As for me and my team...
 

...we weld lots of gears to shafts.

Yes, it can be a problem at times.

Yes, you can warp the gears (that is why I add lots of extra backlash in to my gear meshes -- increase center distance to pull the gears apart a bit, it lets the gears wobble without jamming).

Yes, the welds can break.

Yes, it makes the entire cluster junk if only one of the gears breaks.

Yes, Yes, YES!

But....

....if you can not stress the weld too much, and if you can get a good welder (one who doesn't pound too much heat into the gear) and if you can manage the possible wobble, and if you can design your gear teeth such that they are not likely to break. Welding is a good way to connect one thing to another -- even if one thing is a gear and the other is a shaft.

But for all that, I more or less out of the welding gears to shafts business.

I used to make custom gearboxes at the drop of a hat for FIRST, but the K-3 rule last year more or less knocked me off my horse. I have had a conversion experience! This year our robot will have 10 motors and not one custom gearbox -- not even one custom gear or gear cluster!

I will write likely write a white paper on the topic after the season (you have to give my at least 1 year of advantage for thinking of this idea). The title will be something like: "You've got a lathe, a mill and a welder... ...what more do you need?"

Stay tuned.

Joe J.

P.S. I like to leave shoulders on the shaft when I weld a gear to a shaft so that I can help get the gear square to the shaft.

Re: Strength of welds on gears
 

We actually found a professional broaching shop who is willing to do all our gears for free! So we will use keys, and just tack weld the gears on (or weld something to the shaft) to keep them from sliding along the shaft.

Now I have one more question, a couple of our gears are getting the hubs taken almost all the way off. Is it better to broach them with the hubs on or off? Does it make a difference? With no hubs there would be less material to cut.