This instructables describes and shows how to build a simple gear puller.
If you like to tinker with motors you'll find that a lot of motors from toys and equipment have stubborn pinion gears stuck on the shafts. These can be a pain to remove, and while prying on them or punching them out with a hammer can sometimes work, you risk damaging the motor.
This will show you how to make a very effective gear puller with basic tools and next to no cost.
Step 1: Cutting the Frame
You will need something to act as the frame for the puller. Square metal tubing works great for this as long as the wall is thick enough to tap threads.
I used a piece of 1" square steel tubing with 0.1" wall thickness. I cut it to a length of 0.75" with a hacksaw, it doesn't have to be pretty.
Step 2: Drill the Screw Hole
Drill a pilot hole in the center of the tube, going completely through the tube. This will ensure that everything lines up nicely in the end.
Since I'm using a #10-32 screw for my puller I drilled a 5/32 hole in the top wall and tapped threads into it.
Step 3: Cutting the Shaft Slot.
You will have to add a slot going to the pilot hole in the bottom plate to let the motor shaft in. You can make the slot whatever size you like but it should be bigger than the motor shaft yet smaller than the gear you intend to pull.
There are a variety of ways to do this. Hacksaw, dremel cutting disks, drilling more holes in a path...
Step 4: Modifying the Screw
It is likely that the screw you want to use will be too big to push out the gear you want to take off, a pin will need to be added on the end of the screw for this.
Center the hole the best you can on the end of the screw, a 1/16" is a good size to use as most motor shafts are not that small. You should drill at least a 1/4"-1/2" down.
Step 5: Adding the Pin
You will a pin that is small and very hard so that it will not bend when it is pushing the motor shaft.
I just used a old dull 1/16" drill bit which I put in a vice and tapped it with a hammer to snap it. Eye protection is a good idea just in case.
Put the broken bit into the screw hole and glue it in place. Feel free to use a real pin if its available though.
Step 6: Assemble It and Test It Out!
Thats about it, put the screw into the frame, slide a motor into place and tighten the screw until the motor is safely pushed out of the gear.
Step 7: Gear Pushing
If you need to push a gear back on to a shaft, you can use the same concept with a bigger sized puller.