Thrust bearing question

[homebrewed]

I'm looking at replacement thrust bearings for my desktop mill. While looking at the VXB web site listing for a 10x26x11mm roller bearing I saw some specs that I'm trying to figure out. See here . My question has to do with D vs D1 vs d vs d1. Confusingly (to me anyway), D is closest to d1 and D1 is closest to d in size. I THINK the variation is the difference between the race and washers but that's just a guess. The drawing isn't very helpful in this regard. It's hard to believe that is the tolerance range, gotta be something else. I'd be grateful if someone could shed some light on this.

Thanks!

 

[JimDawson]

Looks like the races have a different ID

 

[homebrewed]

Hi Jim,

You're probably correct. Thinking about it a bit more, the race will rotate at a different rate than the washer. The speed ratio will depend on the ball or roller diameter -- the larger they are, the slower the race will turn relative to the washer. Given that, you don't want the race in close contact with the shaft. That could cause all kinds of problems -- excess wear, frictional loss, binding up, etc.

 

[T Bredehoft]

It does seem a strange way to dimension something. And if they are the same dimension (26 or 12) why are they called out differently?

 

[homebrewed]

Some additional thoughts on these guys. The fixed washer, which is in contact with the non-rotating part of the assembly, also could rub against the shaft -- unless it is prevented from doing so in some way. For thrust bearings that use balls and grooved washers this can be accomplished by machining the shaft so the rotating washer is a close fit, but it is turned down a bit where the fixed washer goes. The balls riding in the grooves ensure that everything is concentric, and all is well.

However, thrust bearings with needles or rollers don't have grooves so the thrust bearing by itself can't enforce concentricity (and therefore can't guarantee that the fixed washer won't rub against the shaft). A separate, standard bearing (or bushing) would be needed to make sure the shaft has the correct relationship to the thrust bearing.

These considerations should be taken into account if you are "upgrading" something, even if that just means replacing ball-style thrust bearings with needle-style thrust bearings.

 

[Chewy]

Just went through this on a work aid I made. My 2 cents (probably wrong, but how I solved it). I made a gas shock collapser. Think shock absorbers, but with a button on end to expand and contract. Used on office chairs. I have an Acme rod that pushes a steel plate. You turn the handle and the plate pushes a mechanisim to collapse the shock. Some shocks get bumped in transit from the supplier and then won't fit in box to ship it to our customers.

On either side of the plate is a snug recess to press in the race with the larger diameter. The race with the smaller ID is on the rod.
Starting from handle: Acme nut pined to rod, small ID race, bearing, large ID race, plate, large ID race, bearing, small ID race, Acme nut pined to rod.
I ran into the different ID's and could not find any answers (that I could make sense of) anywhere on the internet. All bearins show the different ID's but not why. OD is the same on both races. I guess they figured if you buy one you already know how to use it.

The race(s) in the plate is fixed and does not turn. The race(s) on the shaft of course turns with the shaft. Charles