M.L. Toys
M.L. Toys
HobbyMasters M.L. Toys
Information on Motors, Gearing & Gearboxes
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By taz11
After developing a large pile of "spun off" plastic pinions on my bench, I figured it was time to do something about it.

The way it appears is that the gear teeth are not the problem. The problem is that the gear walks off the shaft and away from the metal clip. The metal clip is what keeps the gear from turning on the shaft. Once it spins, it eggs out the hole and now your done :evil: . The gear just floats on the shaft.
pinion fix1.jpg
pinion fix1.jpg (42.3 KiB) Viewed 4024 times

The object here is to keep the gear from walking on the shaft. This will keep it engaged in the metal clip so that it does not spin on the shaft.

I started by filing/grinding a flat on top of the gear. Do not grind off the part that sits in the metal clip! Grind the round portion.
pinion fix2.jpg
pinion fix2.jpg (43.12 KiB) Viewed 4024 times
Next I drilled a 3/32 hole down through the gear (where the ground flat part meets the teeth) and tapped it with a 4-40 tap. I had some extra set screws from my r/c car days. I installed them in the holes. Just snug them, they are threaded into plastic and you don't want to strip them. Remember the idea is ONLY to keep the gear inserted in the metal clip. The clip will do the hard work.

This is the clip on the shaft. (I have yet to see one of these strip)
pinion fix3.jpg
pinion fix3.jpg (41.52 KiB) Viewed 4024 times
Here is the gear re-installed
pinion fix4.jpg
pinion fix4.jpg (42.34 KiB) Viewed 4024 times

Remember not to over-tighten the set screw! It is only threaded into plasic. The clip will do the hard work as long as it stays in contact with the gear.

This has been is service for several months (at 18 volts) and is still going strong.

Check out the original thread here: ... C_ID=18882" onclick=";return false;
Last edited by taz11 on Sat Jan 15, 2011 11:07 am, edited 1 time in total.

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