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.  These (I think) will also serve me as gluing cauls for when I attach the top
and back to the sides:
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 cradle 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 into place 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 outside 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 up 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.
March 19, 2010
I rough-carved the inside of the top, and have been fiddling with it; I have had to glue in some veneer to make
the inner edge (which will be the gluing surface with the sides) perfectly flat.  To check this I put the top face up
on a reference flat surface -- in this case, my table saw.  I put the cradle/caul over it and press down while I try

to slip a .003 inch feeler gauge under the sides.  There were some gaps, where I glue in some veneer.  I plane it
flat and try again with the feeler gauge.

In the meantime, I have started carving the outside of the back.  I've been doing this -- as i did the top -- mostly
with a shallow gouge and a little curved bottomed plane that I made.  Here are three (low-resolution) images of
that process:
After gluing up the two halves, I rough-cut the back to shape on the bandsaw.   Then I scribed a line
around the edge 1/4 inch up from the flat bottom and very-rough-carved to get close to that around the
edge.  Then I used a Wagner Safe-T-Planer in my drill press to establish a flat area all around the

perimeter that will guide my further carving and refinement of the arch.
At this stage I have mainly been working on the neck and heel ends.  The dull areas in the center of the
photo below are as yet untouched and still flat after the center glueup.  You can also see by the dull areas
on the outer edges of the lower bouts that I need to Safe-T-Plane the perimeter again to get the whole
edge down to the thickness of the lowest spots.
Next:  Cleaning up the inside of the top, continued refinement of the back.
April 12, 2010
And that's just what we have:  continued work on the inside of the top and the outside of the back.
Here's the inner (concave) surface of the top.  The photo doesn't convey very well the depth of the
carve, but it's getting close to the final (final rough that is) thickness.  I'll do another thorough pass
with the laminate-trimmer thickness fixture shown above and then smooth it out with plane, gouge,
and scraper.
The dark brown patches around the edges are veneer.  [Long explanation follows]  In one way at least,
archtop construction is a little simpler than flattop:  the edges of the top and back where they join the
sides must be completely flat.  That is to say, the edges of the sides (rims) are parallel.  On an flat top
that is not the case -- in fact the profile of the top-to-side (and back-to-side) joint is very tricky
because the top and back are, paradoxically, gently arched by bending.  So the sides (rims) have to be
narrower at the wide parts of the bouts and wider at the waist, and means also that the gluing surface
of the sides and kerfing has to be profiled to match the arch of the top/back. But on an archtop, the
arch is carved rather than bent, meaning that the edge can (in fact must) stay flat.  Thus the veneer:  I
set the rough-carved top face up on my tablesaw and used feeler gauges to find any spots where the
edge was not in good contact with the table.  I built those spots up with veneer, then planed them back
level with the rest of the edge.
And yet another shot of continuing progress on carving the outside of the back...
In this photo you can see that it's becoming clear that the back is not perfectly bookmatched.  It's close
(see the two dark spots towards the heel edge), but not exact; you can see the grain going off wacky a

bit. as well as a big honking knothole I'll have to fill.  I wondered about this for a while, since I was sure
the original pieces were bookmatched, and then I happened to turn the back over and look at the (as yet)
flat bottom of this piece, and lo and behold it's perfectly bookmatched.  Conclusion:  
I carved the wrong
side
.  Why would I do that??  Conclusion 2:  I glued up the halves upside down, with the bookmatched
side flat and the back side angled.   Why'd I do that?  Conclusion 3:  Failure to think it through.  I just
went with the way the edges were angled when I got them (see the photo at the top of this page).  

Opportunities for failure abound in luthierie, although this mistake won't hurt a thing except my pride
(and a little bit of aesthetics).
May 7, 2010
Still working on the back outer carve.  Much more difficult than the top.... mahogany vs. spruce I guess.
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