Sunday, December 11, 2011

Kaiser Theorbo- Making and Fitting the Extension-Continued

In my last post I was ready to shape the back of the extension. I lay out the line representing the slope on both sides of the  extension.

 I remove the bulk of the material with a bandsaw and finish with a rasp and file. The curve across the extension runs to from one end to the other so I use a block plane to rough out this surface. Once I am satisfied I scrape the curved surface with a flexible scraper to even out the contour and then finish with sandpaper wrapped over a contoured block. I then cut a length of veneer a little oversize and get all the glue up stuff ready: rubber mat, foam strip, gluing board, nearly a dozen clamps and some little contoured wedges. Here's what the glue up looks like.

I assemble all of this on the edge and at one end of my bench. I lay a rubber mat under the veneered face of the extension in order to protect it. Then the extension is put on top. I prebend the end of the veneer on the hot iron and secure it with painter's tape. I use fish glue to glue the veneer in place because it has a long set up time. This characteristic allow me to make changes if I don't get the alignment correct the first time -- which happens. It is a complicated procedure and it has to be done correctly. Once the veneer is in place I lay a strip of foam rubber -- the kind that is available from sporting goods stores to put under sleeping bags. The strip is cut roughly to the  dimensions of the extension. Next comes a piece of lumberyard pine that is cupped from improper drying. I have shaped this piece roughly to the size of the extension and it is laid on cup side down.  Then I apply the clamps insuring that all are equally tight. All of this insures that the veneer is firmly in contact with the curved surface of the extension.

At the neck end I insert six or seven contoured wedges that I have made specifically for this theorbo between the foam and pine board. These wedges push the foam against the veneer and insure good gluing contact. I leave this to dry. The excess is then trimmed. Veneer for the edges is applied in the same manner with suitable pieces of foam and strips of wood. But I don't glue the edges until I have completed the joint for the extension. You'll understand why after I describe making the joint.

Before I begin to form the joint between the neck and the extension I make a full size drawing of the string alignment of the theorbo as it is finished to this stage. This  is intended to show the angle of the fretted neck and the bridge and nut positions. From this I can lay out the line of the first diapason. In this case it is the eighth string. Since I don't want any of the diapasons to hang off the edge of the theorbo head I position the extension so that all of the diapasons fit within the width of the theorbo head that is 65mm wide.

Next I mark a long straight line on the edge of my workbench. This is the layout  line for insuring that the extension is aligned correctly. Then I position the lute upside down  and clamp it to the bench in such a way that the bridge hole for the eighth string and the point where it passes at the end of the fingerboard are correctly aligned to the line on the bench.

In the photo you can see the reference line drawn on a strip of masking tape applied to the bench. The theorbo is firmly clamped to the bench in the alignment that I described. At the far end of the extension I arranged a riser that elevates the extension the proper height. I align the extension left or right along the top surface of the riser to achieve the position that I want for the placement of the first diapason. The height of the riser represents the height of the theorbo head plus the height of the nut. Theorbo extensions bow up under string tension. The only effort I make  to counter-act this tendency is to build in an adjustment factor. I align the extension vertically so that the diapasons will sit on the fingerboard nut before they are tuned to pitch. Once at pitch for a few days I find it necessary to lower the theorbo head nut. I start with a nut height of 25-27mm that is reduced to around 20mm by the time the theorbo is ready for delivery.

Now I can lay out the saw lines on the neck for the joint. This procedure is a combination of experience and guess work. I know how wide I want the extension to be at this point when it is finished (78mm) so I mark this slightly narrow to allow for cleaning up the sawed surface. The minimum gluing surface that I like, front to back, is 35-37mm. If it is a large theorbo like this one I will finish with a surface that is 40mm front to rear. This is because the distance from the nut to the first fret is large enough to allow a comfortable space for the left hand thumb to sit between the end of the extension and the first fret.

 Here's the roughed out joint and the rough fit.


The closer that I can come to laying out the joint correctly the less effort it will be to finish the joint, but there is always the danger of making the joint area larger than first intended so I am conservative when laying it out. I have also made the extension over wide. The excess will be trimmed off later. I finish the joint with files and purpose built contoured sanding blocks. When I think I have it right I remove the lute from bench and check the alignment. I have a simple method for holding the two parts together. I attach two strings to the bridge in the first and eighth bridge holes and then to pegs on each side of the extension. When tension is applied to the strings the extension will be drawn into the joint. Two spring clamps on each side of the neck will stabilize the joint vertically. I equalize the tension on each side by using the same diameter of string and 'tuning' them as I draw the joint together.

Once I am satisfied with the fit I trim the edges of the extension to fit inside the width of the joint allowing for the thickness of the edge veneer that I can now glue on (above photo). This will cover the peg holes but they can be punched out from inside the pegbox slot and re-drilled.

I use a template for laying out the theorbo head but depending on the size of the theorbo I will make the head a little larger or smaller to fit the over-all appearance and balance of the instrument by re-drawing it free-hand. I have traced around the template on a carefully prepared, square edged, block of poplar. I  drill the peg holes and cut the nut and string slots all while the block is square. Then I begin to contour the shape with a single band saw cut on the top surface and others on each side. The photo shows the head completed to this stage. Further contouring is done around the front and bottom front of the head with gouges and files. The head is then test fitted to the extension and glued when finished. I stain the natural colored poplar black to match the black veneer of the extension. After a final test fit of everything I glue the extension in the same manner as I described previously.

The next two photos are of historical theorbo heads. The profile view is of the Railich theorbo head in Bruseels. The other view is of the Alban theorbo head in Nuremberg.

The last photo is from one of my instruments.

This finishes my posts on the Kaiser theorbo. I have omitted several steps in its construction or have not elaborated as much as I might have. I am starting another Kaiser at the beginning of the year. I plan on covering elements of its construction that I missed this time as well as discussing its design features.

There are several other topics that I will relate. I started a Lacote guitar but put it aside while I finished the theorbo and awaited the delivery of a set of tuning machines from Italy. Those are scheduled to arrive in January so I will begin my post on the Lacote  construction soon. John Edwards and I repaired loose bars in his Kaiser theorbo following the advice of Thomas Mace using his treatise from 1676. I'll post that story. I am about to finish a Voboam guitar and although I started it before I began this blog and started documenting everything, I do have photos from various stages of its construction and plan to post those. During this last week, and the coming one as well, I have completely dismantled my workshop and am reorganizing it.

All photos are by the author.

1 comment:

  1. Thanks a lot for the tips. I live in Guatemala and am having the first theorbo built here! I am having a carpenter make it following the UK lute society plans for a theorbo. We are now at the extension building phase and your advice for using the strings' tension to force extension and neck is invaluable. Also the tips on the bowing out of the extension when new.