Locked mitre joints

abacusThis is another autistic training aid; the idea is to illustrate that autistics often leap to one extreme or the other rather than settling somewhere in between. Personally, I think it could also illustrate the way some of us get into a swither because we can see both sides of a debate and the more we think about them the more equal their appeal becomes.

The bead is yew, which has one side darker than the other, and the frame is made from four different woods, clockwise from top: tulip, oak, sapele and laburnum. The rod is pine, which to my surprise was the stiffest 6mm dowel I could find at the time. I decided to do it with multiple woods, to illustrate (well, like the constellation sculpture you can read whatever you like into it but anyway) that wherever we look we see something different.

My first attempt had the frame all in one wood, in fact it was the tulip, and it wasn’t just boring, the proportions didn’t seem right and I did it with straight mitre joints. In the process I rediscovered how much I hate mitre joints. Then I found a locked mitre bit going at half price at Rutlands, just the job – once I’d figured out how to line it up properly on the router table! locking mitre bit sled1Two YouTube videos came to my rescue, one showing how to line up the bit to the fence and the other showing how to make a simple, disposable sled for the workpiece which would keep the wood at a perfect right angle to the cutter both on the vertical cut and the horizontal cut.

The sled is just a piece of plywood that is thick enough to stay straight, with two pieces of wood, the same thickness as the workpiece, screwed on so the workpiece fits snugly between them. The same sled works on both the vertical and horizontal cuts; I just used both ends of it. sled lineupIt holds the workpiece steady, keeps my fingers away from the cutter and is made from offcuts – what could be simpler? It also avoids tearout because the cutter has to cut the sled to the right shape in the process. So I found that the sled got shorter as I went, because it has to be cut down for each try cut until it lines up properly.


For both cuts I attached a piece of board to the fence with clamps. It just had a small cutout to clear the cutter.

After several try cuts (always cut more wood than you need) I finally had the fence and the cutter height adjusted perfectly.

For rounding the pieces before assembly I used a quarter-ellipse cutter, and used spare offcuts to hold the pieces in line with the fence.

The piece is finished with sanding sealer and wax.