Starting a Linear Gearbox

Today I CADed a linear gearbox for the motor. I found nylon gears in the ME stockroom and was able to create a 15:1 gearbox in two stacked stages. These are so much better than the planetary gearbox I was trying to create from scratch.

Processes I tried for making my own gears:

  • 3D printing
    • Absolutely sucks for the small teeth profiles I needed. The profiles weren’t even there. They just sucked. Nothing meshed. Nothing fit. Ugly, awful gears that were only saved from being thrown in the trash by the wish to document the process.
  • CNC routing
    • Worked a whole lot better than 3D printing gears but still kind of sucked. The profiles were a lot nicer but it took forever to cut the gears out of 1/8″ plastic. They meshed and fit together very nicely but the time put into setting it all up was way too much.

And then I found nylon gears. So pretty.

I also found some dowel pins that pressed into the gears to get a good, solid axle.

These gears were bought in bulk by someone (no idea who the actual manufacturer is) and can be used in a mass production setting. I like these a lot better than anything that I was able to create myself.

The only issue I had with these gears was getting one of them to fit on to the motor that was provided for us. The hole in the last 10 tooth gear was too big to be pressed onto the motor shaft. It was down-right sloppy. I was hesitant about gluing the gear onto the motor because this is a $50 super fancy motor. But adhesive is what I ended up using.

I used Permatex medium-strength threadlocker (blue) to attach the gear to the motor shaft. The threadlock created a film around the motor shaft that helped to center the gear on the motor shaft. It didn’t take very long to cure and seems to be holding fairly well. I’m sure that if this ends up being the wrong gear to use, I can force it off the motor shaft without damaging the motor.

Currently, I’m designing a housing to hold the gears in place. I’m planning on 3D printing the housing but it could easily be injection molded if this were put into mass production. The entire gearbox will be around 2 inches long which is considerably smaller than the planetary gearbox monster I previously made.

The issue I’m having right now is trying to figure out what the pitch diameter is of the gears I found. I couldn’t find spec sheets on the gears so I have absolutely no idea what any of the designed dimensions are. I’ve contacted Nagy Hakim, who is the ME stockroom NINJA, about getting specs for the gears and I’m awaiting for a response. If he doesn’t get me that information in the next day or so, I’ll just do some trial and error designing to find the correct center-to-center distant for these gears.


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