# Wooden Centrifugal Puzzle

This is a wooden puzzle.  The two parts lock together and you give it to a friend, asking him to unlock and separate the two parts.  A friend in Germany made this one.  When he handed it to me to solve, I could not until he showed me the secret.  This Instructable will not only show how the puzzle is solved, but will also show how you can make these to give as gifts, especially at Christmas.

I have learned through a link by Make! Magazine that this is called a Duallock Cross Puzzle and it was invented by Nobuyuki Yoshigahara.
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## Step 1: How the parts appear separated

Here you see the two halves of the puzzle separated.  Each half has a center notch and a hole below it.  Internally, there are two holes in each with a piece of dowel pin that can move freely in each hole.  The dowel pins are each a bit longer than the center notch.  The center notch is the width of the wood's thickness on the parts.  I will use some 3/4 inch clear pine.

## Step 2: Readying the puzzle to be solved

The person who solves the puzzle should see you assembling it.  He should know about the two dowel pins.  To assemble the parts, push the dowel pins back into their holes.  Invert one half of the puzzle and let the parts settle into the two notches.

## Step 3: Tumble

Tumble the assembly back and forth so the dowel pins move through the holes in the mating parts.  Hand it to a friend and ask him to solve the puzzle.  If he has seen this before, or is very smart, he will solve it right away.  If he has not seen it before, he will struggle with it until you show him how it is solved.

## Step 4: The solution

I hinted at the solution in the title of this Instructable.  Place the locked puzzle on a flat surface.  With your finger and thumb, spin the puzzle as rapidly as you can.  This creates a centrifugal force that flings the dowel pins outward from the center and releases the two pieces so one can easily be lifted from the other.
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ron.baer21 days ago

I am just starting to get into woodworking, carving and restoring things, mostly my father and grandfather's wood things, mostly bookshelves and coffee tables. Once I am done with my latest resto project I am going to be making one of these for MY grandchildren, and quite a few of the other wooden puzzle/game items I"ve found here! Cheers, ron!

my grandfather gave me one when i was a kid, it never gets old
jšindýlek3 years ago
Hi All !

This Puzzle is similiar with: "Hanayama Cast News"

like this: http://hlavolamy.heureka.cz/hlavolam-hanayama-cast-news/

C.
dombeef3 years ago
Phil B (author)  dombeef3 years ago
Thank you for the message. I saw the new Instructable on the wooden centrifugal puzzle that you linked. His design and construction approach is different from the Instructable I did. The situation reminds me of the numerous laptop supports, knex crossbows, wifi cantennas, and other frequently repeated projects at Instructables. Each of us has the right to present a variation in design that might suit someone else better. My only surprise was that my earlier Instructable did not show in the "Related Instructables" on the right side of the screen. Oh, well...
3 years ago
Should you ask atleast for credit? It is clearly like your design, and the person is not commenting to what I said(it looks like Phil B.'s design, etc) , yet he comments to other people way after I posted the comment.
Phil B (author)  dombeef3 years ago
I was actually copying one given to me by a German friend about ten years ago. Eventually, they all go back to a Japanese man mentioned in the Introduction. The part I worked out was a procedure for making them reliably with the tools I have. I see a couple of people commented that there is an earlier Instructable on the same puzzle. I do not know if he was aware of that or not. Several times I have published something that is very similar to another Instructable by someone else. I link that other Instructable and then explain why and how mine is different from the earlier publication.
justbennett3 years ago
Upon first viewing, I did not realize that these pieces were formed by gluing. While I was trying to figure out how you drilled the holes inside the notch (I'm no woodworker!) I came up with a different idea for the design of this puzzle.

I thought the holes could be drilled from the outside ends of each piece. Then you would replace the appropriate amount of wood with a dowel glued in place. Make sense?

It's only a slight difference in the result and, if you can hide the dowel on the end grain it would really add to the mystery. Thanks for sharing!
Phil B (author)  justbennett3 years ago
I did experiment with what you suggest. There is a tendency for the wood to have different densities within it and these cause the drill bit to drift. That means the holes do not align precisely enough for the dowel pins to move back and forth as well as they need to. I found the less drilling the better. Drilling from the outside ends increases the probability of the bit drifting off center. Thank you for your comment.
grunff3 years ago
Great instructable, thanks for writing it up. But even more impressive is your ingenious use of a radial arm saw as a sander and a drill! Would you care to share how you attached the sanding drum mandrel and the drill chuck to the saw's spindle?
Phil B (author)  grunff3 years ago
Thank you for looking and thank you for your comment. I am not as clever as you suppose. The back end of the motor shaft on Craftsman radial arm saw came from the factory with a 1/2 inch x 20 thread spindle about half of an inch long. It is made to accept a 1/2 x 20 thd. drill chuck. Sears also sold a 3 inch long sanding drum 2 inches in diameter designed to attach to the same thread specifications.
3 years ago
That's pretty neat, thanks for the explanation. Must look out for some similar attachments for my saw :-)
JJYork3 years ago
I enjoyed making your Instructable. Your directions are clear and easy to follow. My puzzles worked the first time. I did use metal pins (stainless) that others suggested and I also used instant glue so I didn't have to worry about sanding and later changing my dimensions.
Phil B (author)  JJYork3 years ago
Thank you for your report and your comment. I am glad it was clear enough and everything worked.
Rob O3 years ago

One change I made was to use a piece of brass tube (ace hardware, cut w pipe cutters) instead of wooden dowel. It looked very cool and worked just like the others which had the dowel.
Phil B (author)  Rob O3 years ago
Thank you for the report. I am glad they have been well-received. The brass tubing is a good idea. I would not have thought the brass tubing has enough mass to work, but the dowels are low in mass, too. The brass would be very attractive with dark wood like oak or walnut. I have made a few to have on-hand. Everytime I demonstrate it for someone I end up giving it away.
albf14 years ago
great instructable, just to say, the centrifugal force doesnt exist, it literally means "force of inwards". what you mean to say is centripetal force, the outwards effect of motion+gravity . =)
4 years ago
Sorry, you have it backward. Centrifugal means outward or away from a center or axis while centripetal means inward or toward a center or axis .
4 years ago
Centrifugal force is quite a valid concept.
Newton's Third law of motion says that for every action there is an equal and opposite reaction.
To move in a curve, you need a force towards the centre. This is a Centripetal force but there must be an equal and opposite force (say on the string of a conker as you swing it) which is directed away from the centre - a centrifugal force. BUT, as soon as you cut the string to remove the centripetal force, the centrifugal, reaction force will disappear. This is similar to the force upwards on your backside as you are sitting in the chair. The force disappears as soon as you get up - it can't throw you up into the air.

If you are ON a spinning object (a spinning frame of reference) you will experience two forces. The centrifugal force will 'feel' as if it is throwing you outwards and if you drop an object it will appear TO YOU to go outwards. A stationary observer will see this object leave your spinning frame on a tangent. It is not thrown out- it will keep moving in the direction in which it was moving when you let it go (in that observers frame). But to you, it has been thrown out and will travel in a curve!
Coriolis force is a wierd one; it is only experienced if you try to move and you will be 'thrown sideways' as you move towards or away from the axis of rotation. As you move away from the centre your tangential speed is less than that of the place you are moving to (it is moving with the same angular velocity as you but its radius is greater). You will have the impression of being pushed to one side as you move towards the place you want to go to. This is why, when air flows from high pressure areas to low pressure areas, on the Earth's surface, it goes in circles to cause hurricains, depressions and tornadoes.
Sit on a child's playground roundabout or spin on an office chair to experience both forces - it is the Coriolis force that is the really disturbing one.
I have a feeling that Physics teachers ban the concept of centrifugal force because they don't feel confident to give (or improve on) the above explanation.
'Real' physicists are quite happy with it. Tension is the common name for the centripetal force. according to many physics lecturers, the centrifugal force doesn't exist.
the force in question would therefore be gravity propelling the blocks away from each other by means of sudden loss of tension/centripetal force (the dowels).
4 years ago
you don't expect me to do coordinate substitution in my head while strapped to a centrifuge, do you?

http://xkcd.com/123/
3 years ago
The xkcd reference totally needed to be made. Thank you
3 years ago
skype, with my non-geeky friend, I asked him if he read about the new ubuntu release (wasn't even thinking about xkcd, I just asked because I was running the new release, as I am now), and you can probably guess his response...
Anthony3124 years ago
If I gave this to one of my friends and asked them to solve it, they would just break it in half and say, "They're in two pieces now. Puzzle solved."
Phil B (author)  Anthony3124 years ago
Have you considered finding new friendss with fewer anger issues?
4 years ago
people normally chase others while holding scissors ready to stab them, right?

anyway, I make an interesting character for a cartoon my friend is working on :D
4 years ago
Tell them to solve it WITHOUT breaking it.
Kryptonite4 years ago
I finished it! Sadly it was a rushed job (I had one hour) and it doesn't line up quite right. It'll take another day to fix. Thanks though! :D
Phil B (author)  Kryptonite4 years ago
I have been there and done that. You may still be able to salvage it. See my longer response to blaisepascal below in which I described drilliing in from an outside end to remove the dowel pin and enlarge the hole in which the dowel slides followed by closing up the hole with a larger dowel. You may also be able to enlarge the hole under the notch so the dowel pins fall into them more easily. I have built several of these several different ways in an attempt to make the results as consistent as possible. I believe what I described in this Instructable is probably the most reliable way and is likely the way my friend in Germany used. (I cannot ask him because he is no longer living.)
4 years ago
I've finished a true copy now! All the pins fit and when it's put together you literally can not see them. I replaced the wooden pins with metal rods, the heavier material along with the smooth sliding surface reduces the angle required for the rods to slide from ~70 degrees to ~30.

Brilliant Instructable, thanks so much! I love making little puzzles like this. :D
Phil B (author)  Kryptonite4 years ago
Thank you for the report. I am glad you got a good one that works well. I thought about using some metal rod. I have some 1/4 inch aluminum rod left over from something. I am hesitant to try steel because it could develop some rust coating from humidity over the years. And, here in the USA we have a couple of large home improvement stores that are in all larger cities (Home Depot and Lowe's). They regularly stock square dowels. I started buying and using 5/8 inch square dowels for the basic stock, rather than going to all of the work of making square stock. The holes I am drilling in the setup from step 9 are about 3/4 of a millimeter off center, but there is enough looseness in the holes that the round dowels still slide into position very well. I have now made and given away seven of these.
4 years ago

I used 8mm round mild steel rod in a 12 mm hole, it gives a little bit of lee way but not too much.
Hobbytik4 years ago
Hello,
This puzzle is already produced and sold for many, many years now.
With a lot of different names. But why do you call it "wooden centrifugal puzzle"? Now you are giving away the principle of this puzzle. Puzzlers have to find out that by their own! That's happy puzzling!
Best regards,
The Netherlands
(Puzzle collector/designer voor about 20 years now)
Phil B (author)  Hobbytik4 years ago
I did not know what to call this puzzle. I found it with an Internet search and some key terms. What I found called it a "wooden centrifugal puzzle." That was before I learned it had been designed by Nobuyuki Yoshigahara who called it a Dual Lock puzzle.
fnirt4 years ago
Thanks for the instructable! I made one of these over the weekend and by the second day I was able to spin it on my palm and open it. This way you can show it to folks, turn slowly around (spin it while your back is turned) and do the reveal -- the whole room doesn't get the answer all at once!
Phil B (author)  fnirt4 years ago
Spinning the puzzle on your hands is a clever idea. Thank you for tryiing this and for reporting back.
qwerty9874 years ago
awsome
Phil B (author)  qwerty9874 years ago
Thanks.
srsantafe4 years ago
Thanks a lot, I realy like puzzles, and this one looks preaty cool
Phil B (author)  srsantafe4 years ago
Thank you for your comment. The idea of the puzzle is simple enough, although clever. The challenge comes in making the parts precisely enough that the puzzle works. It should not be that difficult, but little errors and inaccuracies easily creep into the process.
Jayefuu4 years ago
Congrats you're on make!

http://blog.makezine.com/archive/2010/11/how-to_build_nob_yoshigaharas_dualo.html
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