Atlas 3995 Chattering

[pontiac428]

I have been very careful to set the gearing with the proper spacing. There is slop in the drive train. But again, for these tests I am not using the power feed so that it does add another variable.

Roger that, just trying to contribute to your overall knowledge as you chase this persistent problem. Slop is a bit pejorative, backlash is more accurate a term . Backlash in a gear train is more of a feature than a fault until you try to pick up the same point from either direction, which isn't really applicable to a power feed on a lathe. Either way, since your gear train is turning whether your lead screw is engaged or not, a too-snug gear train can absolutely affect finish, especially when you have demonstrated that you can't reach peak no-load RPM. The main point being Atlas gears aren't perfectly round, and may have tight spots as an effect of that property.