Seeing as I let it out at GCRS, I might as well share here as well..
Not only do we use 2 bearings per side, we also use a hollow tube between the bearings.
The length of this tube is critical and can allow for zero play, looseness or even preload of the bearings.
The shaft is a dead shaft, with tapped holes in the ends. When we tighten the whole thing down, the outer bearing races are forced against shoulders in the drum
The inner bearing races are forced against the ends of the tube and everything is locked in.
This also increases shaft strength, in that the spacer acts as a strengthening member for the shaft.
Example: 4 R6 bearings, shaft is 3/8", spacer is 3/8" ID and 5/8" OD (all Ti)
Result is zero endplay (or preload or some endplay ...depending on how you feel) and rigidity can be like having a 5/8 solid shaft (or close)
This is how some very highspeed precision machine tool spindles are built.....and it works!!!
1) If the tube is longer than the distance between bearing shoulders, then the drum will be able to move slightly relative to the bearings
2) If the tube is shorter than the distance between shoulders, then the bearings will be preloaded
3) If the distances are exactly equal, then there is no preload or looseness, except for possibly as per internal clearances in the bearings.
In any case, whe spinning the drum at a fairly highspeed, we get ZERO heat!! which means less power to drive and quicker spool up.
remeber that in highspeed applications, you have to allow for growth of components.
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