I am running the demo version of Mach3 Version R3.043.022 on a system with Vista with the Vista patch.
When my plasma torch fails to strike, the program interface locks up - the program continues to run but the
controller freezes as well as do the keyboard and mouse. I thought it might be noise interference between the
torch and the controller box as it was fairly close to the unit. However I have moved the control box farther
away and put a metal shield between them but it still freezes. Is this Vista related or still a shielding issue?

I think I may have found the answer in this thread -
http://www.machsupport.com/forum/index.php/topic,20076.0.html

I'll let you know after I add the ground wire to the tip.

Confirmed - adding a ground to the tip allows for reliable arc and no computer freeze.

I may be wrong here but I'd urge some caution about this approach and the thread you linked to. Perhaps someone with in-depth knowlege of plasma cutter electronics can comment.

What you appear to be doing is SIMILAR to how a pilot-arc-start plasma system works. BUT with TWO BIG differences.

1) In a pilot-arc-start system the SHIELD (what you appear to be calling tip) is TEMPORARILLY connected to earth by the start electronics. Once the arc is established this earth connection is automatically removed. You appear to be MAINTAINING this connection throughout.

2) In a pilot-arc-start, for the short time the shield is connected to earth (just enough to establish an arc), the CURRENT is MUCH less than CUTTING current. With yours it's at FULL cutting current.

The result is (I THINK) that with your modification, the arc between electrode and earth is "dithering" between electrode/material (correct) AND electrode/inside-of-shield (incorrect) This can NOT be good for the insides of your torch IMHO - whether it's dangerous or not is another question that I'd want the answer to.

Something to consider. I bet your torch with your modification will fire and STAY lit in air - am I right? No standard commercial torch can or will do this. It may be worth considering why this is.

Ian

I think it has more to do with the fact that they are just shunting the HF directly to ground rather than allowing it to "find" the plate.  If the path of least resistance is through the air to the plate, the process of transferring the arc to the plate cause a huge amount of stray HF in the system.  Dumping it directly to ground eliminates...or greatly reduces that.  My guess is that you're right in that the torch will fire at full voltage in the air.  The torch should not light at full voltage unless there is complete arc transfer.  Grounding the tip may just be fooling the system into thinking it always has a good arc.  If that's the case, then "Arc OK" in Mach3 will not work properly either. 

We bought one of these to play with but ended up giving it away.  Even used at the other end of the shop as a handheld, it effected the CNC machines.