They are balanced but the cast iron bases on a concrete floor just
don't provide enough coefficient of friction to make them stay put.

I need an interface material that grips concrete and cast iron.

The machinery is pretty good quality (ie mostly Baldor) but some of the
pedestals are Harbor Freight crap. (i don't mind buying Baldor buffers
and grinders but their pedestals seem too high priced for what you
get).

I filled some of the pedestals with concrete to give them more mass. It
helps but there's just not enough friction between cast iron and
concrete when motors are spinning at 3600 rpm.