Introduction: Broken Gear Repair

Picture of Broken Gear Repair

Simple way to fix broken gear

Step 1: Materials Needed to Fix Broken Gear

Picture of Materials Needed to Fix Broken Gear

you need a plastic steel epoxy, Popsicle stick, any mixing medium for your epoxy mixture and brush and detergent soap or dish washing liquid.

Step 2: Cleaning

Picture of Cleaning

Be sure that your gear is free from oil and dust. use dish washing or powdered soap and brush to clean the gear

Step 3: Epoxy Mixture

Picture of Epoxy Mixture

mix the two compound and apply it on the broken area.

Step 4: Curing

Picture of Curing

wait for an hour to harden the epoxy, since the epoxy is not hard enough and the epoxy is flowing slowly, you need to monitor the flowing or moving of the epoxy not to stuck in one area of the gear

Step 5: Moulding the Teeth

Picture of Moulding the Teeth

After an hour the resin will going to be hard, just like a clay, position the new mold gear in its gear partner, then rotate slowly to adapt the teeth of the other gear by the way you need to put some grease on the other gear so that the epoxy will not stick to the other gear. rotate it slowly till the rotation will fit to each gear.

Step 6: Total Curing

Picture of Total Curing

remove the gear to the gear box assembly and cure it on a well ventilated area for a day

Step 7: Cured Epoxy Gear

Picture of Cured Epoxy Gear

Install the hardened gear in the gear box, assemble the parts. this gear part belongs to my meat grinder.

Step 8: Video


PaulD374 (author)2017-11-10

For a long-term replacement, make a mould from the repaired item, then use that to cast a new one-piece item, free from the risk of an add-on section breaking away.

jraff (author)2017-01-14

Use very thin plastic sheet, saran wrap instead of the grease.

AlihanC2 (author)2016-09-07

прекрасно, спасибо.

Yonatan24 (author)2016-08-05

I wish I saw this earlier... :)

Thanks. I'll keep this in mind.

FrancisP10 (author)2015-11-05

I used your idea and repaired a worn gear on a powered lift chair. It worked out great, saved me spending $200 on a new motor/gearbox since I couldn't just order a new gear. Thanks.

mistersmith (author)2015-03-30

I did this on my kids powerwheels Jeep. The gear appears to be identical to the one used in this instructable.... WELL DONE SIR!

kompot (author)2015-03-23

Perfect. What if gear is from steel ??

MarkS13 (author)2015-02-20

Well done, thank you very much. I will keep this in mind for future gears.

andrew.mead.1253 (author)2015-02-15

Thumbs-up on that one! The skill quotient involved leans heavily towards that of "timing" and its due, requisite attention.

andrew.mead.1253 (author)2015-02-15

Thumbs-up on that one! The skill quotient involved leans heavily towards that of "timing" and its due, requisite attention.

mf70 (author)2015-02-12

A clever way to repair some gears!

In step five, you say "After an hour the resin will going to be hard, just like a clay, position the new mold gear in its gear partner"

Perhaps you meant, "BEFORE the resin has fully hardened, when it has the stiffness of clay, position the epoxy-coated gear against its gear partner. "

Edgar (author)2015-02-12

This should be taught wherever there are situations where there may be problems to be solved, and no Parts at hand...

Gone to my blog.

MattDoesThat (author)2015-02-12

Excellent solution. Bravo

Atilivs (author)2015-02-08

That was EXACTLY what I was looking for, I have to fix a broken gear in my car's rear door power lock. A new one is way too expensive, and I don't have access to a 3d printer.
I just hope I'll find this kind of epoxy resin here in Italy.

Entropismo (author)Atilivs2015-02-12

Hi! In Spain you can find in plumbery stores a very good epoxy paste that it's used like cold soldering. Here it's commercial name it's Collak, but I supose that will be easy to find something similar in a plumbery store in Italy. It's like a clay with both components in the same cylinder, you just have to smash it, and it's very quick. Also it's supposed that it has a good mechanical resist. And use gloves!

kwhitacre (author)Atilivs2015-02-10

Or see if Sugru will work...

wb7ptr (author)Atilivs2015-02-09

Just be sure to use the strongest version of epoxy you can find, and not the "quick steel" which would set to quickly to mold the gears with. Good luck. I've fixed stuff on cars with epoxy before. It works unless it's on a part that has to take heat.

kenk12 (author)Atilivs2015-02-08

Look at the Instructables about repairing portable bandsaw gear:

J-B Weld has good strength specs. Good luck.

I have a Buick Lucerne with the same door lock issue.

DaniloB1 (author)2015-02-11

Solución muy eficiente y simple, gracias por compartir... Nice Solution! :)

tarekh (author)2015-02-11


handycrowd (author)2015-02-11

I use a needle file set to gently dress each tooth to remove burs, ridges etc. Cleans them up and smooths out wrinkles from the cling film (instead of grease, which I find a bit hit and miss).

Good instructable, too many people bin stuff with busted gears, kudos for kicking it into the limelight :-)

SNEHALCHEVLI (author)2015-02-11

Well Done!!! Its help me....:)

rdunkel1 (author)2015-02-10

Nice, easy, simple fix til you can get or make a more permanent replacement.

anees.ibra1 (author)2015-02-10

perfect and simple

shantinath1000 (author)2015-02-10

This is just BRILLIANT! you need to put this in a contest ASAP! I would vote for this for sure.

shantinath1000 (author)2015-02-10

This is just BRILLIANT! you need to put this in a contest ASAP! I would vote for this for sure.

clazman (author)2015-02-09

I see that Devcon does not mention using this product to repair plastic, but rather metals.

Plastic repair is a broad subject for there are many types of plastics. There has to be a breakdown of the plastic at the interface. Most epoxies do not accomplish that. There is only an exothermic reaction between the resin and the hardener not between it and the substrate.

I learned a lot when I was repairing components on my Fieros. That car used several types of plastics. Each requiring a particular repair regime.

Then their are the thermoplastics and then there are thermoplastics. One is processed with heat and is reversible. The other is an irreversible process.

Within these two categories are many types, each with its own characteristics and repair methods.

The adding of metal is not a fix for the epoxy not bonding to the plastic.

There are products that would be appropriate.for your repair.

I do wish you the best.

_soapy_ (author)clazman2015-02-10

You can also use mechanical keying. Use a small drill bit to drill holes into the part. Drill at various angles through the same hole to form an under cut and then the soft epoxy can expand and form a mechanical plug which physically can't be pulled out without breaking the epoxy or original plastic.

kwhitacre (author)2015-02-10

Have you heard of Sugru? It will do this type of stuff as well as much more. I fixed a missing nut on my drill press and made finger grips on my Mac. I think you'd like it. Your instructions are clear and well done. Thank you.

_soapy_ (author)kwhitacre2015-02-10

Great though Sugru is, it isn't suitable for this. It will mould to the right shape, but it is a firm-to-hard silicone rubber at the end of the day, & that isn't useful for hard plastic gears!

Steel epoxy sets very hard and doesn't flex, which is what you want for this sort of thing.

killbox (author)2015-02-10

you can also use shapeloc/intomorph/friendlyplastic to form a mold, you can cast it off the non damaged(apply a little lube on the part to be cast, 1/2 let it cool. remove it, clean the gear of any grease or oil. put your epoxy on it, apply the mold with a little oil on the mold to keep it from sticking let it fully harden.

baelza.bubba (author)2015-02-10

Now that your gear is repaired ... why not make a silicon mold so that you can make another when it goes wrong again? That is nice work.

ksoem (author)2015-02-09

It could be a solution to broken gears in my son's toy cars which are impossible to get a new ones.

I wonder how strong the newly casted gears are. Will they last some good 6 months? If not, I'd better get a new car for my son.

Exocetid (author)2015-02-08

My God! There is hope yet for our civilization!!! This Instructable is just incredible since the problem that it addresses is a curse that we all must bear. For example, my wife brought an electric pencil sharpener home from her middle school library and asked if I could fix it. When I saw the broken plastic gear, which I have seen so many, many times over the years, I ordered her a new one from Amazon.

I am an engineer and am just blown away by this solution. Bravo! Kudos!

I can't wait until the next thing breaks ?

Tumunga (author)Exocetid2015-02-09

DAMMIT!! About 6 years ago, I bought a consumer (cheap) slushie machine, and the gear that moved the frozen drum broke. It was plastic. This would have fixed the broken gear. GOOD ONE!!

Exocetid (author)Tumunga2015-02-09

I feel your pain―this one's a keeper.

Tumunga (author)2015-02-09

You know? This might be the greatest instructable of ALL TIME!!1!

I couldn't begin to tell you how many things I've owned that have been rendered inoperable because of a stripped plastic gear. KUDOS!!! Sir/Ma'am!@!

danzo321 (author)2015-02-08

Kind of brilliant, if the new teeth hold up. More usual way, but more involved, is to make a simple silicone mold of 2/3 of gear (the good teeth) then move the mold around and finish the last third now over good teeth. Then cast with around 70 durometer urethane.

michaelmays (author)danzo3212015-02-09

I was thinking the same thing (using the good part of the gear as a mold for a new part). For that matter, it might be worth trying to combine two molds to cast a completely new piece. That way, if you're fooling with a gear susceptible to regular abuse, you can always just make a new one.

As to just using a mold on *part* of the gear, I would worry that the "new" part would eventually break off. Maybe that's not really a problem, but simply recasting the whole gear seems to me a surer way of producing a long-lasting replacement.

Of course, I'm saying this like I've ever had to do it before. ;-) Still, this instructable is very clever and a great use for materials most might already have on hand.

danzo321 (author)michaelmays2015-02-09

My reply was standard practice in the industry except that they were aiming toward a hard cast gear which would be used as a pattern for an iron foundry.

fleebell (author)2015-02-08

I tried that a while back with a different epoxie and it didn't hold up very long, the teeth came unglued again.. How long has this version worked for you? I have a couple of things I need to fix also and it would be really nice if these new teeth work well and stays actually stuck onto the gear.

michaelmays (author)fleebell2015-02-09

Does the section with the "new" teeth break off, or do they simply wear down? I was wondering the same thing. If the whole new part is breaking off, it may be worthwhile to bore a few tiny angled holes (maybe 2- or 3mm deep, whatever can be accommodated) into the "old" part of the gear, allowing the epoxy to fill them and form a "cleat": this creates both a chemical bond and a physical anchor.

Of course, if it's just that the epoxy is wearing out or breaking down prematurely, you might simply be looking at having to go through this process as many times as you can stand before just breaking down and buying the replacement. ;-)

fleebell (author)michaelmays2015-02-09

I had the epoxied area locked in well and even pinned using tiny bits of straight pin wire. The teeth were breaking off the rest of the epoxy. I need a stronger or harder curing epoxy I guess.

villalta (author)2015-02-09

Excelente idea.... lo felicito por compartir la tecnica para reparacion del piñon.


absolutekold (author)2015-02-09

Great fix.. One trick taught to me by an old machinist would be using some plastic wrap (Saran like stuff) to wrap the epoxy on the broken gear right before molding. This helps give you a little clearance between gears and saves a lot of cleanup on those teeth if in a precision. I can easily imagine any roughness, peaks, and sharp bits left in the epoxy slowing chewing up the mating surface on the other gear if it's plastic. If you haven't done any cleanup on that gear beyond what is in the photo I'd suggest it or at least check that it isn't beating up on that other gear. This is less of a problem when working with metal but of concern with all fixes where the fix material is notably harder than the original mating surfaces. When that old machinist showed me this trick he had also dremeled off the previous broken threads and drilled 2 locating holes to help affix the epoxy although it isn't necessary for a low speed / low torque application like this (we were working on a lawnmower that he had made a custom geared setup for attaching a snowblower whose motor was doa to a PTO). Keep up being awesome.

** precision application. **

biglabrat (author)2015-02-09

This is great! I use to work in the power tool industry and have seen my share of broken gears. This is a great solution for cheap.

aperkins01096 (author)2015-02-09

Perfect instructable! Thank you for making it short, easy to follow and on one page, too.

robi_ncc (author)2015-02-09

can any one tell me that "what is the relation between speed and torque?"


what is the formula to make pinion?

wb7ptr (author)2015-02-09

I actually repaired the timing gear on a motorcycle one time with that epoxy steel. STRONG stuff. Also repaired the engine block on the same bike. This idea is brilliant and I'm definitely trying it on the transport mechanism of an old tape deck I have which has some plastic gears which are broken. Nothing like an engineer in the fold here!

About This Instructable




Bio: I can imitate improvise and upgrade as long as i can
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