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I am a Sarasota , Fl. Luthier, who happens to own and operate
a small C.P.A. firm. When not practicing as a C.P.A. I am
very much engulfed in building stringed instruments. I am
a Buzz Feiten certified manufacturer and retro-fitter. I
have either built, or retro-fitted, many guitars, with the
Buzz Feiten Tuning System over the years. I truly believe
in the system, having tried and tested many others and have
not found a better one. I realize some players and builders
do not subscribe to Buzz’s thoughts or his system.
This article is not intended to persuade anyone that they
should change to or use any system. It is simply a "how
I do it" article. I do hope that perhaps the article
will inspire you to think more about how and why you intonate
your guitars.
As
you may already know, by design, the system most luthiers
use to calculate fret spacing/placement is flawed (rule
of 18; 12th root of 2). Most of us use this system as there
is nothing better available to us that works in all keys.
Aside from the intervals of these different systems resulting
in extremely sharp results( i.e. equal temperament results
in being 14 cents sharp). We also must deal with the fact
that due to string tension and the fact that the strings
must be bent to play a note ( a fretted note ) you will
find "that the pitches go progressively sharp as you
move backwards from the 12th fret to the nut and progressively
flat as you move up from the 12th fret towards the bridge."
( excerpted from Mike Doolins article on intonation –
article iv.)
By
the way, those who are interested in learning more about
intonation and temperaments should go to Mike Doolin’s
website at www.doolinguitars.com/intonation. Mike has written
a wonderful article. The best I’ve read on the topic.
O.K.,
with all this in mind what can we do? How do we correct
it? Well, we can’t correct it 100% but we can improve
it a great deal. I start out by:
Measuring the scale length so I know exactly what the actual
scale length is.
Next I check to see how flat the fret board is. I use a
Stewmac slotted/notched straight rule . I like my fret boards
to be perfectly straight ( so does Buzz ).
I then look for any fret issues…flatness/level, popping
frets, loose frets, worn frets. All these issues have an
effect on how well the guitar plays in tune. (I use a Stewmac
straight edge to make sure the frets are level.). If there
are any issues they must be corrected before any intonation/BFTS
work can be performed.
Next I calculate the distance ( theoretically)where the
first fret position should be. I measure the actual distance
and compare the two ( taking into account for fret thickness).
Almost every guitar I have ever done this to has resulted
in differences. For some reason, many large manufacturers
and even some small builders/others, just don’t pay
as much attention to where they cut there nut slot as they
should. I use digital calipers to take these measurements
and take the measurement out to three decimal places ( thousandths
of an inch).
I now have to determine how much to remove. BFTS has a certain
amount that is required to be removed based on type of instrument
and string gauge. After comparing what the BFTS amount to
the actual measured amount I know how much to remove. Using
my trusty Jig (radiused block that has two magnets embedded
in order to keep the .008 Japanese saw online) . I remove
the excess. Yet another way of accomplishing this is to
use a BFTS "shelf" Nut. The calculation is the
same I just need to fit the nut and file or grind off the
amount needed to leave the shelf nut with the proper relief.
The
tolerance for cutting off fret board amounts is .003 according
to BFTS specs. So it is important to control the saw and
remove exactly what is needed no more, no less. It’s
not a good day if you need to glue fret board back on. Fortunately
I have never had to do this. Another "fix" would
also be to file a small "flat in the nut and thereby
simulate the amount of fret board being replaced. Using
the "shelf" nut allows you to make a mistake as
you can always get a fresh nut and start over. The fret
board is never cut with this method. Of
course I have to install and slot a new nut if I remove
any fret board material. The old nut is too loose to be
of any use.
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