The major difference between this state and the view I posted last weekend (7/25) is that I performed the size reduction from oversized about .004 down to a sliding fit in the test piece, reamed to a .094" hole. That was done by turning the piece on a strip of sandpaper.
The critical part here was making sure the stem came out the same diameter on the three sections I cut. There's a tendency for any part to deflect due to cutting forces and the bending moment is greatest when cutting at the far end. I cut the far and middle thirds of the stem .005 at a pass (radius). The test cylinder was a little tight just before the taper, but rattled over the first 2/3 of the stem. A micrometer showed it was undersized where the test cylinder was tightest and the rest of the stem was the closer to the right size (working from memory here and I don't remember the size).
I haven't quite understood that, but if there's any real lesson it's the one I already knew. Measure