thicknessing?

[edlee]

Hi to all. I was wondering if anyone could give advice to a beginner on the subject of thicknessing. I'm trying to determine what thickness a spruce soundboard be to get the maxium performance. What are your opinons on this subject? From what I have read everyone has their own personal preferance. Also is the soundboard all one thickness or does it vary? Thanks to all.

[Bob Connor]

It really depends on the stiffness both longitudinally and laterally of the wood that you are working with Lee.

Seeing as this is your first you will have no real idea of what is stiff and what isn't, so I'd suggest that that you take the thickness down to around 2.9mm and try and get some feel for the wood while you are working with it.

Some people like to thin the edges of the lower bout of the soundboard. Take another .4mm off here to provide some more flexibility around the edges.

A lot of what will determine the voice of the guitar from here is what you do with the bracing.

Bob

[Hesh1956]

Ed buddy I saw that you asked this question on the OLF too and got a great answer from Doc Andy Zimmerman.

For the first few guitars you can build to a spec until you gain some understanding as to why most of us treat each piece of wood individually.

For Spruce you can use .115 for tops, sides .080 - .085 and backs .090.

I hope this helps. Also, if you check out LMI's web pages they offer thicknessing services and even though you may not need this they list what thickness they offer too and it's a pretty good guide.

[edlee]

Thanks to Bob and Hesh for the reply. I appreciate the advice you always give. I have been searching high and low trying to learn all I can and it seems that the books I have bought doesn't seem to get straight to the heart of the matter. The Cumpiano book talked in some detail about this matter, but I was reading on another forum with a post he had supposedly written, and he has now change his opinion about how to voice a top. According to the thread he does not rely on tap tone anymore, and states that he thickness sands the tops, bottoms, and sides to what he thinks is suitable, but the thread did not give specifics just ideas so I'm just trying to figure out the best happy medium. Thanks for all the help guys.

[Hesh1956]

Ed I took Cumpiano's statement to mean that he does not agree with tuning individual braces to specific pitches.

Anyway I am not a fan of Cumpiano's book although I certainly will admit that it is a very important work. But these days much of what is in the book, including the use of a building board, even Cumpiano no longer does.

And no one ever mentions Natelson the co-author..... Poor guy....

The best guitar building instructional materials that I have ever read or viewed is Frank Finichio's DVD series. It's pricey but a bargain for what is offered. Frank is a Luthier and a former manufacturing engineer for CF Martin and a great communicator too.

[edlee]

Thanks for the reply Hesh and the advice. I'll look into the Frank Finichio's work. Thanks again Hesh.

[Kim]

Ed,

This from a question and answer session with Bill Cumpiano at luthierforum.com:

Thicknessing criteria

Q: Do you use a specific thickness for tops, backs, and sides, or do your thicknesses depend on the wood species used. I've been reading some conflicting
information on this topic and would love to hear your thoughts.


A: I select all my soundboards for a certain familiar stiffness and springiness, and then reduce them to a specific thickness according to dimensions that have given me good results in the past. These dimension "standards" vary only regarding to the instrument size and the wood specie in question, not according the "tap tones" or "feel" of a particular piece as its being reduced--as some builders claim to do.

Admittedly, this is different claim from what I wrote in my book, which said that I tapped the top as I thinned it, and stopped at a certain ring. That was in 1985 when i wrote the book. Not 20 years later, because my approach has evolved since then.

As to the sides, they are strictly thicknessed in consideration with the bending requirements of the specie involved. And the back is thicknessed, again, according to species and soundbox size, the dimensions that have produced the best results in the past.

Early instrument luthiers call the thickness specs for the plates of their instruments the "scantlings". My scantlings follow.


Summing up, for 16-inch steel string guitars:
Tops: .115 to .120
Backs, hard: .095 to .110
Backs, soft: ..110 to .115

15 to 15.5-inch steel string guitars:
Tops: .100 to .115
Backs, hard: .095 to .100
Backs, soft: .100 to .110

14 to 14.5 steel string guitars
Tops: .095 to .100
Backs, hard: .090 to .095
Backs, soft: .095 to .100

Sides for all guitars (dictated primarily by bending requirements):
hard: .080 to .085 (extremely hard, like cocobolo,etc.: .078)
soft: .085 to .090
(Thorough wetting only, no long soaking or boiling.)

Classic:
Thicknesses are all over the place, depending on whose scheme I'm following. Some schemes have heavy scantlings, some have feather-light scantlings.
But an average would be:

Tops: .080 to .095
Backs, hard. 085 to .090
Backs, soft, .090 to .095

Hope that helps

Kim

[Allen]

I make all my tops a uniform thickness until they are braced and the box is together. Then I may take a little off the outside of the lower bout, with a block by hand, but I will usually wait until the bindings are on if only a little is going to come off. DO NOT DO THIS WITH A POWER SANDER. A powered sander will remove an amazing amount of wood in very short order and before you know it, you've gone too far. I usually will wait until the bindings are on before I take the sandpaper to the outside lower bout because the harder wood of the binding helps limit the amount that you will sand off. We are usually only talking .1 to .3 mm at most.

[James Mc]

The old guy that got me started would take his tops down to about 3mm and cut the shape about 10mm outside the cut line. Then after he had cut out the sound hole, glued the saddle and braced it up he would put it in a jig to tune it. The jig was a thick chunk of ply with his body shape cut out and a neck attached with a couple of heavy braces. The top of the jig was another piece of ply with the same cut out and a gap for the fret board. The ply had a bunch of holes so it could be bolted together like a flange. He would sandwich the top between the ply, bolt it together then string it up so it was like a guitar without a back and sides. He’d then pluck at the strings while resting his fingers (or sometimes his ear) on the top (doing mysterious luthier stuff) and flip it over from time to time so he could trim down braces or thin the soundboard with a thumb plane or sandpaper.

I guess everyone develops their own method, this was his and he said it halved the number of times he would have to pull a top off because he wasn’t happy with the sound (which I watched him do many times). Seemed like good engineering science to me, when I get to the stage of tuning the tops I’ll be making a similar jig.

[Allen]

Be sure to post pictures when it comes time James. Sounds like there is something to be learned there.

[Bob Connor]

Sounds similar to what Ervin Somogyi does James.

If anyone would like to see Ervins vids you can find them here.

Ervins Vids

Bob

[edlee]

Thanks Bob for the amazing info you posted. Sometimes it takes me a little bit to see the light. That info is greatly appreciated on my part. Thanks again Bob.