This is probably the most delicate joinery I've ever done. As I've mentioned in this blog before, we make the display boxes for Su Blackwell, internationally-renowned paper artist.
They are almost always solid ash timber, with a single window at the front and a removable back through which Su inserts the work. However she was recently commissioned to make a sculpture which will be displayed on a boardroom table somewhere in North America, and requires a display box with three sides and the top all made from glass.
The piece being so delicate, and the display box relatively small (35cm wide internally, and 25cm deep), Su asked that the wooden bead which will form the edges of the glazed faces be as slim as possible. I decided that it would be possible for it to be 12mm square. Each section has to include two grooves for glass 4.5mm wide and 3mm deep, leaving very little material at the junctions to form any kind of joint.
The tolerances on this piece were tiny. I had about .25mm to play with left and right on the intersection of the grooves in the base and back into the grooves in the beading. I had to make a joint that would be sound where the beading meets the main pieces, and I used a 10mm beech dowel. Drilling accurately placed holes into end-grain is very difficult, so I drilled four 10mm diameter holes into an ash piece, and then made the beads from this, meaning I could centre these holes in the machining process. I glued the dowels in before the grooves were added on the tablesaw, meaning the grooves carry on into the dowels. Needless to say, it's all very fiddly.
I then had to create a joint where the beads intersect, at the top of the two vertical pieces and where the three horizontal pieces meet at the corners. There really was nothing whatsoever to play with. I started with the mitre joint that joins the horizontal pieces. I butted these mitres together, and then made the smallest part I think I've yet made in my career - two pieces of 4mm birch plywood, 5.5mm square with a 1mm x 1mm square taken out of one corner of each. This was glued into the groove at the meeting point of the mitre, reinforcing it somewhat and creating more of a flat face for the vertical elements to meet. I then made two dowels around 2.5mm in diameter, and fitted these into the ends of the vertical beads. I drilled a corresponding hole into the 4mm plywood section, and this created the joint at the meeting points of the three pieces of beading.
As joints these are obviously not particularly robust, but they have enough strength for the job, which is the main thing. Once the box is assembled and the glass is inserted, the box is very sound.
Su's main worry, once the work has been installed, is going to be the customs officials at the U.S. border, who have taken her work apart before to check it before allowing it into the country. Here's hoping they don't try and get into this box in a hurry...