No, this post is not about furniture possessed by evil spirits. It's about a rather mysterious tool. Anyone making chairs and stools by hand accumulates a stock of tools specific to the tasks of shaping and refining chair parts. Most woodworkers acquire tools that help them make square, flat stock to be made into rectilinear forms. Not so with luthiers and chairmakers. There's hardly a right angle anywhere on a chair that is made to accommodate the human form. Rounded and curved parts are the norm.
At left are some of the tools that I've made for myself. The tool in the top left is a travisher, which is a specialized spoke shave for hollowing and sculpting seats. One starts with the inshave or scorp in the top right and then refines or "fairs" the surfaces with the travisher. The tool in the foreground is the chair devil. I've seen manufactured travishers and inshaves but I think all the chair devils in existence are craftsman made, and that in itself contributes to the mystery of it's construction. Chair devils are scrapers, the blade cuts by means of a burr raised on the tool steel edge with a burnisher. You may be familiar with card scrapers or the venerable Stanley #80 cabinet scraper which is a most useful tool to tame tearout after hand planes have reached their limit. A chair devil is a scraper for parts that are round in cross section, although I have seen examples that are simply flat scrapers held in a handle. In the photo above you can see what it does. The stock is held in the shaving horse and when pulled like a spokeshave, this tool raises curly shavings and leaves the surface of the wood smooth and uniform.
Doesn't take long to generate a pile of shavings. This particular chair devil is made of osage orange, cocobola, brass hardware and a blade made from a card scraper. Brass threaded inserts and counter sunk machine screws hold the blade in place. I've been known to over think the design process, but this is one time that a simple solution landed in my lap. The scraper blade needs to be at approximately 75 degrees relative to the work surface to cut wood fibers, and a chair devil can be made with a bed and throat at that angle, but the method described below is somewhat simpler.
I start with a squared piece of stock 1 1/4" square, 12" long and turn the handles on the lathe, leaving the center portion square. Then cut the bed into the square center section the depth of the cocobola cap, about 3/8". Note that it is important to make the bed dead flat, and the blade is recessed into the osage bed by the thickness of the blade, no more. A throat is cut into the the cocobola cap for shavings to escape, but the throat should be narrower than the blade width, only as wide as the curved area so the blade is captured between the flat areas of the osage bed and cocobola cap. If the blade isn't seated properly, or if there are any gaps between the cap and bed, shavings will clog the throat. Some fine tuning will be necessary to refine the throat so that shavings feed smoothly through the opening.
At this point in the construction process the center portion is still square in cross section. Remove the blade and with a block plane remove wood from the bottom until the desired 75 degree angle is reached, see photo below. The radius can be shaped relative to the bottom plane and then the blade can be marked and shaped. This method eliminates the need to make a blade bed and cap at an acute angle, relying instead on square construction and forming the angle by stock removal after all the major parts are constructed. The devil's in the details.
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| 75 degree angle achieved by planing the bottom |
At left are some of the tools that I've made for myself. The tool in the top left is a travisher, which is a specialized spoke shave for hollowing and sculpting seats. One starts with the inshave or scorp in the top right and then refines or "fairs" the surfaces with the travisher. The tool in the foreground is the chair devil. I've seen manufactured travishers and inshaves but I think all the chair devils in existence are craftsman made, and that in itself contributes to the mystery of it's construction. Chair devils are scrapers, the blade cuts by means of a burr raised on the tool steel edge with a burnisher. You may be familiar with card scrapers or the venerable Stanley #80 cabinet scraper which is a most useful tool to tame tearout after hand planes have reached their limit. A chair devil is a scraper for parts that are round in cross section, although I have seen examples that are simply flat scrapers held in a handle. In the photo above you can see what it does. The stock is held in the shaving horse and when pulled like a spokeshave, this tool raises curly shavings and leaves the surface of the wood smooth and uniform.
I start with a squared piece of stock 1 1/4" square, 12" long and turn the handles on the lathe, leaving the center portion square. Then cut the bed into the square center section the depth of the cocobola cap, about 3/8". Note that it is important to make the bed dead flat, and the blade is recessed into the osage bed by the thickness of the blade, no more. A throat is cut into the the cocobola cap for shavings to escape, but the throat should be narrower than the blade width, only as wide as the curved area so the blade is captured between the flat areas of the osage bed and cocobola cap. If the blade isn't seated properly, or if there are any gaps between the cap and bed, shavings will clog the throat. Some fine tuning will be necessary to refine the throat so that shavings feed smoothly through the opening.
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