Preparing a two-piece violin top

An accurate method for sawing and preparing tonewood before the main process of carving the plate

TRADE SECRETS

Makers reveal their special techniques

The finest tonewoods are expensive and increasingly rare. To get the maximum usable billets out of a tonewood log (and to maximise profit), suppliers trim the individual billets so there is as little wastage as possible for them, but which leaves little wiggle room for the luthier as they prepare the billet for use. Usually coming as a wedge, the billet will require further processing or conversion that calls for considerable accuracy. In this article, I demonstrate the method I use for converting the billet from a wedge into the form required for working a back or front. It reduces the process of conversion to a speedy but accurate exercise, making maximum use of the material available.

The illustrations show the process on a 20-year-old piece of Italian spruce from the Val di Fiemme, reputedly the same forest that supplied the material used by the old masters. The whole process, which in description is quite wordy, can be carried out in 20 minutes or thereabouts, apart from the glue’s drying time.

1a The wood billet as received from the supplier

1b

1c The centre line is marked out

ALL PHOTOS RUDOLF PILSEL

1 This billet has narrow, even growth rings and is nearly perfectly quartersawn (1a). The supplier has marked out an outline for a small viola (1b). First it requires cutting down the centre of its length and opening out like a book to form what will be a two-piece front. To do this I mark a centre line along the thick edge (1c) along which the blade of a bandsaw will travel.

2a Setting up the bandsaw

2b Cutting along the marked line

2c The sawing is complete

2 Prior to cutting, I prepare the bandsaw table by temporarily clamping two pieces of plywood, 10mm thick, to the bandsaw, the long edges of which are parallel to the blade (2a). These act as guides to ensure that the thin edge of the billet remains central to the bandsaw blade, and are measured to be the same distance apart. The bandsaw cut (2b) follows the marked line on the thick edge’s centre, and the thin edge automatically follows the centre between the two plywood guides. After cutting in this way, the two pieces are practically dimensionally identical (2c).

A potential disaster in the making

3 This particular billet, cut into two halves, reveals the luthier’s nightmare: a large resin duct, invisible in the uncut billet, but glaringly obvious when the two pieces are opened like a book. In the wrong place, this resin duct would reduce an expensive would-be instrument front into bass-bar and soundpost wood! In this case, the resin pocket is situated in such a position that a violin front, with a millimetre to spare, will hopefully still be possible.

Adding the timber battens

4 I then take two battens of timber, usually 50mm x 25mm and the same length as each half, and glue each one to the outside sloping part of each piece. Ordinary wood glue suffices for this. When fitted, the profile is as illustrated. Each will require further shaping for it to be ready to fulfil its purpose.

5a Shaping the battens

5b

5 Firstly, each batten is planed square to the flat side of each piece (5a). Secondly, the bandsaw is set to the thickness of the thicker edge of each of the spruce pieces. Then each of the thin edges of the pieces, with its attached squared batten, is stood on its squared edge and cut on the bandsaw (5b). The combined depth of the thin edge of each piece plus the batten is equal to the depth of the thick edge of the piece.

Billets and battens post-shaping

6 The final edge profile is as illustrated. This finished profile allows easy holding in a vice when the edges to be joined are being planed, and provides an excellent surface to allow sash cramps to be used in the gluing process.

7a Ready for edge jointing

7b Gluing up

7 Edge jointing methods vary greatly. Some people use a rubbed joint, wherein the joint is held together solely by air pressure; others make jigs of one sort or another; and still others use various cramps. I am in favour of using sash cramps, and the two glued-on and shaped timber battens equalise and spread the cramping pressure evenly on the joint (7b). The glue I use for this is rabbit-skin glue.

Billets and battens post-shaping

8 When the glue has set, the battens provide an even surface that sits flat on a bench, enabling swift and accurate planning of the front, on to which the violin shape can be marked. The even surface also enables easy cutting out of the violin shape, either using a bandsaw or by hand in a vice.