The perfect 2 cm cube should be .787 inches on each side. The above is a 3 part picture of a cube cut back in 1995 (H=.788 L=.791 and W=.792). The cube has never been sealed with wax or any other varnish type sealers. The cube was cross cut meaning the grain is diagonal when viewed at the end grain.

Although subjected to many humidity levels through many seasons the cube always settles to H=.788 L=.786 and W=.785 within a day or so of dry weather.

Note: The height on all my tests remains the same, which it should be - the expansion contraction is linear through the grain.

On a very dry spell versus a very wet spell the cube may change by as much as .025 which is about 1/40 th of an inch. Not much to most people but very crucial to wood puzzle builders when using small wooden parts.

All of the above becomes moot when the wood is sealed - either wax as I use or some type of varnish. The sealed wood then becomes quite stable.

Prior to gluing cubes you should measure and set the cubes by grain. As above, if the cubes are out by 1/40 inch then 4 cubes glued together compared to 4 others could be out by quite a bit!

Linear expansion can be even more dramatic if the cubes are glued along similar grain faces. It is always best to mix grain patterns.

If the puzzle piece involves a 'U' or 'H' shape then a straight cut cube can make the piece quite stable for many years.

Staining cubes
In an early version of the MindBlock puzzle, I stained (dyed) 32 of the cubes using a quick dry walnut stain to get the tessellated effect and they turned out very well. In a later version I used black and white quick dry paint. See: Versions for examples of these.

I stress the 'quick dry' since a very watery type stain or paint will change the cube tolerances (in some cases by as much as 1/32 inch).

Several companies produce quick drying stains and these can be purchased in small cans. The stains are usually a gelatin type and can be brushed on with a sponge and then quickly wiped dry. The idea then is to stain each cube separately and let dry for a few days. Since normal wood glue needs natural wood to make the bond, leave the surface to be glued bare - this takes some planning ahead ;-) After assembly the puzzle piece can be hand waxed (my preference) or sealed with a varnish or the more popular 'plastic type' varathanes.

Painting cubes
The black/white version was actually spray painted cubes and tumbled in a dryer to keep the cubes separated. The surfaces to be glued were then sanded down to bare wood. I contacted several glue and paint manufacturers to check what products might work with painted surfaces to avoid the sanding step. The only thing that works is the paint itself being used as an adhesive to the dried painted surfaces.

Something about molecular bonding! I know it can be quite strong since some cubes did stick together in the tumble drier and my state-of-the-art testing method for glued surfaces could not split them apart. The extra time needed using the paint as a glue was counter productive (extra drying time). I could produce more puzzles per day using glue on bare wood and simple clamps.

Gluing cubes
Properly glued cubes are hard to break apart and if broken the break usually follows a growth ring on one of the cubes. Similar to welding steel - the weld is usually stronger than either part. Glue is sucked into the wood when it is allowed to set on each piece - about 10 seconds. Much less time if gluing the end grain.

Ordinary white or yellow carpenters wood glue is the best adhesive. Many years ago I tried various modern glues to try and skip the clamping step required - to speed up production (and give me more time for fishing). I used a state-of-the-art testing method - throwing pieces against a concrete wall ;-) Old fashioned carpenters glue and clamping came out the winner! As did a lot of fish!

I use a syringe for accurate measuring and place a small drop of glue on one surface then quickly rub the two surfaces together. The friction produces a little heat which is good. I then separate the cubes to allow the glue to set up (about 10 seconds), then clamp. If done right there should be no seepage of glue and the pieces should not slip when clamping. Too little glue - dries too fast: Too much glue - seepage and slipping.

Almost a science which is why I like using a syringe ;-) And the most important thing is accurate sized cubes. My cubes are within .005 inch, planed, cut and placed in sealed plastic bags on dry days. It is quite amazing what a little humidity can do to small cubes - kinda like a sponge!

See Graphs: for more details about humidity and wood.

The final assembled piece is lightly sanded on the end grain to produce a more even effect - one reason my cubes now have a height slightly greater than either width or length.

If you have any hints to share with other puzzle makers please let me know and I'll add sub directories to this page.