Wednesday, 15 April 2015

Making a sedia tenaglia - part 1

We use our medieval replica furniture not only during re-enactment (such as at castle Hernen), but also in everyday live. Most folding chairs as well as my strycsitten are arranged along the dining table. As we were already planning to move to a new and larger house, there was a need for a larger table and extra chairs as well.  I did want to make a different medieval chair and try to steam bend some wood as well, so my choice was to make a sedia tenaglia.

As photos and information on internet only tell you the height and width of a chair, and not the thickness of the wood used, I looked at an example that was easily available: the replica sedia tenaglia at castle Loevestein. Another great source which I used was the construction plan of Charles Oakley of a 16th century German folding chair, which is actually an Italian style sedia tenaglia. The thickness and width of the legs of the chair in Castle Loevestein were 2.5 and 4.5 cm, respectively. That of the chair of Charles Oakley was 2.54 and 5.08 cm (1 and 2 inch), respectively. My thoughts were going in the same direction 2.5 and 4 cm, respectively. The thickness changed during construction of the chair to 2.0 cm for reasons explained later. This is still robust enough to sit on, and saves weight.

The replica sedia tenaglia at Castle Loevestein, Poederooyen, the Netherlands. This chair does not have a bend backrest. As such it can be nearly flat folded. On the other hand if you lean to much backwards, the chair (with you on it) will tumble backwards. This does not happen if the back of the chair is slightly bend.

Measurements of the folding chair at Castle Loevestein; the width of the chair is approximately 50 cm. The black dots indicate the placement of the pins for the mortise and tenon joints.

As I wanted to have the same seating height for the sedia tenaglia as my x-folding chairs, 44 cm, this measurement was also fixed. I also liked to have a deeper seating plateau than most sedia tenaglia, and chose a depth of 35 cm. Using these sizes, the folding X part of the chair could be drawn. Only the height of the backrest and the curvature of the back were left to be determined. The optimum height for the back of the chair depends on the people for whom it will be made (mainly me and Anne). The optimum curvature depends on the stability of the chair when leaning backwards (i.e. the chair does not tumble backwards when you lean on it), the ergonomics of your back while seating, and the wish to have the chair as flat as possible when folded. I think I succeeded very well in finding the optimum measurements for my sedia tenaglia.

Most of the remaining medieval sedia tenaglia are made from either beech or walnut. I chose oak to make my chair, as the table and all my other chairs were made of oak. Oak is a more difficult material to work with, and tougher to bend. I started to cut and plane the oak to the appropriate thickness and width. The next step was to bend the back, which I will cover in the next post. 

Meanwhile, also the caps for the dowels had to be made. I used tenon cutters in the drill press to make the caps. The trick is to have the piece of oak thicker than the tenon cutter can cut deep. This way, the caps are still attached to the piece of oak which makes is easy to centre the drill bit to make the hole in the centre of the cap to attach it to the dowel. This hole is cut just deep enough to hold the dowel. Then the caps are cut loose with a (Japanese) saw, and if you planned it well, the second round of caps is already waiting for you beneath the previous ones. You just have to drill the centre holes and saw these loose as well. Rounding of the caps is done similarly as with the Savoranola chair: using a belt sander or a rasp.

Seven times two caps are waiting in this piece of oak. 
The tenon cutter has done its job and the first seven caps have their centre hole drilled.

The seven caps are cut from the oak piece along this line (arrow) with a Japanese saw (kataba).

The first seven caps are cut loose; the second row of caps is already present due to the deep drilling of the tenon cutter.

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