Official Luthiers Forum!

I'm working on a new O sized ladder braced slot head. This time around I'm following some of Mr. Brentups direction from his workbook and using a cylindrical top geometry (as well as a thicker top plate and some minor bracing tweaks). He, like most I have seen, uses a domed back geometry. I'm looking at this guitar and wondering why a cylinder top and a dome back? What was the reason for two different shapes?
Obviously the domed geometry provides more interior volume to the box. This guitar is 19" long so changing a 15' dome to a 15' cylinder would lose approximately 1/4" in depth at the center. With the 13" lower bout we could call that about 5 cubic inches (yes, that is some fuzzy math). Is that significant?
On the plus side all I have is perhaps more long term stability of the system. Many times when reading of guitars in need of a neck reset the repairer will note flattening of the back plate as a part of the cause. Would the absence of a longitudinal arch help maintain the geometry of the box?

Your thoughts?

Steve

Well, my notion is that I create a cylindrical back every time I make a back with four parallel lateral braces, the customary array, it seems. Any doming I get is the result of sanding the rim into a dome and clamping the back to it. The back needs some persuasion to conform to the dome.

Published pictures of guitars being built show all kinds of longitudinal stiffeners/spreaders to keep the neck block angle where it needs to be. Some folks who attach the tops first manipulate the distance between the neck and end blocks to fine-tune the neck angle, which gets locked up when the back is attached, closing up the body.

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Peter Havriluk

I think Howard Klepper may have built with a cylindrical back.

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

As I remember Haans had experience with them.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

I use "cylindrical" arching on fronts and backs of octave mandolins. The body also has a reverse taper from what is usually seen on guitars as well.
If you want to retain the same volume just make the sides a little wider.

I'm not totally sure I know what a cylindrical back is. I build my backs with 16' radiused bracing, set at regular intervals, perpendicular to the center line, giving a nice curve. But, I do put a radius on the rims from front to back, But not the same spherical radius people get when using a radius dish.

So I guess no, I don't do a cylindrical back, or even a spherical one.

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Joe Beaver
Maker of Sawdust