Building an ARCHTOP Guitar - Page 1
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March 4, 2010
Hello again!  My next guitarish endeavor is a full-size archtop jazz box.  Hand-carved top and back (of
course), about 17 inches wide.  I'm inspired by Gibson's L5, but I haven't completely decided on what
pickup arrangement I'll be using.  Since I don't have an exact model that I'm copying I can't show you
the exact target like I have on my other guitars, so use these as a general guide to what I'm after:
Once again, Paul Lloret displayed his amazing generosity and bestowed upon me the body wood for
this project.  So my guitar will have a spruce top and the sides and back will be mahogany instead of
(more commonly) maple.  Here is what will become the back, sides, and neck.  The top started life
as triangular flitches like this but I already worked on it before I took this photo.
Preliminary work started as usual with the body mold:
I made the cutaway piece of the mold removeable in case I (or someone) wants to use this body
shape to make a non-cutaway guitar.  Here's a detailed view:
The 'extra' cut running vertically from the cutaway piece is to accommodate a bit of
overlap to make the butt joint at that location a bit easier.  

A second bit of preparation, one that wasn't required for the flat tops, is a pair of carving
cradles to hold the top and the back while they are being worked on:
Here's the top in place, with it's convex profile nearly complete.  For this side, the cradle gives good
access around the edges so that you're not hampered by being too close to the workbench surface.  It's
hard to see but there's a nice arch/belly here:
I need two mirrored cradles
because they need to be able
to hold both the top and the
back  right side up and upside
down.  The workpiece is
supported only around the
edges so that it can be set in
upside down to carve the
concave side.  The little vise
clips on each end hold the
piece down, and the inner
edge of the supporting pieces
is rounded over so as not to
dent the work surface when
it's face down:
I mostly relied on my eyes and my hands to achieve a fair and symmetrical profile on the top of the
top, but it's very hard to detect variations of 1/16 inch or thereabouts.  Therefore I made a thickness
gauge (based on a plan by Bob Benedetto) that reads to an accuracy of about 1/32 inch.
The 'trigger' is a piece of coat hanger.  The 'cable' is a piece of guitar string, and a piece of a bolt
that I hacksawed off and epoxied in forms the bearing at that corner.  I painted the visible part of
the upper tooth white for visibililty and used a chisel to mark 1/16" increments (of course, the teeth
must contact each other exactly where the upper moveable 'jaw' contacts the top rail and thus the
measurement is zero.
Once I had the top of the top profiled like I wanted, I used a fixture (designed by Paul Lloret) to rough
out the inner profile, saving a lot of carving and providing a good starting guide to the necessary depth.
I'll take a little time to describe this in detail. That's a laminate trimmer (small router) with a
roundnose bit (U shaped). The arm to which it's attached is hinged to move up and down, with
the depth of the bit set by a plate at the base of the arm which bears against the bolt at the top.  
Under the bit is a rounded over stop against which the outer surface of the top or back bears; the
distance between this and the bit, of course, is the thickness you want to achieve.  The upright
pine piece that is resting in one of the double row of holes is a moveable stop that bears on the
edge of the workpiece; moving the stop gradually back enables you to cut concentric contours, as
I have started to do here on the top.  The dark brown piece lying on the fixture is just a shopmade
thickness gauge.  You can also see the grid that I marked on the underside of the top to guide me
in measuring whether the top carve is symmetrical
Next, carving the inside of the top, then on to carving the back.