After un-jamming the 3-jaw chuck, I decided it was long past time to remove the accumulated slop in the lathe spindle. Modern lathes have a thrust bearing, usually with tapered needles or some such fancy arrangement. This lathe was shipped in 1928, has hulking brass bearings, and a nut to remove the slop.
If you’re following along in your copy of How to Run a Lathe, it’s Part Number 25 in the elevation view of the lathe, at least in my 1966 “Revised Edition 66”. Various copies are available here & there, but link rot seems to be a common failing.
The gear on the end of the spindle has 30 teeth and the nut thread is 20 TPI. After all these years, turning the nut 3 teeth takes the spindle from “free spinning” to “jammed tight”. The nut had accumulated about four teeth worth of end play before the “free-spinning” stage.
Call it 0.010 inches of play. Enough that I should have adjusted it out long ago, but not a big deal when there’s a tailstock pushing the work against the headstock bearing.
I don’t do any lengthy machining operations that would tend to heat the bearings and reduce the end play. If you do, that’s certainly something to consider.