Introduction: Magnetic Rubik's Dice Cube
I will assume, if you are reading this, that you have already read gfixler's Instructable. The primary purpose of this instructable is to highlight some of my modifications on his idea. So if you are planning on building one of these, I recommend you go and read his now.
The non-symetrical nature of some of the die patterns gives the dice cube an extra element of strategy not present in regular Rubik's Cubes. This variable of rotation is an aspect of the "sudocube," but the dice cube is easier to solve, because each face contains identical figures, and every cubie is unique--two properties of the original Rubik's Cube that are not carried over to the "sudocube."
Equipment & Parts List
- 96 D32 Neodymium magnets (100 pack recommended)
- 12 D62 Neodymium magnets
- 27 3/4" or 19mm dice (30 recommended)
- High Strength & Quick Drying Glue or Epoxy (transparent or translucent)
- 3/16" split point drill bit
- 3/8" split point drill bit
- Scrap Wood or Metal to make a Die Jig
- Carpenter's Square
- Drill Press with stop
- At least 3 clamps - more is better
- Shop Vac
- Standard head screwdriver
Update (2007-07-20)It's been a while since I've been around here; lately my internet has been sporadic at best, and nonexistent at worst. But I'm here now and I'll try to get caught up. I've noticed that the same questions tend to come up again and again in comments, so I've decided to answer some of those here.
All in all, the cube cost me about $60, although at least a third of that was for shipping and handling, as well as the drill bits that I bought specifically for it.
Many people assume that the cube spins just like a normal rubik's cube (I did too at first), but in reality, the faces move in more of a snapping motion, which is quite satisfying, though it doesn't lend itself readily to speedcubing.
If you take the time to analyze the magnet orientations and polarities, you will probably come to the conclusion that creating a 2x2x2 cube with dice and magnets is impossible. Indeed, any magnetic cube with an even number of sides presents some interesting problems, but they aren't insurmountable ones. You just have to think outside the box (or in this case, the cube). I am in fact, currently making at 2x2 cube. I started a few weeks after I finished the 3x3, but I haven't worked on it since then until today. That being said, I should probably have it finished this weekend. I believe that a 4x4 would also be possible, though more difficult and certainly quite heavy. Anything higher than that is probably a pipe dream. (probably)
Update (2007-07-21)Well, I finished the 2x2 cube this morning. It's really not a lot of work once you have the jig finished. In fact, it was more fun to make the 2x2 than the 3x3. That said, the end result for the 2x2 is less cool than the 3x3, and in retrospect, making the 3x3 is much more satisfying in the end. Anyway, check out the 2x2 cube.
Step 1: Get the Magnets.
For the rest of the connections, I used the same D32 magnets that gfixler used.
A total of 108 magnets are needed: 12 D62's and 96 D32's. Buy a 100 pack of D32 magnets, in case you lose a few or glue one in backwards.
When you get your magnets, the first thing you should do is mark them. Connect them all in one long "chain" and use a sharpie or other marker to mark the same side on each magnet. Make sure that the marked sides of the small magnets have the same polarity as the marked sides of the large magnets.
As for polarities, I used this method:
- Core: All faces "Red"
- Centers: Face touching core "Silver," other faces "Red"
- Edges: Faces touching centers "Silver," other faces "Red"
- Corners: All faces "Silver"
Using this method, most of the cubes have both polarities facing inward at some point. This should reduce the stress placed on the glue and reduce the chance of a magnet coming out. Additionally, the corners are attracted to the centers and core, which should help keep the corners stable while turning a layer in the finished cube.
While gluing the magnets in with this method, clamps are only needed for the core and corners. I recommend waiting 24 hours in between gluing the core magnets, as they are strong and very close to each other.
Step 2: Find Some Dice.
Any dice will work, as long as you have 27 identical ones to work with. It is best to get a few extras, since most of the time there will be a few dice with imperfections. The extras can be used for drilling practice, testing glues, etc. Translucent dice may be more expensive but provide for a more interesting cube.
For my cube I ordered 30 red 19mm translucent dice from Uncle's Games.
Inexpensive dice will not be perfect cubes, however, it is likely they will be much closer than gfixler's acrylic cubes. For the purposes of making a dice cube, its not really necessary to have anything more precise than these.
Though I don't have personal experience, I would not recommend "Casino Style" dice as they are usually made of acetate, not acrylic (the glue I used doesn't bond well to acetate), and do not have indented pips, so the ink may rub off during use or make the cube harder to turn. On the other hand, they are probably the easiest (and cheapest) way to get perfect cubes.
Step 3: Organize the Dice.
Most cheap dice will have a few mess ups: ink where it shouldn't be, or no ink where there should be. Most of the time, you can hide all of these by placing the dice wisely, such that the afflicted faces are internal faces. If you can't, use that die as a test die. That's why you ordered extras.
For some reason, a large number (5 or 6) of my dice had a strange "chip" on the edge between the 1 and 4 faces. It wasn't a big problem, and was only apparent on close scrutiny, so I let them be.
I created a spreadsheet in excel to help organize the layers (See below).
Step 4: Make a Die Jig.
You, like myself, may not happen to have a fancy square like gfixler uses to hold the dice for drilling. Fortunately, it is easy to make your own, since the square does not need to be extremely accurate.
Initially, I wanted to use aluminum channel or angle stock to create a square, however after not finding any scraps laying around the shop, I opted for a steel 5.25 to 3.5 inch drive bay converter. It is designed to allow the mounting of a 3.5 inch hard drive in a standard 5.25 inch CD/DVD drive bay.
After attaching the first bracket to a piece of plywood, I used a square to align the second bracket at 90 degrees to the first. A few more screws and I had a nearly perfect square.
The only thing left after that was to add a piece of acetate film (used for overhead projector transparencies) to the bottom. This was probably not necessary, and mostly just got in the way. I think I thought it would prevent scratches to the dice, but now, when I look back, I don't think it helped at all.
Step 5: Set Up Your Tools.
Once your die jig is finished, mounting it is relatively easy. I used gfixler's eyeballing method of rotating the cubes/dice to find the center. See his page for more information.
Once the jig was centered with the drill press, I clamped it to the built in table.
If your drill press doesn't have a built in stop, you may be out of luck. maybe you'll just have to eye things up, or get a new press. If you do have a stop, set it shallower than you want to drill, then slowly deepen it, until a magnet will rest just under the surface of the test die. you don't want the magnets to touch each other.
For the D32 magnets, you will need a 3/16" high speed steel bit. The D62's need a 3/8" bit. If you have bits specifically designed for plastic, use them. Otherwise, use "split point" or "self centering" bits and make sure to let the bit cool down every few holes. You also may want to use water or another coolant to help prevent melting.
You will need a strong glue. I opted for a two-part epoxy from LocTite, purchased from the local Fleet Farm. It dries to a transparent yellow. When it comes to glueing the magnets in, you may need another clamp, especially if you have a slow drying glue like my epoxy.
According to my package, the LocTite sets in 5 minutes, hardens to a usable hardness after 8 hours, and dries completely in 24 hours. For the core, I made sure previously glued magnets had been glued for 24 hours before attempting to add others, but for the others, half an hour or so was enough.
Step 6: Practice.
Use 1 or 2 test cubes to practice drilling, using different glues, setting the stop on the drill press, etc.
It turned out that the epoxy did not produce the "stress fracture" effect gfixler noticed in his cubes. Also good news: with red cubes, you can't even tell that the epoxy isn't completely clear. The bad news: It takes 5 minutes to set, and 8 hours to dry to a "usable" state, according to the label. The glue that dried on the acetate sheet (blank transparency) I used to mix it looks quite similar to the stuff that's used to bond fiberglass.
Step 7: Drill & Glue the Dice.
After you've practiced drilling and gluing on the test die (dice), proceed to the 3/16" pieces.
This step will take longer than any other, including marking the magnets, which you may have realized, is also quite tedious.
As you pick up each die to work on from the die guide, you may want to put a dot on the center of each face that will be drilled, with a sharpie, to prevent accidentally drilling the wrong side.
After the 3/16" holes, drill the 3/8" ones. I found that using some clamps helped keep the die stationary while being acted on by the greater force of the larger diameter bit.
After drilling, put some glue in one of the holes and then a stick of two magnets (make sure you get the polarities right). Wipe off any excess glue on the die or magnet face. My glue was very negotiable when it came to this, and came off easily most of the time. When more than one magnet are in a die with the same polarities facing out, you will probably need to clamp them together. The second magnet ensures that the glued magnet will be set under the surface of the die. The glue sometimes seeps out of the seams as it dries, but it can be removed with a screwdriver as long as it is not completely hardened. It stays about the consistency of caramel for several hours.
I experienced only a few problems with drilling and gluing. One was if the glue ran up the sides of the hole too much, an air pocket could sometimes be created between the die and magnet, pushing the magnet out. When this happened, I let the magnet come out and cleaned both it and the die with a towel before trying again.
Another problem was, if the hole was slightly too shallow, the magnet would not fit in the hole all the way, and my first reaction was to clamp it really hard. This was a mistake. Although the glue itself didn't cause stress fractures, putting that much force on the plastic in the bottom of the hole did. This only happened to me on a few magnets however, so it wasn't a big problem. I would suggest that instead of forcing the magnet in, you should take it out and drill the hole deeper or use less glue.
When the glue dries, glue another magnet in, until all sides are glued. Try not to drop or connect the dice until they have completely dried. For the stronger magnets, you may want to wait longer before unclamping the die, so it doesn't fly out.
Step 8: Assemble the Cube.
Start with the core and bring the centers into contact with it. Make sure to get the right sides in the right place. The sum of any face and it's opposite face should be 7, and if the 1 face is on top, and the 2 face is towards you, the 3 face should be to the right and 4 to the left.
Next place the edges, and lastly the corners.
And that's it. Turn your cube and enjoy the fruits of your hard work.