The associated two jpg files show the hardware I developed to mount 8"
diameter by 1" thick grinding wheels with a 1" diameter arbor hole to a
Ryobi BGH827 8" bench grinder.

This grinder, given to me by a well-meaning relative, vibrated badly
right from the box, starting a long saga of attempt after attempt to
tame it.  The basic problem is that too many corners were cut in design
and construction, and how many of the cut corners would save money was
unclear.  Perhaps the engineers didn't understand how to design a
grinder.

The following major problems were found:

1.  The motor shaft is 0.666" in diamtere, which is turned down to
0.624" diameter to accept a wheel with a 5/8" hole.  The resulting
shoulder is only (0.666-0.624)/2= 0.021" high, which isn't nearly
enough.

2.  The wheel is held by two pressed steel dished washers.  Where the
5/8" diameter center hole is punched, the metal is pulled down into a
curve.  The inner dished washer rests on the shoulder and wobbles around
because the curve is much wider than the shoulder, and so the washer is
not reliably held perpendicular to the arbor shaft.

3.  The 5/8" diameter arbor shaft between the shoulder and the start of
the M16-2 threads is too short, forcing the outer dished washer to ride
on the threads, versus on the 5/8" shaft.

3.  The outer dished washer is held by a M16-2 nut.  The nut threads are
drunken, and the arbor threads may also be drunken, so the nut does not
press evenly upon the dished washer.  The dished washer fits the M16-2
thread loosely, and so can run off center.

The solution takes advantage of the availability of grinding wheels with
1" diameter center holes.  This gives us sufficient room to replace the
pressed steel dished washers with machined flanged half-sleeves that
constrain the wheel to run perpendicular to the arbor shaft despite the
many problems described above.


Description of images: "Grindstone_Mounting_Hardware_1.jpg"

The two aluminum things at the top are the two flanged half-sleeves.  On
each, the sleeve part is about 7/16" long, so when assembled with a 1"
thick grinding wheel in between, the sleeves don't quite touch.

Working from left to right, the items below the steel ruler are:

A hardened steel washer that rests against the arbor-shaft shoulder on
one side and against one aluminum flanged half-sleeve on the other side.
 The purpose of the washer is to prevent the shoulder from chewing into
the aluminum.

A M16-2 hex nut.  There are two, one threaded right-handeld, the other
left-handed.

A convex spherical steel washer intended for a 5/8" bolt.


Description of images: "Grindstone_Mounting_Hardware_2.jpg"

The two aluminum things at the top are the same two flanged
half-sleeves, but turned over.  On the left flanged half-sleeve, one can
see the undercut that accomodates the hardened steel washer.  On the
right flanged half-sleeve, one can see the conical seat which accepts
the curved side of the spherical washer.  The angle between the cone and
a flat surface is 14 degrees.  Use of a spherical washer and mating cone
allows even a nut and arbor with drunken threads to nonetheless press
evenly upon the flanged half-sleeve and thus grinding wheel.

The dot pattern in the background helps the camera find the correct
focus.


Last updated on 9 March 2009 by Joseph Gwinn.