Wooden Burr Puzzles

 

Wooden Burr Puzzles

Notch a few sticks
and drive your friends crazy.

By Jock Holmen

Something’s got to give when
pieces of wood intersect at 90° angles.
That’s the reality behind the curious
assemblies shown here. Known as burr
puzzles, because they resemble seed
burrs, these brain-teasers consist of
three or more notched pieces that go
together at right angles. Give one of
these tricksters to an unsuspecting
friend and watch the fun.
Disassembling each puzzle is the easy
part. Putting the pieces back together
is the real challenge!

Precision is the key to making the
puzzles work effectively. Each part
must be accurately marked, milled
and cut.

The first step for all three puzzles
is to mill long 3/4” x 3/4” blanks. Use a
caliper to measure the thicknesses
precisely and make sure the blanks
are square. Then cut the individual
puzzle pieces to exact length from
the blanks.

A shopmade jig makes it easy to
notch the pieces for all three puzzles
on the tablesaw, using a dado set
(Fig. A, below). This jig consists of a
sled with runners, a clamp and a
fence. The runners fit the saw’s miter
slots, so the sled makes perpendicular
cuts. For clean, tearout-free results,
a different part of the jig should be
dedicated to each notch size. If, as
shown, the blade is offset between
the runners, you can use both sides
of the sled. For safety, the jig’s wide
fence houses the dado set from both
directions. Stop blocks and spacers
precisely position the pieces, so the
notches (dadoes, actually) are accurately
cut. Like the puzzle pieces
themselves, the spacers must be precisely
cut. To set up the jig, clamp one
stop block to the right of the slot (the
exact distance—called the Jig Set-Up
Dimension—depends on the puzzle
you’re creating). Use a puzzle piece
and the spacers to locate and clamp
the other stop. After you’ve installed
each piece, secure it with the toggle
clamp before you cut the dado (see
Source, below).

The dadoes have to fit perfectly,
so always make extra puzzle pieces,
and start by making test cuts. Testing
the dado widths and depths is pretty
easy, because most of the pieces go
together with lap joints. When the
dados fit snugly, their widths are correct;
when the joint surfaces are
flush, the dado depths are correct.
The pieces will go together more
easily if you lightly sand their edges.
That’s it; you’re ready to go.

Click any image to view a larger version.

The Three Piece Burr

The Six Piece Burr

The Twelve Piece Burr

The Three Piece Burr

In appearance, this puzzle is my
favorite, because of its perfect, simple
symmetry. It’s the only puzzle of the
three that requires cutting dadoes in
two sizes (see Fig. B, opposite).

 

Make the pieces

1. Cut 2-1/4″ blocks from square 3/4″
stock, including extras for test cuts.

2. Set up the saw and the jig to cut 3/8″
by 3/8″ dadoes.

3. Clamp the jig’s right stop block 1-1/8″
from the edge of the 3/8″ slot.

4. Snug a test piece and both 3/8″ spacers
against the right stop. Butt the left stop
block against the spacers and clamp it.

5. Cut dadoes in a couple test pieces. Fit
them together to check the dadoes’ width
and depth; make necessary adjustments.

6. Install Piece A and cut the first dado
(Photo 1).

7. Rotate Piece A, reposition the spacers
and cut the second dado (Photo 2).

8. Turn the jig around and set it up to cut
3/8″ by 3/4″ dadoes.

9. Clamp the right stop block 1-1/8″ from
the edge of the 3/4″ slot.

10. Repeat Steps 4 and 5.

11. Install Piece B with one spacer at each
end. Cut the first dado (Photo 3).

12. Rotate Piece B one-quarter turn
toward the dado set and cut the second
dado.

13. Install Piece C and repeat Steps 11
and 12.

14. Ease the corners of the bridge on
Piece C to create an octagon.

 

Assemble the puzzle

1. Connect Pieces A and C.

2. Install Piece B from the top.

3. Rotate Piece C one-quarter turn.

Fig. A: Dadoing Jig

1. Cut a 3/8″ by 3/8″ dado after clamping the stop blocks in position
and installing Piece A with both spacers to the left.

2. Cut a second dado in Piece A after rotating it one-quarter turn
toward the dado set and re-installing it with one spacer at each
end.

3. Use the opposite side of the jig to cut 3/4″ wide dadoes in Pieces
B and C. Cut the first dado, rotate each piece one-quarter turn
toward the dado set, and then cut a second dado. Make these cuts
with one spacer installed at each end.

Fig. B: Dimensions

The Six Piece Burr

By all accounts, this burr is the
most well known, because the six
pieces can be notched in so many different
ways and still assemble to create
the same form.

 

Make the pieces

1. Cut 2-1/2″ long blocks from square 3/4″
stock, including extras for test cuts (Fig. C,
above).

2. Set up the saw and the jig to cut 3/8″ by
3/4″ dadoes.

3. Clamp the jig’s right stop block 1-1/4″ from
the edge of the 3/4″ slot.

4. Snug a 3/8″ spacer against the right stop,
followed by a test piece and the remaining
3/8″ spacer. Butt and clamp the left stop block
against the spacer.

5. Cut dadoes in a couple test pieces. Fit them
together to check the dadoes’ width and
depth, and make necessary adjustments.

6. Set aside Piece A; it’s already done.

7. To complete Piece B, install it in the jig with
a spacer at each end and cut a dado.

8. Repeat Step 7, using Pieces C, D, E and F. 9. To complete Piece C, rotate it one-quarter
turn toward the dado set. Install it with both
spacers to the left and cut a second dado.

9. Repeat Step 8, using Pieces D, E and F.
Complete these pieces by moving both spacers
to the right and cutting a third dado.

 

Assemble the puzzle

1.Connect Pieces C and D.

2. Drop in Piece E from the top.

3. Slide in Piece F from the front.

4. Slide in Piece B from the side.

5. Slide in Piece A from the front.

Fig. C: Dimensions

The Twelve Piece Burr

A good nickname for this puzzle is
“The Intimidator,” because all twelve
pieces are identical, and taking the puzzle
apart is as confounding as putting it
together.

 

Make the pieces

1. Cut 4-1/2″ long blocks from square 3/4″
stock, including extras for test cuts (Fig D,
above).

2. Make a pair of 3/4″ x 3/4″ x 7/8″ spacers.

3. Set up the saw and the jig to cut 3/8″ by
3/4″ dadoes.

4. Clamp the jig’s right stop block 1-7/8″ from
the edge of the 3/4″ slot.

5. Snug a 3/4″ spacer against the right stop,
followed by a test piece and the other 3/4″
spacer. Butt and clamp the left stop block
against the spacer.

6. Cut dadoes in a couple test pieces. Fit them
together to check the dadoes’ width and
depth, and make necessary adjustments.

7. Cut this dado in all twelve pieces.

8. Flip the piece end for end and reinstall it
between the two spacers. Cut a second dado
in all twelve pieces. Both dadoes should be in
the same face.

9. Rotate the piece one-quarter turn toward
the dado set and reinstall it with both 3/4″
spacers on the left. Cut this dado in all twelve
pieces. This last cut creates a tab, which can be
used to help assemble the puzzle.

 

Assemble the puzzle

1. Assemble four pieces to form a tic-tac-toe
grid. Orient two vertical pieces with their tabs
on the right and facing to the front. Then
install the two horizontal pieces with their tabs
on the inside and facing to the back. A rectangular
space should appear in the center.

2. Install the next two pieces with their tabs on
the left and facing up. Slide in one piece from
the left side, until it locks around the vertical
piece. Slide the second piece halfway through
the rectangular space from the front. Then
move it to the right, to lock around the other
vertical piece.

3. Install the next two pieces with their tabs on
the inside and facing down. Slide them down
from above and lock them in place. You now
have two intersecting tic-tac-toe grids.

4. Slide the horizontal tic-tac-toe grid to the left.

5. Install the last four pieces. Orient the two vertical
pieces with their tabs on the outside and
facing to the right. Slide in one from the front
and one from the back. Lock them in place.
Orient the two horizontal pieces with their tabs
on the outside and facing to the left. Install one
of these pieces from the top, and one from the
bottom. You may have to hold onto the bottom
piece during the next step.
6. Complete the puzzle by sliding the horizontal
and vertical assemblies together.

Source

(Note: Product availability and costs are subject to change since original publication date.)

Woodcraft, woodcraft.com, 800-225-1153,
Toggle Clamp, #143938.

This story originally appeared in American Woodworker June/July 2009, issue #142.

Purchase this back issue.

Fig. D: Dimensions