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.
The Smell of Molten Projects in the Morning 
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[…] I had to remove the lathe’s quick-change gear cover to tweak the spindle takeup adjustment nut. […]
[…] Purists will quibble that I should have used the four-jaw chuck. Turns out the three-jaw has under 1 mil of runout, which is as good as one could possibly want in light of the bearings. […]