I made this brooch as an 80th birthday present for my Gran. I came up with the idea of making a brooch involving some kind of planet design. It took quite a few revisions, but eventually I came up with something that I was happy with.

The construction involved CNC milling, silicone mould making and pewter casting to create the finished brooch.

My first sketch of the brooch

To find the position of the planets I used the Fourmilab Solar System Live site. This lets you enter a date and shows you the relative position of all the planets at that time, perfect.

After I had my basic map of the solar system, I had a new problem…coming up with an attractive design. I went through a lot of rough sketches:

My final paper sketch

The nice clean vector version

2D view of the tooling vectors

3D Relief of the Brooch

The Brooch machined into a slice of Delrin

The mould had some alterations

The channels have been opened up

The tinkering involved cutting the finest channels in the mould with a scalpel to enlarge them to the point where the pewter would flow reliably. I decided this would be  quicker than remaking the Delrin mould multiple times and that I could file/sand off the excess.

The two-part wooden back piece of the mould

Two of the things that I  discovered along the way that helped me get a cast I was happy with were that if you dust the silicone mould with talcum powder then that helps the pewter flow much more easily. Secondly, preheating everything I could also helped a lot with getting the pewter to flow into the thinnest sections. I used a heat gun to preheat the silicone mould and a blowtorch to preheat the metal funnel.

In the end I managed to get a cast I was happy with and then it was just a few hours of sanding away from being finished! Easy!

Finished cast pewter brooch

All in all I think it was worth the effort and the main thing was that my Gran really liked it.

I was looking for a project that involved mould making, and asked my girlfriend if she wanted me to make her anything…she decided on some Seahorse earrings, so I set to work.

As you can see in the image above, I started by creating a 3D model in a fantastic program called ZBrush which allows you to sculpt digitally. When I was happy with the model I imported it into Artcam, a program for creating CNC toolpaths. I layed the model out mirrored so I could make a two-part mould. I included registration holes/bumps so that the two halves would line up correctly later on. Finally the mould was milled on my CNC machine into a slice of Delrin plastic, which cuts nice and cleanly.

Above you can see the silicone that will become the final mould setting in the Delrin master. I used RTV-101 from a company called Tiranti. I chose it because it’s temperature resistant to over 250C and so would be perfect for pewter casting. It’s fully cured in 5 hours or so, I just left it over night.

Here you can see the nice silicone cast. It’s taken up the detail really well and I managed to get rid of all the air bubbles with some strategic tapping when I poured the silicone.

Here’s a close up shot of the silicone mould.

The mould was then trimmed and cut in two. Luckily the registration holes lined up as planned.

The two halves fit together nicely. You can see the air channel to the left of the pouring hole.

For pouring I clamped the mould halves between some bit of MDF.

This is my first cast from the mould. I used some black polyurethane casting resin that I had as it was a bit easier than messing about with pewter. It came out very well, the only dodgy bit was the very end of the tail, but that was my fault for putting the air channel in right above it.

Ah a fine little fellow! It’s a good feeling to get a proper physical version of something that you created on a computer.

Finally we have the finished product. Casting in pewter wasn’t quite as easy as the plastic. It doesn’t like to flow into all the crevices of the mould on its own, so I made a simple metal funnel with some pipe and the end of a small CO2 canister (the kind you find in BB guns). I heated the funnel up in the blowtorch I was using to melt the pewter, this stopped the metal solidifying instantly instead of flowing into the mould. With a pair of pliers I held my funnel into the opening of the silicone mould and then quickly poured the pewter. Because it has nowhere else to go, the weight of the metal above forces the pewter into all the corners nicely. Before using the funnel I was getting very poor detail and incomplete filling.

After giving them a bit of a polish and hooking some earring bits through the holes, they were done! I’m pretty happy with the way they came out, pretty close to my original computer model at least.

Using my little CNC machine I knocked up this little star to go on the top of our Christmas tree. It was cut from a piece of 2mm x 40mm aluminium stock using a 2 flute 1mm end mill. The pic above shows it still held in place in the stock by 2 small tabs I added to the outline toolpath.

Here’s the star popped out and given a bit of a polish.

Finally, it’s in place on the top of our tree.