After getting the Z axis moving, I turned my attention to generating linear movement with a servo drive. My initial concept of using the milling machine’s factory lead screws and driving them with a timing belt pulley combination was ok, but I was assuming that most of the backlash was coming from the shaft end supports. Time to re design the end supports and use angular contact bearings.

 

I re designed the shaft end supports and machined mounting blocks for angular contact bearings etc.

Improving the X axis     

Grae-Tech 

After some testing of my new shaft support, I discovered that most of the backlash in the table was coming from the leadscrew nut! Bummer! I removed the heavy table and inspected the nut. See how the manufacturer had tried to compensate for backlash, cutting a small slot in the brass nut, and inserting a small threaded screw to squeeze the nut to try and eliminate backlash. This sort of worked, but I was worried that as the nut wore, I would have to keep tightening the backlash adjustment screw. When climb milling the table jumped all over the place and I knew that if this was going to be any good as a CNC machine I would have to replace the cheap acme thread screws with ball-screws.

 

Time to get some ballscrews!