Hi andrsn;
Hotz is correct about electrical phasing, and the best place to start. ER collets are dependable to RPM's effective for grinding, sanding, and polishing.
The concern will be attachments and SPM [surface feet per minute]. I'd pirate RPM info from commercial tools and reduce by a good percentage until proven safe. Some people get 12" disks to shear flange screws or fly apart at speeds a common motor will attain. Grinding wheels are sensitive to this, sanding less so, a buffing wheel can decorate your shop like a pillow fight.