I start by reporting the latest renovation (not an Old Gura), a Swedish lute built by the Dane Peder Stochholm in 1906. I found some facts and pictures of him in the book "Danish guitars - and their builders" by Kenneth Brögger.
The last paragraph was grim: "Despite the wide recognition he enjoyed, the quality of his work and his large output, like most other musical instrument makers, Peder Stochholm struggled with power all his life".
So, what is a "Swedish lute"? Wikipedia has the answer:
"The Swedish lute is a lute that was first developed from a cistern by the instrument builder Mathias Petter Kraft in the second half of the 1700th century. The instrument has a theorized neck with several exposed bass strings. The modern Swedish lute usually has 6 strings across the fingerboard and 4 or more free basses.”
It resembles a harp guitar, but the Swedish lute has a curved neck and drop-shaped body with a round bottom. The six strings are tuned like a regular guitar.
This lute had unusually few bass strings, only three. The bridge had been replaced, and the sound hole decoration had been loosened, probably to be able to glue cracks in the top. The "ship" itself, the round bottom, was in good condition, the top had several cracks and the string height was high. The neck, probably walnut, was also in good condition and the tuning screws were also of good quality. An odd detail was that the ebony fingerboard had a thick oak shim glued between the fingerboard and the neck. I thought it was a later addition, but it is supposed to be original.
The binding was as wide as the top was thick, so it was not difficult to detach the top from the round bottom. The replaced bridge was a "string through" bridge, but the original had string pins as the holes in the top showed. The ribbing in the top was a bit special with a latticework of thin and carelessly carved ribs. One of the ribs had three mysterious holes as well. No bridge plate.
To deal with the round bottom I made a special jig, but later realized I needed to do something more practical and general, it's not often I have round bottom instruments, but it happens.
The top was deformed, so the first step was to moisten the top and put it under pressure overnight to flatten it. The cracks were then glued with hot hide glue.
I wasn't impressed with the original ribbing, but tried to replicate it with a custom variation of my standard ribbing with a spruce bridgeplate and A-frame around the sound hole. An extra thin spruce patch reinforced the top on the side with the bass strings. The replaced bridge was replaced with a rosewood peg bridge in the style of a bridge in one of the pictures in the book, but which may not have been original. Perhaps, or most likely, the original bridge on this one was not rectangular but some type of a mustache stall, but the wound in the top from the replaced bridge had to be covered.
The fretboard was loosened and a carbon fiber rod milled in. There was talk of stringing it with steel strings and then it is always good to have a stiffer neck. It ended up getting nylon strings.
The neck was glued and secured with a screw in a tongue through the neck block. By loosening the screw, soaking loose the glue around the tongue, and driving a wedge of maple under it, I was able to bend back the neck angle. A new way to reset a neck! It worked well. Household plastic protected the label from water.
When I measured for intonation, I realized I had a problem. Presumably the original bridge had a long fret right at the front edge of the bridge, while the replaced bridge had a saddle placed about 3 mm further into the bridge. The replaced bridge had never intoned well, with the saddle 3 mm too far back. My problem was that I don't want to move either the bridge or the fingerboard, the bridge has to hide the wound in the top and the trapezoidal shape of the fingerboard would result in an edge to the neck if it were to be moved 3 mm closer to the bridge (and the saddle would be 3 mm thicker). My solution was to fill in the old fret slots with glued ebony sticks and saw new fret slots 3 mm further down the fingerboard. Even the mother-of-pearl decorations had to be moved, a drying crack was filled with superglue. A triangular ebony shim under the fretboard was glued in after the neck reset.
To simplify life and avoid making a new jig for each round-bottomed instrument, and to be able to glue the top back on the round bottom, I made new cauls for my bottom-gluing jig with some hardware from Jula. The special plate angle is one fence fittings which had an extra hole drilled. The white round things are rubber plastic furniture feet.
The fence fitting can be turned to the right angle. The screw to the plate through the angle on the inner side is not fully tightened, which allows you to slide the caul in or out a few cm (the outer screw is tightened tightly). The hooks are attachment points for elastic "rubber bands", halved inner tubes for a bicycle.
I made 10 of these cauls, but realized I needed more attachment points for the inner tubes - now I have 15 more next time. I also used straps around the table to hold the top in place.
After the first fitting, I could tell that the top had to be made wider to fit. The "ship" was stable and solidly built, and the shape of the edge could not be changed. The binding around the top was made of three thin birch/maple strips. I added a fourth on the outside, all around. The white wood was conjured away with the miracle chemical potassium permanganate.
The top was then glued with hot hide glue mixed with 10% urea to extend the opening time. With the help of inner hoses and straps, I was able to seal all the cracks. I cheated with some pieces of tape too (needed more cauls).
The cauls came in handy when the frets had to be mounted. The hook can be unscrewed if it is in the way.
The position of the saddle was measured, and two saddles were fitted and intoned. The nylon bass strings were intended for an acoustic bass. As ordered, the string height was 3 mm on the bass side and 2,8 mm on the treble side at the 12th fret. The end plug was missing, so I fitted a leftover matching end plug from previous renovations. The decoration was glued in with fish glue. The top received a coat of spirit varnish.
After vibrating, it sounds like a classical guitar with a little extra string reverb. A guitar band is a must!