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  #16  
Old 12-21-2017, 11:59 AM
dekutree64 dekutree64 is offline
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Quote:
Originally Posted by Otterhound View Post
Ebony is more dense than rosewood .
The static load on a bridge is something that needs to be considered as well .
Would a more loaded and lighter bridge be equal compensation for a less loaded and heavier bridge .
An example can be found in auto racing where lighter vehicles are loaded through aerodynamics that effectively make parts of the vehicle heavier/more loaded .
Convert this to a guitar where a lighter bridge can , through loading , do what the heavier bridge does with less loading . Heavier loading can be obtained through greater break angle , thicker strings , longer scale , combinations of these ...........
Think in terms of frequency and resonance.

There are 3 main variables to resonance: mass, stiffness, and size.
High mass=low frequency
High stiffness=high frequency
Large size=low frequency

So if you lighten up on the bridge, frequency will go up. But if you reduce the torque on the soundboard (lower string tension, or setting the neck angle for a lower target string height), then you can loosen up the bracing without the soundboard going S-shaped over time, and get the frequency back down that way. It's a good trick for small guitars, which naturally tend toward high frequency.

In general, light-and-loose guitars are louder than stiff-and-heavy. But louder means that any unevenness in the frequency response will be more obvious, so it's harder to make them sound "good".

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Originally Posted by Ned Milburn View Post
In general, the lighter the bridge, the less sustain you'll have. The heavier the bridge, the more sustain. (Try brass bridge pins and brass saddle for an experiment.) The tone that has become acceptable and desired is one that calls for a standard range of bridge mass. This is part of the issue.
Right... Ervin Somogyi calls this "type 1 sustain". But there's also "type 2 sustain" provided by a low damping live back, which acts as a flywheel. So you can have your cake and eat it too.

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Originally Posted by Otterhound View Post
Must that weight be contained totally within the physical bridge itself ?
No, but I think the location is important. For example, dead weight added by a thick layer of finish over the whole soundboard will probably have a different effect than dead weight added by brass bridge pins. But the saddle, pins, and bridge plate can be considered part of the bridge, since they're all in about the same place and more or less rigidly connected to eachother.
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  #17  
Old 12-21-2017, 12:00 PM
LouieAtienza LouieAtienza is offline
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Originally Posted by hat View Post
A lot of the detrimental effects of string tension and torque/loading is transferred directly to the top plate, through the bridge, and bridge plate. What if part of that loading and stress could be re-applied to the x braces directly? I am thinking of a cross brace located where the bridge pins are located - a brace that has it's ends resting on top of the main X braces. that way, the pull is not on the top directly, but rather acting directly on the main braces, which then cause the top to deflect and vibrate.
There is a brace that links the X brace legs, it is the bridge itself.

One of the reasons pinless bridges are used is to facilitate lattice bracing, which can be directly under where the bridge would be, possibly causing interference with bridge pins. While the bracing can be arranged that theee is clearance, it remives freedom of placement
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  #18  
Old 12-21-2017, 12:08 PM
hat hat is offline
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Originally Posted by LouieAtienza View Post
There is a brace that links the X brace legs, it is the bridge itself.

One of the reasons pinless bridges are used is to facilitate lattice bracing, which can be directly under where the bridge would be, possibly causing interference with bridge pins. While the bracing can be arranged that theee is clearance, it remives freedom of placement
right, but the bridge is on the top, or stressor side of the braces. Part of the cause of bridge peeling, and top warping. I am thinking of moving that stress to the underneath side (far side) or the most reinforced side of the top.
Think of it like this, you have a plastic bucket full of water. Will you try to pick it up by grasping the lid, or by the bottom of the bucket? ( I know, poor analogy)
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  #19  
Old 12-21-2017, 12:09 PM
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Quote:
Originally Posted by Otterhound View Post
Both and all of them .
Parsing this into separate items is not where I am going on this .
I'll try again .
What is the reason for a bridge to be 3/8" or 11/32" thick/deep behind where the saddle/s are located ?
The height of strings off the top needs to be about 1/2". The saddle needs to have about 1/8" projection above the bridge. The bridge needs to be 1/2"-1/8"= 3/8" thick.

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Originally Posted by Otterhound View Post
Must that weight be contained totally within the physical bridge itself ?
No.

I see where you're going, and I do believe that you may be able to make a lighter than normal bridge by using a lexan plate to anchor the strings.

There are other ways. I slant the saddle back about 8, which greatly reduces the load the saddle puts on the front of the slot, so the slot can be closer to the front of the bridge. I angle the pins back at about the same angle. The bridge is full height for the front half, the back half angles from full height to about 1/16" thick. The last bridge I made was madrose and weighed less than 20 grams.
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  #20  
Old 12-21-2017, 01:27 PM
redir redir is offline
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Quote:
Originally Posted by Otterhound View Post
Both and all of them .
Parsing this into separate items is not where I am going on this .
I'll try again .
What is the reason for a bridge to be 3/8" or 11/32" thick/deep behind where the saddle/s are located ?
Ah, I got ya now. I think John answered your question but I start the tapering off right at the bridge pin holes and feather down to about 1/8th inch.

I remember reading about a bridge design in Symogi's book, I forgot the luthier now, but he designed he bridge to be more or less an I-Beam laying on it's side such that the I-beam flanges were the front and rear of the bridge and the web was in the middle. This was done mostly on the wings of course but the idea was to loose weight while retaining strength.
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  #21  
Old 12-21-2017, 01:29 PM
LouieAtienza LouieAtienza is offline
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Originally Posted by hat View Post
right, but the bridge is on the top, or stressor side of the braces. Part of the cause of bridge peeling, and top warping. I am thinking of moving that stress to the underneath side (far side) or the most reinforced side of the top.
Think of it like this, you have a plastic bucket full of water. Will you try to pick it up by grasping the lid, or by the bottom of the bucket? ( I know, poor analogy)
While you will reduce deflection of the bridge, I don't believe it's all that necessary - or even desirable, especially if you're after that vintage Martin sound (that most folks are after.) I don't even mind if my top gets a little bulge. In fact I build my tops almost perfectly flat (and VERY slightly ramp the upper bout past the UTB)... no solera, no dome, no radius dish for the top. Sure, it's a great look when a top has zero hump behind the bridge and looks like a perfect dome. But for my ears it doesn't produce a sound I prefer. Also I might be crazy, but I find the guitar plays stiffer (but can handle heavier gauge strings) when the bridge area is overly stiff.

I've retopped a couple plywood top guitars (and have one now) where the bridge had rotated at least 20-25 degrees, warping the top - and the bridge didn't release. Peel is not the problem if you glued the bridge right, and you have sufficient support under the bridge. It could be just 1-2mm past the back of the bridge if you want. Of course if you designed a flexible bridge plate that's another story.
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  #22  
Old 12-21-2017, 01:30 PM
LouieAtienza LouieAtienza is offline
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Quote:
Originally Posted by redir View Post
Ah, I got ya now. I think John answered your question but I start the tapering off right at the bridge pin holes and feather down to about 1/8th inch.

I remember reading about a bridge design in Symogi's book, I forgot the luthier now, but he designed he bridge to be more or less an I-Beam laying on it's side such that the I-beam flanges were the front and rear of the bridge and the web was in the middle. This was done mostly on the wings of course but the idea was to loose weight while retaining strength.
Gilbert...
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  #23  
Old 12-21-2017, 06:01 PM
Otterhound Otterhound is offline
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Quote:
Originally Posted by Rodger Knox View Post
The height of strings off the top needs to be about 1/2". The saddle needs to have about 1/8" projection above the bridge. The bridge needs to be 1/2"-1/8"= 3/8" thick.



No.

I see where you're going, and I do believe that you may be able to make a lighter than normal bridge by using a lexan plate to anchor the strings.

There are other ways. I slant the saddle back about 8, which greatly reduces the load the saddle puts on the front of the slot, so the slot can be closer to the front of the bridge. I angle the pins back at about the same angle. The bridge is full height for the front half, the back half angles from full height to about 1/16" thick. The last bridge I made was madrose and weighed less than 20 grams.
Very close .
By lowering the point on the top of the bridge where the string emerge , there will be less leverage creating shear on the bridge . Combine that with a bridge shape that can enhance strength and the ability to place mass/weight directly under the bridge and easily change the shape and the mass/weight of the anchoring piece , in my case lexan , it should be possible to reduce shear and tune by mass/weight via the bridge area .
Since there is no requirement of a surface for pins to anchor to like in a conventional bridge , bridge design can be optimized for stiffness with no real sacrifice . As long as the bridge can handle the load created by the saddle/s it's shape and mass/weight can be modified as needed or desired .
I made this pinless bridge to a design that it actually does not need because that design is based on a pinned bridge . I could have greatly lessened the effect of shear by making the lever much shorter .
Because mass/weight can now be added or taken away as desired , I can add to the bass side and/or limit/lessen the treble or any combination that I choose via the plate under the bridge plate that anchors the strings . By having the strings anchored to this plate , it makes the plate an integral part of the bridge .
Please excuse me if I am using inaccurate terminology .
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  #24  
Old 12-21-2017, 07:57 PM
John Arnold John Arnold is offline
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Notwithstanding the inaccurate terminology, your logic is not sound.

Quote:
By lowering the point on the top of the bridge where the string emerge , there will be less leverage creating shear on the bridge.
That is not true. All you are doing by lowering the string exit point is increasing the string break angle across the saddle, which will result in more side force on the saddle. The 'leverage' you speak of (torque, actually) is created by the string height off the top. The only way to reduce this torque is to reduce string tension or lower the string height.
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  #25  
Old 12-21-2017, 08:13 PM
Otterhound Otterhound is offline
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Quote:
Originally Posted by John Arnold View Post
Notwithstanding the inaccurate terminology, your logic is not sound.



That is not true. All you are doing by lowering the string exit point is increasing the string break angle across the saddle, which will result in more side force on the saddle. The 'leverage' you speak of (torque, actually) is created by the string height off the top. The only way to reduce this torque is to reduce string tension or lower the string height.
Let me see if I have this correctly .
A string travels straight upward from a fixed point and is under tension .
At a point , that string changes direction . At the point that the string changes direction there are no forces in play .
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  #26  
Old 12-21-2017, 09:15 PM
Otterhound Otterhound is offline
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OK .
Bridge plate thickness .125
Top thickness .125
Bridge thickness .375
Total .625

Bridge plate thickness .125
Top thickness .125
Bridge thickness .150
Total .400
While these are random numbers that mirror real world numbers , I am using them to try to show my point .
Will these 2 setups have identical forces acting on them given that saddles height , string anchor point and string tension are identical ? I say no .
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  #27  
Old 12-21-2017, 09:42 PM
LouieAtienza LouieAtienza is offline
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I believe, regardless of how the bridge is shaped, you can diagram any bridge by its base length, height at top of saddle (relative to top of the soundboard), and distance (average) from front of bridge to saddle. I postulate, that if the interface between bridge and saddle is strong enough, for bridges of equal "triangular" diagram, it doesn't really matter much where the string is anchored as far as how the bridge affects the top, because the length behind the bridge is so short that the string at that length acts as a rigid bar, and any difference in stretch would be negligible.
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  #28  
Old 12-21-2017, 10:50 PM
runamuck runamuck is offline
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Quote:
Originally Posted by Otterhound View Post
OK .
Bridge plate thickness .125
Top thickness .125
Bridge thickness .375
Total .625

Bridge plate thickness .125
Top thickness .125
Bridge thickness .150
Total .400
While these are random numbers that mirror real world numbers , I am using them to try to show my point .
Will these 2 setups have identical forces acting on them given that saddles height , string anchor point and string tension are identical ? I say no .
I think you're wrong. For a thought experiment, imagine a bridge an inch thick compared to a bridge a foot thick . The distance the string travels vertically is irrelevant until it leaves at X angle.
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  #29  
Old 12-22-2017, 12:10 AM
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Bruce Sexauer Bruce Sexauer is offline
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Otterhound: You appear to be confusing shear with torsion (twisting). Shear forces will remain the same as they are dependent on string tension, which does not change. Torsion is a function of leverage and can be loosely defined, in terms of the bridge, by the length of the base in relation to the height of the saddle off the top. I.e.: 1 3/8" x 1/2", which is typical in my work. Perhaps counter-intuitively, it doesn't make a lot of difference whether the bridge is pins or non-pins. The conventional bridge nearly everybody uses is rigid enough that it is best thought of as a solid unit including the saddle and the bridge pins AND the strings from the saddle to the ball end. By extension, the top and bridge plate directly under the footprint of the bridge are part of the mass equation, but perhaps less so of the torsional equation, and not at all of the shear equation.

The important point here is to think of the bridge (from the side) as a solid triangular geometric form with a specific variable footprint, depending on design.

The problem with lowering the height is that since the shear does not change, the footprint cannot be diminished, and the top structure must be able to hold the tension, while at the same time the torsion has been reduced below the level required to drive the top. The up shot is that the guitar may act overbuilt, sound thin, and lack volume. . . or so I'd expect.

I have written of this concept before and taken some criticism, but it is how I think of it and it has served me well.

Also, your suggested bridge plate is a bit thick IMO. I believe few go over .1", and I find .075" very adequate.

This thread has proven more interesting that I first expected.
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  #30  
Old 12-22-2017, 12:29 AM
charles Tauber charles Tauber is offline
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Diagrams of what Bruce stated.



I'll repeat this one from my response in your other thread. (From http://www.mimf.com/phpbb/viewtopic....=1126&start=20)


Last edited by charles Tauber; 12-22-2017 at 09:16 PM.
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