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Jaakko Fagerlund
05-12-2013, 03:34 PM
I was just browsing bearings from a supplier and happened to bump in to these double row angular contact bearings. I'm just wondering, if one fixes the outside diameter solidly and then attaches the shaft with a nut on the center portion of the bearing, how much end float does this thing have? I didn't see anything about this in the catalog and quick googling didn't turn up any magical solution to my question.

Rich Carlstedt
05-12-2013, 04:30 PM
Jaakko

Depends if they are "DT" ground ?
Usually "DT" are sold in pairs (for spindles etc)
DT grounds means the bearing you mentioned are preloaded by design, when you install them.
The inner race will stand proud from the outer race, and when you install them and force the two races to be aligned, you get the proper preload (designed)
Putting the outer races face to face is called DB and requires a nut on the shaft for compression as you mentioned
Putting the inner races face to face is called DF and requires a compression activity on the outer races
When bearings are stacked in the same direction, it is called DT

Rich

macona
05-12-2013, 04:34 PM
5200 series bearings?

Rich Carlstedt
05-12-2013, 04:35 PM
I should have asked if you were referring to a one piece double row bearing such as a SKF 5300 ?
They are already preloaded and are meant to be installed without end shaft adjustment. If you add such adjustment
you will detract from the life of the bearing , but that may be quite a long time ??
]
Rich

darryl
05-12-2013, 04:39 PM
If the races are mirror image, then you'd expect that it would have a pre-load spec since there's nothing you could change except the tightness of the press-fit. Since there doesn't seem to be any defining specs, it's probably not designed for any critical application- maybe a water pump bearing, or an idler shaft bearing.

Offhand, I would think that an angular contact bearing would be meant to take a pre-load to control end float, but a double row ac bearing would then seem to be at least partially defeated in this type of application. If the races were both in the same direction, then it would be a bearing that doubles the loading capacity- still requiring some method of pre-loading it.

Can only guess at this point.

Rich Carlstedt
05-12-2013, 04:47 PM
If the races are mirror image, then you'd expect that it would have a pre-load spec since there's nothing you could change except the tightness of the press-fit. Since there doesn't seem to be any defining specs, it's probably not designed for any critical application- maybe a water pump bearing, or an idler shaft bearing.

Offhand, I would think that an angular contact bearing would be meant to take a pre-load to control end float, but a double row ac bearing would then seem to be at least partially defeated in this type of application. If the races were both in the same direction, then it would be a bearing that doubles the loading capacity- still requiring some method of pre-loading it.

Can only guess at this point.

Yes, generally such bearings ( 5300 ie) do not require loading and work with pumps or applications that you want to limit axial movement.
All ball bearings suffer from axial movement as the balls deform in the race. A double " AC" bearing is meant to reduce this to a minimum

Rich

Forrest Addy
05-12-2013, 06:37 PM
A double row angular contact bearings Vs single row. Single row bearings have some radial clearance and are not intended for preloading via dilation of the inner race through controlling the bearing seat size. They require several thousandths end-float to function properly in responce to end-loading. Visualize the unit loading between ball and race if there was no radial clearance: a small radius tangent to a somewhat larger radius produces large radial forces Do the geomery something like the over-center action of a toggle or a punch press; a little deliberate en float reduces unit loading in thrust by orders of magnitude. Internal clearance in a plain radial ball bearing is not "slop" or indicative of wear or quality. It's allowance for race dilation and unit loading control of the thrust component of the applied load.

In my experience the end-float in an un-mounted plain radial ball bearing can vary but if I had to put a number on it maybe 1% of the inner race size would be my WAG. It depends of the bearing manufacturer's practice and their internal clearance code if present in the bearing numbe. YMM, of course, V.

A double row radial bearing is designed for a single package solution for restricting end float in a "wide" or "cartridge bearing" form factor.

How much end-float in a double row angular contact ball bearing? This is one of the "it depends" questions. If the manufacturer built the bearing with the right internal clearance you can calibrate the shaft diameter to dilate the inner race to provide a preload. If the as-supplied internal clearance is zero, a very light press (0.0015' to 0.0002" thereabouts) would provide a preload of sorts but you may have to make a few trials on sample shaft stubs to get it to suit your application.

If your application is critical, you're cutting corners, and your time is your own to spend, I suggest you conduct a survey where you make a zero clearance bearing fit on a piece of scrap material and thread it for a bearing nut. Leave it in the lathe chuck. Mount the bering. Using an 0.0001" reading indicator positioned to register radial movement force, start the spindle at say 200 RPM. Force the outer race towards and away from the indicator. The object is to centralize the balls in their running configuration and thus maximize the radial clearance reading. Note the reading for later reference.

Next determine the end play if present. This requires confining the outer race to pallalel motion and for that I can make no suggestion that doesn't require elaborate apparatus but you can yaw the outer race each direction and perhaps gain some insight of the bearing's operating parameters; yes, it's guesswork.

If radial clearance is present, you can size the bearing fit to take up that clearance and, if you wish a little preload, add a tenth or so.

All the above is "gold plate" activity. Chances are you will improve the running accuracy of the double row angular contact bearing if you guess right but, generally speaking, if you install them to manufacturer's specs you will be OK. These are not spindle bearings so don't attempt to use them as such. Their best application is controlling end float in rotating assamblies for pumps, worm gear thrust, drill presses, ider pulleys and gears, geared transmission, etc.

Jaakko Fagerlund
05-12-2013, 11:52 PM
5200 series bearings?
Yup, forgot to mention about this.

And thank you all for the explanations, got what I was after :)