The pulley is aluminum and presumably the set screws will be some kind of
steel alloy so they are three times the density of the aluminum, which
should make up for the "missing" volume from the threads and hex key socket.
They might even be too heavy. Considering how close they are to the shaft,
I bet the balance will be pretty much dead on with just the two plain set
screws. If you set up the knife edges it would be interesting to check the
pulley before you drill and tap the set screw holes, just to make sure it is
dead on, and then you could see if the set screws change anything.

-----
Regards,
Carl Ijames

"DoN. Nichols" wrote in message
...

On 2014-08-06, Pete Keillor wrote:
I'm to the point of turning the drive wheel for the belt grinder I'm
building for my son. It'll be 6061 Al, 6" dia. x 2" wide, running on
a 3/4" keyed shaft, and turn up to 3800 rpm. I figure I'll put a
setscrew on the key and another at 90 deg., which will require
drilling from the circumference. I can drill holes opposite to help
balance.

Any suggestions on how to balance this for a hobbyist? I'm not buying
a balancer, but could build something. Or just spin it up and see how
it does? Thanks.

Hmmm ... if you make the screw enough bigger (and perhaps an
Allen head cap screw (if you have hollow ends and hubs within that),
you could compensate for the mass missing from the drum surface. Then
no need to drill an extra hole opposite. Maybe add a nut for locking
and extra mass, too.

Enjoy,
DoN.

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