How to determine the right thickness for the back? (Full Version)

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Ahmed Flamenco -> How to determine the right thickness for the back? (Sep. 16 2015 10:37:28)

hello guys,
I was working on a sycamore back and I used the jet plane so as to make it coplanar for bracing, and at the end I realized that the thinnest parts are 2 mm.
I am worried because I've heard that back should not be too thin so as not to have the same resonant frequency of the top that finally results in lower sound.



Stephen Eden -> RE: How to determine the right thickness for the back? (Sep. 16 2015 11:02:00)

This comes down to preference and experience. You should consider how you would like the back to work on your guitars too. I've seen them around 1.5mm and there are probably thinner backs out there too. There are also backs out there that are a lot thicker too.



tri7/5 -> RE: How to determine the right thickness for the back? (Sep. 16 2015 12:29:01)

Andres Marvi makes his back and sides at nearly 3mm when using brazilian. He prefers working with a stiff sound box and all the sound forced through the top.



constructordeguitarras -> RE: How to determine the right thickness for the back? (Sep. 16 2015 15:04:41)

You got it that thin using an automatic planer without it exploding?



Ahmed Flamenco -> RE: How to determine the right thickness for the back? (Sep. 16 2015 15:08:20)

at first i used belt sander then jack planer, in the post I said jet but I meant jack[:D]



constructordeguitarras -> RE: How to determine the right thickness for the back? (Sep. 16 2015 15:10:04)

If the back seems too thin, go a little heavier on the bracing. Maybe use 4 or 5 back bars.



Ahmed Flamenco -> RE: How to determine the right thickness for the back? (Sep. 16 2015 15:14:53)

I used 3 only but wider than the Santos plan and I glued stripes in the center.It is now stiff. but I'm still little worried what its sound gonna be.



constructordeguitarras -> RE: How to determine the right thickness for the back? (Sep. 16 2015 15:15:51)

I think stiffness is what matters.



Ahmed Flamenco -> RE: How to determine the right thickness for the back? (Sep. 16 2015 15:21:27)

but at some edge where thickness is 2 mm it is flexible.



constructordeguitarras -> RE: How to determine the right thickness for the back? (Sep. 16 2015 15:25:33)

That sounds good to me for a flamenco guitar. Mine are about 2.5 mm in the center and 2.0 at the edges. Once it's glued to the sides, the edges will be supported by the sides and no longer so flexible.



Ahmed Flamenco -> RE: How to determine the right thickness for the back? (Sep. 16 2015 15:40:56)

Ok thanks Mr.Ethan [:D] I hope that this guitar be better than the first one.



constructordeguitarras -> RE: How to determine the right thickness for the back? (Sep. 16 2015 16:26:25)

You're welcome. The soundboard is much more important for sound quality than the back.



Anders Eliasson -> RE: How to determine the right thickness for the back? (Sep. 16 2015 21:39:12)

You dont say what kind of wood you are using, so its difficult to say anything about the subject

2mm at the edges is pretty standard for hardwoods. Cypress is normally kept a few tenth of a millimeter thicker.



Ahmed Flamenco -> RE: How to determine the right thickness for the back? (Sep. 16 2015 22:36:25)

quote:

You dont say what kind of wood you are using, so its difficult to say anything about the subject

2mm at the edges is pretty standard for hardwoods. Cypress is normally kept a few tenth of a millimeter thicker.

sycamore



Anders Eliasson -> RE: How to determine the right thickness for the back? (Sep. 17 2015 7:12:42)

Sycamore has a very dead taptone and is structurally stable, so your 2mm near the edge could be reasonable.
But it depends on how well the wood has been cut. If its quatersawn all the way across the width, it should be fine at 2mm at the edges, if its not, then 2mm will be to little.

Ahmed, you always look for the fast and easy answers and guitarmaking (and life) is not like that. It is impossible to give you a good answer without touching the wood.



Ahmed Flamenco -> RE: How to determine the right thickness for the back? (Sep. 17 2015 12:22:07)

quote:

If its quatersawn all the way across the width, it should be fine at 2mm at the edges, if its not, then 2mm will be to little.

For each half it is quartersawn for edge but flat sawn at the center.



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Anders Eliasson -> RE: How to determine the right thickness for the back? (Sep. 18 2015 8:47:44)

Thats what i call a flatsawn set of wood.
I would never use it. Sorry, but I prefer being honest.



Ahmed Flamenco -> RE: How to determine the right thickness for the back? (Sep. 18 2015 11:44:45)

quote:

I would never use it

that's because appearance , stiffness or being sycamore.



Jeff Highland -> RE: How to determine the right thickness for the back? (Sep. 18 2015 21:00:18)

I agree with Anders, I would not use it, for a number of reasons.
I would strongly encourage you Ahmed to change your attitude to building from a focus on how cheaply you can build to a pursuit of excellence.
You will never manage to build a guitar cheaper than Asian factories can produce it.
Choosing quality materials is part of the build process, as is being prepared to throw away a component you have cut wrongly, thinned excessively, or cracked when bending.



Ahmed Flamenco -> RE: How to determine the right thickness for the back? (Sep. 18 2015 22:32:46)

For the current moment I cannot go to expensive materials for also many reasons, I'm not sure to sell it for high price ,that's because cypress and Indian rosewood are not available in my country and I don't want to ship anything to me right now , I might use cypress and Indian rosewood but not now.



Jeff Highland -> RE: How to determine the right thickness for the back? (Sep. 18 2015 23:25:53)

I'm not talking about using expensive materials just defect free and appropriate cut, and having an attitude of striving for excellence rather than good enough.



Ahmed Flamenco -> RE: How to determine the right thickness for the back? (Sep. 18 2015 23:38:41)

what is the defect you are talking about,being flat sawn is a defect?



Jeff Highland -> RE: How to determine the right thickness for the back? (Sep. 18 2015 23:48:49)

I am talking about choosing wood in general to be defect free and by appropriate cut I mean quartersawn rather than flatsawn and with minimal runout



Ahmed Flamenco -> RE: How to determine the right thickness for the back? (Sep. 18 2015 23:59:48)

but that was the wood available when I went to buy woods, I bought just two pieces for the back.
Do you think I'd better search for a quarter sawn wood?
also I don't use wood with cracks,when I was using paduk for another guitar and it cracked I didn't use it.



constructordeguitarras -> RE: How to determine the right thickness for the back? (Sep. 19 2015 0:15:13)

Personally, I prefer wood with defects, as on the guitar I have been playing since I made it two years ago:



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Andy Culpepper -> RE: How to determine the right thickness for the back? (Sep. 19 2015 0:27:58)

Ahmed, considering your situation I would try to find some high quality, locally sourced (alternative) woods for your guitar making. I honestly don't know if that's possible in Egypt but if you do some research and talk to wood workers you might be surprised.

Finding high quality wood (quartersawn, resonant, well dried/aged) is much more important than the type of wood you use, and a number of "alternative" species fit the bill just fine. If you source your materials locally they can often be cheap, even free.

Right now I'm building a guitar out of all North American woods: Cherry back and sides, Walnut neck, Hickory fingerboard, Englemann top and I've come to the realization that "tonewood" (e.g. you can only use Cypress and Rosewood) is a myth.



Ahmed Flamenco -> RE: How to determine the right thickness for the back? (Sep. 19 2015 0:45:24)

And that is exactly what I am doing , I am governed by woods I find ,I even contacted with wood suppliers that import woods to Egypt, I am working on a flamenco blanca made of sycamore and IMO it is not bad at all then I will work on a classical made of paduk(I will buy new paduk sides), then after these I will decide what to do.



alcazaba -> RE: How to determine the right thickness for the back? (Sep. 19 2015 1:41:09)

I have never used flatsawn wood in guitar building, and I hate the idea, but other people do.
If am not mistaken, those high figured woods on steel string guitars are flatsawn. Not sure how problematic they are though.
Still, get the best wood and tools you can!



printer2 -> RE: How to determine the right thickness for the back? (Sep. 19 2015 2:29:58)

Did a search on acoustic guitars built with Sycamore not many made with it but enough where I would not think twice about using it when you are first starting out. Looked at the picture of your wood, yes flat sawn. Much better if it was quarter sawn. Seems that you may not know why quarter sawn is the cut of choice. With humidity changes wood expands or contracts. There is more movement with a piece of wood that is flat sawn than a piece that is quarter sawn.

That being said I made some guitars out of Pine, the quarter sawn back on one cracked while another with flat sawn wood did not. Just goes to show that all wood is not equal. Or I built the flat sawn one when the humidity was low and it had a better chance of staying whole. But given a choice I would build with quarter sawn.

While I am still a new builder I did build an all Walnut guitar (steel string) out of some flat sawn wood. Just used it as I did not know if a Walnut top will sound any good so why waste good wood on an experiment. As luck had it the guitar sounded pretty decent and a year in it survived with no cracks. Recently I built another Pine guitar (nylon), it was just to be a quick build to try out some ideas. I really like how the neck turned out, will have to be real careful with it as it is made out of spruce.

With each guitar I learn something or try something new. They are not worth much but they did not cost me much either. These are my learning guitars, the better ones I will give away. I have a nice stack of wood to make guitars out of but am saving it for when I think I can do it justice (soon). I see no problem learning the skills in making a guitar with less desirable wood. There is enough things you need to learn to do right to build a guitar. I have been asked if I wanted to sell any of these and I declined because I do not want to set the value of guitars I build as low as what I can get for them. They are of value to me as learning tools.

It is up to you to decide what it is you are trying to achieve with the guitars you build. While you have been given some good advice in this forum sometimes you can get some value from coloring outside the lines.



keith -> RE: How to determine the right thickness for the back? (Sep. 19 2015 11:15:38)

A lot of companies use Sycamore for lower level flamenco guitars. Cordoba is one that comes to mind. The companies do not specify if the Sycamore is European (a maple) or American (a plane) but many look to have the European type. Most laminate the Sycamore--not sure if is due to economics or the properties of the wood. The wood database reports both types are fairly stable and have a t/r ratio of 1.7 and a tangential shrinkage in the low 8's.



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