bracing design question

[peter havriluk]

I'm building myself a 13-fret 25.4 scale length little dreadnought (about OO size, shrunken from herringbone drawing) and I'm using Ken Cierpolowski's bracing template for his 'Norman Blake' design interpretation. Ken drew one transverse tone bar, at right angles to the center line, I suspect out of respect to Larrivee.

Questions: (1) Ken specified 9/16 x 1/4 inches for the x' brace. My temptation is to straight-taper the 'x' braces to 1/4" high at the ends. Any reason not to?
(2) Ken specified 1/2 x 1/4 inches for the transverse brace. My temptation is to taper this one from full height at the center to 1/4" at the ends. winding up at the
same height as the 'x' brace ends in the same neighborhood.
(3) Any reason I can't taper the finger braces from full height in the center to flush at both ends?

Comments, observations, opinions, and warnings will be cherished.

Thanks, folks.

[Dave Bagwill]

Hi Peter - sounds like a fun project.
Those 1/4" wide braces should work fine; I'd be tempted to glue them all on full-spec, and then tap around to hear if it 'talks' to you at all. It might be fine just leaving it at that. Since you really can't thin the braces much, all you could do to enhance the response of the top would be to remove material from the height of the braces - which will weaken the brace a bit. (Tall and thin= max strength.) Sneak up on it, that's my motto. Take off a little, tap, repeat.
As for the transverse brace - that's the brace that will form and maintain the dome of the top, along with the lower x-braces so I'd be careful about taking it down much. I would in fact make it a 5/16" wide brace which would give some room for carving and tapping.
But we all have our theories and they all seem to work out. I hope others will chime in.

[peter havriluk]

Dave, you've illustrated the ambiguity of doing these things. Very nicely. Thank you very much. I hadn't considered the contribution of the lateral brace, not really a tone bar, to the maintenance of the shallow dome of the soundboard. I was also hoping to flush out comments someone may have collected from Ken. And get an idea of what happens when braces are tapered. I could never figure out what gets served by putting in a meaty brace and then scalloping the daylights out of it.

I hadn't considered tapping and trimming after the bracing gets installed. I think that's a process that works best when a builder stops tinkering and starts counting his blessings. I think I'd have a hard time understanding that I'd gotten all I was going to get from trimming and that stopping would be wise.

Thanks again.

[John Parchem]

For clarity here is a picture of Ken's bracing pattern and a bit of discussion.
http://www.acousticguitarconstructionfo ... =11&t=1783

I never really got the idea of the 3 lateral braces under the X, but have no issue with them. Ken's bracing pattern was not a scallop but a parabolic shape. You can take the finger braces to flush at both ends. I think tapering the X to flush would take too much off, you can taper but finish off the ends after you establish the taper. I leave the upper part of the X brace at full height from the top of the bridge to an 1 1/2" from the end until I carve the to the height I tuck into the linings. The upper part of the X is taking a lot of the string load.

[peter havriluk]

John, thanks for the clarification and the link. And the picture in the link is of the template I have; we're on the same page. I don't think Ken was pitching three transverse braces, I think the upper two were intended to be traced to locate the bridge plate and the only brace is the bottom one. Ken's notes on the template didn't address this, but he didn't mention the height of these two either, if he intended to box in the bridge plate.

[John Parchem]

John, thanks for the clarification and the link. And the picture in the link is of the template I have; we're on the same page. I don't think Ken was pitching three transverse braces, I think the upper two were intended to be traced to locate the bridge plate and the only brace is the bottom one. Ken's notes on the template didn't address this, but he didn't mention the height of these two either, if he intended to box in the bridge plate.

Thanks you! I see that now and it helps me understand Ken's comments. knowing this I would like to address the idea of the slanted vs the lateral tone bar. There are many builders that like to add a touch of asymmetry to the bracing pattern to get a more interesting voice. With the diagonal tone bar the effective stiffness is different one side to other. The theory is that it gives areas better for high notes and areas better for low notes.

There also classical builders that add a diagonal tone bar under the lower transverse brace for the same desired effect.

[peter havriluk]

John, I'm inexperienced in building, this one will be my sixth, and just about everything I touch carries surprises and enlightenment. I braced the last four all by myself, using the SWAG principle of bracing. I figured to do this one following Ken's template, hoping he'd already done some of the heavy thinking and it would work out reasonably well without a suite of builder's adjustments which I'm not sure I'd succeed at anyway. Besides which I don't have one that uses a lateral brace instead of a tone bar.

Thanks to you and Dave Bagwell, I think I have a good-enough idea of how to execute Ken's bracing suggestions on this one. It's always an adventure to see what kinds of trouble I get myself into.