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Walnut back and sides question

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Re: Walnut back and sides question

Postby Bob Meidinger » Fri Jan 20, 2017 3:41 pm

Somewhere in my reading I saw an example of using bracing on the sides to reinforce the side. I suppose this might have some effect on tone but might be an option to limit cupping.

Thanks for your thoughts. Its nice to talk to people who are involved in guitar building. Luthiers in my part of the country are few and far between.
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Re: Walnut back and sides question

Postby Brian Evans » Sat Jan 21, 2017 9:19 am

Normally you do indeed use braces on the sides of the instrument, more to guard against cracking in use than to prevent cupping, but I expect it would help to stabilize the sides. Mine cupped into the radius of the bends, so they kind of stick out a bit at the waist, and in around the lower bout. Nothing is noticeable in the upper bout. I'm just putting it down to one more thing I need to learn about. I plan to change the way I make and install my side braces and linings next time, to see what happens.
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Re: Walnut back and sides question

Postby Bob Meidinger » Sat Jan 21, 2017 12:22 pm

I worked out of the book by Natelson & Cumpiano for my first and only build. I don't recall anything about side bracing so I didn't use any. Made a four string without doing enough research so I used a 25.4" scale length which requires too much string tension for some tunings and makes the reach required for many chords hard I not impossible for me to do. Could play it with regular guitar tuning, but want to use different mandolin and banjo tuninngs. I play it now using GDAE tuning and it works fine. Intonation is still not too good and must have to do with my string height as it is good at the 12th fret. Any suggestions?
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Re: Walnut back and sides question

Postby Alan Carruth » Sat Jan 21, 2017 7:15 pm

I use side tapes to help resist cracking. With quartered wood you should not need bracing to resist cupping, particualarly wiith walnut, which is quite stable. I have seen side cracks that could have been caused by bracing. In both cases the side wood was soft and the sides deep, and the bracing didn't shrink in length as much as the sides did in width. The cracks went right across the braces.
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Re: Walnut back and sides question

Postby Bob Meidinger » Sat Jan 21, 2017 10:34 pm

After thinking about side bracing I agree with you that side bracing would be asking for failure. The side to side movement of 4" wood during humidity changes or drying over time would produce movement as much as 1/16" inch over the width of a 4" side, depending on the wood type. Calculated for walnut, based on a 7% moisture change over time)* The grain on the bracing would be perpendicular to the sides, not allowing wood movement in the sides. Doesn't sound like much but the tensions produced would be destructive, especially to the glue over time.
I might try bending some flat sawn walnut just to see what happens.

*www.workshoppages.com/WS/Articles/Wood-Movement-Charts.pdf

Thanks for bringing this to my attention!
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Re: Walnut back and sides question

Postby Barry Daniels » Sun Jan 22, 2017 11:20 am

After thinking about side bracing I agree with you that side bracing would be asking for failure.


That has not been my experience with many guitars over 4 decades. However, I don't expose my instruments to extremes of humidity. For example, if you are going to use your guitar outside in the rain forest, then side braces might be an issue. In that case, tape would be better.
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Re: Walnut back and sides question

Postby Bob Meidinger » Sun Jan 22, 2017 1:08 pm

I can tell you that furniture built in a low humidity state like Wyoming and moved to say Seattle or Houston, will experience a change of up to 7% or more average humidity change. Wood moisture content changes accordingly, hence the question. If you've been building guitars for forty years without problem then it is most likely a moot point. I assume you are using 1/4 sawn wood. I am looking at flat sawn.

Thanks for the input
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Re: Walnut back and sides question

Postby Barry Daniels » Sun Jan 22, 2017 5:22 pm

Mostly quartersawn. I have seen other issues related to humidity but not side braces. I think their short length minimizes the problem.
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Re: Walnut back and sides question

Postby Alan Carruth » Sun Jan 22, 2017 6:10 pm

I admit that I've only seen that problem twice in over forty years of building and repairing guitars. The instruments in question were imports; both the same model from a factory in Australia. The sides were quite deep, although I didn't measure them. Up until then I'd always considered it a theoretical issue, but there you go. Given that, and the reality of shrinkage hysteresis, I do wonder about side braces over the long term.

The other thing about side braces is that you have to be careful about how you do the ends. We used to get repair instruction from time to time in my violin making classes, from a woman who worked for the Met in NY. She pointed out that there can be a stress riser at the end of a brace. If you stop the brace short of the liner most of the stress if it gets hit will be concentrated at the end, and the side can crack right along the edge of the liner: just where it's hardest to fix. Side braces have to be inlet into the liner, or else tapered down to nothing over a reasonably long distance to distribute the stress.
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Re: Walnut back and sides question

Postby Bob Meidinger » Sun Jan 22, 2017 11:00 pm

I'm going to use my 1/4 sawn for starters, but I might start with a build out of flat sawn only use a lesser grade top. I can sure use the experience.

You've all been a big help Thanks!!!
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Re: Walnut back and sides question

Postby Bob Shanklin » Sun Jan 22, 2017 11:17 pm

Alan Carruth wrote: She pointed out that there can be a stress riser at the end of a brace. If you stop the brace short of the liner most of the stress if it gets hit will be concentrated at the end, and the side can crack right along the edge of the liner: just where it's hardest to fix. Side braces have to be inlet into the liner, or else tapered down to nothing over a reasonably long distance to distribute the stress.


That is the reason I make my side braces full height of the side, and run the liner between the braces.

Bob
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Re: Walnut back and sides question

Postby Bob Meidinger » Mon Jan 23, 2017 1:07 am

Sounds right to me
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Re: Walnut back and sides question

Postby Bob Hammond » Sat Jan 28, 2017 1:16 pm

Hello, I built a guitar from flatsawn black walnut a few years back (back, sides, & neck, with spruce soundboard, ebony bridge & fingerboard, maple & ebony bindings, all hot hide glued). There were no problems at all with bending or with dimensional changes that led to warping or cracking, despite a very stressful journey. I gave it to a friend from Argentina upon completion of his Ph.D., and when it came time for him to move back to Argentina, I was appalled at the shipping scheme.

It was a cold day in early March. The guitar was in a nylon gig bag that he placed in the back seat of his car, the car into an overseas shipping container, the container was trucked to New Orleans, sat in a yard for a week or three, was loaded onto a ship, the ship sailed to Chile(crossing the Equator) and was unloaded to sit for a while in Chilean summer sunshine, was trucked to Cordoba, Argentina where it sat in a customs yard for a week or two until the container was examined and finally cleared. When the guitar was finally brought out of the bag, it was in good condition. Maybe I overbuilt it?
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Re: Walnut back and sides question

Postby Bob Meidinger » Sat Jan 28, 2017 10:10 pm

Wow!! That's quite a journey. You must be a very good builder!!!
Thanks for sharing
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Re: Walnut back and sides question

Postby Mark Day » Thu Feb 16, 2017 2:40 pm

"Early" guitars, as in Renaissance and Baroque guitars, and vihuelas often have multi-piece backs so it is not without precedence. I also like building things from trees I have known ; )
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