|Monthly Tech-Tip |
A project to use 3D printing to create molds for making bricks. I am inspired by bricks made across the Canadian prairies during the 19th and 20th centuries. I will experiment with making both compressed earth blocks and fired bricks. I am particularly excited about the possibility of making metallic bricks using Plainsman Fire-Red and St. Rose Red materials (firing them at cone 10R). And about using their Kaosand - it is only suitable as a minor ingredient in plastic bodies but has enough plasticity to hold together as a brick (and should dry quickly with minimal shrinkage).
The "frog" is the indentation in pressed bricks. I drew this design in Fusion 360. For initial testing I was able to oil the 3D printed form (having no infill), compress the clay directly against it and get good extraction. This is version 2, I maximized the amount of draft on the letters (it is a tricky process because of some of the tight angles). This is a very good example of the power that 3D printing puts into the hands of a small business. Thanks to Keeley Haftner for opening my eyes to this possibility.
I was using a heavy metal tamper to force high-water-content powder (about 12%) into a wooden form to make bricks. I use snug-fitted wooden spacers against the clay itself and deliver the blows to them. It became quickly evident, that even with 3/4 inch wood, my tamper can deliver greater pressure than the mold can withstand. I then switched to 3/4 inch plywood. With the same result! A metal mold seemed to be the next step but that was going to involve considerable expenditure. And were other problems: Removing the brick after pressing it in would be very difficult, metal molds are only practical if you have a machine with both pressing and extraction cycles. Another issue was getting a good logo impression on the frog: The clay is not hard enough to pull away from the mold without edges and pieces breaking off. In the end, for making sample bricks, a plastic mold and wetter clay are a better option.
The fact that it broke was not the only issue. A mold that I could disassemble seemed like a good idea but the pressure developed during ramming sticks the clay to the wood is such a way it is difficult to part them. This was another step is realizing, that for my goals of just making some demonstration bricks, it would be better to use a plaster mold and softer clay.
The lettering on the frog does not have enough of a draft to release well. The oil soap I was using as a parting-agent did not work as well as canola oil. And the water content of the clay was too low to make it compress enough to get good surfaces.
Compressed Earth Blocks
|By Tony Hansen|
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