Fiendish
Knot Puzzle
By John Cauley
Download this Fiendish Knot Puzzle Project with complete plans and step-by-step instructions from AWBookstore.com.
Here’s a puzzle that’s devilishly difficult to solve but
quite easy to make. You only need some 3/4" hardwood
dowel rods, a 3/4" Forstner bit, a tablesaw and a drill
press. At the end of one day in the shop you’ll have a dozen of
these inexpensive brainteasers to tantalize your friends.
Use dowels made from a hard wood (see Sources, below).
The kind of dowels you’d find at the local hardware store are
probably too soft to cut cleanly, but birch is OK. You’ll need about
24" of dowel to make one puzzle. A 36" hardwood dowel costs
from $5 to $10, depending on the species.
Follow steps 1 through 8 to make this puzzle. The last step is
the hardest—that’s where you have to put it together!
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Each puzzle piece is notched in
a different pattern. The drilling jig is
designed to automatically locate the
center and offset notches.
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Click on any of the images to view a larger version
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Accurately aligned holes are the secret to making this
puzzle work. Make a jig for drilling half-round notches, lock the jig
in place on your drill press table and you’re ready to go.
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1. Cut the puzzle pieces to length safely and
accurately with this jig. You’ll need seven 2-1/2"
long dowel pieces in all, six for the puzzle plus
one extra to balance the drilling jig. Also, cut four 3/8"
long pieces to use as spacers in the drilling jig.
The trick in using this dowel-cutting jig is to avoid
trapping the cut-off piece between the stop block and the
blade. Instead, butt the dowel up to a removable spacer.
Caution: Withdraw the spacer before you make the cut. The blade guard must be removed for this cut. Be careful.
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2. Make the drilling jig by cutting V-grooves into
a hardwood block. First, draw the layout below on
both ends of the block with a combination square.
Tilt your tablesaw blade 45°and raise it 1/2" above the table.
Move the fence to align the blade with cut #1. Make the cut,
turn the board end-for-end and make cut #2. Repeat the
process for cuts #3 and #4. Caution: Use a push stick and
stand to the right of your fence when cutting these pieces.
There’s a chance the waste may kick back at you.
When you’re done, check the jig for accuracy by
nesting two dowels in the grooves. Their sides should touch.
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3. Assemble the drilling jig. Cut the V-groove block in
half to make the top and bottom pieces of the drilling jig.
Stack the pieces together and drill a 3⁄4" dia. hole exactly
in the center.
Cut four stop blocks from the triangular waste pieces left over
from ripping the grooves. The puzzle pieces and spacers are
locked between the stop blocks when you set up the jig (see Step
#4). For a tight fit, first glue block A to the jig. To position block B,
place one of your puzzle pieces and both 3/8" spacers in the jig
and butt them up to block A. Then butt block B to all three pieces
and glue it to the jig.
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4. Drill center notches in three pairs of puzzle
pieces by nesting them between spacers in the
drilling jig.
In this set-up, the spacers locate the puzzle piece in the
exact center of the jig. In the next steps, the spacers will be
shifted around so you can drill notches that are offset from
the center by exactly one-half the diameter of the dowel.
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5. Insert alignment blocks into the jig for
drilling the second set of offset notches. The
alignment blocks turn the puzzle pieces 90°
to the center notch.
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6. Cut these V-shaped blocks with
a shop-made mitering jig. You’ll need
one block for each puzzle piece.
Note: These blocks are too small to cut
safely with a power tool.
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7. Arrange the drilling jig for offset notches. Drill
piece #1 and the extra piece as shown above to
make a left offset notch. Drill pieces #2 and #3 the
same way.
Then, shift the spacers to the opposite ends and drill a
second set of right offset notches in pieces #2 and #3. Drill
pieces #4 and #5 with the spacers in their new positions
(see Step 5).
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8. Assemble the puzzle. The numbers
used to identify the pieces also represent the
order of assembly. This puzzle is so fiendish
that we suggest you lightly write the number
of each piece on the end to help you figure it out!
If the pieces fit too tightly, you can enlarge the
notches with sandpaper wrapped around a dowel.
This story originally appeared in American Woodworker June 2001, issue #87.
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Download this Fiendish Knot Puzzle Project with complete plans and step-by-step instructions from AWBookstore.com.
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