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Bridge Experiment
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Author:  fryovanni [ Tue Nov 28, 2006 4:16 pm ]
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I mentioned in another thread that I would post up a couple pics of a bridge design I am experimenting with. The saddle height was not adjusted fully, and this is not a finished guitar(it is a test rig at this point). So forgive the sloppy look.

For what it is worth the weight of the bridge and stop piece was 34 grams at install(African Blackwood). The stop piece aligns with the main X-braces and the outside edges of the bridge also are aligned on the braces.


Since taking the pics I have set the action, played the guitar for a short period. From the short period it has been in action it has performed well, but of course it will take time to tell if it will settle in poorly. It does seem pretty responsive. Anyhow here are the pics.


Be kind it is my first post and it is just an experiment(I am not making for or selling this guitar to anyone).





Peace,Rich
Author:  JohnAbercrombie [ Tue Nov 28, 2006 4:42 pm ]
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Rich-
I missed your original post, but that's a very creative approach- thinking 'outside the box' (something I find pretty difficult to do most of the time).

I'm interested in your guess about how much of the strain of the strings is taken by the stop piece, and how much by the sharp bend at the back of the bridge?

BTW, that's about the nicest-looking test jig I've seen.

John
Author:  fryovanni [ Tue Nov 28, 2006 4:50 pm ]
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Hesh, First I have to say I have been watching your builds for a while. I love your work.

     The front piece and bridge set on the main X braces. The tip of the front piece is on the X crossing.

Peace,Rich

John,
    That was the one thing I had no idea how to quantify when I was dreaming this up in CAD. I did the best I could to create the smoothest radius as the stings wrap under(I had a real fear that binding could make for tuning issues). I can say that the tension is near full(a string should have equal tension throughout it's length barring something binds it) between the bridge and stop piece. The upward angle from the front of the bridge to the stop piece is doing it's job and is lifting the front of the bridge. I have had no issues keeping it in tune(again I take that as a positive sign there is not a binding problem). The concept was to "balance" the bridge and try to keep it in a more neutral state(as opposed to constantly fighting the twisting action). Another fear I had was how much would this effect vibration created by the twisting action of the bridge while playing. Since I can't really quantify that. All I can say is that it seems to be responcive, has good volume, gets loud when played hard, but it is very hard to overdrive the top.fryovanni39050.0447337963
Author:  Jocafa [ Tue Nov 28, 2006 5:34 pm ]
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I dig it. I love it when you guys tinker and experiment :)
Author:  Scott van Linge [ Wed Nov 29, 2006 2:54 am ]
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Rich,

Very nice design. It certainly will get energy into the X brace for distribution. The engineering would seem to be countering the normal downward force above the bridge, too.

It's too bad you felt it necessary to request niceness, but I understand...

Scott
Author:  LanceK [ Wed Nov 29, 2006 3:02 am ]
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Interesting!


Good stuff, thanks for sharing Rich!



Author:  crazymanmichael [ Wed Nov 29, 2006 3:09 am ]
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it is interesting that this is the second bridge posted in the past week wherein the strings wrap through the bridge in this fashion, though the anchor on this one is different.

whilst this one would be less likely to pull off due to its larger footprint, i still think the rotational moment on the bridge is problematic, with the same sort of consequences postulated in the earlier instance.

it will be interesting to see whether they come to pass.crazymanmichael39050.4652777778
Author:  gozierdt [ Wed Nov 29, 2006 3:21 am ]
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I'm looking at it as a Mechanical Engineer. What the design does is change the force distribution. Normally the bridge sees a couple (rotation force) that is trying to lift the rear of the bridge. This force is resisted by the bridge and the top, which deform by the back end of the bridge lifting slightly, and the front end dropping. In this thread's design the bridge is seeing a straight pull equal to twice the tension in all the strings (each string pulls twice on the bridge, once below from the stop block, once above from the nut/headstock). The force causes a shear force to be set up in the bridge connection to the top. Since the net of the forces is still slightly above the top surface, a rotation force is also created. The net reaction may not be very much different from a standard bridge, because while the net force is closer to the top in this design, the force is twice as big. I suspect the net effect is not very much different.

The stop block will see a force pulling towards the heel, located very close to the top. The fact that the block is located right over the X-brace intersection means it will easily resist the rotation force, but the smaller surface area means the shear forces at the top/block interface are larger than a standard bridge by the ratio of the surface area of the two. Looks to me like the stop block has about 1/4 of the area of a standard bridge, so the shear is 4X as much. Not knowing typical shear strengths in this joint, I don't know how close it would be to failure.

I don't mean to be negative by my comments. I like thinking outside the box, and the design is creative, and looks very nice to me.

Author:  Mike Mahar [ Wed Nov 29, 2006 3:51 am ]
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What are the acoustic reasons for this bridge? I mean, what effect are you trying to have on the sound? If it is just a change for looks, that's cool. Changing things just to make a visual difference is a fine thing to do. I just want to know if you have some underlying acoustic theory you are trying to test.
Author:  Don Williams [ Wed Nov 29, 2006 3:53 am ]
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Let me say that I like the look, and as John mentioned, it is thinking outside the box. I think I've seen someone else do something similar, although I can't remember where (Jeff Babicz?).
I also think Gene is very right in that the shear force on the front piece is substantial. If this fails, that is where it will do so. Perhaps you can make that section bigger (wider, deeper), and reduce the size of the bottom section.
Good thinking! Keep those ideas coming...



Don Williams39050.495787037
Author:  Mike Mahar [ Wed Nov 29, 2006 4:06 am ]
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Since the front piece overlaps the X brace, you could pin it right through the top into the brace. It is so close to the junction of the X that I doubt that it would have any effect on the sound.
Author:  martinedwards [ Wed Nov 29, 2006 4:40 am ]
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I'm with the engineers on this one.

a pinned bridge pulls on the whole top/bridge/bridgeplate sandwich. this takes the disadvantages of a pinless bridge (which my luthier tutor Sam Irwin of Lowden says is an AWFUL idea) and multiplies them (even though it does look cool!!!
Author:  Howard Klepper [ Wed Nov 29, 2006 5:40 am ]
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[QUOTE=gozierdt] I'm looking at it as a Mechanical Engineer. In this thread's design the bridge is seeing a straight pull equal to twice the tension in all the strings (each string pulls twice on the bridge, once below from the stop block, once above from the nut/headstock).
[/QUOTE]

I"m not a Mechanical Engineer, but this can't be right. The pull of the strings is not doubled by wrapping around 180? and going to a fixed anchor. The bridge sees half the pull from each side--the rest gets passed on to the string on the other side, so it only gets the tension of the strings once. Think of a rope with a weight on it going around a pulley to a fixed anchor.
Author:  JBreault [ Wed Nov 29, 2006 6:01 am ]
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Howard, that is a good way to think about it...especially with the anchor so far away from the bridge.

Rich, I too like the look of your bridge. It is a very interesting concept.
Author:  MSpencer [ Wed Nov 29, 2006 6:04 am ]
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Cool!

Mike
Author:  fryovanni [ Wed Nov 29, 2006 6:26 am ]
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Thank you for all of your input. I will certainly be taking notes here.

As far as why I am trying this. It has nothing to do with looks(personally I don't prefer this look over traditional pinned bridges). I have tried to explain a bit of my thought process in the first post and responce to John. Basically the main focus I had in doing this was " The concept was to "balance" the bridge and try to keep it in a more neutral state". By getting the bridge to rest closer to a neutral position(without trying to twist). This hopefully will help avoid deformation and posiibly allow for lighter bracing. I had also felt like the sound board would be able to more accurately and easily accept a vibrating wave if it had more equal resistance in the upward and downward motion.

As far as the Pull. The pull on the bridge will not be greater from what I make of this. The top piece or stop piece does have a smaller foot print and it will take more force per. unit of surface area. However... and this was just my thinking(I could be wrong), It will not be subjected to the directional forces that can chip away at a bridges glue joint. I could be very wrong, and it could fail miserably(a screw could remedy that as you suggested).

Peace,Rich
Author:  letseatpaste [ Wed Nov 29, 2006 6:31 am ]
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'Nother engineer type here... (I've got limited luthier experience but I think I have a decent handle on physics... If I'm wrong, speak up)

This bridge would work like a pulley system, and the force on the bridge would have to be double the force of the strings. The force on where the string's ball ends anchor would be equal to the force of the strings pull.

If the bridge only saw half the pull of the strings from each side... you'd have pretty floppy buzzy strings on the playing end.

I'd agree with Martin, I think this doubles the disadvantage of a pinless bridge... The disadvantage being that instead of the string ball ends pulling up against the bridge plate on the inside of the guitar, your bridge/top glue joint has to be able to withstand the shear and rotational forces directly from the strings.
Author:  fryovanni [ Wed Nov 29, 2006 7:39 am ]
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I think I follow what your saying. The soundboard will see 100% of the string pull. The Bridge glue joint on a pinned bridge will see some of the pull and the bridge plate will see some of the pull(some acting on the glue joint some acting on the bridge plate below the glue joint). I think the oint of confusion(for me at least) was the doubling of pulling force. You still have the same amount of force pulling on the soundboard. It is just how much force is seen by the glue joint, and it would have to be 100% in my case.

I realised this would be the case. Again though my idea was to have the forces acting on the soundboard be more linear without losing the hold on the saddle. In this design you recieve downward force as with most pinned, plus additional "clamping" force as the strings try to raise the front of the bridge(in hopes that would improve the saddle/string coupling).

I suppose additional measures could be taken to reinforce the glue joint. At this point I see nothing indicating it is going to fail(but it is early). Generally failure starts at the rear of the bridge. If this bridge minimizes the rotational force. It is possible that the bridges glue joint would have enough strength to handle additional shear. I guess that is why I am testing. Physics and theory are a good start, but real world testing is the only true test of a theory.

Peace,Rich
Author:  Don Williams [ Wed Nov 29, 2006 7:54 am ]
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I gotta go dig out my old Statics textbook...
Author:  Howard Klepper [ Wed Nov 29, 2006 8:00 am ]
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Hmmm. I was thinking of the bridge as a movable pulley. Now I'm thinking it should be seen as a fixed one, so it would see twice the force. I was wrong before.
Author:  letseatpaste [ Wed Nov 29, 2006 8:13 am ]
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Wikipedia's helpful for refreshers on stuff like this (I looked before I posted to make sure I was thinking about it correctly)...

Wikipedia Pulleys page
Author:  Serge Poirier [ Wed Nov 29, 2006 8:45 am ]
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Cool looking bridge, that's for sure!
Author:  Cocephus [ Wed Nov 29, 2006 11:25 am ]
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Rich, I admire your courage in posting your bridge. In a craft so steeped in tradition and adhering to proven methods, most of us are reluctant to step forward and show what we come up with in our own little worlds for fear of ridicule.
We can`t go through life with blinders on, can we?
Author:  Mike Dotson [ Wed Nov 29, 2006 11:26 am ]
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It's not round, all the sound's gonna get stuck inside
it! (I'm not an engineer, but I like trains a lot)

Seriously, an interesting idea and ya never know till
ya try! Mike Dotson39050.8103240741
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