TRSmith wrote: I still am not sure what lapping does-is it like treating the parts with rubbing compound to smooth everything out so no pesky powder flakes can escape in between the moving parts?
Lapping mates the two parts to fit together precisely, just like any "precision" machine's parts fit, and yes, so those pesky flakes will go where they're supposed to.
Also allows the unit to work smoother with less effort.