Magic Coin Bank

Mystery and illusion via a tricky mirror

Overall dimensions: 81⁄2 × 81⁄2 × 81⁄2"

This fun and mysterious bank is sure to delight children of all ages. Coins dropped in the slot seem to disappear, leaving the box empty except for a small wooden cube which appears to float in the center. The secret to the illusion is an internal mirror set at a 45° angle, creating the impression that the bank is hollow, while the money drops into the section behind the mirror.

There’s no magic to building this project, but you’ll certainly learn some woodworking tricks. They include a great lesson in spline joinery, with hidden splines used to attach the case parts, and keyed splines used to join the mitered front and rear frames. The only specialty supplies involved are a “front-surface” mirror and a checkerboard-patterned paper liner for the interior. See the Convenience-Plus Buying Guide for the mirror source, and go to woodcraftmagazine.com/magpatterns to print out the liner pattern.

I made this box from sassafras, which is relatively soft and easy to work with both hand and power tools. As an added bonus, freshly cut sassafras exudes a delightful, spicy aroma that will leave your shop smelling exotic for several days. However, you can use any wood of your choosing to build the bank. Although you could use glass for the front of the box, I chose to use acrylic to provide for child safety. 

Make the case

1 Mill a 36" length of stock for the box sides to the thickness and width shown in the Cut List. Then cut each individual side (A) about 1⁄8" oversized in length for now. Mark the mating ends for reassembly later in their original sequence to ensure grain continuity around the box. Orient the one mismatched corner to be on the underside; then mark the top piece to identify it as such.

2 Tilt the blade on your tablesaw to 45°, and miter one end of each side (A). Use a stop on your miter gauge fence to help keep the pieces from slipping as you cut. Reset the stop to cut the pieces to final length while mitering the other ends, as shown in Photo A.

Adjust the fence and blade height to cut the 3⁄8"-deep spline slots 1⁄8" in from the inside edge of the miter.
Cut the coin slot on the router table in two passes, using stopblocks to limit the slot’s length.

3 With the saw blade still tilted at 45°, position your rip fence to cut the 3⁄8"-deep spline slots in the mitered ends, where shown in Figure 1. Guide the mitered ends along the fence to make the cuts as shown in Photo B.

4 Cut a piece of 3⁄4"-thick stock to 21⁄4" wide × 18" long to use as spline stock. Then use scrap to set up the saw for a 1⁄8"-thick rip that creates a snug fit in your spline slots. With that saw setting, resaw two lengths of 21⁄4"-wide stock from your 18"-long piece; then crosscut 12 pieces 11⁄16" long from that to use as case splines. Save the rest of the material for the frame splines to be made later.

5 Chuck a 1⁄4" straight bit in your table-mounted router, and cut the coin slot, centering it in the top piece as shown in Photo C.

Sawing the grooves

Saw the 13⁄32"-deep grooves for the mirror. Set the miter gauge at 45° to the blade, and use the same stop position for both opposing cuts. Cut the right-hand piece with its end against the fence and the left-hand piece with its side against the fence.

6 Lay out the grooves for the mirror on the two opposing box sides (A), as shown in Figure 2. Make the cuts on the tablesaw, as shown in Photos D and E. You can use the same stop setting for both pieces, but you’ll need to load the pieces onto the miter gauge in two different orientations. On one piece, the mitered end rests against the fence, and on the other, the side goes against the fence. Use a plywood backer to minimize exit tear-out. After making both initial cuts, reposition the stop and make a second pass on each piece to widen the cuts to 3⁄16".

7 Make up four 7 × 8" clamping cauls from scraps of 1⁄4"-thick plywood with 45° strips glued and screwed at either end. Clamp the cauls to the sides; then dry-fit the four sides together, as shown in Photo F. When you are happy with the fit, glue the box together.

Make the Frames

1 Cut the front and back frame pieces (B) about 1⁄16" longer than the sizes shown in the Cut List. This will create slightly oversized frames that you’ll trim flush to the case after assembly.

2 Using a miter gauge and stop, miter the ends of the pieces to 45°. Glue four of the pieces together to make up the front frame, as shown in Photo G.

3 Cut centered 1⁄4"-wide × 1⁄4"-deep grooves in the remaining four frame pieces, where shown in Figure 1, to accept the back panel (C).

4 Cut a piece of stock for the back panel to the size shown in the Cut List. Saw or rout 3⁄8"-wide rabbets in the edges to create tongues that fit in the rear frame grooves.

5 Drill a 11⁄2"-diameter hole through the center of the back panel. Then use a coping saw to cut opposing notches at the perimeter, as shown in the Back Hole and Plug Detail in Figure 1.

6 Glue the back frame together as you did with the front frame. Be sure to slip the back panel (C) in its grooves before clamping the pieces (B) together.

7 Turn a 11⁄2"-diameter plug (D) with a 7⁄8" long spigot, as shown in the Back Hole and Plug Detail in Figure 1. (If you don’t have a thick enough piece of sassafras, either glue up thinner pieces or use another species such as oak.) Test the fit of the spigot in its hole. Drill a 1⁄4"-diameter hole through the spigot, and glue a 2" length of 1⁄4"-diameter dowel in place to serve as a lock.

8 With the blade raised 1", saw centered spline slots in the corners of both frames by carrying each across the blade at a 45° angle, using a jig like the one shown in Photo H.

9 Cut the previously unused spline material into slightly oversized triangular splines to fit in the slots. Swab the pieces with glue, and tap them home, as shown in Photo I. When dry, trim the splines flush with a chisel and block plane.

10 Rout a 1⁄4"-wide × 1⁄4"-deep rabbet around the inside of the front frame, and then square the corners with a chisel.

11 Make the retaining strips (E) that hold in the acrylic panel, as shown in the Retaining Strip Detail in Figure 1. The best approach here is to saw or rout the 1⁄8" × 1⁄4" rabbet in the edge of a 1⁄2"-thick board; then rip the 1⁄4"-wide retaining strip from the rabbeted edge. Crosscut the strips to the lengths shown in the Cut List; then miter the pieces to fit the rabbet in the front frame.

Glue the splines into their slots, and then tap them home to fully seat them before clamping at the frame corners.
To avoid breaking the mirror, carefully slide both it and the backer into the box grooves at the same time.

Assemble and finish the box

1 Glue the back frame to the back of the box.

2 Print out the liners on cover stock or other heavy paper, and trim them to fit inside the box. If you need to make the pieces smaller, trim an equal amount off each side to keep the borders an even width. Brush rubber cement on the back side of the liner pieces and on the inside surfaces of the box and allow it to dry. Then carefully adhere the liners to the inside of the box.

3 Cut the mirror to 8 × 95⁄8". Note: This mirror is very thin. To avoid cracking it, handle it carefully when removing the protective plastic covering and when cutting it.

4 Saw the acrylic to 611⁄16 × 611⁄16". A standard carbide combination blade on the tablesaw will do the job fine.

5 Cut the floating block (F) to the size shown in the Cut List, using quartersawn material so the grain pattern doesn’t spoil the illusion in the mirror (see Figure 1). Finish the block with shellac; then affix it to the mirror at its center, using cyanoacrylate (CA) glue.

6 Cut a piece of 1⁄8"-thick plywood to 8 × 95⁄8" to serve as a backer (G) for the mirror. Then carefully slip the backer and mirror into their grooves at the same time, as shown in Photo J.

7 Place the acrylic in its rabbets in the front frame, and then attach the retaining strips (E) to the frame using #4 × 1⁄2" wood screws. Clean the inside surface of the acrylic thoroughly.

8 Screw the front frame to the box with eight #6 × 11⁄2" trim head screws. Plane, scrape, and sand the edges of both frames to flush them to the box sides. Then sand the whole box through 220 grit.

9 Temporarily apply masking tape to the acrylic to protect it, and then apply several coats of your favorite wood finish. I used spray shellac. 

About Our Designer/Builder

Ken Burton has been working with wood for more than 30 years. Most summers you can find him teaching workshops at the Yestermorrow Design/Build School in Warren, Vermont, or at Peters Valley Craft Center in Layton, New Jersey.

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