So what did the old-timers know that we don't??? The reason I ask is my old McDougall just uses a bronze/brass/??? block with a threaded hole in it. This is a WWII-era 20" lathe. The block for both the cross-slide and compound is about 1.5"-2" long, the shaft is about 5/8" diameter, 0.200" per turn. (rant on - There are times I'd like to punch the guy that decided on 5 tpi...hard to turn the compound smoothly and get a nice finish - rant off.) The compound has 0.005"-0.006" of backlash, cross-slide has about the same. Obviously it has worked for these older lathes....
Different grade of material to make the nut?
Threaded hole slightly undersize?
Obviously they knew something back then.....
Andrew