Building an Acoustic Guitar - Page 3
February 13, 2006. And then, drum roll please, it was time to glue the top to the back.
That was when I first realized that I had made a screwup alert screwup alert mistake.
When I had gotten the sides prepared and lined I had blithely traced their outline onto the
top. When I went ahead and cut the top to the 'final' profile for gluing, I discovered that I
had cut a bit too deeply in one or two places and there was an appreciable gap in a couple of
places where the top did not reach the sides. Now the binding that goes on the corners will
negate a certain amount of slop, but not much, and my chosen purfling (the stripes or inlay
that go between the binding and the body proper) was quite narrow, so I realized with
dismay that in one or two spots I was outside my binding cover-up tolerance. This was not
a happy moment.
So I did some thinking, or at least at the time I thought it was thinking. The worst spot was
right at the waist. I realized that when I traced the top I had thoughtlessly done so by laying
the sides down loose on the top, rather that with them in the mold with the waist prop in
place. I could, however, flex the sides a bit to draw in the waist to close to
binding-cover-up tolerance, so I went with that idea when I glued on the top, as below.
See the blue band running around the sides? That's a belt clamp that I used to cinch
up and pull in the waist so that the side came in under the top a bit and mitigated the
error I made when I cut the top too small. This, however, was a BAD IDEA.
Anyone who has built an acoustic guitar will have been saying that very thing to him
or herself for quite a few lines now. Because what I did when I cinched it in like that
was mis-align the neck end of the body. When I proudly removed the top and sides
from the mold I realized that the neck was going to point, ahem, the wrong way.
So I panicked, assumed I had killed the guitar, and placed an order with Luthier's
Mercantile for materials for another body. Soon after, though, I spoke with my
father-in-law (luthier and calm peron) who convinced me to try and unglue the top
with heat and moisture and see if I could fix the error. So I put my order on hold and
gave it a shot. Eventually I was able with the aid of a boiling kettle and an iron to
detach the top from the neck block to just past the waist and reglue it in the mold
with prop in place and completely free of stupid cinching belt clamps:
I'm still not 100% sure it's 100% right, and I won't know for sure until I go to fit the
neck, but it's a whole lot better. And here's what it looks like from the inside:
Two final additions to the bracing can be seen: a wide thin spruce brace between the neck block and
walnut crossbrace, and a maple bridge plate. This strengthens the area beneath the bridge and
provides solid support for the string holes and pegs.
I fit the back on tonight, working as I did with the top to make a good tight fit between the back and
sides, cutting away linings to accommodate braces and leveling the sides to allow for the
front-to-back arch as well as the side-to-side arch. Before I glue the back on I'll brush a light coat of
shellac on all the interior surfaces to seal them a bit and cut down on humidity stresses.
In the meantime, while all that glue was drying, I worked on the neck, installing the truss rod and
veneering the headstock. The truss rod is a curved bar of steel that can be tightened to put upward
pressure on the center of the neck to counteract bow caused by string tension. I routed a slot for it
on my router table, installed the truss rod, and covered it with a spline of bubinga wood (again, no
appropriate sized mahogany left). Bubinga is plenty strong, though. I had a very thin rosewood
veneer for the headstock, so I beefed it up with a little slice of walnut that I put between it and the
You can see the bubinga strip down the center of the neck. This picture is pretty funny, actually. I
glued and clamped this up, took the picture, and went back inside to go to bed. I was amost there (the
bed) when I cried "Good heavens!" (or words to that effect) and ran back out to the shop as fast as I
could go. I was just in time (barely) to rescue the veneer from being glued quite solidly to the pine
block I'm using for a caul. Glue will bleed through a thin veneer quite readily and as you can see I had
forgotten to put wax paper in between it and the caul. Some swearing and glue scraping later, I had it
properly set up and all is well.
February 26, 2006. Here is the completed
headstock, afer cutting the final profile and
inlaying teeny mother-of-pearl dots around
the circle cutout. It's my own design... you
may or may not like it, but it's distinctive!
Once the headstock veneer was applied and the headstock cut to profile, I began the
process of shaping the neck. This I did with, as you can see, rasp, file, carving gouge,
chisel, spokeshave, and sandpaper. This photo is at an intermediate point in the process;
you can see that I've done a fair amount of work on the heel (the gouge came in
extremely handy here) but have only just started shaping the neck. For that job, my
low-angle spokeshave was ideal. A half-round file for touchups, and some sandpaper,
and that's all you need really-- I didn't find a lot of use for my rasp in this job, although
it's pretty coarse and a finer one might work out well.
Here's a closeup of the heel in mid-carve.
Below is the mostly completed neck. From here just a few touchups are needed, like the end of the scarf
joint and taking out a couple of flat spots on the bottom. Here also is my completed fretboard, which
process I did not document with photos. After I thicknessed the fretboard blank and made one side straight
and square, I took it up to Paul Llorets. Paul has a couple of fixtures that I needed, to wit: A very precise
miter box specially designed for cutting fret slots, and a 12-inch radius sanding form. So first I laid out the
fret locations using measurements for a 25-inch scale length (which is the length of the vibrating portion
strings from nut to bridge. I did this very carefully, transferring the measurements from thousanths of an
inch into 64ths and using a magnifying lamp to mark the locations. Then I carried the lines across the board
with a square and cut them using the miter box. Then I drilled holes and glued in the marker dots, which
are gold shaded mother-of-pearl, though this photo doesn't show the color very well. And then I attached it
to a piece of particle board with double-sided tape and sanded in the radius on Paul's form by holding on to
the backing board and running the fretboard over the sandpaper until the flat portion in the center
disappeared. I will trim off the excess length with the test cuts when I fit the fretboard to the neck and
Paul tells me this fretboard is Brazilian rosewood, which is highly valued but now very endangered and
illegal to cut and sell due to conservation laws. But this piece (and the headstock veneer) are thirty-some
years old and predate the ban. And I've had it for about ten years now since he gave me the wood for this
Then it was time to turn back to the body and begin the work of installing the edge bindings. I was wary at
first of using an electric router for the job and had decided to cut the ledges with a hand tool called a
purfling cutter. I went so far as to make a purfling cutter for myself but preliminary trials on scrap wood
convinced me that the router might be a better choice for me after all. So I rigged up a temporary router
table out of particle board. I fashioned a stop from scrap with a tongue projecting over the bit to control
the width of the cut, the depth being determined by the height of the cutter. The second piece of scrap is
to keep the stop from getting pushed out of position as I moved the guitar right-to-left against the cutter's
rotation. A few test cuts and gentle adjusting taps with a mallet got me zeroed in and I made my cuts quite
nicely, with no drama.
Here's a closeup of the completed
ledges. The reason for the two ledges is
that I'm going to insert a decorative strip
of black/white purfling between the main
binding and the main body of the guitar.
The upper edge is kind of furry but the
cut is smooth and it won't be an issue by
the time I scrape the binding and purfling
flush and sand it.
Then it's back to the bending pipe to prepare the trim by pre-bending it to shape. The outer
binding is maple and the purfling is maple/fiber laminations. Either would break easily if I tried
to install them without bending them first. Here I've completed the left top binding and have
just put the waist into its corresponding purfling.
The top of the guitar is flat enough that I was able to use it just like this; I'll have to accommodate the
back's greater arch with a shim that provides a little ramp so that the cut can be uniform all the way
around the back.
March 1, 2006. Either would break easily, indeed. In fact I * screwup alert * broke both that piece
of purfling and the right top binding (the straight piece above) night before last by being too aggressive
with my bending. Ironically, they had survived a lengthy incursion into my shop that day by my pack
of wild dogs only to be destroyed by me. So what to do? I had a nice long straight-grained piece of
maple handy so I have cut new bindings (top and back, so all will match) and I'll give it another go.
The good thing about this is that now I have plenty more in case I screw it up again.. The purfling...
well, I'm going to try to butt-joint it when I glue it up. That may or may not work, but I've already
created the recess for it and if I have to buy new purfling it will have to be the same exact width as
this, and... well, you see.
P.S. Here's another funny story. I had made up a label with my signature to glue to the inside of the back
to be visible through the soundhole. I went to some trouble -- experimenting with design, doing a number
of signatures so I could pick the best one, using acid-free paper and a Sharpie for everlasting permanence.
I then carefully and thoroughly glued the label to the back, doing so before applying the shellac for the best
glue surface. Then I went to shellac the inside of the body and back before gluing on the back as I
mentioned above. When I got to the label area, I paused... should I shellac over the label? Let's see: the
glue is water-based and the shellac is alcohol-based, so the glue probably won't be affected; the alcohol
probably won't affect the paper too badly either; the shellac will leave a light coat on the paper and perhaps
yellow it a bit but that's cool... OK! And I swiped the brush over the label. Only to realize an instant later
that the ink was alcohol based. After a couple of seconds my carefully prepared label was a huge illegible
smudge. So I had to scrape it off and make another. This time I used pencil. Funny, huh?.
March 14, 2006. Just after I wrote the previous
entry I somehow broke the remaining length of
purfling into several pieces so I conceded defeat
and ordered more. Extra this time. When it
arrived I found that it was a shade narrower than
what I had, .080 inches instead of .085 inches. I
did realize this when I ordered it; I couldn't find
what I wanted at .085 so I got the closest I could.
Anyway, of course I had already routed for the
.085. This meant that the ledge for the purfling
was now too wide and would leave an unsightly
gap if I didn't do something about it. So I did
something about it. I carefully trimmed the inner
wall of the binding section to narrow the purfling
ledge with a chisel. This solved my purfling
problem but it means my binding will be a hair
thicker (wider) than I had intended it to be, but no
So I bent the new (top) bindings that I made a couple of weeks ago. It went much more smoothly this
time; I had a better idea of what I was doing, and I think also that the different maple helped. To my
pleasant surprise, the new purfling was sufficiently flexible that I didn't have to prebend it at all. So I
went ahead and glued it up. I used tape to hold it while gluing, like this...
There are several different tactics for gluing binding -- I decided on tape because of simplicity and the
need to do some extra strong pressing in spots that rubber bands or cord wrap just couldn't do. This
is a special low-stretch low-creep clean-removal tape from Luthier's Mercantile. Still, one has to be
careful as the tape will tend to pull out slivers of the spruce when it's removed.
The binding won't be quite so wide as this after I trim it down flush with the sides.
Cross-section of the edge of the top