I recently acquired a somewhat rusty used Rockwell 6" bench grinder
(model No 23-612 F573 G6-202-17 1/3 HM 115vac single phase, 3250 rpm).
It is in the process of getting new bearings (the old ones tick when
running, probably due to bits of metal in the grease).

This unit is old-time US, made of cast iron, and weighs a ton. And runs
smoothly, except for the ticks.

The mystery is the wheel flanges. The arbor is 0.500" diameter, and the
wheel flanges (that hold the grinding wheel) are die-cast aluminum alloy
and are about 0.425" thick along the arbor shaft, and are equipped with
two keyslots spaced 180 degrees apart. In the arbor shaft there was a
0.095" diameter by 5/16" deep radial hole with a spiral pin pressed in,
with the tip sticking out, and engaging one of the two keyway slots
(which are 0.117" wide) of the inner flanges. The spiral pins had
largely sheared off, and had chewed a groove and raised a divot on the
inside of the flange, where the radial pin rested. Both sides were
equally affected.

I was able to drill the pin stubs out without damaging the arbor shaft,
using a 0.088" diameter HSS drill in a hand drill, using black sulfur
oil.

My first thought was that this should have been a woodruff key, but the
keyslot is halfway between the standard sizes. But I could mill a
woodruff key slot in the shaft and widen the keyslot in the flange
washer.

My second though was that the original design probably had a single
close-fitting but loose pin that went all the way through the arbor, and
engaged both keyslots.

My third thought was to wonder why the scroll pins both sheared off.
They don't lead that hard a life, so what happened? Maybe I don't want
to make this too strong.

My fourth thought was to observe that few modern bench grinders have
such pins or keys. What problem did they solve?

Comments?

Joe Gwinn