Mendel: Prusa durable z-axis motor coupling

thingiverse

For a durable flexible coupling on z-axis motors, use a round bar with minimum diameter 14mm and length 25mm in Mendel: Prusa RepRap machine design. Face off both ends and drill a 5mm through hole at one end. Next, drill a 6.5mm hole 15mm deep without centre drilling. Tap an M8 thread into the 6.5mm hole using cutting lubricant. File a flat on the end with 5mm hole and insert motor shaft into it, making sure 2mm of the shaft is past the 3mm hole. Clamp motor and part securely, drill through both 3mm holes, then assemble using M3 hex bolt, washers, and nylock nut. Attach to z-axis stud with an M8 plain nut. Check out the YouTube links for animated CAD simulation and a machine in use at Digital Manufacturing Laboratory in Bath.