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  PRELOAD CALCULATION  


Once the initial end play has been removed (ball contact angle = ao), then further axial load (preload) will cause axial displacement d at ball contact angle a. Formulae to calculate loaded contact angle a, initial (no load) contact angle ao and axial displacement d under a given preload are as follows:

In considering general bearing handling, it is important to consider the graph below of displacement vs. preload force. Note that the y-axis displacement is given in microns and the x-axis force is in kilograms. What this means is that a small discplacement of the bearing rings relative to each other will produce a large force. Comparing this graph with the maximum static axial load for a small bearing will show that a displacement of (say) 12.5 microns (.0005") will be sufficient to destroy many small bearings. This is why solid clamping methods of preload do not work except for duplex pair bearings. The typical spread in axial play is 5-10 times the given radial play of a bearing. So that a bearing with 5 - 8 microns of radial play will have at least a 15 micron spread in axial play and there will be no single shim thickness that will allow all bearings from a batch to be clamp preloaded without some of them being damaged (brinelled).





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