Burr Knot Puzzle

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I have made the Burr Knot Puzzle in the past with a scrollsaw. I wanted to make one on my SO3. I saw a version on Pentrist that would work for the CNC. The usual Burr Knot has square corners that my SO3 cannot do on inside corners. I dont want to have to chop out the corners square. The one I saw has rounded edges and will work a CNC.

Here is the classic Burr Knot Puzzle

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This one has rounded corners. I will have to cut the pieces out and then run them through the router with a bull nose router bit which I have.

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This one is not the one I saw earlier but similar. That is why I hate Pinterist because there is way too much to see.

Here is my .c2d file picture.

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I have not cut it yet. But will try in the next few days.

rounded_burr_knot_puzzle.c2d (112 KB)

The puzzle is deceivingly simple.

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I haven’t met a puzzle that couldn’t be solved with a simple hammer :yum:

Looks cool, looking forward to seeing how they turn out :slightly_smiling_face:

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@gdon_2003 I haven’t looked closely at this but for the square corner puzzle could you draw rectangles in the open inside spaces then use rest machining with a small endmill to square the corners?

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The problem is sourcing a smaller endmill with a sufficiently long cutting length.

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True… Wouldn’t it be nice if someone made long small endmills that had no deflection issues :laughing:

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That is a really smart approach, especially considering the limits of inside corners on a CNC. Using a rounded-edge version sounds like a practical way to avoid extra hand work. Would love to see how your SO3 version turns out once itis finished.

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I got the Burr Knot cut out. This version is a failure. I will try again. All failure leads to success.

The bull nose 3/4" did not work. Partly because I have an Incra Positioner and the split fence had to be separated and that made the short pieces unstable.

So I tried a round over bit with a bearing. That was better but also a failure.

I will rethink this and find a solution.

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As with most men hope springs eternal.

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Guy, there is something about the dimensions that aren’t always revealed publicly. I can dig out the detail file if you want to go down that path. I like your rounded version better.

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I would be interested if you can find the information. Since my failure you could say I have a Burr under my saddle.

In the first drawing above everything is based on .75" units or multiples/divisions of it.

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I sent you a DM, Guy.

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I have made a few burr puzzles by using dog bones in the inside corners. It can be a pain to put them all in manually. I coded a very alpha dog bone extruded rectangle in OpenSCAD that works pretty well. The same thing could be done manually by subtracting cylinders with your desired bit diameter from each inside corner.

When finished, they really aren’t that noticeable and they can also be used to impress your friends and relatives with how clever you are by explaining how you got around the problem. :stuck_out_tongue:

There is also a very sophisticated dog bone plugin in Fusion 360. It does the whole thing automatically.

If anyone wants my OpenSCAD dog bone hack, let me know.

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I’d be very interested in the code — put it on Github?

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Sure, no problem. Here it is.

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