THC Out of control

If anybody happens upon this relic post, a resistor in the DIV circuit failed open circuit, so no signal could get through the VIM.

How long did it cut for before raising?

What are your machine settings and what’s your live voltage saying?

Is your usb cable going near the work clamp cable?

This is exactly what I was having happen to me when I had all my issues, but I had a few things going on.

  1. I thought I was cutting .250 steel, but it actually measured .270

  2. Laptop was plugged in (live voltage was in the 20s.)

  3. Z axis was dirty, but it was binding and piercing too high.

how close is the cutter to the table? I have mine on the opposite side of the table from the control box.

what’s your psi going into the cutter?

USB goes from the MCB to the front L corner where I have my stand. Work clamp goes from cutter (on cart @ front right) around rear R leg to center of the table, IE diagonally opposite the USB. Settings were 40 amps and 55psi, .12” pierce, .6 delay, .03 cut. Completed 48 holes @ 3/16 and about 13 inches of outline before rising. I completed the rest of my outline cuts using straight cut and these settings. Supply to the cutter is 90psi measured at a regulator coming off a 60 gallon tank, which is fed through 1” copper drip leg set by compressor tanks set to deliver at 140 and 160psi. Total storage is 97 gallons. I have a coalescing filter, a good sized desiccant filter and a MotorGuard on the cart where the cutter sits. The beads are still blue and the MotorGuard dry. If I remember correctly, live voltage was reading 100 volts and change when I looked. I didn’t check at the end, because I was rushing to shut down before it fried another expense retainer cap and shielded nozzle.

Have you tried putting the work clamp directly on the material?

What do the consumeables look like that came out of the torch right after that failure?

you might want to raise the psi at the cutter to at least 60 psi. That’s a lil low for 3/16.

He’s cutting 11 gauge stainless I think.

The holes were 3/16

yup i see that now… Even at 10 gauge, i have my psi to around 60.

@Jemejia idk if you do this but i set my air dial to about 5 psi higher than what my target psi is because once it starts cutting the psi drops around 5 psi.

not sure about the Z raising part but once i forgot to turn on the compressor and was cutting good until it lost pressure and the last line it was trying to cut looked like yours.

It’s taking 55psi during the cut. I set it while running, using the air setting position on the switch. 55psi is the book setting and it works well. I’m not losing arc or failing to penetrate or anything like that. The torch went from .03 inches to .5 inches and I stopped the cut.

@browndog it’s not losing arc. The work circuit is strong and complete. If it weren’t, I probably would have seen a bad pierce or it would have lost arc. Even a half inch high, I didn’t get an arc lost message.

@browndog it happens with just work lead on material, work lead and jumper on material or work lead on slat and jumper on material.

Try this and see if it helps.

If you are using the hand torch up the psi to 60 + 20 seconds post flow, put the work clamp on the metal not the table.

If your using a machine torch up the psi to 65+20 seconds post flow (machine torch’s seem to need a little more psi) and the work clamp on the metal


@mechanic416 I have been following the cut chart you sent me and am happy enough with the cut quality (considering it’s air cut stainless and always needs a cleaning), but will try higher pressure.

@nicaDd Now I’m outvoted, so I’ll go higher.

If I’m understanding, about 10 seconds into a cut, after air flow stabilized, THC saw a low voltage value and called for a Z move to compensate. And then another and another and another and so on in rapid succession until I heard the arc sound change and shut it off. If low, but constant, pressure is somehow affecting voltage, I would expect an immediate effect that would be taken into account by Smart Voltage. Or a gradual effect that would cause THC to ramp up gradually from the outset, which it does not. What am I missing?

I think you need to try a different cutter to try and narrow it down. See if someone locally can swing by and swap out.

I’ve tried two Cut 60s with identical results. Other people have good luck with them, so I’d be surprised if I had two duds. I don’t know anyone with a cutter and compatible CNC connection to swap in. Thanks for the suggestions.

have you tried non shielded consumables? I’m never used shielded and don’t know why one would on a CNC machine.

Shielded consumables work very well on metal 1/8" and thicker. With THC they should work even better.

I am guessing there is some kind of RF interference some were to cause this. The plasma cutter will not cause this if the air pressure and post flow is set right. It keeps putting out voltage as its cutting and the THC controller should read it and do its job. Maybe the THC controller is bad or has a lose wire or plug. Would not matter what consumables you are using.

Yes, the problem happens with shielded and unshielded, metal from 18 gauge to 1/2, mild and stainless, low and high air pressure. Pretty sure it’s an electronics issue, but I already bought a new MCB, so that’s not it. After a lot of back and forth here, with LS customer service and on FB group, I am no closer to a working table than I was in September when I alerted LS to this problem.

I’m by no stretch an expert at this. (I don’t even have my pro yet) But I once had my plasma start cutting poorly after long cuts and it turned out to be the power cord. Just throwing this out there. A check of the incoming voltage and amperage would be easy enough.

Edit: I was confused and that was a different problem. On this, the torchheight went out of control. It has happened on two different machines, so I don’t think it’s the power cable.