The following article by Al Fischer orginally appeared in the May, 1974 issue of the SCAVM Bulletin:
Al Fischer was an engineer for General Motors where he worked directly with another ingenious engineer: none other than Charles Kettering. Al's retired now and lives in La Jolla, California. He made his first violin in 1939.
Al was a SCAVM member from January of 1968 until his death in May, 1999. He was president of the Association during 1970. He was a regular contributor to our Bulletin and designed numerous ingenious jigs and fixtures useful in instrument making. He was well known for the application of power tools to the art, but was very adept in the application of hand tools as well.
To bend thin strips of wood to a predesigned curvature and have them retain that curvature requires reorienting the structure or fibers of the wood; otherwise it will spring back to its original form. The common method of doing this is to use a combination of heat and moisture which transforms the wood to a semi-plastic state, and, when cooled and dried, the wood retains its bent shape.
The moisture is easily supplied by soaking the rib material in water for about 15 minutes, and the ideal, clean method of applying the heat is with an electrically heated, thermostatically controlled, bending iron. The violin supply houses have such bending irons listed in their catalogues for approximately $80 [in 1974, editor], if one can afford it, and having one, you have to master the art of bending the ribs, by trial and error, to the curvature of the rib mold you are using.
To take the guesswork out of bending ribs to fit a mold, bending irons have been devised to have the correct curvature of the upper, center, and lower bouts, and the method used for heating the bending irons varies according to what is available around the workshop. I made such a set of bending irons with built in electric heating elements, and with care they do a good job of bending and forming the ribs to fit the mold exactly. The problem is the average violin maker or the amateur making a violin or two as a hobby, does not have the know-how or the metal working tools and equipment to make such sophisticated bending irons. While many violin makers use this method, I feel the bending procedure is completely reversed in that the heat should be applied before the rib is bent over the form so it will be in a plastic state to easily bend to the curvature of the form.
A demonstration on rib bending by Kelvin Savell a year or so ago [1973, editor}, and also by Roger O'Donnell last year made use of this technique by using an electric household iron to heat the flat rib before bending over a wooden form. I feel this is the correct approach, and it has additional merit in that the cost of equipment for rib bending becomes almost negligible. The forms can be made inexpensively from scraps of a good quality 3/4" plywood, and shaped with the same tools that are required in making the violin itself. A discarded electric steam dry iron with the thermostat still is workable condition is an ideal source of heat. The thermostat should be adjustable to a temperature that will not scorch the rib material. A lot of steam irons get fouled up by the user not using distilled water and are soon donated to the Goodwill who sell them for about 50¢ for the usable parts. Regardless of how fouled up the sole plate may be, a little sanding with emery cloth will clean it to the bare metal which makes it again usable for a heat source for bending ribs.
In forming violin ribs I find it more convenient to handle the rib material and the wood form, rather than the hot iron, so the iron should be clamped by the handle in your bench vise with the sole plate up. Lacking a vice, the iron can be provided with some simple wooden bracket to support it in this mode on top of the bench. If you are bending ribs for a cello, you may want to reverse this procedure because of the forms being so much larger and awkward to handle.
You will find it necessary to anchor or clamp one end of the rib material to the form at the correct starting point, and once the rib is bent around the form some means must be provided to hold the rib to the form until it has thoroughly dried. A thin sheet metal strip of aluminum, brass, or stainless steel, with a hard-rolled spring temper will do the job very nicely. Avoid using steel as it will rust and stain the wet rib material. The spring temper is preferred as that it will stay flat and free of kinks and will be reasonably straight for starting the bend as it must lie in close contact with the rib material before bending.
The center bout which has fairly sharp bends on both ends requires
the thinnest backup material, and I found the side from an aluminum
pop-top can works well here. Remove the curl from the material
by pulling it over a round broom handle. Brass shim stock available
at some hardware stores around .008 to .010 inches thick is also
suitable. The metal backup strip is fastened to the wood form
by sandwiching it between two strips of 16 ga. .050 aluminum and
fastening with two wood screws. You may want to vary the .050
thickness to suit the thickness of your rib material. The other
end is held in place with a 4 inch spring clamp. Refer to fig.
1 for details.
The forms for bending the ribs for the upper and lower bouts are similar, except for size. Here we can use a heavier material for the backup strip, and because the local metal surplus dealer had a quantity of 25 gauge .020" stainless steel on hand I made use of it. One end was preformed to conform to the sharp radius of the corner and the other end was bent to provide a ledge for the spring clamp. On these forms a curved clamping block is used to clamp the rib material tightly to the form at the sharp reverse bend. A dowel pin made from a small plated nail is helpful in keeping the parts properly aligned while being clamped. Refer to Fig. 2 for details.
Here the end of the rib material is preformed roughly with the heat from the iron using the back up metal strip as a form. it is then assembled with the rib end against the dowel p in and clamped. The straight rib sticking out from the form is then laid on the iron as shown in Fig. 3 and the form rolled up as the wood becomes plastic. A spring clamp holds the backup metal strip tightly around the form until the rib material is thoroughly dry. It is a good idea to wear canvas gloves for this operation because the backup metal becomes fairly hot.
Bending the ribs for the center bout is similar except no preforming is necessary. One end of the wet rib material is wedged against the .050 space and then the backup strip is laid flat on the iron and rolled up as described above. The rolling up can be done quickly when brought to the correct heat because you are heating a large area instead of just a narrow section as with a heated bending iron.
If the spring clamps are released before the rib material is thoroughly dry, the ribs will tend to straighten, so thorough drying is essential. This can be accomplished in an hour or so in the kitchen oven at around 150 degrees F. If you are not in a hurry, overnight in a warm spot by the furnace or on top of the water heater should do it. The drying operation shows the advantage of using spring clamps. If clamped tight at both ends, the metal backing strip, especially aluminum, expands much more than the wood form when heated and will bow out away from the form. This could allow a deformity to develop in the rib curvature. With the spring clamp the rib is always held tight against the form.
It is a good idea to seal the wooden form against moisture or steam from the wet rib material. I used a clear thin epoxy varnish applied with a small piece of cloth ù allowing the wood to soak up as much as it could and then wiping the excess off with a paper towel. This saves cleaning brushes and works quite well to give a waterproof wear-resistant finish. A coat of shellac or sealer should seal the wood equally as well.
There will usually be a small amount of springback from the original curvature of the form, so if you want the ribs to fit the rib mold exactly, you will want to compensate for this by exaggerating the curvature of the bending form slightly. Since it is made of wood it is easy to modify and a little experimenting will give you perfect fitting ribs every time.
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