Archive for September, 2011

Making Wooden Hypercubes

Thursday, September 1st, 2011


Accuracy is everything when you are trying to make this shape, or you get ugly corners.

Or worse.

This is the smallest inside-out projected tesseract model I ever made out of 1/4 inch thick wood using the CNC overhead CAD/CAM router.

It’s small enough to hold in my hand, and you may already have seen the picture of me doing exactly that on my blog and on Facebook.

The router eventually broke down and we had no funds to repair it. But while it lasted it was a glorious thing. The vacuum table held the wood flat and motionless, and the the computer numerically-controlled 3-axis overhead router would glide through the wood, cutting the edge bevels for two rhombi at the same time as it grooved through the thin birch maple and oak panelling while the attatched shop vac sucked up all the sawdust. Then we would shut it off and collect the rhombi.  The required tolerance demanded such accuracy.

The rhombi were glued together with Elmer’s carpenter wood glue; the seams were kept pressed together for the time needed for the glue to dry by using stretched duct tape to exert continuous tension. Of course, duct tape leaves its own glue residue on the wood, which had to be thoroughly cleaned and sanded off before we could apply the stain or in some cases clear polyurethane sealant. This one I made for myself, too small to be a loudspeaker, so I did not bother to stain it. I like the look of natural wood grain just as much as stained wood.

hypercubesOrdinarily, the design would have included four half-rhombi and a square to mount the woofer on. But I liked making this one a complete rhombic dodecahedron since it would never hold a woofer. I have kept it with me over the years, as I was forced to turn from hypercube speaker builder to career programmer. A memento, if you will, of my life that could have been, that must have been…on another timeline.

The rhombic dodecahedron can be thought of as the boundary of a inside-out projected tesseract. It is also identical to the boundary of the parallel projection of the hypercube onto 3-space.

tripanelsWe worked out assembly-line methods for the building; after spending a day cutting rhombi, half-rhombi and squares we would spread out some newspaper on the warehouse floor. First we would glue three rhombi at a time together and then set the 3-panel subassemblies to dry. By the time we had finished glueing all of the 3-panels we needed together, the first ones were dry enough to proceed. Then we would take two 3-panels and glue them together to form a 4-edge corner subassembly, a hex-panel.

hexpanelBy the time we finished the hex-panels, the first ones were dry. Then we would take a hex-panel, glue in two more rhombi, and it would be ready for the four triangles (half-rhombi) and the square baffle plate.

After the glue dried, the duct tape was stripped off and the cabinets were sanded, stained, and sealed. Then we were ready to install the backplate in the rear rhombus where the input terminals go, the frequency-dividing crossover network that sent the highs to the tweeter and the bass to the woofer. And then finally the woofer would be front-mounted onto the baffle plate and sealed to it with a bead of silicone rubber.  No one taught us; we had to work it all out for ourselves.

hypercube-loudspeakerBut the end result was always worth the trouble of learning how to make it. We thought they were beautiful.

Not everyone agreed, obviously.

Their loss.  Next post, I’ll cover more details about how they were tested.

Must sleep. –MRK

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