The 18th-century Shoulder Knife

This is an excerpt from “To Make as Perfectly as Possible: Roubo on Marquetry” by  André-Jacob Roubo; translation by Donald C. Williams, Michele Pietryka-Pagán & Philippe Lafargue.

One of the joys of researching the old ways of doing things is that every so often you encounter an amazing “new” way of accomplishing some task. Such is the case with the shoulder knife, an indispensable tool in the ateliers of Roubo’s world. The tool’s utility is remarkable, and I am still discovering new uses for it.

We all have our favorite shop knives; mine is a Swiss chip-carving tip that gets used in many ways. And – like you – I have tuned it exactly to my preferences. Yet, more and more I find myself reaching for the shoulder knife that I made at about the time this book project began.

One of the issues of knife work is balancing the power and control integral to its use. Typically one of the limitations is the amount of force you can bring to the cutting tip, and the precise control you can exert on it. The determining factor is often the amount of handle you can grab comfortably. In fact, that is why my favorite knife has a small blade but a comparatively large handle. Still, I am limited to having only one hand on the handle. A shoulder knife overcomes that because the handle extends all the way from the knife tip to, well, your shoulder. You can obtain great power and control because it allows you to grab its handle firmly with both hands and leverage it off your shoulder.

The shoulder knife has practically disappeared from the woodworker’s tool kit, and to my knowledge only one company supplies them commercially. Making one is fairly straightforward. Although it is a simple tool, mastering it is not so.

The first step in making a shoulder knife is to make a pattern so it fits exactly your upper body’s dimensions and posture relative to the work surface. You can make a template from something as simple and disposable as heavy cardboard. A good starting point is to simply grab a yardstick tip in your hands, drape the stick over your shoulder and make note of the measurement from the work surface to your shoulder. Mark this out on the cardboard, then draw an arc to mimic the curve of your shoulder. Cut this out and compare it to your own body. Revise it until the match is the one you want. I made perhaps a half-dozen patterns until I got what I wanted, and then I cut that pattern out of three or four layers of cardboard and bonded them together to make it sturdy enough so I could get a good feel for its shape and fit. Just to make sure, I made a final pattern out of a piece of 6/4 softwood.

I selected a piece of scrap walnut to make my first knife, and a slab of ancient oak for the second, which is a few inches longer than the first. I used disparate methods for building each.

I made the walnut knife from two pieces of 3/4″ stock laminated together to make setting the blade much easier – even though the final thickness was 1–1/8″. I traced my pattern on both pieces and cut out the shape of the handle. Using a knife and chisel, I excavated a void matching the shaft of a Swiss blade purchased at a woodworking store on the two inner faces that were to be glued together in the final assembly. When the fit was perfect, I glued the whole package together with hide glue, with the knife blade embedded in and protruding about 1″ from the long handle.

For the oak-handled knife, I started with a 6/4 slab, then traced and cut out the shape I wanted. When I was satisfied with the overall shape, I sliced it lengthwise on the band saw. Recycling an old chip-carving blade, I excavated a pocket for the knife haft, then temporarily tack-glued the two pieces back together to shape the handle. (This is unlike the first knife when I assembled the knife and then shaped it.)

With spokeshaves and files I shaped the handle to my preference, inserted the blade and glued the whole thing back together with hot hide glue. After shaping the business ends and adding compression-fitting brass ferrules, I coated both handles with shellac and wax, made the leather blade guards and called them complete.

My skill at using the shoulder knife is growing, but it is not yet to the degree where it is second-nature. But classical marqueteurs probably used it about the way we would use a scalpel for cutting filigree in paper.

One of the main differences between the manner of creating marquetry between the way I did it for decades and the way that Roubo practiced the art has to do with the assembling the compositional elements into the background. I had previously always sawn them together in fairly typical tarsia a encastro technique, and frankly it is still the practice where I feel the most comfort. But for Roubo and his contemporaries, the elements were often set into the background by scribing the element’s outline into the background with a shoulder knife after the background had been glued to the substrate.

This is in great measure the definition of David Pye’s “workmanship of risk.” Careful examination of enough old pieces of marquetry will indeed reveal instances where the knife got away from the marqueter.

— MB