Press fit on a sleeve bearing?

[jmarkwolf]

I'm selecting a bearing for a 3/8in dia shaft for a project, and am wondering about the relative merits of sleeve vs ball vs roller bearings.

My application is not terribly critical, but I'm not finding a lot of options for my 3/8in dia shaft.

Some of which are "sleeve" bearings that specify a "press fit". This seems like a misnomer to me. If the shaft were pressed in, how is it going to spin in the sleeve?

[Toolguy]

In that situation the sleeve is pressed in to the hole in the framework with the shaft turning in the sleeve. Sometimes the sleeve will be undersized after pressing, but can be reamed to an exact fit for the shaft. A .001 slip fit for the shaft is common, but you can make any class of fit you want it to be. A press fit for the OD is usually .001 up to an inch, then .001 more for each additional inch.

[Mcgyver]

Some of which are "sleeve" bearings that specify a "press fit".

sounds like maybe you're thinking sintered bearings. The bearing is a press fit into the housing not the shaft.

machinery's handbook shows how to calculate the interference fit and bore dia to end up with clearance desired, but generally a hole reamed to nominal will get you a typical clearance for a shaft. These style of are so called self lubricating and should not be reamed afterward.

as for the relative merits of different bearings.....it could fill a book without a lot more info. Press in sintered bronze bearings are an adequate solution for low speed low force applications not requiring a lot of accuracy. You should have a really good finish on the shaft (which would benefit from hardening)....but without details on the app its guesswork

[brian Rupnow]

If you use an "on size" reamer to ream the hole which an oilite bronze bushing fits into, then the bushing will be a light press fit. These bushing are made with a slightly oversize outer diameter and inner diameter. When you press them into an "on size" hole, the inner diameter will close up just enough to be a perfect fit on the shaft. For instance, if you use a bushing listed as 3/8" i.d. and 1/2" o.d., then use an "on size" 1/2" reamer to ream the hole. The bushing will, in reality be a couple of tenths bigger than the 1/2".

[J Tiers]

Definitely NOT trying to "start something" here....... but.....

The sintered bronze work pretty well for electric motor speeds, up to 3600 rpm certainly with smaller shafts up to an inch at least. I have motors with them that are decades old, with original bearings and still working fine. There is a general maximum surface speed (shaft surface vs bearing), which I do not recall.

They actually may NOT work so well at slow speeds, and a roller or ball might be better at low speeds especialy if there is much side force. The bearing may be worn faster by the friction before the oil comes out into the clearance. As a variety of "plain" bearing, they depend on oil forming enough of a coating to prevent metal-to-metal contact (which would quickly wear the bearing). But the oil is in the pores and only comes out when the shaft is spinning.

With side force and slow speeds, a ball or roller bearing is ideal, always ready, essentially no sliding action, needing just enough oil or grease to lube the rollers in their cage, and carry off heat.

[6PTsocket]

In that situation the sleeve is pressed in to the hole in the framework with the shaft turning in the sleeve. Sometimes the sleeve will be undersized after pressing, but can be reamed to an exact fit for the shaft. A .001 slip fit for the shaft is common, but you can make any class of fit you want it to be. A press fit for the OD is usually .001 up to an inch, then .001 more for each additional inch.

That is good info. I always wondered how much over sized a press fit was. Does it depend on the material and what is being pressed? Are a bronze bushing, a steel sleeve, a ball bearing, a post all .001 or are they different?

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[Toolguy]

The .001 press fit is pretty standard for most smaller parts. This means that the part being pressed in is .001 larger than the hole it's going in. A press fit is also called an interference fit. In some finicky applications, the amount of interference may be .0002 or .0005, but seldom over .001. If the hole and the part are both the same diameter, it is still a light press fit. Even a hardened steel drill bushing pressed into an aluminum plate will make the inside of the bushing smaller. Ball bearings have their own specs depending on the type and precision of the bearing, often less than .001. These specs can be obtained from the bearing maker.

You may want a .002 press fit on a plastic piece to keep the bushing in place. The plastic won't exert as much side force as metal.

For a big punch press with a 6" od bronze bearing and a 4" crank journal, you would make the bearing 6.006 od and the bore 4.006 id. When in place, the od will be 6.000 and id will be 4.000.

[Mcgyver]

Definitely NOT trying to "start something" here....... but.....
.

I don't disagree with your points, but not knowing the application we could go on forever.....I've a Schaublin and Rivetts with a plain bearings.....then there's the plain bearing in the elevating device of your lawnmower.

[6PTsocket]

The .001 press fit is pretty standard for most smaller parts. This means that the part being pressed in is .001 larger than the hole it's going in. A press fit is also called an interference fit. In some finicky applications, the amount of interference may be .0002 or .0005, but seldom over .001. If the hole and the part are both the same diameter, it is still a light press fit. Even a hardened steel drill bushing pressed into an aluminum plate will make the inside of the bushing smaller. Ball bearings have their own specs depending on the type and precision of the bearing, often less than .001. These specs can be obtained from the bearing maker.

You may want a .002 press fit on a plastic piece to keep the bushing in place. The plastic won't exert as much side force as metal.

For a big punch press with a 6" od bronze bearing and a 4" crank journal, you would make the bearing 6.006 od and the bore 4.006 id. When in place, the od will be 6.000 and id will be 4.000.

Thank you again.

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[J Tiers]

I don't disagree with your points, but not knowing the application we could go on forever.....I've a Schaublin and Rivetts with a plain bearings.....then there's the plain bearing in the elevating device of your lawnmower.

Not suggesting everyone uses the best bearing..... usually the cheapest that works.

And, a "plain bearing" is not always a sintered bearing, which is s specific type of plain bearing. My Rivett 608, most SB, and generations of older lathes, not to mention old railroad cars, all use plain bearings, but they tend to get a lot of oil via drip, or a wick arrangement for positive supply. They all may turn slowly in RPM, although the surface speed may be relatively higher, as the bearings are generally of good size.

My comments were restricted ONLY to the sintered type, where the oil is normally in the pores, and only comes out when the shaft is spinning (according the the makers of them, anyhow, I have no personal direct knowledge of it).

I have a tiller with plain sintered bearing at the top of the "down-shaft", where there is little side force. It still "egged out", but it was pretty old with a lot of use. The bottom bearings are all roller, they are slow high force bearings.

[jmarkwolf]

Original poster here.

Thanks for the discussion everyone.

I posted a description of the bearing in question below.

[IMG][/IMG]

As you see it clearly states "press fit", but I'm holding the bearing in my hand, and that inner sleeve is not free to spin.

Consequently, it seems to me, if I turn the shaft diameter to be a press fit, the shaft will basically be seized in the sleeve, which appears to be "fixed" to the housing.

In which case it seems like it should be a slip fit, more like the babitt bearings around an automobile crankshaft, and not a press fit.

Please advise. And be gentle, I'm not knowledgable on such things.

[enl]

As you see it clearly states "press fit", but I'm holding the bearing in my hand, and that inner sleeve is not free to spin.

Consequently, it seems to me, if I turn the shaft diameter to be a press fit, the shaft will basically be seized in the sleeve, which appears to be "fixed" to the housing.

In which case it seems like it should be a slip fit, more like the babitt bearings around an automobile crankshaft, and not a press fit.

Please advise. And be gentle, I'm not knowledgable on such things.

I believe that the 'press fit' spec means that the bushing is a press fit into the aluminum frame. The drawing indicates that the bore, as delivered to you, should be 0.0008" to 0.0015" larger then 3/8" (stupid mixed fraction and decimal....), or between 0.3758" and 0.3765"

[Mcgyver]

That does seem strange....agree with enl. Mistake by McMaster? I'd want to see the manufacturers info before taking it as the gospel.

btw, pillow blocks like that can be difficult to work with in that its hard to achieve perfect alignment. That means the shaft is fighting itself and bearings - binding. The solution is self aligning bearings - they're the thing to use when you don't have a lot of a control and precision on the mounting.

Bunting and maybe others makes self alignment sintered plain bearings - either as inserts or pillow blocks

see page 227-229

http://www.buntingbearings.com/pdf/Bunting%20Product%20Catalog%20040610.pdf

[J Tiers]

I'm selecting a bearing for a 3/8in dia shaft for a project, and am wondering about the relative merits of sleeve vs ball vs roller bearings.

....

Sleeve bearing aka "journal bearing", plain bearing, etc. Cheap, can be effective, self-oiled bronze wants some reasonable rotation speed to oil correctly, not good for high speeds or heavy loads without special design. Do "wear out" eventually

Ball bearing.. No necessarily expensive, comes in all levels of precision, good for "medium" radiial forces, and some axial force. "Angular contact" bearings take more axial force. Speeds up to over 100,000 rpm for special designs. Do not "wear out", but eventually fail from metal fatigue . Available open, shielded, and sealed. Sealed and shielded are normally pre-greased. "Conrad" types typically the least asial force, "deep groove" more, Angular contact take the most. "Standard" types have some "clearance" , or "rattle room" in the balls and races.

Roller bearings Available as radial only, or tapered, which can take axial forces. Available in all precisions, typically intended for slower speeds than ball bearings, can be made to take the heaviest radial loads. Otherwise similar to ball bearings in application.

[Toolguy]

I believe the press fit in the chart was an error by the chart maker. Either through ignorance or inattention. The ID tolerances below that would be the right amount for a clearance or slip fit. JTiers above has a good summary in the post above.