Now if you aren't tied to being satisfied with the trash they sell in
stores, you can buy a random surplus two-speed motor with two shafts
and have both: a slow speed with fine, good wheel for tool grinding, as

well as a fast speed with trashy cheap wheel for fabrication, rough
grinding, etc. Also: think about whether all you want to do is
grinding. My grinder has a wheel on one side and a wire brush on the
other and I use the wire brush more than the grinder.