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Bridge Design
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Author:  Darryl Young [ Thu Jan 17, 2013 9:20 pm ]
Post subject:  Bridge Design
I'm making a bridge for the 00 I'm building that is the same size as a pyramid bridge but I plan to thin the wings so they will have no pyramid. I've no idea what you call this style bridge, sorry.

Anyhow, I'm curious to hear your thoughts on how the thickness of the wings of the bridge affects the vibration modes and tone of the guitar. Also the length of the bridge likely comes into play as a 6" long bridge spans a larger percentage of the width of the lower bout rt han it would on a dreadnaught.

So I would appreciate you sharing your thoughts and/or maybe hearing how thing you leave the wings on your bridges.......or what standard (if any) Martin has used.
Author:  meddlingfool [ Thu Jan 17, 2013 11:09 pm ]
Post subject:  Re: Bridge Design
I believe it's call a 'rectangle'....

Yuk yuk. I leave my wings at 3/32 because I've never found a rationale for doing anything else.
Author:  nyazzip [ Fri Jan 18, 2013 12:45 am ]
Post subject:  Re: Bridge Design
i am totally, 100% unqualified to make any assertations about acoustic instruments, but i wonder if having more mass on the bass wing, and having a very thin treble wing, might be a good thing. kind of like a violin, and the "bass bar" that runs longitudinally on the "bass" side of the top. it might make for a more focused, balanced tone across the range of frequencies
Author:  Clinchriver [ Fri Jan 18, 2013 5:51 am ]
Post subject:  Re: Bridge Design
I made a pyramid bridge for my 14 fret size O, classic design (they look good) fun to make and the guitar sounds great. I used persimmon, the bridge weighed 15 grams. Gibson used a plain rectangle on many of their smaller guitars. I probably go around .095/.100
Author:  Alan Carruth [ Fri Jan 18, 2013 11:41 am ]
Post subject:  Re: Bridge Design
It's a little hard to say exactly what effects the thickness and mass of the bridge wings will have on a steel string guitar with X bracing. On a fan braced top shaving the wings can alter the sound because they tend to flex a lot when the top vibrates in it's 'cross tripole' resonant mode, but you often don't see that mode on X braced tops. I'm not aware of much work on the acoustical effects of the bridge wings on steel strings, so here's your chance to advance science! ;)
Author:  Darryl Young [ Fri Jan 18, 2013 7:28 pm ]
Post subject:  Re: Bridge Design
Thanks for the info provided. Since this is a Norman Blkake style with a 12 fret neck on a 14 fret body, the bridge is further down toward the middle of the lower bout. So only the front edge of bridge sits on top of the X brace arms and that is out right at the end of the bridge wings. This has me wondering if I should leave the wings thicker/stiffer than normal.
Author:  Tom West [ Sat Jan 19, 2013 9:12 am ]
Post subject:  Re: Bridge Design
Darryl: I will tell you what I have been tending towards. Minimum bridge 1"by 6" with the wings about .100"-.125". I do the wings on the table saw with a 8" blade which gives a 4" radius. I think the normal radius on say a Martin belly bridge is 2". The bigger radius tends to give a bit more stiffness to the wings. Some folks almost eliminate the radius entirely. The thinking is that one wants to drive the X rather than sit between the branches of the X just going up and down. My example is greatly exagerated of course but is just to give credance to the design.
Tom
Author:  Darryl Young [ Sat Jan 19, 2013 11:04 pm ]
Post subject:  Re: Bridge Design
Thanks for that info Tom.
Author:  John Arnold [ Sun Jan 20, 2013 12:06 am ]
Post subject:  Re: Bridge Design
I call it a straight bridge.
Quote:
So only the front edge of bridge sits on top of the X brace arms and that is out right at the end of the bridge wings. This has me wondering if I should leave the wings thicker/stiffer than normal.

I haven't studied the Norman Blake Models (other than to play Norman's at his house), but I have a strong aversion to any bracing design where the bottom corners of the bridge do not reach the X-braces. On those that do not, there is a strong tendency for a crease developing at each end of the bridge, with an exaggerated bulge below the bridge.
My rule of thumb is to make the bridge wings thicker on forward-X braced guitars (up to about 0.120"), and thinner on rear-X braced guitars (as thin as 0.085").
Another 'trick' to make the bridge stiffer is to shorten the scooped portion on each end.
Quote:
I do the wings on the table saw with a 8" blade which gives a 4" radius. I think the normal radius on say a Martin belly bridge is 2". The bigger radius tends to give a bit more stiffness to the wings.

Martin bridges have a 1" radius, which I generate with a 2" diameter sanding drum mounted in the drill press. I also use 3" sanding drums, for a 1 1/2" radius.
Author:  Tom West [ Sun Jan 20, 2013 6:27 am ]
Post subject:  Re: Bridge Design
John: Thanks for jumping in with the correct radius on the Martin bridges. For folks that are not aware John has a vast knowledge of Martin guitars.He also posts lots of good data on the UMGF.
Tom
Author:  Darryl Young [ Sun Jan 20, 2013 8:53 am ]
Post subject:  Re: Re: Bridge Design
Thanks for this information John, very helpful.

I'm not totally comfortable with the concept either so I have a backup plan. The front edge of the bridge does sit over the X brace arms. For the back of the bridge, I made PMTE brace that goes between X brace arms along the back of the bridge plate. I made it out of Brazillian Rosewood and fitted it before closing the box. If I have issues, I'll glue this brace in place.

John Arnold wrote:
I call it a straight bridge.
Quote:
So only the front edge of bridge sits on top of the X brace arms and that is out right at the end of the bridge wings. This has me wondering if I should leave the wings thicker/stiffer than normal.

I haven't studied the Norman Blake Models (other than to play Norman's at his house), but I have a strong aversion to any bracing design where the bottom corners of the bridge do not reach the X-braces. On those that do not, there is a strong tendency for a crease developing at each end of the bridge, with an exaggerated bulge below the bridge.
My rule of thumb is to make the bridge wings thicker on forward-X braced guitars (up to about 0.120"), and thinner on rear-X braced guitars (as thin as 0.085").
Another 'trick' to make the bridge stiffer is to shorten the scooped portion on each end.
Quote:
I do the wings on the table saw with a 8" blade which gives a 4" radius. I think the normal radius on say a Martin belly bridge is 2". The bigger radius tends to give a bit more stiffness to the wings.

Martin bridges have a 1" radius, which I generate with a 2" diameter sanding drum mounted in the drill press. I also use 3" sanding drums, for a 1 1/2" radius.
Author:  Darryl Young [ Sun Jan 20, 2013 3:47 pm ]
Post subject:  Re: Bridge Design
John, I'm curious what did you think about the sound of Norman Blake's 000?
Author:  John Arnold [ Mon Jan 21, 2013 4:34 pm ]
Post subject:  Re: Bridge Design
Quote:
I made PMTE brace that goes between X brace arms along the back of the bridge plate. I made it out of Brazillian Rosewood and fitted it before closing the box. If I have issues, I'll glue this brace in place.

Good idea. I haven't done a PMTE, but I am familiar with the principal.
Quote:
John, I'm curious what did you think about the sound of Norman Blake's 000?

It was not as impressive as I was expecting. The problem was that I had already played a number of vintage Martins and Gibsons that day, and the Martin NB just sounded like a new guitar that had not been played very much.
Author:  Darryl Young [ Mon Jan 21, 2013 5:11 pm ]
Post subject:  Re: Bridge Design
To give credit where credit is due, the PMTE idea came from Mario.
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