# 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

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.
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__-_-_-__1 year ago
(removed by author or community request)
1 year ago
They can now print WOOD ? That will save a lot of drilling and sawing.
1 year ago
I wish there was a like button. That was genius.
1 year ago
wood is an inferior material.
5 months ago

They actually have printed food and functioning organs! Random fact you now know.

5 months ago

o'really captain obvious?

1 year ago
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....
1 year ago
who cares?!? you can even print metals.
collegecultivator7 months ago

Awesome and I just suggested to my son that this would be a great class woodshop project. Project using math skills ='s too awesome! Thank you.

Nice! Wonder if something similar can be done with a walking stick...
dudes1 year 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)
ProfHankD1 year 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)  ProfHankD1 year 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.
stechi1 year 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!
thegnome54 (author)  stechi1 year 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!
1 year 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.....
poofrabbit1 year 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)  poofrabbit1 year 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!
fretted1 year 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 !
stayputnik1 year 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!
woodpuppy1 year 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.
petercd1 year 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.
jujubee311 year ago
Are there any other tools you can use for this besides the ones listed I find havs those exact ones
smoak1 year 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.
1 year ago
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...
jujubee311 year ago
I voted and faved u
obviousgenius1 year 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.
throbscottle1 year ago
Nice - should produce some head scratching!
bLiTzJoN1 year 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!
unclmike1 year 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)  unclmike1 year 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?
Spokehedz1 year ago
Mother Blanking Genius.
Makedo1 year 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.
1 year ago
You want to use H2O because it softens the fibers. Oil is not a solvent for the cellulose...
stechi1 year 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.
claudg19501 year 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)  claudg19501 year ago
Ah, great idea! I don't think I have one of those, but it sounds like it would work quite well.
Oscelot1 year ago
I'm so tempted to do this inside a sphere to make a cat toy.
patbking1 year ago
I am going to make it
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