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In preparing and dimensioning your top plates for bracing, in what order of importance would you rate the following three criteria; Weight, Thickness, Flexibility/deflection? Also would like to know your rationale behind it. Or if you have a different standard than one of these, I would like to learn about it.

Thanks.

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Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

Brian: When first selecting plates I like to have light,stiff wood that has a nice clear sustaining tap tone. This for me is all done by feel and senses. Once I start thicknessing the plate my only concern is deflection or flexibility. The weight and thickness is what it is when I'm happy with the flexing. Not too much concrete here but it's what I do.
Tom

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A person who has never made a mistake has never made anything!!!

Then do you have any default thicknesses? such as no thiner than.... or must be at least this thin?

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Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

Brian: I think the thinest I've gone is .100 with a stiff top. Most end up around .110 -115 and that is before final surfacing for finishing. Folks go thinner and also use thicker tops. The top and bracing have to work together as a system. If you can get your hands on Kent Everett's DVD on top voicing it's a good starting point. John Mayes also has a DVD on the same subject. Somogyi's books give you lots of things to ponder. A lot of folks will tell you to build more. This is generally the real key.
Tom

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A person who has never made a mistake has never made anything!!!

Hey Brian,

If you are the Brian I think you are we spoke briefly at ASIA, it was nice to meet you.

For me the thickness is entirely dependent on the stiffness. I will thin it down until it feels right and meets some of the data I want to see based on other guitars of mine I had liked. In terms of weight I calculate the density while the wood is still rectangular and oversized. I will generally choose wood with a lower density for guitars that I want to be more responsive and heavier wood for more headroom. This is not universal, but it is a healthy stereotype I think.

I don't have a hard number I look for in terms of thickness, many of my tops are tapered in places anyway. I have gone under .1 successfully and also left tops much thicker successfully, it really depends on the wood and how you want the guitar to respond.

I prefer wood that has a low ratio of long to cross grain stiffness for all my guitars. This is my personal preference and I try as best as I can to choose the wood when going through the stacks that is not flexible across the grain. This can be problematic of course because the wood is all different thicknesses. I just try the best I can.

I hope that helps.

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Burton
http://www.legeytinstruments.com
Brookline, MA.

Burton, Yes that was me. Good to meet you also, I have an idea for some tuner buttons I want to talk with you about sometime. Maybe this winter I'll have a chance to work out my ideas on it.

So far it seems flexibility is the main gauge used, though the lack of responses leads me to believe that most have not put a lot of thought into how each of these parameters can and do effect tone, volume & sustain. What led me to ponder this is the fact that overall system flexibility ( of the top plate ) is controlled largely by the bracing, its lay-out and the way it is shaped. That said, is the flexibility of the plate itself really that crucial? Perhaps one should pay closer attention to one of the other two parameters in prepping the plate for bracing. Does the bracing have enough influence on the overall that simply using a uniform thickness, as I believe all major manufacturers do, is actually the best approach? Or would it be better to strive for a more consistent mass? Plate mass after all will have a lot to do with signal decay and is the first thing the signal must overcome to make use of the system's flexibility to produce sound. Of course as with flexibility, mass must be considered as a whole after bracing.

I am also generally more interested in why someone does what they do the way they do it than simply how they do something. For me understanding why something is done is very important. It will often lead my thoughts in directions they wouldn't normally go, pointing out things I hadn't seen or thought were inconsequential. It also sometimes helps me find the best process for accomplishing things when I know why they are done.

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Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

Watching Kent Everett's great "Voicing" videos, he thins the top plate to an audible "floppiness" (ie stiffness/flexibiluity), consistant from plate to plate, and the thickness finishes where it finishes (subject to a specific lower limit he sets for that species). Mass is of interest but again, it is what it is, and doesn't enter the decision process.

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Dave
Milton, ON

I'm with Burton for the most part. I think the................ usable density is hard to tell from a rough piece though. A set that seems to be really dense, may also be really stiff, but hard to tell in rough form. It's possible that what appears to be a low density top needs to be .115" thick to meet my deflection needs. What appears to be a more dense top may only need to be .095". In the end the final weight could be the same, or the denser piece could even be a few gram lighter.

Reguarding stiffness along the grain, vs. across the grain. IME along the grain stiffness (end to end) is what keeps a guitar together, so it's (kinda) most important. It's my belief that a top that's also relatively stiff across the grain will offer more headroom. One that's looser across the grain will be more responsive. Compare an average Sitka topped guitar to a similar Englemann topped guitar. All things being equal (or as equal as possible) the Sitka topped guitar will have more headroom, and the Englemann topped one will be more responsive. Sitka is usually stiffer across the grain than Englemann.

Obviously different styles of building, and bracing will affect what you need from a top. I've had tops that I thought would be great ,but after joining and getting close to final dimensions I didn't like them. I can't tell alot about them until their joined, and thinned some.

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I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

For Sitka, .110 will be a pretty good ballpark figure for a dread if you want to build by dimension. I've been doing deflection testing lately and have found that thinning to .175 deflection with a 5lb weight at 18" spread makes things about right "for me". It'd probably be a safe place to start anyway.
I think you may not be getting a ton of answers because the question is actually a massive Pandora's box who's real answer is, "depends, on everything..."
I highly recommend the Gore/Gilet books. They will enable you to answer your question yourself.

Yes, the Trevor Gore book will give you a method of determining target thickness by measuring tap frequencies of the board before jointing and thicknessing.
There is a user determined flexibility factor in the equations which will allow you to adjust for your preferences, but get consistent flexibility results for different samples.

In the end the final weight could be the same, or the denser piece could even be a few gram lighter.

In general, the opposite is true. That is because stiffness is roughly proportional to density, and stiffness is proprotional to the cube of the thickness. A thicker low density top will have a better stiffness to weight ratio than a thinner, high density top.
The 'cube rule' also explains why the bracing provides most of the stiffness.
However, that does not mean that the low density top or tall, thin braces will always produce a better guitar. That is because there are other considerations.
I have been building for over 30 years, and I have never weighed any of the parts of a guitar. In my way of thinking, the weight of a guitar should be determined by the densities of the woods selected. In other words, if you want a lightweight guitar, use low density woods, rather than denser woods that must be thinned too much to achieve a certain weight target.
My experience also encompasses guitar repair, including the classic vintage guitars. I have seen all manner of 'repairs' and modifications done to guitars, some more successful than others. I know that guitars with thin tops tend to be loud, but have less sustain and a more percussive sound. They also tend to transmit a lot of string noise. Tops that are too thick tend to produce a sound that is bright with lots of sustain, but not as punchy. I have also learned that weight is not all that important, because I have played excellent guitars in all weight classes....light, average, and heavy.

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John

That's why I am more interested in the logic behind what someone is doing rather than what is being done. While my experience with this may be limited it is growing every day. The observations on response vs. headroom are very useful information. I have been tracking both weight and deflection on my tops thus far, both as a plate and braced. The observation that led to this question was that I've had two top plates thus far that thicknessed to the same dimension (0.110"), the first deflected slightly less ( 0.020") yet was about 8% lighter. I would have guessed the heavier top would have had less deflection. Another top I am working on will most likely not go much under 0.120 to hit the same deflection and will be a bit heavier still. All are sitka, and the one that will be the thickest also has the tightest grain, again not quite what I would have expected. Yes the numbers in all three categories are close across the board, but it started me to wonder which of these parameters was really important. What I am really trying to find is the best approach for me to get the best results on a consistent basis. For me the woodworking comes natural, this is where the learning begins.

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Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

When I got into this stuff around 13 years ago I started by thicknessing to spec. (around .115 for an OM and .125 for a dred) and used standard Martin type brace scalloping. Felt the wood, tapped it, and wrote everything down throughout the bracing and voicing process. Then saw how the guitar sounded and had good people play it. Later added stuff like deflection testing, brace voicing tweaks, and thinning the edges after the box was closed. I think it's a career long process and there are no shortcuts as there are so many variables.
I can tell you that I probably started by overbuilding a little, went to underbuilding a bit and now I'm voicing a little tighter again. Good players and my own ear tell me these are the best guitars I've made so the battle goes on. I don't think it ever really ends.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

This kind of discussion is incredibly valuable to me as I am just getting started on my first guitar. As much as I plan to follow "plans", the subjective criteria involved in making decisions about each top is as close to "magic" as I think you get in building.

I appreciate the differences in approach, and have to say that I don't think there is a right answer, just alot of ways to get to the right place -

Sorry - back to your regularly scheduled program -

Search previous discussions on stiffness testing for tops. You should be able to measure stiffness, weight, thickness and anything else you think is important - before you start building. You need to have confidence that these measurements are accurate and repeatable. When you make a few more guitars, check the values against the guitars you like and those you don't. Repeat what you like and avoid what didn't sound so good.
I find it interesting that some would suggest a thickness when they do not know how stiff the top is and what size body it will go on. I have built OM's and SJ's with thickness from .115 to 0.075". I also have my own bracing scheme that supports those thin tops. Tops that thin are really pushing the limit. Be careful!

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"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.