I found that "kit" in this case meant a box full of stock parts and some general, poorly-illustrated instructions, so the project turned out to be quite a bit more work than I had bargained for. I borrowed heavily on the work of others before me to make my project ultimately successful. If your soldering skills are rusty, they won't be by the time you are done with this project.
After reading a number of others' build blogs, I generally adopted and followed along with the one I found on the PyroElectro website. Chris had developed an alternative perfboard layout and had also gone to the trouble of creating some expanded circuit diagrams that turned out to be quite helpful during the build process. He was also kind enough to provide some advice (and encouragement) along the way.
After building my first assembly jig with the recommended spacing, I immediately found that some of the bent-over cathodes would barely reach to the next leg. I made a second fixture with a couple mm closer spacing to allow for easier soldering. I believe the final measurement was 14 mm between centers. After using masking tape to hold the LED being soldered on several layers, I came up with a little tool that would hold the next LED in exact alignment. It consisted of a small wooden dowel with a saw kerf sized to hold the cathode. A piece of plastic straw with a notch cut in it would slide over the kerf to hold the LED in place.
If you build this project, you would be well-advised to test your LEDs at every step. I tested them before soldering into the layers, after each row, after the layer was done and between soldering the layers together. It's a tedious, but necessary operation. Out of the 500+ LEDs in the bag, I found 2 that looked perfectly fine on the exterior, but failed to light up when connected to a power source.
Note: Count your parts. My bag of LEDs was about 10 short on the parts count needed to complete the kit. Jameco was very responsive and sent me replacement parts right away.
Some of the soldering on the perfboard proved to be quite challenging. I found it essential to mark and number everything as much as possible to avoid confusion. It's easy to transpose connections when flipping the board over. Daisy-chaining the register chips proved to be the most nightmarish soldering operation. Here's where a kit a PCB would have really nice. At some joints, there were 3 or more points to be connected on a single solder pad and keeping the solder from bridging to an adjacent pad was tricky (have a solder sucker handy). I ended up searching around the web and finding some 26 AWG solid hookup wire, which made the process much easier as you could fit at least 3 wires into the perfboard holes. Again, test, mark, test. Despite my slow, meticulous progress, I still found a couple joints that should/shouldn't have continuity during the assembly of the board.
The ribbon cables simplified hookup with the cube, but presented their own challenges. Since only half the conductors were used, the directions suggested cutting away the unused wires. I found it was much easier to cut the wires into pairs and just twist the two together. It was just too easy to cut or pull away insulation if you tried to get single conductors. I also found it helpful to adjust the length of each ribbon so that the ends all ended up approximately the same length when they were folded inside the enclosure. Lastly, because of the enclosure I came up with, getting the cable ends to stay on the LEDs long enough to solder them was just way too frustrating. I overcame this by crimping some female pins on the ends of the wires and then soldering them in place once they were attached inside the box. Again, mark, test, check (you're getting it!)
Check out the LED Cube tutorials here on Instructables for some more great tips and sketches to get you going:
A few other useful links: