New Mobo

[Jonathan]

I have done a clean install of XP pro up to SP3 reinstalled Mach3 and set it up to use the native LPT1

Perhaps try LinuxCNC? Even if you don't want to use it in the long term, if it works you'll know it's a software problem.

The only up-side of the issue is that I am saving money by not breaking cutters. Is there a market for 3.17mm diameter TC rods about 25mm long ?

I occasionally use the bench grinder to turn them into V-cutters, which are fine for simple PCBs. I've got enough for now though!