On Jan 10, 9:27*am, Bob Engelhardt wrote:
In the latest issue of HSM, there is a tip from a reader about static
balancing, using the arbor-on-rails technique. *He uses a lathe bed to
get a level foundation, which is a good idea, if your wheel is small enough.

He says to turn the ends of the arbor down to .150 or less, because "The
smaller the diameter of the axle bearing surface, the more accurate your
balance will be." *This sounds exactly backwards to me. *It seems to me
that smaller diameters have greater resistance to rolling and hence
would be less accurate.

Am I missing something?

Bob

Moment of inertia will be bigger with larger diameter, also weight
will be greater. Makes a difference if you're using two knife edges
like I've seen done for lighter weight parts like model airplane
propellors. Maybe not so much with two flats on a lathe bed and a big
grinding wheel. If you get too small in relation to the weight of
the object you're trying to balance, the shaft is going to bend and
screw you up that way. For static balancing of discs like grinding
wheels, I'd be more apt to build/adapt a jig like a low-end car tire
balancer with a cone, a pointed pivot and a bullseye bubble level.

Stan