Neil -
You've experienced the same thing I(and I'm sure many others) have being the "systems integrator" on our homebuilt cnc. Have you tried the freebie version of MACH2? You could check and see if the ipm problem is a software hang up or hardware/controller (stepper3) challenge. Power and motor come to mind too. And its always good to check for the loose fittings etc in the mechanical set up too as nervis1 suggested.
BTW - it would be really cool if someone with heaps of experience could post an integration checklist. Something that lists what they know works really well together. For example - I see a lot of users very happy with Xylotex and Mach2 with PacSci 23 motors -- and get good rapids and ipm while milling. I've got 66percent of that and am considering Xylotex for the second system. But would love to hear of other configs too. Gives us all something to strive for without spending the little excess capital we may have.
:cheers: Jim
Experience is the BEST Teacher. Is that why it usually arrives in a shower of sparks, flash of light, loud bang, a cloud of smoke, AND -- a BILL to pay? You usually get it -- just after you need it.