Locating Fixture for Fitting the Bass Bar to the Violin Belly
By Antonio Rizzo, Torrance, CA
The bass bar should be located and fitted to the inside of the belly in a perpendicular position, relative to the belly/rib gluing surface and inclined relative to the centerline. The fixture shown properly locates the bass bar while it is being fitted to the belly, maintaining it perpendicularly and provides a repeated point of departure for fitting.
After graduating the top, lay out the location of the bass bar, allowing the bridge foot overlap of 1 to 1-
Locate this point with a pencil mark. A line drawn from the upper bout point to the lower bout point establishes the inclination. The bar however, may not necessarily lie on this line but should be parallel to it. Importantly is the relationship to the bridge foot and perpendicularly with the top gluing surface.
The fixture is made from a ¾” piece of plywood, approximately 11″ x 16″. It has a violin shaped cutout the size of the inside of the linings. This provides a clamping surface for the belly, the same as when it is glued to the ribs. A rail that locates the bass bar is made from 1″ stock and is attached to the top of the fixture with an approximate inclination and offset for the bridge foot relationship. It protrudes into the cutout and shaped close to the graduated surface of the belly, with clearance on the “F” hole side so it doesn’t interfere with the belly. Four legs are fixed to each corner supporting the fixture with belly and clamps attached.
Attach the belly to the underside of the fixture, positioning the pencil mark locations for the inclination and bridge foot relative to the rail. Clamp the belly with cleats or hold it in place with spring clamps with soft jaws to prevent marring the edges. Fitting is done by the chalk method.The belly/bass bar area is chalked. The bar is placed against the perpendicular rail and longitudinally located from the top edge of the plate, with pencil marks at each end. From this point the bar is firmly held against the rail and slid back and forth a light amount, say one or two mm, to chalk mark the high spots on the bar. Remove the high spots till a continuous chalked surface is evident.
To carry this thought further, one could also adapt a scheme for using this fixture to hold the bass bar in place while gluing. There is nothing novel about this method…just another way to do it.