Effect of spacers
Effect of spacers
(OP)
I think I have a good question for all the people in bearing design applications. I have two different opinions from experience bearing guys. If I add a spacer between two angular contact bearings, both agreed on the fact that it will increase the system rigidity. But one says that it will lower the load on each bearing, thus increase the bearing life, because the load is better distributed. The other one says that it's the opposite, because the system becomes more rigid, the bearings carry more moment load, thus shorten the bearing life. I find that really interesting and I'd like to know if someone has an answer or an idea.





RE: Effect of spacers
I think both answers are right, and wrong, without better definition. If the moment is due to a forced displacement (like 3 misaligned bores)individual bearing loads might be less with small bearing C-C distance.
If a radial load is hung from a shaft cantilevered by the 2 bearings the loads would be greater with closer spacing.
RE: Effect of spacers
Ravi
http://www.gearsandbearings.com
RE: Effect of spacers
Adding a spacer between two angular contact ball bearings will not increase the radial or the axial rigidity of the system unless the spacer increases the bearing(s) preload. As to the moment rigidity of the system, spacing the bearings farther apart will certainly increase the ability of the system to carry load and its rigidity.
However, icreased rigidity is a double-edged sword. Induced loads due to alignment errors etc. will subject the system to greater loads and thus lower life.
RE: Effect of spacers
RE: Effect of spacers
RE: Effect of spacers
RE: Effect of spacers
For angular contact precision spindle bearings adding a spacer improves the heat/temperature related speed rating significantly. The common explanation is a high speed bearing is walking on the edge of heat rejection, and the extra spacer (and shaft and housing) provides a larger opportunity for conduction and convection.
My wife likes to cuddle when she is cold. Eventually we both are warmer.
RE: Effect of spacers
You said using a three bearings housings is a bad Idea. Could you explain me why? Can someone tell me what would be the misalignment limit for back-to-back angular contact ball bearings? I calculated the misalignment created by the load by assumpting that the shaft was built-in (the spindle is overhung). So I calculated the shaft slope and than, the angle at the bearing.
RE: Effect of spacers
If your calculated shaft deflection is more than a few 0.0001 inch then the middle bearing loads are likely to be hundreds of pounds. Making a spindle system stiffer by sprinkling bearings along the shaft can be pretty hard to do. With any overhang at all the ratio is likely to be something like 70% shaft, 30% bearings. Better to put a fatter shaft in there.
RE: Effect of spacers
RE: Effect of spacers
RE: Effect of spacers
Can I get a reasonably accurate sketch of your bearing arrangement and loading somehow?
The bearing manufacturers are often technically very helpful, even with one-off applications.
Thanks,
Dan T (moose)
RE: Effect of spacers