Question about probing (X edge, Y edge, hole centres finding etc.) on all-metal machines.

With the recent upgrade of my cnc machine to all metal parts, the tool and the workpiece are always electrically connected. This means I can no longer use croc clips on the tool and workpiece together with Mach3 2010 screenset (which is excellent by the way, best few pounds ever spent on this hobby!) to probe to the workpiece edges.

My previous machine used 2 layers of 18mm ply for the gantry sides so was electrically isolated. The probe was only active when the tool touched the work so Mach3 could set the edge locations.

To try and get around this I wrapped a sheet of lining paper around the part before tightening it up in the vice, but there was enough conduction through the paper for the probe to be active all the time. I took the part out of the vice and it had not ripped through the paper.

I have thought above putting glass fibre sheets (the type for making circuit boards) under the vice, plus a mica washer under the bolt head to electrically isolate the vice.

Or I could try and make up a plastic spacer of a very accurately known thickness, with a piece of metal over the top and a wire/clip to the metal, then hold the plastic side of that against the edge I want to probe to find the edge. Then type in the thickness of that part into Mach3 to get the true edge position.

I can't be the first to have come across this - what is everyone else doing to probe the edges of the workpiece? I don't want to go back to the paper-trap method which was laborious to say the least.

Thanks