Download project plans at
8" plywood at least 400mm×280mm for the
backboard. I used birch.
Closed-grain hardwood 1× 4 (¾"× 3½"), 4' long for
the toggles and horizontal pieces. I used birch
because I like its light color, but maple would
Wood 2× 6 ( 1½"× 5½"), 4' long for the vertical
pieces and base. I used spruce.
Carpenter’s glue and sandpaper
1¼" finishing nails ( 13)
Washers ( 6)
Wood screws: #4×¾" ( 4) and #6× 1½" ( 4)
Small, loose spring or rubber band
Marbles, 15mm–16mm in diameter ( 12)
Computer with printer and paper to print out plans
Band saw or jigsaw
Drill or drill press
Drill bits: e", W", r", ¼", and 0" The 0"
bit, for the marble holes, is an unusual size; try
a specialty woodworking supplier like Lee Valley
Tools ( leevalley.com), Woodcraft (woodcraft.
com), or Rockler ( rockler.com). Substituting ¾"
holes won’t align the marbles as well; 3" holes
can work if you carefully select smaller marbles.
11" Forstner bit or fine band saw blade or
Keyhole saw or file
82 Make: Volume 20
Build Your Marble Adder
Time: A Weekend Complexity: Moderate
1. Mark the layout on the
You can use my project plans, or you can design
your own (see sidebar on page 85). Note that I use
metric measurements in general, but standard sizes
for the drill bits and some materials.
1a. Download the project plans from makezine.
com/20/marble_adder and print them at full size,
not scaled. If you can print oversize, use the full
template plan.png. Otherwise, print out the tiled
version, plan_p1 through plan_p4, and align and
glue the 4 pieces together. Also print at full size the
templates toggles_template.png, for Step 2, and
sliders.png, for Step 3.
1b. Cut the plywood to 400mm×280mm and clamp
the template centered on top.
1c. Transfer the key locations from the template
onto the plywood. For the positions of the holes,
I used an awl to punch through the template and
into the wood. For the horizontal and vertical
pieces, I transferred the positions of key corners by
Diagrams and photography by Matthias Wandel