TR8 MakerWheel prototype for rack and pinion actuator

A project log for Mekamantis

A fun and functional 3-axis hybrid parallel robot that fits on your desktop

Scott WinrothScott Winroth 08/25/2019 at 05:380 Comments

Finished 3D printing the first TR8 MakerWheel prototype for use with a TR8 x 8(P2) screw (for those not familiar with the terminology, this means an 8 mm diameter trapezoidal thread with 2 mm pitch and 4 starts).  TR8 screws are typically used as lead screws.  We are using one for the z-axis.  However, we are also looking at using them in the rack and pinion actuators controlling the x and y axes.  The screw acts as the "rack".  Four idler MakerWheels (like the one shown in the photo) support each screw and allow it to translate along a path parallel to the axis of motion. A MakerWheel pinion coupled to a NEMA 17 stepper motor controls the position of the screw.  

Standard M8 threaded rod is also being explored as a lower cost option.  In general, TR8 screws are more expensive than M8 threaded rod but provide much better quality and precision.  They also provide a larger thread pitch (TR8 pitch is 2 mm vs. 1.25 mm for M8) and a squarer thread profile.  From my experience, larger pitch threads are easier to 3D print and provide better strength.