Plasma Anti dive/THC tuning

Hi All, we have the dual spindle/plasma machine and I’ve started to learn the plasma side. I’m having trouble with the torch getting knocked off/plunging too deep on cuts fairly often. I’ve tried raising the cut height in sheetcam to .1 and that helped some (but I think that’s too much), and playing with the target voltage doesn’t seem to help much. I should note that I’m using the mach 4 config that has both spindle and plasma, and it doesn’t seem to have the other tuning options that the manual for the plasma shows.

I do see the THC up and down lights working, but I’m not sure where I should adjust to get it to stop getting knocked off.

I also wonder if the tip is getting stuck on the material itself? I have the recommended amount of air going through the torch, I’ve set it to 125psi

I run into this when I am cutting really thick material and pierces leave a good amount of top side slag while the plasma is boring down through the material. Tends to happen on 3/8~1/2in and thicker.

Something to always check, is the ground clamp in good condition and are the “teeth” on it really getting through the mill-scale and making a good electrical connection? When pushing 30, 45 or more Amperes through those tiny little contact points and at the same time having a THC that is trying to servo the ‘Z-axis’ accurately to +/- a volt or two requires a good connection. Any paint or extra heavy mill scale on the part when one attaches the ground lead can lead to variation. (doesn’t hurt to just buzz that spot with an angle grinder to rule that out as a source of the problem)

Also, is the ground clamp on the edge of the water tank using water & slats to make the connection? I apologize if this question is too basic, … not trying to be insulting here, I’ve noticed I’ve forgotten to connect the ground clamp right to the part I am cutting a time or two. I use Sodium Nitrate in the water tank to help cut down on rust and that really helps with conductive so you can get it to cut but it won’t be a very good cut.

Along those same lines, did you connect the sense line for the THC way out at the ground clamp like AVID suggests, or did you connect it back near the plasma power source. This will have a much smaller effect than paint or mill scale, but that connection really does want to be out at the ground clamp.

I do notice that the consumables makes a difference. The fine cut consumables tend to lead to the torch riding much closer to the surface.

I also had a 5-pack of 3;rd oarty electrodes that I purchased of ali-express that I ended up throwing away because they caused the torch to ride too low. I do use cheaper eBay electrodes without much problem, not sure if that was just one vendor or maybe even just one production run.

Another item that makes a difference is the material being cut. When cutting aluminum and stainless steel the arc gap spears to be much smaller for a given arc voltage.

I’m running the older version of Mach (Mach-3) so I might not be the best person to look at configuration files for you. I do remember that back when I was getting started, I was having this problem. AVID had me pull a fresh version of the configuration files from their web site.

Thank you for the response! I did hit the spot for the ground clamp with the sanding pad and confirm that the ohmic touch off plate reads well. I’m cutting 10 gauge but I have some slag build up on the cap, I noticed, so I cleaned that off and will try again later today. probably stuck there from my initial attempts.

The ground clamp is attached to the material itself

As far as the sense line for the THC, do you mean the ohmic touch off box thing? Because I believe the THC is connected via that 14 pin cable on the back of the hypertherm. The one from the ohmic touch box is connected to the other side of the ground clamp itself.

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@Arcrunner , Yes, I was talking about the connection of the sense line to the ground clamp. Some people connect that at the plasma cutter end of the ground clamp instead of out at the clamp itself. (this is a picture from the Avid setup guide)

I connected mine to the other handle than the one shown in the picture so I don’t have to clean both the top AND the bottom of my material when cutting material that has excessive “unidentified - goop” on it.

10Ga cuts super easy and pierces so very fast it is unlikely there is enough slag on top of the plate to make a difference.

If the material is mild steel and you are not using fine cut consumable (please confirm) then that rules out a bunch of potential issues.

Are you using Mach-3 or Mach-4 with the setup?

Also, which plasma cutter are you using?

Screenshot 2023-05-04 001356

As a test, have you considered swapping out the ohmic sense ring? Those are a consumable, although they wear super slow. Have you made sure the sense wire has a good connection to it?

Along this line of questioning, how worn are the consumables? Is the electrode above / below it’s pierce count recomendations and is it worn? Is the Nozzle worn or plugged? Is the swirl ring worn or plugged? and of course the same question for the shroud?

And a last big question. How clean / dry is the air supply?

I don’t believe it is the fine cut consumable, I purchased the Hypertherm 45xp from Avid and it included 2 sets of consumables. I have literally only made 11 pierces testing.

I’ll check when I get back to work on the condition, but other than the slag on the ohmic ring, I think it looked okay. It’s my first time running a plasma cutter so I’m not ruling out maybe not running with correct settings for my initial test. The electrician had us start with the torch set to 30 amps to see if it would trip the breaker before we got to full power.

I’ve verified connection to the ohmic cap by touching the ground clamp to the cap and the light in the ohmic box and the indicator in MACH 4 show ACTIVE. I’ve also put the clamp on the material directly (never via the table/slats), and brought the material to touch the ohmic cap to verify the ohmic touch off responds in MACH and the box itself.

I put a dryer after the compressor and before the longer hose run, and there’s also the filter on the torch itself. When it does cut, it’s not as clean, there is material sticking up, so maybe it’s not enough air? Again, set to 125 PSI, but maybe the max of 135 is needed? Hypertherm manual has max of 135, and 125 is right in the middle of the range.

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I run an air dryer in addition to the filter as well. I’ve got a separate regulator set for the plasma cutter and I run it down near the lower end of the range, so I would tend not to focus on that.

One thing to do quickly as a test is to throw in the alternate set of consumables and run some tests.

One can tell the fine cut consumables from the standard/heavy cut consumables by looks. (see below)

Just double checking the settings there. Is the controller set up to run 128V and travel speed somewhere around 180ipm or greater? And just double checking, the plasma cutter is set up to run at full current (45A) dialed in on the front face of the 45XP?

not sure if your still having problems but i had loose connections in the box that the wire from the sheild goes into at the gantry. i was having the same problem (they were loose) then it stopping using the ohmic for finding zero and switched to the mechanical switch , that when the connection came completly off the connector.