I’m a bit behind in posting here. I completed the 6 piece Burr before Christmas, but haven’t had any time since to post or to do anything more out in the shop. Lots of wonderful family events and doing things with my kids while they were home (Plus a few less fun things that just happen and had to be dealt with.)
In my browsing about these Burr puzzles, I came across this online version of a book on polyhedral dissection as it relates to puzzles. I found it quite fascinating. Thought some of you might be interested too:
http://www.johnrausch.com/PuzzlingWorld/default.htmThere are literally hundreds of variations of a 6 piece Burr puzzle. This one is a common one (so I am led to believe) and uses 6 uniquely notched pieces. I found the pieces documented here:
http://www.craftsmanspace.com/free-projects/about-the-burr-puzzles.htmlAnd the six pieces look like this. Note the letter I wrote beside each piece. This was to help me keep them straight when working.
Since I had leftover 5/8” square aluminum bar available from my 12 piece puzzle, I used that for the 6 piece too. For this puzzle, each piece needed to only be 3 units long (where a unit is the width of the piece), so I cut 6 pieces and milled them down to size. My 5/8” stock was actually 5 thou over, so the length was 3 x 0.630 = 1.890”.
There was a bit of symmetry in these pieces, but nowhere near as much as in the 12 piece. So, I chose to go a different direction in making these parts. I decided to just work from one side. So I setup a table of coordinates for a ‘left side’ and ‘right side’ cut for each notch that was needed, as shown in the sketches below:
Then I dialed in the position of my stop, set zero on the DRO, and went to work on one of the pieces (Piece “B” I believe).
The minimum width notches required were 5/16”. So I used a 3/16” end mill to do all the milling. On this part, I’ve already milled the left and right edges very carefully, and am now just milling out the middle of the notch, which happens to be two units wide.
Here’s the first notch completed in piece B.
Then I rotated it 90 degrees, and milled out a 1/2 unit wide notch.
Here I am starting on piece C (I started labeling them. I need all the help I can get!)
Here’s the process I followed for each notch. First, I would dial in the DRO at ~30 thou less than the actual desired edge, and cut multiple passes to the desired depth (which was always 1/2 unit, plus 2 thou.)
Then, at full depth, I would mill to the actual desired position of the edge of the notch. I always did it so that the final pass was a climbing mill pass of 1-2 thou to get a nice smooth finish.
Then I would do exactly the same to the other side. If there was something extra in the middle (as with piece B) I’d go back and remove that last.
Then I rotated piece C, and did an offset notch on that face. Unfortunately, I apparently failed to get a picture of that operation.
After piece C, comes, you guessed it, piece D.
I repeated the same process to cut the notch in this piece. Note that the notches are in different locations for each piece.
Then I rotated it, and cut the next notch in a different side.
Now, Piece D is a special piece. It actually contains a blind notch – by that I mean one that isn’t just a cut through. In this portion, only 1/4 of the cross section of the piece is removed. To do this, I CAREFULLY milled a half notch from one direction:
Then flipped it back to the original position. Here you can see the curve left by the 3/16” end mill. Next step will be to do exactly the same pattern here, to take out that curve on the bottom.
Like this:
Unfortunately, that sill leaves a little nubbin down in the blind corner that is curved on two sides, so the notch doesn’t REALLY go all they way down to the corner.
To open up that last little bit of the notch I used a chisel and cut down from all three sides to remove that little piece. This worked just fine for me, using the aluminum, but if you were using steel, you’d probably have to come up with a different method to clean up that corner.
Next, I did…. Piece A! Did I trick you? I actually started with this piece, but as I was working on this one, it became clear that I'd screwed up my calculations. So I had to re-do them, and consequently, had to re-do Piece A. And here it is, with the first notch removed.
The second notch on piece A is on the same side, but is a 1/2 unit notch, as you can see.
And finally, Piece E. It required a wide, 2 unit notch to be removed from one side:
And a single unit notch to be made in the center on another side.
And here is my original picture with all 6 completed pieces.
I actually had to go back and widen my notches a bit. I wanted to make this one a little tighter than my first puzzle, so I tried make each notch only 1.5-2 thousandths extra in width. But that was just not enough freedom to make the whole thing fit together. I ended up going back and taking a few more thou more off of each edge. This freed it up enough that things worked very nicely. Maybe its a little too lose however, but it works, and I'm happy.
Here are the completed beauty shots:
If (when?) I do another one, I’m going to be more careful on my notch positioning and see if I can make the tighter tolerances work. The gaps I have now had to be this wide to make it work, but now it’s just a little loser than I’d like. I’m sure if I improve my accuracy all around I can improve on that.
But all in all, I’m pretty tickled with how they turned out. And these puzzles were a very fun little diversion!
Thanks,
Kim