I called Ryobi and complained about the world-shaking side-to-side vibration. Their first reaction was to send me four new flanges.
Their second reaction was to ask if the spindles were bent. Hmm. I hadn't thought of that, but it's certainly possible. The grinder is shipped with those heavy 8" diameter by 1" wide gray wheels in place on those little 5/8" shafts, and if the box were dropped, it could happen. The box doesn't look like it was dropped, but if the pallet were dropped, the box would look OK. But the dial indicator shows less than
0.001" of runout, so that isn't the problem.Looking at the shafts, it's apparent that the shoulder upon which the inner flange rests isn't very large. The shaft in the motor is 0.667" (17mm nominal), turned down to 0.627" (5/8" nominal), for a shoulder height of 0.020" (0.5 mm). When one looks at a flange that has been resting on this shoulder, the edge mark is halfway down the slope where the sheet metal was pulled out of plane by the 5/8 punch that made the center hole through which the shaft passes.
Part of the solution was to buy two precision hard steel thrust washers (MSC 03548187), one per wheel, to rest upon this narrow shoulder and provide a larger bearing area for the sheet-metal flanges. This cut the wobble perhaps in half, but didn't completely solve the problem: The mating surface of the inner flange also needs to be flatter.
Flattening was done by hand grinding with wet-dry sandpaper face up on a granite surface plate. This almost worked. The problem is that the wet-dry paper is too soft, allowing the edges of the ground area to be turned down, and the thrust washer was resting upon the turned-down region near the shaft.
So, went fully traditional (for mirror grinding anyway), using ordinary valve-grinding compound on a piece of plate glass. This worked, reducing the wobble to about 0.002" on the first attempt, though it's slow going because the flange metal (mild steel) is really a bit too soft for grinding this way. Nonetheless, I'll probably be able to get to less than 0.001" with a little more elbow grease.
When the four new flanges arrive, I'll probably ask a friend with a Clausing lathe to face them off, now that I know that this is the solution.
The mystery is why Ryobi uses such lousy flanges. Adequate flanges cannot cost that much, and the current bad flanges undermine the whole affair. It reeks of using good fabric with bad thread while making clothing.
Joe Gwinn.