Tuesday, November 3, 2015

Building a StaufferTerz guitar

I recently finished a model of Johann Georg Stauffer's terz guitar  Cat. No. 4152 in the Berlin Musical Instrument Museum. This guitar was on display when I was in the museum examining their Christoph Koch theorbo several years ago and that piqued my interest.

Many of my lute/baroque guitar clients play 19th century guitar and I have tried to finish one or two guitars a year for the last twenty years. Recently I have been able to spend more time with them; either by scheduling museum visits, doing restorations and repairs and other opportunities. These occasions are recorded in my 'Older Posts'.

A technical drawing for this instrument is available from the museum.

The guitar's dimensions:
string length 554mm
body length 390mm
upper bout 228mm
waist 161mm
lower hour 290mm
maximum rib depth (tail) 77mm, minimum (neck block) 56mm

I built an inside mold  and immediately set about assembling the side ribs. The model has a very tight waist and I was extra careful while making this bend. I made the side ribs about 1.7mm thick over-all but thinned out the waist area to 1.4mm. I wear heavy deer-skin gloves while I bend guitar  ribs. The gloves enable me to cup my hands over the wood and to hold it firmly on the hot iron. In this way I can feel the wood fibers soften and gauge the amount of pressure I can safely apply. I clamped the bent side ribs securely in the mold and set it aside.

The guitar has a raised fingerboard that rides above the soundboard.  The heel of the neck sits in a deep V shaped slot cut into the front block. A simple screw mechanism allows the neck angle to be adjusted with a clock key. It is an ingenious device that was an important  and popular feature of nineteenth century Viennese guitars.

The mechanism is simple in principle but constructing it needs to be done accurately in order for it to operate smoothly. I find it easier to achieve this if I rough out the front block and neck/heel right after the ribs are assembled. This photo show the rear of the block with part of the mechanism in place. The guitar is upside down and you can see the bottom of the slot in the front of the block.

Here is the slot shown in the finished guitar. A wood dowel (shown in both photos)  protrudes through the centre of the upper part of the block. This fits into a blind hole (visible in the next photo) in the rear of the heel.

The dark area is discoloration

The dowel and the surrounding area acts as the fulcrum for the neck to pivot. It also keeps the neck from shifting out of position. The area beneath this is cut back in such a way that only the upper most area is in contact with the rear of the slot. Since the neck pivots on this point the hole must be slightly larger that the dowel.

Here is the mechanism laid out and partially assembled.

From the left, the anchor is the square plate attached to a hollow cylinder that is threaded inside and out. The square part is visible in one of the above photos. It is inlaid into the rear of the block. This keeps it from turning when the mechanism is adjusted. The washer is threaded and securely locks (as shown above) this part of the mechanism in the front block. The hexagon shaped cylinder is open at the front as seen in the photo below, but closed at its rear, except for a hole that allows the adjustment rod to pass through.

The rod passes through the heel. It is threaded at the rear end so that it screws into the rear cylinder. At the front it has a collar (above photo) that holds the rod in the front cylinder. The clock key fits the squared end of the rod.  A quarter turn in direction or the other will change the pitch of the neck raising or lowering the height of the strings above the fingerboard.

This has been a wordy description but here's one last photo that shows the roughed-out nature of the neck. The heel is a separate block glued to the neck. The sides of the heel are cut and planed to the contour that matches the V slot. At the rear part, the heel is cut away leaving a ledge. This is the location of the dowel and the point where the neck pivots in the slot.

And here is the entire neck showing all of the details of its construction. The peg head is attached with a v-joint. The extension that supports the flying fingerboard is attached with a half-lap joint and then tapered to achieve the characteristic Viennese fingerboard.

In the next post on this guitar I'll describe constructing the soundboard, back and bridge and my procedure for polishing the guitar.

All photos by the author.

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