I've been lucky to play with a lot of different 6-piece burrs recently. I'm especially interested in the most complex ones, but without special tricks like coordinated moves, non-standard pieces, internal mobile parts, magnets etc.

Here are the ones I own, or tried. For each one, I give the number of assemblies (the ways the pieces could fit together, but that may not be actually built), the number of solutions, and the number of moves needed to disassemble it (first piece, then second piece, etc).

**Philippe Dubois**

Assemblies : 2

Solutions : 1

Moves : 6.4

It was my first burr. Very straightforward because it only has 2 assemblies. Ideal for beginners in "holey 6-piece burrs".

**Peter Marineau - Burr B (or "Piston")**

Assemblies : 10

Solutions : 1

Moves : 9.3

Much later, at last, I could grab another hollow design, and to my pleasure, it was more complex than the Philippe Dubois. With 10 assemblies, the construction of the puzzle starting from the disassembled pieces is a longer process. That's with it that I started to use the "Solving burrs" method.

**Bill Cutler & Brian Young - Mega Six**(Ive got three of them )

Assemblies : 20

Solution : 1

Moves : 10

THE hardest six piece burr, according to Mrpuzzle. I don't know if this is true, but this was indeed the first one that I failed to solve ! It features a subtlety that I failed to see entierely : two of the pieces has an ambiguous orientation (two of their sides may be the "back" side). After one hour, I realized it for one of them, but this one actually had its "natural" back outside, and after another hour, I forfeited without noticing the other one.

I liked this puzzle so much that I then bought the Craftsman edition. Later, Maurice Vigouroux made the splendid white one in curly sycamore for me. Unlike Brian Young's one, it has no glued cubes. The unmillable pieces are chiseled.

**Edward Hordern - Modification of burr B**

Assemblies : 6 (the one on the right side, with three colours)

Solution : 1 (the one on the right side, with three colours)

Moves : 10

When I met Maurice Vigouroux, who had been interested in 6-piece burrs too, he gave me that one. It is a bit more difficult than burr B, because a move has to be stopped before the end for another piece to move. With the original Burr B, all moves must be performed until the end.

However, it remains much easier than the Mega Six.

*** No picture ***

**Bruce Love - Love's Dozen (with three colours)**

Assemblies : 4

Solution : 1

Moves : 12.3

This is the highest number of moves for a 6-piece burr. The solution is not unique, but if the pieces are made from three different woods, like the "Modification of Burr B", the 12 moves solution is enforced.

I made it with LiveCubes. I was a bit disappointed to see that it was just another variation around Burr B. I still find the Mega Six more complex.

While I was visiting Maurice, I decided to have a look at his old 6-piece crosses. We gathered every one from his attic, and got a full bucket of them in the living room. And it's not just an image, we really carried them inside a bucket !

There were about 50 of them. I didn't have the time to solve them all, so I just looked at the way they could be disassembled. I discarded the ones with only one or two moves. Then I narrowed the selection to the ones with the most interesting or elegant disassembling sequences.

Here is what Maurice made that week :

**Bill Cutler - Computer's Choice 5 holes**

Assemblies : 7

Solution : 1

Moves : 9

I think that this one is quite hard. It has the same ambiguous piece as the Mega Six. The rest of the sequence is not so intricate and bizarre, but on the other hand, it features a very nice dead end in the disassembling sequence.

The Mega Six also has one, but you can't lose yourself in it, because it happens if you deliberately leave in place the piece that should be removed and go on.

In this puzzle, you can't miss the dead end. You go straight into it after a few moves. And it even features a variation ! That's actually a move that leads into two close dead ends.

You must go back and find a more subtle move in order to disassemble the puzzle.

**Derwin Brown - Puzzle #23**

Assemblies : 9

Solution : 1

Moves : 6

I liked the way this puzzle opens. It separates into two halves after the 6th move.

To be honest, The Mega Six, the Computer's Choice 5 holes, the love's 1 and Abad's level 6.7 also do.

This one also have an ambiguous piece, but it is maybe not very difficult to spot.

This is the puzzle that I chose for the article about Solving Burrs, because following the method, we find the right assembly quite fast.

Overall, I prefer the Computer's Choice 5 holes and the Mega Six.

**Bruce Love - Love's 1, with three colours**

Assemblies : 4

Solution : 2

Moves : 6, or 6.2

I selected this one because the disassembling sequence looked nice. It must be manufactured with three colours for the solutions to have at least 6 moves.

It also has an ambiguous piece, but unfortunately, it must be placed in its "natural" orientation.

I still prefer Mega Six and Computer's Choice.

**Bill Cutler - L46AA with dowels**

Assemblies : 1

Solution : 1

Moves : 6 with 8 units pieces or 10 with 10 units pieces

This one is very interesting. Its disassembling sequence features a lot of dead ends. It is not very long, not very hard, but awfully confusing ! Today, I have disassembled it about 30 times, and I'm still unable to find the right moves without making a mistake first.

The bare design features many uninteresting assemblies. So many that coloured pieces are not enough to enforce the level 6 one. Maurice found a smart way to solve this problem. Each piece is marked with a dowel on its side, and the dowels must be gathered in two opposed groups.

We later identified this burr as being a small variation of Bill Cutler's L46AA notchable... The only difference is that Maurice can mill the pieces, so this one has one more voxel and is not notchable. The extra voxel does not change anything.

Bill and Jerry McFarland draw a black line around the puzzle in order to enforce the solution.

When we made it with Maurice, we had to use coloured pieces in addition to the dowels. I later realized, completely by chance, that choosing another location for the two groups of dowels allowed to use only one colour.

I learned online, in Ishino's website, I think, that if the pieces are 10 voxels long, the solution requires 10 moves instead of 6. I then built this bigger model with livecubes.

The missing voxels at the end of the pieces were a study about beveling the end of the pieces, like in "Diagonal Burrs". It would have looked like this :

I also found that to get 10 moves, only one pair of pieces have to be 10 voxels, and another can be 6 voxels short :

But I don't like the final shape.

I think that this burr is brillant. It may become my prefered one, above the Mega Six, once I get one in wood.

Lately, I was intrigued by another design listed in Ishino's website :

**Rafael Juan Guarinos Abad - Abad's level 6.7**

Assemblies : 25

Solution : 1

Moves : 6.7

With 25 assemblies, and one ambiguous piece (which unfortunately goes in the "right" position), it compares to the Mega Six for the difficulty of the assembling challenge.

There is no problem with the ambiguous piece, but on the other hand, only one of the extra assemblies of the Mega Six allows some moves that leads the puzzlist to think that it may be the right solution, while in most of Abad's 6.7 assemblies, some moves can be performed, and each time we find a new assembly, we must take a moment to ponder if it is a solution or not.

For me it looks

*as difficult*as the Mega Six.

It seems very hard to manufacture, because it has 8 internal corners (un-notchable, un-millable), including two opposite ones in a single voxel, the worse configuration for chiseling the pieces.

One interesting feature is that the total number of moves is 16. This is huge. More than the 14 moves of the Mega Six (which is nothing else than a variation of the Computer's Choice level 10, highest level with a unique solution).

Love's Dozen has 18 moves. Burr B has 15. The other high level burrs that I know have 14 moves or less.

I can't be sure, but Abad's level 6.7 may well be

*the 6-piece burr with the highest total number of moves*and a unique solution (the Love's Dozen needs coloured pieces to have a unique solution).

This feature has never been completely analyzed because Bill Cutler's gigantic analysis of all 6-pieces designs only took into account the number of moves

*for the first piece*. In that analysis, Abad's level 6.7 is just a random level 6 puzzle among millions of others.

It stands out because the second piece needs 7 more moves to be taken out.