Press fit of a bearing

[Totty]

I am trying to press a small bearing (.3125 OD) into a medical instrument, and was wondering if harder materials hold a press fit better than softer ones (ie 303 SS). I am trying to explore all options on how to hold the bearing in there.

 

[stressriser]

I think the actual material selection is insignificant. Guidelines for every material, and the particular class of fit, will specify bearing retention suitable for your application.

First decide what material you need, then choose the proper bearing, and then determine the fit parameters.

Assembly, service and performance are the determining factors on the method you choose. Contact a mechanical engineer for design advice, it won't take long for a qualified person to solve your problem.

 

[Ralph2]

Can you try a dab of "locktite"?

 

[stressriser]

Locktite is used for a "Push" fit, and not a "press" fit. Specifically it is referred to as "bearing retainer." You should use it when frequent service is required and a heat source can be used to melt the "glue."

 

[Totty]

Interestingly enough we've tried loctite, masterbond, and trabond. Even an FN4 press fit won't do the job. I was hoping a surface finish or material selection could help out along with a larger interference.

 

[stressriser]

So I assume the bearing is falling out.

A proper press fit is going to hold the outer case, and it is not going to fall out unless there is too much thrust load.... or there is thermal expansion of the bore.

Press fits for soft material is not the same as for hard material, obviously because some materials are more maluable and they compress differently.

When I can not use a press fit, because sometimes I want the shaft pressed, and you can't press both, I use a flanged bearing and hold it in place with a screw. Or I C-Bore a bit and use a retaining ring.

I can not imagine a good press fit falling out. I don't think you are using a FN4 press fit without destroying the bearing, unless is it very large and the outer case is made of iron. FN4 fits are usually shrink fits, pressing to these are impractable. If you did happen to use a fit like this, it is not "falling" out.

 

[motorworks]

Hi
I am not sure if you are pressing the bearing onto the shaft or into the housing,but you could try a light knurl on the shaft or housing.This would allow something extra for the bearing to "grab" on to.
eddie

http://www.geocities.com/motorworksnf/123

 

[diamondjim]

I am wondering why it must be press fit
into the i.d. of the part. are you just
trying to retain it from slipping axially?
or are you trying to assure that it turns
with the part and not creep? Loctite does make
products that if you turn the part radially
into the part it eventually will sieze or
bond itself. I think the bond is to keep
it from turning within the part rather than
to hold it axially from moving. Is there a
spec on the interference that must be attained?
I am assuming you are talking about a radial
bearing.

 

[Mandrake22]

Totty,

What grades of Loctite have you tried? For bonding cylindrical metallic parts with clearance fits of up to .005" gap, I would recommend something like #609.

http://www.loctite.com/catalog/product.html?ProductLine=609+++++++++++++++++

http://www.loctite.com/datasheets/tds/Product_609.pdf

Something to keep in mind (I didn't to my chagrin in one application!) is the reduction of strength with increasing temperature. Note that in the data sheet I have linked, that at 150°C the strength is about 30% of the room temp value. If you have a high temp application, look at #648 or similar.

 

[Philrock]

My experience has been that press fitting of small bearings is very risky - the manufacturer said not to do it. Every time I tried, I got bad results - very rough-running bearings.

Loctite should work. You may have to take great care in surface preparation - solvent degreasing and perhaps even a light phosphoric acid etch. Loctite activators also make a big difference.

pdr@baymachinedesign.com

 

[rustythevibeguy]

You press fit that bearing with too little clearance and you will take the internal clearance out of the bearing instantly.

People think of bearings as being "rigid" which is far from true. In fact one of the most popular bearings for fan shafts is a bearing that uses a tapered adapter between the bearing race and the shaft. You tighten the locking nut which essentially pushes the bearing onto the taper, the inner race actually expands and the internal bearing clearance is reduced.

I have not used it to mount bearings, but if you will use Loctite's Black Max (a one part adhesive) with a push fit, I can almost assure you it will not come loose.

 

[negotiator]

Once bearing is placed into position (depth of penetration)
swage the opening so the ball will never 'fall out'. The
tips of ball-point pens approach this seizure and they are
a quick manufacturing step that I have used. I now get 1%
of net profits from this............

thestocksguy@hotmail.com

 

[Carrera2]

if the bearing/opening tolerance is per the manufacturer's specs, call the bearing manufacturer's engineering department and relate the problem. arbitrarily changing the press fit dimensional tolerance can (and probably will) cause premature bearing failure. if there is clearance, you may consider cutting a "snap ring/cir-clip-type" groove or using a removable surface-mounted retainer ring. this will have results similar to the swaged/peened/staked type retention method mentioned in negotiator's post. the main difference with a cir-clip or surface retainer method will be easier removal of the bearing for replacement. mechanical retention will allow for the use correct tolerancing for the press fit and positive retention security that you will never have to worry about- lets face it, at this point, you will likely be obsessed with checking that bearing for the foreseeable future.

 

[cheratian]

considering ur question the material may be ss 304.boc I haven't heard upto now the use of ss303. for ur information u may select an other suitable bearing from a variaty of bearing cataloge available in market knowing the exact parameter of ur selection. Another thing is that press is never never used for fitting of bearing and it is totaly wrong practices.It doe only effect the bearing clearances but fail its operation. so u might study the fitting of bearing too.