On Fri, 31 Jul 2009 13:39:44 -0700, "Bill Noble"
wrote:

if you have a scope, and a strobe, and the speaker "accelerometer", then why
not just "do it right" - make a paint mark on the wheel as an "index", synch
the strobe to the rotational speed and synch the scope and see where the
peak is WRT your accelerometer location and then just add weight at the one
place where it is most effective?

Things are not as simple as they may appear. There will be phase lag
in the accelerometer (speaker with reference mass). In addition, the
grinder on compliant mount is very probably operating well above
resonance (as Jon noted) so the acceleration vector will very probably
lag the location of the imbalance.

Jim's method combines quadrature resolution of the error vector with
trial -and- careful observation to make phase ambiguity irrelevant. No
reference marker sensor needed, don't even need an o'scope.

Brilliant!