Assembling the Jauch Lute Bowl

At the end of my last post I had started to assemble the bowl. I made good progress and have finished. With a new mould like this one I never know how difficult it is going to be to assemble the ribs. Each lute is different although there are similarities within in each style. This lute proved to be no different.

The three centre ribs went on easily. I was careful to trim them to the required widths. I added the ebony spacer to each rib before I glued the rib in place. Had this been a solid mould I would have glued the spacers at the same time as I glued the rib to its neighbour. But with an open mould there is always the danger that the spacer will drop a little below the surface of the two ribs. This method is slower but more accurate.

NOTE: I used my usual method of shaping ribs on a long plane mounted upside down which must be nearly universal for lute makers. You can see this technique in my Post Archive from September 28, 2011.

After the first three ribs things became a little more challenging. Since there is some flattening in the design of the bowl and particularly because the bowl becomes relatively deeper around the front block the ribs develop an odd shape that is difficult to make. Here is a series of photos of the profile in paper of the 5th rib on the treble side counting from the edge. The top edge has been shaped to fit to the previous rib and the bottom edge has been shaped to fit within the rib lines of the mould.

The straight line is added for reference. It is not a centre line. You can see the difference develop on the right side of the photo.  The bottom edge has a smooth curve but the top edge has gone flat.

This is the middle third of the rib. The bottom edge continues its smooth arc while the top edge has actually gone negative. That is, it has become concave. The deepest and widest point of the bowl is denoted with an arrow on the right of the photo.

 The two sides of the rear of the rib appear more conventional, but interestingly, it is the top that has a tighter arc. All of these features are a result of the flattening. With bowls that have a more pronounced flattening the rib shape is more exaggerated. The negative aspect is greater and the arc of the bottom edge of the rib at the rear becomes straighter and in extreme flattening, reverses. Crazy!

All in all, I was pleased with the way the new mould worked out. There were some problems though. I hadn't gotten several facets flat so the rib sat too high. That was easily remedied. At several other places it was obvious that I had filed the facet too low and the rib wouldn't make contact with the mould. My temporary fix for this problem is to insert a small piece of card stock wrapped in clear plastic tape. This provides a surface for the rib to sit on. Before I assemble another bowl on this mould I can make a permanent fix if I choose.

The rear area worked out really well. The rib ends came nicely together without problems and they maintained a uniformity of widths.

Once the bowl was assembled I cleaned it up to a respectable finish. Usually, I like to apply the apron or at this time. But I didn't build that capability into the mould. I had decided to follow another sequence because of what I have been seeing in historical lutes and guitars recently.  The inside clasp in lutes or the end blocks in guitars are often shaped to provide a good gluing surface for the belly but are otherwise reduced in size and mass. Also, I had seen one instance where the bowl apparently was papered before the inside clasp was applied. So I decided to paper the bowl, apply the clasp and then glue on the apron in that order. I use 90 lb water colour paper.  As the glue  and paper dry it creates  tension laterally across each rib and it was that effect that I wanted to concentrate in the rear area of the bowl. It seems to me that delicate instruments require extraordinary treatment of seemingly insignificant features.

I wrapped the outer surface of the bowl in plastic tape in order to protect it and made a wooden form that fit the contour of the rear edge of the bowl. Clamped in place, it and the plastic tape secure the form of the bowl while I apply the paper and the clasp. This photo was taken after I glued the clasp in place. Naturally I used more clamps. The clasp is spruce 6mm thick tapering along the top surface to 1.5mm at the ends. Before I glue the belly in place I will taper it in the other direction as well down to 1.5mm along the bottom edge.

To apply the apron I use as many clamps as would fit. The little wooden cauls are concave so that the top and bottom edges of the apron are in firmly in contact with the bowl.

I have thinned out the soundboard material and have started to carve a triple rose of the lute. I am using a different cutting method for these roses than I did for the Kaiser theorbo in previous posts. I'll report on this soon.

Building a Baroque Lute Mould - Continued

At the end of my last post I had finished "roughing out" the mould. There was still lots to do! I had carefully band-sawed the arc of each piece but the angle of the edge of each was only approximate. Remember that the profile of the center axis is not the same as the profile of the face and therefore the angle changes along the course of each arc. I used a rasp initially, followed by files and finally various curved sanding blocks, rocking back and forth, with each tool from one cross-section to the other to smooth the transition. Working thoughtfully, the proper angle was obtained.

Now I had to lay out the position of each rib.  I drew this diagram of the larger cross-section from the lute plan. The width of the 15 ribs average 35 -36 mm wide but there is much variation. The two edge ribs are significantly narrower ( 26 and 29 mm) than the average. Presumably, they were originally as wide or wider than the average. But at some time the bowl was cut down which was and still is the usual method to lower a troublesomely high string height. Several ribs are 34 mm wide while another is only 31. Such variations are commonly found in surviving lutes although our modern aesthetic prefers a more uniform treatment. A millimeter or two here or there is almost unavoidable and I am willing to accept such variation when I am assembling a lute bowl as long as the discrepancy is not obvious.

I did want the two edge ribs to be wider than the others. I measured the distance along the arc of each cross-section and divided by 15. For example, the largest cross-section is 538 mm so each rib would be 35.87 mm wide measured along the curve of the cross-section. I rounded that up to 36 mm and added 4 mm to make the edge rib 40 mm wide at the widest point. Subtracting the width of these two ribs from the total left me with 458 mm for the remaining 13 ribs which works out to 35.23 mm per rib. Remember that this represents the distance along the curved surface of the cross section and therefore must be measured with a flexible ruler. I repeated this process for each cross section. This takes time.

Before I cut the facets for each rib on the cross-sections

I wanted to be sure that the points I marked out created smooth transitions from one section to the next. I used a flexible ruler secured on edge with two clamps. This gave me two free hands to hold the ruler and mark the rib line. In order to create a smooth rib line I found that it was necessary to wander a little from the rib divisions that I had marked off. This is where the variations in rib widths creep in.

Ivo Magherini photo

  I wasn't sure how the rib lines were going to run over the rear section of the mould. If these lines are badly laid out it will be very difficult to assemble the ribs around the rear of the bowl.  On the original each side of the bowl is different! On the treble side the ribs nearly come to a point but on the bass they spread out and would join well below the level of the soundboard. I tried several times but had trouble marking rib lines that looked reasonable.

 Finally, I covered the area with painter's tape and drew more attempts on that surface. Ultimately I got something I liked. I pricked through the tape along the lines with a pin and used these marks to pencil in the appropriate lines.

When I was confident that these rib lines would result in nicely shaped ribs, I created the individual facets using a rasp and files. I replaced the front of the mould with material for the front block and shaped that to the proper contour.

While I was building the mould I prepared a set of curly maple ribs, so when I finished the mould I could begin the work that I really enjoy.

Building a Lute Mould for a Jauch Baroque Lute

Ivo Magherini's drawing of the 1734 Andreas Jauch 

My newest project is the construction of a model of the Andreas Jauch baroque lute that is in the Musikmuseet, Copenhagen. Fellow lute maker Ivo Magherini generously sent me a copy of the working drawing, photos, fact sheet and report that he made when he measured the instrument a few years ago.

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.

These were glued to the longitudinal section in the appropriates locations.

When all of the sections were added I filled in the front block area and the rear area of the bowl and shaped them to  reasonable contours. That finished "roughing out " the mould. I still had to mark off the mould into individual ribs. 

I'll explain my method for this in a few days. 

When Magherini measured this instrument the lighting was dim and the workspace inadequate, which explains the dark photo. Visiting instrument makers find varying work conditions at museums; from well-equipped laboratories to a shared table in a storage room.  I understand the Copenhagen collection has moved to a new building.

Information about surviving lutes is always valuable and  much appreciated. Thank you Ivo.