In thread "Rockwell 6" bench grinder - anti-rotation pins" first posted on 4 March 2012, the matter of the anti-rotation pins and their reason to exist was debated. The upshot was that I decided to retain the anti-rotation feature.
I have now finished rebuilding the grinder:
Both bearings were replaced. The bearings are commodity type 6203, with double seals. Cost $10 apiece. Installation required making of a pair of aluminum-tipped pushers, so the new bearing could be tapped into place with a lead hammer. The ticking is gone.
The mating faces between motor end bells and wheelguards were flycut flat, to make a wobble-free joint. The original surfaces were as cast. Removed about 0.010" of stock from each part, each of which is about1/4" thick. Don't know how necessary this was, but with the motor apart the machining was easy.
Milled two 0.125" wide feather-key grooves in the motor shaft, under the inner flange washers. Again, with the motor apart and the original bearings removed, this was easily done on the vertical mill.
Faced the diemetal flange washers, so the wheel-bearing faces are parallel to the faces that rest on the shaft shoulder or nut face. They were off by a few degrees, enough to cause a large wobble.
The diemetal (Zamak?) machines like cast iron, the chips being a coarse powder, and it turns out that the best way to get good surface finish was a steady flow of compressed air, to blow the chip dust away before it gets back into the cut. The difference in finish was dramatic. Cutting wet didn't work near as well, but I suppose flood cooling would have washed the chips away too.
Using a square jewler's file, filed one keyway groove in each of the inner washers a bit wider, to accept the 0.125" key.
Replaced the very worn abrasive wheels. Coarse is 46 grit, and fine is100 grit. (I find 60 grit to be too close to 46.)
Machined a pair of aluminum arbor adapters to adapt the 1" holes in the wheels to the 0.500" arbor shafts. The adapters are a hand push fit in the wheels, and a slip fit on the arbors. This largely prevents radial motion of the wheels, which was quite large before.
After dressing the wheels, the vibration is minimal, and one can make very precise grinds.
You may recall the saga of the vibrating 8" Ryobi bench grinder, documented in multiple threads over 2009. This rebuilt old 6" Rockwell grinder makes the Ryobi look sick, even after the various improvements made back then. The Ryobi is a clumsy clone of the Rockwell, which is based on Baldor grinders. Ryobi left no corner uncut. (The motor unit of the Rockwell is made by Baldor.)
I have also found another reason for the anti-rotation feature - it makes wheel removal and installation easy. One just holds the wheel in one hand and a wrench in the other, and tightens or loosens the nut, without fuss.