#61
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If we define the break angle as the angle formed between the vertical saddle, and the string as it passes over the saddle en route to contacting the bridge at the top of the bridgepin hole, then it follows that no matter how thick the Lexan plate is, the break angle is going to remain exactly the same. The only way that thickening the Lexan could affect the break angle would be if the string made no contact at any point with the wood of the bridge , and went straight from the Lexan to the top of the saddle..... which seems both impractical and counter-productive. |
#62
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Rodger Knox, PE 1917 Martin 0-28 1956 Gibson J-50 et al |
#63
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#64
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#65
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I heave been giving thought on how to make this loading thing simple to understand .
What prevents the bridge on an instrument in the violin/double bass family from simply rolling forward and falling over due to torsional force ? |
#66
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When you tune up an instrument with this style bridge, sometimes tightening the strings can pull the bridge forward, but this is easily corrected as the strings are tightened to full pitch.
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---- Ned Milburn NSDCC Master Artisan Dartmouth, Nova Scotia |
#67
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Perhaps, more detailed than you'd like, but this seems a good treatment of the subject, page 35, Section 3.4, and page 49, Section 3.19.
https://books.google.ca/books?id=WbW...bridge&f=false To summarize, unlike a guitar, the strings break over the violin bridge with no part of the string being horizontal. Instead, the portion of the string between nut and bridge forms one angle while the portion of the string from bridge to tail piece forms a different angle. This gives rise to a relatively small difference in horizontal forces being applied to the violin bridge. Friction between strings, in their grooves in the bridge, and the bridge prevents the bridge from tipping. This is a different situation than a guitar bridge, pinned or not and is probably not particularly relevant to guitar design, unless speaking of guitars with tailpieces. People have done the static analysis of a pinned guitar bridge: it is not something new. Here is one such example in which Alan contributed: http://www.mimf.com/phpbb/viewtopic....=1126&start=20 Last edited by charles Tauber; 12-16-2017 at 11:44 AM. |
#68
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The only way there'd be a "torsional" force on the bridge is if somehow the string tension on one side is greater than the other. If for some reason the bridge does tip over a little , as Ned points out, you can easily straighten it.
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#69
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Rodger Knox, PE 1917 Martin 0-28 1956 Gibson J-50 et al Last edited by Rodger Knox; 12-16-2017 at 02:00 PM. |
#70
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I would guess that the sound from putting a soundpost on a flat top would be akin to listening to a violinist play "pizzicato". The big difference is that these stringed instruments with sounposts are bowed, not picked or strummed.
And yes you are correct about the plate frequencies; I stand corrected. But even so, both plates are not vibrating sympathetically to each other, meaning in a "mirrored" pattern. |
#71
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I vaguely remember that whole discussion. Dave Malicky used to also post on the CNC Zone, though I haven't seem him there in a while. He is a SolidWorks whiz, and I always wanted to ask him if he could do a FEA in a model guitar top...
There is a conclusion that I had come up with a while back, and I'm sure more than a few have - that is , if one mitigates or at least controls the amount of top deformation behind the bridge, then bridge "pull" or "peel" off the top is eliminated, barring glue creep, cut fiber, or other defect. I think it's one of the side-benefits of lattice bracing that extends over the bridge-plate - that area behind the bridge have very little to no flex, reducing the rotation of the bridge about its leading edge. Thus, a rear-loaded pinless bridge would survive just fine on a top built as such (which would be one reason a pinless bridge was used in the first place) |
#72
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#73
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You cannot peel what does not bend, no matter what peeling force you apply. It could only shear, or catastrophically fail. At least one thing has to bend.. If both pieces bend, it helps resist peeling as well, which is one reason for tapering braces, or even the bridge wings... |
#74
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The reason for tapering brace ends, as I understand it, is to reduce/eliminate stress conentrations caused by sudden changes in cross section. Two rigid bodies adhered together can be separated without distortion if the separation forces, in this case a moment, exceed the strength of the adhesive or materials being adhered. Distortion is not a prerequisite for the failure. The question is then how significant a factor in guitar bridge failure is due to the distortion and “peeling” vs. Simply exceeding the material or adhesive strength, or creep of the adhesive. Since hire glue is reported to not creep, it would appear that creep could be removed as a cause in such joints. Last edited by charles Tauber; 12-17-2017 at 10:55 AM. |
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While the rigid bridge may not "peel" away from the top, the flexible top may be thought of as peeling away from the bridge . . . Perhaps.
Properly made Violin family bridges come very close to bisecting the string's break angle, and thus are driven nearly straight into the top plate. There is a great deal of what I think of as imperfectly understood conceptual information in this thread. |