Cube within a cube puzzle

My cross inside a cube wasn't as interesting as I had hoped, so I figured I should still try to make a cube within a cube puzzle. But I still wanted to give it my own twist.

The typical cube within a cube is made by drilling with a large Forstner bit from all six sides until a cube inside is almost freed up. The corners are then cut with a knife.

But I figured more square-ish holes, cut with my pantorouter machine would be more efficient. I could have a larger cube on the inside without getting as close to the outside edges of the cube as I would with round holes.

To add to the challenge, I decided to make my square holes with a dovetail bit, so that the holes would be larger on the inside. I also made it a cube within a cube within a cube, for extra challenge.

A catch with the dovetail bit is that it can't plunge. So I had to pre-drill some holes in each face to start already plunged.

I wanted to cut the inside cube first. But before I could carve the inside with the dovetail bit, I had to make some room for the bit's 1/2" wide shank. So I used a 3/4" (19mm) straight bit, with the smaller template, to carve out part of the less-deep cavity to make room.

I had to be careful aligning everything. More about that in my previous article about a similar puzzle.

With the first cavity cut out, I had enough room to work the inner cavity with the dovetail bit.

Checking the depth of cut. The catch with using a dovetail bit is, you can't gradually increase the depth. With the bit widest at the tip, a non-full-depth pass will cut away material that a full depth pass would not.

After routing all four sides, I cut the corners with a carving knife to free up the cube. There is less attachment than there would be if I used round holes, but the corners of the holes are still round, so there is still attachment.

After freeing the cube I also chamfered its edges to give it a bit more slack inside.

Next, switching to the larger template. Unfortunately, this meant re-doing the alignment.

Here, I'm cutting the final face. I saved an end-grain face for last. The end grain faces are easiest to cut with the router because as the bit moves side to side, the bit itself is cutting side-grain.

Finished cuts. I had to "cheat" a little bit. Some of the slots at the edges were not deep enough, so I put the cube on the machine in different orientations and re-milled some of the edges to make the slots all about the same.

I first tried freeing up the corners with a carving knife, but was afraid I might split the cube apart. I also kept slipping and gouging other parts of the cube. So after that, I switched to a cheap thin carving chisel to punch through the corners

Similar to the inside-most cube, it was hard to rotate that cube freely, so I chamfered the corners. It's still a bit tricky to turn the inside cube. If it's turned on an axis parallel to one of the edges it jams, so it always has to be rotated diagonally.

I have to say, this cube within a cube within a cube turned out much more interesting than my captive cross cube

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