How low can you go? Or how to underbuild a guitar

[tippie53]

You are right there is a science to how you brace a top . I am of an engineering back ground and like to use a weight and deflection . I must be doing something right , my guitars sell and they sound great. There are many schools , pre stress , radius , flat , you have to find what fits your philosophy and technique.
You do need to keep records and understand cause and effect relationships. I do not believe there is only 1 way to make a guitar , I have seen so many things that work . I to believe science can tell you more than relying on luck. I also read the books and understand the science and I think we both help many here . I hope we all learn.

[Herman]

Thanks for your comments guys,

John and Ken, you built a lot of guitars. Were there some, at a point, that collapsed? As a vendor you are not waiting for that, because it gives a lot of trouble.
But if you are building on "the edge", one would aspect to have a collaps guitar now and then.
Did that ever happen?

My guitars are structually sound and perform better than the average guitar in the stores. I could rest my case and keep doing my thing, but I think I'll give the 70%-guitar a try in the near future. Probably a waist of time and money but still a lot of fun and forumactivity.

Your pigheaded friend from Holland
Herman

edit: waist=waste, I got it twice as difficult as you. Got to work on the guitars and on my english.

[tippie53]

None that collapsed but I found I did over build in the beginning. I also found that I tried a few times to tweak my early guitars and over did that , and that caused a few top failures . Here is what I learned.
The top is under many stresses . How material will carry a stress determines how you want to use it . How you shape it can influence the stiffness . This doesn't really change the strength but it will take the plastic limit and yeild limits closer to the same point . Wood can take more tensional load the compressive load , as in compression the point of gyration will deform the structure , in tension you won't have gyration.
I started to use real data , measured weight to a given size and span and measured the amount the sample moved Then after bracing added weight to see how much it took to move the same amount This gives you a ratio. That way you can work into a number that gives you the builder what you are looking for .
When you look at a top you have areas where the forces will couple , the area between the neck block and the bridge is one , you have a rotational force applies to the neck block and the bridge and on top of that you also have a compressive force . Here is the area of the top that is the most critical for structure . Behind the bridge you have a tensional force . This is where you can work braces more that under the heavier load .
On top of this you can influence stiffness by the shape , a dome has more structural integrity than a plane. Also how you construct the bridge plate area can also play into this equation . What this means is you have to figure what the top can withstand , the amount of glue surface area and how it applies the energy to the top , and Mass. Thinner braces may be as stiff as a wider one depending on height and the strength of the material . This is why you need to keep records so you can compare data.
The golden era of guitars is often considered the pre war time , here Martin had a small bridge plate , Hot Hide glue on the construction , a slightly heavier top than today and tucked braces . Also the Popsicle brace was not used at this time. You have to decide , are you going to design your guitar or copy an old design or a something in between.
My building heros are Alan Caruth , Wayne Henderson , and David Nichols. There are many ways to build and you have to find what you like . I like what a friend once said to me " Building guitars looks hard , but it is harder than it looks".
Find what you like and keep records .

[kencierp]

Herman,
I have no reports of any of my guitars or any other instruments or products collapsing. KIS (keep it simple) --- use common sense, practical proven models and all will go well. If you like the way your instruments look and sound, well is that not the whole idea?

[kencierp]

Didn't the Beach Boys do a song about "Good Gyrations"?

[tippie53]

I think Cream tried , it was on the flip side of Inagodaveda I think it was called gyrtooties

[Herman]

Yes, I do keep records, even those from the Beach boys and Cream. And my goal is not to build a guitar that collapses, but it is more a twist of my mind that struggles with the assumption that the best sounding guitar is the one that is light as possible and on the verge of collapsing.

But thinking about what you just said leads me to another assumption.
You talk about the wonderful guitars you've seen. And they all were intact. Could it be that the best sounding guitars do not need the edge of light building? Does a good guitar need that much stiffness for good sound, that it inherently has the strenght to stay intact?

My tease for you in other words: Is there is no need to seek for a guitar that is bult on the edge, because its sound will suffer from its light structure?

have a good weekend
Herman

[kencierp]

Guitar making is fun, challenging, scientific, rewarding, stressful, delightful, artful, and sometimes humorous!

Truth is -- wood is an organic material, each and every piece is different plus the sound produced by any given guitar is almost totally subjective depending on the listener. And there are the myths, which as seen here can be inaccurately relayed in good faith as facts -- what is one to do?

Experimenting until you find your ideal -- perhaps? But how many will you have to make until your sample is large enough to be accurate -- SPC standards dictate about 100 for each element -- Geeezzz who has time for that?

Here's what I've done and recommend -- find a guitar that sounds good/right to you and copy it as best you can.

The organic thing will no doubt play into the outcome as well as the fact that if it is a vintage instrument -- the aging component cannot be duplicated --

And I subscribe to the theory that guitar making can be easier then it looks.

Yes to me its all fun!

[tippie53]

Guitars are as individual as we are. When ever you have a subjective interpretation of the out come it mean you have to decide what it is you like . Like ken says if can be challenging trying the whole nine yards .
If you get hooked , it can become a passion. If you like it and it suits you , that is all that matters. Ken and I may banter back and forth and we play devils advocate to each other but I like to think we still have a mutual respect. We may do different things but we have a passion for what we do. Hopefully we all learn from each other.

[Darryl Young]

Another point I wanted to make. Between "slightly overbuilt" and "immediate failure attempting to bring strings to tension" is a gap. Wood creeps over time when its under tension and at one end of that gap it happens very slowly and at the other end of the gap (not enough stiffness), it can happen very quickly. So when you push it toward "barely enough stiffness", you aren't driving toward a cliff where you are perfectly safe right to the edge then catastrophic failure. If you under build, it's more like you may need a neck reset in 6 months or 1 year instead of 10 or 20 years down the road.

This is why some folks add carbon fiber to their braces. CF doesn't creep over time (or at least it's tiny compared to wood) and it allows one to go less stiff while controlling creep.

I don't recall all the details, but Rod True on the OLF once built a guitar with a redwood top that failed overnight after string up. He said the guitar was amazing for a while right after tightening the strings......in fact, he said he heard things he had never heard before!

Also, the distribution of stiffness is important. You can add a lot of stiffness to the soundboard but if it's in the wrong place you've gained little to nothing structurally.......and may have hurt the sound of the guitar. Same with building lightweight........you can have a lightweight guitar that is overbuilt and a heavy guitar that is under built.