Thrust Bearing Binding 1

[steris]

I was making a mockup to test out a new design and stumbled across an unexpected problem. I have a stud with a threaded end welded to a flat plate. The stud (1/2-13)is used as an axle for a few components. The assembly order is:

Plate with threaded stud
Thrust ball bearing #1
Gear/Cam with ball bearings
Thrust ball bearing #2
lock washer
nut

The design intent was that the gear/cam is rotated around the axle thereby actuating the follower. The follower will exert a force of ~50lbs on the cam which would then press the gear/cam onto bearing #1. Bearing #2 serves to allow the gear/cam to rotate freely while the lock washer & nut hold the assembly in place.

The problem is that once I tighten the nut enough to secure the assembly, the thrust bearings bind up and the gear/cam cannot rotate. The thrust bearings are sized for upwards of 3000lbs dynamic load. I have tried many different type of thrust bearings from needle roller to ball bearing.

Am I exceeding the load rating of the bearings just by tightening the nut? I am only tightening the nut enough to partly deflect the lock washer.

Any thoughts would be greatly appreciated. Thanks!

Best,
Steris

 

[MikeHalloran]

Preloading a stack of stuff between a couple of thrust bearings requires that all the parts in the stack be damn near perfect.

The usual arrangement would be to shim the assembly so that the nut tigthtens against a sleeve, or the inner race of the radial bearing, and a precisely controlled axialy play is allowed/ designed in to the mounting for the thrust bearings. ... so that you can't reduce the play to zero no matter how tight you make the nut.





Mike Halloran
Pembroke Pines, FL, USA

 

[Eratosthenes]

You didn't say how fast you are going to run the assembly. Typically, thrust bearings, especially needle roller types, should always be loaded to prevent skidding. Standard practice is adding a (soft) belleville spring of proper size and load/deflection characteristics after thrust bearing #2.