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Originally Posted by Matt Reiland
Our team actually takes the opposite approach to this, we try to weld anything that we can but we start with robust materials that are highly unlikely to break. Welding the gears to the shaft after everything is the way you want it takes one more failure point out of the equations (Assuming you have someone who is excellent at welding versus other options such as set screws, pins etc) Again this past year in debug of the Team45 transmission it was a hare narrow and ended up being in high & low at the same time in a high power shift. This immediately locked up the transmission and send a shockwave through the gears, shearing the pinion off the drill motor, all other welded gears were unharmed and lasted the entire year and are still going strong.
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I guess I ought to clarify my point here. The reason that I suggested against welding gears to shafts is essentially for a couple of reasons:
1. If you break teeth on any gear on that shaft, all the gears on that shaft are essentially garbage because you can't remove them.
2. Welding around gearboxes has potential for splashing of metal in between teeth inadvertently, and that's BAD NEWS.
You said that you had to replace a drill motor, but your gears were unharmed. Personally, I'd much rather replace a gear than an entire motor since they're cheaper and easier to attain, and easier to have spares of too.
To follow with that, I always try to use keys since the allow you to salvage your gears after a critical failure, but have shear strength much higher than set screws or pins. I'd agree they don't have the strength of a nice solid weld, but read on...
If you were careful and took some time to calculate the absolute max torque that you would have on a properly functioning gear box (and add a little safety factor for good measure), I think you'd really like to have whatever is holding your gears fail first, rather than the teeth on the gear or a shaft within the box. I'd much rather replace a key, pin or screw before anything else.
Just a few more cents on some really good thoughts flowing from a lot of folks. Keep 'em flowing.
Matt