View Full Version : inside out ball bearings

08-03-2008, 05:13 PM
Not practical, of course. It takes a lot of work with a dremel to turn a ball bearing inside out. Then you have to surface grind the entire inside of the ball without having an access hole. Tricky at best.

On to the sane part of this post- I'm wondering whiat operating parameters change when operating a ball bearing with the inner race non-rotating and the outer race rotating. Idler pulleys would be an example of this. Seems to me that with the outer race rotating, the grease fill would be forced to constantly flow into the path of the circulating balls, unlike the norm where the inner race rotates and the grease is not subjected to centrifugal force.

In general, I see a heating limitation as the grease is constantly being pushed out of the way, a sealing problem if the grease can squeeze out between the outer race and whatever seals or shields are in place, and possibly an increase in load bearing capacity as the grease would be constantly forced to try to occupy the raceway that the balls run in. It seems that a lower rpm limit and a reqirement to use seals rather than shields would be about it. Any thoughts on this?

08-03-2008, 07:31 PM
Not sure what you're asking but here's a little input anyway. I'm around lots of serpentine belt idler pulleys every day in the auto svc. bidness and can assure you that they're dirt cheap, run pretty fast in a high heat, high vibration environment, don't leak grease and last almost forever. They've probably evolved over the years as far as materials, lubricants and clearances go to optimize the cost/performance ratio.

I pinched a handful of them left over from a recall a few years back and have used them for various machine belt tensioners. They just run & run & run!:)

08-03-2008, 07:56 PM
No change in loading or lubrication.Same number of balls will be in contact with the races regardless.

The lubrication requirement between balls and races is much less than that between balls and cage.Ever notice that a bearing can sound like it has rocks in it and run for a long time until the cage finally fails and then it's sudden death?The cage is basically moving the same volume of grease around and also holding the same amount in each revolution.Soon as the lube is gone the gage gets rapidly eaten up and then it's toast.

In idlers the life expectancy of idlers running in the horizontal plane is usually less than those running vertical,why?Probably due to a combination of higher axial load and gravity pulling grease down and out of the bearing and contaminates being pulled down and in.

08-03-2008, 08:09 PM
I didn't ever occur to me that there would be any difference. At low rpm they will last forever and at high rpm the centrifugal force far exceeds anything gravity has to offer. For instance, a bearing with a radius to the balls of 3 cm spinning at 6000 rpm has the balls under 1207 gees. It's the centrifugal force acting on the balls themselves which is the main limit as they deform the outer race. That's why you can get bearings with ceramic balls as they are much lighter.