[paulmacc]

Well, after months of frustration with the stupid thing I thought I'd finally make my first post and see if someone can help. I inherited a plasma table, came with a 6600 Chinese controller that didn't work so I upgraded to a G540 which has worked fine with Mach3 and a UC100 from CNCDrive. As the table was not made very strong, it is not flat over the entire cutting surface so the larger the piece the more the chance that the torch will hit and stuff things up. I added a floating head (and Z zeroing on each cut start) which helped for small cuts but as soon as you try a long cut you have the same problem. So, I looked for THC's and for whatever reason(Price mainly) decided on a Proma THC 150 as it was cheap-ish and seemed it would be 'easy' to setup.

I have a Everlast PowerPlasma 50 with a CNC port with a voltage divider which I thought would work with the THC...it doesn't ! The output from the CNC port is simply too weak to work the THC and so after a lot of wasted time I changed to using the RAW voltage inputs on the THC to connect to the plasma torch and work leads. This part at least works fine, giving me a good reading of torch voltage. I am not using the ARC OK output as I don't have any spare inputs on the G540. It's wired as follows;

Input
1 torch UP
2 torch DOWN
3 Limits and Home for X, Y, Z (not Z home)
4 Limits and Home for A and Z Home

I have 2 steppers on the X Axis and have split the Home for X and A over 2 inputs so I can square the gantry when it's homed.

If I enable THC in MACH3 and start the torch with the on screen button and manually jog the torch I can cut with quite good THC. It will move up and down and do quite a good job.

If however I try to run a GCode file to cut something the torch will move to the start of the piece, fire and sit there not moving with the gcode frozen at the M03 command. Dsiable THC and it will cut fine, but with no THC.

WHY!!??

I have checked and checked settings, wiring, grounding etc to the point where my head hurts! All cables are shielded and grounded, the table is grounded to a brass peg outside the shed, the cabinet is isolated from the table and grounded through the earth on the 240v power plug. I have 'Allow THC control.....' checked in the Ports and Pins Screen.

It's really starting to get to me now!! The fact that the THC WILL control the height when I cut manually by jogging, but not when I run gcode it what annoys me the most. I'd rather it just didn't work at all, at least then I'd have a reason to throw it out and try something else.

I am using the PLASMA screen that came with MACH3 and in SHEETCAM the MP1000-THC post processor(with a couple of small changes)

I'm beginning to think that I'm just stupid and have made a basic mistake somewhere in that settings. Seems like with the THC on it fires the torch and stops, waiting for an ARC OK signal, but I don't have ARC OK enabled in the ports and pins screen. The fact that it WILL work when I manually jog would seem to suggest the the wiring is correct??

If anyone could offer some help it would be greatly appreciated. :-)

[OlfCNC]

I would try to enable the Arc OK signal with configuring it to an unused port and pin like 0, 0 and set the Active Low setting in the way so it will be always active and try to run code this way.
Since you not using the Arc OK input it is not a problem then that it is always active and it might solve your problem. At least I think it worths a try.

[paulmacc]

Thanks OlfCNC, I gave that a try but no luck. However, I tried doing the same thing on another computer with a fresh install of MACH3, default settings and not connected to anything and it did exactly the same thing.

I therefore think I was right and I am just stupid and have forgotten to set some basic setting, though I can't for the live of me see what.

[OlfCNC]

And what if you actually set the Arc OK input to a physical input pin with an active on state, just to test if the system is really waiting for the arc OK signal?
I know you wrote you have no free input pins, but for a test you could configure it for example to the same pin as your e-stop input in it's inactive state.

[paulmacc]

Yep, I tried that too. Disabled the limits on one input and setup for ARC OK instead, but again same result. The Proma Manual says that it's not needed to work but can be used if wanted as an option. I'm just at a loss as to why it stops and why, even on a fresh install, with default settings for plasma, on a computer not connected to any controller, THC, G540 etc it still does the same thing??

I just think I must be missing something that I haven't set in MACH3. Yet everything works fine without THC on and the THC WILL work if I turn it on and manually jog the torch to cut. It will go up and down as needed.

Frustrating to say the least. :-/

[paulmacc]

Well... it works! But I don't know what got it working which is frustrating. I did find that with The THC Options all UNCHECKED in Ports & Pins---> Mill Options, it works when I check THC On on the Run Screen. WTF?

Anyway, I finally have THC working on my table. Won't say it the best THC, but it's certainly better than no THC. I've done some long detailed cuts on 1.6mm sheet that really started to bow up towards the end and it handle it fine. Don't think I could cut much faster that 1500mm/m as the THC speed can't be more than about 5% before it starts to chase up and down as it over shoots.

[nachoz]

I also upgraded from a tb6560 to the gecko g540 with uc100 and my problems are: without thc after the first cut the z axis raises and won't come down for the second cut. And with the proma THC on it will not move at all. I can't seem to figure out my z axis or Proma issues either.