What causes turntable rumble

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!

Nsgarch...Doc Draper first developed Inertial Guidance for aircraft. The first US Navy Inertial guidance system, MK1, for the Polaris missile was actually a clone of a German design for the V2 which (fortunately) never got into production. Draper's main contribution was the floated Inertial Rate-Integrating Gyro, IRIG, both for attitude sensing and as a component within the Pendulous Integrating Gyro Accelerometer, PIGA. MIT Instrumentation Lab got the guidance system contract because at the time they had the best gyro expertise. I worked on Mk1 (a bit) and all subsequent systems including the next generation, not yet deployed.

I never heard him called "Rusty". Where did that come from? It was always "Doc".

"Doc" was what all the kids and faculty called him. I think the "Rusty" must have come from the people out at Hanscom Field, where he arranged for us to use the Link trainer . . . . a very colorful man.