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 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?

1 reply

I can't believe that I forgot that important bit of information! Make sure to press it through the end grain of the cube. I have edited the instructable to make that step easier to understand.

How much work time do you have to get the ball in? How slow do you go? That is, did you tighten ,wait, tighten, or slow even pressure over how many seconds or minutes?

I hope I am clear that I am asking how long it should take to get the ball in as well as how long do I have to work with it?

I am using doug fir as that was what was available and I had one just break on my less hole while the drill press (in 4 places at once) so putting pressure on this will be interesting.

I am soaking now (not sure if that is effective as jayhitek seemed to have failures with even long soaks and boils but I dont know what wood he used. )

So what was the push rate tomatoskins?

4 replies

In Boatbuilding by Howard Chappelle, he writes that Douglas fir and yellow pine "can only be steamed or boiled to very slight curves." He writes that this is also true for most tropical hardwoods. For extreme curvature, he recommends rock elm (try to find that these days!), ash, and hickory. For less extreme bends, he writes that white oak, beech, birch, maple and red gum are suitable. I'm assuming that the same applies in this situation. I'm sure other sources will discuss other woods. I wonder what happens to poplar? I also wonder what species you can get 4 X 4's in.

Chappelle also writes that pressure helps. So perhaps putting the cube in a pressure cooker will speed things up. He still wants you to soak the wood first, though. If it was my pressure cooker, I think I'd insist on maple. I understand it's less toxic. So a low cost source might be firewood. Firewood, however, does tend to crack at the ends, which you'd probably have to cut off. The right way to dry wood, if you're going to use it to build things, is to seal the ends, maybe with paint, so they don't dry out faster and crack. Maybe one could make this out of green wood (i.e. still wet after cutting the tree), although I don't know if it would crack or not when dried. It might not be straight after drying.

If I remember correctly it was fairly slow, but I didn't stop in the middle of it. I didn't time it and I made this almost a year ago so I'm not entirely sure how long it took. I would say at a constant rate. Sorry I can't be of more help than that.

How likely is it the size of the wood vs species. I tried making a block out of white cedar. The forstner bit was requiring too much pressure as it pushed through the interior it took a junk out. I could see it splitting at the spot as the bit was coming down, I just bought the bit and it felt sharp, HOWEVER , my drill press can only do 600 rpm on its slowest and I did read that you need 300 speed for a forstner to work properly,

I think your hole saw was the better solution, especially for end grain.

I wonder if the size of my block matters? My table saw can not rip down a 4x4 to 3" To have clean sides , since flipping did not line up. I end up with a 2 13/16" cube. But even the cedar boiled and still wet from the factory split right open and the ball was not any further .

I do admit, I did not soak for 36 hours. When these cubes split the wood is wet. But is long term soaking the key vs boiling?

I am doing a test of hole size. I have measured and traced the dry cube side, a cube face after boiling for 30 mintues and an over night soak. I have traced each hole and can tell you on white cedar there is no significant change in hole size. I will let it soak to the 36 hours and check again before and after heating it up But I suspect heating it is not the going ot show any expansion, If the mode works it will be the water allow it to compress the fibers and then expand back after not expand the actual hole.

On the Forstner bit, maybe you could put some kind of cross piece on the chuck and turn it by hand? Or I suppose you could find an old fashioned bit brace. Long ago, they had big ones shaped so that you could bear down on them with your chest.

It's probably best to boil for an hour. If I recall correctly, boat builders have a rule of thumb to steam for an hour per inch of thickness before bending ribs. But maybe this trick is a bit more severe than bending ribs in the usual manner.

I wish it stayed in and works inside of it.

This is amazing!

have you actually used liquid ammonia as my brief research does not show household ammonia will do anything. The bending forums say it is wishful thinking and that only the ammonia gas is going to work to soften wood. However, for this method ,maybe they are wrong so it would be great to read if betwys1 as found it does work to soak in household ammonia and was it straight from the bottle or mixed with water.