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I'm curious how you decide what thickness you use on the back of your guitars. Do you use a standard thickness for a given species of wood? Do you thin it till it just becomes "musical" and flops like one would do when thinning a top? Maybe you have some other method. Does your thickness vary much with the species of wood used?

I'm assuming the answer to this question will depend on your philosophy of the function of the back, stiff and reflective or responsive. Which method do you use to build?

If you want a responsive back on your guitar, leaving it too thick may hurt your sound to some degree. If you thin the back too much, what bad things can happen? Can it contribute to neck block rotation or other structural issues?

I appreciate your thoughts. I'm really interested more in your philosophy and thoughts more than precise measurements though ball park numbers are help.

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Formerly known as Adaboy.......

.095" , I am not aware of structural problems. Seems to give a good "weight" to the tone and feel of the guitar. Lots of disagreement on weather the back and sides contribute or do not contribute to the soundbox as just a structural support or tone quality. I think the light back ads to tone.

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Greg
http://garibaldiinstruments.com/

Well, on the Ditson, I was aiming for light and responsive.
The back is 0.085-0.090" thick, Quartersawn cherry.
This guitar is 14" across the lower bout, though... so quite small.

I am not sure which way I am going to go on the next one... except that the back and sides will be quartersawn red Oak... and the sides will be very stiff.

Thanks

John

Yes and no, rosewoods or rosewood-like tonewoods are usually heavier and stiffer than mahogany, maple or walnut-like tonewoods, thus tend to get thinner. Some woods are also tougher than others, regardless of weight.
It also depends on the size of the guitar, smaller bodies can handle thinner plates.
I can go from about .060" for, say, a perfectly quartersawn, stiff and resonant Honduran RW or cocobolo back on a single 0 type of guitar to .110" for a mahogany back on a D type guitar.
It all depends on when the back feels and sounds "right". I usually have the top of the same guitar at hand when I thickness the back. The back doesn't carry the load the top does BTW.
An all-koa 00-type guitar I just put together has a .106" top and a .102" back. Both plates perfectly quartersawn, I picked the substantially stiffer and lighter set for the top. If used as the back I probably could have gone down to around .085".

Personally I like to build the lightest guitar I can. Up to a limit. Like a top, too thin a back and something is lost, besides the larger potential for cracks.
If I want a more reflective back I brace it accordingly. I would use taller capped braces, and I also cap the back centre strip on all guitars. I tend to cap the braces on larger guitars (000-type and up), and leave them low and thin on smaller guitars.
The dimensions of the back braces are important, especially on the lower bout.
IME projection and power are never a problem on a small body.

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

I have seen backs as heavy as .125 and as light as .080. I think the key is more to match bracing to the plate. Personally I use a deflection test and go from there though I will say most of my backs are .095 to .105

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Thanks for the replies everyone.

How much difference in back thickness would be typical between an OM sized box and a Dreadnaught sized box?

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Formerly known as Adaboy.......