#1
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Break angle and downward pressure on guitar top
Hi Im an amateur luthier drafting my next guitar. Im thinking it will be a kind of flat top with 20' radius and with a kind of tailpiece, inspired by makers like Batson Guitars. Now Im doing some online research to find out what kind of pressure on the top that the strings will exert.
This led me to a thread in another forum where someone gave an example on how to calculate the downward pressure at the bridge. It included cos which is way beyond my math knowledge but when I tried his algorithm I got nervous: If a set of light strings has a tension of 75 kg (165 pounds) and the strings break angle over the bridge is 15 degrees (which is what I had in mind) the downward force/pressure at the bridge will be around 60 kg (130 pounds). Can this really be correct?
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Ulf, Sweden Lindholm guitar C.Fox C-Sonoma Old parlor |
#2
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Quote:
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Derek Coombs Youtube -> Website -> Music -> Tabs Guitars by Mark Blanchard, Albert&Mueller, Paul Woolson, Collings, Composite Acoustics, and Derek Coombs "Reality is that which when you stop believing in it, doesn't go away." Woods hands pick by eye and ear
Made to one with pride and love To be that we hold so dear A voice from heavens above |
#3
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Quote:
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Derek Coombs Youtube -> Website -> Music -> Tabs Guitars by Mark Blanchard, Albert&Mueller, Paul Woolson, Collings, Composite Acoustics, and Derek Coombs "Reality is that which when you stop believing in it, doesn't go away." Woods hands pick by eye and ear
Made to one with pride and love To be that we hold so dear A voice from heavens above |
#4
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Thanks for your reply Rick but were not talking a pin bridge here. Im thinking about archtop type of guitar like the ones Batson Guitars make - a flattop but with a tailpiece.
Ulf
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Ulf, Sweden Lindholm guitar C.Fox C-Sonoma Old parlor |
#5
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Quote:
Frank Sanns Last edited by FrankS; 03-18-2012 at 10:22 AM. |
#6
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#7
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Frank and Rick, sorry for not being accurate in my question. We are not talking a pin bridge here but a guitar with a tailpiece construction, which means there is no pull on the bridge, no torsional forces - just pressure dictated by the strings break angle as I understand it.
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Ulf, Sweden Lindholm guitar C.Fox C-Sonoma Old parlor |
#8
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Ulf, Sweden Lindholm guitar C.Fox C-Sonoma Old parlor |
#9
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It's not the cosine it's the sine. So the sine of 15 degrees is 0.259 and the downforce is 165 lbs x 0.259 = 42.7 lbs.
It can't be the cosine because the cosine of a 0 degree angle is 1 and 165 lbs x 1 = 165 lbs, meaning that a guitar with no break angle would have all the string tension pointing down on the top. Also, the cosine of 90 degrees is 0, and a guitar with strings perpendicular to the top wouldn't have 0 downforce, it'd have 165 lbs of downforce (don't worry about the direction, it'd be a screwy instrument anyway). With sine the reverse is true, the sine of 0 degrees is 0 and the sine of 90 degrees is 1 and that's what you'd intuitively expect when guessing about downforce. |
#10
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Quote:
See this link for a handy calculator http://liutaiomottola.com/formulae/downforce.htm
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Derek Coombs Youtube -> Website -> Music -> Tabs Guitars by Mark Blanchard, Albert&Mueller, Paul Woolson, Collings, Composite Acoustics, and Derek Coombs "Reality is that which when you stop believing in it, doesn't go away." Woods hands pick by eye and ear
Made to one with pride and love To be that we hold so dear A voice from heavens above |
#11
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Thats great, just what I needed. Thanks!
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Ulf, Sweden Lindholm guitar C.Fox C-Sonoma Old parlor |
#12
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A fifteen minute lesson in trigonometry can go a long way.
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Guild CO-2 Guild JF30-12 Guild D55 Goodall Grand Concert Cutaway Walnut/Italian Spruce Santa Cruz Brazilian VJ Taylor 8 String Baritone Blueberry - Grand Concert Magnum Opus J450 Eastman AJ815 Parker PA-24 Babicz Jumbo Identity Walden G730 Silvercreek T170 Charvell 150 SC Takimine G406s |
#13
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I don't know. In my case it would take at least twice that long just to understand the meaning of that word.
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Ulf, Sweden Lindholm guitar C.Fox C-Sonoma Old parlor |
#14
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Basically, it's the study of triangles. I bet I could teach it to you in fifteen minutes.
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Guild CO-2 Guild JF30-12 Guild D55 Goodall Grand Concert Cutaway Walnut/Italian Spruce Santa Cruz Brazilian VJ Taylor 8 String Baritone Blueberry - Grand Concert Magnum Opus J450 Eastman AJ815 Parker PA-24 Babicz Jumbo Identity Walden G730 Silvercreek T170 Charvell 150 SC Takimine G406s |
#15
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In that case Robj you must be a hell of a teacher!!
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Ulf, Sweden Lindholm guitar C.Fox C-Sonoma Old parlor |