Matching a Gear to Keyed Shaft of DC Motor


I ordered a motor for a personal project as well as some gears. The shaft is keyed on the DC motor. How would I bore out the hole of the gear to fit snugly on the shaft of the DC Motor. Here is a picture. Any help is greatly appreciated as I am stumped on this part of my project.


  • Matthew

your gear barely looks like it has a larger diameter than the OD of the shaft. Are you sure it’ll fit when bored out, and not damage the teeth?

Yup Positive. Here is a more clear picture at a better angle. The gear is made of a nylon material. Is it possible to bore it out, put it on the shaft than fill in the void with a material that will cure/harden? I can’t think of any other way to get this gear to fit snugly on the end of the keyed shaft. :confused:

How much torque will the gear be transmitting? A lot, or a little?

16in-lbs of torque. Maybe I could get the shaft out of the motor and turn that down with a lathe to fit the inside diameter of the gear so I don’t have to bore out the gear. I don’t know what type of screw head that is though to get the bracket off.

It looks like a hex wrench can get those screws off. Anyways, I believe you’re going to need a special broach to cut that shape into the gear.

How about boring out the gear to match the OD of the “D” part of the motor shaft and then drill and tap a set screw crossways in the round hub of the gear to press on the flat of the “D”?

What I would do is throw (not literally) the whole motor onto the mill. Then I’d put a couple parallel bars in the vise, set the shaft (large part) on those, then clamp the vise on the shaft. The body of the motor would hang out the side of the vise. Then I’d center it up with an edgefinder going off the insde face of the vise jaws. Then I’d go in with an endmill and mill a keyway in the motor shaft (large part of the shaft). Then I’d bore the gear to fit over the shaft, and then I’d broach a keyway in the gear.

Of course, this would only work if the gear is big enough to be bored out to fit over the big part of the shaft, and the shaft has to be a standard size.

As for your question about filling in the voids, you may be able to use some sort of epoxy but I’m not sure if it would work.

What would probably be the best solution would be to set up the gear in a mill (preferable with dro). You can use an indexing head and a collet to hold it so you clamp on all the teeth so you won’t flatten any. You won’t need to clamp very tight. Then get the gear centered by the bore. Then get an endmill of diameter that is the distance from flat to flat of the shaft. Then mill in the gear, the shape of the shaft. Of course this only works if the distance from flat to flat on the shaft is a standard size.

May I ask, why are you using a plastic gear as opposed to a metal one?

i personally would use a set screw as deepwater suggested (just make sure the screw doesn’t come loose…). but, if you don’t want to do that, here’s a post from Dr. Joe about attaching gears to the output of the globe motor, which has a similar output shaft:

We have used double-D broached holes on metal gears with the Globe motors. It worked just fine. When we modified last year’s robot as a practice bot for this year, those gears wound up working a lot harder than they were designed to. They still work just fine. Not sure how the plastic gear will work, but a D shaft will probably work bettter than a key way or set screw.