Materials:

7x7x3/4" steel plate
10' of 3/4" square steel tubing
5 colors of el wire, each color is a single strand approximately 8ft, each color forms a "band" of parallel strands, 10 strands wide, each strand is 2.2mm thick
EL Wire splitter 5-output
12 VDC EL Wire inverter capable of lighting 27-40 ft
12 VDC Wall transformer

Tools:

More than you're likely to have lying around the house. I do all my work at TechShop in San Francisco

manual mill/cnc tormach
bandsaw
drill & tap
weldor
angle grinder
powder coater
soldering iron

Step 1: 3D Model

Design the location of the wires in a 3D modeling program (or just use my design). You don't need the cube to be structurally accurate for this part (ie: made up of hollow bars, etc), you're just trying to figure out the spacing and placement of the wires so that none of the color bands collide with the others.

Step 2: Facing and Milling

I used hot rolled steel which is cheaper than cold rolled, but requires more finishing. My plate arrived covered in limescale and rust. I first faced it on a manual mill.

Then I hollowed out a pocket in the bottom of the plate using a CNC tormach, cause I was tired of milling manually :) . I left raised corners in the pocket, recessed from the bottom surface of the cube just enough to rest an acrylic plate on the corners and have it sit flush with the bottom of the cube. Then I drilled and tapped holes in the raised corners so that I could later screw the acrylic plate into place. That plate will end up holding all the wiring in the pocket.
(Note: a similar resulting shape could probably be achieved by welding a thin steel plate onto a welded square made from the tubing, but I'm not a very experienced welder and I optimized design for the cleanest looking cube.)

Step 3: Cutting Posts

Next I cut the square tubing for the cube edges. I cut 4 bars to 7" in length at their widest point, at 45 degree angles on both ends, tapering in, so they would form a square. This square would be the top of the cube. Then I cut 4 bars with straight cuts to be 5.5" in length. These form the "posts" that hold the square above the base. You may need to grind down the posts to get them as close as possible in length.

Then I milled the channels for the EL wire to run through. These are cut according the the 3D model. Make sure that the channel "teeth" are facing the direction that the EL wire will be pulled in. Also drill the holes in the cube base according to the 3D model.

Step 4: Welding Cube

Time to weld! First you'll tack weld each of the posts to the base. Try to get them as straight, square, and close to the corners of the base as possible.

Next I tack welded the top square together. It may have been a better idea to add the top bars one at a time to the top of the posts, but as I've mentioned, I haven't welded very much so this is just the order I went in. If you don’t properly clamp everything to the welding surface you’ll warp your bars and ruin all the hard work you put into cutting/grinding the bars to be the proper length. When I was done tack welding my square, it rocked instead of laying flat on a table. :(
Next I positioned my square on top of the posts and clamped every piece I possibly could. At this point I had to leave some clamps loose, try to knock the posts straight with a mallet, then tighten the clamps when all the pieces seemed to line up in a reasonably square fashion. Tack weld the square to the posts.

When everything is tack welded and reasonably cube shaped, go ahead and fully weld all the joints. I only welded the outer joints so I wouldn’t need to grind down messy inner joint welds with a dremel. There shouldn’t be more than a crack between any posts on the inner joints, and once the cube is powder coated, they’re barely visible, and only from very strange viewing angles.

Next I used an angel grinder to smooth out the welds and round out the corners, since the square tubing had rounded edges.

Step 5: Soldering EL Wire

Next I powder coated the cube matte black. Finally it was time to run the EL wire.

I followed this tutorial to solder connectors to my EL wire. As in the article, I originally ordered all my wire and supplies from thatscoolwire.com. I was reasonably pleased with everything that they sent, but it’s hard to get a good sense of how the colors will look when lit from online pictures, and 1 of the colors that I ordered (the purple) glowed much dimmer than the rest. I ended up taking my other 4 colors to Fun House Productions in West Oakland and they lit a couple different colors until I found one that matched mine in brightness and looked good with my existing colors. I ended up returning to them later to buy extra connectors, a power cord extension, and a toggle switch.

The toggle switch will need to be connected to the length of wire between the power source and the inverter. If you were to connect it to the length of wire between the inverter and the EL Wire, when you turned the switch off you would blow your inverter. (For this same reason you should never plug your power source into your inverter when you don’t have the EL wire also connected to the inverter).

Step 6: Stringing EL Wire

Once each wire had a connector properly soldered to one end, I strung the wires, feeding the loose end up through a hole in the base of the cube and then back down through the next hole, forming a long U shape of wire, which I would then catch on one of the milled “teeth”. Don’t leave the wire too loose, but at the end of this step it will not be anywhere near as taut as it will be in the finished product.

Note: EL Wire is reasonably delicate, so don’t try to yank the wire taut through sharp channels. If you strip the outer lining of the wire you will short the entire circuit. At this and later points in the assembly I managed to strip or kink my wire and short the entire circuit about 4 times. I had to unstring the wire, sometimes a bit of electrical tape around the stripped area was sufficient, other times I had to cut off the damaged length of wire and start the stringing process again.

Step 7: Shimming EL Wire

In order to pull the wire taut I used toothpicks as shims on the underside of the cube. Each “stitch” of wire leaves a loop on the underside of the cube, and I slowly (and carefully!) pushed toothpicks under the loops, pulling the strands of wire inside the cube taut. (Careful, this is the other point at which I stripped/kinked my wire and shorted my circuit.)

Step 8: Acrylic Plate

Once the wire was sufficiently taut I used plastic ties to bundle the ends of the wire strands and applied epoxy liberally to all the wire exposed on the bottom of the cube.

Next I cut a clear acrylic plate on a laser cutter to fit the pocket in the base of the cube, with holes for the corner screws, a hole in the center for the power cord, and with my signature etched into it. I bundled all the wires into the pocket in the base of the cube and screwed the acrylic plate into place to hold them in place.

Step 9:

Finally, after having utilized every possible technique and machine that I had learned, the cube was finished, with just enough time to pack it up and give it away as a Christmas present, never to see it again.