Official Luthiers Forum!

Hi guys
I have a few sets of Koa and one of these sets has a top as well. Now I know that as a rule you guys don't particularly like Koa tops for their tonal values. However, seeing as i've got this extra one I'm going to use it.

Could somebody please tell me what thickness they would recommend for a Koa top.

The body shape is my own. It's a cutaway roughly based on a Grand Auditorium. The bracing will be a standard X-brace. I cannot find any info on thicknessing a Koa top.
Many thanks,
Mat

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Thanks Tony

Shall I start it at the same thickness as a spruce and then thin it to the areas you mention?

Start with a thickness of .105"-.110" brace and tune. in the lowerbout edges and belly you will likely end up around .095"-.098"

I am building a half size guitar out of koa and I am thinking that due to the smaller size the top should be thinner than the specs for a full sized one. I am thinking somewhere in the .09 range. Any thoughts.
Bob

Thanks Michael
I'm still new to this building process and previously i've only used spruce to a level thickness.
I don't know if i'm reading your reply correctly but it looks like you are saying brace the top first and then thickness the edges. Is this right? That seems quite hard to me.
- Mat

The top of any guitar should exhibit some thinning toward the outer edges of the lower bout while
maintaining full thickness in the center area an upper bout.

This thinning of the area around the perimeter acts to achieve a similar result to that of the recurve
portion of the top on an archtop guitar, violin, viola, cello or other classical stringed instrument with a
carved top.

The carving of that recurve is citical to the overall tone, volume and response of a carved top instrument
and the thinning of the edges of the top on a steel string guitar can make a dramatic difference as well.

On a flat top guitar, though, the thinning can be done after the top is installed to the back/side rim
assembly and before binding is installed.

Regards,
Kevin Gallagher/Omega Guitars

I've only built a dozen or so Koa topped guitars, and all of them had tops that were around .120 (learned this from Dana B). If you get your top too thin you'll end up with some pretty bad belly behind the bridge (say that fast ten times). Most hardwoods do not have anywhere near the longitudinal stiffness spruce does. Just another thing to keep in mind.

_________________
John Mayes
http://www.mayesluthier.com

also Koa is like a sponge...it absorbs moisture very quickly and efficiently...this exacerbates the effect that John describes above...my 22 year old Taylor K20 has had the neck reset about 4 times under warranty, and the most likely cause was improper control of the environment on my part...between having lived in Santa Cruz, Ca for the first 3 years of its life, and the last 19 years in central Texas that guitar has had its troubles...none of my spruce topped guitars have had any of the problems that one has...

in spite of this, I would still recommend an all koa guitar for those that like them...they are great recording platforms and mine has proved to be an excellent stage instrument because it very rarely feeds back

Thanks for all your advice.
Think i'll go with the .120 and see how we go.
- Mat