|Building my 2nd
Acoustic Guitar - Page 1
OK, here we go again. I'm starting another guitar build -- my third, and second acoustic.
This time I'm shooting for a somewhat more old-fashioned style, the 000 size with 12th fret
body join and slotted peghead. Like my first acoustic, this one will be a good bit smaller than
the standard dreadnought size. Back before the 1930s, it was standard for guitar necks to join
the body at the 12th fret. Sometime around there Martin started offering guitars with 14th fret
joins, which gave the player better high-fret accessibility and which quickly caught on and
became the de facto standard which has persisted to this day. Many believe, though, that the
longer-bodied "12th-fret" guitars had a better tone, and this body style is experiencing a bit of
a comeback. Anyway, this is what's appealing to me now, so that's what I'm gonna build.
Here's an example of one by Martin:
As in my first acoustic, I'll be using spruce for the top, and mahogany for the sides,
back, and neck. As before, the wood for the body was given to me by Paul Lloret. The
long board that I'll use for the neck was mine, and I bought the ebony fretboard and
bridge blank, as well as the spruce bracing stock, at a luthierie symposium.
The first job was to purchase plans, which I got from Luthier's Mercantile. Once that was
accomplished, I made a body template from polyacrylic sheet that I got at Home Depot. I'm
not sure the exact thickness, but it's the thicker, rather than the thinner, stuff. I just laid it over
the plan and traced it from centerline to centerline, then cut it on the bandsaw and faired and
smoothed it with sandpaper. This was the template I used to make my mold.
Once the mold was assembled, I ensured that the inside surface was smooth and fair, and
that it was exactly 90 degrees to the bench top. Here I'm working on the inner surface
with spokeshaves and sandpaper wrapped around a dowel. (What looks like a yellow bar in
the mold is just a broom in the corner.)
I made my mold from 3/4" baltic birch-type plywood. I made eight rectangular blanks the size of
the template, then bandsawed the shape within 1/4 inch. Then I finished the profiles on my
router table. I screwed the template to the blanks and used a top-bearing pattern cutting bit.
Then to minimize weight and allow for clamping the top and back I cut the outer edge down to
two inches on all but the bottom blanks, which gave me purchase to clamp the mold to my
bench. Two reasons for that: 1) to defeat any twist that might creep in during construction and
2) to hold the mold steady when I glue on the top and back..I joined the halves together with
plates at the top and bottom joins. Next I drilled slightly angled holes all around the outside and
inserted pegs, which will allow me to use rubber bands to clamp the top and back when I glue
them on, For the pegs I used a few pencils that I cut into 1-inch lengths.
The mold is the frame that the
sides are clamped to after
bending to help them set in
their proper shape, and to hold
the sides secure while the top
and back are glued on. It's
therefore critical that the mold
be as accurate and stable as
possible, while also being light
enough to move around and
handle easily. Last time I used
a mold that was just a
baseboard and some L-hooks,
but though it had some
advantages I wasn't really
happy with that arrangement.
It did ease making the butt joint
where the sides meet at the top
and back, but I think I need
more in the way of clamping
the bent sides and less
opportunity for marring the
sides sliding them in and out of
the mold. Anyway...
December 3, 2007
And that's as far as I've gotten. Next I guess I'll thickness and bend the sides, then joint and
thickness the top and back, rough out the bracing, etc.
December 15, 2007
Tonight I finally started work on the guitar itself. I began with the sides. The first job is to
thickness them to somewhere around .09 inch. For that I used a No. 4 1/2 handplane and some
double-sided tape. Since the sides are so thin (.14 inch or so when I started), normal clamping
methods don't really work, so I just tape 'em down. Here I'm in process on one of the sides; you
can see how the figure on this quartersawn mahogany is beginning to show itself.
Man, my mouth's watering over that grain. Anyway, once I got both sides to around .09 inches thick,
I cut them to profile. To get a nice front-to-back curve on the back once the sides are bent, the edge
that will attach to the back needs to be cut to a long compound curve. I traced this curve from the
plan onto another piece of acrylic, cut that on the bandsaw and smoothed it fair with spokeshaves,
files, and sandpaper. Then I traced it on the sides. You have to be very careful at this step to keep
your inside-outside and top-bottom straight. Once I established where the ends of the finished sides
would be (they are cut a little long for bending) I decided which surfaces I wanted outside and which
way I wanted them facing, and wrote them on the sides before I profiled them. Here are the plan, my
acrylic template, and the sides, on which I've written "lower bout/neck end/inside" etc. to keep myself
The sides are ready for bending....
December 17, 2007
And.. .here we go a-bending. The next photo is your basic pipe-bending setup.
OK, what we got here is your basic sturdy copper pipe, somewhat smaller in radius than the tightest curve
in your design, with a heat-keeper vented plug made from a peanut butter jar lid. That's resting on a piece
of slate on a little plywood stand, held there by U-shaped threaded rods (you can bend them yourself--I
did). This assembly is held down to my bench by two holdfasts. Then you got your propane torch,
resting on the little stand I made, and lit by the butane lighter. The spray bottle contains distilled water, and
I use it to wet the wood. The two blocks I use for applying the bending pressure to help even it out and
lessen the twist I would create by pressing too hard either with my fingertips or the heels of my hands.
The square is to assess whether there's any twist, and the curved piece of wood is a side in progress.
Adjust the burner so that the pipe is very hot... not so hot that sprayed water will just bounce off of it, but
so that sprayed water will evaporate/burn off very very quickly. When you wet your wood and apply it to
the pipe, the steam is what will loosen the wood fibers and allow it to bend. Learning how to bend properly
is largely a matter of trial and error (still pretty much a trial for me), but basically find the apex or center of
your curve and start there. Put the apex over the pipe and hold your hands (or blocks) 6 - 7 inches apart
and rock slowly. Apply firm but not heavy pressure. You should see steam coming up off the top of the
wood. Keep wetting the wood as it dries. Eventually it will bend. Be patient and check frequently because
sometimes you can't feel it bending. Other times you will sense the point at which the wood goes 'plastic'
and you can feel it give. It's not a quick process -- the bend you see in these photos took me about an
hour and a half to achieve.
And here's one of the really good reasons for having a real mold instead of the L-hook contraption that I
used on my first acoustic:
Not only can I use it for reference as I'm bending, I can clamp the sucker in there when my
bending session is over. I separated the halves of my mold by removing the screws from the end
plates. I then remoistened the bent portion of the side and clamped it down, carefully lining up the
end line with the centerline of the mold, so that the wood wouldn't spring back and lose its
'memory' of the curve -- as it dries I'm hoping the memory will set with the proper curve in place.
Here's another view:
I had some 1"x1" maple pieces
lying around, so I cut them
into 3-4" lengths and used
them as clamping cauls. After
I set it up the first time I
realized that the bearing
surface of the cauls really
should be as narrow as
possible, so I used a block
plane to knock the corners off
Next: more bending. Then neck and heel blocks, linings, and heel wedge ...
*** Not my Guitar! To see my finished product click here. **