Mach3
Candcnc electronics
Sheetcam
Hypertherm PM1250

In the beginning, to mark hole centres I did hole centre piercing (drill operation with plasma tool in Sheetcam), but yuk I didn't like that, a ragged hole with a hard nitrided surface, requiring cobalt drills to get through. So instead of piercing I tried either very short pierce delays or no pierce delay at all to give me a dimple on the surface of the steel. Problem then was I could never get a nice shallow round crater in the top of the steel, it was more like a shallow hole but I'd often get a bit of blowout at the side.

Anyway to cut a long story short I ended up learning microcontroller programming and built a dedicated external circuit to go between the computer and the plasma cutter. I now have the fast accurate hole marking I've always wanted. I get nothing more than a tiny round crater in the top of the steel, perfect for accurately locating a drill point or even a centre punch if I want to enlarge them.

HOLE CENTRE MARKING WITH CNC PLASMA - YouTube

I'd love to know if anyone knows of a way to achieve this result (i.e. using the same control gear as above) without having to resort to an independent external circuit.