So now that you’ve ordered all the components and are probably waiting for deliveries to come in, let me continue with explaining how you are going to build the actual LED cube itself.
Building the cube
The most important aspect of the LED cube is the fact that all the LEDs are lined up perfectly. There are some LED cube examples out there that have great effects and colors, but the whole “wow” effect is just missing because the LEDs are not lined up at all. Saying they have to line up is one thing, but since we will be soldering 512 LEDs by hand, actually accomplishing that is a whole other thing.
To make sure every single layer is lined up perfectly, I used the mould you can see below. I’ve just used a piece of wood and drew some intersecting lines on it. The distance between the intersections should be about 2mm less than the length of the shortest leg on your LED (this is called the cathode or negative side). This will allow for the legs to overlap a little for soldering purposes.
Since you’ve bought 3mm LEDs you can drill holes on each intersection with a 3mm drill bit. The bottom part of the LED will be a little bit bigger so they should fit snugly. You can see some additional smaller holes on the left, but you don’t have to worry about those right now. They will come into play later on. Once you’ve drilled the holes you are sure that all the LEDs on every layer (because these 64 holes will become 1 single layer of the cube) will be in the same position. And as an added bonus, you can use the mould as the base for the cube, because the standing legs of the bottom LED layer will fit through the holes as well.
For soldering the LEDs together I’ve started with a horizontal top row. Make sure you bend the cathode legs of the LEDs 90 degrees in the same direction for every LED and make sure they touch slightly. In my case they were all pointing to the right. Once you’ve positioned them, you can solder them together. You will also notice that the last LED will have its leg sticking out. In the end you will have to cut it, but leave it on for now. It will allow you easier access to the layer for testing purposes.
Then move on to the other LEDs and position them in vertical columns, making sure the second one from the top has its cathode leg touching the horizontal row you’ve just soldered. If you’re right-handed it is probably going to be best to start from the left and work your way to the right side of the layer. Once you’ve done all 8 columns every LED should be connected and your should have a kind of long comb structure. This whole structure is kind of flimsy at this point, so you’ll have to take some steel wire, straighten it and solder that on top of the structure. I wanted to take no risks so I actually added 3 additional reinforcement wires, as you can see on the right side of the image above.
This is also a good point to test the connections. What you’ve actually done is connected the negative legs of all the LEDs together. That means that the easiest way to test the LEDs is to have a 3-5V power source, attach a 220 Ohm resistor and use 2 small wires to connect the LEDs one by one. Actually, the value doesn’t matter that much at this point since we will be connecting the LED for a very short period, so you could use one of the 120 Ohm ones as well. Remember that I’ve told you not to cut that one leg that is sticking out? Well, you can use that one now to connect it to the negative wire. Then you can simply touch the leg that is sticking upwards of each LED with the positive wire and it should light up.
Why should you test the connections right now? Well, LEDs are electronic components and as mentioned before they don’t cope that well with heat. Since you have been soldering very close to the actual LED component, you may have overheated one the is broken now. Now is the time to find that out, so you can still replace it. That will be a lot harder if you have soldered the layers together and maybe plain impossible if you find a broken LED in the middle of the cube.
At this point you have one layer finished, so that’s one down, 7 more to go. Just be careful when getting the LED structure out of the mould to make sure you don’t bend it. This is tedious work and requires some concentration to work on this small scale, but I can assure you it’s a great stress reliever 
. After a couple of layers you should have accomplished what I’ve shown in the picture below. And that’s only the half-way point…
After you’ve completed all 8 layers you can start with soldering the layers together. Again you will be using the mould, so you can actually leave the last layer in there for starters. Of course, you have to make sure that the layer you put on top of it is actually parallel to the bottom one. I found the easiest way to do this is using something to put in between the layers. I’ve used some small pieces of wood that I cut to the proper thickness. The upwards pointing legs (anode) of the bottom layer have to be bent slightly to get around the LED of the next layer to connect to the upwards pointing leg (anode).
I would also recommend soldering the corners first, then the edges, the middle and again working your way to the outside of the cube. Once this layer is done, keep the bottom one in the mould and just move the wooden spacer one level up and start again. The first couple of layers are not going to feel that sturdy, but once you’ve soldered about 3-4 layers together things will feel a lot better. Again, better safe than sorry, so test each layer after you’ve soldered them together. This will allow you to find broken LEDs again or even connections you’ve forgotten to solder. After all, there are a lot of connections to do…
After you’ve completed all 8 layers, you can now safely remove the cube from the mold and turn it around. You result should look something like you see in the picture above. If you’ve tested every single LED again, you can nog finally cut off the cathodes that are sticking out to the side.
This is also the time to drill the smaller holes you saw in the first picture. These will be necessary to guide wires that connect each layer to the controller.I’ll explain that in more detail in the next part…
You have now finished the cube and you can stick all of the anodes through the 64 holes of the mould. This is not as simple as it sounds, because it is like threading 64 needles simultaneous . After you’ve done that you just bend the legs around the wooden mould on the underside and that is sufficient to hold the cube in place.