I've been working on the base. It's a struggle to hold the assembly steady for drilling. If you don't own ratchet straps, I find it easier to leave the top side edges and bottom surface level and flat at this point. This provides a bearing surface to allow me to clamp a caul to the top of the seat. This can then be pipe clamped to the bench. In addition to holding the assembly secure for drilling, it fully seats the legs into the sockets, so that I can accurately reference the proper heights for the holes.
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I was eager to try out my new brace and bits, but it was easy enough this time to just use a Forstner bit, using blue tape between the legs to serve as an angle guide. Galbert and Buchanan have great methods for transfering the exact angles to bevel squares, but I find it easier to drill these in place. I measure DOWN from the bottom of the seat, not up from the bench, because my legs have not been finally leveled.
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Dunbar's book has some fancy equations for calculating the lengths of the stretchers. I prefer to just cut them over-sized, and then trim them to fit. This is where a Dozuki really comes in handy. It can make 1/32" fine cuts on the end of a 1/2" tenon without tearing fibers. It's also possible to shoot the edges with a block plane. It's tempting to keep the stretchers a little too long: when the stretcher is seated into the legs, the tapered tenons of the legs will be too narrow to fit into the bottom of the seat holes. However, this is precisely the point. I use the topside holes to determine the final length of the stretcher, since this is the final resting point. To assemble, I had to insert the stretcher partially into the legs, and simultaneously push the legs into the sockets, while seating the stretcher into the leg tenons. This tricky fit is what keeps the whole thing together. The fit is remarkably forgiving, as pressure is distributed between the four legs.
I also like doing the final shaping on the lathe. I'm trying to make the swoops more fair curves, and less linear. Using a drill chuck at the tail stock, and pin jaws at the head stock allows me to mount the trimmed stretcher back into the lathe and hold it by its tenons. A good side effect is that the jaws protect the tenon from the skew blade, which prevents inadvertently shaving their thickness; so I can fit the tenon thickness and length perfectly before the final shaping. The jaws even compress the tenon slightly, which helps them slide in and out of the mortises a little better.
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