Make your own wooden puzzle

An easy wooden puzzle to make?

If you're a beginner, choose a wooden cube or the standard devil's knot: both are starter projects. Don't take them for simple, though. Accurate square sticks are hard to make, and without a table saw and a drill press you won't get good work. What each puzzle asks of you:

• The wooden cube (Soma cube): small cubes of the same size, glued into pieces.
• The devil's knot: only six pieces, but notches that must be cut exactly.
• The snake cube: 27 cubes to drill one by one, straight through or at a right angle depending on their place in the snake. It's the project with the most drilling, and oversized holes let the corners slip out of line.

The calendar puzzle, cut from a thin panel, isn't covered on this page.

Best wood for puzzles

Choose wood that is well dried, planed, and above all not warped. For trial pieces, use poplar, basswood, fir or pine; oak or cherry give a more finished object; birch and walnut are used for the contrast between light and dark. Walnut drills very cleanly.

Hardwoods (red oak, sugar maple, yellow birch) are dense and heavy, hard to drill, and resist crushing well. Softwoods (fir, pine, spruce) are softer and less dense. Poplar and basswood are hardwoods whose density is close to that of softwoods.

Look first at stability, meaning how much the wood moves when the humidity changes. Most temperate hardwoods are fairly unstable, which is a real problem for puzzles whose pieces fit together. Honduras mahogany and cedar do better, and some tropical woods, such as teak, are more stable still, but teak glues poorly. Two fine-grained woods, according to their technical sheets:

• beech has a very fine grain, gives very beautiful surfaces when sanded and finished, and glues very well, but it's rated as moving noticeably with humidity (medium to good stability in service);
• sycamore maple has a fine grain and glues acceptably, but its stability in service is rated “not very stable.”

Avoid low-grade woods (the ones called “secondary woods”): they're unstable, have a rough surface or glue badly. Avoid monkey pod too: the cheap puzzles made of it warp.

Keep your puzzles out of the light: most woods darken in daylight, and red woods such as padauk lose their color.

Ready-made cubes and square sticks

A square stick of planed wood is a long, thin piece of square or rectangular section. Sawn into cubes, a square stick gives the small cubes of the snake and of the wooden cube; notched, it gives the sticks of the devil's knot.

Making regular square sticks yourself is hard, especially since every piece of wood is a little warped: saw them slightly oversize, then plane them to size. For cubes, a section of 1 in (25.4 mm) is a good first choice, and 3/4 in (19 mm) is enough for many cube puzzles: the plan offers cubes of 15, 20 or 25 mm per side, so square sticks of the same section. For the devil's knot, the plan offers sticks with a section of 30, 40 or 50 mm. Calipers are the minimum for measuring, a micrometer for serious work.

Saw the cubes from a square stick, with a stop set with calipers. You can also buy raw wooden cubes in bulk: what matters is that they are a constant size.

For cubes or sticks bought ready to use, measure them before you start: every piece of wood is a little warped, and cubes must be a constant size.

Fit and precision: make it snug, then sand

Accuracy is the key: a sawing error adds up when you glue cubes together. A good devil's knot slides easily and fits exactly.

Work in two steps. Interlocking puzzles are most satisfying when the pieces fit well, but not too tightly: make them slightly too snug, then sand with care. The less you sand, the better, because too much sanding quickly ruins the accuracy. Also make a few extra pieces, for test cuts.

Don't set a clearance in millimeters: a method (snug first, then sand) is worth more than a value, because wood moves.

• Wood varies by about 2% between summer and winter, and up to ten times more across the grain than along its length.
• Higher humidity tightens most interlocking puzzles. Devil's knots are particularly sensitive to it: use the most stable woods for them.
• Orient the grain of all the blocks in the same direction: it almost cancels the effect for some puzzles.
• Tangential shrinkage (along the growth rings) is about twice radial shrinkage (toward the center of the tree), and shrinkage along the length is very small.
• Without planned clearance, pieces gape or bind depending on humidity. Keep the puzzle at around 30 to 40% relative humidity, as a puzzle workshop advises.

Gluing, sanding and finishing

Sanding. Sand as little as possible. Break sharp edges with a file and round the corners with sandpaper. For cubes, chamfer (cut at a bevel) the long edges of the stick before cutting it up, which is simpler than chamfering each cube. Lightly sand the edges of the pieces of a devil's knot: they go together more easily.

Gluing. Use wood glue (yellow aliphatic glue): it's the most satisfying, strong, fairly quick, and flexible enough that the joints don't pop when the humidity changes. For cubes, glue on a flat surface with a ruler and a square. Hold all the cubes together with tape or rubber bands, then glue only the joints you want; wax or wax paper stops an unwanted joint from setting. For a puzzle with several solutions, this method doesn't work: only meticulous accuracy will do.

Finishing. Several finishes are described, and the authors don't agree on the best one:

• a clear lacquer in a thin coat, applied with an artist's brush, improves the look and protects against dirt; to finish, use extra fine steel wool, wax and buffing;
• a varnish applied with a pad of paper towel rather than a brush, which puts it into the holes: a finish rated particularly beautiful;
• oil in about three coats, with steel wool between coats;
• for an oily wood such as padauk, which sometimes interferes with oil and water based finishes, shellac works.

For a snake, finish before drilling, or finish the sticks before cutting them up.

The wooden cube: how to make a Soma cube

A Soma cube is made from 27 small wooden cubes, glued into pieces with wood glue and held with rubber bands while drying. Whatever their size, the cubes must all be identical. The accuracy and gluing advice above applies as it stands. The build plan on the wooden cube page draws each piece layer by layer, with its cubes numbered and its faces to glue.

How to make a wooden snake cube

A snake cube is made of 27 or 64 cubes linked together. The link runs straight through some cubes and turns 90 degrees in others; the cubes turn freely. Every cube except the two at the ends has two faces drilled at their center: two opposite faces for a straight cube, two adjacent faces for a corner. The build plan on the snake cube page draws the unfolded snake and the drilling of each cube.

• Make a drawing of the unrolled snake at full scale: it's very useful.
• Use a brad point bit made for wood, not a metal drill bit, and always position the piece with a jig (a support that holds the piece and guides the bit), never on a simple pencil mark.
• For a straight cube, use a bit only slightly larger than the cord, with the piece held firmly.
• For a corner, drill two shallow holes at the center of the two adjacent faces, then join them with a diagonal hole. Don't enlarge the holes much: they let the corners slip out of line. A diagonal hole on its own is hard to place, and its sharp edge can damage the cord.
• At both ends, a wider hole, three quarters of the way down, holds the knot of the cord. You can close the end holes with wooden plugs cut with a hole cutter.

Cord or elastic? Opinions differ. A snake cube is usually linked by an elastic cord. One maker advises against elastic cord for a wooden snake: the tension needed exceeds what it can bear, and stretched rubber degrades over time. That maker pulls a non-elastic cord “moderately” tight along its whole length, a few cubes at a time because of the friction in the corners. The cord's diameter and length aren't given here: the only reference is a bit only slightly larger than the cord.

The devil's knot: 6-piece burr puzzle plans

A devil's knot is made of six notched square sticks, all the same length, at least three times as long as they are wide, in three perpendicular pairs. The unit is half the width of the stick: if the section (the width of the stick) is two units, the notches are one unit wide and deep, or a multiple, and each piece can be seen as made of unit cubes. The notches are all in the crossing zone and stay invisible once the knot is assembled. The build plan on the devil's knot page gives the position of each notch from the left end of the stick.

Three published examples of dimensions for a devil's knot plan:

• six blocks of 6 x 2 x 2 cm;
• a 3/4 in (19 mm) square stick for blocks of 2 1/2 in (63.5 mm);
• sticks of 1 x 1 x 4 in (25.4 x 25.4 x 101.6 mm).

The length isn't always free: one of the knots described in a book no longer goes together if the pieces are longer than three times their width. In Emboîto, choose 3, 4 or 5 times the width to match the length of your pieces; the plan gives the resulting length.

Prefer “notchable” pieces, made with a saw or a router, to those that can't be sawn and have to be made with a chisel or by gluing cubes: they're preferable for practical and aesthetic reasons. Make the notches on a table saw with a set of dado blades and a jig, or on a band saw, marking the lines before cutting. Set the blade to half the width of the stick: it gives the depth.

On test cuts made in extra pieces, check the width of the notches (so that the fit is right) and their depth (so that the faces sit flush, at the same level).

Staying safe with tools and dust

Wear safety glasses with side shields or goggles, hearing protection and, if needed, a respirator; avoid loose clothing and jewelry. Keep guards in place, use clean, sharp blades, unplug the machine before changing or adjusting a blade, and secure the pieces for drilling, sanding, cutting or routing. A push stick and jigs keep your hands out of the cutting line. A dull blade shows itself by its sound, its resistance, inexact cuts and burn marks. Don't blow sawdust away with compressed air.

Wood dust, whatever the species, is classed among the proven human carcinogens; it irritates and can cause allergies. Prevention rests on capture at the source, cleaning by vacuum and protective equipment.

For each machine, occupational health and safety bodies publish detailed instructions, to be read before you use it.