Great example model. Thanks. To push the parts together is a bit tricky. I was scared to break it too, but it went okay.
And I used small wood screws instead of M3 screws. (edited)
All of the parts were printed on a Prusa MK3S with 15% honeycomb infill and 3 perimeters. All of the parts came out looking great but were very hard to put together. I even sanded some of the parts to help get them together. I broke the part that holds the 3 planet gears putting it together. The model did work but once the parts go together they will not come back apart. All parts were made with PLA. Might make some small adjustments on the gear carrier so it goes together better. It also looks like there are small holes to screw in the planet gears? Not sure.
Looks like the original instructions call for M3 screws https://www.thingiverse.com/thing:18291