Blowing water off torch tip prior to ohmic touch

[motoguy]

Jim Colt posted this in another forum:

If you keep the water low enough so it does not splash mass quantities on the torch....then ohmic will work fine with a water table. If water gets on the surface of the material.....expect the ohmic sensor to sense the surface of the water, not the metal. If water gets back inside the torch.....often it will cause a false sense as well as it shorts from the shield to the nozzle internally.

The water in a water table becomes full of suspended solids of the metal you are cutting....which raises the conductivity of the water.

One way to make the ohmic function work better with high water levels is to activate the torch postflow before sensing the material. You can do that by modifying your machine code to do a quick (1/2second or less) pulse on the plasma on input....if quick enough the torch will not fire but the airflow will activate. This blows water out of the torch and keeps water away from the sensing area.

Jim Colt Hypertherm

After reading this, I remembered the drips of water hanging off the end of my torch tip while cutting. I had the water table roughly 3/8" or so below the 16GA stuff I was cutting.

How would I go about doing what Jim mentions above, with Mach3, Ethercut/DTHCIV, sheetcam, etc? Is there a rule I can create in Sheetcam that will insert the Gcode during the touch-off section of code? Or would I need to manually enter some code at each touch off point? This sounds like a great idea, based on the little I've seen using my table so far (water everywhere).

[Stout]

If you are continuously cutting, then the post flow should stay on long enough to blow water away from the new pierce location. If not, then assuming you have a Hypertherm machine, turn the amp dial all the way down to zero amps to activate the air flow before you begin your cut.

[tcaudle]

The POST on the EtherCUt has a macro (M900) that is called just prior to the torch firing at a pierce to check if the ohmic sensor is ON (Clogged) and stops and warns the operator. Concept is if the ohmic is already triggered it will cause it NOT to plunge down but to "sense " it too high. If it goes down an misses than its not water on the tip and something is wrong in the conduction circuit or the materiel really rusty or has a coating.

The Ohmic sensor depends on the fact that the PLATE terminal of the Ohmic Sensor module has good connection to the plate THROUGH the table structure. The TIP input has to make good connection to the Shield of the torch.

Most often cause is that the PLATE side path is not good . You can test with an ohm meter on low ohms (or "squeaker" continuity tester) Put one side on the "PLATE input of the Ohmic sensor module and the other on the plate in several places. Should be lao ohms (less than 10) On some tables the gantry is not making very good connection to the table structure or the plate being cut is not making very good connection to the table

Ultimately the Ohmic sensor is nothing more that a continuity tester that turns on an isolated switch

[whiskeymike]

I would be very curious to know how to do this as well. There have been a few times I wanted to turn on the air without firing the torch.