Ball screw bearings, finding preload

[bmklawt]

I bought new bearings for the ball screws on my mill, SKF 7204 BECBP.
http://www.skf.com/skf/productcatalo...did=1230020204

I have read conflicting information on how to install them.
It appears the best way would be installing them back to back, but I have read the inner rings should be clamped tight and also read the outer rings should be clamped tight when there back to back.

I am not sure I understand the proload either and can't decipher what it is form the SKF website.

This is what I think I need to do, find what the preload is (weight) and measure the defection of the outer race when this weight is placed on the bearing.

Take this measurement X 2 and shim between the races of the two bearings and clamp tight the inner rings and I will have the correct preload.

Do I have this right.
How do I find the preload

Your help is greatly appreciated,
Bruce

[RICHARD ZASTROW]

The specified preload is ground into the pair of bearings. When you clamp the inner races together in a back to back (DB) pair, they are preloaded.

Clamping the outer races to a fixed shoulder in a housing prevents axial motion of the ball screw.

No shimming is required.

Dick Z

ADD: The SKF bearing numbers listed above do not indicate preload or accuracy class. 7204 BECBP indicates a 7200 series 20mm bore, 40 deg. contact angle, paired bearings with a glass fiber cage. Missing are grade such as P4 and preload letter such as A = light preload; B = preload greater than A; C = preload greater than B; CA = small axial internal clearance. This info is from an SKF General Catalog.

[bmklawt]

I bought these because they said thery were ABEC 5
It also says on the bearing 0770 and explorer, I found this on the SKF website.


SKF Explorer angular contact ball bearings are manufactured only as bearings for universal matching with P6 dimensional accuracy and P5 running accuracy.