Originally Posted by Still Bill
After having done four diff rings, I can say that it does a very good job...on good rings.
Also helped me identify that one of those four rings was a reject because its surface was too uneven.
Which is why sometimes I use 400 for bad rings. I've pulled Associated rings from the package that were pitted and quite frankly garbage and cut them with 400 until flat, then smoothed out the deep grooves and put a desirable finish on them with 600.
From the pictures you posted of the sanding disc remind me of modeling sandpaper which IMO is far too fine to get most rings flat and will also polish rings too much not allowing the balls to grip without tightening the diff too much putting extra stress on the thrust assembly, resulting in frequent rebuilds.
I think my diffs last a long time because I can run them loose plus I don't use a bunch of excess lube which only attracts dirt which also prematurely wears diffs. Diff lube is only there to keep the balls cool. I literally put a dab of lube in my hand, put the diff balls in the lube and install them in the diff, that is all the lube the diff needs.
Another diff killer is over tightening the diff before working it in. Always work a diff when tightening it up and break it in before setting it to race spec.