Gluing the C-bouts using a Cremonese mould

An alternative method for this part of the process, which may be more authentic than the standard procedure

Makers reveal their special techniques

When I was a student at the Newark School of Violin Making, we were taught to glue the C-bouts of our instruments using a trapezium wedge. This is the method still used by the majority of luthiers I know, and works well as long as the corner-blocks are cut square. However, while working with François Denis I learnt a different method, probably closer to that used by the old Cremonese makers, which makes it possible to glue a rib that is not perfectly bent but which, once glued, follows the mould perfectly.

The moulds and counterforms exhibited at Cremona’s Museo del Violino (MdV) show that the technique used at the time of Stradivari was different. In those days, rib structures were commonly mounted without a mould.

It was necessary to bend the ribs quickly, because the heating process was harder to control than it is today.

The method described here seems to me more authentic, as it can be applied to a block that is not perfectly square. It also has the advantage of being fast and efficient. Additionally, I like to leave tool marks and make asymmetrical volutes and slightly irregular purfling, so it seems more logical for me to use this method of gluing, closer in spirit to that used in the time of the great masters.

Drawings of Stradivari’s counterforms and rods

ALL PHOTOS FANY BOUREL

1 Here are my drawings of the Stradivari counterforms and rods on display at the MdV. Each counterform is marked to indicate which one corresponds to a particular mould. The moulds themselves do not have holes at the level of the C-bouts, but only small holes at the level of each block. Wooden rods would slide into these holes, to fix a string in place that would tighten the counterform to the cleat. This clamping process did not require metal clamps, which were rare at the time.

String, rods and my counterforms

2 I use a string made from hemp, around 1.2m long, with a loop at both ends to secure the string to the rod. This string looks a little rustic but is ideal because it does not slip and is very strong. I tried using several other types of nylon twine, both thick and thin, but they were very slippery and required a lot of strength to use; I had to wear leather gloves to grip hard enough and prevent them from slipping. My counterforms are made from beech, but any hard wood will do. They must have rounded chamfers to allow the string to hold well and not break. The rods are of fairly hard exotic wood (I use pernambuco from a broken bow) and have a saw cut at each end, serving as a hook to fix the string in place.

A counterform helps check the corner-block curves

3 As well as a set of counterforms, I have made small models of the corners, identical to those kept at the MdV. I use these to trace the shape of the corner on the blocks. Once I have cut the blocks, I use counterforms to adjust the curve. If necessary, I repeat this step until I am satisfied with the result. (This photo also shows the location of the hole to insert the rod later.)

Fitting the loop on the rods and positioning the counterform

One turn around the rods

Pass the string to the other side

Position the counterform with two turns round the rod

Pass to the other side to renew the operation

4 Before bending the ribs, I am c areful to add 4mm more height than the blocks (for a violin and a viola). This margin makes it possible to tolerate slight twists while bending and to glue the rib very quickly. I also add 2 or 3mm to the length on each side.

Once the bending is finished, I lower the bending iron to 40 degrees and let the counterforms heat up on it. I then fix the mould in the vice, so I can use both hands for the next part of the process.

I put soap on the mould just after the blocks, to prevent the splint from sticking to it. Then I pass the rod through the hole and insert the loop of the string at the end of the rod. I apply hot glue to the block and the rib, and then position the counterform without trying to tighten too much for the moment.

The twine is wound around the blocks

5 I perform the same o peration a second time, but tightening well this time. When there is 15cm of string remaining, I make a few turns on the rod and hook the string in the notch at the end of it.

A hammer blow helps correct the curve

6 I clean off the glue (without using too much water) and turn the mould over in the vice. Then I repeat the process for the C-bout rib on the other side.

If the rib doesn’t lie well against the mould, I give a little hammer blow with a wedge on the end of the rib and it will flatten perfectly. I am careful to use a block that is wider or of the same width as the rib, so as not to split it when tapping.

I tighten the second C-bout rib fairly quickly, so I can move it with a hammer blow before the glue sets.