MAKING THE BOW AND ARM

The arm and bow of the sack-back Windsor anchor the chair’s back­rest, tying the spindles into a strong and comfortable structure. The grace­ful curves of both pieces are achieved through steam bending, a process that may well be the most challenging part of making the chair.

The two essential elements of wood­steaming are a steam generator and an enclosed steamer. The version shown in the photo at right and described on page
83 is shop-made from ABS pipe. Be sure to make the steamer longer than the bow and arm, and seal it tightly to keep the steam from escaping. Include a small drain hole at one end and place the steamer on a slight incline, however, to allow the condensed steam to run out. If you are using a gas-powered steam
source, it is safest to do your steaming outside. If you are using green wood, 15 to 20 minutes of steaming should make the piece sufficiently pliable to bend around a form. Air-dried lum­ber requires twice as much steaming. It will take about one week for a bent piece of 1-inch-thick stock to dry.

ANATOMY OF A BOW AND ARM

dOW

± %" dia. 7

PREPARING THE STOCK

1 Squaring the bow and arm

Drawknife the bow and arm roughly to size (page 74), then use a bench plane to square the pieces and flatten their sides. Secure the blank between bench dogs on your workbench. Starting at one end of the stock, guide the plane across the sur­face to the other end; keep the sole of the tool flat on the workpiece and apply mod­erate downward pressure (right). Plane the arm until it is % by % inches; for the bow, refer to the anatomy illustration opposite.

2

Shaping the bow into a cylinder

Secure the bow blank in your shaving horse and start shaping the piece with a drawknife. Bracing the end of the stock against your chest, drawknife the blank into a cylinder (left); work with the wood grain throughout. As shown in the diagram opposite, make the final diameter of the bow % inch; it should taper down to ^ inch starting about 8 inches from each end. As you work on the thinner end of the workpiece, reposition the blank in the shaving horse so that less stock extends out from under the crossbar. Switch to a spokeshave to give the bow a smoother surface finish (above), handling it as you did the drawknife.

1 Building a bending jig

Build a bending jig like the one shown at left to bend the bow and arm of a sack – back Windsor chair. Cut two pieces of %-inch plywood to the desired curve of the bow and arm, then screw them together to make the form. Mount the form on a %-inch plywood base and mark the center of the form near its top edge. Then cut the stop block from hardwood and screw it to the base, and bore the two ^-inch – diameter dowel holes into the base. The space between the block and dowels and the form should equal the thickness of the workpiece plus the wedges used to secure it in place. Finally, prepare the dowels and wedges, then clamp the base to a work surface.

2

Securing the bow around the form

Once the workpiece has been sufficiently steamed, remove it from the steamer (page 80) and place it on the bending jig. Align the middle of the bow with the center mark on the form and clamp the stock to the middle of the form by tapping wedges in place. Pull one end of the workpiece toward the form firmly and steadily until it contacts the side of the form. Insert a dowel into the hole in the base and tap in a wedge to secure the bow in place. Repeat for the other side of the workpiece (above). Work quickly to complete the bend.

3

Maintaining the bend with string

Tie a length of string tightly between the ends of the bow (above) and begin steaming the arm. Once the arm is ready for bending, you can remove the bow and bend the arm as in step 2. The string will keep the bow bent until it dries.

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A SHOP-MADE PIPE STEAMER

An economical and durable wood steamer like the one shown below can be fashioned from 2-by-4s and

4- inch-diameter ABS pipe and fit­tings. The device features support racks inside the pipe and a remov­able cap at each end for easy access. The steam source is a water can con­nected to the steamer by a length of plastic hose; the water in the can is heated by a propane-fired cooker. (This setup should only be used out­doors). The steam source should have a removable, screw-type cap.

To build the steamer, start with a length of schedule 80 ABS pipe longer than the bow and arm. Cut it in half and drill a series of holes through both pipe halves to accommodate 3/s-inch zinc-coated machine bolts and nuts
as shown. These bolts will support wood inside the steamer to prevent it from lying in condensed water. (The zinc coating will prevent the bolts from staining the wood). Drill the holes below the centerline of the pipe to provide room for the wood. Install the bolts, using steel and rubber washers
on both sides to make an airtight seal. Now glue both halves of the pipe to an ABS T connector. Drill a /2-inch drain hole at one end to release moisture and excess pressure. Then glue a connector pipe cut from 1/-inch ABS pipe to the spout of the T connector. Next, cut a length of plastic hose that will connect the steamer to the water can; the fittings required for the water can end are shown above. (The fittings for the steamer end of the hose are identical, except that an ABS end cap is used instead of the water can cap; the end cap is glued and screwed to the connector pipe.) Make sure the fittings are airtight. Lastly, build a 2-by-4 frame to sup­port the steamer. Nail a small support block at one end so the steamer will rest on a slight incline and the excess water will run out of the drain hole.

To use the steamer, carefully con­nect the gas cooker to a propane tank. Fill the water can, attach the cap and hose to it, and set the can on the cooker. Secure the removable end caps on the steamer, light the cooker, and let the steamer build up steam. (Caution: Do not let the steamer or steam source become pressurized.)