If you look up the specs of an air die grinder tool you will see they are the same sort of layout (less the inbuilt motor and water cooling). It' just a case off finding an appropriate size collet chuck against motor with similar size spindle. Push out spindle and replace with collet chuck (collars etc). Thats what i am changing my spindle motor for. By the way the shank on a die grinder is really too short to be used like this unless the motor is mounted off the unit and belt. The chinese collet chucks can be got with a 14mm shank and 1/2" which match a lot of suitable size motors out ther (diasbled cart's/ buggy motors, DC and large spindles :-)). Pop in to your nearest mobility centre and you will see what i mean, may even sell you a secondhand motor for a few quid from there repair shops normally on site. Whilst you are there ask them for a speed controller, you change the current limiter (that's what stops the pavement road nights brigade from speeding). Maybe some ideas in there to save inventing the wheel???