Class 6: Progessing the body

 Last Wednesday's class (12/15) had me working on all parts of the body: sides, back and top.

Sides

The sides that I glued up with the end blocks last week were ready to prepare for gluing on the top and back.

The first step was to sand the back side on a circular sanding dish (seen to the right) with the same 15 foot radius curve used throughout the back.  This will prepare the edges of sides, and
especially the blocks at the neck and heel, to hold the same curve that the back is being set to.







Following the sanding, I started to glue in the kerfing that will run along the inside edges of sides along both the top and back.  The flexible kerfing provides a surface to which the top and back can be glued, extending the glue surface past the 3-4 millimeter thickness of the sides themselves.
This is a fairly simple operation, but one, as seen in these pictures, that make extensive
use of clamps.

End piece

Edward gave a demonstration during the class of fitting an tail piece in the body.  The shape of this piece is angular (long trapezoid) so that the piece of contrasting wood can be fit tight into the cutout made in the body.

This cutout is right over the heel block; the tail piece is decorative but also used ot hide a less than perfect fit of the sides.  The side joint at the neck end will be covered by the neck itself.  The notch is cut using a pull saw, then cleaned out
with a chisel.  I'll be using a piece of Koa to match the bindings, and will probably add black purfling strips for contrast.

Carving back braces

I worked on carving the braces on the back of my guitar.  Carving the braces reduces their mass while trying to preserve their strengths, hence the use of a curve.  The braces are tappered down to 5 mm at the edges where the ends of the brace will be fit into the sides.


Carving is done with a chisel, in successive strokes until the top of the curve is set about 60 mm from the edge of the top.  The trick to get a gentle cuve that preserves mass towards the center of the  back.  My braces tend to be carved a little on the steep side.

Top

I worked further in this class on gluing in the braces on the top.  In the picture, the transverse brace is being glued on.  This brace has a 1/4" hole drilled through the center to accomodate the end of the neck truss rod.  The hole is centered 4 mm above (below) the top, so that the outside edge of the hole is just inside the brace.

I also cut and glued the bridge plate from a scrap pice of walnut.  This is glued directly under the bridge to accommodate the ball ends of the steel strings which pull back up against the top.  The plate protects the soft spruce.  The piece is cut slightly off the direction of the grain so that the ends do not pull against a single fault line in the grain.

Back fitting

Edward provided a final demonstration of how to fit the back to the sides.  I'll be working on this when I return from our break.
The back is centered over the sides and the location of the braces is marked with a pencil on the outside of the sides.  It's important to remember the cuts for the braces run straight  across, not perpendicular to the outside curve of the side.










Next a back saw is used to make very shallow cuts for the edges of the notches.  Better to cut to shallow than too deep.

















The notches are then cut out with a small chisel.  Each joint can be tested by placing a small light inside the guitar and placing the top over the sides to see if any light comes through between the back and the side.










I'm hoping to come in once over our winter break to get everything else finished up on the sides and top so that I can begin fitting my back once class starts up again.