As with tools I’m trying to keep jigs simple and few. But this is chair making so they’re unavoidable.
Jigs and forms are used for bending, aligning and holding pieces of timber. Given that chairs are fairly complex shapes with lots of curves the jigs chair makers use get pretty specialised and this can put off the novice.
Leg bends seem to attract the most complex jigs. Have a look at Jeff Lefkowitz’s jig-as-artwork for the double curves in Boggs chairs. Wonderful. But if we’re building country ladder backs or Arts and Crafts chairs we only need one simple bend and we can get that with a block and a few clamps. Not much of a barrier to entry.
The back slat forms are more involved. I have used the traditional ladder style for these but I don’t really like them. If you don’t prebend the pieces they produce more of a kink than a curve and are better employed as drying forms after the slats have been mostly set in a more supportive form.
This jig will do double duty to hold the slat when carving the shape into it and so is worth spending some time on. If you want to cut down on the work you can just build the convex side and clamp the pieces to it but I have found that the sandwich method is better all round.
If you really want to cut down on jig building you can clamp the ends of the slats to the bench over the block but it won’t give you much control of the curve and ties up bench space.
Drilling holes in legs also seems to attract a lot of complexity. There are all kinds of shop-made devices for marking a centre line and drilling a hole. Mirrors, spirit level jigs and lasers all come out to solve the problem: how do you drill at a correct and consistent angle?
This is the simplest method I can find. I put a leg on the two joiner’s saddles I used for planing and scraping earlier and clamp them down. Then I mark the centreline by the extremely complicated method of using a right angle block of wood with some pencil graphite on it. This leaves me with a neat line along the length of the leg. Given that my bench top is flat I can then use this as a reference surface to judge whether I’m drilling straight. A square on the bench takes care of the angle.
The second set of holes in each leg must be at a specific angle to the first. Loosen the clamps or holdfasts, insert a dowel or stretcher, slide up a parallel sided block with a bevel gauge on it, clamp it all back down. Mark the centreline and drill. Harder to explain than to do!
It’s not really a jig but the chair stick is worth mentioning. I build mine rather robustly from the same section stock as the legs. This means that when I lay a leg next to the stick flat on the bench I can put a square across both to mark all of the joinery.
Akin to the chair stick is the bevel board. I put all of the angles needed for each chair on it. Given that the geometry of chairs is fairly well established you might never need to make more than one.