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Orgone Technical Bulletin # 35
Easy Tetrahedron and Pyramid Molds
How to easily make a tetrahedral mold for casting resin. I have not tried this with polyester resin, but it works great with epoxy.
First, since I happened to have some heavy non-corrugated card stock, I cut out a triangle to use as a template. Can be used many times.
It need not be equilateral. One can make real pointy tets if one wants. But I usually like to re-cast my tets inside cones, so make them of similar slope as funnel molds.
Then, I used that template to trace outlines of 3 triangles in cardboard, cut them, and coated the best side of each with wide clear tape as shown:Then I cut the excess tape off.
I try to avoid getting wrinkles in the tape, but it really doesn't much matter if I will later be casting over the tet.
Then I tape the 3 triangles together using more tape like this.
I only tape in 2 places, and on the taped inner sides of the triangles.
I left a slight gap for hinge space. Because I wasn't thinking. Hadn't made one in years. You don't need hinge space, because it's on the inside.
But it's OK, one can get rid of that excess in a later step.
Next, I fold the pieces into a tetrahedral shape with the slick sides inward.
And tape the loose ends together from the outside. Press those edges together so they are snug.
Then, do the same for the other 2. This is where I got rid of the excess gap.
Et voila. A wide-mouth jar or yoghurt cup holds the mold when pouring. As one nears the top in successive pours (you don't want to do too much at once and have it overheat and melt the tape) it gets easier and easier to see how level you are, and you can make adjustments in the mold position.
I suppose one could make pyramid molds in the same way, but there is a big advantage to using this method for tets instead. With a tet, the 3 sides hold the shape of the mold rigidly. With a pyramid, you would need to somehow brace the 4 sides so they stay even. I have not tried this.
I use no lube on the tape.
If one is careful in removing the cast item (cut tape along one edge to remove), one can probably re-use it at least once, but the 2nd cast is likely to have some more flaws.
I made 2 such molds, and here are the tets from them. A bit concave-looking. Thicker cardboard probably would avoid that.
Also some wire edges that could be sanded off. But I'm going to re-cast them in cones anyway.
Sep. 25, '09: Lately I have been a lot more into pyramids. I still haven't re-cast the above tets.
Today I made a pyramid mold. To hold it in position, I set it into a Rubbermaid container that is fairly squarish; close enough to keep things in place. I put a couple old D cells in the bottom so that the container would not be so easily knocked over.
One could also saw square holes into plywood with a saber saw to make a table to set pyramids into.
One could also make molds out of a single piece of carboard, scoring only partway with a knife where it folds. I'll try that next time.
Am pouring today; we'll see how this turns out.
Oct. 3, '09: If I had lubed the mold, maybe I could have salvaged it for another use. But I had to bend up the sides to peel the mold off.
The pyramid turned out OK. The base is just slightly out-of-square.
I sanded it a bit and painted it with metallic paints: