Hi Rob,

Many thanks for the suggestion - I think I may have checked and shimmed that already, but in a slightly different way. I cut two 6mm diameter holes in an MDF scrap board, along the X-axis. I then inserted two precision 6mm metal dowels in the holes, and set an engineer's square against them. I then fixed a DTI to the router bracket and ran it along the other edge of the square in the direction of the Y-axis to check for squareness. Initially it was out but some strategically placed shim washers got it to within 0.02mm over a 150mm run. This is what aligned my circular errors to the X & Y axes, such that one is oversize and the other undersize. The max and min diameters were previously off axis. Does this achieve the same result as you were suggesting? If not, then please feel free to clarify!

Hi Neale,

A good suggestion and one I had considered. However, since one axis runs over and one under, I assume missing steps can't be my issue? Surely they would be both undersize if I had missing steps? Also, I see the error with a single MDI move, hence the wrong edges setting is unlikely I think, as that only comes into play as you do reversals as you say. I have played with pulse widths and polarities anyway, but with no effect.

Worth adding that I was the one that set up the Mach3, so it is all my own work - it was just the mechanics that I took on. I take all the blame therefore for the electronics and software, but I'm currently pretty comfortable that it is OK, having seen the issues remain unchanged with a swap of the drive cables to the motors. But I am here to be proved otherwise!!

Any more bright ideas most welcome! Or I re-pose the initial question. Could it be C7 ballscrew accuracy, where I need to tune the steps accordingly?

Cheers
Graeme