Home Made Plasma

I have been working on a Plasma/Router table for awhile now. Primarily for Plasma, I have built it from left over steel, powder coating the frame. It is a rack and pinion with one drive for the Y Axis. I have used Chinese steppers with TB6600 drivers. I have a dedicated Windows XP PC for this and my Shoptask. Using Mach 3, I have started with Sheetcam. I have an older Lincoln ProCut25 that I have wired in with a Proma THC. I am still working out bugs, but Les from Sheetcam has been more than helpful overcoming issues that arose from the Procuts safetys. All my cables are shielded and well grounded, but I am having issues with the movement stalling right after firing the torch. I am open to suggestions. I am going to try increasing stall time between firing and movement and also changing acceleration tuning on the motors. Again, any ideas would be appreciated. I will try to upload pics in the near future.

Well, I thought I had it rolling. I shut the machine down and came back a few days later and it is doing the same thing. If I run the program with the torch off, it runs perfect. When I power up the torch, the table stalls with the torch ignition and Mach show it still moving. I opened the control panel door, moved the wiring to see if anything was loose and clamped a ground lead from the table to an earth ground. No errors then. So I am still trying to figure where the problem lies.

Have you driven a ground rod and grounded your table?

Have you figured this out yet? I've mounted my old procut 25 to my cnc mill table but always manually triggered the arc. I ran wires from inside the case to a button rather than touch the trigger on the torch handle. I'm curious how you handled the air delay to start the arc. Once a cut has been made and the air is still on, the arc will restart instantly. However the first time the trigger is pressed there's a significant delay. I don't yet have THC but plan on it eventually. Are you manually triggering the air and keeping it on until the job is done? Any insight would be appreciated!

One of the basic signals that help with automated plasma cutting is the ARC OK (AKA Ok-to-Move; Transfer. Arc valid,etc) Some plasmas have that signal, some do not (The ProCut does not). It's used to HOLD motion until the control gets a valid arc (current is actually flowing) so it factors out all of the delays . If the motion starts as soon as the torch fires it will not compensate for the delay for air to start. Only other way is to program in a pause at the first pierce in G-code (G4 P ## )where ## is in decimal seconds) There are lots of other niggly little issues; like the pierce needs to be done higher than the cut, and there needs to be IHS (initial height sensing ) before each pierce because the metal warps and is seldom perfectly flat. Doing plasma cutting with no THC is like skiing barefoot: everything has to be perfect or its a real mess The thinner the metal the worse it is.

You didn't say which make/model of plasma cutter you are using. Many of the lower cost import cutters simply aren't suitable for CNC use due to the excessive electrical noise they produce when the torch is fired. I've used a number of Hypertherm cutters onCNC machines and have had no issues... I have a (fairly new) import cutter and as soon as it fires the computer freaks out and all signals going to the diiver/steppers pretty much shut down. Some folks have tried numerous ways to combat the issue with shielding, grounding and isolation techniques, but results are usually not very effective or more commonly completely useless. Your results may very depending on the machine and cutter make, but the time, effort and cost pretty much out weight simply getting a plasma cutter that is tested and proven to work well on CNC machines,

A THC is definitely great feature and very helpful, but isn't a necessity unless you are cutting thin metal which warps easy or when cutting large pieces/long cuts which may may have significant metal to torch height differences across long spans. If you have a simple micro switch floating torch mount that resets zero before each pierce/cut, you'll have very few issues on shorter cuts spans on other than light gauge metals. Doing a "dry" run without the torch on will help identify height issues that you may be able to do a little "adjusting" of the metal to eliminate before actually cutting.

Thank you for your response. Apparently I did not understand the difference from an earth ground and grounding through the electrical system. I ran a dedicated separate earth ground and it appears to have resolved that issue. Now I am working on fine tuning speeds and the Proma THC. Thanks Again!

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Originally Posted by quintc

Have you figured this out yet? I've mounted my old procut 25 to my cnc mill table but always manually triggered the arc. I ran wires from inside the case to a button rather than touch the trigger on the torch handle. I'm curious how you handled the air delay to start the arc. Once a cut has been made and the air is still on, the arc will restart instantly. However the first time the trigger is pressed there's a significant delay. I don't yet have THC but plan on it eventually. Are you manually triggering the air and keeping it on until the job is done? Any insight would be appreciated!

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I wired into the case like you did. The moderator at Sheetcam was very helpful on providing insight on modifying the post for this torch. It essentially fires the torch in the air and then lowers to it's first cut. Now that the post code has been modified, it automatically puts in the line to do that.