Planetary Reduction Gear for NEMA 17 with Ratio of 5:1 and 25 GT2 Teeth

Planetary reduction gear for belted z-axis driven by NEMA 17 stepper motor. It has a reduction ratio of 5:1 and 25 GT2 teeth. This results in 10 mm/rotation.

It may be mounted as a drop-in extension/replacement if your current drive has 25 teeth or close.

This is sufficient to prevent z-axis drop on power loss on experimental crossed cantilever 3d printer (see Casual CNC channel on YouTube) and might be suitable for other printers as well.

You will need following extra parts:

• 3 ball bearings sized 3 mm (inner) 6 mm (outer) and 2.5 mm (depth).
• 1 ball bearing  sized 5mm (inner) 11 mm (outer) and 5 mm (depth).
• 4 M3 25 mm screws.

The parts in the video were printed on Creality K1C using TINMORRY ABS Pro filament with following key parameters:

• Orca Slicer
• Generic ABS profile
• Flow rate set to 0.98
• 0.2 mm layer height
• “Precise wall” option on

It is essential, that parts are not sitting too tight. Prefer some backlash with lower friction over tight assembly. As a basic test, install the planetary reduction gear(s) on belted z-axis without the sun gear and see if axis still goes down. Expected: It should go down! Another positive sign is that a minimal drop is present on power off. This way backlash should not matter as the system is pre-loaded constantly in one direction. 

There are 2 sizes of the case to choose from:

• 42 x 42 mm - same size as NEMA 17
• 40.4 x 40.4 mm - if space is tight

Video on assembly and mounting: