V-belts and Plain Headstock Bearings

[gwrdriver]

I have this little old (emphasis on old) Atlas 6" lathe, which I'm going to renovate. It has a plain bearing headstock so in age that would place it near the introduction of the Atlas 6's, perhaps as early as 1940. I've had this machine stored for a long time, and never used it, and in running it up for the first time I noticed that although the primary motor to counter-shaft belt is quite snug, but in normal operating position the secondary counter-shaft to spindle belt runs quite loose. To loose to attribute it to stretching, because the belt is still in sound condition.

This running tension can of course be tightened up, but my question is, would it have been typical practice to run plain bearing lathes with lower V-belt tension in order to reduce wear on the bearings? I'm going to be reworking the belt drive and replacing the belts but don't want to put too much tension in the secondary belt if that would put excessive wear on the spindle bearings.

[Steggy]

...but my question is, would it have been typical practice to run plain bearing lathes with lower V-belt tension in order to reduce wear on the bearings? I'm going to be reworking the belt drive and replacing the belts but don't want to put too much tension in the secondary belt if that would put excessive wear on the spindle bearings.

V-belts don’t need a lot of tension to function. As the belt wraps around the sheave, the belt sidewalls slightly bulge to grip the sheave. It is this sidewall bulging that gives the belt-and-sheave combination its power transmission capability.

It is important that consistent belt tension be maintained under load. The intermediate shaft (aka jackshaft) support must be rigidly held in position as loading comes and goes. Otherwise, the belt will slip, especially at low spindle speeds.

I recommend belt tension be such that a push with your forefinger or thumb will deflect the belt approximately 3/4" in the middle of the span. Higher tension than that will not significantly increase load capacity, but will accelerate belt stretching. Needless to say, sheave grooves should be kept free of oil and other contamination.

Regarding spindle bearing wear, the unit loading on those bearings due to belt tension is actually quite low, as the bearings have a lot of contact area and don’t see the sort of high P/V values that accelerate wear. As long as you keep the bearings well-oiled, you will be fine.

[gwrdriver]

About the same relative belt deflection I run on everything else then. Thanks.