, they said it arrived damaged and to claim from courier. I had sent by Parcel2Go and they asked for info and pics which I supplied, they then said 1 day before the expiry that the pics were not suitable but refused to discuss what they wanted until after the deadline. So in the end I never got the money. Local tool sales had deliberately damaged the welder as was evident from the pictures they sent and when I sent a courier in to collect the damaged welder they told the courier there was nothing to collect, three times that happened. They didnt want to send back as they knew that the pics had shown that the damage wasnt actually bad, bashed corner of case and knobs removed rather than pulled off, they had sent excellent pics showing the damage but from them it was obvious it was not shipping damage. For example pic showed damage to box of  upper corner and damage to welder was lower opposite corner, knobs supposedly ripped off and circuit boards being wrecked but pics showed no drag marks on plastic from grub screws so they had obviously been unscrewed.

Anyway sorry to vent but just make sure if you do buy one of these cheap Chinese plasmas that you get from a local place where you can visit them personally if things go tits up.




Hood
« Last Edit: September 21, 2012, 04:22:59 AM by Hood »
Re: Plasma conversion
« Reply #4 on: September 21, 2012, 05:15:27 AM »
OK Hood noted, pressed the wrong key in my first post it was £500 for one at a local supplier. I must admit I have had no problems with buying from China, buy their 3mm slot drills at £2.50 each with free postage and they last longer than £7 UK ones. I also bought my stepper drives from China at £43 each which were delivered in 7 days. exactly the same ones in the UK were £76 and 4 weeks delivery, suppose they get them from China hence the long delivery. However there is always a first time, lets hope I ain't put the mockers on any future buys from China.
PS waiting for four 3mm cutters lets hope they arrive.
That bloke wants another 6 copper shapes to keep him going so will do them and investigate flood coolant and Plasma cutting, as I said life's to short to get involved in mass production, had enough of that when I was working for a living.

Offline Hood

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Re: Plasma conversion
« Reply #5 on: September 21, 2012, 06:41:35 AM »
Dont get me wrong Jim, lots of good stuff comes out of China, my previous welder came from there and lasted 3 years of very hard use but it was sold by a reputable company (Parweld) that likely bought higher quality ones and also checked them over so that they conformed to the CE marking rather than just having a CE marking. My warning was buying cheap from the internet when you cant get to the sellers premises personally if something goes wrong.

Stepper motors tend to be made to a good enough quality, even some lathes are but there are different price ranges coming out of the same factories in China and the dealers in the UK punting the really cheap stuff are very fussy on which they choose, ie they buy the real crap.

Hood
Re: Plasma conversion
« Reply #6 on: September 21, 2012, 09:42:45 AM »
Plasma will cut anything that conducts electricity.  Copper produced a lot more smoke and mess that steel though.  0.7mm is some thin material.  You'll need to have your feedrates up around 160+IPM.  Some mills can't move that fast.  Can you sub the job to someone who has a plasma table?  You could also build a small XY table pretty cheap.  For a few small parts now and then, I wouldn't even worry about a THC.

Keep in mind, most, if not all of the the Chinese plasma cutters use HF arc start, and that cause all sorts of havoc with your CNC electronics.
Re: Plasma conversion
« Reply #7 on: September 21, 2012, 03:06:07 PM »
Thanks for all the information, going off the idea my mill is nowhere fast enough in the x y axis. and I have noted the HF problems. Jim

Offline Hood

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Re: Plasma conversion
« Reply #8 on: September 21, 2012, 03:18:43 PM »
rrc1962
I am interested whether my thinking was correct or not in that copper would need higher currents. I just thought this going on my welding experience but thinking about it plasma likely doesnt really have to heat up the material like welding does so possibly there is no problems?
Hood

Offline BR549

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Re: Plasma conversion
« Reply #9 on: September 21, 2012, 04:25:46 PM »
Another thing to consider is the plasma DUST will eat your machine alive worst than grinder dust. Once it is there almost impossible to get it off the machine fully.

Still takes a lot more heat(amps) for alum and copper than steel.

(;-) TP