Mendel: Prusa durable z-axis motor coupling

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{{Development |name = Mendel: Prusa durable z-axis motor coupling |status = working |image = Mendel- Prusa durable z-axis motor coupling.JPG |description = This is an alternative design for the z-axis motor coupling for the RepRap Mendel: Prusa. |license = GPL |author = Chris Hanton |reprap = Mendel |categories = Mendel Variations |cadModel = File:Prusa coupling.stlFile:Prusa coupling.model


This is a design for a new, more durable flexible coupling ( for use on the z-axis motors in the Mendel: Prusa RepRap machine design. The design allows for 2-3 degrees of play, but can be adjusted depending on how it's machined.

Please see the following YouTube link that shows the an animated CAD simulation of the design: ( and here is the design manufactured and in use: ( The RepRap machine filmed in the above video is one of the two Mendel: Prusa machines located at the Digital Manufacturing Laboratory in Bath. (


Start with some round bar with minimum diameter 14mm and minimum length 25mm. On a lathe, face off one end making sure to use coolant where needed. Next, ensuring that the lathe headstock is concentric, centre drill the recently machined face and drill a 5mm diameter through hole. Turn the bar around in the lathe and face off the other end. Drill a 6.5mm diameter hole 15mm deep - note there is no need to centre drill as the 5mm hole runs through the entire rod length. Disengage the lathe clutch so the chuck can be turned by hand freely. With an M8 tap in the head stock, using cutting lubricant, cut an M8 thread into the 6.5mm diameter hole you have just drilled.

File a flat onto the end of the part which has the 5mm hole. Insert just enough of the motor shaft into the 5mm hole so that approximately 2mm of the shaft is past the 3mm through hole. Clamp the motor and part securely so they do not move independently. Drill into the 3mm hole again, this time cutting going through the motor shaft as well as the part.

Assembly: insert the motor shaft into the 5mm diameter hole, use an M3 hex bolt, M3 washers and an M3 nylock to attach it. Screw an M8 plain nut onto the z-axis stud, screw the stud into the M8 thread of the part and then tighten the M8 nut up to the part.

Required Tools

Bench Vice Drill Files Lathe