Thick Metal Ohmic Issues

[zackdrews]

Hello everyone, just working on solving some cut quality and control issues I have been having.

I have a Cutting Edge 4x8 table which uses MyPlasmCNC and a Hypertherm 105 Sync. It is a water table and I slow my speeds 20-30% from cut chart per Hypertherms instruction for better performance with that. Torch is mounted square in all directions. I have cut everything up to 5/8 with no issues, setting Arc voltage and using the ohmic thc. The parts are are very good.

The issues start when I try to cut thicker materials, so far 1.25 and 1.5 have caused problems. The bevel on the good side of the cut is exceeding the 1-3 degrees. And what I suspect is the cause is the fact I have to disable my ohmic THC, which tends to have my arc voltages running high. If I I enable it, the cut will start fine and then a few inches in the torch hits the material and trips my breakaway sensors.

I am not sure if this is a sensing issue caused by the wider kerf and lower speed or what this could be. I have tried adjusting my torch height lower, but it seems the voltages always read high until it crashes.

The last attempt I had 8 ipm speed, with 105 Sync cartridge. The cartridge has two cuts on it, maybe 30-40 minutes of cutting. Both cuts got completed with the ohmic turned off and arc voltage was up around 180 as nothing I did seemed to lower that number.

Thanks in advance,

Zack

[68rscamaro]

sounds like you need to raise the target voltage if the torch is diving into the material.
I think you may be confused in the difference between thc and ohmic sensing.

[tcaudle]

The cut charts for the 105 indicate the you should do an edge start (not a pierce) on 1" and above .

The fact you are getting good cuts on thinner material shows its a METHODS issue .

Ohmic is not part of the THC operation. All it does is establish the top of material prior to the pierce . Its all about VOLTAGE (arc volts as you cut)

Hard to do a touch off with an edge cut! It has to be a specail set of moves that first do a touch off on the mateial then moves the torch off the edge to do the pierce and THEN start the cut,

The other factor is feedrate and how that might vary as it cuts . Feedrate changes how much material is being cut by the arc and that changes the voltage . The more you slow down (for any reason) the HIGHER the arc volts and the more torch dive you get.

Its vital that you have EXCELLENT current flow AT THE CUT. Meaning the workcalmp connection needs to be solid to the material. Think about jumping off a diesel motor with a dead battery. The connections that carry all that current have to have a really good connection to work. Simply clipping to the table or the slats may not give you the full current path you need to cut thick material at 100+ amps.

I am not sure how well you are going to be able to use that THC with that thick of material .