Quote Originally Posted by dsc View Post
As for expansion John, I'm guessing you meant thermal expansion, which would force the housings further apart and increase the preload? this shouldn't be an issue as all the parts will stay close to room temperature all the time.

Regards,
dsc.
Would depend on the materials of the housing and spindle and what the source of the heat was. If the spindle is hotter it will decrease the preload.

Is not usually a problem with slower running spindles like lathe headstocks or gearboxes which are oil filled as the oil evens the temperatures out. More of a problem with HS spindles where a lot of the heat is generated by the bearings and the rotor and the housing is cooled from the outside.