An Axe to Grind

I carved a fair amount of the first sand mold using hardwood pottery tools. They worked well, but wore down pretty quickly. I switched to a set of dental tools, which don’t wear down as easily, but don’t necessarily speed up the process. I could see making a set of bronze tools for carving the material. One of the tools has a small spoon shaped end that is perfect for cutting even and consistent flanges.
The depth of various parts of the mold is measured with a bamboo skewer. I shared a studio with a potter who used them to make sure that his pots were uniformly sized and borrowed the idea. I can make a mark on one skewer to measure the depth and then move it over to the duplicate half of the mold and place it on the mirror image of the first place. A second skewer is laid across the mold, perpendicular to the upright measuring skewer. This easily shows me how much deeper I have to carve.
The sides of the molds are scored with a hacksaw to make sure that they are properly aligned for casting.

After carving a couple molds I’ve found I can turn out a set of them in about an hour. Although they aren't permanent molds, that’s not bad considering that these molds hold up much better than the clay molds I made last semester.

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The two palstaves after a little bit of cleanup.

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Unfortunately this type of mold tends to crack as the metal cools. However, they are still a great substitute for sandstone.

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Delta resin with silica sand mold for a palstave.

This semester I began with a new mold material. Delta resin with silica sand and catalyst. This is a resin based medium that duplicates soft sandstone. It’s easily carved, even with wooden modeling tools and has a texture that is remarkably like sandstone. Unfortunately the resin breaks down at high temperatures and while it makes a great mold, it still is only good for one pour. On the plus side the carving goes quickly and I don’t have to wait for it to dry as I did with the clay molds. It didn’t take long to make molds for two axes and they were ready to cast with only a little preparation. To make a smoother surface I mixed graphite and zircon (50/50) and added enough denatured alcohol to make a thin solution. This was painted inside the mold and then lit to burn off the alcohol.

The molds did not require warming and after clamping they were ready to cast. This time I used a standard bronze of 90% Cu and 10% Sn. The pour went beautifully and the axes need very little finishing. I was able to break off most of the flashing with my fingers and used a grinder to take off the sprue. I had expected some shrinkage and so had made the molds slightly larger than the models. However, there was no shrinkage so I’ll have to allow for that for the next pouring. I now have a set of axes as soon as I can find some serviceable branches to make into hafts.

Notes: In order to estimate the amount of metal needed, sand is poured into the mold and then weighed. The weight of the sand x 5.3 = the amount of metal needed for casting.

References: Potratz, Wayne 2005 Hot Metal (Minneapolis: Turtle Sign Company)

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