Been grinding the other ER32 collets, have some observations about them.
None of them (so far) have the correct taper, don't have straight sides, and are eccentric (by up to 0.003")
What's worse, is that they looked so nice and shiny, until I took a closer look. It seems that they were rather roughly cut, then someone spent considerable time at the buffing wheel to make them pretty. So, this is what to expect from import tooling, pretty junk. Oh, well. After grinding, they're better than they were.
Now I'm ready to work on my high-dollar, high-precision SYIC Techniks 8mm collet.
It appears to be much better quality, smoother bore finish, proper chamfering of bore edges, no sign of buffing wheel cover-up funny business.
But, under the magnifying glass I found numerous nano-sized metal hairs emerging from the slits. They're stuck there and don't wash away with cleaner. Had to meticulously scrape them out with a fine dental pick.
The mandrel has been turned dead true, then collet fitted and painted. Checked its taper with the dial gauge, looks very close.
Started with a light 0.0005" cut, and let the powered compound make several passes until spark-out.
There is a very slight wasp-waist shape here, and it's very slightly eccentric, revealed by the residual paint in the circled area.
But, we're only talking a few microns here.
Advanced the cross slide another 0.0005", and let the powered compound make numerous passes until spark-out.
The collet cleaned-up nicely, no more indicator paint left.
Changed over to a medium Craytex wheel to polish-out the grinding.
Finished, oiled, put back into its wrapper for later testing.