Pre Loaded Bearing
Pre Loaded Bearing
(OP)
I guess I have always assumed that one could purchase deep groove radial bearings with an initial preload. And I said so in a design meeting. Then looking at an SKF catalog, I don't see how to specify this. I'll call SKF Monday but I thought I'd ask here this weekend to see if I'm just Blowing Smoke.
The application is intermittant slow rotation (1 rps) with light loads. We can't tolerate any play in the bearings (precision mechanism). We would mount the inner race with Loctite and the outer race with a Tolerance Ring to avoid additional bearing race squeeze and to eliminate race play.
The application is intermittant slow rotation (1 rps) with light loads. We can't tolerate any play in the bearings (precision mechanism). We would mount the inner race with Loctite and the outer race with a Tolerance Ring to avoid additional bearing race squeeze and to eliminate race play.





RE: Pre Loaded Bearing
To prevent the free play between the races to the housing and the shaft you can use fress fit or glue or tolerance ring. For the inner bearing free play the correct and accurate way is to order a matched pair of bearings designed to limit the free play and to induce a designed preload when assembled correctly.
RE: Pre Loaded Bearing
Johnny Pellin
RE: Pre Loaded Bearing
I have the impression that angle contact bearings are frequently used in precision applications.
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RE: Pre Loaded Bearing
RE: Pre Loaded Bearing
It's one rev per second. I can't state the exact application but the mechanism will be used to move a platform +/- 1 mm and to any stopping position in between. A positioning servo drives a gearbox which drives an eccentric (Crankshaft?). We need to achieve, say, 2 micron repeatability (I will probably have to compensate for positioning accuracy in software).
I can probably get away with ABEC 7 C0 bearings but no clearance would be ideal. I could also use angular contact bearings in pairs but that doubles the number of bearings and the inner and outer races have to be clamped (mechanical and assembly complexity).
I'm open to any suggestions.
RE: Pre Loaded Bearing
The only real help I can give is that it can be done.
We manufacture our own spinneretts for synthetic fiber which requires positioning on the order of your OP. I was never directly involved in the positioning aspect of the manufacturing process but do remember a few things about our machines. These machines were capable of making any hole pattern one could draw.
The original machines (1960's) used ball bearings whereas the later models use some high precision needle bearings.
Our positioning was accomplished by using a pantograph that translated the require movement of the work piece from a cam. The ratio of movement imparted by the pantograph was greater than 50::1 and could be stacked or run in parallel to achieve the desired motion of the work piece.
As I recall the early ball bearings were supplied by Torrington. We were fortunate that there was bearing depot at the local Naval Air Station and they would checkout each bearing. Later I know that we gleaned some information from Pope about their spindle bearings that was incorporated in the machines. There was also some work with RBC on their thin section bearings.
For the life of me I can't recall the supplier of the needle bearings and right now can't think of anyone to call.
Here is the type cutting and precision we were doing.
We beat the precision stated here.
Shapes
http://www.nippon-nz.com/english/jigyo/index.html
Precision
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RE: Pre Loaded Bearing
Machine tool spindles use bearings paired at the bearing factory, with the axial faces of the races lapped so that when they are squeezed together, a controlled preload exists. (Effectively, they are used as angular contact bearings, even though they are still called radial bearings.)
Electric motor manufacturers commonly preload generic radial bearings by fixing one and assembling the other with a 'preload spring' between the bearing race and a shoulder.
At the 2 micron level, do not be surprised to see trajectory errors associated with the passage of a single ball past a given spot on a race.
Mike Halloran
Pembroke Pines, FL, USA
RE: Pre Loaded Bearing
Thanks. My real concern is how much of a numb-nuts (SP) I'm going to appear when the preloaded radial bearings are not available. Probably I'll say that I really meant accurately controlled clearance bearings.
But theoretically, I don't see why you could not make preloaded radial bearings. It's a matter of selective fitting the races and balls. But, as others have said, there are many practical (and possibly historical) reasons this isn't done or is not commonly done.
1) They might brinnel just sitting on the shelf.
2) Every idiot in the world would select them, use press fits on the races, run them at high speed and then blame the bearing manufacturer when they immediately fail.
3) Many other reasons.
MikeHalloran,
You are absolutely correct about bearing running accuracy. The accuracy of the gear box will be at least 10 times worse and I'll probably need to have high accuracy linear encoder feed back to get to the exact position I need.
RE: Pre Loaded Bearing
http://www
Mike Halloran
Pembroke Pines, FL, USA
RE: Pre Loaded Bearing
Also look at the following brochure from RBC.
http://www
RE: Pre Loaded Bearing
Mike Halloran
Pembroke Pines, FL, USA
RE: Pre Loaded Bearing
Thanks for the X Bearing suggestion, I'm looking into them but so far they are larger that I need (I need something in the range of 1/2 in, ID, 1 in. OD).
I'm now certain the bearings I thought were preloaded radial bearings were actually X bearings (SKF calls them 4 point bearings). Their external appearance is the same.
I also think I see why preloaded radial bearings do not exist; any axial load would quickly overload the bearing.
RE: Pre Loaded Bearing
You could try and get a real accurately machined interference fit, between the shaft, bearing and bearing housing. I would suggest you try this out, as this should take care of fine clearences in the bearing.
Regards
RE: Pre Loaded Bearing