drilling

Jigs and techniques
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Jigs and techniques

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.

Curved on three faces this simple block acts as the bending form with the legs clamped to the bench and then later as the drying form with the legs tied across it. Here I’m lining it all up before steaming.

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.

Simple…

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!

Just the bevel gauge. The chair is made in England.

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.

Not essential – you might not think it’s worth making for your first chair – but it’s definitely worth it if you plan to build more.

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.

Not for this chair! This is for a bench I built last year but you get the idea – mark the angles on a piece of wood and then you can quickly reset or check your bevel gauge.

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Everything I know about screwing

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The first thing I know is that it’s impossible to resist a ribald pun. Even my normally clean-minded wife couldn’t help a snigger when she asked if I was screwing around in the workshop on my own this evening.

I had some brass, slot-head screws delivered to work today. A colleague looked at them lying on my desk and wondered aloud how you avoid destroying the heads. So I started to tell him. Half way through his eyes glazed over and he wandered off.

 

So for all those who know next to nothing about screwing but actually care:

1. Use a screwdriver that fits. I have a lot of screwdrivers and often pick up cheap old ones when I find them. Each different size of screw head needs a different driver. The tip of the screwdriver should fit so well that it will hold the screw without support. Because most screwdrivers are manufactured to fit a range of screws they don’t work for any particularly well. Grind each screwdriver tip to the size of the slot.

2. Use a screwdriver with a tip with parallel sides. The one at the bottom is manufactured properly. The one at the top is going to get ground to get rid of the taper in the tip. It will end up with a tip that has concave sides. The end will be very close to parallel. Because most of my tools are still in packing boxes this new addition has escaped the grinder for the time being. But its days of tapered mediocrity are numbered.

Tips

 

3. Use a tapered drill for the pilot hole. To be fair I rarely do this. I only have a couple of tapered drill bits and am too mean to buy bits I’m going to use once in a blue moon. However if you want to ensure that your timber doesn’t split under the wedging action of a screw a tapered bit means that the taper in the screw is accommodated. However I always…

4. Use the right sized bit for the pilot hole and drill it full depth. Classic Marine has a useful chart. What do you mean you don’t have a 7/64″ bit?

5. Drill a clearance hole if you want to draw two pieces together. If you think for a moment about the way a screw works it’s obvious that if it goes though a pilot hole in one piece and into a pilot hole in another no matter how hard you drive the screw if will not draw the pieces together if the threads are properly engaged in the upper piece. But if the threads of the screw slide though the clearance hole and catch in the pilot hole of the lower piece then as the head draws up to the upper piece it will pull the two together.

5. Clamp pieces together. If there’s a gap when you screw two pieces together there will always be a gap. If you clamp them tight, drill your pilot hole and then screw them together they’ll remain tight.

6.  When using brass screws use a steel screw first. I’ve lost count of the number of heads I’ve wrung off brass screws. However drilling the right size pilot hole and then cutting threads in the wood with a steel screw reduces the load needed on the brass screw. I wish I did this more.

7. Wax the threads. This is such an easy thing to do and makes so much difference.

Screw and wax

 

I have a small pot of softer wax made from beeswax and turpentine somewhere but it’s hiding in a box so I used candle wax this evening. I’m convinced the softer wax sticks to the screw better and so the effect lasts longer but I may be kidding myself. Certainly the difference between no wax and wax is immeasurably greater than different types of wax.

8.  In corners use a “turn screw”. Which is just an old word for a screwdriver with a flat on the shaft. You can put pressure on the top of the handle and turn the driver with an adjustable spanner. You actually need surprisingly little downward pressure. This means that even in an awkward position you can keep the screwdriver vertical and the tip fully engaged, reducing the chance of it breaking free and damaging the head.

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9. Tighten them up evenly. Your work can shift when screwing it down. To avoid this tighten the screws most of the way. Make sure everything is still where you want it and then tighten them all down bit by bit. If you tighten one in one corner of the workpiece it can spring the opposite corner up in the air making life rather difficult.

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10. Clocking screws is a fool’s errand. You can adjust the countersink hole. But this puts the screws at different heights. You can over tighten some or leave others loose. But this is just self-defeating.  Or you can go to the frankly absurd lengths of putting each screw in your drill press and sanding a fraction off the back of the head, then putting the screw back in the hole to see if it now fits and is “timed” with all the others. Or you could just demonstrate your superior craftsmanship and understanding by correctly tightening each one and then leaving the blessed things alone.

11. A brace with a screwdriver bit is very handy. Use your 6″ brace. The 14″ is asking for trouble. It’s even more important that the bit fits the screw because you’re going to be putting a devil of a lot of torque on it and it’ll skate off without hesitation.

12. If you’re drilling a pilot hole in exterior timber dribble wood preservative in the hole first. My father-in-law will even go the lengths of setting up a tiny funnel into the hole and filling it with preservative and hardener. This then acts as a reservoir to keep feeding the wood as   it soaks up the preservative.

13. In soft wood drill the pilot hole over size and then pour in thinned epoxy. Wax the screw very thoroughly and when the epoxy is green (not completely cured and still fairly soft) drive in the screw.  If you ever want to get the screw out heat the head to soften the epoxy with a soldering iron. I have a gas powered one for cutting rope and it works a treat.

Attributions: I have learnt all of this from other people: my father (who got it from his toolmaker father and his cabinet maker grandfather), my father-in-law, from the online and published works of Chris Schwarz, Bob Smalser, Tim Roussau and Greg Rossel. I use all these techniques and am happy with them, if you’ve got others or improvements let me know. As I remember, learn about and use other techniques I update this page.

St.John