Wednesday, October 12, 2011

Inside the Kaiser bowl

I have been away for a week but in the few days before leaving I removed the bowl from the mould, papered over the inside of the rib joints, made and glued the inside apron in place. I also shaped the wood core for the neck, fitted the joint between the neck and the bowl and made and glued on the decorative veneer. In this blog I will describe my work inside the bowl.

Since I had previously loosened the ribs from the mould as I constructed the bowl I had no difficulty in removing the finished bowl from the mould. Three tiny spots of glue had held the front block to the mould and the rear tips of the ribs were glued to the mould during construction. Both spots were released by slipping a small knife between the bowl and the mould. The bowl then slid off the mould.

I lightly scraped the inside of the rib joints with a curved scraper in order to prepare the surface for gluing on the paper reinforcement strips. For the paper I use 90 lbs hot press water colour paper cut into strips 7 mm wide. Their application is sticky and tedious. I soak each strip for a few seconds in the hot water bath that I use to heat the glue. My "glue pot" is visible in the upper right of the photo. The glue is a thin hide glue made from pellets or "pearls" that I buy from Lee Valley Tools. I apply glue generously to both the water-logged paper and the joint. After pressing a few strips into place I clean up the area with a hot damp cloth. When finished, I insert a temporary "false belly" inside the top edge of the bowl. This keeps everything stable while the glue dries.

 Learning from Mistakes. The second lute that I built was made with 21 (I think) maple ribs without spacers. I found the construction terribly difficult. One day I found that it was easier than before so I worked late. When I finished the bowl I was elated. But when I glued in the paper strips and returned after going home for the day I found that the outside of the rib joints had opened up. Not separated but puckered up -- open on the outside but firmly glued on the inside. My beautiful joints were wreaked. Since then, I cover the outside of the bowl completely with plastic wrapping tape before I remove it from the mould and I leave it there until the glue from the papering is dry.

Here is a photo of the inside apron glued in place. I think that the size, shape and the material that the inside rear apron or contre-brague is made from is very important. When I have seen this feature in old lutes it is apparent that makers and re-builders (in recent centuries) have fashioned and re-fashioned this construction feature to suit some conceived purpose. The apron serves two uses; it stiffens the rear of the bowl and it provides a gluing surface for the belly. But when you think about it, how much do you want to stiffen the bowl and how much gluing surface do you want to provide?  Obviously the degree of stiffening effects the resonance of the instrument. Opinions vary.

It has gotten late and I want to dig up some old photos to make my point. So I will continue in a day or two.

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