How Thick Do You Make Your Tops.

[crash6882]

I was wondering how thick everyone made their tops, and if you make it thinner towards the edges to allow it to vibrate more.

[scab]

I've only built 1 acoustic (2 more are in the process) for school, and we do all of our tops (as students) to .125" (1/8"). I have not experimented with thinning the edges (which I hope to someday).

I do know that most classical guitars are thinned at the edges to allow the soundboard to vibrate and move more.

Looking forward to hearing someone who has experimented with this...

Thanks for bringing up the topic!!

Scab

[fryovanni]

The thickness of my tops vary from soundboard to soundboard. Depending on the wood itself and the size of the body and strings. It is safer to overbuild, both in the initial sense and down the road in terms of longevity. Basic generally safe numbers for Stiffer types of spruce would be .125", possibly a few thousandths thicker for Englemann. Western Red Cedar, Redwood and such would probably be safe to assume .140" thickness. I can tell you I have built with very stiff spruce thinned to .090" and has been very stable, but I feel like I may have lost a bit of sparkle although bass responce was super(I suspect I was a little brace heavy and soundboard light).

You need to consider long grain stiffness and cross grain stiffness. Think about the brace pattern you are using and size of the body (braces oriented perpendicular to the long grain will increase cross grain stiffness very well, the closer to parallel with relation to long grain you increase longtitudinal stiffness better, X bracing is a compramise and can be adjusted a bit closer to one or the other orientation to adjust a little). The height of braces increases stiffness much quicker than adding width, even though the overall volume of wood is the same. Increasing the thickness of a soundboard is going to increase the stiffness, but also adds a lot of volume. Adding a brace (making a smaller area taller) increases strength much more efficiently than just using a thicker soundboard. You have to be sure though that you strike a balance between the stiffness of the soundboard and braces. Even though bracing is more efficient, extreamly strong braces and a weak sounboard will lose efficiency (like hanging a sheet over a steel beam, the sheet will not move with the beam very well). Some bracing patterns have attempted to brace under more of the surface (such as lattice) in an attempt to use more strength from the bracing by providing a fuller support system. Double tops attempt to use the advantage of strength gained from height and skins. Ideally your goal should be to strike the good balance between top and bracing (your bridge of course is also a brace, and is definately part of this balancing act).

This is really a huge subject, and theories as well as materials and methods are abundent. Certainly not a subject that could be addressed in one topic. Play it safer till you get a feel for what is needed. Keep concept of bracing and the soundboard act as a unit in the front of your mind. Don't get confused with different bracing patterns and trying to micro manage areas of the board (not to say you will not want to make small adjusments, but don't lose the big picture).

Hope that made some sense , it is just my thoughts right now. I can say over the years my understanding and experience as well as perspective from others have changed my thinking several times.

Peace,Rich

[jammy]

I first thickness the top until it feels flexible enough, brace it, and install it.

I then thin the top's edges around the lower bout to "open up" the tone a little. I makes a noticeable difference!

Unfortunately both procedures are done to what feels/sounds right to me, so I can't really give you any figures I'm afraid

[GoodWood]

I first thickness the top until it feels flexible enough, brace it, and install it.

I then thin the top's edges around the lower bout to "open up" the tone a little. I makes a noticeable difference!

Unfortunately both procedures are done to what feels/sounds right to me, so I can't really give you any figures I'm afraid

It depends on what kind of wood. Cedar, Engleman,Sitka,Euro Spruce, Adi, in that order of stiffness.

I have Carpathian Spruce top thinned to about 1.08 with adi braces. (Shoudl have gone to 1.12) I have to redo some finger braces. This is for a 15.8 lower bout, 25.4 steel string. I may use light strings on it, but to my hands, it felt stiff, I just did little bit off the lower bout brace. I probably wont sand much off the lower bout, its pretty thin for a first build.

I have also notice (I think) that the Sitka brace stock that I had was actually stiffer, but a bit heavier than the Adi brace stock, and darker in color. So the stuff out there can really vary on stiffness. The Englman I had you could feel the difference.

I am going to set up a brace stiffness gauge soon, for the next guitar.

YOu should be going by a book or by plans, and both are usually 'overbuilt' to some degree.