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I have been thinking a lot about the arch radius of the horizontal braces and I decided to calculate the theoretical radius assuming that the top is a straight line from the neck block to the pliage and again from the pliage to the tail block. The angle of my pliage is about 7 degrees (as bent) with 2.5 deg at the neck end and 4.5 degrees at the tail. That is assuming those angles are relative to the top edge of the sides of the guitar and also assuming that the edge of the sides are straight.

So assuming that we are going to pull the edges of the top down to meet the sides and that the sides are much stiffer than the top in the direction we are pulling the top then almost all the bending will be done to the top (i.e. the sides are very rigid in that direction). Also assuming that we are trying to keep the pliage angle roughly the same as it is right now in the 'free' condition (i.e. not constrained to the sides of the guitar) then the edges of the top will have to bend down to meet the sides everywhere except at the neck and tail blocks (i.e. down the center). Hence, the need to 'radius' the horizontal braces.

I calculated the theoretical radius for each brace at each of the 5 (or 4, I have not yet decided if this will be a 4 or 5 brace) horizontal brace positions for my geometry (short scale, 14 frets clear).

If 'x' is the height of the top down the center (relative to the tops of the sides) and 'y' is the distance to the sides from the centerline at each brace location (half of the width of the brace) then the arch radius of the brace will be:

r = x/2 + y^^2/2x (from our geometry class, Pythagorean theorem for triangles)

If I assume a 4 fret 'D' hole style I get these radii:

r1 = 6'4"

r2 = 3'11"

r3 = 4'8"

r4 = 5'7"

These numbers are WAY different than what they have in the book by Collins (r1 = r2 = 12', and all the others are 7')

I admit I need to double check my measurements and calcs but just curious what the other luthiers out there are using for their horizontal brace radii and pliage angles. Also, if I don't make the top of the sides perfectly straight (i.e. hump it up near the waist area) that will change things a lot but looking at the Charle plans the sides of the Selmac are straight (but I have never examined an original Selmer).

Thanks

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## Comments

Hmmm....???

Does anyone know if the original Selmer sides are straight (i.e. NOT humped up at the waist area)? I've never actually seen an original. My Gallatos look straight though.

Thanks

Brace 1 radius = 8' 7.1"

Brace 2 radius = 4' 7.9"

Brace 3 radius = 5' 10.7"

Brace 4 radius = 6' 5.7"

Brace 5 radius = 11' 9.4"

Since the Charle plans don't seem to address this level of detail I'm curious if any of the other BYO'ers out there have gone thru this math as well and if these numbers seem to make sense??? Feel free to chime in or PM.

Thanks