Seating a bearing

[brt]

Folks,

I have a project I'm working on where I need to install a bearing into a pocket on a plate and then a shaft through the bearing. The bearing is .5" OD x .25" ID ball bearing, pretty similar to what you'd use on a router bit.

My plan is to mill a .495" pocket in the plate (CNC interpolation with a .25" end mill?) to accept the bearing and to turn the shaft to .255". Both shaft and plate are 6061 Al. Then I was planning to heat the plate in an oven to about 200F and push the bearing into the plate with a 1 ton arbor press. Then I was planning to cool the shaft either in the freezer or with dry ice and push it into the bearing with the same arbor press. During the latter operation, the inner race of the bearing would be firmly supported from below.

The project requires three such components.

What do you think?

 

[jumps4]

hi
I'm no machinist but i have been a mechanic all my life
the .005 difference is way to much. it wont go together you probably need to be in the .0005 range of difference
hopefully one of the real machinists will reply but i'm pretty sure i'm right
steve

 

[metalmaster]

without knowing the application of the parts it is hard to say what the proper fit is.
I think .001 press fit will work out better for you on the outside diameter.
for the inside I would go with .2500 to .2505

mike

 

[Starlight Tools]

brt

Your interference fits will probably casue the bearing to tighten up beyond useful.

A bearing of that size should not need the bearing seat to be heated or the shaft cooled to install. It should be able to be pressed in cold. One side or the other should have an intererference fit, but not much more than a thou or two at the most. The other fit should be just a bit tighter than a slip fit. Would have to consult the machineries handbook for exact amounts. One very acceptable way to retain a bearing is with Loctite Bearing Retainer, 690

Now of course most of the bearings I install, the shaft and seat are already made, and all I have to do is add or replace the bearing.

Press the bearing using a sleeve that is the size of the race being seated, IE outer race into bearing seat, inner race onto shaft. Avoid pressing on the opposite race as that will force the balls into the races and cause damage.

Walter

 

[brt]

brt

Your interference fits will probably casue the bearing to tighten up beyond useful.

A bearing of that size should not need the bearing seat to be heated or the shaft cooled to install. It should be able to be pressed in cold. One side or the other should have an intererference fit, but not much more than a thou or two at the most. The other fit should be just a bit tighter than a slip fit. Would have to consult the machineries handbook for exact amounts. One very acceptable way to retain a bearing is with Loctite Bearing Retainer, 690

Now of course most of the bearings I install, the shaft and seat are already made, and all I have to do is add or replace the bearing.

Press the bearing using a sleeve that is the size of the race being seated, IE outer race into bearing seat, inner race onto shaft. Avoid pressing on the opposite race as that will force the balls into the races and cause damage.

Walter

Thanks! I'll bump the fit down to .001 (.501 for the plate and .251 for the shaft) and then use Loctite 690. I'll post the pistures of the first try when its done.

 

[brt]

I couldn't find Loctite 690. But I found 640 (http://www.henkelna.com/cps/rde/xch...tredDotUID=productfinder&redDotUID=0000000HZO) and 660 (http://www.henkelna.com/cps/rde/xch...tredDotUID=productfinder&redDotUID=0000000HWS) which both sound applicable. What do you think?

 

[jumps4]

you really only need the loctite if your fit is a bit loose
you should be able to get it at an autoparts store
just use the permanent type
steve

 

[PIKEMAN]

Most any good outfit that sells bearings will have a bearing spec book that will give an acceptable range of sizes for the shaft and mounting hole for the bearings they sell. When I sold auto parts, we always had a BCA bearing spec book, and a National seal spec book for just this type of info. BCA and Timken MAY have websites where you could access this info by part number.

 

[brt]

Thanks for good advice, everyone. It will help a lot.

 

[Tony Wells]

Bearings fits are not really all that simple. As you can see, there are many widely differing opinions on how they should fit, and for each opinion, there is a proper application. In general, it's necessary to know a good deal about the specifics of the bearing application as far as load, precision required, material of housing and shaft, surface finish of both, and many other factors. You could consult some of the online resources published by bearing manufacturers for the whole story.

In very general terms, the sizes are determined partly based on calculations done from the actual diameters and lengths of the housing and shaft. Obviously, the longer engagement is the more force is required to press the bearing in, and the shaft as well. So then it follows that the fit should be looser on a longer bearing....all other things being equal. By the information you have given, if the finish is 63 Ra (approx) in the bore, and the bore is housed in a part that is at least 3x the bore diameter in width, and 2x in thickness, the fit should be no more than 0.0002T. On the shaft, again given the information you presented, the shaft should be 0.0000-0.0002T. If you run the sizes tighter, then you risk closing up the clearances designed into the bearing and creating problems with overheating and lubrication issues. You didn't give us the proposed speed, and this can change things dramatically.

Also, no retaining compound is necessary.