Impossible Marble in Truncated Cube

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Picture of Impossible Marble in Truncated Cube
This project was inspired by a youtube video. I came up with the shape and the method to cut and stain it. This turned out to involve more interesting math and woodworking problems than I had expected!

If you want to make one yourself, you will need:
  • Wood (preferably a soft wood like pine)
  • A nice marble
  • Woodworking machinery (drill press, table saw, bandsaw)
  • A good vice
  • A way to boil water
  • Optionally, sanding and finishing supplies
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Step 1: Cut A Cube And Drill Holes

Picture of Cut A Cube And Drill Holes
Cut yourself a cube. I did this with a table saw sled and a stopper block. Once you have the distance you want set, you can simply rotate the wood around until you've cut it down to the right size on all three axes.

For the holes you'll again want to set up some stopper blocks. Find the center of one side of the cube and center it perfectly under your drill press, then fix two pieces of wood to form a corner that you can true it up against. Now drill through from all sides. It might be best to go through each side rather than through the entire cube in order to minimize any tear-out.

The big question here is what size the drill bit should be. There's some fun geometry involved that you can read about in my blog entry about this project here, but all you really need to know is that the drill needs to be at least 71%, or [1/sqrt(2)] the diameter of the marble. This is the size ratio at which the marble will be touching the corners of the intersecting tubes. If you want your marble to rattle around a bit, try something like 80-90% of the marble's diameter. I went with 73% because I didn't have any bigger drill bits on hand. My marble can be rotated, but doesn't rattle.
Advar6 months ago
Nice! Wonder if something similar can be done with a walking stick...
dudes7 months ago
to help with the cracking problem, let the cube dry in a paper bag. I know it sound weird and I don't know why it works, but it does (usually)
ProfHankD7 months ago
I just did a bunch of these as a little project with a couple of 5 and 12 year old girls.

I used pine cut from a 2x4, microwaved the wood blocks individually in a teacup with a half-cup of water and a little plate over it for 1+1 minutes, and used a hand clamp to force the marble in. To push it all the way in (not just flush), I found it easiest to use a socket fitting over the marble as I clamped it. I let them dry for a while, sanded them, and then the girls painted them and extras with the marble outside (to show the challenge) with watercolors that let the wood grain show through. Total time less than 3 hours! A very nice science/art project....

The 12 year old gets the science, the 5 year old mostly liked painting it. ;-)

thegnome54 (author)  ProfHankD7 months ago
Those are awesome! That makes me really happy to see, thanks so much for sharing. I look forward to doing these sorts of things with kids when I become an uncle/father myself.
__-_-_-__8 months ago
or just use a 3D printer.
They can now print WOOD ? That will save a lot of drilling and sawing.
They can print a wood fiber/plastic composite rather like sawdust with a PLA binder. You can even tone it (e.g., to create a fake woodgrain) by tweaking the temperature during printing to lightly brown the wood. PLA is such a great material to print that I've not been tempted to try the fake wood....
who cares?!? you can even print metals.
I wish there was a like button. That was genius.
wood is an inferior material.
stechi7 months ago
Ok, I've done one, what do you think?

Marble 14.8mm, holes 12mm, mahogany (or similar)
Steamed in a vegetable steamer, in the steam, not in the water. I did a test piece for an hour, it went through so easily with a lever press I made and a small socket, so I just heated this one 45mins. I don't think the point is to cook the wood, only to make sure it is heated through, so my next one might be just 15 mins. Finished with a little fine sanding and rubbed in some wax polish. Very happy to have another home-made curiosity, thanks for the idea!
Marble in cube.jpg
thegnome54 (author)  stechi7 months ago
That is absolutely beautiful! I love the way the edges of the holes are smoothed. How loose is the marble with that ratio? Thanks for sharing!
stechi thegnome547 months ago
Glad you like it! The edges of the holes were going to be chamfered but on the first one my lousy drill chattered, so I sanded them by hand (thumb) and gave them a more rounded edge. The marble can move about 2mm each way so it rattles a bit, and you can tell it really is a marble and see it is impossibly trapped. I'll see if I can find out how to vote for you.....
poofrabbit7 months ago
Hey congratulations on being a finalist in the weekend projects contest! I really love this. Not only do I want to make one (I'm hunting for a really wicked marble) but I am going to see if we can't do this as a project for the boys next year at the camp I work for. Good luck and again gratz!
thegnome54 (author)  poofrabbit7 months ago
Oh wow, thanks! I hadn't realized that I was a finalist. I'm glad so many have enjoyed my instructable. It's really wonderful to think that I'll have helped/inspired people to have fun with woodworking. Good luck finding that marble!
fretted7 months ago
Stain it before you boil it 3 or 4 good coats of stain will hold up to a boiling then your stained all the way through ! make sure you let the stain dry completely before boiling !
stayputnik7 months ago
Great job! Here's a suggestion for the press-in tool the next time you do this... try using the socket from the socket wrench instead of the block. It's nice and hard, will fit into the hole if you pick one small enough, and already has a hole in the end for stabilizing the marble. Cool project... thanks for posting it!
woodpuppy7 months ago
Neat! Here in Germany you can buy a powder for dying wood to any color you like. Mix it with water and throw the cube into the mix. The water Perls off the glass marble! After drying time of the cube and any thing is on the marble just shake the cube under running water. Then use some tung-oil to finish and or polish the cube.
petercd7 months ago
I used the kettle to boil the water, popped the cube inside and then just put it out of the way to soak for 3 hours.
A glass sitting on top of the cube holds it under the water line.
kettle boil.JPG
jujubee318 months ago
Are there any other tools you can use for this besides the ones listed I find havs those exact ones
smoak8 months ago
Love it, adding this to my long list of "projects to do"
I figured you would split the wood along the grain then glue it back together with the marble inside for an invisible seam. Interesting.
That could be done. It is possible to make a glue line disappear.

Now I know what to do with all the marbles I cut out of old spray paint cans...
jujubee318 months ago
I voted and faved u
obviousgenius8 months ago
I'm going to do this. I just looked at the pics, because it's real early in the morning and the kids are getting up for school, but this reminds me of the ending of Men In Black 1 when looking back at earth from one of the infinite possible creators perspective. I shall have one of these. Beautifully done.
throbscottle8 months ago
Nice - should produce some head scratching!
bLiTzJoN8 months ago
I'm going to do 10 min on the stove with an inverted vegetable steamer with a rock on it to keep it submerged. I've done the tooth'n'nail project but only one end of the block was submerged. That was for a Christmas present for my Grandfather who loves to do woodworking projects. I do believe I have found a project for this upcoming Christmas. Thanks!
unclmike8 months ago
Good job. Next time (if there is one) toss a tea bag or two into the water when you boil the wood and it should stain the cube nicely. You could also use a bit of food coloring to get a different look.
thegnome54 (author)  unclmike8 months ago
Cool idea! I'll be sure to throw some tea in with my next boiled-wood project. I wonder if that would give a lasting odor as well?
Spokehedz8 months ago
Mother Blanking Genius.
Makedo8 months ago
You can use a vegetable steamer to warm up the cube. If you soak the wood you will loose the natural oils. use linseed oil to help prevent cracking afterwards. I wonder if boiling it in oil would work? In most cases of heating the wood by steam you only have about 45 seconds tops to do what you need before you have to reheat. I recommend heating the wood next to the vise and do not allow the cold vise to touch the project. even a wooden vise needs to have some warmth.
You want to use H2O because it softens the fibers. Oil is not a solvent for the cellulose...
stechi8 months ago
Lovely idea, I hope to try this!

It would be great if people would mention the results they got with different woods and different processes e.g. boiling or soaking, water or oil.
claudg19508 months ago
Great job.
It should be easier if you do all the inner sanding before putting the ball in.
I would see if I may use one of those spherical grinding stones --the type that you attach to a hand drill-- to navigate inside the central hole, and expand it.
Well done anyway
thegnome54 (author)  claudg19508 months ago
Ah, great idea! I don't think I have one of those, but it sounds like it would work quite well.
Oscelot8 months ago
I'm so tempted to do this inside a sphere to make a cat toy.
patbking8 months ago
I am going to make it
blomeclown8 months ago
That's so neat. I'll have to get my woodworking tools out of storage and try it.
You had some questions about the finish. Have you considered a "burnt wood finish"?
Do a Google search--there's a few YouTube videos demonstrating how it's done.
The nice thing about this technique is that you can vary the color by controlling how much initial charring you get and, if it's too dark, by a little extra sanding. It also lends itself well to a Danish oil finish that eliminates the drips common with varnish or poly on a small piece.
Bill WW8 months ago
Fantastic! I'll do this for sure, thank you.

All I need is the marble. I have plenty of wood species to try, hope they work as well as yours did!
thegnome54 (author)  Bill WW8 months ago
Awesome! I'd love to see what you come up with. I tried the 'impossible nail' trick with what I believe was some cherry a while back. It did compress after boiling, but not as much as a softer wood would. You can probably just go for a higher bit-to-marble ratio to make the insertion easier on denser species.

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