DIY Hardened gears

Originally Posted by kona

I should have prefaced by saying this only works with carbon steel. As others have said, the quality of steel makes a difference. The sdp-si gears seem to work well and doesn't rust afterwards. However, the traxxas gears I've done rusts within a day or 2 just exposed to air. They are probably using cheap steel, but the surface does seem harder (using the file test) than before hardening.

The hardened layer with this method is going to be much thinner than if done in a factory with a controlled environment. The way this works is that the powder creates a carbon rich environment as you heat it to hardening temperature. The more carbon in steel, the better it is for quench hardening. The longer you heat it, the deeper the carbon penetration and thicker the hardened layer.

I would think things like dogbones and drive cups could be hardened as well, but haven't tried. Would hardening the spur and the pinion be beneficial? As with anything, experiment and your mileage may vary.

Hey, you should probably toss your newly hardened gears in your oven at home and leave them in there for 2 hours at 400 deg. or so. Right now they are probably pretty brittle and you wouldn't want to start shearing off teeth.

Originally Posted by 1maxdude

Hey, you should probably toss your newly hardened gears in your oven at home and leave them in there for 2 hours at 400 deg. or so. Right now they are probably pretty brittle and you wouldn't want to start shearing off teeth.

to remove the brittleness you need to temper the gears after you harden them, also quenching in water causes a fast temp drop which gives the you the hardest result but makes it the most brittle and gives you the highest chance that you will get warping...in the past I have heated parts to about 1500 degs and than quenched in motor oil, I than brush off the carbon residue and reheat to about 500 degs to temper

here is a link to help explain the hardening process

http://www.armourarchive.org/essays/...treating.shtml

I haven't had any problems with not tempering. I don't know if tempering is necessary since this is case hardening and only the very thin surface layer is hardened. The bulk of the part should be low carbon steel and therefore does not harden.

I also haven't had any warping, but it could be a problem especially with larger parts.

Originally Posted by kona

I haven't had any problems with not tempering. I don't know if tempering is necessary since this is case hardening and only the very thin surface layer is hardened. The bulk of the part should be low carbon steel and therefore does not harden.

I also haven't had any warping, but it could be a problem especially with larger parts.

I am not familiar with the powder coating ...maybe using it does protect it somewhat, the part would be more prone to warping if you went directly from heating to quencing in water. When you quench in oil it lowers the temp slower decreasing the chance of warping and cracking, oil is also a good source of carbon

Originally Posted by kona

I haven't had any problems with not tempering. I don't know if tempering is necessary since this is case hardening and only the very thin surface layer is hardened. The bulk of the part should be low carbon steel and therefore does not harden.

I also haven't had any warping, but it could be a problem especially with larger parts.

It will still harden,not as hard as the surface,but it will still harden. If you cut the gear across and measured the hardness, it would decrease as you get twoards the middle, but you'd still be harder than before. Also, they probably don't spend a whole lot of time and money engineering and machining those gears to exacting tolerances, and your probably going to have a lot of imperfections that would be a hot spot for bad stuff to start happening at the surface if you don't temper. And yeah like the metallica guy said, use oil rather than water. Water is more severe of a quench than oil. It'll be just as good, but will have less of a tendency to crack. Im pretty sure warping that small of a gear isn't an issue, but still it will in fact keep distortion down more than water. I think if you temper your gear at 400, you will relieve the stress while not sacrificing too much surface hardness. It will fail prematurely in the as quenched condition. I've never seen anyone use anything untempered without it cracking/breaking. Even 300 would be better than nothing.