On Sep 15, 3:00*am, trg-s338 wrote:
Newbie here with perhaps a basic basic question. *Need to grove a
circle in a custom aluminum mounting plate for a C-face motor with a
protruding locating ring

But, you don't have a mill? Why not saw a ring from thick
sheet stock, file to fit the interior (or exterior) of the
motor face, then fasten to the plate with drill/tap/countersink
and flathead screws?