French Connection III, The

Chronicle of the Early American Industries Association, Inc., The, Dec 2004 by Packham, Jim

This little topic started with a reference to a French cooper's compass in my article "Threads in Wood" (The Chronicle 56, no. 2 [2003]. 56-67) Then a letter from Karl West (The Chronicle56, no. 3 [2003]: 128) under the heading, "The French Connection," raised the puzzle of how it is possible to connect the parts of this tool. Under the heading, "French Connection, Part Deux," my letter in the next issue (The Chronicle 66, no. 4 [2003]: 169) described a solution very briefly. Following is a more detailed description of the French cooper's compass with a solution to the connection puzzle.

Old time coopers made each cask to its intended shape and capacity almost entirely by eye and experience. Every stave and hoop was hand-fitted. When it was time to have heads inserted into the chime grooves, it was necessary to measure and make each head exactly the right diameter for a tight fit for that particular cask.

The size for each head was found by trial and error. A pair of compasses was adjusted to roughly the right size radius. The cooper put the point ofone arm into the chime and then would "walk" the compass around the chime groove six times. The compass setting was adjusted until it went exactly six steps around the groove, at which point the compass had the precise radius for marking and cutting that head circle (Figure 1). It can be shown by geometry that the radius of a circle will inscribe six equal chords within the circumference of the circle.

Most coopers used a pair of compasses constructed with two straight arms joined by a hinge pin. Adjustment of this compass often involved a "wing" that could be clamped for rigidity. However, some coopers in France used a compass made with a bentwood bow (Figure 2). The arms of this compass are adjusted by a cross piece having right-handed threads at one end and left-handed threads at the other end, so that turning the cross piece opens or closes the arms against the spring of the wooden how piece.

There are four key elements involved in making a French cooper's compass: wood suitahlc for bending and threading, threading tools, steam bending, and very important-a two-stage bending jig. Other construction steps will be fairly obvious to those familiar with woodworking.

White ash is very good for the bow piece because it bends very well and also accepts internal threading; white oak also can be used. The cross piece should be pearwood or boxwood for strong external threading, but again white oak is acceptable (Figure 3).

Matched sets of righthanded and left-handed screw boxes and taps are almost nonexistent. In twenty-five years of collecting screw boxes and taps, I have seen only two complete sets. Fortunately, the Beall Tool Co. of Newark, New Jersey, made right-arid left-handed jigs for threading with a router, plus right- and left-handed taps. This was a much more economical solution than buying a thread cutting lathe, and simpler than making a lefthanded screw box and tap to match a right-handed box and tap.

The bow piece for a practical compass has a principal cross-section about ¼ inches by 1 ¼ inches. About forty-five minutes in a steam box is sufficient for that much cross-section. As with all steam bending, it is good practice to have the bending strap, jig, clamping blocks, and clamps all ready before steaming, and to have tried a "dry run" to make sure everything fits.

Inspection of a French cooper's compass shows that it has only a limited range of adjustment before the cross piece threads bind tightly in the bow piece threads. It can close only so far, and it cannot be removed. Connecting the cross piece into the bow piece seems to be a physical impossibility. This is the puzzle that Karl West identified. Thus, initial assembly requires a little ingenuity. One solution is as follows.

Rather than initially bending the bow piece to its final semicircular shape, it is bent initially to a shape that is the long half of an ellipse. The elliptical length should be just enough for the bent arms to span the whole cross piece. As the cross piece is gradually threaded into the arms, the bow piece is gradually changed from an elliptical shape to a circular shape. This can be done readily with movable jig blocks (figures 4 and 5).

The finished French compass is shown in Figure 6. This particular compass can be set to a radius between 8 frac12; and 9 ½ inches, which would be a good size for wine casks in the twenty-five-to thirty-five gallon (U.S.) range. It is believed that each French cooper had a compass for each size of cask that he intended to make and that this explains why a significant number of these compasses still can be found.

Most English language references to this tool call it a "French cooper's compass" or a "French wine-cooper's compass." In the French language, there are several terms used.

Diderot in the eighteenth century called it a compass de bois (wooden compass) as a tool for makers of round boxes. And he called it compass à resort (spring compass) as a tool for coopers. The 1977 award-winning publication, Le Livre de L'outil by Belter, Lamothe, and Marquis, labels this tool as compass cintré avis ou, compass Bourginon (screw-arch compass or Burgundian compass). This raises the possibility that this special type of compass was used first by the wine coopers of Burgundy.