Yeah, I wan't thinking about tarting up a dodgy machine tool so much as a way, using absolute encoders, to avoid homing and get 'limit switches' which I don't have now. Also I like the idea of controlling for the 'actual' position. I acknowledge that nothing's perfect and that the encoders have measurement errors and the mill will have some bendiness / alignment errors. I like the concept better though than relying on the stepper/servo's idea of where the position is plus a fixed value per axis of 'backlash'.

My mill has no missed steps and about 40 microns backlash on X and 80 on Y and Z - although I plan to measure those more accurately soon.

Alan