Resin Casting Gears for Power Wheels




About: tons of prototypes, lots of proof of concepts and the final version is something completely different part of the story.

This is my very first instructable and I hope you will enjoy it.

Please any mistakes caused by my bad english. :-)

Some of you will ask me the question, why not just buy a ready to go gear from the shop or ebay for the usual $19,95. You don't need to ask me that, as I have produced these gears as POC for myself to know if it works this way and if I am able to it. Maybe some tim will come and I will need the procedure to make some gears quick and will not be able to buy any replacement parts. Also remember, these parts are much stronger than that you can get in your store.

Step 1: 1. What Do We Need for the Mould Mixture

For the first step we will need any silicone fill, but not the one you use for the bath works.

For the first step I have used "Creato RTV/NV" available almost everywhere, but quite expensive. It is about 30€/kg.

It is simple to use. Just take a smaller sample form, put it on the scale and set tara. Keep a piece of paper between the scale and the form as the Creato components and not easy to be taken off any surface.

Once done, fill the RTV (the white silicon rubber) into the form filling it at about 80%. The wight you can read at your scale is now 96-98% of your mixture. The missing 2-4% will need to be filled by the hardener (NV).

Once you're done having the 100% mould mixture, mix it for about 10 Minutes to be sure having a constantly deployed the hardener.

Step 2: 2. Preparing the Gears to Be Copied

ok. The silicon mixture is ready and now the gears, which are not damaged need to be cleaned ( I have used a usual industrial cleaner). Afterwards a simple electronics contact cleaner "Kontakt 60" can bee used to prevent any resting of silicon an plastic gears. I know there are those very special chemicals, but the $3,99 spray works like a charm. Use it only as much as you can see the gears being wet. than put them with the bigger site to the bottom. That's it!

Now the tricky part. Spray the cleaner on the surface of your mould.

For the smaller gear I've used the "Ferrero Rocher Chocolates - 16Pcs" Box.

For the bigger one a 50 DVD spindle is the best choice, but wasting more silicon! It is up to you.

The tricky part of this step is to keep the silicon at even surface, preventing uneven moulds. This will cause difficulties on creation or resin forms later on.

Step 3: 3. Silicon - Cosmetics After 24-36h

After 3 days I took a look at the forms. It looks like it is better to keep it in a warm place. MY work bench was too cold and I moved them to another room. The result was a finished form after 12h. You can just touch the surface after 24h and it should feel like,... a piece of hard silicon.

Remove the forming gear (i was using the contact 60) and once it is out, remove the silicon form out of the plastic form.

Once done, turn the form upside-down and prepare the surface cutting any faulty fillings. This Step is very important. However, it only works this way as the biggest part has to be at the top. You will want to be able to pull it out afterwards.

Ok, here is my favorite: Use the contact-60 to prepare the surface for filling with resin. ;-)

Step 4: 4. Preparing the Epoxy Resin and Filling the Form

Somewhere, I really do not remember where, but it was mentioned in any blog to use metal powder or smaller parts to make larger resin fillings stronger and quick force resistant.

I did take some of those Metal parts from my work bench and mixed it with the resin.

Oh, yes the resin is the "L" with 2:1 given mix proportion requirement. It needs about 5h to begin to get hard.

You will ask me, why not to take the 3 or 5 minute version. It is very simple to answer those questions. : It would get too hot and break by itself, or get burned or get unstable. This is the right component to create a stable gear.

Once you have a form filled with 2pcs of resin and 1pcs of hardener, put the metal powder into it and begin to mix it together. You don't need to hurry. 5 hours is a long time. I have spent 5 Minutes on mixing all together until the resin did not look like two different fluids being mixed, but like one constant fluid with metal dirt.

After filling about 80% of the form you have to start to put some attention to the surface and look if it is still even.Fill more and more of the resin and look at the leveling. When everything is ok, than put more resin than needed and it will be a little bit less once dried. It should not be more than 1%, but maybe you will be missing it like I did. Try to prevent it as it is simpler to polish the surface, until You have the exact height, than trying to put more resin after 2-3 days and expect the "sandwiched" resin will last like it was a one piece construction .

Step 5: 5. Pulling Out the Gears, Cleaning, Polishing

My favorite KONTAKT-60 has been used to pull out the gears out of silicon preventing any damage in the white mass. The cleaning has been done with the usual industrial cleaner. The polishing was easy. I used all my existing wood tools for that purpose.

Step 6: 6. the Result

the very final and funny step was to compare the original gearbox and the refurbished one. Of course the original one was very quite due to soft plastic. I suppose, the this is the reason for building such devices will need to be tough. My rebuild would last a lot but maybe when getting broken, it would just destroy both new gears directly.

We will see. The test with 18V on both gear boxes in parallel was ok for a 10 Minutes run without any resistance on the wheels. For now it is very stable built and holding the gear by myself did not stop tu make the turns and went forward forcing the turns to slip through my hand easily.

Please let me know if also you have been able to rebuild any gears using this method.



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    56 Discussions


    1 year ago

    Hi, is it possible to some advice about casting a mould my dad wants to try and recast this (please see attached picture) but with the heads of the cog so worn down will he be able to make a cast?

    Many thanks.

    1 reply

    Reply 1 year ago

    Hi there oxbox,
    good question! I would proceed like this : Prepare all for the silicon and put the broken gear like described above. Let the silicon be hard, take out the gear and then cut out the silicon part at the place, where the gear had the missing heads. Perform the cut along the maximum radius of the heads which are still not broken. Just like a circle along the maximum radius of the heads. Afterward go for filling with resin and hardening and now a tricky part.
    There will be a note of the vendor of the resin you will use pointing to the time, when the resin ist still good for any forming after casting, before it gets really hard. It is like "after 3h it is easy to cut and after 5h it is hard enough and really hard". It would than be possible to take it out of the silicon after 3h and cut the heads in to it.
    What I did is to cut with a knife the heads and test the gearing. When it was not enough or uneven, than I used a small drill to do the cosmetics, until it worked fine. It took me some 3 hours until I was happy with it.

    I hope it helps.
    Please let me know how your little project is progressing and if you were successful.
    I wish you the best!


    2 years ago

    glad i ran into this this. my daughters hummer stripped the smallest gear that makes contact with thhe motor now i can repair it!


    4 years ago on Introduction

    thank you you explained tare much clearer than I did how is the gear holding up? well I hope

    Hi robi_ncc, the exact formulas can be found in the package if the components and I took it exactly like mentioned by the vendor. The only difference was the metal powder and temperature. I kept the part hardening in a temperature about 20 degrees Celsius for about 24-48h, which the first was for the smaller gear and the second for the bigger one. Afterwards, I took the parts into about 25 degrees for a day.
    I hope it helps.
    Many thanks for your comments!

    Hi there robi_ncc. To be honest, I used the formulas given by the vendor. For the mold it was something about 6/100 and for the resin 50/100. But it always depends on the products use use. For the powder it was less than 20g for both gears mixed up with the mixed up resin and hardener mixture. The most important part of the procedure was to wait 30 minutes and remix the powder - resin solution, otherwise the metal goes too much to the bottom. The gears I have made were not perfekt, as you can see on the pictures, bit for the next time I would try to wait another 30 Minutes and afterwards try to fill the mold. We will see.

    Thanks for your comments!


    Reply 5 years ago on Introduction

    Then, you will love this one, by another Gizmo Maker, a 1/5 Sherman Tank, made of wood, for anyone to make:


    Reply 4 years ago on Introduction

    Edgar, this is amazing! I just went through your blog and all mentioned sourced given by your URLs in the blog. Some of them has been bookmarked. ;-) My son is now 6y old and I think about to spent some time and money to build and custom a kids quad next year. I was thinking about a 4WD, but those are mostly built for adults. I did not find any solution for kids so far. Maybe a good frame and additional front drive will be the solution next year. ;-)

    Many Thanks for your comments!


    Reply 4 years ago on Introduction

    My pleasure, to divulge these things. :)

    Well, I don't know about quads, but this is a 3 wheeled Project, that can be added a 4th wheel, and a differential gear train for it:


    4 years ago on Step 6

    Very nice. Thank you for sharing. Did you use a sharp razor knife to trim the mould?

    Bill WW

    5 years ago on Introduction

    Good work on your first Intructable.

    You said "why not just buy a ready to go gear from the shop or ebay for the usual $19,95."

    This site is all about designing/building things. As someone said, spending 8 hours building rather than spending $8 buying. You did great describing the design/build process.

    3 replies
    jhproutyBill WW

    Reply 5 years ago on Introduction

    Johnny - great instructable, I'm thinking about applications as I write this. And Bill, you hit the nail on the head - it isn't about the object, its the process of getting there. I'm new to all this and having fun - though my wife wonders why I don't just find it on line sometimes!

    Thanks jhprouty! Do it and please let me know if the instructions worked for you. I really like the instructables page as You can share so many information about your smaller and larger projects including electronics, cooking, woodwork and e.g. making cakes! :-)


    5 years ago on Introduction

    very useful instructable thanks I will try it to make a gear and replace my scanner's broken gear.....