How to Make a Gravity Puzzle (Brain Game)

Here’s a little brain game you can easily
make to impress the smartest people you know.
The idea has been around forever, but most
people still can’t do it. The challenge is
simple .. just balance these 14 nails on a
single nail head.
For this project I started by making a template
for a platform design I want to try. If you
like it, you can have it for free. I’m getting
ready to tape this to a piece of wood, and
I want these edges flush, but a little overhang
on these others. I found a 3/4″ panel of birch
wood in a scrap pile at the home improvement
store, and my paper template goes right in
the corner. A little duct tape will hold it
in place just enough to help me cut holes
for some nails. A total of 15 holes for 15
nails. I’ve got a 9/64″ drill bit that looks
about the right size, so that goes in the
chuck of my drill press. And once I’ve got
it in secure, I’ll drill a test hole in some
junk wood to double check these 3″ framing
nails will fit. I can manipulate the nail
easily, and the hole is still tight enough
to support the spike firmly in place. Perfect!
Lowering the bit next to the edge of the board
will help me gauge the depth of the hole,
and I can set these nuts to stop the press
from drilling any deeper. I think I’m ready
to drill some holes. I’m being careful to
drill all 15 markers to the same depth, and
before I move on I’ll insert a nail in each
hole and check the tops of the nail heads
to see if they’re all level. Looking good.
Let’s move on. The nails come out and it’s
over to the chop saw to cut the other 2 sides
off the template. These cuts are good, and
I’m happy with it so far, but let’s go one
step further and take it to the router table
for some finishing work. I’ve got a 3/8″ beading
bit and i’m testing the profile cut on some
scrap wood. It looks like that’s going to
work, so I can place the block with the nail
holes facing down and carefully router the
edges. This bit is spinning at 20,000 rpm
so I have to be very careful not to lose a
finger here. Ok the edges are done, but a
little furry, so I’ll sand that off with some
100 grit sandpaper, then hit the top as well
to get it ready for some color. I like how
it’s looking now, so time to grab some leftover
stain and shake it up, wearing gloves of course.
This is a “Rosewood” color stain and one of
my project nails will help get the lid off.
I’ll use a rolled up paper towel to apply
the stain to the bottom, top, and edges, making
sure every surface gets a liberal coating.
This will soak for about 3 minutes, then I’ll
use another paper towel to remove the excess
so that it looks like this. After about 2
hours of drying, I’ll insert a nail in the
center hole, and grab some wood finish that
will seal the wood and give this a somewhat
glossy look. When the sides are all sprayed
I’ll prop it up to dry for another couple
of hours. If this looks like more work than
you want to put into this project, you could
always just grab any old piece of wood and
a hammer and nail it in just about anywhere.
It’s as easy as that. But maybe you don’t
have a hammer? Go find a rock. Just a couple
of taps and you’re ready to go. If you don’t
have a rock? How about an attractive assistant?
You can use any method you can think of, as
long as your nail is straight up like this.
Alright it looks like the finish is dry, and
we’ve got the nails set in place. Now you
can challenge your friends to balance all
the outer nails on the lone inner one. All
the nails have to balance at the same time,
and can only touch the center nail head. I’ve
seen some pretty creative attempts at getting
this to work. I say “attempts” because typically
it’s fail after fail after fail. When your
player is sufficiently discouraged and claims
it’s impossible, this is where you get to
show off your brilliance. Here’s the super
simple pattern that was discovered long long
ago, and works amazingly well. Lay one nail
on the table, and mesh the other nails over
top, one after the other, like this, until
you have 6 nails laid out on either side.
This last nail goes on top, pointing the other
direction, and the pattern is complete. To
make this effective, grab the bottom nail
on both ends with your middle fingertips,
and while lifting slowly, use your thumbs
to hold the top nail down until all the nail-heads
catch. At this point you can remove your thumbs,
and place the entire structure in position.
Well that was easy! The center of gravity
of the entire unit is lower than the balance
point, making this amazingly stable. I also
discovered that the nails can be compacted
and even more nails added! I just added 9
more nails for a total of 23, and it’s still
holding firm. I just made another stack of
22 nails, and am seeing if I can get them
to balance on top. Ooh, a little shifting,
but they’ve held. I’ll take my chances with
another group of 22, and now this structure
is up to 67 nails! When I try one more stack
of 22 spikes, it’s about finished, but wait,
it actually stayed up! Well there you have
it, 89 nails balanced on 1 nail head. At this
point, the center of gravity is high, and
the base is narrow, so it takes mad ninja
skills to balance any more. I even got this
to work with stacks of up to 15 matches. And
even when they were lit on fire they held
their place on top of those little match sticks
amazingly well. How many nails can you get
to balance? That’s it for now. If you liked
this project, perhaps you’ll like some of
my others. Check them out at

Author Since: Mar 11, 2019

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