Bearing Design

[Plifter365]

Hi everyone, my boss is very difficult to get a long with and I was looking for some answers to sort through what he says, and what I've read.

The design is for a spindle that uses only one bearing. There is very little axial or radial loads. The I.D. of the bearing is 1.75", and it is a 3/16 bearing. Because of the location of the spindle we only use one bearing. And does not run at a high RPM.

Currently we use a 4-point contact bearing to keep out "wobble" in the shaft. The bearing does not act as expected and has more drag than required.

I belive it best to go to a 2-point radial contact bearing to support the belt that is around the bearing. The belt which turns the spindle runs directly on the centerline of the bearing. Is it standard to use two 2-point contact bearings, reversed?

This brings up the issue of preload. My boss tells me that preload is the Pre-load in the bearing as its made, with some kind of an interference fit between the balls and outer races. From what I've read, preload of a bearing is defined by its fit with the shaft and the housing.

Are my assumptions about preload and bearings right?

 

[diskullman]

Could be a good application for a needle bearing.

Russell Giuliano

 

[dimjim]

There are two types of preloads.
One as your boss says and the other
relies on a press fit on the bore or shaft
to create a preload in the bearing.
If you want stability ie no wobble,
you may need the preload. Preload
does create greater drag or torque.
You might want to use a clearance
bearing and see if the wobble is
excessive.

 

[MikeHalloran]

Did you figure out why the "X" bearing is dragging?



Mike Halloran
Pembroke Pines, FL, USA

 

[Plifter365]

No, we havn't figured out the source of the drag, it feels like the X-bearing needs to be preloaded to get good friction chacteristics. When I say preload I mean and axial force on the inner race, and the opposite axial force on the outer race.