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I have a set of KOA (back, sides and soundboard material) I bought some time ago and was goiing to use it to make an OLF SJ model. Just pulled it off the shelf and only to discover the thickness is around .11 and still needs some finish sanding so thinking I will be at .10 when done.

Two questions then - what are your thoughts on thickness for KOA soundboard and any special considerations for bracing?

from memory, a person posted about a year ago that .125 minimum was needed to prevent bellying behind the bridge.

my '86 Taylor K20-CE has a .125 top and it's bellied pretty severely though that was most likely caused by exposure to the high humidity of Santa Cruz, Ca during the first years of its life...koa grabs moisture like a sponge (or so Bob Taylor told me) and if left in the expanded state will set into that position therefore exacerbating the problem...

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I would deflection test it and see how stiff it is JJ ....

_________________
Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

1927 Martin 0-17K: 0.085 - 0.090", deeply scalloped 1/4" braces, under 1/2" high at center of X, and little bellying after 82 years of constant tension and living in the Northeast. Go figure.

They don't make koa like they used to.

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Ken Franklin
clumsy yet persistent
https://www.kenfranklinukulele.com

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also a 0 body type has a 13 1/2" lower bout which is a bit smaller than an SJ with a 15 1/2" bout...and from the given age of that Martin it should have a 12 fret body joint which might also make a difference...

Koa has a different strength to weight ratio than spruce. I have seen some older Martins in the .090 range and they were 00 size. SO make a smaller parlor with it , That should allow you to use the set. I am sure you will not be disappointed.

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Thanks all for your input. As I read this thread my mind has gone back and forth from "I could use it" to "I better not use it for this build". John, I like your idea of using it on a parlor build - an all Koa parlor would be pretty cool. So back to the drawing table then for my OLF SJ

Bob C. started a post on Olive wood and I was checking out that option on Hibbon site. Really had my heart set on KOA though so stopping at uncle Bobs this Thursday on my way home from a business trip to see what he has in the candy store.

Mike P and John Hall have it right: a skinny little 12-fret 0 size with a short scale puts lots less stress on the top than a 15 1/2", 14-fret, long scale guitar. Still ... koa can be pretty strong and has good cross-grain stiffness. I don't know about going thicker than spruce; sounds unnecessarily heavy and stiff.

I've built a fair pile of olive backed guitars. It's interesting wood. Don't know what to compare it to either tonally or structurally. I liked it for some instruments but it's not first choice for many. Write if you want more info.

Rick