What causes turntable rumble

Elizabeth, I think A.J. van den Hul and my mechanical engineering colleagues at MIT would strongly disagree with you ;--)

Neil

rumble is there on all records and only when a record is playing. had increased VTF as recommended on a prior thread because the cart didn't sound very good and someone suggested to increase VTF to max recommended to sound better. cart has 50 hours and sounds better probably due to more break-in, but with rumble. I'll drop the VTF back today and see/hear what happens
added a few drops of sewing machine oil to bearing which was almost dry, thought not completely

Nsgarch..."Wiffle grooves" are usually used on air bearings such as those in the gyros of the missile guidance systems I worked with. However, as Elizabeth says, regular journal bearings without grooves do pump oil quite nicely. Go look at any mechanical engineering text book.

By the way, your MIT connections don't impress me. Been there, done that.

Eldartford, I didn't know you were an alum! What year did you graduate, what course?

Wiffle grooves are not just a feature of air bearings (and BTW, many air bearings DO NOT use them, opting instead for multiple inlets in the manifold.) Grooves are also used on the Caliburn TT (I think) or some other expensive TT's that use a recirculating lubricant system.

But simple rotation alone creates no pumping action, and besides, what would be the benefit of "pumping action" if the bearing is filled with an adequate amount of lubricant which doesn't require cooling ;--) Metal to metal contact however is a problem. It is virtually assured in belt drive TT's; or whenever the tolerances are a little sloppy. No amount of lubricant will actually keep the metal surfaces from making contact, and that's among the causes of rumble noise.