Caged needle bearings and continuously rotating shaft. 1

[whitetop]

I am having a problem with axial shaft thrusting in a design of a continuously rotating shaft supported on caged needle bearings. I was under the impression that one purpose of the cage was to prevent needle skewing and transforming the bearing into a threaded nut. Where did I go wrong?

 

[MikeHalloran]

You still need a thrust bearing or two to locate the shaft.



Mike Halloran
Pembroke Pines, FL, USA

 

[whitetop]

MikeHalloran:

Thanks for the reply. I should have defined the application more thoroughly. The design included a thrust bearing to prevent the shaft from moving axially in the only direction that I thought would be a problem. At one end of the shaft sits a bevel gear pinion; the thrust of the bevel gear set would tend to open the mesh creating more backlash. I didn't prevent shaft movement in the other direction expecting no other axial forces that would tend to tighten the mesh to the point of locking the system. What is the source of this force? Even with a cage separating the rollers is there still enough roller skew to cause this problem?

 

[MikeHalloran]

Bevel gears are generated to run with a controlled lash, not zero lash.

Take a pair in your hands and press them lightly together. Feel how the teeth scuff on each other? Now try to displace one ever so slightly along the tooth axis. They will bind up tight.

Yeah, I'd have thought it was a clever design, too. I outsmart myself at least twice a day.



Mike Halloran
Pembroke Pines, FL, USA