Hi Jazz,
A few details to update you

The machine has rack & pinion drive to the x and y axes and 10x25 ballscrew to Z Y axis has 2 motors with the drivers connected to the same pulse/dir circuit. All motors have 5:1 reduction drive to the screw/pinion via toothed belt. Motors for X and Y are set to 1600 steps per rev and machine output set to 0.01042mm/step, the rack pitch is approx 4.15mm which is confirmed by the drive ratio and machine setting. I therefore calculate the maximum speed of the motor in rapid at 10000mm per min is 600RPM. Drive current is 4.86A. The motors are Nema34 type about 115mm body length They have 86BYGF 450B on them but a google search reveals only ads for machines no specs. The machine manufacturer reckon they have no details they can let me have. Hope this all helps.

I take your point about using Mach3, I'll be getting around to making the change asap. NcStudio offers no motor tuning facilities at all, it's not possible to alter the pulse duration.

I do have a USB driven breakout board for use with Mach 3 which has on board a PWM spindle control circuit and differential drive outputs for step/dir. I would like to make use of the PWM spindle control but have also been looking at the smoothstepper board which may mean better control. Any thoughts?

Many thanks again for whatever you can do.

Bob.