Copying a Key

I have not posted recently, and I am receiving comments complaining about that fact. I will blog twice today, and with cool stuff!

First, would you like to be able to easily make a perfect copy of a key? I figured out a way to do it. I started by building a linear 3D scanner, which I will describe in my next post, but a quicker and less technical way to do it uses urethane casting.

I purchased “Rebound 25” from eBay, which is “Brushable Silicone Rubber.” This is a two-part system that hardens in to a flexible, carve-able mold. I mixed enough to fill a small paper coffee cup and suspended a key using two bent paper clips. Here is an image os the key suspended as the rubber cured.

IMG_6177 - Copy

Once the rubber cured, I twisted and removed the key. Then I sliced one side of the new mold so that a cast key would be easy to remove.

Here is a picture of the sliced open mold.


I allowed the mold to close, put it back in a new cup, and poured in “Specialty Resin and Chemical Model-Pro.” That is a two-part urethane plastic. I mixed equal parts of ‘A’ and ‘B,’ poured then in and bumped the table top to make sure all air bubbles came out.

Here are two pictures of that process.

Once the plastic hardened (about 15 minutes) – turns white, I removed the key copy as shown in the pictures below.

The key was weak, and broke without much force.


My next step was to add a paperclip core. I carefully pushed in a metal shaft and poured a new key as shown below.

IMG_6194 - Copy

After this key cured, I cut off the top plastic with a bandsaw and clipped off the top of the paper clip with a wire cutter. The result feels strong enough to function as a key.

I am now interested in adding carbon fiber pieces or fiberglass shreds to the resin. I am pretty sure that I will need to evacuate the mold to remove all air and make sure the thicker material finds its way to the bottom of the mold. Like I said though, I am pretty sure that this plastic key will work. I plan to duplicate several test keys to verify that the result is reliable and consistent.

This complete arrangement is based on inexpensive, commercially available material. I thought about it, and tried it this morning. It seems to work pretty well. The key copy looks identical to the original, and I can make as many copies as I want. The mold is reusable.


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