I want to measure the internal radial(or axial)clearance in a practical way before and after mounting the bearing(taper roller or angular contact) on shaft.can you help me?
Taper roller bearings the clearance is often measured using a jack or other mechanical means to push the assembly in both directions to zero clearance. In clearance applications tighten the adjusting nut until all clearance is gone, then release the nut a known amount of turns, a 12tpi nut will give .008 clearance when backed off 1/12th of a turn.
When using angular contact ball bearings do not use too much force you can brinnel the raceways, use the weight of the part to pre load and adjust clearance carefully.
In preload situations, use the zero clearance tightening, back off to verify clearance then tighten and turn the nut additional degrees of arc to obtain desired preload.