|Ivo Magherini's drawing of the 1734 Andreas Jauch|
Before I can begin to construct the mould that I will use to assemble the bowl I need to analyze its contours and make cardboard templates. On the drawing you can see the contour of the face, the centre axis of the back of the bowl and two cross-section contours. Historical lute bowls often display a sophisticated design for enclosing space. This Jauch is no exception. The bowl is flattened in the deepest (and widest) part. As the rib lines flow toward the front of the bowl this shape changes to a point where its depth is equal to half the width. Then, at the front block, the bowl is deeper than half the width. The photo demonstrates the flattening while my diagram illustrates the transition from one region to another.
|Ivo Magherini photo|
The two larger cross-sections are from Ivo's drawing. For comparison, the broken line represents a semi-circle. I created the smaller cross-section which is near the front block. You can see the flattening of the two larger arcs while the smaller arc is noticeably deeper. Making this transition is tricky even when a lot of information is available.
The problem I faced was to construct a number of cross-sections that accurately represented the contours of the bowl from the limited amount of information contained in the drawing. I need to create enough cross-sections so that there is one about every two inches. Here's how I did it.
At any spot along the centre line of the lute I can determine the bowl's width and depth, plus I have the two known cross-sections from the lute drawing. The image (below) represents the method.
The scribed arc on the card stock is the contour of the larger of the two cross-sections from the drawing. I want to use it to create the arc for the centre cross-section (the widest and deepest point of the bowl) while retaining the characteristic shape. I marked the width and depth for the arc on the card stock and aligned a flexible ruler to those points, allowing the ruler to mirror the smaller arc. I repeated this procedure several times for various points along the length of the bowl. Each new arc formed the basis for its neighbour.
Then I arranged the templates on the drawing to see if the result looked reasonable.
Once I was satisfied that I had made enough templates I transferred them to pieces of pine wood that I had previously prepared for this mould. I set the bandsaw table at a slight angle to represent to slope of each section of the bowl and cut out each member.