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string pressure

Hi. I appreciate your site and vision.

I'm building my first guitar, and would like to know going in how much pressure a set of light strings will exert onto my bridge (the downward force, at 90 degrees to the strings) when stretched from a tailpiece. I am told this pressure is greater when the angle across the bridge is more extreme; I don't need to know if this asssertion is true; I just need a technohack estimate to help me build a strong but sensitive face, using my own strut system. BTW, the pressure from nut to tailpiece, linearly, is something like 179.2 lbs.

thanks much!

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Permalink Reply by Ottie(Skydog)Noble on June 30, 2012 at 7:06pm

If I remember right its 3 barley corns per sq inch

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Permalink Reply by Ron "Oily" Sprague on June 30, 2012 at 7:58pm

Joe,

Here's some background on what strings do when under tension, and how to calculate that linear string tension (I know, not what you're asking for, but good background nonetheless):

http://www.noyceguitars.com/Technotes/Articles/T3.html

There are several online tension calculations for various string gauges / sets when tuned to standard pitch; here are a couple that also reference other information, from string manufacturers like D'Addario:

http://www.mcdonaldstrings.com/stringxxiii.html

http://wahiduddin.net/calc/calc_guitar_string.htm

I understand that you are not looking for the linear string tension, but instead for the downward vector force of a string bent at 90 degrees across a saddle. Here's some sites I found rather quickly with Google, that may answer your needs:

http://www.liutaiomottola.com/formulae/downforce.htm

http://mowrystrings.com/downloads.htm

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Permalink Reply by Joe Berg on July 1, 2012 at 11:52am

Perfect (if that is not an insult hereabouts)! the

http://www.liutaiomottola.com/formulae/downforce.htm

site has a nifty swifty calculator that tells me that my light strings, bent at 17 degrees over a saddle (someone, somewhere claims this is optimal) exerts 53 lbs of force onto the face.

So I found the right site after all. Thanks much! I'll boast or moan when I finish my own (wow! Lyrics too!).

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Permalink Reply by Ron "Oily" Sprague on July 1, 2012 at 5:55pm

Joe,

Glad that worked for you. When you get done with your build, it would be interesting for the gearheads and CBG wonks around here to see your build, and a write-up of your calcs so we can link to it when someone else, as they invariably will, asks this same question 3 weeks or 7 months from now :-)

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Permalink Reply by Huntz Meyer on July 1, 2012 at 3:10am

I'd solve it for you, but what's the fun in that? Just need to resolve the force vector:

http://www.physicsclassroom.com/class/vectors/u3l1e.cfm

Huntz

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Permalink Reply by Ron "Oily" Sprague on July 1, 2012 at 8:50am

Awwww, c'mon, Huntz, ya gave him the easy way out! >:-E I was holding that site in reserve...

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Permalink Reply by Slowpaw Steve T on July 1, 2012 at 5:26am

I 've made a number of successful builds and never found the need to be concerned about this, i found most cigar box lids should support the pressure from the strings at the bridge easily enough, or as with my builds if all/part of the through-neck is supporting the bridge directly below it. It is important for the neck/body joints to be made as rigid as possible, otherwise distortion will occur with the neck bending while playing.

btw if you find the answer to your question let us know! (-;

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Permalink Reply by MichaelS Country Boy Guitars on July 2, 2012 at 1:51am

Are you sure about that tension being 179Lbs?? I think if it where that high alot of the tail pieces you see here would be flying off. I found this web page that puts the linear tension closer to 20Lbs which sounds much more realistic to me. What do you technohacks think?

http://www.daddario.com/DAstringtensionguide.Page?sid=9c6c2dc2-7c10...

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Permalink Reply by MichaelS Country Boy Guitars on July 2, 2012 at 1:53am

Here is another cool calculator of string tensions etc.

http://wahiduddin.net/calc/calc_guitar_string.htm

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Permalink Reply by Joe Berg on July 2, 2012 at 7:24am

I'm very, very new at this, but I'm wondering if your 20lbs is per string, for extra lights?

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Permalink Reply by MichaelS Country Boy Guitars on July 2, 2012 at 8:53am

Joe, if you look at the D'addarrio site they have the low E string, a .046 wound, at 17.5 pounds. !79 pounds of pressure would be breaking strings and really hard on the fingers when fretting. I don't know about the bridge pressure, which is your real question. So far I have on;y had a problem with one box flexing from the bridge so it is a concern and a good question.

You may be correct in that the 179 is for all 6 strings, I have not added up D'addarios figures but that makes more sense, mine are all 3 string so half that for the average cbg.