A Folding Armchair

Some years back, Master Hal Raeburn made me a folding chair with arms. It is a very comfortable design whose only fault is that it does not fold very flat and so is a bit of a nuisance to transport--at least when my wagon is packed and overflowing for Pennsic. The design goes back to at least the 14th century; the 16th century version is sometimes called a "Dantesca" chair. This year I decided to make a scaled down version for my son. Since I am not as good a woodworker as Hal, I simplified the design somewhat. I also modified it in order to make it possible to take the chair apart.

General Considerations

I used oak, which is a strong wood and readily available; if you use something weaker, such as pine, you may want to alter the design to use thicker pieces. The figures show the pieces at 100%--scaled for the chair I use, not the 90% version I made my son. I am 5' 3 1/2" and my chair was made specifically for me; if you are substantially taller or shorter you may want to scale the design accordingly. The easiest way of making patterns is to copy the figures from this webbed article into a drawing program, scale as desired and print.
For cutting curved pieces I used a band saw. If you don't have access to one, use an electric jig saw. If you don't have that, a hand jig saw should do it, although I expect it will take longer.
For blind mortresses--the sockets in the chair arms and feet--I first drilled a hole of the appropriate size then used chisels to square it. For grooves I used a table saw; if you don't have access to one a hand saw, or a chisel, should work.

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Macintosh HD:Users:davidfriedman:Documents:Home Page:Medieval:Articles:folding_armchairrtf01.pict
Making the Chair

On the left is the chair Hal made for me, on the right the chair I made for my son. Figure 1 is a cutting pattern for one of the four S shaped pieces that make up the main structure. The pieces are identical except for the holes (A) drilled part way through them for the horizontal dowels to fit into--on two pieces they are on one side of the board, on two the other side.
The tricky part of these shaped pieces is that the circle (B) in the center of each is only half the thickness of the board, in order that two can fit together as shown on the next page (bottom right).
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I found that the easiest way to make them was to first cut out the piece, then use an adjustable drill bit, set for the radius of B. The bit cuts a circular groove and also removes the wood inside the circle, although not to the full depth of the groove. Additional wood can be removed with a chisel.
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Macintosh HD:Users:davidfriedman:Documents:Home Page:Medieval:Articles:folding_armchairrtf04.pict

Figure 2 shows the arms and feet; thickness, the dimension not shown, is 2". The shaded squares (D) are blind mortresses--sockets that the tabs (C) on the end of the S pieces fit into. The shaded region E is a groove that the back slides into. Its exact width sshould be the same as the thickness of the back, either 1/2" or 3/4" depending on your relative preference for lightness or strength.
For the chair I made my son, which was scaled to 90% of the full sized chair whose measurements are shown, I used 3/4" oak for the S shaped pieces. The original was 1" hardwood--which might be better for a full sized chair intended to be used by a reasonably heavy adult. You will also need four dowels. Their length should be the distance between the near sides of the sockets in arms and legs, since that is the separation of your two pairs of S pieces, plus twice the depth of hole A, into which they fit--from the separation of the sockets in Figure 2, that comes to 12 3/4"+3/4"=13 1/2", assuming the holes are 3/8" deep. Diameter should be the same as hole A--about 1" for the full sized version of the chair.
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Macintosh HD:Users:davidfriedman:Documents:Home Page:Medieval:Articles:folding_armchairrtf06.pict

Once you have cut all the pieces and made sure that the pairs of S shaped pieces fit together and that tabs C fit into sockets D, the next step is to drill a hole at the center of
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each circle B. To make the two pivot pieces that go through those holes, cut two 2 3/4" lengths of 7/8" hardwood dowel and two circles of 3/4" hardwood the same size as circle B. Drill a 7/8" hole part way through the center of each circle and glue the dowel into it, giving the mushroom shaped piece shown to the left.
Assemble two S pieces and one pivot piece as shown below. Repeat for the other pair of S pieces. Make sure to assemble the legs so that all the holes A, drilled part way through, face inwards and both pivot pieces face outwards. Assemble the whole thing, with tabs in slots and dowels in holes A.

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Macintosh HD:Users:davidfriedman:Documents:Home Page:Medieval:Articles:folding_armchairrtf09.pict

To keep the pivot from coming out, drill a hole through the pivot dowel on the inside side of the S pieces and put a small dowel through it, as shown above. The picture below shows how it now looks--a chair minus back and seat.

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Figure 3

Figure 3 is an approximate cutting diagram for the back--its aesthetic excellence should be credited to Hal, whose design I copied. Use either 1/2" or 3/4" wood. Scale, or otherwise modify, the figure so the slots (G) are the right distance apart, and the right width, to fit into the grooves in the arms. This is best done after you have the rest of the chair assembled, since the exact separation of the arms depends on the exact angle at which the S shaped pieces cross, which in turn depends on fine details of the pieces.

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Figure 4


The seat consists of two support pieces of oak about 2"x1 3/4"x 16 1/4" and one piece about 12 3/4" x 12 1/2" x 1/2" that makes the seat itself; figure 4 shows a side view of one of the supports. The 1/2" piece goes into grooves cut into the inside surface of the supports--the surface away from the adjacent S piece. Exact dimensions should be calculated, like the exact form of the back, after the rest of the chair is done and you can measure the separation of the two upper dowels. The pictures below show a top and bottom view of the assembled seat.
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Macintosh HD:Users:davidfriedman:Documents:Home Page:Medieval:Articles:folding_armchairrtf14.pict

For my chair, I made the grooves 3/8" wide and 1/2" deep, then planed half an inch on each side of the seat down to 3/8" to fit, but if that is too much trouble you could use 1/2" wide grooves instead. The outside surface of the thick pieces is inset at the end--shaded area F--so that the edge of the assembled seat can fit partly over the adjacent S piece, as shown below.

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The chair, minus back and seat, consists of two closed loops of wood--front S piece to foot to back S piece to arm to front S piece again. In Hal's version, one of the S pairs crosses right over left, the other left over right, with the result that one of the two loops is just inside the other. This prevents the loops from moving forward or back with regard to each other, supplementing the effect of the cross pins on the pivot pieces. It also means that the two loops can, in principle, be separated without taking either apart. In practice, however, the chair is sufficiently rigid so that it would be difficult to separate the crossing pieces far enough to make that possible.
One way to make the chair more transportable is to never glue on the arms, legs, and dowels, relying instead on the tabs being tight enough in the sockets to hold the piece together. That is what I did on the 90% version I made for my son; since I am writing this after making it but before using it at Pennsic, I don't yet know whether there will be any problem with spontaneous disassembly. If so, I have glue in my toolbox.
For an earlier and smaller version of the chair I used a different system. The paired S pieces cross the same way, which means that the two loops are interlocked but, once the pivots are removed, not held together. I left one foot and the corresponding pair of dowels unglued; removing them lets me separate the two loops, which nest together much better separately than together.

Final Comments

Once everything is made, sand or file round any sharp edges or corners that you don't want sharp, assemble it, glue on feet, arms, and dowels (or not, depending on whether you want to be able to disassemble it later). I finish my furniture by wiping on boiled linseed oil, leaving it fifteen minutes or so, wiping it off, and repeating four or more hours later, then letting the whole thing dry for a few days. The result on oak looks beautiful and provides some protection, although perhaps less than with more modern finishes. Linseed oil is a period material; I have been told that it was used for finishing furniture in period but have not actually seen the evidence. I have also been told that a linseed oil finish works better if you use oil heated to 135° F, but have not yet tried doing it that way.