Thanks for the idea...I will try this tomorrow (finished for the night now!)

One thing I have just done, is changed the Z axis to 1/8th stepping (and calibrated the machine - again!) the error is down to 0.1mm (ie between Y0 & Y10 ...in oter words a 10mm line) - which actually might be correct because i put a V cutter in the collet, lowered it to just touch the copper at Y0 then slowly moved towards Y10 & the line disappeared, so this 0.1mm disrepancy might be true deflection in the copper board itself...I'll havea better idea tomorrow when I can do a proper cut!