Hi Neil - I'm working on a 2.5D edge finding/contouring probing wizard for Mach3. Please see
http://www.machsupport.com/forum/ind...ic,4456.0.html
It seems that there may be a bug in the G31 code. Currently Art is taking a look and hopefully there'll be a fix soon.
Basically after a G31 I back off with a G01 (all in incremental mode). Sometimes Mach doesn't execute the G01 so the probe tries the next G31 but of course it's already touching so etc. etc.
Ian