After de-greasing, cleaning and lapping the ways on my new machine I re-assembled it and adjusted the gibs until everything ran smooth as silk with zero play. I have to say that I was very impressed with how easy the whole process was and how well thought out the whole machine and its conversion is. However, I was a little surprised to see that on all the new, conversion bits, everything was marked out and drilled by hand - the scribe marks are plain to see. I would have thought that an operation like this would have called for jigs and fixtures at least, if only to speed production.
Herin lay a small problem - when the Y axis was at its inner most limit with the stepper motor virtually up against the ball nut, the motor was virtually unable to be rotated by hand via the coupler. The X axis was just fine and was very easy to rotate by hand. I think this is a good test to see if there is any binding in the system.
On careful inspection, the two tapered pins that locate the motor plate to the saddle were not quite lined up but because the pins were tapered they were able to be located. Another slight problem was that the two 6mm cap headed screws that hold the plate against the saddle were drilled and tapped slightly off centre. This should not have been too much of a problem as the holes were drilled slightly oversize to accomodate a slight misalignment. However, because these hole had been counterbored with a drill bit and not a counterbore bit, the seat for the caphead was tapered and not flat. This caused the plate to move slightly when the screws were tightened.
I found that by only using one of the locating pins I could get the table to move freely but everytime I tightened the screws, the plate was displaced enough to cause binding again. The solution was fairly simple. I drilled the clearance hole out a little more, to 7.5mm to allow for the misalignment, and then counterbored the hole properly to give a flat bottom to seat the screws on.
Job sorted - now when I use the one pin and tighten the screws everything stays in place as there is no taper at the bottom of the holes to divert the force of tightening. It is a fairly simple modification but one that has made the world of difference to the operation of the Y axis when at or near its inner limit.