"we disengaged the Pinions from the racks and ran a circle cutting programme. All three motors are jerking while turning. We are now very sure that this is a electically related problem.
" Well done! That is a very helpful diagnosis. The problem sure is electrical or software.

Because the circle completes fully and there are no errors in position, I believe that interference is not the problem.

It looks like Mach3 and your PC are having problems giving evenly and correctly spaced pulses to the steppers.

I hope that you have the Mach kernel speed set to 25kHz. Config > Ports & Pins. I have heard that you shouldn't set it higher unless you have a very good reason.

May I suggest that you take this problem to the Mach support forums?

Gerald,

Problem sorted out!

My computer guy whom I recruited to the design jobs on Artcam had accidently enabled the Auto limit overide button on the settings page (press Alt6 on main menu). He has done this to overcome a problem at some point of our testing stage and forgoton to switch it back to the disabled stage.

I feel that when we are overiding limits on mach 3 the programme goes on to a safe mode and due to this does not obey many of the commands that go through a G code based sequence of events (programme). This is why the machine behaved well while running on the Joging mode and not on a programme mode.