Tuesday, October 18, 2011

Kaiser Theorbo Neck

Here's the Kaiser propped up on a chair with the rough neck blank sitting in place.  The neck blank is made from three pieces of edge glued straight grain sitka spruce. It is slightly over size in all dimensions. I cut the angle in the front block of the bowl and a matching angle in the neck blank. To hold the blank in place while I adjust the angle I use two wood tabs that extend across the joint. These are screwed and glued lightly to the front block. Once the angle is correct I tack glue the neck blank in place. When the glue dries I drill a hole through the front block into the neck blank and insert a screw. Once this is secure I can lay out the lute's center line, the edges of the neck, its length and the curvature of the neck which will match the profile of the front of the bowl.

After detaching the blank I shape it to its finished contours with a  block plane and a flexible steel scraper making sure that neck's curvature is smooth and comfortable to hold. I then apply a primer coat of glue. This neck, when the lute is finished, with the fingerboard and neck veneer in place will be 107 mm wide and 30 mm thick at the neck joint.

 In earlier years I have used various woods for neck blanks; basswood, poplar, maple and walnut. There is something to be said for each choice. But now I want my neck wood to be actively acoustical and I think spruce offers that.

I usually choose to apply an ebony veneer or an ebony veneer with
white holly spacers numbering from 7 to 19. Here I decided to forego the holly spacers and alternate ebony and walnut strips . I had several  ebony ribs left over from another project so I cut these into narrow strips of the necessary length and width and glued them together with an equal number of walnut strips, face to face. When the glue dried I planed one edge of this assemblage flat. Then I laid out the line that represented the taper from one end to the other. I planed that flat and separated the strips by submersing them in hot water. When dry I laid them out edge to edge in order to check for straightness. It is a good idea to plane a slight bevel on the under side of each edge as this allows the assembled veneer pieces to bend around the curvature of the neck. When I lay out the veneer pieces I stretch painter's tape over them to hold them together. More glue is applied to the neck blank and the veneer is taped into place and secured with elastic wrap. The photo shows this sequence after the glue has dried and I have begun to unwrap the neck.

I always make the width of the veneer covering less than what is necessary to completely cover the neck. The reason for this is that if it is slightly too broad wrapping the neck with elastic will cause the the sheet of veneer to bunch up and not lie smoothly on the neck surface or it will damage the two outside edges. To finish the edges I lightly plane a flat edge perpendicular to the fingerboard face of the neck. This allows me to cover this surface with a thin rectangular strip of matching wood. Subsequently these two pieces are levelled with the surface of the veneer. The photo shows one side that has already been levelled and blended into the veneer while the other side is awaiting the same treatment.

After rechecking the neck alignment the neck can be glued in place. Previously, I found that the viscosity of glue caused the neck to slip up the surface of the front block when I tightened the screw resulting in a mis-aligned neck. That is the reason I use the wooden tabs that I described at the beginning of this post.

Interestingly, while reviewing the museum photos of the Alban theorbo in the German National Museum I found one that suggested just such an arrangement. Two holes, among others, were drilled in the top of the front block in a position just where such tabs would be located.

Photo: MIR 908
Property of German National Museum, Nuremberg

1 comment:

  1. Hi, Michael,
    Recently it has been sold (quite cheap, I think) A tiorba kaiser at an auction in UK.