Wolf Eel is the designation assigned based on number of posts. I see you are Hermit Crab.
I built my own 3D printer based on the Prussia I3 design a few years ago from ebay parts. Works well, cost a lot - full kits are now lots less on Amazon. Still, I did it to learn hence not choosing a kit.
As for the gears, There are some gear design tools available (free) and some in various cad packages. I use Tinkercad - the online cad program as it's done all I want and isn't a vertical slope to learn.
I use calipers to size everything, draw lots of measured diagrams, etc. I did learn that parts shrink when made, and otherwise aren't 100% perfect to original size. My advice is to make some stuff, measure the made stuff and then adjust accordingly.
I also found you can build smaller elements like the gear, a cylinder, another (smaller or larger) cylinder, etc. and test fit them. They print quicker than the whole thing, and use less filament. THEN, when all the pieces fit, you can "assemble" the whole thing in slic3r and it will print as one item! Slic3r is the "slicing" program I use that takes model code and converts it to printer code. There are others but I like Slic3r.
Mostly it's "make one, find the problems, fix and repeat". My first gear took about 6 iterations even when I thought I was close.
In that light, I'd say it's not really feasible to do this kind of iterative design/build without your own printer.
I use PLA as my filament as it's easy to print. As for wear/tear longevity, I made a cave line spool at the same time (July 2017) and have taken it in my pocket on every dive since. It's still in perfect shape, so I have no real fears about using PLA for SCUBA stuff. I also dive ocean all the time.