I have been restoring a Westbury (original form) milling machine and
have just about finished with the spindle group.  On reassembling it
appears that the angular contact races should be preloaded.  However,
I have no idea how much preload to apply as I've not come across angular
contact ball races before.

When assembling normal spindles I'm used to tighting the nut over the
back bearing until I can feel no percetible end play, checked with a
dial gauge for critical applications, but I assume with these angular
contact bearings I need to make it a bit tighter to apply the pre-load.

Can anyone give me an idea how this should be adjusted?

Alan