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IndustryArena Forum > MetalWorking > Moldmaking > How to make 1 gram molds for gold (1/2 gram for silver) and various 1 oz shapes

# Thread: How to make 1 gram molds for gold (1/2 gram for silver) and various 1 oz shapes

1. ## How to make 1 gram molds for gold (1/2 gram for silver) and various 1 oz shapes

So i pulled the trigger on this idea the other day and i plan on melting my own gold and silver products. I bought a CNC router (probably overpaid but oh well) and it is on route. I am curious mainly on how to use this machine to make graphite molds of 1 gram size bar or round (gold) and also 1 oz (silver) molds with various shapes. Are there any good video to watch on how to do this? do i just need to know more math to figure out the dimensions of the cut? any help you can throw my way to get this off the ground would be very welcome

2. ## Re: How to make 1 gram molds for gold (1/2 gram for silver) and various 1 oz shapes

Calculating the volume to an odd shape cavity is more art than science. But Archimedes figured out how to do this a couple thousand years ago. The easy way to do it in this case, would be to make what you think is about correct, cast the piece, and weigh it. Then make corrections to the scale of the drawing as a percentage of the original weight and try again. The good news is that graphite machines very easy, messy, but easy.

3. ## Re: How to make 1 gram molds for gold (1/2 gram for silver) and various 1 oz shapes

thank you! i will experiment nd figure out how best to do this! thanks agin

4. ## Re: How to make 1 gram molds for gold (1/2 gram for silver) and various 1 oz shapes

These would have to be 2-piece molds, since you're never going to be able to fill an open-face mold accurately enough. Also, a gram of metal isn't going to fill the mold from the force of gravity alone; surface tension will make it want to form a sphere that will perch on top of your graphite mold but not go in. An ounce will probably dribble down in there to some extent, but isn't enough metal to produce a good casting. Also, graphite acts as a heat sink, so your molds would need to be pre-heated to work effectively. You could look into adapting your molds to work in a centrifugal casting machine, which is what jewelers and dental technicians often use to force small quantities of metal into molds.

While graphite is machinable, it wears tooling out quickly. It also makes a fine dust that's conductive, and will short out any electronic equipment it manages to infiltrate. You might think about machining your items in wax or something less problematic to work with, then sending the models you produce to a production casting house for replication - expect a pretty long learning curve before you're making good cast metal products yourself.

5. ## Re: How to make 1 gram molds for gold (1/2 gram for silver) and various 1 oz shapes

I hope that you realise that a mold made for silver would make a gold shape that would be nearly 2x heavier. ( just read your post title.... you are aware)

Checkout "density" of different materials .... this talks about material volume relating to it's mass.
It is possible to calculate the ingot mass on the actual volume of the cavity, and get close to your required mass