Sunday, March 28, 2010

Diamond Key

The challenge of this block design was to make an interlocking block that could release from a simple mold. An interlock sticks the block together, but this interlock can’t get stuck in a mold. This apparent contradiction was overcome by using elements of symmetry in the design.

This design evolved over different versions, and I continue to play around with different configurations. After designing the simple, tapered triangular block I looked at a more efficient way to connect the blocks at their abutting faces.

I decided on an independent diamond-shaped key, which was sunk halfway into the abutting edges of two adjacent blocks. The triangular blocks are made with half-diamond shaped recesses (keyways) on each of their three abutting faces. The diamond-shaped keys are made with an obtuse angle of 120 degrees and an acute angle of 60 degrees.

Blocks are assembled by first stacking with triangular tips pointing up, and placing keys into the keyways. Then blocks are inserted between the first course, with tips pointing down. Blocks are able to assemble without any undercut. For example, if the independent key were shaped like a square, there would be an undercut (or draft, negative angle) and the blocks couldn’t be assembled. This illustration shows it better than words can describe it. If you click on the picture you can see it better.
There are a couple of problems with this system. First, the independent keys require that a relatively large number of them be made. It would be better if the key and keyway were an integrated part of the block. Second –and more critical- is the fact that these blocks don’t readily release from a simple two-piece mold. This means that these blocks couldn’t readily be made on regular block machine.

The system works pretty well though. Years ago I made a prototype out of concrete, using hinged plywood molds. The blocks were used to build a dome dog house for my dog Maximillian. This early prototype dome now sits atop a cupola on a much larger dome at my property in Alfred NY.

How could an interlocking block be made on a block machine? The diamond-shaped key & keyway system pointed the direction toward a better solution, and we’ll look at that tomorrow.

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