Copy a Key by Casting!




This Instructable will walk you through the steps required to copy a key just like secret agents do in movies. This includes making the impression of the key and casting it in zinc metal. Note that while copying keys that you own is absolutely fine, copying somebody else's key without permission or with malicious intent is almost certainly an offense punishable by law.

I really enjoyed the process of creating this key copy, mostly because I was shocked to discover that it actually worked. What had started as an offhand, careless afternoon activity turned into a viable copy of my house key. Enough small talk - let's begin key smithing!

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Step 1: Make the Molding Compound

As I said before, this project was not very planned. I was bored and wanted to make a copy of my key in one day, so I had to get creative in order to accomplish the whole process in one day. Thus, some of the steps listed here may be less than standard, but hey - they worked!

To copy the key, you will need an impressionable substance capable of withstanding the molten zinc at ~800°F. Plaster works well for this purpose, as shown in this video. However, plaster also has a bunch of water in it and takes quite a while to dry out completely. When pouring molten metal, you do not want water in your mold - it will create steam, bubbles, and possible explosions. So, in order to copy the key on one day, I had to figure something else out. My solution was very creative, to say the least. :)

I used dried-out carpenter's wood filler paste as the base material for my molding compound. It was the first good item that I saw around the house. If you replicate this project, you should mix around 3/4 cup of wood filler with a very small amount of water. Mix it well; it should be a soupy paste. Next, add some flour to your paste until it becomes thicker. Eventually, you should be able to remove it from your mixing container and then knead it like bread dough.

Note: This project is not gluten-free. :)

After you have kneaded your dough until it is soft and well-mixed, it should feel just like a good hunk of bread dough.

Step 2: Make the Key Impression I

Grab your key and some Pam (or other) baking spray and get ready to bake some metal-casting bread! Once you have your key and know its general size, make a cardboard box to hold the molding compound. You can do this by cutting an oblong plus sign into some cardboard and then taping up the arms of the plus. Then, press about half of your molding compound into the box and pack it in tightly. There should still be about half of the depth of the box left for the other half of the mold.

After your mold half is in the box, grease it with your Pam (mineral/cooking oil should work just fine) and then press your key into the center. The key should go in about half way.

Once the key is in the mold half, dry the mold out the harden it. Since my family has a bird in the house and birds are sensitive to poor air quality, placing my mold in the oven and baking the heck out of it was not an option (possible fumes could be problematic). Thus, I has to get creative again. I used a powerful work lamp as a makeshift oven to sufficiently dry the mold face out. I placed the lamp directly over the mold and made sure that there wasn't much space between the mold and the bulb. Surprisingly, the mold got quite hot in the miniature "oven." Just a note of warning as I write this - keep an eye on your mold to be ready in case anything goes awry. The insurance company would have a good laugh if you told them you burned your house down using a lamp as an oven. :)

After your mold is nice and hard, take it out, turn the lamp off, and proceed to the next step.

Step 3: Make the Key Impression II

When you disassemble your mold to remove the key later, you will need a reliable way to reassemble it. Use a drill bit and a drill/drill press to make four shallow holes in your mold block. These will translate into bumps on your second mold block that will line up every time.

Now, re-grease the mold face and take out the rest of your molding "dough." Firmly press it into the cardboard box, making sure to press the dough into all the details on the key. Then, place the entire assembly back under the lamp "oven" for a while.

Once the mold has baked for a while, take it out and slice off the cardboard box. Mine had absorbed some water so it was very soft and easy to remove. Put the mold back into the lamp "oven" to bake for a while longer.

After the mold is hard enough to knock knuckles firmly on, take the mold halves apart. The grease should have made a non-stick layer, so they should release easily. Remove the key carefully with the edge of a knife or flathead screwdriver and return it to its proper place.

If your mold halves still feel moist, bake them until they are harder and completely dried out.

Step 4: Finish Mold

Now that the mold is dried out, we need a way for the metal to enter the key impression. Using a utility knife or small coping saw, cut away at the top of the key mold to create a sprue channel for the metal to flow down into the key. I added mouseovers on the first picture to illustrate where these are located. It helps during the metal pour if you make the top of the sprue wider, like a funnel.

Additinally, the air inside the key impression must be displaced by the molten metal. To facilitate that process, cut some tiny air vents in the mold. Don't make them too big, or the metal will flow right on out of your mold. Foreshadowing!

When the mold is done, put it together again (those dimples and bumps work so nicely, don't they?) and tape it together. Electrical tape works well for this job, as do rubber bands.

Step 5: Cast the Key!

This is the fun part! Molten metal! I really love metals in their liquid state. They are just so awesome!

Zinc is a great metal for casting this project, so grab some pennies made after 1982. You will probably want about 10. Also get a torch, propane or otherwise, and cut a soup can down to about 1" of side wall. This will be your crucible.

Put the pennies in your crucible and hold the crucible with some long-handled pliers. Apply the torch to the pennies and don't by shy - zinc needs a fair bit of heat to melt with a torch. Once the pennies are molten, scrape off the copper shells with a screwdriver. The screwdriver should not be harmed in this process - any metal stuck to the head can be easily pried off.

After you can see the shiny surface of the molten zinc, pour it into your funnel-shaped sprue on your mold in a smooth motion. Don't pour it too fast or else you run the risk of spilling. It is fine if the metal overflows from the sprue - this will just be removed in a later step.

Step 6: Fail Once

Here is where the project gets really interesting. When I melted what I thought was an ingot made from a zinc wheel weight, it melted within seconds. Maybe 15 of them. Surprising for zinc. Or maybe it wasn't zinc... I poured the metal into the mold and it promptly ran out the bottom. This is why it is good to have something under your mold to catch any mishaps. Apparently, I had a crack in my mold seam.

After I collected the metal from the bottom of the mold, I remelted it and recast it. The metal left in the crack in the seam of the mold prevented any more from running out. However, I didn't have enough metal in my crucible, so the key didn't fill all the way. To fix the problem, I melted some zinc "pot metal" that I had lying around and then poured that in on top.

I opened the mold up after the metal had cooled and... horrors! It didn't work! There were two junctions where I had poured molten metal on solid metal, and they had not fused at all. Additionally, the metal had run out along the seam of the mold all over the place! The key was a dismal failure.

On top of all this, the supposed "zinc wheel weight" was most certainly not zinc. It was very bendable... not good for a key. I really don't know what it could be, since I had previously scratched it and it seemed too hard for lead, which is another common wheel weight metal. I discarded the soft metal and saved the zinc pot metal that I had poured on top. Time to try again!

Step 7: Fail Twice

Since the metal had flowed into the seam of my mold, I added some clamps to squish the mold together better. I also added a zinc penny ingot to my zinc pot metal rescued from key attempt one. I then melted this combination and poured it into the mold again.

I opened up the mold again and... gasp! It was defective to a grand degree! Apparently I had put too much pressure on the mold and had squished its features into each other. At least this time the metal was nice and solid instead of bendy!

Metal is reusable for casting purposes (awesome, huh?), so it is time to try yet again...

Step 8: Third Time's the Charm!

To fix the squished mold, I brought back my house key and put it in the mold again to restore it's original shape. Then, I used some simple rubber bands to hold it together. I set it up on my wood base to catch any spills, melted the defective zinc key, and...

It worked! As you can see from the third picture, the metal did not overflow into the seams nor did it fail to fill out the key impression. The fourth picture shows the casting.

Here I would like to draw attention to an important point. What saved this project from being discarded as a failure was perseverance. Even though I failed an astounding two times (my other casting projects have turned out on the first try), I kept modifying my approach and trying again. This principle is the basis for science and invention and can be applied to any endeavor. "If at first you don't succeed: Try, try again." - William Edward Hickson

Step 9: Finish the Key

Admittedly, the cast key doesn't look like much right now. However, it shows promise.

Your casting may turn out just like mine - rough. If that happens, it is still salvagable. Another great time to work on maker perseverance. :)

First, cut off the sprue and the air vents. Then, use small jeweler's files or other mini files to remove the extra bits stuck to the key notches. Since you will not be doing this illegally (right?) and will have unrestricted access to the key you are copying, you can lay one over the other as a template for touch-up filing. File the key until its dimensions match those of your original key's.

My key had some metal in the grooves, so that had to be removed as well. For minor cases of this issue, a triangle or square mini file works very well. For bigger cases, use a Dremel with an abrasive cutting wheel and keep your original key handy as a reference. I found that it was helpful to periodically test the key in the lock to gauge where I was at in terms of shape.

Once your key fits smoothly all the way into the lock, try turning it. If it works, you are done! If your key doesn't turn in the lock (like mine), then you probably didn't get the notches quite right. I found that watching this video and reading up on locks was helpful in understanding what was going on. Take your original key out again and closely compare it to your copy by placing them on top of each other. Are there any teeth that are too large? Is there metal in a place that it shouldn't be? Try a few minor modifications with a mini file and test the key in the lock again. Mine worked after two touch-ups.

After your key is done, drill a keyring hole in the handle and smooth any rough edges on the handle with some sandpaper. Brush it lightly with a wire brush and then wash any grime off. Then, admire your handiwork!

Just to prove that this actually works, I made a spy-movie themed clip on a dark night of me testing the key in my lock. As you can see, I try the door beforehand and it is deadbolted, so the door wasn't unlocked the whole time. :)

It is pretty amazing what a few spare hours and an inquisitive mind can do! I began this project by using unconventional materials for just about everything with no knowledge of key-copying whatsoever and ended up with a fully functional house key! If I can do it, so can you! Give it a shot today and prove your Mission Impossible mettle!



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    54 Discussions


    Reply 3 years ago

    I honestly don't know. If you got your aluminum hot enough and poured quickly into your mold (a funnel-shaped depression might help), I would give it a good chance of success. You should try it!

    My mother took a correspondence course on locksmithing in the 60's so as a child I was familiar with the ideas of getting the key right. Later, as a custodian at a high school, I was always irritated that the teachers would let certain kids walk around with the keys and trust them with them for hours. As a result, some little genius copied those keys and there was a set the kids themselves had. I was accused of not doing proper secutiry when I kept begging them to change the locks and not trust the kids with their keys. Yes, the kids got in several times. Once got a saw from the metal shop and then went in the office to try to saw the safe open. They set off the fire alarm making smoke doing so. There was never any money stored in the safe, the office staff just kept paperwork in there. If there had been money it would not have been much, very small, unsuccessful school.


    Reply 4 years ago on Introduction

    It's great you tried it! I would recommend melting some zinc pennies, because zinc is much harder (and stiffer) than pewter. Also, watch that the sneaky key doesn't break itself off in your lock. :)


    4 years ago on Step 9

    I do commend you on your self discipline, and the understanding that without failure it's difficult to understand the success.

    1 reply

    Reply 4 years ago on Step 9

    Thank you. It is quite nice to look back and see that repeating the failed procedure eventually led to such a rewarding success.


    4 years ago on Step 9

    Maybe a tip- The vents should go to the top. The vents and sprue should attach at flat parts you will have less difficulty cleaning up the pattern when you remove the casting from the mold.

    key molding.jpg
    1 reply

    Reply 4 years ago on Step 9

    Hey thanks! That sounds like good advice for the next time I do this and for anybody replicating their own keys. Also, thank you for including the picture - it helps with visualization.


    4 years ago on Introduction


    What kind of bottle of gas is that? Is it propane? mapp gas, etc. What would i look at lowes or walmart regarding that gas bottle?

    1 reply

    Reply 4 years ago on Introduction

    I used propane with a normal entry-level self-igniting torch head. MAPP gas would work just as well and could probably be used for other high-heat metal-melting projects (gold, etc). In a store, you should find the blowtorches in the plumbing or general tools section. Good luck!


    4 years ago

    Nice job. I would like to point out to all those critics out there (especially ac-dc) that this IS instructables where we are supposed to find new ways of doing things, and have a blast doing it! Though purchasing a key may be a better way to acquire a house key, this was obviously a hobby project and was a cheap and fun way of doing it.

    1 reply

    Reply 4 years ago

    Thank you! It was a very fun project, especially playing with a molding compound that I am nearly certain nobody has used before.


    Reply 4 years ago on Introduction

    It's your own fault if you choose to live so far from civilization that it takes 30 mi. drives just to get a key made anywhere.

    Otherwise, time is money so yes rather than spending an hour or more doing this it would be cheaper to pay a buck to get one made and it'll last a lot longer, work a lot better in a less than perfectly clean/operational lock cylinder.

    Spy angle aside, if you're supposed to have a copy of a key then have one made that's good for the life of the lock ahead of time.


    Reply 4 years ago on Introduction

    Either way, I've got a half dozen key machines, but without the key to copy and a blank to cut it on to, casting is a lot faster!

    There are plenty of keys out there that your local hardware store doesn't have, and even some your locksmith can't get hold of.

    Good Instructable. Needless to say, there are "secret squirrel" versions of this available.


    Reply 4 years ago on Introduction

    Well actually, I have experimented with Field's metal, and it is quite fun! I keep a blog, so you can read about what I did with it right here: In a sort of funny coincidence, I contributed to the very Wikipedia page you referenced me to! Field's metal is also an awesome substitute for mercury.


    4 years ago on Introduction

    you can download "CIA Field Expedient Key Casting Manual" to see something similar. I would think with all the epoxy resins out there you could use some type of plastic you could use instead of metal? might only produce a key that could be used a few times though.