The air bearing is ideally suited to ultra-high-speed shafts where shear in a liquid lubricant would be excessive. In these systems the viscosity of the air is sufficient to provide entrainment and a hydrodynamic cushion (see Streibeck curve). Studying this characteristic of hydrodynamic bearings shows the slower the tangential velocity of the shaft relative to the bearing and lower the viscosity of the lubricant, the thinner the lubricating film.
A 10 mm shaft diameter turning at 33.33 RPM only has a tangential velocity of 17 mm/s, extremely slow. Also, the lubricant is air which has a viscosity 3000 times lower than that of typical oils used as lubricants. This likely results in an air film of a tens or single digits of microns.
This is not such a good idea in TT bearings, either for the tonearm or platter. They must be linked together as tightly as possible to eliminate any differential movement. Radial differential movement in between the platter and stylus is a good description of the desired cartridge output signal. Due to the low viscosity of air, the radial tracking forces will likely be able to modulate the air film thickness, so the differential relationship between the platter and stylus will not be fixed as it needs to be. This would seem to apply to air-levitation platter systems as well.
Of course, I could be full of s#!t...
Cheers,
Howie
p.s. I wrote a white paper on lubrication targeting automotive systems. If you are really bored you can find it here.
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Daniel: That is suitably overkill! Given a ball bearing and pointed spindle, if made precisely enough can have a 3 minute spin down there certainly isn't a friction problem to deal with and IMO if you have vibration problems a minus-k is a better approach.
Howie: I never said they were a good idea. Vac holddown has some positives but I doubt I will ever get to try it.
Howie: I never said they were a good idea. Vac holddown has some positives but I doubt I will ever get to try it.
Howie,
Off audio, but on bearings... Turret presses used for sheet metal use bronze bushings for the turret. Normal clearance between the punch and die is 10% of the metal thickness. So for .032" thick material a wiggle of .003" would not just not allow for a clean punch but would dramatically increase punch and die wear. As mine is a small unit with only 50 tons of force...
Normal lubtication method is to pump oil into the main bronze bearings about every eight hour shift. As the machines ain't cheap many are run 24 hours a day.
Very easy to find used machines on the market. One I follow is asking $7,000 for a used machine. New $185,000.00. Not surprisingly been on the market for a while. Of course moving such a machine is not exactly easy or cheap.
So for some funny reason I have always considered lubrication of major importance! Now my machine is about 22 years old and still seems to be good. The test is quite simple you punch a hole and look to see if the punch stress material flow is uniform around the hole edges.
The oil that came with the machine appeared to my eye to be asphaltic based. Of course around here paraffinic is considered better. Instead I have been using "synthetic" almost. In reality Mobil 1 automotive stuff. Not sure what is better and actually available these days.
I still keep around several single weights paraffinic oils, just to avoid multi-weights from getting into things like sharpening stones to small motor bearings. (I have seen folks ruin "oil stones" by putting automotive oil on them. The correct oil can be kerosine or lard added to kerosine, but few seem to know that!)
I suspect if I knew about the bearing issues and cost of these machines, just after college, I would have considered a business of buying used machines and refurbishing the bearings and upgrading the computer controls. Buy for under 10K and sell for 100K! Downside of course is the market probably is less than 50 units per year.
Off audio, but on bearings... Turret presses used for sheet metal use bronze bushings for the turret. Normal clearance between the punch and die is 10% of the metal thickness. So for .032" thick material a wiggle of .003" would not just not allow for a clean punch but would dramatically increase punch and die wear. As mine is a small unit with only 50 tons of force...
Normal lubtication method is to pump oil into the main bronze bearings about every eight hour shift. As the machines ain't cheap many are run 24 hours a day.
Very easy to find used machines on the market. One I follow is asking $7,000 for a used machine. New $185,000.00. Not surprisingly been on the market for a while. Of course moving such a machine is not exactly easy or cheap.
So for some funny reason I have always considered lubrication of major importance! Now my machine is about 22 years old and still seems to be good. The test is quite simple you punch a hole and look to see if the punch stress material flow is uniform around the hole edges.
The oil that came with the machine appeared to my eye to be asphaltic based. Of course around here paraffinic is considered better. Instead I have been using "synthetic" almost. In reality Mobil 1 automotive stuff. Not sure what is better and actually available these days.
I still keep around several single weights paraffinic oils, just to avoid multi-weights from getting into things like sharpening stones to small motor bearings. (I have seen folks ruin "oil stones" by putting automotive oil on them. The correct oil can be kerosine or lard added to kerosine, but few seem to know that!)
I suspect if I knew about the bearing issues and cost of these machines, just after college, I would have considered a business of buying used machines and refurbishing the bearings and upgrading the computer controls. Buy for under 10K and sell for 100K! Downside of course is the market probably is less than 50 units per year.
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Hey Ed!
The issue with using PCEO (Passenger Car Engine Oil) in other uses is the additive package. The base oils are all commodity items refined by the major companies and available raw...if you want to buy 55 gallon drums of the stuff...which I did (but not with my own money!) in an effort to test base oil characteristics with specific additive blends.
So the thing which makes synthetic oil so stable WRT temperature extremes and chemical attack is twofold: 1) it's lack of dangling (unterminated) atomic bonds which would leave it open to reacting with other substances, and 2) it's homogeniety; being synthesized by reacting precursors in a closely controlled process results in a very high percentage of molecules all being the same as opposed to mineral oils which are fractionally distilled into batches of many different molecules which all happen to have similar boiling points.
This chemical stability makes base synthetic oil have lower adhesion to things like the metal it is trying to protect. This characteristic is what gave it a bad name in the 1970's when it was first introduced to the general public (it had been in military use since WWII). Fortunately since then polar additives have been added to synthetic PCEO to counteract this propensity and in general modern synthetic oils are the premium choice for most applications.
Enuf.
Howie
A LOT. Although, like with anything else the first couple probably take 20x as long as the later ones, when you actually know what you're doing. I bought a baby baby lathe and am going through this right now. Vertical wall of learning curve. But fun.
Also 100% agree that at low RPM an hydrostatic bearing would be better than an air, but also messy.
I think these are pretty stiff.
However if the platter is 25-50 lbs. and shares a plinth with the tonearm base which is similar I don't think there will be much differential motion between them regardless of the bearing. Not enough force.
Turntables are an interesting problem but something of a dead end.
Attachments
Howie,
As Bonnie has spent too much time away getting stale with the common language here, let me translate.
"I am lazy and like things presented to me as simply as possible. So please cut and paste the important parts here. The selection and editing involved is also a nice touch."
Of course, as I am also lazy, let me second the opinion!
. !!!'
I also noted that in the cited paper no footnoted references included any of my papers! Not really unexpected as I haven't written any on that subject.
As Bonnie has spent too much time away getting stale with the common language here, let me translate.
"I am lazy and like things presented to me as simply as possible. So please cut and paste the important parts here. The selection and editing involved is also a nice touch."
Of course, as I am also lazy, let me second the opinion!
. !!!'I also noted that in the cited paper no footnoted references included any of my papers! Not really unexpected as I haven't written any on that subject.
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No you are not.
For low rpm applications, static air bearings might be used, which require external air supply pressurization system (pump noise? Complexity?).
Hydrodynamic air bearing (foil bearings) do not require external pressurization system but rotor shaft rotational speed has to be very high.
The only place I have seen air bearings on aircrafts is at the shaft of the air-cycle machine (a component of the cabin cooling air conditioning system) revolving at >10k rpm
http://www.rddynamics.com/pdfs/foil-97-gt-347.pdf
https://web.archive.org/web/2016030...acfm-2010/contributed/fluidmechinery/1017.pdf
https://pdfs.semanticscholar.org/07...775.120988561.1597494177-927980438.1597494177
George
Of course they're a dead end! How much of the music industry outside of streaming is not shrinking?
Yeah the blockhead spindles are very nice from what I've read (haven't seen one in person). My original comment about precision spindles was meant in all of its tongue in cheek, as I'm 2500% sure the mistracking of the groove itself in the record would greatly outdo the runout of even a modest bearing setup. Not that, in general, the folks macing precision machines make turntables.
George -- while the air compressor itself is obnoxiously loud, the air bypassing our high speed spindle at work is very quiet. So a compressed air tank or a large pressure tank that lasts long enough wouldn't be beyond reason if someone starts with the presumption of an air bearing TT. I'd see much greater value in making a "TT to end all TT's" for commercially capturing (and touchup) of antiquated vinyl with no masters around. Get as good a digital capture as you can.
I perceive that you guys are thinking of fixing problems that have been addressed over the last 40 years or more. What is important in phono reproduction is a turntable that effectively does its job, much like a car that will get you to work, the store, etc, and back.
Last night I listened to a Zoom conversation about audible turntable adjustment that would drive almost anyone here, crazy. It was a dozen careful adjustments too far. To appreciate a good vinyl recording mainly consists of a clean, not too worn, record, a decent phono cartridge, and turntable without too much rumble, or wow and flutter. To get the best performance, takes a lot more money, better cartridge, playback electronics, and turntable sensibly set up according to the rules, but it is not absolutely necessary to appreciate what a vinyl record can sometimes give, beyond a CD or equivalent playback.
The people that I was listening to last night went far beyond this to using special test equipment, test discs, hired expert, etc, etc. Even I don't bother to go to this level, and I doubt than many here will as well.
Last night I listened to a Zoom conversation about audible turntable adjustment that would drive almost anyone here, crazy. It was a dozen careful adjustments too far. To appreciate a good vinyl recording mainly consists of a clean, not too worn, record, a decent phono cartridge, and turntable without too much rumble, or wow and flutter. To get the best performance, takes a lot more money, better cartridge, playback electronics, and turntable sensibly set up according to the rules, but it is not absolutely necessary to appreciate what a vinyl record can sometimes give, beyond a CD or equivalent playback.
The people that I was listening to last night went far beyond this to using special test equipment, test discs, hired expert, etc, etc. Even I don't bother to go to this level, and I doubt than many here will as well.
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if you need an exceptional bearing the blockheads are wonderful. I have used them in magnetic disc trackwriters and on turntables. Andy Payor solved both the compressor and the dry air problems pretty well for a consumer table. The bearing doesn't use a lot of air so the compressor is not that large. it still needs a large box and should be remote if possible. The vacuum holddown works well but everything needs to be clean before you flip the switch.
This is what I have never been able to figure out. Diana Krall's voice is heavily processed, as I noticed in all of her vocal excretions I have been confronted with.
Yet, many audiophiles use this super processed voice to determine how natural a stereo set up sounds.
