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Secret Chessboard Compartment

From MAKE Magazine

This project first appeared on the pages of MAKE magazine.

Unlock a secret compartment with magnetic chess pieces.

Author: Andrew Lewis
Time required: Example: 15 to 30 minutes
Difficulty: Moderate

Everyone needs somewhere to stash stuff, and this chessboard provides a cunning hiding place whether you’re a super-spy or a super-villain. Moving the chess pieces across the board in a particular way will unlock a secret compartment that you can use to hide diamonds, baseball cards, or the evidence linking you to the crime of the century.

Sections

Relevant parts

Molding plaster (10lbs or 5kg), high-strength, Hydro-Stone such as Hydro-Stone or Denscal (Herculite Stone or Crystacast in the U.K.
Latex chess set molds, including chessmen and 2" square molds for the tiles
Acrylic paint
Acrylic clear coat optional
Rare earth magnets (4), bar small enough to fit inside the base of the chess pieces

Relevant parts (continued)

PVA adhesive such as carpenter's glue or ordinary white glue
Medium-density fiberboard (MDF), ¼" thick
Medium-density fiberboard (MDF) (2), 16" squares for the chessboard top and base
Medium-density fiberboard (MDF), 8"×12" for the drawer base
Lumber (2), 1×2×16" for the chessboard sides. Remember that 1×2 dimensional lumber actually measures ¾"×1¾".
Lumber, 1×2×12½" for the chessboard back
Lumber (2), 1×2×31" for the chessboard front
Lumber (2), 2×2×14½" for the drawer guides
Hardwood (2), 1"×½"×8" for the drawer's front and back
Hardwood (2), 1"×½"×12" for the drawer's sides
Hardwood (2), strip, ¼"×½", 11½" lengths for drawer runners
Hardwood, trim boards, 2½"×¼" I used reclaimed oak.

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Edit Step 1 — Cast the chessmen and tiles. ¶

Wash the latex molds in soapy water, and let any excess water drain out.
Mix the plaster with water and pour into the molds. The correct powder to water ratio for Herculite is about 2:1, but a good general rule is to aim for the consistency of thick pancake batter. Support the latex molds with jars or tins, so that the pieces don’t fall over.

Edit Step 2 — Remove the pieces from the molds. ¶

Once the plaster is firm and dry (in an hour or so), you can remove the pieces from the molds. You’ll need to produce a complete set of chessmen from the molds, and also 64 tiles. Making the tiles might take a while, but it’s worth the effort.

Edit Step 3 — Paint the chessmen and tiles. ¶

Once you’ve molded all the pieces, you can paint them with acrylic paint. The color scheme is up to you, but a more traditional look will probably attract less attention. Chess pieces tend to look best when left unvarnished, while the tiles will benefit from a layer of clear acrylic.

Edit Step 4 — Install magnets in 2 chessmen. ¶

You need to install bar magnets into 2 of the pieces, so that they can be used to activate the locking mechanism. The easiest way to do this is to hollow out the bottom of the chess pieces with a hobby drill or similar tool, and then glue the magnet in place before covering the hole with plaster.

Edit Step 5 — Seal the MDF pieces. ¶

Start by sealing the MDF pieces with a 50% solution of PVA adhesive and water.

Edit Step 6 — Glue the wood sides to the chessboard base. ¶

Glue boards all around the edge of the MDF base like the sides of a box, except for an 8¼" gap centered on the front (where the secret drawer will be). The thickness of these side boards isn’t critical (I used ¾"-thick 1×2 stock), although a height of at least 1¾" is recommended. You can improve on the strength of the glue with heavy-duty staples or tacks, but these aren’t absolutely necessary.

Edit Step 7 — Add the drawer guides and runners. ¶

Cut a slot the same size as the bar magnets across the top of each drawer guide, then glue the guides into place on the base.
A small plug of wood should be glued into the outside end of each slot to stop the magnets from falling out. Also glue the ¼"×½" drawer runners to the base; these go under the drawer to make it easier to slide the drawer open and closed.

Edit Step 8 — Make a simple drawer. ¶

Glue 1"×½" sides, the front, and the back to the 8"×12" MDF drawer base. I miter-cut the corners for strength and appearance.
To make the drawer look more presentable, you can either line it with material or apply a coat of paint. The drawer should slide freely between the drawer guides, and it should be the same height as the sides of the box (or nearly so).

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