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  #31  
Old 12-17-2019, 08:00 PM
John Arnold John Arnold is offline
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Braces stiffen the top, and will keep it flatter. It also can make the top more responsive to high frequencies. Without braces, a 1/8" top will distort some.
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Would it make sense to add mass to the bass side, treble side or would it make no difference?
Adding mass to the bass side of the bridge has been done.....Charles briefly mentioned the Kasha system. It is but one example of the vast number of experiments that have been done to improve guitar design.
There is nothing wrong with doing experiments; I have a few test mules myself. But the chances are, it has already been tried before.

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Casting aspersions on a line of thinking without knowing the goal is far from fair dinkum.
Maybe it is time to state your goal, since your original question has been answered. A bridge entirely north of the where the strings come through the top cannot lift. It may slide up, but not lift.
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  #32  
Old 12-17-2019, 09:33 PM
printer2 printer2 is offline
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Originally Posted by Otterhound View Post
Since I have failed to see a response from the party that you are quoting , I will ask again . Am I permitted to utilize bracing on the 1/8" plywood ?
I have changed nothing from the real world . I am questioning them .
Casting dispersions on a line of thinking without knowing the goal is far from fair dinkum .
But of course you can.
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  #33  
Old 12-17-2019, 10:43 PM
charles Tauber charles Tauber is offline
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Quote:
Originally Posted by John Arnold View Post
Adding mass to the bass side of the bridge has been done.....Charles briefly mentioned the Kasha system. It is but one example of the vast number of experiments that have been done to improve guitar design.
Central to the Kasha system was the bridge arrangement and the top bracing beneath it. The bridge was wider and thinner on the bass side - adding mass but proportionately less stiffness - was split in the middle - to allow independent response of bass and treble - and was taller and narrower on the treble side - adding stiffness in greater proportion than mass. It was part of Kasha's attempt to implement impedance matching into guitar design. There were lots of other "tricks" that comprised the Kasha system, but that is the part relevant to the question about adding mass to the bridge. Whether or not his design was successful - or achieved what was claimed - depends upon who you ask.

Steve Klein borrowed the basic Kasha bridge design, making his own variation of it, without using the Kasha bracing system.

Alan has cleverly suggested that one can stick tac putty on a guitar bridge - or elsewhere - to non-permanently add mass where ever one wants, in an effort to see what influence the mass has on response. Similarly, one could also use rare Earth magnets.
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  #34  
Old 12-18-2019, 06:52 AM
ClaptonWannabe2 ClaptonWannabe2 is offline
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Quote:
Originally Posted by Otterhound View Post
It is a simple test mule and was never considered to be a functional instrument .
Thanks anyway mate .
You should have this in the OP. I wanted to call a wood rescue service to confiscate the wood in those bins/barrels.
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  #35  
Old 12-18-2019, 08:11 AM
redir redir is offline
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Quote:
Originally Posted by Otterhound View Post
Since I have failed to see a response from the party that you are quoting , I will ask again . Am I permitted to utilize bracing on the 1/8" plywood ?
Ok I'm going to play thread manager here and say, yes you are permitted to brace the top. Now get busy

I'm going to guess that the reason why you are asking this is because you can then make the top as stiff as the board, or relatively stiff, and then once again it brings up your original point. And again I can only guess at that too, that your original point is why do acoustic guitar bridges even need glue when they are pinned down in the same manor as your board or even a braced thin top???
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  #36  
Old 12-18-2019, 08:25 AM
JonWint JonWint is offline
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Wasn't this sufficiently answered in your earlier thread?

https://www.acousticguitarforum.com/...=544324&page=2

If you define a point of interest, I will draw you a free body diagram for a typical wood bridge on a thin spruce top.

Your photo shows a system with a rigid (relative to an acoustic guitar) metal bridge on a rigid wood top. Those forces between the bridge and the top will be much different than a wood bridge on a 0.110" thick spruce top.

BTW, trig is not required to determine actual forces. You can scale the force vectors if draw to scale.

[IMG][/IMG]
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  #37  
Old 12-18-2019, 11:20 AM
agfsteve agfsteve is offline
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I have no guitar building experience, but I would think one thing you'd want to make sure of in any "normal" build is that the bridge is attached firmly (bonded) to the soundboard, so that the force from the strings is transferred (via the bridge) to the top.

So regardless of whether it's possible to glue (or screw or bolt) the bridge to the top, you would want to do it.

Right? As I said, I have no experience, I'm just interested.
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  #38  
Old 12-18-2019, 02:57 PM
Otterhound Otterhound is offline
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Quote:
Originally Posted by ClaptonWannabe2 View Post
You should have this in the OP. I wanted to call a wood rescue service to confiscate the wood in those bins/barrels.
I have plans for some of this wood . Most of it won't fit into any barrel I know of .
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  #39  
Old 12-18-2019, 03:12 PM
Otterhound Otterhound is offline
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Quote:
Originally Posted by redir View Post
Ok I'm going to play thread manager here and say, yes you are permitted to brace the top. Now get busy

I'm going to guess that the reason why you are asking this is because you can then make the top as stiff as the board, or relatively stiff, and then once again it brings up your original point. And again I can only guess at that too, that your original point is why do acoustic guitar bridges even need glue when they are pinned down in the same manor as your board or even a braced thin top???
You are close . I only want to see if a point of equilibrium can be achieved and still have a functional/responsive top .
I am of the opinion that bridge pins , which are anchored to the bridge , are a major contributing factor to the tendency of the rear of a conventional bridge to elevate . With the bridge being above the plane of the top as evidence .
In none of the diagrams that I recall , do I see any consideration for the fact that a clamping factor exists from the string ends to where the strings break across the rear of the bridge . The torque is increased be the height at which the strings break over the rear of the bridge . by lowering that point this specific factor should be lessened while increasing the clamping factor .
This all functions as a system .
Bt stiffening the area where the bridge lies , torque will also be somewhat compensated for .
With a stop in place at the front of the bridge , the tendency to move forward is eliminated and tension is resolved to the string ends under the top .
Please forgive my lack of formal training and ability to translate my thoughts into scientific terms/jargon .
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  #40  
Old 12-18-2019, 03:15 PM
Otterhound Otterhound is offline
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Quote:
Originally Posted by redir View Post
Ok I'm going to play thread manager here and say, yes you are permitted to brace the top. Now get busy
Will a 12 fret 0 in German Spruce over Maple suffice ?
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  #41  
Old 12-18-2019, 03:52 PM
Peter Wilcox Peter Wilcox is offline
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Here's a long thread from years ago that discusses some of the points brought up here. It's a long read, contentious at times, and comes to no significant conclusions.

https://www.mimf.com//phpbb/viewtopic.php?f=3&t=1126
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  #42  
Old 12-18-2019, 03:58 PM
John Arnold John Arnold is offline
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Quote:
I would think one thing you'd want to make sure of in any "normal" build is that the bridge is attached firmly (bonded) to the soundboard, so that the force from the strings is transferred (via the bridge) to the top.
So regardless of whether it's possible to glue (or screw or bolt) the bridge to the top, you would want to do it.
Bridges are not glued on archtop instruments.

Quote:
The torque is increased be the height at which the strings break over the rear of the bridge . by lowering that point this specific factor should be lessened while increasing the clamping factor.
You are only partly right. Changing the string break angle does alter the downforce on the saddle. This is what you are referring to as the 'clamping factor'. But as you increase the break angle (lowering the string exit point from the bridge), you reduce the force the strings put on that part of the bridge.

Most importantly:
None of this changes the torque which causes the bridge south of the pins to lift. This torque will always be the sum of the string tension and the height of the strings above the top.
There are several approaches to eliminating the bridge pins; none of them have any bearing on this truth.

There are ways to reduce or eliminate torque on a top, but this is not one of them.

After reading the previous thread, I see a source of some confusion.

Quote:
If you have a bridge with a thickness of 3/8 inch - bridge and have an additional 1/8 inch - saddle projection (total 1/2 inch), then swap it with another unit where say the bridge is 1/4 inch thick and the saddle projection is a 1/4 inch (total 1/2 inch) then the top will deflect differently under the same tension and have a different bulge.

The break angle actually is a critical angle and it has a resultant moment centre which will move accordingly with a change in said break angle, the bridge itself also has a centre of gravity which plays an important role in our equations, the load (moment) has a centre point, the distance between the bridges gravity point and the "moment" centre point moves the ""twisting force" of the bridge, the total amount of the force is the same in both bridge examples but the effect on the top will be different.
IMHO, none of this is true.

Last edited by John Arnold; 12-18-2019 at 04:15 PM.
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  #43  
Old 12-18-2019, 08:26 PM
JonWint JonWint is offline
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The higher above the top (thicker bridge) the strings bend over the bridge toward the saddle, the greater the amount of torque generated at that point where the strings leave the pin holes. The metal bridge has a minimum height above the top. Thus, lower moment at the point of string bend than a wood bridge.

The further back (south) that the strings are from the saddle, the greater the bridge area that will be in compression against the top. Also, the clamping (vertical) force will be further from the saddle compression force line. The pressure at the bridge base will be more uniform due to the greater distance between the force couple.

Remember that the bridge torque will belly the top and it will want to separate from the bridge at that edge. The bridge is significantly stiffer than the top. The tension in the glue will be maximum at the edge of the bridge as the top curves away from the rotating bridge and will want to peel and lift.
You can’t reduce the total torque on a bridge system. You can modify the bridge shape, saddle, and pin hole locations to change bridge/top bearing pressures and tendency to lift.

All of this can be modeled in modern design software with finite element analysis capability and provide whatever answers are desired. That, however, is beyond my ability and desire. (I finished undergrad engineering with a slide rule for personal computing. A room full of IBM mainframes and card punch entry was the other choice.)

[IMG][/IMG]
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