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Soundboard Processing |
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The Soundboard is undeniably the
heart of the tone of a guitar. I only use master-grade tops, mostly
supplied by my friend Eric Warner of Pacific Rim Tonewoods. Here I
am laying out the best orientation of the two book-matched leaves of
the rough-sawn soundboard set. |
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The second step is to establish a
rough seam that is straight and flat. Here I am using my precision
jointer to square up the edges.
Not all the master-grade tops make it
into one of my guitars. Many of the ultimate tops do not make my
grade and end up being used for other things, such as braces
and transverse grafts.
The controls for the
spray booth are to my right. |
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In order to have the soundboard
fit in the fixtures for further processing, I rip the two halves to
a consistent dimension. This known dimension also allows me to make
the tests later to determine the physical characteristics of the top
such as strength-to-weight ratio and deflection. |
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Here the rough set is being cut to
22" long. By milling all the soundboards to these common dimensions,
I can rely on my tests to give me consistent results for the weight
parameters. |
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Now I am ready to mill the
ultra-precise soundboard centerseam joint. This is the most critical
glue joint of the guitar. The CNC creates as perfect a joint as
possible. |
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The fixture for milling the
soundboard (and the back later) have embedded neodymium magnets. |
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These magnets (the most powerful
on earth) allow me to clamp an otherwise unwieldy and large
soundboard right at the edge where the milling is happening. |
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This is the 1" bar with matching
magnets. This set-up quickly clamps both halves of the soundboard so
they can be milled in one shot. |
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This is the 1" ball mill milling
the joint at 10,000 rpm. This ball mill is used in shaping necks,
bridges and other curvy shapes. |
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But in those other operations only
the radius at the bottom is used for the cuts. The sides are not
ever used much. So using the sides of the ball-mill makes sense as
they are always pristine. I use a different section of the cutter to
mill the backs--a harder surface that will wear the edge slightly |
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The incredibly sharp edge of the
helical mill leaves a beautiful glue surface. The spruce or cedar or
redwood just feathers off the wood. |
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The seam is then "candled"; that
is, the halves are held together and checked for tightness with a
light source behind. This guarantees the integrity of the seam. |
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The human eye can detect 1/50
millionth of an inch of light. This is about as fine a limit of
accuracy as possible, even with technical gadgets. Here the close-up
of the mill shows the helical structure of the fine-grained carbide.
The length of the cutting edge is 4".
Tools like these, while
expensive, create parts and glue seams that are perfect. Plus it is
always more fun to use quality tools that perform to such exacting
standards.
There are lots of areas in
working wood where we must make intuitive judgments and trust our
instincts. But the glue joint is not one of them. Here we want to
know with certainty. |
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