We’ve seen several methods of repairing plastic gears. After all, a gear is usually the same all the way around, so it is very tempting to duplicate a good part to replace a damaged part. That’s exactly what [repairman 101] does in the video below. He uses hot glue to form a temporary mold and casts a resin replacement in place with a part of a common staple as a metal reinforcement.

The process starts with using a hobby tool to remove even more of the damaged gear, making a V-shaped slot to accept the repair. The next step is to create a mold. To do that, he takes a piece of plastic and uses hot glue to secure it near a good part of the gear. Then, he fills the area with more hot glue and carefully removes it.

He uses WD-40 as a mold release. He moves the mold to the damaged area and cuts a bit of wire to serve as a support, using a soldering iron to melt it into the gear’s body. Some resin fills the mold, and once it is cured, the gear requires a little rework, but then it seems to work fine.

We would be tempted to use some 3D printing resin with UV curing, since we have it on hand. Then again, you could easily scan the gear, repair it digitally on the computer and just print a new one. That would work, too.

We’ve seen the same process using candle wax and epoxy. If you want to see an example of just printing an entire replacement, we’ve seen that, too.