Cup question,

[Welder Kenny]

Hey Guys, I'm running a pm 65 with a homemade table running shee tcam with a promo thc, do I need to keep my cup clean so it can since the metal for thc voltage?? my table was running great only cut about 200 inches of 3/8 A.R.500 and the thc went crazy?? Raised up maybe 1/4 inch on far end and then lowered towards the front of the cut. this thc is driving me nuts, running through consumables like candy..just when I think I know what I'm doing its acts up like a,, well I wont say it....

[weldguy]

I am not familiar with your promo thc at all but keeping your cup (cap) clean should have nothing to do with your problem. The arc voltage is measured and when the arc get longer the voltage increases, when the arc gets shorter the voltage decreases. Your THC is supposed to read the voltage change and know whether to raise or lower the torch to get the arc length correct which maintains a consistent cutting height. Sounds like an issue with your promo's setup or something but on 3/8" plate you really don;t even need THC, the material won't warp so just set your height and leave THC off until you find a guy here who knows promo and can help.

[acourtjester]

Have you check the "O" ring in the torch, also you did not say what your pierce height is, you can blow a cup is a heart beat if to low.

[beefy]

The arc voltage is not measured from the cap, it is measured from the hafnium insert in the electrode inside the cap. As the hafnium insert wears it goes deeper inside the electrode and the arc gets longer. Thus to counteract this a THC would bring the torch down a little to get the voltage back within limits (i.e. shorten the arc back to correct length). For this very reason some cutting systems initially record the arc voltage for a short time at the beginning of a cut with THC off but with cut height correct. The system averages these initial voltage readings then uses that value to set the THC volts. This helps counteract the gradual wear of the hafnium, as well as other factors that can change arc voltage.

My opinion on needing a THC or not for thicker plate ?? That really depends on if the sheet to be cut is perfectly planar/parallel with your X and Y axis. That would mean your table slats were installed to make that so. And then do the slats stay perfectly planar after some cutting. Slag build up can raise the level of the slats in places. I've seen photos of slats where the slag build up looked like grey cauliflower LOL, so I'm sure the sheet no longer sit planar on that table.

[djreiswig]

If the sheet isn't close to perpendicular to the torch the thc isn't going to solve your problems. Your going to run into some funky angularity on your edges.
This is going to be more noticeable the thicker your material gets.

[Welder Kenny]

Wow never looked at it from that angle, if the plate is on an angle, I'll talking 1* then my holes and cut will be off by 1* interesting?? as I use my table which we all do the slates will effect the levelness of the table?? very interesting..