Magnetic Acrylic Rubik's Cube

Step 6 Drill out the central piece

The central piece requires 6 holes, one per side, dead center. At first, I tried using a drill stop clamped onto the bit itself, but this is disasterous. The acrylic going up the flutes gets caught in there, and becomes a heated spinneret of fibers that instantly wraps around the bit, creating a solid acrylic chamfer between the bit and stop that then immediately cuts conically into the plastic. Once I remembered that my drill press had a stop built in, I got perfectly clean holes every time.

I drilled all holes for the project a little shallow first, then tested with a magnet as I slightly drilled more each time, up to the stop value I set in, until the magnet was just a hair's width lower than the surface of the cubes. As the cubes aren't all exact, I couldn't just rely on the stop itself.

The trick is to not let the magnets touch. In that last hair's width, their force becomes tremendous, and it's much harder to shear them apart. Better to let them be lower than the surface, and have only the acrylic surfaces slide against each other.

The magnets themselves slid in to an almost air-tight seal. Their slippery nickel-plating helped a lot here. To get the magnet back out after I tested it, I simply pushed the block up against part of the drill press, and it fly out and stick to the metal. In this way, I could keep drilling just a bit more and dropping the magnet back in to test for the right depth. Many times, however, the holes were the perfect depth after the first drilling.

Comments

[Erik Andersen]

The force magnets exert on each other is explained by the inverse square law. Say you have 2 magnets (with opposite poles facing each other) 2mm apart. Now you move then to 1mm. You just halved the distance so the inverse square law says the force will be four times as powerful! Inverse square law works like this:invert the fraction that the current distance is of the original distance and then multiply it by itself. 1/2 inverted =2/1 2/1 (two) times 2/1 = 4

[adastria]

That is not entirely accurate. That would only be true if the magnets in question were magnetic monopolies (meaning one was entirely north and one was entirely south). Although nothing in Maxwell's equations forbids these from existing (on the contrary, if they did exist it would explain charge quantization) none have ever been seen. The magnets we deal with in every day life are rather more complicated. In the far field (so on a length scale much larger than that of the magnet) they usually approximate a dipole field, which obeys an inverse cube law. In the near field It depends on the shape of the magnet and the way that the magnetization is distributed within the magnet. It is probably best to deal with this as a multi pole expansion that can be truncated to whatever accuracy you like.

[Zazou]

del B = 0 forbids magnetic monopoles. You need to rewrite Maxwell's equations somewhat to allow for them.

[blahblah86]

do i remember an episode of big bang theory in which sheldon discovers a way to make monopoles possible?

[adastria]

Clearly.
Look, physical laws are descriptive, not prescriptive. The only reason that magnetic fields have zero divergence (<nabla,B>=0...remember inner product. as you state it you are taking the gradient not the divergence) is that monopoles have not yet been observed. Obviously, Maxwell's equations could be modified to include magnetic charge. As is they just have that charge set to zero.

[Zazou]

Apologies--should have been div rather than del. Of course physical laws are descriptive, but by what you've said, you may as well say "nothing about the laws of thermodynamics forbids free energy devices". The presumption behind such a comment is that the mentioned law is an accurate model of the physical universe, otherwise you're just talking in tautologies.