I was grinding something tonight and the wheel on the 4 1/2 grinder was
not true, it was bouncing around like crazy.. I didn't think I could
true a wheel, but I took my diamond dresser for a bench grinder and
trued the fiber impregnated wheel. It worked great.. I didn't think the
impregnated wheels could be trued, but it was worth a try since I didn't
have a new wheel available.

Hope that helps someone.
--
Jeff