The tops of violins and cellos are made of spruce and thin enough to vibrate. The tops of violins overhang the edges of the ribs by a few millimetres and thus are susceptible to being bumped or knocked or damaged. Most commonly damaged are the corners of the C bouts. But also the edges themselves can come away.
Whilst quite repairable they can take some time. if the edge is small enough and doesn’t extend beyond the purling then a new piece of spruce can be fitted and trimmed to match the existing top plate.
If however the top plate edge is long or extends beyond the purfling them often some structural component must be added to it. One technique is to half edge (or double edge) the top plate, that is a laminate of 2 offset spruce layers, which can give stronger mechanical connection than a simple butt joint. Selective skewing of the grain lines on the underside can further enhance strength. Of course it takes a bit more time. Here are some pics of a few edges I’ve worked on . Also see my article on a corner replacement.
So why does the top over hang you might ask? Good question, because thats how they have always made them is one answer…but an unsatisfactory one. Ask any wood worker about getting to pieces of timber to meet together perfectly and you will realise thats why there is a little bit of an over hang on many things eg door frames.
Also the top plates are made of spruce and fabulous tone wood, but it shrinks a few % over time, where as the maple bottom and sides much less so, so over time the top plate will come down in size a bit, so a few mm overhang might come in handy. In fact on old instruments it is not uncommon common to see the ribs almost poking out from the top plate.’
