8-Ball in Solid Wood Cube





Introduction: 8-Ball in Solid Wood Cube

There is something magical about wood puzzles. This mystery leaves the mind searching for any rationalization, any form of understanding that will answer the question of "How did that happen?" In this instructable, I will show you how to put an 8-ball into a block of wood so you can leave others searching for an answer themselves.

Step 1: Parts

You will need:

Step 2: Joint and Plane 4x4

Using a joiner and planer, take the overall size of the 4x4 down to 3" x 3" and cut into a 3" x 3" x 3" cube.

Step 3: Mark the Center of the Cube

Using a straight edge, mark the center of the cube so you know where to drill the holes.

Step 4: Router Edges

Using a 1/4" roundover bit, router the cube starting with the end grain using a push block to prevent tear out.

Step 5: Drill Holes

Using a 1-7/8" hole saw or forstner bit, drill out the center. Drill one side of the end grain then the other. Slowly work your way around the cube removing the wood plugs as you go.

Step 6: Sand Cube

Using sandpaper, smooth the cube and remove all sharp edges from the drilled holes. This will help later when the 8-ball is placed inside the cube.

Step 7: Soak and Boil the Cube

Using enough water to cover the cube, soak it for at least 24 hours. I soaked this cube for 36 hours just to be safe. After soaking, boil it for an hour to ensure proper saturation. Since wood floats, place something on top of the cube to hold it underwater. I used a glass vase I had nearby.

Step 8: Lubricate the 8-Ball

I covered the 8-ball with paste wax to act as lubricant for the next step.

Step 9: Press 8-Ball in Place

After the cube is finished boiling, use a bench vise to press the 8-ball inside the cube through the end grain. Do this slowly to prevent the wood from cracking. If you push cross grain you will split your cube. I used a cut off piece of PVC to press against the 8-ball to protect it from the vice.


The reason this step works, is because of how trees are formed. Pretend that the bundle of matches in the photos above are the straw-like fibers of a tree (xylem). When the fibers of the wood get heated and saturated with water, they become flexible and stretchy. This allows you press the ball through the end grain of the wood. If you try to press the ball through the side grain, the wood doesn't move as easily, and in our project you risk possibly breaking the cube.

Step 10: Final Sanding

The cube will no longer be smooth because it soaked in water for so long. Once the cube dries overnight, sand it smooth. Be sure to sand the inside of the cube as well. I found the best method was to do it by hand to prevent scratching the 8-ball.

Step 11: Apply Finish

I finished my cube with a beeswax oil mixture found online. Apply liberally with a rag. I used this finish for two reasons. If there was still water inside the wood I didn't want to trap it there and risk the finish bubbling, and I didn't want any finish to change the look and smoothness of the 8-ball.

Step 12: How to Remove the 8-Ball

Other than potentially boiling the cube and 8-ball again and repeating the process done before, the only way to get the ball out is to break the cube around it. Using a chisel, this test cube was no match and the 8-ball was easily removed.

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The three holes drilled through the cube in perfect alignment intersect at eight points that outline an inner cube. The largest sphere that could theoretically fit in the puzzle would contain that inner cube, i.e., the length of the diagonal between opposite corners of the inner cube would equal the diameter of the inner sphere.

The diameter of the drilled holes would equal the diagonal of a face of the inner cube. If that hole diameter = square root of 2, then the edge of the inner cube = 1, and the cube diagonal = sqrt 3. Ratio of max diameter of inner sphere to drilled hole diameter is sqrt 3/sqrt 2 = 1.732/1.414 = 1.225:1. That could be increased slightly by sanding the corners of the inner cube.

Diameter of a solid sphere to be forced into the puzzle is limited practically by the compressibility and resilience of the soaked & boiled wood fibers. Ratio of the standard 8 ball diameter (2.25") to hole size (1.875") is 1.2:1, close to the maximum. I'm surprised it works so well. When all is said and done, what is the resulting diameter of the hole you forced the ball into? In other words, how much were the wood fibers permanently compressed?






I love it.

Please do more.

I can tell you that from all the ideas that came to my mind on how to do this, your solution didn't even surface. And I must admit I don't think any of the solutions I thought of would have worked. Quite enlightening, so thanks for taking the time to illustrate!

I like it! The science lesson is good, too!

Looks pretty and it's also a cool way to tease your friends! They will probably have no idea how you put the ball inside the cube :)

Good job.

Thanks for the matches & science lesson, for us slower persons.

Nice Job! I did a smaller one in response to "Impossible marble in Truncated Cube" and I found I didn't need to soak the wood, I just used a vegetable steamer, and it didn't take long, I think it just needed the heat to soak through. I think it is probably better for the wood if water doesn't soak in too much.

Interesting project and very nice instructions and pictures!

to prevent cracking, did you. push against the grain?