Originally Posted by leswatts Yeah annealing, inserts, grinding off case and even hard machining all work.
The really interesting part is workholding. On some screws, particularly rolled ones,
the outer lands have a burr from the rolling process. They are not accurate datums for the raceways, so holding in a chuck or collet can create big errors. If possible, I check the lands with an indicator on the carriage with it set for threading at the ballscrew pitch. Then shim and adjust as needed. Someone else might have a better way... |
[I used some heavy aluminum wire, wrapped in the track, to provide a consistent surface for gripping in the lathe. It fell nicely into the smooth part of the screw, and seemed to hold it on center. I also used Les' method of removing the case-hardened layer on the end before I did that; using a large grinding wheel and revolving the part, it was possible to keep it more or less round. The bottoms of the lands give a good indication of where it's at. I made some gizmos for holding a couple of ball-nuts together with wave-washers in between, so as to eliminate backlash. It seemed to work, although if screwed too tightly together they add too much resistance.]
Andrew Werby
www.computersculpture.com