Doc Reveals Mystery of Building Fortune Chair #1
By: Roger Moister
Guild member Dr. Andy Wilkerson came up from LaGrange for the June
12th meeting to explain how he built Michael Fortune's Chair #1. The chair has walnut legs and arms, maple curved slats for its back and a black leather seat. It's modern looking, as shown, and sits very well with good “bottom” comfort. Andy built the chair at the Marc Adams School of Woodworking under Fortune's instruction in a class starting in Fall 2016, making 2 trips to the school near Indianapolis to complete it.
Since Chair #1 is curvaceous, Andy began his presentation by talking about shaping wood. He described the common methods as band sawing using a pattern, then smoothing with rasps and sanding, or using a router; laminating thin strips using a form in the glue up; kerf bending by making multiple saw cuts 90 degrees to the length leaving a small edge which bends; and boiling wood as a variation of steam bending as used for shaker boxes.
He also described the two methods used for the chair: Hot pipe bending, where damp wood is gently flexed and rubbed back and forth around a pipe heated with a torch and then clamped to a form, as used for the back slats of Chair #1, and also steam bending as he used for the legs and arms of Chair #1.
To steam bend wood, Andy explained you need air dried wood -- that is, wood dried by outside air; 1 year per 1 inch of thickness. The wood can start out 14-20% moisture content, but it needs to go down to 8% after it dries post bending. The best woods to steam bend are walnut, oak, cherry, and maple. Avoid exotic woods for steam bending, laminating thin strips instead. For bending the legs and arms for Chair #1, air dried wood was steamed for about 2 hours. The billet was then secured in a stout strap device with stops at each end. The steamed billet was then bent against a previously constructed form, clamped, and allowed to
cool for a few minutes. The bent billet was then transferred to a duplicate form, clamped to it and allowed to dry for 10 to 20 days. Once removed, a pattern was placed on the bent billet, traced and band sawed to shape. Refining the shape was then done with rasps, files, scrapers and sandpaper. (The straps and stops for bending are available from Lee Valley) Mortises can be added to the bent form by using a Fortune jig as described in #197 Fine Woodworking 74-75 (2008). The chair was glued up with G2 epoxy because it has a 1 hour open time and fills voids if necessary, and allowed to dry overnight.
On bending wood, Andy explained wood does not stretch; it compresses. In bending a billet a block is placed at each end and pressure applied to move the axis of the billet from its center line in the billet to the convex side while held under pressure and bound by a strap to keep that side of the billet from breaking. When bent, the convex side remains the same length as it was when straight while the concave side compresses and actually gets shorter.
In addition to his chair, Andy also illustrated the results of bending wood with his beautiful set of shaker boxes.
Andy also described upholstering Chair #1, which involves 8 materials. It starts with a quarter inch Baltic birch plywood seat cut to fit the chair. The plywood has narrow slots cut in it to help it flex to make the seat cover tight and to let air escape when sat on. Over the plywood seat is a quarter inch of high density styrene foam. Then another piece of the same foam cut as a strip goes around the seat perimeter with its edge cut to a 45 degree miter to enable packing medium density urethane foam next to it. This was followed by a layer of low density urethane foam and then cotton muslin stretched tight. Andy covered his seat with leather and will put dark polyester on the seat bottom to achieve a finished look. Loctite spray adhesive #200 or #300 was used to hold the layers of foam together.
Andy showed us a Fortune jig to flex the seat while stapling on the leather so when releasing the jig, the flex of the plywood was maintained by the tautness of the muslin and outer covering of leather to keep the seat tight. Additionally, 2 short bolts in the front and back of the seat help maintain the flex of the plywood while secured to the chair. (Leather is available at Tandy Leather, and most other materials can be purchased from Joanne's or Walmart, according to Andy.) He referenced a Fortune article at #163 Fine Woodworking 54-58 (2003) on the upholstery process.
The finish on Chair #1 was Watco oil applied with a plastic pad, then sanded 180-220 followed by a soaking coat of boiled linseed oil which was wiped off. He followed this with 3 coats of polyurethane thinned 25-50% with mineral spirits and sanding 320-400 between coats.
All of this left us admiring Andy's Chair # 1 and his hard work to make it, thinking maybe we might enroll in a Marc Adams class to build one ourselves.