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Hello all,

Short version:  When building a classical guitar, is it necessary to taper or radius the kerfing to match the arch of the top, or is the top flat enough to apply the kerfing "as is square?"


Long version:

I'm in the midst of building my first classical after two extremely successful steel string builds.

I'm at the point where I could glue on the kerfing.

The steel strings were done referencing the Cumpiano, Kinkade and Sloan methods. 
Accordingly (to Kinkade), I matched the top to the sides with a tapered or radiused kerfing. 

However with the Classical, I'm also using a workboard for the first time which I'm finding makes it very difficult to get that 1 - 1.5 degree taper onto the kerfed lining.  Cumpiano instructs to use a sanding board (which I assume is flat) to get the kerfing leveled. 

I'm seriously distraught that some weird dimple will show up down the road if the kerfing isn't radiused.

Thanks in advance for any help or insight you can lend

Dave

Dave,

Take what I am about to tell you with a grain of salt because I havent built any classicals.

It is my understanding that if you are going to radius the top and back, the sides and kerfed ribbons need to be radiused. By sanding them in a radius dish (I am assuming that cumpiano really means a radius sanding dish), you end up with the sides and the kerfed linings completely in line with no bumps or other irregularities that would cause you grief down the road. This method also sands a radius into the neck and heel blocks so that it gives you extra gluing surface when the top and back are attached. It also goes to reason that if you are going to have a perfectly flat top and/or back, then you would want to sand everything flat and true after the kerfed ribbon linings are glued in place.

I'm curious..... what radius are you going to give the top and back?

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Reguards,

Ken H

Ken,
Thanks for the reply

In the Cumpiano text, he instructs the builder to construct a sanding board from flat plywood and face it with coarse sandpaper. 

No further mention of cupping the board or anything like that is given.

As for the radius... I honestly have no idea.  I should.  I really should. But the text doesn't mention the specific radius.  It DOES give specific dimensions for the tapering of each brace.  (about 1/8" over 15" brace on the back, and 1/16" on the lower transverse brace on the top) 
The work board is shimmed with 1/8" cork to all the dome to exist when assembling.

In general, Classical guitars are usually made with individual blocks. The top and sides are secured in place before hand and the blocks are glued in place one at a time.

My soundboards are flat in the upper bout and radiued in the lower bout. So when I make the blocks I make the ones for the upper bout square and the ones for the lower bout to fit the angle between the sides and the top. You could easily make them all square and fit them with just a few swipes of a file.

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Another option is to use the Romanillos method, also used in the Courtnall book, "Making Master Guitars", and that is to radius the upper bout in the solera, but when carving out the dish for the upper bout, leave a level area around the perimeter of the upper bout that remains flat.  The radiused portion starts about 1 to 1 1/2mm inside the ribs of the guitar.  That way all of the tentellones or kerfed linings remain square at the junction between top and ribs.  The only difference between the Romanillos version of this is that he uses a raised section on the lower bout that is tapered at the edges from the waist to the widest section of the upper bout, and the ribs are attached on the outside of the top instead of resting on the edge of the top, so the top is trimmed to the actual size of the area inside the ribs, and the ribs are then trimmed down to the top to acommodate the slope of the radius across the lower bout created by the tapered, raised solera.

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Waddy

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[QUOTE=livemo1]

Short version:  When building a classical guitar, is it necessary to taper or radius the kerfing to match the arch of the top, or is the top flat enough to apply the kerfing "as is square?"

[/QUOTE]

Dave,

Short Version: Assuming you are following the book's plans, "As is square" should be fine.

Long Version: Many (most?) advocate radiusing the kerfing/lining to the radius of the top or back. I can say that, having built a classical with William, that we just sanded the (continuous strip, slotted) kerfing flush on a FLAT board and then glued it to the top. The back was done also with a flat board, as shown in his book. You DO need to arch the head block where it meets the back though or you WILL end up with a dimple there. We used a plane to accomplish this.

Joe

Wow everyone,
Thanks for the replies and the info.

No two are the same.

You'd think this guitar building stuff was as much art as it is science.