Templates for sinking
The shape of the overall sink is of vital importance for the later backing and tuning. The main idea is to make the surface between the notes concave spherical in shape. But, in order to make the notes in the outer circle raise properly during the later backing, there must be a deviation from the concave shape near the rim. The surface should be straight or slightly convex here, resembling the final shape of the outer notes.
When the pan is backed, the surface between the outer notes should be lowered down to form a uniform spherical shape. Since the outer notes of the lower tuned pans are bigger and higher, the height of the convex part near the rim has to be higher in a degree corresponding to the height of the final note dents.
The template graphs given in fig. A.4 and A.5 have a special design. The pattern for each pan involves two shapes: one for the shape of the surface between the notes of the finished pan and one showing the shape measured through the highest note. The shape to be used during the sinking phase is the higher one, because at this stage material should be left to form the notes later. This template is the most important one.
The second shape is given to show what the overall shape should be after backing, grooving and levelling. This template can be used after the backing to check that the surface between the notes has an even, spherical shape.
The best way to make sinking templates out of the patterns below is to copy the page twice for each pattern. Then take one of the copies and turn it back to front, to form a left and right side of the template. Paste the left and right shapes together, carefully adjusting them to match the correct depth of the basin for the intended pan. The next thing is to paste the template to some stiff material that can serve as a guiding template during the sinking.
The straight lines at the top of the patterns should not be included in the template, they are there just to serve as a reference to the vertical outer side of the drum. These lines should be vertical when you paste the left and right parts together. Last, cut the template after the shape lines.
Fig. A.4 Sinking templates for tenor, double second, cello and six bass. Full scale right side. Cross-section of the surface along the groove and through the most convex note for each pan. Drawing by Johan Larsson.
Fig. A.5 Sinking templates for double tenor, guitar and tenor bass. Full scale right side. Cross-section of the surface along the groove and through the most convex note for each pan. Drawing by Johan Larsson.