So I started off by downloading the gear rings from this person https://www.thingiverse.com/thing:2850756, who remixed it from this person https://www.thingiverse.com/thing:2105705.

With over 1,300 likes, I figured it was a good one. Well, what I found was that the housing pieces wouldn't fit together properly because the creator didn't allow for any tolerance between the parts. Lots of comments said people were having to glue it together to get it to work. That and it seemed as though it was made for toddlers, and I couldn't fit my sausage fingers in the holes. Seriously. It brought back Zoolander flashbacks ("What is this? A center for ANTS?!?").

I recreated the housing for the gears entirely using Fusion 360. I also made it big enough for an actual adult to use.

UPDATE: To all my minions, I've heard your comments, your complaints, your praises and your curses. To everyone who commented something actually helpful, thank you. I appreciate the feedback. Some of y'all though...didn't get hugged enough as kids. Are y'all gonna be OK? That said, I'VE RESIZED THE GEARS CORRECTLY SO NO MORE SCALING! YAY YOU!!!

TL;DR
Original files no workie. I make better.
Print two of the ring housing.
Print one left gear.
Print one right gear.
It snaps together pretty easy and shouldn't come apart unless you really want it to.