MechanicalRebuild shelfHand tools, works as-is

Gears

Also called plastic gear, printer gear, planetary.

Printers, toys, and tool transmissions. Plastic gears with a broken tooth are why the machine was scrapped; the other gears in the train may be perfect. Module and pressure angle are rarely marked. Keep a meshing pair together.

If you are new to this category

Rods, gears, belts, magnets, screws, and boxes. Printers are the best source of straight steel rod and toothed belts. Screws from a laptop are tiny and specific; a random screw in a laptop hole strips the plastic. Bag them by the machine they came from.

If two parts were meshing or riding together, keep them as a pair. A gear from one toy rarely fits a gear from another.

Inside a hard drive

The two curved blocks on the steel plates are the magnets, and they are the prize. Slide them apart. Do not pry straight up. The flat coil on the arm is a short-travel motor. The platters are not a useful material, and on some drives they are glass.

Sheet metal and glass. Case steel, shattered platters, lamp glass, and magnet chips cut deeper than they look.

Specification. The right-hand column is what is typical. The label on the part in your hand wins if they disagree.
What to look for	Usual figure
Match	Two gears mesh if they were designed to. A random pair from two toys will not, even if the teeth look similar.
Bore	Often a D-shaft. Save the shaft with the gear.

Volts are electrical pressure, amps are how much current is flowing, and ohms are how hard the part resists that flow. A higher voltage than the part was built for is how salvage parts die on the bench. If a cell in the table says “read the stamp”, that stamp is the whole specification.

What people actually use it for

A reduction you build around the original pair
Replacing a stripped gear in an identical machine

Leave this one when

The bore is wallowed out. A loose gear on a shaft will strip the next tooth.

Buying a new one is the better idea when

Catalog gears of a stated module, once more than two have to mesh.

How to tell if this one still works

Spin the pair. One tight spot per revolution means a bent shaft or a bruised tooth.

Tools you will want: Hands.

Where people actually find it

7 notes, most useful first. “Leave it” means the part is in that machine and you should not take it: it is dangerous, worn out, or only useful if you already know that exact repair.

Harvest at a glance
From	Call	How many	How often	Where it sits
Desk or box fan	Prize	a set	usually	Oscillation gearbox.
Motorized toy	Prize	a box	always	The gearbox.
CD / DVD / Blu-ray drive	Worth it	a handful	usually	Tray mechanism.
Inkjet printer	Worth it	many	always	Paper path.
Laser printer	Worth it	a box	always	Drive train.
Paper shredder	Worth it	a train	always	Between motor and cutters.
Blender	Bonus	1	sometimes	Coupler.

Prize — take this firstDesk or box fana set · usually
In this particular machine
A worm and a small geartrain. This is the clever part.
Where to look
Oscillation gearbox.
How to get it out
Keep it assembled.
The condition to expect
Often good when the motor is not.
Prize — take this firstMotorized toya box · always
In this particular machine
Keep meshing pairs. One stripped tooth is the usual reason you have the toy.
Where to look
The gearbox.
How to get it out
Bag the set.
The condition to expect
Mixed.
Worth pullingCD / DVD / Blu-ray drivea handful · usually
In this particular machine
Small plastic, some with a clutch.
Where to look
Tray mechanism.
How to get it out
Keep meshing pairs together.
The condition to expect
One stripped gear is typical.
Worth pullingInkjet printermany · always
In this particular machine
A whole gearbox.
Where to look
Paper path.
How to get it out
Keep the stack in order if you want the ratio.
The condition to expect
One broken tooth is common.
Worth pullingLaser printera box · always
In this particular machine
Some metal, mostly plastic.
Where to look
Drive train.
How to get it out
Photograph the train.
The condition to expect
Watch for one stripped gear.
Worth pullingPaper shreddera train · always
In this particular machine
Some steel. The plastic one is often stripped, which is the fault.
Where to look
Between motor and cutters.
How to get it out
Keep the metal pair.
The condition to expect
Mixed.
Bonus, if you are already in thereBlender1 · sometimes
In this particular machine
A plastic dog that strips.
Where to look
Coupler.
How to get it out
That is the failure. The motor shaft under it is the part.
The condition to expect
Stripped.