Official Luthiers Forum!

Q 1 I made a couple of ukes and decided to try a terz guitar, like the Martin 5/18. Tried various low tech ways of radiussing the back and found it really difficult. Since the Terz is much the same size as a baritone uke, (c20" scale)is it possible to have a decent sounding instrument with a flat back and soundboard, like a uke? Sure I can see a radius is better, more volume, stiffness etc but it seems such a small difference. Is there a cut off point in size of body where radiussed back and soundboard become mandatory?

Q2 Second issue, I used a lovely piece of figured walnut for the back, but it seems to want to warp for a living. Final insult was me leaving it outside all night by mistake ( don't ask) and it got rained on. It was already braced and warped like mad with a one inch high wave at one point, I cut the braces off quick (whilst wearing dressing gown and slippers) to avoid it tearing itself apart and clamped it between boards, which seemed to work. At first it took on a slight concave shape which was fine, but then it changed to a radical convex shape rather like a manta ray. Ive reclamped it up. Is this back always going to be a nightmare, or will it clamp flat if left long enough, and make a decent instrument with flat braces?

Any comments much appreciated

If you build flat you want to build as dry as you can in your shop. It is so your plates can only expand and not shrink, which will make them cave in, and perhaps crack.
A lot of Renaissance and Baroque guitars were built with flat backs and tops, so go for it if you feel the urge.

However, building with a slight arch or radius is not very difficult. You can shape your braces to a shallow radius and glue them flat on the plates. When the glue is dry you plates will magically have a radius or arch in them. If the radius is shallow you can shape your rim flat and glue the plates on it without any issue.

See this thread:
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=32375

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Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

Hi Yvonne,

The simple answer is that you do not need a radius no matter the size of the guitar. The radius gives a little protection against drops in humidity causing cracks among other things, but you can easily build without a radius.
Second, that piece of walnut might be pretty, but it might also be unstable. If you sticker it, i.e. put it on two sticks of wood that run across the grain and elevate it off of the table, add two more sticks on top so they line up with the first two, then put weight on the whole thing, it might help. You want air to be able to flow over the top and bottom of the wood equally or the wood will lose or gain moisture from the air more quickly on the exposed side and cup, or turn into a manta ray as you put it.
If, after several days or longer(depending on how dry it was to begin with) of the wood being stickered like that, the wood continues to misbehave, you probably do not want to build with it. If it gets flat and stays flat without weight, but still stickered, you will probably be fine.
I hope this was helpful.

Tony

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http://www.CostaGuitars.com
PMoMC

Thanks Tony and Laurel that is really helpful. Thanks guys xx