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Forces on a guitar's neck

  1. Dec 10, 2005 #1
    Hi, I am trying to find out the amount of force applied to a guitar's neck by its strings. This is because I've heard a lot of people telling me to change the strings of my guitar one by one so that the tension doesn't vary too much at once. I am a bit scepticle about that...

    How do you go about calculating the resulting force on a pivot itself inccured by the tensionned string?

    My guess is that most of the forces are parallel to the guitar's neck and a small amount is not. If that would be true, it wouldn't make much difference if all the strings were changed at once, or one by one since the neck would not bend forward or backward.

    http://static.howstuffworks.com/gif/guitar-scale-length.gif

    Matt
     
    Last edited: Dec 10, 2005
  2. jcsd
  3. Dec 10, 2005 #2
    Well, that really depends on the thickness of the strings and how sturdy your guitar is. I've heard that advice as well and I think it pertains to acoustic guitars more as it seems to me that its neck is attached less sturdily than on an electric. In addition, steel strings on an acoustic are typically much thicker than steel strings on an electric and thus require more force to get them in tune.
     
  4. Dec 10, 2005 #3

    FredGarvin

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    In the giutars I have seen, there is a metal rod that is built into the neck to take the majority of the loading created by the strings. The wood neck itself doesn't carry much of the load. The rod is adjustable, so I can't really say that it's all that important to do one at a time unless you don't want to play around with adjusting it again.

    http://www.projectguitar.com/tut/img/stv46.jpg
     
  5. Dec 10, 2005 #4

    Astronuc

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    http://www.pacificsites.net/~dog/StringTensionApplet.html

    As Jelfish indicated, it depends on the type of string.

    In the above quote, # = lbf (pound force), and the 23#, 23#, 30#, 30#, 30#, 26# arrangement has 162# force. The moment is relatively low because the moment arm on the bridge is a few mm.

    Electric guitar - http://www.noyceguitars.com/Technotes/Articles/T3.html
    This site shows an example with about 47 gkf (103#) of load.
     
  6. Dec 10, 2005 #5

    brewnog

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    This rod (it's called a truss rod) only helps to stop the neck itself bending, it doesn't run the full length of the strings. There's still a considerable bending moment applied to the guitar body itself at the bottom of the neck. This is where I've seen guitars snap due to overtightening of the strings (admittedly they were 12-string guitars, but these are built stronger, often with twin truss rods).

    I personally try to change my strings one at a time, unless the neck needs a really good clean.
     
  7. Dec 10, 2005 #6

    FredGarvin

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    Well, if it's reducing the amount of curvature in the neck, then it is reducing the stress in the neck. So really the neck doesn't break, the joint between the body and the neck is what breaks. So are we really talking about the neck or the forces on that joint?
     
  8. Dec 10, 2005 #7

    Danger

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    The only forces on the neck of any guitar that I've dealt with are from my fingers trying to strangle the ***** because it won't make music.
    Okay, okay... I'm going back to GD.
     
  9. Dec 10, 2005 #8

    krab

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    It's a good idea to change them one by one but not because of possible damage to the guitar (unless it's a really cheap one). If you remove all the strings, and install a new one, and tune it, it will be way off when you add and tune the next one, and so on. Finally you'll get all the strings on and every time you think one string is right on, the others are out of tune again. Takes a long time. This is because the bend of the neck does change ever so slightly every time you change the tension on a string. The cheaper the guitar, the bigger the change.
     
  10. Dec 10, 2005 #9
    There can be as much as 200 pounds of pull on the average guitar neck when the strings are tuned to pitch. Taking off all the strings won't hurt it at all if it's done correctly. Always take the strings off one by one by turning the pegs to losen the strings. Cutting all the strings at one time (as some people do) can cause problems. When all that tension is released at once it can cause the neck to spring back too far and damage it.

    Also tuning the strings back up is not such a big problem as alluded to earlier. New strings streatch quite a bit, and will freequently go out of tune until they stretch enough.

    The reason I change strings one at a time is so that the bridge doesnt fall off or get out of adjustment, as can happen on guitars with a les paul style bridge. Also some tremolo equipped guitars will see the tremolo pulled hard onto the body of the guitar causing marks in the wood if all the strings are removed without blocking the tremolo.

    If you do take all the strings off its best not to leave the guitar like that for more than a day or so.
     
  11. Dec 10, 2005 #10
    My Warped Acoustic

    I can say for sure that the effect of string tension does effect things on acoustics mainly. My bridge is slowly giving way: the soundhole area has some buckling, and the body behind some bucking. Also where the neck joins the body, some cracking due to stress is seen in the finish.

    Try changing string guages on any guitar. Going to heaver strings puts enough additional bending torque on the neck that the truss rod will require adjusting to bring it back. Once the strings get too far from the fretboard (really high action) this effect will obviously amplify.

    As for the changing of the strings, aside from tuning problems as mentioned, I dont think there is much worry. The only thing that comes to mind is fatiguing due to cyclical stess, but unless the strings are changed every day, no probs.

    Cheers.
     
  12. Dec 13, 2005 #11
    This is can actually be a big deal with guitars. Not all of them have the truss rod. They say if you were to put steel strings on a classical guitar (which uses nylon) it can be a disaster for the neck.
     
  13. Dec 14, 2005 #12
    This happened with a broken guitar I bought and fixed. Someone seemed to have done a Pete Townsend on a really expensive, hand made acoustic I found at the swap meet. Once I fixed the broken neck and started to restring it, each one I added threw the previous ones off. It had to be retuned constantly for a while before it "settled down".
     
  14. Jan 18, 2011 #13
    actually the amount off effect the bending of the neck will have on your tuning is so slight that you would not be able to notice it with a tuner or your ear. if you actually have an issue with this it is probably due to the bridge of the guitar being a floating bridge, originally designed by floyd rose. the reason you get this is because the bridge is not actually bolted down to the body of the guitar but is suspended between the force of the strings and the force of a set of springs inside a cavity within the guitar's body. you cannot change all the strings at once with a floyd rose style bridge because obviously the springs will just force the bridge into destroying anything that it runs into. tuning one of these is an old problem for guitarists being that it takes a long time to get each string to the exact right tuning without messing up the rest of the strings, so you end up tuning several times, until you eventually get tired of it and stick a block of wood under the bridge and leave it like that
     
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