I’ve seen fiberglass reinforced nylon gears used with success in commercial injection molded gearboxes. It can definitely help by increasing gear stiffness.

However 3D printing with fiberglass causes rapid nozzle wear, and recently people are saying that fiberglass reinforced 3D printing filaments represent a human hazard.

Since I’ve managed to get my gears to work without reinforcement, I’ve not tried it.

One thing I do with printed gears is make the gear teeth much larger than would be strictly needed in an injection molded solution. This lets me deal with reduced material performance compared to injection molding.

You might be interested in resin casting technique. It gives amazing results. Lcamtuf wrote a whole series about this:

http://lcamtuf.coredump.cx/gcnc/ch1/

and very nice article for make zine:

https://makezine.com/2014/03/21/resin-casting-going-from-cad...

Have printed many spools of CF and glass filled nylons using nozzles with tips made from ruby.

Check out “Hardcore Ruby” nozzles, now there are even diamond nozzles.

I print with 0.25mm nozzle in nylon, fine enough for Module=1.5 teeth.

A 0.15mm nozzle would make an acceptable Module=1 gear I would guess.

Yes I’ve seen ruby nozzles. Expensive though.

I actually print with a 1.2mm nozzle as I want to print big parts. I’ve even got the e3d Supervolcano hot end. :)