Re: Z axis - Quill or Column
My mill conversion is now 4 years old, and it may be of interest how it has gone after doing a fair amount of work.
Basic Mill - (Larger bench top Mill/Drill Dovetail Column) - I would do the same again, an ideal machine for my usage.
Ballscrews - Cheap Chinese (Ebay types) - still going well with no end play. Supplied support bearings / housings all replaced, not up to the job.
Conversion - The large servos and gecko drives - No issues, works well. Certainly overpowered, but no downside to date. (I haven't crashed yet, however)
Wear - Support bearings excepted (Now 2 years on SKF's no Problem) all checks out. I check each axis every 6 months or so, measure backlash / disconnect motors and "Feel" for issues with the slides. Slides, if there is any wear, they have worn in not out. barely touched the gibs.
Quill - Remains locked at all times, I would say that if you have a dovetail column, drive it not the quill.
The only regret that I have is not fitting a 2.2kw VSD to the 1.5kw Spindle motor. The motor is 4 pole 1.5kw. I run up to 100 Hz to give 3000 rpm, and is well capable of the higher power above 1500 rpm. The spindle has cut-out on current limit a couple of times.