Quote Originally Posted by jjr2001 View Post
Thanks Toolmaker51, I did not know that some machines used DC motors for the lead screw.
I thought all the professional tools used change gears.

Thanks for the info,
Cheers, JR
To be perfectly accurate the lead screw depends on synchronization with spindle to produce threads. Lathes with one screw were common, but threading is less common than turning; wear on a single screw eventually may not thread as well.

A feed screw that can deviate from a prescribed rate, [ie DC motor] to improve or tune cutting conditions, time included. Most of us developed a sense what RPM looks right for so & do diameter, feed is less intuitive. What appears a good finish can be a result of rubbing, not cutting. Careful measurements might show an expected size reduction is less than what dial indicates. Just as possible, when a 'coarse' finish is precisely on size.

In general I judge a cut by a continual helix, somewhat thread-like. Finish in a pre-honed cylinder is another way to visualize it. As a cutting edge breaks down, the finish degrades. Rough or finish, a consistent appearance is near certainty one end is same as other, or tapers at prescribed rate
In job shops, we apply finishes according to intended use of a particular feature; a bearing bore deserves more attention than say, a shaft connecting two hubs. Too fine is a burden on shop rate just like too coarse requires secondary work.
When we re-open post holiday I'll get a picture to illustrate this.