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In Reply to: RE: Inverted bearing vs. oil well bearing posted by Hiendmuse on April 16, 2014 at 19:33:39
The oil stays at the bottom of a conventional bearing.The design of the "inverted" bearing is based on a static analysis of stability which goes out the window as soon as the platter rotates, introducing precession. It is as good an example of audio paraphysics as you will find.
Mark Kelly
Edits: 04/17/14Follow Ups:
A non'technical description is as follows:
An inverted bearing with the same tolerance as a conventional oil well bearing (let's say .0005" tolerance) and the belt running through the center of the bearing shaft will precursor less than the oil well bearing every time, every time, every time.
The oil well bearing spends it's entire existance trying to fall over on its side but is captured by the bushings so it can't but it will keep trying. I can actually balance an inverted bearing with no bushings if I spend a little time and it will stay in place. the oil bath bearing will always fall over.
Mark, what are you thinking???? To much time in the lab??
Oil can also stay put in an inverted bearing. Every time I've pulled the platter on my Sota Millennia, the oil is right where I left it during assembly.
Precession is a "wobble" and that is not possible with either type of bearing unless there is excessive play in the sleeve bushings of the bearing shaft. On the other hand, if precession were a problem in either case, it would be much more likely to occur in a statically unstable design than in a stable design.
Furthermore, there is no relationship saying that something statically stable must therefore be dynamically unstable. Inverted bearings are both statically and dynamically stable designs. At any rate, it is not possible for an inverted bearing to be less dynamically stable than a non-inverted bearing. Think about it. What would have a tendency to "wobble" more -- a bearing supporting a mass well below its center of gravity or a bearing supporting a mass at or above its center of gravity?
In my opinion, if both bearings are designed properly, there will be no appreciable difference in performance. However, the inverted design is actually more stable, both statically and dynamically.
Best regards,
John Elison
If the bearing precision is sufficient to constrain precession, it is also sufficient to constrain any instability introduced by the COM being above the bearing point.This renders the rest of your argument moot.
Mark Kelly
Edits: 04/17/14 04/17/14 04/17/14
The word is sufficient and it is never sufficient, especially six months after owning it!!
> If the bearing precision is sufficient to contraint precession, it is also sufficient
> to constrain any instability introduced by the COM being above the bearing point.
If you had read and understood my argument, that is exactly what I said. On the other hand, inverted bearings are both statically and dynamically stable whereas non-inverted bearings are neither.
Better luck next time, Mark.
John Elison
yes, we just studied this in physics this week, precession would be more likely when the bearing is way below the COM, rather than closer to the COM...
Don't use that crap with me, John.
Mark Kelly
Hi Mark...I really do hope that your line of work has absolutely nothing to do with "engineering" anything!?!?
Rick.
-Mark, he makes -or did, make the Motor Controllers for Win's Saskia TT.
He may know more than you think-no?
Just suggesting ,
Des
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