tapered roller bearings

[Harold_V]

I've watched that YT video before Ron. I seem to recall a mention that there still being made, but those Gamet bearings are pretty famous world wide for there high accuracy and have an eye watering price to match.

Yep! That's the make of the bearing in the headstock of my Graziano.

they were using using simple sleeve bearing lathes to bore and grind master gauges to far under sub 10ths accuracy. It's a much more sophisticated and expensive system than any ball or roller type bearing, but Moore Tools purposely uses sleeve bearings today on there high speed nano capable machine tool spindles.

In keeping with that thought, Cincinnati uses what they call a Filmatic bearing in their centerless grinders. A hydraulic tensioned sleeve bearing, for lack of a better description. Anyone who has operated a Cincinnati can attest that holding .000050" is pretty much routine. In spite of their ungainly appearance, they are a high precision machine.

H

[John Hasler]

Hydrostatic bearings. Extremely low noise and vibration but limited side load capacity.
A relatively "perfect fit" for use in a centerless, where end pressure is almost non-existent. Only the slight pressure developed by the through-feed rate and depth of cut. Insignificant for all practical purposes.

H

[pete]

Or air bearings, https://www.youtube.com/watch?v=sFrVdoOhu1Q This one isn't too shabby for a home shop built lathe. Of course it helps to remember the guy who did it is a literal billionaire. Commercial air bearings and super finishing the shaft to the roundness and tight fit tolerances is probably more costly or at least about the same as those high end Gamets. But I've always wondered if sintered oilite bearings would work at a much lesser accuracy and performance level.

[Harold_V]

But I've always wondered if sintered oilite bearings would work at a much lesser accuracy and performance level.

Without a means to adjust clearance, likely not. Sintered oil bearings tend to wear the shaft, in spite of the fact that they work for common applications. Without a means to limit clearance, I strongly suspect that holding roundness (and size and taper) could become troublesome. Could be wrong, though. That's why the Filmatic bearing works so well in a centerless. It does that.

H

[pete]

Yep that almost exact roundness and very precise close fit real air bearings requires then it very likely makes the thought about trying oilite worthless. There's a few Youtube videos showing shafts almost impossible to turn by hand and then freely spinning almost frictionless once the air pressure is applied.

[Rich_Carlstedt]

Which makes me wonder;
Considering most of us simply don't ever work to such exacting standards, would a good quality normal tolerance bearing set do ok?
How much runout would one expect from modern regular high quality tapered roller bearings?

Maybe .002 to .003" ( .05-.07mm) ..which is common in Automotive bearings..
here is the problem fellows that you need to understand . I hear ---" I used cheap bearings and they had "0" runout "
Can that be real ? Yes
Will it always happen..? NO
You must understand how THEY make bearings to understand ----Why !
While Bearing Makers grade the bearing components, it is the final assembly that "may " determine the quality ( Called "Grade" )
Please Know that a Roller bearing quality grade goes from 0 ( excellent ) to 5 ( Poor) - which is opposite of Ball bearing grades !

Lets say in this example , we have 3 parts, a roller, a inner race and a outer race ( 3 Parts)
So the Makers assembles the bearing and then measures it , and say it is TOO thick- even though the 3 parts were all a Perfect "0"
in inspection, the thickness downgrades it to Grade 3 bearing as that is the thickness that it matches.
Well, if you have Preload rings in the spindle housing that determine the preload, this is a bad bearing, but if you have a adjustable nut, The bearing even though it is a "3" is perfect in running !
So you can get a bearing that is prefect for your application- BUT If you want total assurance that the machine will work to your satisfaction, you have to make sure the bearing Grade is sufficient.
SO the Maker may put a perfect roller with less than perfect OD and ID Rings and the bearing is perfect ( a "0")
So the bearing maker makes 1000 bearings in a run- he would like them to be all superior but that is NOT the real world and he winds up with
75 Perfect bearings and those are "0" and then 100 that are 1's and 100 that are 3's and 725 that are 5"s for the total run
Then in final inspection they are stamped or marked and packaged as such .
So what really happens is THEY try to make perfect... and then mark them as they come out.
Try making a handfull of washers in your lathe ..make 20... some will be dead nuts and some will be too thick and some thinner /
Besides all this, don't forget, many precision bearings are "Matched" , so the Makers know they will be used as a "Pair" in the installation and they select the very best for this application -----the most perfect of the most perfect !
And know also that these 'precision bearings " will also have their High Points marked ( copper Dot) so eccentricities are known in installation.

So a bearing is not a bearing, it is an assembly of parts that go round and round and not all rounds are round !
Rich
Edit
You could say they all start out perfect and the rejects are culled out and sold as cheaper "Seconds"