by Marsh Collins
While I was working on my friend’s rebarelling job, I encountered one of those annoyances that had been sneaking up on me for a long time: The tailstock spindle screw on my ancient 11″ South Bend lathe was so worn that it often failed to eject a Morse taper tool, requiring that I unscrew the tailstock nut and reach through the screw hole with a knockout rod to remove the tool.
The cure was relatively simple, once I sat down and analyzed the cause. Since the removal of the tool required the screw to protrude from the inner end of the socket far enough to give the MT the initial push, it was obvious the wear on the screw end was enough that it could not do its job. How to lengthen the screw?
My first thought was to drill and tap the end of the screw to take a setscrew, making it now adjustable. But—the Acme screw thread wasn’t big enough at the root to allow much of a setscrew, so that was out.
The next thought was to allow the screw to protrude a few thousandths farther into the small end of the taper in the spindle, making up for the wear. The screw and shaft are machined from a single piece of steel. The collar being turned in Photo 1 functions as a spacer within the body of the tailstock. Thus, to do this without creating a new problem at the wheel end, I turned a spacer washer to the thickness I intended to advance the screw end, approximately 3/32″ (Photo 2). I chose 3/32″ over 1/8″ because some of my MT tools are a bit short on the tang end.
Then, chucking up the screw shaft, I turned the same amount off the front face of the screw collar (Photo 1), which abuts the spindle when it is fully retracted. This allowed the screw to protrude 3/32″ farther into the spindle cavity and contact the MT tool when fully retracted. It worked fine!