I'm restoring my 1963 Clausing 8520 mill ( pictures here if interested) and in the process am replacing the spindle bearings. I've read through many posts on the Yahoo Group and have just gotten more confused. Talked to a few bearing "engineers" (ya right) at SKF and they don't seem to have solid answers either.
The spindle takes a pair of 7205 angular contact bearings that are held in place by a locking washer and nut. I was able to find on the MRC site that the torque on the nut should be 23-50 ft-lb. but can't seem to find answers to the following:
Should the bearings be mounted "face to face" (where the contact lines of the bearings converge inward), or "back to back"?
I can order bearings that are ground and sold as a matching set in either "b to b" or "f to f" that when mounted together and the retaining nut tightened give a "light preload".
I can also order bearings that are not matched but are for "universal pairing" that are about half the cost and are made to mount either way. Some posts on the Yahoo Group mention that to apply a preload to these bearings a shim is needed between them either on the inner or outer race, others say none is needed. If the bearings are made to mount either way how can they be preloaded without the use of a shim? If needed how thick should it be?
The machine came fitted with standard bearings and no shims so I can't go by what was there.
Any experts here? Thanks in advance!