Hello All
 I built a cnc plasma machine a few years ago and I was running with Mach 2 and no THC. I recently upgraded it with Bob Campbell's assembled enclosure and new stepper motors and I hooked up the THC300 and changed to Mach 3. I am running an older ESAB plasma unit with the high frequency start. I grounded my table and plasma unit to earth ground. When I ran a test program the torch would fault on the  THC and would stop. I would click the reset and the motors would start growling and jerking. I would have to reboot the computer to stop the growling. I thought I was getting noise back through the THC, so I disconnected the THC and just hooked a relay to an output to turn torch on and off. I made two test cuts, it seemed ok. On the third one the motors started growling and jerking. This time is it ran the program all the way through. It wasn't losing steps,because it went back to the spot it started and cut off. It was about half the size of what it should of been. Can this still be noise from the plasma or is this a problem with Mach.

Thanks
Chuck

you say it was half the size it should have been, was this just on the last run or all three? If on all could your new steppers be 0.9 degree (400step/rev) rather than the usual 1.8 degree (200step/rev)?
Hood

It was just the third one, the first two cut normal, the motors sounded right. When I ran the third, the motors started started growling at the start of the cut,with the THC unhooked it did not fault and stop. It finished the cut right where it started, just about half the size of the rest. Same program.

Are none of the plasma users on here going to help this guy?

I have no experience of running plasma cutting but have designed plasma torches for welding. High frequency (HF) start systems radiate large amounts of radio frequency noise. The torch lead acts as an radio transmitter and all your wiring acts as a receiver. HF is death to computers! More modern systems use a pulse system to ionize the arc gas and initiate an internal pilot arc of a few amps. When this is brought near the material, the main arc amps are turned on.

Torch height control (THC) is usually looking at the voltage produced between the torch and the job. This is filtered, isolated and used by the control system to tell Mach to vary the Z axis to maintain a constant height. Ask your THC supplier if it will cope with your HF system. Have you a choice of continuous HF or at start only? If you have, use start only and this may reduce HF during cutting at the expense of loosing your arc but saving your computer. Earth your table to the plasma power source and back to the mains switch. Make sure none of the earths on the control side are connected to the table, the THC should be opto isolated. THC is only needed on sheet material that may warp.

I hope my random ramblings are of some help and wait for some of the experts to give you more assistance.

Ian

Does it run fine if you dont start the torch?

Hood

Yes it runs find as long as I don't fire the torch, if I had built a router, I would of been fine. I am thinking about buying a new plasma unit. I am looking at a Thermal Dynamics, Cutmaster 51. Does anyone know for sure if a manual unit has a place for arc ok and tip voltage?

You are getting a TON of noise in your system You will need to shield better or use the plasma from HyperTherm (on of the newer ones)

hey , really new to  all this bought a thermal dynamics auto cut 200amp, had same prob finally had to move cables Way from stepper cables hung the torch cable from a trolley and everything is great now hope this helps