Removing Drill pinion

Does anybody have anybody have any ideas as to how to get the drill motor pinion off?

A really small gear puller or some sort of set-up in a press.

This thread has lots of information about how to do so the right way. Basically, use an Arbor press to remove it, but don’t, under any circumstances, try the Dremel technique. We’ve already had to replace two motors because of it.

Ok, I still don’t get how i am supposed to fit a plate between the pinion and the drill body. Do i dremel out a space to put a plate, and then press it off?

Funny but stupid idea:
1.) Put the whole motor in a lathe chuck.
2.) Somehow lock the chuck from spinning.
3.) apply power to the motor
4.) slowly lathe the gear down to a peice of foil and slide it off.

or you could stuck some assorded stuff into the motor to jam the rotors and use the lathe as normal. Please don’t try either of these things.

Seriously though, we need some help here.

What Sarah fails to mention is that the motors were not ruined as a result of grinding the gears. The motors were dropped long after they had thier pinions removed, and the brushes broke. As far as pressing, it is by far the easier and better way to remove the pinion, however if you do not have access in any way to a press and still need to remove the pinion, my method does work. By dremeling, I did not use a cutting wheel, rather a grinding stone. See the details in the thread that Sarah reffered you to, but the gist is that the hardend steel of the pinion is becomes brittle when it is very thin. By grinding it down to a very thin layer between it and the shaft, just tightening the gear in a vice should cause the gear to crack in half and fall off of the shaft. PM me if you would like some more details.


The first thing (4 steps) might actually work. But I don’t recommend it unless you have a spare. I would not try the second thing (jam the motor) at all. With pretty much anything other than pressing or pulling, you run the risk of getting metal chips or dust in the motor which coule run the bushings, cut insulation on the windings, and/or create a catasrophic electrical short.

I had an RC airplane motor with a pressed gear that I wanted to get off. I tried heating it up, that didn’t work. Then I tried holding the gear (with a custom little plate) and tapping the motor back through it. That didn’t work. Finally, I tried sticking a little piece of plate or little pliers or something in between the back of the gear and the front of the motor and using it like a lever prying the gear off the shaft. This worked. Now, this was a junk motor I was getting the gear off of, so I can’t really say how the motor stood up to my torture, but the gear came out pretty much fine.

If you don’t have a press or don’t know how to set it up in there, you could try the leverage thing. That is the next least risky. But I really don’t know how tight that gear is on there. In any case other than a strait press off, you should be at least prepared to get a new motor if something goes wrong. I have a link of where to get it if you need it.

I have attached a drawing (PDF file) of a gear puller assembly and the details to make it. It is one made part that can be made with a manual mill or anything else you can get creative with. I used an M4 screw, but you can use anything smaller than 5mm (that is the size of the shaft).

I hope this helps,


TC-2004-700-001.pdf (56.7 KB)

TC-2004-700-001.pdf (56.7 KB)

Sorry, I’m so late on this - hope you’ve already solved it; but here’s two good methods.

#1: You don’t care if you distroy the pinion;
Use a dremmeling tool with cut-off wheel. Cut as deep as you can into the pinion without cutting the shaft (lengthwise, between two teeth). Place pinion on anvil or other solid surface. Drive a cold chisel or center punch into the slot you cut. The gear will split in half.

#2: You want to save the pinion;
Get a faucet handle puller (~$7) from any hardware and a butane jewler’s torch. Grind or belt sand the jaws of the puller so that they’ll fit under the pulley. Cut the pin on the puller to a length of 1/2 inch and grind it to a point. Drill a dimple in the center of the motor shaft. Mount puller to pinion and apply a modest force - not too much, the puller is a cheapo. Heat the pinion with the torch. Give the puller another turn or so; when you hear a POP, it’s ready to turn all the way off.


There is a device commonly referred to as a bearing removal tool, it is a split plate that bolts together and has a small hole in the center that has a huge countersink so that it slide under a relatively small gap such as the gap between the drill motor and the pinion. The bolts are tightened and then the whole thing is put in a press so that the motor/pinion is supported (hanging from) the tool. Then the drill motor shaft is pressed out of the pinion in much the same way that the tool shown in one of the previous posts works.

I would be reluctant to cut away the gear (pinion) unless you do a thorough job of masking the motor. If the metallic dust gets into the wrong place in your motor, it could trash the motor quickly.

If you choose to press a replacement gear on the shaft of a somewhat similar number of teeth (but different pitch), stay with a .0002-.0005 interference fit (press). If you go much tighter, you may yield the gear and you could easily lose the press i.e the gear now spins on the shaft.

Good luck

Not to sound like a broken record, but do not cut away the pinion if you want to keep the motor. You may be successful a few times and not damage the motor, but this method is not necessary and has a high probability of trashing the motor. There are several methods in this thread that will work time and time again, but the pinion cutting method is just not one of them.

I have pulled off many pinions (both old drill, new drill, and FP) without any failures using the methods I describe above.

Of coarse, you may do what you want; but don’t say I didn’t warn you.


How does one get a .0005 interference fit with the replacement gear? Are metric reamers sized .02mm under readily available? Where would I find such a tool?

Basically, I got .7 mod gears from PIC-Design to mate the Bosch to the rest of the gearbox, but I am having fits trying to get the spacing correct. No such problems with the 20dp gears from Martin Sprocket…

Hi all, just thought I’d throw in my two cents. First of all our team (368) is taking a year off (everyone is burnt out), so unfortunately we won’t be able to join in on all the fun.

Over the past two years we have been removing our pinion gears using an arbor press which has been a real pain as those gears are on pretty tight and have more than once bent our pinion removing fixture.

While rumaging through my tool box the other day, I came across a Craftsman (sears) nut splitter and all of a sudden it occured to me that this might be the easiest (destructive) way to remove it. Since I had a broken bosch motor from last year (brush assembly broke off, I decided to try the nut splitter on the pinion gear to see how it would work. After carefully aligning it on the pinion gear, I grabed the nutsplitter with a wrench so as not to put any pressure on the shaft of the motor and used another small wrench on the screw that forces the nut, or in this case the pinion gear into the anvil. In two seconds, I heard a little cracking sound. The pinion gear is hardened and brittle and with very little pressure at all, the nut splitter put a hairline crack in the pinion gear and it basically just slid off the shaft without damaging the shaft. Basically the anvil gets wedged between the teeth of the pinion and causes the teeth to split apart (the anvil fits between the teeth but does not bottom out) as you apply pressure to the screw.

A nutsplitter from Sears is about $15.00 or so and definitely is the quickest and easiest way I found to remove a pinion gear off of the bosch motor. Only a little pressure is required and but you may have to reset the nutsplitter on the pinion gear as the screw may break a few of the teeth off first.

I wish I had figured this out two years ago which would have saved us a lot of time. If anyone has an old damaged bosch, try it for themselves. It works great. Just remember to go slow and easy on the screw as it doesn’t take much effort.

Again, this method will work as long as you don’t mind destroying the pinion gear. Lastly, I only tried this on last years bosch motor so it might not work that well on the fp motor which has a much larger pinion gear.

If anyone tries this, let me know how it worked for you.

Oh well, have fun, wish we could be compete with you all as we never did make a robot that could pull itself up on a bar.

For those of you who do not know Paul, he is one of the best mechanical guys around. If he says something about motors, believe it. He won’t steer you wrong. I would trust him with my robot.

For anyone who has pressed the gear off and then pressed their own back on, how did you all make sure that you were doingit perfectly straight, so that you didnt put any side load on the bearing in the drill motor. The best way I can think of would be to support the tiny little piece of the shaft that runs through the back of the drill motor, then press the new gear on.


To get a .0002-.0005 press fit, you have to measure the actual shaft diameters as they vary from motor to motor. The actuals on the motors we had were somewhere around the .197 (inch) diameter but varied within .0005. We also found that two of our motors had slightly damaged shafts from where the pinion was pressed improperly. We then had a local machine shop make the parts. Two machining methods will work quite well; jig grinding or honing. A reamer is not as consistent as you would think.

To press a new gear on, you would need to support the shaft at the back of the rotor and then press axially so that no force is directed into the stationary portions of the motor. A good arbor press is valuable. A higher quality vise would also work (where the jaws maintain a decent parallelism under load). Always have at least a second set of hands helping while doing this unless you develop some ingenious tooling. Red Loctite is also a good idea (not in lieu of the press fit but to augment it), but as most people will warn you about Loctite, cleanliness of the surfaces prior to applying the Loctite is critical.

Good Luck