A simple casting mould for hot metal key copying

Copying keys with hot metal (94 °C) casting.

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This casting mould can be used to copy keys with hot metal casting. The aluminium cast holds a temperatur resistant clay which will give a negative form of the key you want to copy. The negative form is then used for casting.
I did some experiments in the past with silicon moulds, but I was not satisfied with the long (≈ 1 h) cureing of the silicon. Since I am into lockpicking and related topics at the moment I found a video from DeviantOllam on Youtube and this was the inspiration for this project.
This is the first time for me working with a mill, so excuse the crudity of the finished object. I am sure that one with more experience with this kind of machine will have a nicer looking result.

About the metal alloy

I used Rose's metal for three main resons over Wood's metal.

First I has a higher melding point and is therefore mechanically stronger at the same temperature than the lower melting alloy. Mechanical strengh is an important factor for copyed key since the turn of the core puts a lot of torsion on the key. Softer metals break or bend easier.

Roses metal: 94 °C

Woods metal: 70 °C

The second reason is the chemical compostion of the alloys. Roses metal does not contain cadmium. Both of them are composed of Bismuth, Lead and Tin (and Cadmium for Wood's metal). The lead makes both them not the most healthy alloys but at least Roeses metal does not contain lead.

The third reason is especially important for casing: Roses metal does not contract on cooling.

svg+xml - 2.97 kB - 12/01/2019 at 19:51


  • 1 × Rose's metal, melting point 98 °C alternative wood's metal (mp. 70 °C)
  • 1 × heat resistent clay e.g. Fimo clay
  • 1 × Sheet aluminium, about 10 mm thick
  • 1 × talcum powder

  • 1
    Milling the mould

    In this section I wil briefly discribe the steps of making the mould.

    I choose a pice of 10 mm scrap aluminium sheet metal to start with and cut a strip out of it with a angle grinder.

    The markings are about 7 x 4.5 cm apart (see drawing). the pieces were cut to length with a bandsaw. The bottom egde was already straight so I used this as a reference for flattening the other edges with the mill. The last step to get the raw aluminium pieces was to remove the top layer of paint. Accidentlly I removed a lot more then I wanted (about 1 mm per side) and endet up with 8 mm thick pices.

    The cutout is 4.5 mm deep. I milled the broader part of the mould with the same tool (32 mm) I used to remove the top layer from the stock material. The lenghly section was milled with a 20 mm tool. Strangely the second tool made a much nicer surface than the bigger one (I also used this to flatten the sides)I have no clue why, I guess I have a lot to lern :)

    For the alignment pins I taped the two pieces together and drilled the 3 mm holes. Some 3 mm round scrap metal was cut to length and the pins were glued in with epoxy.

    So after some final touches at the beld grinder to smooth the corners I ended up with this:

  • 2
    Key dublication

    Step 1: Fill the cavity of the mould with Fimo or a equivalent polymer clay and flatten the clay e.g with a round pice of wood or core follower. To prevent the two clay parts from sticking together while making the key indentation, powder some talkum on it (Potato starch also works fine). 

    Step 2: Position the key in a way that the teeth are fully surrounded with clay. The more of the upper part of the key you can include the better.

    Now press the to halfs together, stepping on it helps. The excess clay is squirted out. You can form a funnel out of this for easier pouring.

    Step 3: Carefully open the mould and remove the key. Take care that you do not damage the indentation. Then take a pointy object (e.g. a pick) and make a thin canal from the tip of the indentation/key to the top so, that the air can escape while pouring the molten metal into the cast.

    Step 4: Heat the alloy (Rose's or Wood's metal) above the melting point and quickly pour it in the mould. Wait a couple of minutes for the metal to cool down then open the mould carefully. If the key is only partially casted, the alloy was not hot enough and cooled down to quickly.

    (Sorry for the blurry picture :/)

    Step 5: Remove the key from the mould. You may have to remove some excess material, but usually it works right away. Be carefull when inserting the key into the lock, although the alloy is quite hard it is not as hard as the original key. When inserting the key for the first time you may need to wiggle a bit until it works properly. After that the key is "ground" to fit. Here I dublicated the key from a Brug Wächter Gamma 700 pad lock.

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