Hi Keith
You say you adapter is almost round with a slice cut out, right?
That would be for a key, and if your motor shaft also has a key way than
you could use a key to keep your adapter from turning, the set screws
would keep it from sliding off.
However there is not much torque normally when buffing or polishing so
just using the set screws should be ok, but if you ever have a problem
with the adapter slipping get a key in there that will stop it.

Did you mount your motor in a box already ??
Make sure you have enough ventilation in there.
I have a small motor buffer, I have it just sit on the bench, have look
if you will it's in one of my photo albums, I find that there is not
that much dust buildup and never bothered to enclose it.

http://homepage.mac.com/l.vanderloo/PhotoAlbum25.html

Have fun and take care
Leo Van Der Loo

Keith Young wrote:

Hi

Unfortunately mechanical skills are not my forte. I am mounting a buffer
atachment to my used motor.This comes with a shaft adapter which is almost
completely round with a slice cut out. Am I supposed to place the set screws
so that they contact and tighten thru the cutout to the motor shaft, or
tighten them on the adapter itself?
Its a dumb question? but having said that I am of the belief that there are
no stupid questions, maybe stupid answers.

Help
Keith
Newfoundland