Official Luthiers Forum!

Cumpiano and Natelson say they do not use molds, preferring the "free-standing assembly" method. Their case against a mold states, "This can bind permanent deforming stresses into the instrument, which are likely to impair the instrument's tone and may result in structural failure." They're referring to cases where the sides are improperly bent, then forced into conformity with a mold.

I'm wondering (reminder that I've yet to build anything), isn't that exactly what's being done to a radiused back? And in this case, possibly effecting part of the sound mechanism? Or am I missing the point of why the backs are radiused? Just a little confused!

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DES - Shepherd, MI

No, a radiused back is not being forced into a pressure area. Rather the back which is pliable is put into a bowl. The braces are radiused on the edge that fits against the back. Then the braces push the pliable back down into the bowl and the glue sets leaving the back with the radius from the bowl and the braces(which are the same radii). There is very little if any stress on the back. It follows the curve of the braces(another thing wood does very well). This protects the guitar back from cracking if the guitar starts to dry out. The radiused back will pull down to a less radii, but a flat back would pull the grain apart. (A crack in otherwords.) A mould is great as long as your sides match it. So when you build your mould you also build your side bending mould to match. Your side bender will have a bit more bend to it then your mould will to compensate for spring back of the wood. Tops are radiused for the same reason. Flat tops are not truly flat. Hope this helps answer your question.

In every thing we build we impart stresses. The trick is to balance the the stress to the gain in strength. The back being arched does impart a small amount of stress on the back plates paralell to the direction of the grain. But then again the grain is braced which interrupts those stresses, and the arc or dome gives the back plate a far greater structural strength at the joint and against outside forces. So the stress we imparted on the back plates in order to form the dome are out weighed and almost completely overcome by the strength we have gained by bracing and doming. This is the same thing going on in dome roofed stadiums. Strength to weight ratio is always the Holy Grail

Wow! ask a good question...get two Great answers! Only at OLF! My two cents...I like stress...I am always stressed out! KIDDING! Even the old violin makers purposely introduced stress into their bracings/tops. They did it for tone purposes. With age, the stress tends to lessen and that is why violins were made to be opened, re-braced, and re-stressed if you will. Guitar players just can't handle that concept so we build are mousetraps to stay shut forever...( i learned this from Bob Benedetto so if you disagree call him ) Sounds like it makes sense to me!

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Dave Bland

remember...

"If it doesn't play in tune...it's just pretty wood"

Daryn,
I have yet to use a mold or form for assembling or bending. I am from the Cumpiano school and I stay with his approach because I like to design and build differently shaped guitars. I too was once concerned about “built-in stresses” and how they would seem to work against a successful build. I have been told that compared to the stress that the strings impart to the whole structure, a little built in stress during construction is insignificant. In order for the top and back to help hold up over time, we build a dome into them. As explained earlier.
I hope this helps, if not, food for thought anyway.

Wade

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Wade
Nashua, NH
http://www.wadefx.com

Froggy Bottoms builds without molds...

Molds, just help keep things lined up, using internal cauls. I dont' think there is much stress involved at all, consistent shapes and sides perpendicular to the front and back are my main aim.

There is nothing wrong with doing it different as long as you are successful.   

Once, again, I appreciate the wisdom that comes from experience.

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DES - Shepherd, MI