What causes turntable rumble

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.

Nsgarch...Although I attended MIT I transferred and graduated elsewhere in 1961. BMe. My work involved ongoing relationship (40+ years)with MIT Instrumentation Lab, now Draper lab.

The gyro wheel with air bearings is not driven by air jets, but rather by a motor. The wheel assembly is sealed.

It's been many years, but I seem to remember that the viscosity of the lubricant drags it into the narrowed part of the bearing clearance. As I said, check your text book (or maybe look in Google).

Colonel "Rusty" Draper, who for those who don't know, developed the Inertial Guidance System for our early guided missiles, was also the faculty advisor for the MIT Flying Club (which still blows my mind!) My favorite story (of his) was when he thought he was going to die, as he was flying a WWI 'Jenny' over Logan Airport, and the entire tail assembly fell off! (and he had no parachute ;--) He cut the engine, and hoped the wind would blow him toward Boston Harbor; instead, the airplane just "slowly maple-leafed to the ground" as he put it, "and I just walked away!" I often wonder (but never thought to ask him) if that's is where he got the idea for the inertial Guidance System!!

As for the TT bearings: if you suspect a little bearing noise is getting into your music ;--) please just try some of v.d.H's spindle oil, OK? Unlike so many what I call "Emperor's New Clothes" audio products, you will definitely hear an improvement in terms of quieter background, especially on old belt drive units. I know this because, besides my guinea-pig self (who of course sprung for a $50 three-lifetime-supply bottle of the stuff;--) I shared some with at least 4 others who said it made a real difference. Of course THEY got it for free, so I guess they wouldn't say it sucked!