Ref.: http://mmd.foxtail.com/Pictures/auto-electric1.html

It is an intriguing geometry and the shape of the components is very
strange, especially the motor housing.  My guess is that the motor
shaft had a drive collar on it which was positioned between the motor
bearing and the outer edge of the driven disc.  The hub may have had
a toroidal crown on it so it would have driven a narrower portion of
the edge of the driven disc, not the face of the driven disc.

More likely, the driven disc had a crown to the edge and was driven by
a flat faced hub on the motor shaft.  Perhaps the crud around the base
of the driven disc support arbor is stuff fretted away from the edge
of the driven disc.  When enough wore away that the driven disc became
flat, it would wear even faster and not be very serviceable anymore.
The 1/16" space would not be involved in the driving.  The motor would
be slid axially to load the hub against the edge of the driven disc.

Can you see how the motor comes apart?  It looks like it was built
like a ship in a bottle!

Karl Petersen
Washington, Illinois