Sunday, November 9, 2014

Robert Ingham's Dovetail Paring Jig

I've been thinking lately about hand tool jigs for very specific operations. If you've used hand tools much, you've learned about the value of jigs for often-performed, generalized operations like making a square end on a board with a bench hook and/or shooting board. I'm thinking about more specialized jigs that don't get used for every single project, but come in handy for guiding a tool along a carefully limited path to produce consistent, accurate results. This baseline paring jig for dovetails is a perfect example.

In 2005 I had the good fortune to attend Art in Action near Oxford, England, and spend some time watching Robert Ingham cut dovetails for very small drawers by hand. He was using a couple of deceptively simple-looking jigs for cutting a clean baseline and marking the pin board from his finished tails. I have never been entirely happy with the baselines in my dovetails; trimming the sockets between pins or tails perfectly flush has always seemed far too fiddly for me, taking too much time for results that are quite easy to muff with a single stroke a hair too deep. Seeing Ingham's jig was an “aha” moment, and I spent some time talking to him. Considering he's among England's two or three most influential living woodworkers, he was patient, generous with his time, unassuming, and engaging. He explained how he'd made it, how he might change it, and seemed to listen with interest to my reaction. I walked away thinking two things: “I need to make one of those,” and “what a nice guy!”

A few weeks ago I finally got around to making the jig I wanted. I was invited to demonstrate cutting dovetails by hand at Woodtoberfest, the fall festival at Hardwoods Incorporated, my favorite retail lumber and plywood dealer in the Atlanta area. At this point in my career, I've given the same-old same-old dovetail demonstration enough times to want to do something different, so I decided this jig would be part of the demonstration. It works as well as I've imagined, quite a treat! Several people who saw the demonstration ordered Ingham's book via smartphone on the spot, so the jig obviously struck a chord with some.

The jig is simple to make, but getting things neat & square takes a bit of time. Between 2005 and now, Ingham has published a book, Cutting-Edge Cabinetmaking, with detailed instructions for making and using the jig. If you decide to make your own version, it's worth taking a look at his account. On the other hand, a clever person could figure this out from looking at the pictures here. There are no set sizes as far as length and width. The angle between the top (covered with high-pressure laminate) and the rear face (against which the workpiece is clamped) MUST be 90 degrees, and the fixed fence and sliding clamp have to be thinner than the workpiece; otherwise, as long as there's room for the full width of your workpiece between the sliding clamp and the fixed fence, you should be fine.

Using the jig takes a bit of finesse. Obviously, your baseline needs to be precisely aligned with the top of the jig. If you don't cut the bulk of the waste out closely enough with the coping or fret saw, you need to begin the trimming process by tilting your chisel so that it slides along the rear corner of the jig, and gradually bring it closer to horizontal after each stroke. In a wide socket, you can get a relatively narrow area down to flush with your narrowest chisel, and then use a wider chisel to take a series of very small bites to finish up. The wider chisel is handy because it's easier to keep perfectly flush on top of the jig. Your chisel needs to be as sharp as you can get it, and I find that a lower sharpening angle, like 20 degrees, is the way to go. Remember, you're paring out very thin shavings, so a mallet would be harmful to wood or chisel. A pair of skew chisels is a good idea for the angled sockets between pins, and you'll quickly learn that you need bevel-edged chisels for the spaces between tails to avoid unsightly bruising.
 The back face of the jig, showing how the screw that holds the sliding clamp in place is countersunk to allow the assembly to be clamped in a bench vise.

 Here's how you clamp the workpiece in the jig. I'm watching to be sure the scribed baseline is aligned with the top of the jig. My left index finger is holding the sliding clamp tight, my left pinky is holding the workpiece so it doesn't slide, and my right hand is tightening the clamp's screw.

 The loaded jig clamped into my bench vise. A sacrificial back board prevents blowout at the end of the cut. Unlike typical paring setups, this one lets the chisel be horizontal. It's quite easy to use the jig while seated on a stool, a real benefit if your back ever hurts.

 Using my narrowest chisel, 1/8 inch, to establish a narrow area pared to final depth. Notice how simple it is to hold the chisel flat against the plastic surface, which is hard and slippery. Chisels used with this jig need flat backs!

Here I've switched to a slightly wider chisel, but you can see I'm still taking quite small bites as I pare my way across the socket.

A skew chisel lets me reach right into the corner of the socket. This wouldn't be necessary if I pared from the outside of the joint towards the inside, but this way, I don't have to scribe a baseline on the show face of the finished box, which I consider a real plus.

Read Robert Ingham's book and perhaps you'll be prompted to rethink some of your assumptions about using hand tools. I was taught to be careful and gradually pare down to the baseline freehand, in a three step process that first made a hill in the middle of the socket and then planed it flat. This jig greatly simplifies that process. Some might say that it's a sad example of “de-skilling” a process that any true craftsman must master through repetition (like using a honing jig for sharpening), but from my perspective as a teacher, it seems that this jig will let my students spend more of their time focusing on what really makes for strong, beautiful dovetails: accurate sawing of tails and pins.

I hope to have these jigs available for all my future dovetail students.

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