An atherectomy device with an exchangeable drive shaft is disclosed, having a drive shaft gear at a distal end of the exchangeable drive shaft for meshing engagement with a prime mover gear on the output shaft of the prime mover. The exchangeable drive shaft is inserted into an opening at the distal end of the handle housing and moved axially in a proximal direction. Surface features on at least the prime mover housing and the engageable drive shaft help to align the drive shaft gear with the prime mover gear for meshing engagement.