This is a replacement spool for the rope starter on a 1980's Johnson outboard motor (6-8 HP). The manufacturer has discontinued making the part and used ones are hard to find. I modeled the spool with the original dimensions and then created another copy to thicken up walls that, I feel, are too thin for a 3D printed part. I printed the part in a horizonal position so the layers were in the best orientation against shear stresses. I also used PETG filament as a minimum until I can print it in nylon. I fear PLA would be too brittle. So far so good! Hope this can help someone else.

Prusa

I3 MK3S

Yes

Yes

0.20

100%

Since the original part failed due to shear stress, I printed this part in a horizontal position so that the layer lines are perpendicular to the torsional shear stress. Due to the orientation and round nature of the part, a raft was necessary.

Supports are required, but only up to slightly past half way. You just need enough support to get the inner cylinder to start printing. After that, the printer had no problem. I just added a support blocker to the top half of the print and positioned it a few layers (3) above where the inner cylinder starts to print. Removing the supports, even deep inside the inner cylinder, was easier than I thought.

Although I used PETG (all that I have currently), I would recommend nylon. I'm still a little worried about how much heat the part will experience, so please choose a material that can hold up to as high of a temperature as possible and has some toughness to it for the initial stress in cranking over the motor. I'll update as I experience more use.