Press fitting bearings

[swong46]

Hey guys, how much smaller do you design the bearing hole of an upright if a bearing is to be lightly pressed in? IE, it will still use a rear flange and retaining clip to hold it.

Also if a hub is to be pressed into the bearing, how much bigger should the hub be?

[sbrenaman]

-- deformation = alpha * (Tf - Ti) * Length
-- Pressure created by an interference fit - Shigley's 8th edition, section 3-16. This will help you decide how much interference is necessary to hold the bearings in the upright at your operating lateral loads.

If you're using aluminum uprights, you need to know what the operating temperature is of your uprights. If you're going to rely solely on a flange and circlip to hold the bearings in, are you sure you want to have a scenario where a hard material like steel is going to be loose in a soft material like aluminum?

[The AFX Master]

Originally posted by sbrenaman:
-- deformation = alpha * (Tf - Ti) * Length
-- Pressure created by an interference fit - Shigley's 8th edition, section 3-16. This will help you decide how much interference is necessary to hold the bearings in the upright at your operating lateral loads.

If you're using aluminum uprights, you need to know what the operating temperature is of your uprights. If you're going to rely solely on a flange and circlip to hold the bearings in, are you sure you want to have a scenario where a hard material like steel is going to be loose in a soft material like aluminum?

I digress from part of the first paragraph, bearings must be hold axially by physical means other than friction (ie: shoulders on the bore or shaft). Circlips are also a no-no way to hold bearings axially.

In fact, tolerances used to hold stuff for such loads axially will ruin most ball or roller bearings upon installation.

Thermal expansion is a issue with aluminum housing, it will expand a little bit more than the bearing, so, take it into account too if the part is going to get hot.

SKF reccomends a series of tolerances for shafts and housings for all their bearings at their website. Generally, these tolerances are calculated for steel housings, so, if you´re using aluminum housings (as usual in uprights, diff carriers and so on) you may go a little bit tighter with the interference. That is, using the highest (or heavy duty) recomended press fit.

Read skf.com, tons of useful info and calculators there.

[coleasterling]

Why are circlips a no-no for holding bearings in axially? I don't think I've ever heard that before. Do you mean that they are inadequate when the bearings are the sole means of keeping the diff mounts from parallelograming?

[Mazur]

Originally posted by coleasterling:
Why are circlips a no-no for holding bearings in axially? I don't think I've ever heard that before. Do you mean that they are inadequate when the bearings are the sole means of keeping the diff mounts from parallelograming?

Circlips are OK as a safety measure so your bearing doesn't fly out of your upright under extreme cases, but the bearing should be held in axially by the radial load caused by the interference fit with the bearing housing.

Either way, you're going to need a press fit if you don't want your outer race slipping on inside of the housing.

[exFSAE]

You really only need your "press fit" to be fairly snug to locate the thing. It's not like it has to transmit any torque. I wouldn't use the press to retain the thing axially. In my experience, 0.0005" - 0.0008" press per inch of diameter was sufficient.

Pretty easy to use "positive" stops to retain the bearing axially. Nothing wrong with a C-clip, so long as its used on the lightly loaded side.

[Mike Cook]

I agree with ex...
The maximum press I do is about .001" per inch press fit for aluminum housings, and .0005" per inch for steel housings. This is a rule of thumb that I was taught and I have modified it slightly based on experience. In general, you should probably calculate these things, but its good to have a rough idea to make sure your calculations make sense.

In some cases (like rocker bearings) where the axial loads are very small, and the press fit is just to prevent slop, I do as small of press as I can. This makes it easier to get the bearings out when the time comes.


::On Edit: This brings up a small pet peeve of mine. When you design your parts...for the love of god, take a few extra minutes to design a way to press the races out.


Mike