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I'm wondering what the pros/cons of using a rectangle bridge on a dreadnaught guitar would be. I've seen plenty of dreads with both styles of bridge. For those who build with the rectangle, what is your reasoning behind it? Do you do anything different with the bracing or bridge plate when using a rectangle bridge? What dimensions/weight do you aim for?

Looking forward to hearing some feedback on this subject. Teach me something!

Zac

I like rectangular bridges with light gauge strings. The lower mass is a bit more responsive.
The obvious disadvantage is less gluing surface, meaning it is more likely to lift with medium strings or a long scale.

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John

The gram weight is more important than the shape IMO. Heavier bridges dampen top vibration no matter what their shape is.

A rectangular bridge should be no more inclined to lift than a belly bridge, I should think, as the thinner rectangular shape is inclined to roll forward with the top torsion stress.

The string thickness shouldn't really matter with a pinned bridge as the strings don't directly pull on the bridge itself but rather catch against the bridge plate inside the guitar, since we're talking dreadnaughts, not classical. BTW classical bridges are typically rectangular WITH the strings pulling directly on them.

Often when bridges are lifting, it starts at the corners of the ends, when the top distorts to the degree that it forces the bridge to separate from the top, and the belly part of a belly bridge doesn't extend that far.

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Old growth, shmold growth!

Rectangular bridges are lighter.............more responsive..!
Tom

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A person who has never made a mistake has never made anything!!!

Interesting generalizations here. Personally, I think the material is just as critical to damping as size / shape. Ebony dampens more than rosewood, depending on the piece/species of rosewood. In general, there is a difference.

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"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

I use rectangle cause they're faster to make. 6"x1", 3/8" height after sanding the radius in the bottom which usually takes out 1/32"...

One question is would a heavy rectangle damp more than a light belly bridge? Say, if the rectangle weighed quite a bit more than the belly bridge which has a bigger footprint?

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Old growth, shmold growth!

Or even, if a belly bridge weighed identically to a smaller rectangle, would it damp more?

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Old growth, shmold growth!

Weight is the key to my mind. Not only in the bridge but also the entire top system. Only so much power in the strings, higher weight is harder to get into motion.
Tom

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A person who has never made a mistake has never made anything!!!

Wide flat things are harder to tip over than narrow tall things. The "back corners" of a belly bridge are removed from the area where the stress would be greatest - at the back of the bridge.
Martin developed the belly bridge when the heavier gauge steel strings became popular, (and for dreadnoughts they still are for many people) to avoid warranty work I've been told or read (Longworth?).
If I was building for bluegrass I think I'd use a belly bridge.

I agree, that's why I think bridges don't lift from torsion stress though.

Most of the time when I see a bridge lifting, belly or rectangle, it's one side or the other.

If you think about the type of stress, IE bellying up, it makes sense that the ends lift first. Bridges don't lift due to the torsion stress or the strings pulling on them (for pinned bridges) , but rather the torsion stress causes the top to bulge in the center, and the BULGE is what causes the bridge to lift. One or the other sides pops up first typically, at least in all the repairs I've seen. I've even seen bridges where both wings have popped up and the center, with the belly, is still attached.

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Old growth, shmold growth!

That makes sense, thanks.
Does a stiffer bridge, one without scalloped wings (ala somogyi), aid in preventing the top from bellying?

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We are all in the gutter but some of us are looking at guitars.

It seems to me they belly no matter what.

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Old growth, shmold growth!

Norman Blake is quoted as saying " Never trust a guitar without at least a little belly".
Tom

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A person who has never made a mistake has never made anything!!!

Precisely why I posed the question. I've seen a lot of bluegrass guitars with the rectangle bridge, including those built by some of our members here (Arnt Rian, grumpy) and I was hoping for some insight into why they use it. I like the clean look, and I'm wondering what the tonal differences may be as well. As Tom stated, "Rectangular bridges are lighter..........more responsive!". That interests me. If the big concern is that the bridge may lift, how much of this can be overcome by using sound technique when gluing it down (freshly scraped joint, proper matching of top radius to bridge bottom, etc.)?

Thank you all for your responses so far.

Zac

Hi Zac, I usually use rectangular bridges on my dreads. I glue them on with hot hide glue, and so far none have lifted, as far as I know. I've built them like that for at least 10 years, and most have medium strings, so I'm pretty confident about the stability. I don't make the tops of my guitars super thin (at least not in the middle), I use very stiff red spruce tops, and the scalloping isn't that drastic, so the bellying isn't too bad. I guess a narrower bridge will tend to tip more forward than a "deeper" bridge, so you have to keep that in mind with the rest of the structure. My standard wood for bridges is African blackwood, which is quite dense, so I like to make the bridges small to keep the weight down, the rectangular shape helps with that. I guess some of the inspiration for the narrow, light bridges come from the old Gibsons, which are some of my favourite sounding guitars. I also like the way my guitars sound with these bridges, I guess that is the main "why" I keep using them.

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Rian Gitar og Mandolin

A distinction without a difference. The bridge has torque on it from the strings. The greater the string tension and the greater the string height over the top, the greater the torque. The torque is the same...... whether the string is anchored underneath or tied on the bridge. The only difference is what happens when the back of the bridge pulls loose.


The bridge is a brace connecting the two X-braces, and a wider bridge is stiffer along its length. In other words, it is more resistant to bellying.
There is much precedent for using rectangular bridges on dreads with medium strings....just look at 1930's Gibsons. While most are short scale, there is the long scale AJ.
In other words, do whatever you like....just use good practice when gluing on a bridge. It is by far the most common glue joint to come apart.

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John

I don't think that's quite true.

If the strings are anchored to the bridgeplate, the only torque stress on the bridge is from the strings pushing forward against the saddle, and being anchored inside the guitar, squeezing the bridge to the top because the strings are also pressing DOWN..

That's a different stress than if the strings were pulling up against the actual bottom of the bridge AS WELL as pushing forward and down on the saddle. The lifting/torquing would be greater as the construct would become more of an actual BRIDGE lever. The torquing would be more concentrated on the wooden bridge piece rather than distributed across the top and bracing structures through the bridge plate contact.

I've seen lifting bridges from bulges on the former, I've seen entire bridges ripped clean off, taking some of the top with them, on the latter as the strings wore through the bridge plate and top, and started to pull directly on the bottom of the bridge. At that point the acceleration of the demise of the guitar is considerable.



The bellying occurs mostly BEHIND the bridge, with the part of the bulge extending under the bridge causing the lifting. Guitars with thinner tops and smaller lower face braces belly more, regardless of the bridge.

But I agree that the bridge is the most common glue joint to come apart.

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Old growth, shmold growth!

Thanks for weighing in, Arnt, you answered a lot of the questions I have. I've admired your instruments for quite some time. Have any of them made their way to the States? I'd love the chance to play one, I'm willing to bet they sound as good as they look!

Great discussion and i always wondered about some of the wild shaped bridges I've seen on many many guitars. Seems mostly aesthetic and given to heavy and dense designs which is a bit counter to the light bridge philosophy.

For those of you using a rectangular shaped bridge what are the typical dimensions you choose? I've built most all my bridges 1" x approx. 6" - 7" depending on 'X' location. I was wondering if a slightly wider, say 1 1/4", bridge might help stabilize that area a bit without going full belly.

On another note I've seen all kinds of shapes on some of the (others opinions) best sounding guitars in the world so maybe the importance of shape is overstated?

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Thank You and Best To All

I think overall weight is more important than the precise shape of the bridge.

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Old growth, shmold growth!

I have read from at least one great builder who likes low weight/large area bridges.

Not true. Torque on the bridge is only a function of the string height and string tension.

All you are describing is a different outcome when the bridge lifts. Before that happens, the torque (which is what causes the top to lift below the bridge and sink above the bridge) is the same......provided the string height and string tension are the same.

Torque produces equal and opposite forces on each side of the bridge. The reason that the tops on most steel string guitars do not sink an equal amount above the bridge is because the X-bracing is stiffer there in relation to the bridge.

6" by 1". I have made a few that were 6 1/4" long, and some Gibson style that were a bit narrower (15/16").

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John

There's more to it than that. the effect of the torque is different based on how and where the string is anchored, inside the guitar or directly on the wood of the bridge.

One levers the bridge piece more than the other.

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Old growth, shmold growth!

Right! That's why the bellying occurs behind the bridge.
Also, wood is elastic, the bulge behind and under the back of the bridge is actually stretched wood that has attained a new memory.

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Old growth, shmold growth!