12-Piece Burr Puzzle

[Kim]

I decided to take a little break from my Steam Tractor and do something different.

I’ve actually got a little time off between now and the end of the year and I hope to spend some of it in the shop!  And a little project I’ve been wanting to do for a long time now is to make a Burr Puzzle.  If you’ve not heard of Burr Puzzles before, Wikipedia defines it as: “an interlocking puzzle consisting of notched sticks, combined to make one three-dimensional, usually symmetrical unit.”  If you want to read more about it, the article can be found here: https://en.wikipedia.org/wiki/Burr_puzzle.

Burr Puzzles can come in many sizes and shapes, but I’m making a fairly standard 12-piece Burr.  In this puzzle, as the name implies, there are 12 pieces with each piece being identical (not often the case with Burr Puzzles).

Here’s what a wooden one looks like:


And here are the pieces:


I chose to make this one from 5/8” square Aluminum stock.  I selected this size to keep the cost reasonable, but make it large enough to be fun to play with.  A 4’ length of 5/8” square 6061 cost me about $10 (including prorated shipping) from Online Metals.

Here are the quick plans I sketched up to help guide my work:


I started by cutting 14 pieces, just over 3 1/8” long.  This was how many I could get out of the 4’ piece.  I only need 12, but I figured I’d start with a couple of extras just for fun.  Then I cleaned up the ends and cut them to exactly 3.125” in length on the mill.


In the next picture, you can see the scrap of steel I clamped on one end of the mill vice to act as a stop.  Since I’m making 12 identical pieces, I needed a good reference point to line everything up with.  This is very sold and is working well to keep things uniform.  I just have to make sure all the swarf is out before I tighten down the vice.

As it turns out, not only are all 12 pieces identical, they are also symmetrical.  So, the stop comes in doubly handy (i.e. I get to use it 24 times per operation, not just 12! ).

Here I’m roughing out one side of the center notch.


Then I flip the part around – not moving anything else:


And rough out the other half of the notch.  Since my mill is small, I took multiple passes to get the full depth.


And a long and repetitive time later, I’ve got the first notch roughed out in all 14 pieces!


Then I switched to a 4-flute end mill, and did a little trial and error to make the notch the exact width I needed.  Turns out the 5/8” stock I have is actually 0.630” wide.  I made the notches about 0.001” wider on each side to give a nice fit, but still allow things to move well.  I did this by a little trial and error.  I also adjusted the depth to be exactly 1/2 (plus 0.001”) of the width of the stock.

Here I’m making a pass on one side:


And the flipped it around and made a pass on the other side of the notch.


With the notches finished up, I can now connect two of them together, like so:




This doesn’t seem like much, but it took me about 5+ hours to do this first notch. There are two more notches I have to cut, so I’m less than ½ way done.  (More than 1/3 though, since I also cut them & cleaned up the ends).

Kim


Edit: Some setting got changed in Picasa so I was uploading huge files.  Sorry about that. I've fixed it now.

[PStechPaul]

Interesting project. It might be cool to use some brass and steel, or perhaps some plastic or even wood, for variety and visual appeal. Aluminum anodizing would be interesting as well.

[b.lindsey]

Very Nice Kim. I really like this as a change of pace. May even have to have a go at one of these if only to sit on the desk and confuse people

Bill

[Kim]

Thanks Paul and Bill,

I considered brass, even half brass.  But at 6x the cost ($48 for 4'), I decided to stick with aluminum for playing around with.  I looked at Stainless too, but it costs almost as much brass ($39 for 4').  But you're right.  Mixing it up a little would look good!  I think you'd end up having to mill the size of the stock too - I'm not sure 5/8" brass is going to be the same size as my 5/8" AL (which was 0.630").

Kim

[Kim]

After completing the center notch, I moved to the outer two notches.  They are on a different side than the first notch. So, I have to make sure and orient all the parts correctly.  Again, I used the rougher to remove most of the material.  I set it up so that it left a bit on the side and on the bottom to be removed with the 4 flue end mill.


Four passes later, the first notch is done (or at least, half roughed out ).


And one the other side:


Then I repositioned to take the other half of the notch.  On side, then flip it around, and do the other.  This shows both sides having been completed.


Next, the final passes with the 4-flute end mill. Here’s the inside of one notch completed.


And then the other side:


With the center notch, I could test it right away by taking a cut on both sides, then test fitting another piece in the notch.  But for the outer notches, I couldn’t do that.  It was a whole different setup for the two sides of the outer notches.  So, to determine the final position of the inside edge of the outer notches I used the edge of the center notch that had already been completed and lined it up with that.  And 'lined up' would be correct, except that the notches are wider, to give a little room for the pieces to slide.  So, there should actually be some overlap between the two notches - the overlap would be the amount of that extra room for a sliding fit.

Before I go on, I have to correct something I said in my first post.  I said I left an extra 0.001” on each side to allow a nice sliding fit.  That was completely wrong.  That’s what I THOUGHT I’d do, but in the end, I left 0.003” on each side (that’s an extra 0.006” for the total notch width).  I obtained this by trial and error, and it seemed pretty good.  0.001" wasn't enough space.

Here's a picture of what I'm trying to say. Hopefully that will help:


So, what I did was to make sure that the inside edge of the OUTER notch, was 0.006” inside the edge of the center notch (because each of the edges was 0.003” over than the ‘ideal’ line).  To do this, I used a 0.006” feeler gauge, as shown in these pictures.  (unfortunately, I wasn’t smart enough to take the pictures while I was doing it – these were staged later, with finished parts).

This shows a piece slid into the center notch, and the feeler gauge placed between them, like so:


My theory was, that I could feel if the edge of the outer notch lined up with the edge of the piece (the underside of the feeler gauge) and make sure it was flush.


This apparently worked well enough.  And once I got the insides done, the outside was easy – just make it .636” away from the inside face

And here is a completed piece:


After some fun with a deburring wheel, here they are:




And the final test; assembling 12 of them into the final puzzle shape:




I’m pretty pleased with it!

As Paul mentioned, I could have done it with some contrasting metal types and it would have been pretty.  But I’m pleased with the aluminum.  Maybe next time I’ll branch out.

Thanks for taking a look,
Kim

[chucketn]

Nice work, and a very interesting diversion.

Chuck

[Kim]

Thanks Chuck!
Kim

[fumopuc]

Hi Kim, that is fun. I like it.
If you visit an anodising company, you will get the bars with different colours.
Or may be a starter kit for DIY anodising ?

[Dave Otto]

Interesting project Kim and it turned out very nice!
I was thinking along the same lines as Achim. The puzzle would look great if all the parts were anodized in an assortment of colors.

Nice work,
Dave

[b.lindsey]

I love it Kim!!  I definitely have this on the to do list now. I also enjoyed looking through some of the resource links you posted as well.

Bill

[Kim]

Thanks Achim, Dave, and Bill,

Yeah, there are some really interesting info up on the internet about Burr puzzles.

I had so much fun with this one, I decided to make a 6-piece one too. Apparently there are millions of variations of a 6 piece Burr.  I'm only doing one   (I know, what a weenie!  ).

Kim

[b.lindsey]

Hope you will document it as well. Could these be done smaller say using 3/8" square stock?

Bill

[Kim]

Yes, I think you could use whatever size suits you.  3/8" would work fine.  It just gets smaller.  The wooden one I have was 3/4" square and each piece was 4" long.  At 5/8", each piece was 3 1/8" (about).  At 3/8" they'd be just 1 7/8" long.  Might be really cute to do it smaller.  And a lot less metal to turn into swarf!

Kim

[b.lindsey]

And a bit less pricey for brass or stainless in smaller sizes. I see the type of burr you made (altekruse). Did you come up with the dimensions or find a pattern and then scale it?

Bill

[crueby]

Neat puzzle! I had made a wood one a while back, they can be real mind benders. Someone had sent me a website with lots of designs for them, have to see if I have a link...