3:1 gear stages that can be assembled to get a gear ratio to any power of 3.
I needed to reduce the speed of a motor by a large degree. My first tries used a a worm gear, but I didn't have my support settings dialed in well enough to print one yet. I went with this design so it would be easy to add or remove stages depending on the desired gear ratio.
For my current project, I am using 6 stages of gear reduction. 3^6=729 so I have a 729:1 reduction in speed. Included with this is a 1:729 increase in torque.
Print one of the gear stages and one gear mount. Be careful depending on your machine, as the raft for the gear stage just barely fit on my ToM ABP.
The two pieces screw together using an M3 socket head screw. I used leftover M3x16's from building my ToM, however there is room for larger and smaller lengths. Any extra length of bolt will simply fall into the cutout in front of the gear two stages behind itself, and this actually helps to line them up better as well.
Screw the gear mounts down to a scrap piece of wood, as shown in the pictures. Holes are provided for 2 screws, however I used just the inner hole because it gave more play for the gears (preventing them from jamming) and also more precision in placement because the second screw always seems to move it out of place. Both might be a good idea for just the first one.