[awemawson]

John,

Thanks for that. I do have a copy of that exact manual even down to the same persons handwriting on the front cover

It's been suggested that maybe my problem is due to the phasing of L1, L2 and U & V - the manual (page 12) calls for L1 & U to be in phase, which they are on my machine, and also for L2 & V to be in phase. now L2 is grounded so how the heck do you check its phase, however U&V are definitely anti phase.

I assume that you have just added your 4th servo board to the same transformer set up originally driving the existing three axis? In which case yours must be correct, however as mines not on an Interact, I've had a transformer wound whose secondary replicates the 180-0-180-380 of the Interact one and I'm pretty certain it's right, but it's one variable I can't be certain of.

Do you have a 'scope so we could compare results?

I put the big lump of a chuck on to see if it affected the acceleration negatively - no change perceptable

Andrew