Rob Stoakley strives towards finishing his coffee table
There’s just one last little thing that needs to be done before the final assembly and that’s to make the wedges for the thru’ tenons. If you recollect, I mentioned in the ‘Bond…James Bond’ entry that the joint was complicated, but ‘all would be explained’.
Looking carefully at the first drawing numbered ‘A’, you can see the joint prepared, ready for gluing, with the wedges hovering over the bandsaw saw cuts. The sectioned mortice has been slightly flared by around 1mm each side so that it’s now wedge-shaped, the tenon being 5mm longer than the mortice, with the saw cuts not quite reaching to the shoulder line.
What’s needed is for the wedges to be inserted right to the bottom of the saw cuts and, once inserted, they’ll force the thinner section of the tenon into the wedged portion of the mortice, so that there’s no gap.
Now this sounds easy, but it’s not, as once the glue goes on and the wedges start to be hammered in, they will not, I repeat, will not come out! So you’ve got to get it spot on first time.
The wedges need to be around 2 or 3mm longer than the saw cuts and sufficiently wide at the top to force the tenon over and into the wedge. If they’re too skinny you’ll end up with a gap and if they’re too short they won’t reach right down to the bottom of the saw cut or you won’t have enough material on the end to strike with a hammer.
Looking now at the sectioned drawing of the completed joint numbered ‘B’, you can see that the wedges have forced the tenon over into the tapered part of the mortice and are fractionally proud of the surface.
A really dense hardwood is best for the wedges as anything soft will simply crumble when it’s tapped in with a hammer. Ebony, African blackwood and rosewood are all excellent, but to be a little different, I’m using some holly that I collected from Stourhead earlier in the year. Making them is simplicity itself if you use a little plywood jig and then run it past the bandsaw blade each time. The ply has a triangular cut-out in it and the block (already prepared to the correct length) is turned over each time a cut is made so that the grain is always straight. It takes a little bit of fiddling with the jig and bandsaw fence to make sure that the wedges exactly fit the profile of the joint, but once a correct wedge has been made, it’s the work of moments to slice off as many as you need… and they’ll all be identical.