3 mins
Making a soundpost jig
A useful device to help luthiers cut a soundpost to its correct length, and to make its top and bottom angles
Lutherie
Imbued with an almost mystic aura, the soundpost is an essential part of a stringed instrument’s set-up. It connects the front and back plates, which oscillate around it. Fitting it precisely can bring out the full potential of an instrument’s sound and timbre, whereas locating it incorrectly has the opposite effect. The post has no standard length or thickness: for a violin the diameter can be 6–6.5mm, a viola 6.5–7mm, and a cello 11–12mm, depending on the individual instrument. The adjustment of the length, however, is critical: too short and the post will be too close to the treble rib; too long and it will stand too near the centre of the instrument.
Professional luthiers who fit soundpost after soundpost as a matter of course become adept at measuring and estimating the correct length of a post, but even here, minute adjustments with a knife or a file take time and can produce ragged edges and inaccuracies in the orientation of the grain on opposing ends of the post. A simple, easily made holding device obviates the problem of grain orientation, and makes it very simple to hold the post securely while adjusting the length.
1a
A mahogany block
1b
Planing the block square
ALL PHOTOS RUDOLF PILSEL
1 A block of suitable hardwood is required (1a). A maple offcut is ideal but for the process shown here I had an offcut of mahogany to hand. I plane the block square (1b) and cut it to the desired dimensions: for a violin soundpost I make the length 140mm, width 50mm and thickness less than the length of the finished soundpost.
The hole is marked out
2 Again for a violin soundpost, I mark out the position of a hole which, when drilled, will be the same diameter as the post. Here the diameter is 6.5mm, while the centre of the hole is 14mm from one edge and 80mm from one end of the block.
A drill makes the hole
3 I initially drill the hole with an engineer’s centre drill, which will guide the point of an ordinary t wist drill to its correct position. The hole passes vertically completely through the block.
A saw kerf allows the hole to be tightened
4 Then I use a bandsaw to make a saw kerf in the block from one end. The kerf extends into the hole, allowing it to be slightly variable in diameter when the kerfed end of the block is placed in a vice. Reducing the diameter of the hole makes it a very secure clamp on an inserted length of soundpost material.
The slope of the inner plate is marked
How the block looks with the planed curve
5 On the block ends, I mark out a curved chamfer or a slope corresponding to the shape of the violin’s inner plate surface, at the point where the post needs to fit. Then I plane this to shape. The angle of the chamfer will vary according to the curvature of the particular instrument. The adjustment is easily made with a plane.
6a
The soundpost material is inserted
6b
Cutting with a sharp chisel
6 I insert a length of soundpost material with the grain at right angles to that of the block (6a). Then I gently ti ghten the block in a vice, so the soundpost material is firmly held in place. Using a razor-sharp chisel I cut the end of the post (6b) until it is flush with the surface of the block, leaving a clean end perfectly shaped for fitting.
Measuring the soundpost
7 Next, I measure the required length of soundpost m aterial using a measuring tool, and cut it slightly over length. Then I adjust the post to its correct length, having inserted the post into the block with the grain in the correct orientation. Again, a razor-sharp chisel cleanly cuts the post end.
The finished soundpost
8 The post can then b e fitted into the instrument in the usual way. If the post still requires a fraction off its length, it can easily be reinserted into the block and trimmed. When fitted, the post should sit precisely in its correct location with its ends accurately cut and the orientation of the grain perfectly at right angles to that of the plates.