October 14, 2009

Laser Cut Burrs

As I mentioned in a previous post, a while ago I found an open access fabrication lab that has laser cutters available for public use. I decided that it would be interesting to make a few board burrs, since they can easily be cut out of a flat sheet of wood with a laser cutter. The first one I tried to make is a variation on a puzzle I had seen on Pavel Curtis's website, PavelsPuzzles.com, which he calls Six Tabbed Planks. You can buy this nice looking acrylic version from him here.

Pavel happened upon the design while at the 19th annual International Puzzle Party. Part of the party included an excursion to see Edward Hordern's puzzle collection: he had one of the largest puzzle collections in the world! (Unfortunately, Horndern passed away back in 2000.) At Horndern's home, there was a huge tent set up with tables and various puzzles from his collection on the tables. Pavel found Six Tabbed Planks on one of these tables. He couldn't solve it in the time that he had, so he decided to jot down the design for later reference. This slip of paper remained in his wallet for six years until he finally got around to having the puzzle made.

Interesting story, eh? Unfortunately, nobody knows who the designer is, but it is a cool little puzzle. I think it looks very nice in the acrylic that Pavel used, but my material at hand was plywood, so that is what I used!

The design I ended up making is a variation on this design by David Rousseau named "Pavel's Search" that I found on Ishino's site, Puzzle Will Be Played. The structure is similar, but it is a level five burr, meaning that five moves are required to remove the first piece.

This design is quite simple to make using a vector drawing program, so I sketched it up and set the laser cutter to work. It took a bit of calibration to get the holes to be the correct size for the tabs, since the width of the laser is not negligible when it comes to a precise fit, but eventually I got it right.

I decided to stain the wood and finish it with wax to give it a darker tone. In hindsight, I think the natural wood probably would have looked better. Oh well! It is definitely a cool little puzzle. Some burrs are very difficult due to the large number of pieces and potential assemblies. This has six pieces, two assemblies, and one solution.

An assembly means that all the pieces will fit together in a certain way, but not necessarily that you could physically manipulate the pieces to arrive at that assembly. For example, two solid rings could physically be interlocked if you could magically teleport them together, but there is no physical way to assemble them in this manner without breaking things. This is an assembly without a corresponding solution.

If there are lots of assemblies but only one solution to a burr, it can be quite challenging to determine which assembly is the correct one. Basically what you can do is think about a given assembly and see if you can figure out how to disassemble the burr to the point where you can add the final piece in. (I say this like it is a rule, but that's just the way I do it. How do you do it?). So the reason this puzzle isn't too hard is that you there are not too many assemblies that you need to try. Also, three of the pieces are identical which also reduces the amount of trial and error.

Ok, that was a big detour considering that most of you already know that, but I thought it would be fun to try to explain it. Did it make any sense? I hope so.

The second puzzle I decided to make was Chocolate Dip Burr by Bill Cutler and Frans de Vreugd. This was a design that I had also seen on Ishino's site, Puzzle Will Be Played, back when I was doing a lot of burrs with LiveCube. This is a very cool puzzle because without the coloring there are 21 solutions of varying levels (number of moves to remove the first piece), but if you arrange the pieces so that half of the burr is dark and the other half is light there is only one solution (with 16 assemblies). This solution requires 13 moves to remove the first piece, so this is quite a challenging puzzle.

This puzzle was also a breeze to make with the laser cutter. My file was corrupted and I was able to redo it in about 15 minutes, just to give you an idea for how easy it is. I made it out of 1/4th inch plywood, which results in a fairly tiny puzzle, but the laser cutter doesn't work as well on thicker material. To finish it, I stained half of the puzzle to make the dark side and left the other half natural for the light side.

It was a bit tricky to half-stain these tiny pieces but I came up with what I thought was a pretty clever solution. I actually dipped the half-stained pieces in the stain, but to prevent the stain from wicking up the wood past where I wanted it to go, I used a knife to score the line where I wanted the stain to stop. That way, the stain would wick up just to the point where I wanted it to stop! It worked like a charm. I polished the finished puzzle with some wax.

This puzzle was a real beast to solve. I worked on it for a few days without much luck, but eventually figured it out. Even though there are 16 assemblies, some of them are clearly impossible, so you can dismiss those right away. Some of the moves were pretty tricky, especially considering I haven't done many board burrs, so it took me quite a while. This type of burr can be very challenging!

Tomorrow, I'll write about a nice little two-piece disentanglement puzzle from Japan with a really cool final move.

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