Ring casting (by alaric)
A friend has asked me to cast her some silver wedding rings. So I am adapting my aluminium casting experience to silver...
The thing to use for silver moulds is cuttlefish bone, which is soft enough to easily carve into shapes, but can withstand the heat of molten silver. For a single pour, at any rate.
In order to get a repeatably round shape of the correct diameters for the two rings, and so I can quickly carve new moulds if my pouring fails so I can try again, I decided to make boring tools that carve ring shapes of the correct diameters.
As you can see, they're made from nails, hard soldered together, and ground to a cutting tooth at the end. The central spike goes down a guide hole I drill in the cuttlefish in advance.
The tool needs to come down exactly perpendicular to the flat surface of the cuttlefish (made by sawing one side off and then sanding it flat), so I made a special jig to hold them:
Then it's just a matter of fitting the tool in a chuck and bringing it down. I first tried rotating the tool by hand, but the result was a bit rubbish, so I bit the bullet and just turned the Dremel motor on, which produce a quite perfect circle.
I made a couple of moulds, each with a matched flat cuttlefish to go on the other side. I had to carve channels for the silver to flow in by hand, using a screwdriver for rough gouging and a craft knife for the finer parts.
The silver was heated by blowtorch, in a refactory cup called a scorifier:
But first I had to prepare the silver I was given - in the form of a coin, which I felt a bit bad about sawing in half:
I melted half of the silver and poured it into the first (roughest!) mould:
When I cracked it open, it seemed I'd not used enough silver, but everything had otherwise gone well:
So I pulled the incomplete casting out, crushed it up, and added the other half of the silver, and gave the second mould a go. Here's a picture of it with the channels cut, before I clamped it:
I put it all together and got ready for some melting:
But this time, as soon as I started pouring, the silver suddenly froze on me, so hardly anything went into the mould:
It seems that the larger mass of silver wasn't heated up quite as far as the first pour had. I need to rearrange my firebricks to make a better forge to heat the silver in, so heat loss is slower, I suspect...
Metalworking | alaric | 
Mon 28th Nov 2011 10:26 pm
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By Faré, Sun 4th Dec 2011 @ 10:58 pm
I thought the thing to do was (1) design the ring with CAD software (2) get it printed (3) make a silicon mold of the printout (4) pour liquid silver in the mold (5) ... (6) profit