MAKING A JIG
MAKING AND USING A JIG FOR CENTRALISING PLATES
A useful tool for keeping a plate or rib structure in the exact centre at all times
BY STEPHEN QUINNEY Luthier based in Toronto, Canada
It is often a challenge to locate the centre of a rib structure accurately, in order to position an endpin or centre a neck mortise or button. Placing a flexible ruler across the bouts and projecting marks down to the edge of the plate is adequate, but a ruler can distort easily when bent over the archings, resulting in off-centre marks.
I use this jig for new instrument making.
To locate the centre of a plate with worn edges the reference is usually taken from the position of the purfling, and this jig cannot help with that. But it can locate the centre of the rib structure before the plates are attached, or with just the top attached, or with both plates attached. I can mark the button position by referencing the centre of the belly or the back, or both. I also use it to find the centre of the belly edge for marking the neck mortise and the saddle.