Grizzly G0709 threading problems

[RDTS]

Have you thought about the chain of gears that drives your lead screw -- You have the headstock end gears feeding into the input of the gearbox. Then gears and shafts in the gearbox. If any gear in the drive chain is somehow slipping a bit on its shaft -- that will give you a finer pitch while it's slipping. Is that possible? Could a gear be missing a key, and it's just tight on the shaft but slips a bit here and there? Or something similar?

John

Unlikely a gear could slip just barely like that. Generally if they shear a key the spin and do nothing.

 

[RDTS]

Update: Found the problem although the new lead screw and half nuts helped. Nothing about this in the manual. There is a threaded portion in the apron hand wheel that you take a spanner or in my case a needle nose and tighten. First back off the middle setscrew then tighten the large flat threaded portion with your needle nose. Just tight enough that while the hand wheel is turning by itself while your half nut is engaged it won't fall on the downturn because of gravity. After you verify your table isn't lurching anymore because the wheel isn't falling then tighten the middle setscrew. I believe this lurching was screwing up my thread pitch just enough to cause me to have to go deeper on my cut to compensate. The upside is to get to the solution I brought everything else up to speed and the overall machine performs better now. My next lathe will be a good used old American Iron or a Taiwan made one from PM as anything Chinese in my experience require a good look at and trouble shooting to get the bugs out.