Here's how I made this six-piece ball puzzle bauble for the Christmas tree.
Of course it's not impossible, but it does look like it is when completed.
I used a mix of power and hand tools, but you could use whatever you have available.
I'm entering it into the Holiday Decor Contest, so if you like it please vote for it there :-)
Step 1: Material Preparation
I first planed some mahogany down to about ¼" thick
tip: Thickness isn't too important, but it will determine the width of the cut-outs you make later on
Step 2: Making It Round
To make a ball, the six pieces all need to be approximately semi-circular.
I found the best way to do this was to bore out most of the inner portion with a forstner bit, and then, using the same centre point, use a hole saw to cut the outer edge, again not all the way through.
These three circular rings can now be sawn through in half.
Step 3: Cut-Outs & Separation of Parts
The joints for the puzzle ball were cut using a cross-cut sled on the table saw.
A notch is made in the outside middle of each half-ring, the same width as the material thickness, and halfway through (see photo).
Smaller notches are made on the inside, ends of the half-rings, halfway across the ring, and half the material thickness deep (see photo).
Then the six half-rings are fully sawn out of the board, following the curves made by the forstner bit and hole saw, using a fret saw or coping saw.
Step 4: Assembly
The six half-rings can now be assembled into a ball!
This is easier with more than two hands, and can only be accomplished because the half-rings are not quite full half circles (that would be impossible).
Note. Depending on how much material was lost when sawing the rings in half, you may need to adjust the pieces slightly before they can be forced into a ball.
Tip: Drying out the pieces in a low oven overnight can also help. This will shrink them across the grain a little.
Step 5: Swell and Finish (Optional)
Just as drying out the pieces can aid in assembly, swelling the pieces can help to tighten up the assembled ball.
One method for doing this is to soak in linseed oil, which, if after swelling, is then boiled will fix the size once the boiled oil cures. This is perhaps a little dangerous, as the oil can combust when heated, so do take all necessary precautions.
Step 6: Hang and Enjoy!
I looped some ribbon through the finished ball to hang it from the Christmas tree.
Lighting from behind with an LED tree light bulb looks good at night.
Thanks for reading my instructable, and please vote if you enjoyed it at Holiday Decor Contest - thanks ;-)