Page 1 of 4 123 ... LastLast
Results 1 to 10 of 35

Thread: Structure question for the pros...

  1. #1
    Join Date
    Mar 2010
    Location
    East Texas
    Posts
    3,306

    Default Structure question for the pros...

    Hey guys.. I have a question about the strength in a ukes (or guitar for that matter) design. Is the top, back and sides of an acoustic part of the structure integrety of the instrument. I am sure it does provide some, but is it mostly the job of the internal bracing and lining? I'm pretty sure I have an idea of the answer, but would still like to hear from you guys that have been building for years.

    The reason I ask this in part it because I as many know I been building little mini ukes, in preparation to build full scale this next spring. I have read by many of you that thin is one of the many secrets of getting resonance from the top. The mini ukes I have been building have been 1.5mm thick top and bottom, with 1mm thick sides. I understand that is about what many build with even tenors. I am trying to squeeze as much sound out of these little minis as I can by playing with bracing etc. I am building one now with the top, bottom and sides all being barely 1mm thick. Man, it is almost like working with paper. It feels so fragil as I work with it, on such a small scale. I hope it doesn't end up folding up like a cheap lawn chair when I string it up, lol.. It will have lining, and bracing like the others I've built, I am just curious how much structure 1mm thick, at this size will provide.
    Mahalo Ke Akua
    ------------------
    Ohana SK-35 a.k.a. "IZ"
    Ohana SK-21 a.k.a. "Ku'u poki'i <Kapookie>"
    Lanikai LU-21 a.k.a. "Cinderella"
    Epiphone Les Paul Concert Uke "Lil' Lester"
    Harmony Banjo Uke a.k.a. "Bango"
    Gibson Les Paul a.k.a. "Hobo Ted"
    Epiphone Les Paul Studio a.k.a. "Barnabas"
    Epiphone Les Paul a.k.a. "Blaze"
    Gretsch Tenor Banjo a.k.a. "Jed"
    Supertone 406, 5 string Banjo a.k.a. "GrandPa Jones"
    Fernendes Telecaster "Suemeh"

  2. #2
    Join Date
    Dec 2009
    Location
    cairns, australia
    Posts
    880

    Default

    Whole books have been written on the subject of structural integrity. Whole careers have been meeked out on the subject.

    How well do you understand the cube rule of engineering and how it applies to beam length, width and height? There's not time to explain it all here but it is the golden rule of structural integrity. Then you need to get your head around what and where forces are acting in a uke strung to pitch. Once you've got your head around these things you'll have a better idea of where you can lighten things up and where things need to be beefed up.

    P.S. I'm certainly no pro. I do try to gather information from as many sources as possible. I've got a bunch of books on instrument construction, I borrow from the library, I read alot on the internet (although you have to wade through a lot of crap to find the few gems), and I talk with luthiers when I can.
    Liam Ryan.
    Cairns, Australia.
    Stump Jump Ukulele Co.
    Stump Jump on Facebook

  3. #3
    Join Date
    May 2010
    Location
    Cairns, Australia
    Posts
    2,308

    Default

    All of them play a huge role in the structural integrity of the instrument. As Liam said, you need to understand the cube rule. It applies not only to the bracing that you add to the structure, but also to those members that you are applying it to. The top, back and sides. And to make things even more interesting, the cube rule not only applies to the width and hight of a piece is, it also applies to it's length.

    Quick lesson. If you have a piece of wood 1 unit tall by 1 unit wide it will have a stiffness of 1x1x1=1 a weight coefficient of 1

    If you have a piece of wood 1 unit tall by 2 units wide you have a stiffness of 1x1x1x2=2 and a weight coefficient of 2

    But if you have a piece that is 2 units tall by 1 unit wide you have a stiffness of 2x2x2x1=8 and a weight coefficient of just 2

    So you can see that by increasing the hight of a brace, or top or back you get an exponentially stiffer piece but it's only a little heavier. In instruments, most times you are looking for light vs heavy.

    You've got a hell of a lot of reading and study ahead of you. From there you take informed decisions to the workshop and start glueing up pieces of wood.

  4. #4
    Join Date
    Aug 2008
    Location
    Wales, UK
    Posts
    5,145

    Default

    Your sidea are a bit thin mate!

  5. #5
    Join Date
    Mar 2010
    Location
    East Texas
    Posts
    3,306

    Default

    I am not a structural engineer, nor know all the structural engineering formulas. But I do have a good better than average understanding of physics and engineering. I can see why more understanding of the forces can greatly improve design skills. I don't think most people realize the stresses string tensions put on an instrument. I think even I understanding that pretty good even under estimated it. My very 1st Aphid developed a crack near the heel, but almost immediatly I realized my mistake and made some adjustment to my design, and all the ones since has had no issues. But Pete, I hear ya brother. I think slightly thicker on the sides would greatly improve structure so I can get away with a thinner sound board.. I might take that a bit over 1mm up to 1.5.
    Mahalo Ke Akua
    ------------------
    Ohana SK-35 a.k.a. "IZ"
    Ohana SK-21 a.k.a. "Ku'u poki'i <Kapookie>"
    Lanikai LU-21 a.k.a. "Cinderella"
    Epiphone Les Paul Concert Uke "Lil' Lester"
    Harmony Banjo Uke a.k.a. "Bango"
    Gibson Les Paul a.k.a. "Hobo Ted"
    Epiphone Les Paul Studio a.k.a. "Barnabas"
    Epiphone Les Paul a.k.a. "Blaze"
    Gretsch Tenor Banjo a.k.a. "Jed"
    Supertone 406, 5 string Banjo a.k.a. "GrandPa Jones"
    Fernendes Telecaster "Suemeh"

  6. #6
    Join Date
    Jul 2011
    Location
    central CA
    Posts
    634

    Default

    Quote Originally Posted by liam_fnq View Post
    Whole books have been written on the subject of structural integrity. Whole careers have been meeked out on the subject.
    Can you recommend a good book to start??
    Thanks!
    My Real name is Terry Harris

  7. #7
    Join Date
    Mar 2009
    Location
    Hudson, MA
    Posts
    1,512

    Default

    Don't forget its not just string tension that stresses the body. It has to hold up to normal use and a bit of abuse....you might put your finger right through it on bad strum or punch a hole in it taking it out of the case.
    There's a limit to how thin you can go. Thinning the top is good to a point to decrease weight. But at some point you start losing because the top isn't stiff enough to transmit vibrations and you lose sustain and volume.
    There is a reason why the the range of top thickness you'll find is pretty tight....between 0.070" to 0.090". I guess the sweet spot is in that 0.020" range somewhere.

  8. #8
    Join Date
    Aug 2008
    Location
    Wales, UK
    Posts
    5,145

    Default

    It's not about 'weight'. Tone and volume come from the 'stiffness' of the front relative to it's thickness. Go to youtube and the front end of the bill collings factory tour video he shows what looks like a mastergrade front as floppy as a sheet of rubber - absolutely no good for boutique guitars. His comment - $500 guitar maybe.... You also have to stress the front into a curve and brace it approriately with wood which 'likes' your front. There's a bit more to it than a few calculations....

  9. #9
    Join Date
    May 2010
    Location
    Cairns, Australia
    Posts
    2,308

    Default

    Quote Originally Posted by resoman View Post
    Can you recommend a good book to start??
    Thanks!
    A very good set of books that cover some of this are by Ervin Somogyi. They are called "The Responsive Guitar" and "Making the Responsive Guitar". They are pricey, but you will find that nothing in the luthier craft is cheap. He also has a DVD called "Voicing The Guitar" that is pretty good. Ervin doesn't give you a magic formula, but rather gets you thinking about what and why you do things.

    A really good DVD on a similar vein is "Voicing a Steel String Guitar" by Kent Everett. Same deal here. While it has to do with guitars, the concepts are exactly the same. Different bracing patterns, but the physics still apply.

    There are heaps of other books etc. out there that I'm sure will help out. These are just a few that I found particularly helpful that I have on the shelf.

    And lets not forget David Hurd's contribution to the science, particularly because his specialty is ukuleles. "Left Brain Luthierie". It's pretty in depth and not for the faint of heart if you're not really the science geek type. You can find some of the information in the book on his website.

  10. #10
    Join Date
    May 2010
    Location
    Cairns, Australia
    Posts
    2,308

    Default

    Also regarding the thickness of your components now. You say you are using a 1mm thick top as compared to what I think was a 2mm one an a previous build. Your 1mm top now is 8 times less stiff as compared to the 2mm one without taking any bracing into consideration.

    This isn't necessarily a bad thing. You just need to keep in mind that it does need to be stiff enough to hold up. Design your bracing accordingly.

    I build a line of ukes that have a top thickness in the lower bout of just 0.8 - 0.9mm thick, but they are lattice braced with balsa and Carbon Fibre. The tops are incredibly stiff. The hard part about building them is to not end up having them too stiff. They are based on an idea pioneered by Australian Luthier Greg Smallman who makes some incredible Spanish Style guitars.

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •