Thursday, September 18, 2014

Repair: Hermann Hauser III 1999

Hauser is one of the most important guitar building dynasties in the history of the classical guitar. This beautiful maple and spruce guitar is a testament to that.  The workmanship on this guitar is almost perfect.  I say almost because it came to me for the repair of an intonation problem.  As you will see, an analysis of the scale length, nut position and compensation led me to the conclusion that the edge of the nut was too far from the first fret, and this was bringing the notes of the first few frets sharp. Making the problem worse was the fact that the nut was tilted back.

This guitar is proof that as guitar builders, we all have our "bad days", even the masters like Mr. Hauser III.

First I had to figure out the scale length of the guitar, since it wasn't 650 mm. Using my calipers I measured the exact distance from the 1st to 12th fret. Then I compared it to tables of scale lengths and it came out to be a 645 mm scale length.

Now I knew what the correct measurement from the nut to first fret should be, and I saw that the measurement was off by .174 mm further from the first fret from what the theoretical nut position should be.  The tilt-back nut made this a little more.  Still not much, but a classical guitar should also have a compensation set closer to the first fret of about .5 to 1 mm.  I chose to set it .75 mm closer to the first fret.

So now I had a measurement to shoot for.  I had to cut the end of the fingerboard to reach this new length and also repair the tilt-back.  This is definitely not easy, so if you're not an experienced luthier, don't try this on an expensive guitar.

The nut was also slightly tilted toward the bass side, in other words, closer to the first fret on the bass side, so I took this side as my reference to know which thickness of saw cut to make. It turned out that about a .9 mm kerf was needed, but to play if safe I used a saw of about a .6 mm kerf, knowing I would have to do cleaning up.

After this was done I spent considerable time squaring everything up so that I would have exactly .75 mm of compensation with the nut perpendicular to the surface of the fingerboard.  The part of the headplate that mates up with the back of the nut also had to be worked on extensively to be square and parallel so that a shim of Brazilian rosewood could be added to the back of the nut that would be the same thickness throughout.

After the shim was cut to length and shaped I glued it on using hide glue. Next I shaped and slotted the new nut which is exactly 3/16" thick or 4.76 mm (as was the original).

The intonation problem was thus fixed and this beautiful instrument is now even more enjoyable!

1 comment:

Unknown said...

Awesome post, very interesting.