Sunday, December 27, 2015

Building a Louis Panormo - Part 2

I finished the model of a Louis Panormo guitar that was the subject of my post from 10/10/15. It is closely based on a Panormo that I restored in 2014 ( see 7/9/14).

Harris Becker, director of the guitar program at Long Island University Post, had commissioned a renaissance lute and when he came to Toronto to pick it up I showed him the work I was doing on my Panormo. Harris reserved the instrument and last week he was back in Toronto to pick it up.

My previous post about this guitar focused on my description of assembling the guitar on a solera.  The technique requires finishing the soundboard with the rosette in place and most of the shaping done on the heel and slipper foot part of the neck. In this post I will take up the story where I left off.

There are a number of steps that are required before the side ribs can be glued to the soundboard. The first step I had done earlier - drawing the contour of the top on the back of the soundboard before I assembled the fan struts and harmonic bars. The side ribs will be bent precisely to this shape and then glued to the top positioning them on that line.  But the front edge of each rib needed to be trimmed so that it fits in the slot that is cut into the side of the front block. This needs to be a tight fit both for strength and appearance.

The tail block has an interesting shape - fairly wide (80mm) but bevelled on the edges so the maximum gluing surface to the back is reduced while the gluing surface to the soundboard is rectangular and measures 80mm wide by 13mm front to back.  The tail block was previously glued to the top taking care that it was perfectly up-right.

The side ribs are held in place while the glue dries with threaded rod screw clamps.

The  top lining for the soundboard is composed of dozens of small triangular block glue in place separately. I made these from Spanish cedar, the same wood as the neck assembly and tail block. They are glued by setting them in a puddle of hot glue, holding them in place for a few seconds and moving to the next one. I wanted to feel more secure about this technique so I used a small stick of wood the height of the sides and a small spring clamp. After setting the piece in a puddle of glue I place one end of the stick against the top of the rib and the other against the  face of the block. When the spring clamp pinches the rib and stick together at the top, the bottom of the stick pushes the block down against the soundboard and in against the rib.  With a few sticks and clamps I work from one quadrant of guitar frame to another thus allowing the glue a few seconds longer to set-up.

Panormo No. 2154, built 1834

Panormo tied down the ends of the fan struts by gluing the lining block right on top. This was probably his usual method as I have seen this in several of his guitars. Note the toothed plane marks on the side ribs.

The inside linings for the back need to be carefully bent to the proper contour. I made a simple but accurate template out of plywood, heat bent two strips of Spanish cedar and allowed them to set in the form until they were needed.

The back slopes forward from the tail where the rib depth is 92mm to the neck joint where the depth is 87mm. This is not an abrupt change but it is still necessary to account for this when gluing the linings.  The difficulty arises in bending the interior linings because they must conform to both the outline of the guitar and the sloping profile of the sides as well as fitting snuggly against the inside of the ribs.  I employed the same technique as I did when assembling the terz guitar. See my post: Building a Stauffer Terz Guitar - Part 2 from 20/11/15.

Panormo used deep back linings, perhaps because he also used thin sides.  These linings are about 19mm by 3mm.  Of the original Panormo's that I have examined the sides vary from 1.6mm to 1.0mm with perhaps a general thickness of 1.2 - 1.3mm.  Areas on one guitar     measured .5mm! From what I understand about Spanish guitar making tradition, thin sides are standard and Panormo did advertise himself, "Guitars in the Spanish Style". The back linings are tapered to a thin edge. In the photo I lined the side with a strip of duct tape to protect them while I vigorously scraped and sanded the linings to a thin edge.

The back  of the original guitar is arched 5mm across the lower bout, 4mm at the waist and 3mm across the upper bout. I made an arched contouring jig out of flexible plywood about 35cm wide and glued  three concaved forms to it; one with a 5mm arch over the 35cm width, the middle one 6mm and the last 7mm. Coarse sandpaper was glued to the business side of the jig. By thoughtfully rubbing the board over the guitar sides both before the back linings are made (as seen in the photo) and again to level them once they are glued in place I can create a smooth transition from one end of the guitar to the other. When it is time to glue the back with its corresponding arched braces to the sides the contours will match perfectly.

 Here the back is ready to glue onto the sides. There are only two bars. Other early Spanish makers built guitars with only the two lower bars. They obviously felt there was an acoustical advantage and that the size of the slipper foot compensated structurally for the missing third bar.


Panormo No. 2154
The bridge design deserves special attention. This is the original Panormo bridge. The raised front edge acts as a saddle. The bridge pins sit in a trough that is about 6mm deep. As a result the strings have a lot of down bearing. The bridge is ebony and the central block measures 23mm front to rear and 230mm wide. The strings span is 62mm and the string height is 10mm. The "eyes" are add-on pieces but the wings are shaped as part of the central block.

I modified the Panormo design in one important aspect. The raised front edge of the Panormo design is straight and does not compensate for the slight difference in pitch between strings of different diameters when each is depressed. As a result such guitars always play a little out of tune. I modified the front edge by creating a flat surface where the ridge had been and cutting a saddle slot as found on modern guitars.  I then fashioned a saddle in ebony and shaped it to compensate for each string. The result is visible as a wavy line.

This close-up shows the depth of the bridge pin trough, the sharp angle of the strings over the saddle, the high string height and the angled sides of the bridge block.

Since the soundboard is domed a few millimetres I shaped the bottom of the bridge to match.

I used African Blackwood for the fingerboard and small mandolin style T- frets. The tuners are Rogers' replicas of Baker tuners that Panormo frequently used.  I planned to fill the grain of the rosewood and spanish cedar so I applied enough shellac to the soundboard and maple peg head to seal those woods against accidentally staining them.

The Indian rosewood  was filled with a commercial filler with a little burnt sienna  pigment added to the mix to bring out the red undertone. The neck was filled with a light mahogany filler mixed with enough neutral colored filler to lighten the mix.

Once the filler was thoroughly dry and lightly sanded I started applying shellac with a French polish technique using blond flakes dissolved in alcohol. 

After allowing the finish to harden for several weeks I rubbed it down first with fine pumice and finished it with rottenstone using mineral oil as a lubricate.

I'm finishing a thirteen course baroque lute after Hanns Burkholtzer and anonymous E. 25. I'll soon have details and photo album.

All photos by the author.

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