I would secure them to the shaft with retaining clips (http://www.andymark.com/Retainer-Clip-p/am-0033.htm). You’re already using a key with the gear/shaft on the CIM, so all you need to do is ensure it doesn’t slide off. A retaining clip on either side will do that for you without any issue.
According to AndyMark, the CIM motor shaft is 0.313" +/- 0.0004. The 15 tooth steel gear is 0.313" bore. I’m guessing it wasn’t intended to be held on the shaft as a press fit, although you may need a little force to get it on there due to the tolerances.
Edit: What exact 15T gear are you using? I assumed, I know a bad idea, you are using the 15T with the 2mm keyway.
If a press was required during install, then the I’d investigate the alignment and position of the gears being meshed. Is the motor tightened all the way? Is the gearbox properly lubed? These types of things can cause additional stress on the system. Typically we press and forget; although we haven’t pressed any CIM/MiniCIM pinions.
I’d give AndyMark a call. Even better if you can grab a pair of calipers and take a good measurement of the motor shaft and the pinion bore before hand. If the pinion is sliding off the shaft, then it won’t be transferring proper torque, so a retaining clip won’t help. If you need a quick fix, I’d recommend red loctite.
Assuming that the looseness is the result of the existing pinions wearing down and not the shaft of the CIM motor, then pressing new pinions on with loctite should result in a better fit generally.
It’s a shame these gears don’t have key slots in them, if they did all you would have to do is retain the ends of the gear on the shaft (though I understand the geometry of the gears makes this difficult).
I think you’re looking at the wrong gear, I believe he’s referring to THIS gear which does not have a keyway and must be press fit, according to the page.
Won’t work, (what I’m assuming is) the gear in question does not have a keyway, so retaining it on the ends will prevent it from falling off, but won’t stop it from free spinning on the motor shaft.
Perhaps OP can confirm which specific gear they’re using or what gearbox it’s going into?
I have had good luck with the loctite gear/bearing retaining compounds in these application. NOT the thread locker. Be sure to use the right one. Better yet. Talk to AndyMark directly. They can give you a specific recommendation.
We also had this problem with our practice bot, but ours stayed on the motor shaft. Basically, the motor shaft would spin, but the pinion would not. These pinions do not have a keyway, they are pressed on. So we ended up tack welding the pinions onto the motor shaft as a precaution for our competition robot.
We replaced the motor on our practice robot with a new one, no weld, and have not seen this issue since, so maybe it was a bad batch of motors.
I believe team 291 also had a similar issue to you, where the pinion rode off the motor shaft.
I use Loctite 609. It is green, but don’t go by that. Lots of different grades of green Loctite. It is good for up to .006" on the Dia. .006 is actually pretty loose. Anymore than that I would probably be replacing parts. Both pieces have to be completely clean and grease free for a good bond. You will probably have to go to an industrial supply house (IE grainger, McmasterCarr, Fastenal) or mail order to get it. You only need the small bottle. A little goes a long way. I would still talk to AndyMark about your issue.