View Full Version : cordless drill planetary gearsets- uses

10-17-2008, 05:37 PM
I happened upon a used 18volt Makita drill/hammer drill that a friend was tossing in the garbage as he had no more batteries..
So I took it apart to find a very nice 3 speed planetary transmission with clutch. All hardened steel, Each stage uses from 3-5 satellites so there is always a lot of gear tooth contact made. Shows no wear at all.

Locking the1st internal ring gear results in low speed.
Locking the 2nd internal ring gear gives 2nd.
Locking 2 and 3 together and letting them spin gives high speed.
The clutch is also very nice.

I'm thinking of using this gearset on the line boring machine I am making for speed reduction.
I'll take pics tomorrow of the unit, but does anybody think these gearsets are strong enough to handle a 600watt mini mill motor?
It is small but comparing it to the gear drive on a stock mini mill with just a few gear teeth in mesh makes me think it may be much stronger.

I would make a complete new aluminum housing for this transmission.
Just wondering if anybody has tinkered with some of the better planetary gearsets in the newer drills.

10-17-2008, 07:16 PM
Haven't looked at that, but I have been pondering a larger set of planetaries (perhaps from a sub-compact car auto trans?) and building a 3:1 (or whatever convenient) speeder for my big 20" VSG drill press...

10-17-2008, 09:12 PM
Well, I'm trying to keep size in perspective. I have built a few auto Transmissions for racing and I do have 2 trannys in my garage for parts. When you consider you can easily run 800+hp through a relatively mildly built TH400 it makes you think about the size of the gears etc needed for a HSM machine!! Nobody needs that sort of strength in a HSM machine.
A planetary gear box seems to be able to have great power capacity in a small/compact size.
I know these little hand held drills can deliver a lot of torque. My line boring machine project is well under 1hp. I look at the size of the back gears on my SB9A and they seem huge. But consider the actual tooth mesh and it's not a huge amount of metal meshing at a given time.
Here's the gear box below I am talking about, I have a can next to it for scale.
The plastic gears show the gears and mesh on a stock mini mill.
On my extremely modified 9x20 lathe I was able to twist a grade 5- 3/8" diameter bolt in half at only 40rpm using only two 5mm wide polyflex belts for the power transfer. This was a torque test I did to determine if the extra belt would help.


10-17-2008, 11:55 PM
Very neat little gear set. I wonder if it would handle the over-drive application I've been thinking of?

I was only mentioning the auto trans gear-set because that is what came to my mind for the speeder. And mainly because it would be easy to get, probably free. And when you're going to burn that many hours in a project, it's good if the components are free (I'm sure you can relate). :D But that gear set you've got might even work for me. Problem is, I'm going the other way, so it's got to stand the mechanical disadvantage and the high rpm balance/vibration issues. Probably no big deal, because the only purpose for the speeder is 1/2 and smaller drills (depending on material).

I've also thought about mounting a pulley on MT3 and driving a secondary spindle that clamps to the quill (like some Bridgeport accessories). My quill could easily handle the side load and it would simplify things (for building anyway), though not exactly compact. I find the idea of a small "box" with MT3 drive that you sock into place with a stabilizer bar like a tapping head much more appealing. Extra points for multiple speed selector. :D

10-18-2008, 01:53 AM
Interesting. I find that generally those planetary gearsets have reasonably well fitting gears and are plenty strong enough. I think if you support the sections in a housing with accuracy and with a low amount of play, you'd have a decent reduction drive. The input shaft must be well centered to keep noise down and pressures equally distributed through the teeth. If all the parts stayed lined up during high torque useage, then I think it isn't a stretch to say it could handle a horse or so. The input gear is not large, and the limitation might be the strength of the bond it has to the driving shaft.

I would think also that intermittent loading would be hard on a gearbox like those. A workaround might be to have some small friction available on the output side so the teeth would always be in contact, and intermittent cutting actions wouldn't be able to hammer the gears as much.

Stronger than the plastic gears that you show- hunh? What are those from, a fisher price toy? :)

I could tell a story about how strong (or not) one set of non-planetary gears has been for me- this in an expensive bosch cordless drill. I broke the teeth twice while boring some holes in wood with a spade drill bit. I'll go with the planetary gearset any day over that parallel shaft gear arrangement.

10-18-2008, 02:11 AM
Stronger than the plastic gears that you show- hunh? What are those from, a fisher price toy? :)


NOPE, genuine original plastic transmission gears from the Mini Mill.

10-18-2008, 02:23 AM
Dewalt gearboxes from drills are popular in the robot builder groups.

All sorts of mods for them:


10-18-2008, 09:09 AM
Well Ok, I'm going to give it a shot. Out of curiosity last night I took my corded 1/2" hammer drill that'll do some serious damage if your not careful apart and looked at the gear set. It's not even as rugged looking as this one from the Makita.
Thanks for the link Macona. All sorts of good parts for custom builds there!
Keep an eye out for discarded cordless drills. Some nice parts in them!

10-20-2008, 03:21 PM
This is what I made this weekend. A new aluminum housing for the Makita gearset.
Very close tolerances and the clutch and high speed assembly now will run in bronze sleeves. No comparison to the stock setup.

All the gears that need to be packed away-

This is the input side of the gearbox. The lighter splined sleeve is what shifts the transmission from gear to gear. The dark splined sleeve is bonded to the housing( look closely and you can see through the lighter sleeve to see it is locked to the splines in the housing to keep it from rotating. This is used for gears 1 and 2. When the moveable splined sleeve is slid all the way back away from the stationary splines it locks the the splines on 2 of the ring gears together and then spins in the housing for high speed. Interesting setup.

Input end with the gears all installed-

This is the output end and clutch planetary.

I still need to make an input bearing assembly which will be adjustable for centerline and a clutch and output bearing assembly.

Then a sliding fork to shift it.

This should be a trick little transmission for my mill.

10-20-2008, 05:05 PM
Those gears look sintered instead of machined. How does that affect it's strength?

10-20-2008, 05:24 PM
I really don't know. Powdered metal parts can be pretty hi-tech and very strong. All sorts of engine parts use powdered metal components.
I just know these gear drives are pretty darned rugged.