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Laminated Cello Bridge to Avoid Warping


Brad Dorsey
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On another bridge thread, Dwight Brown said:

"A maple bridge with a laminate in the middle might be interesting to stabilize bridges from warping. Especially student ‘cello bridges which were the bane of my existence as a school orchestra director!"

We have all seen warped bridges, and they are especially a problem on student cellos.

My first thought was that Dwight's idea is interesting.  My next thought was that it wouldn't work.  A laminate in the middle would lie along the neutral axis of the bridge, where it wouldn't be subject to either tension or compression, so it wouldn't act as a reinforcement.

Is my analysis correct?

In trying to imagine how a warp-free bridge could be designed, I imagined a bridge with carbon fibers running vertically on the outer faces of both sides.  I assume that when a bridge warps one side is subject to tension and the other to compression.  So whichever way the bridge tried to warp, the fibers on one side would resist the tension on that side, preventing warpage.

Does that make sense?

Maybe not, because maybe when a bridge warps it is entirely due to the concave side being compressed and not at all to the convex side lengthening.

Am I over-thinking this?

And the carbon fibers would make fitting the feet and cutting the height difficult, and they would make planing the thickness impossible.

How would you design a warp-free cello bridge?

 

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I'm not especially qualified to answer this, but your your idea that it would work on the outside of the bridge but not inside doesn't make sense to me. For one thing, whatever is left inside is now the inside laminate. You're looking for a stiff material resistant to bending that also works accoustically. There also would be no need to run it through the feet. Probably better to use a traditional bridge and keep it perpendicular. If you end up with a bad bridge get a better one. Granted, my experience is with fiddles and not cellos.

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7 hours ago, Brad Dorsey said:

On another bridge thread, Dwight Brown said:

"A maple bridge with a laminate in the middle might be interesting to stabilize bridges from warping. Especially student ‘cello bridges which were the bane of my existence as a school orchestra director!"

We have all seen warped bridges, and they are especially a problem on student cellos.

My first thought was that Dwight's idea is interesting.  My next thought was that it wouldn't work.  A laminate in the middle would lie along the neutral axis of the bridge, where it wouldn't be subject to either tension or compression, so it wouldn't act as a reinforcement.

Is my analysis correct?

In trying to imagine how a warp-free bridge could be designed, I imagined a bridge with carbon fibers running vertically on the outer faces of both sides.  I assume that when a bridge warps one side is subject to tension and the other to compression.  So whichever way the bridge tried to warp, the fibers on one side would resist the tension on that side, preventing warpage.

Does that make sense?

Maybe not, because maybe when a bridge warps it is entirely due to the concave side being compressed and not at all to the convex side lengthening.

Am I over-thinking this?

And the carbon fibers would make fitting the feet and cutting the height difficult, and they would make planing the thickness impossible.

How would you design a warp-free cello bridge?

 

I think that your analysis is pretty close. Here's a thought. How about applying some carbon fibers AFTER the bridge is trimmed and fitted. Rather than putting carbon fiber over the whole faces, what about adding some strips a carbon tow (thin ribbon, like you see in woven fabric), front and back? The stuff is really strong, and it might not take much to do it.

Excuse my mouse drawing skills, but something like this:

cellobridge.jpg

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13 hours ago, Brad Dorsey said:

My first thought was that Dwight's idea is interesting.  My next thought was that it wouldn't work.  A laminate in the middle would lie along the neutral axis of the bridge, where it wouldn't be subject to either tension or compression, so it wouldn't act as a reinforcement.

Why would it have to be in the middle? It seems to me the tailpiece-side face (in compression) is the weak spot, and adding a layer of wood on that side with the grain parallel to the compression might help. 

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6 hours ago, glebert said:

Why would it have to be in the middle? It seems to me the tailpiece-side face (in compression) is the weak spot, and adding a layer of wood on that side with the grain parallel to the compression might help. 

Cello bridges warp in both directions, so any warp preventative would need to have front-to-back symmetry.

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21 hours ago, Brad Dorsey said:

>

My first thought was that Dwight's idea is interesting.  My next thought was that it wouldn't work.  A laminate in the middle would lie along the neutral axis of the bridge, where it wouldn't be subject to either tension or compression, so it wouldn't act as a reinforcement.

Is my analysis correct?

In trying to imagine how a warp-free bridge could be designed, I imagined a bridge with carbon fibers running vertically on the outer faces of both sides.  I assume that when a bridge warps one side is subject to tension and the other to compression.  So whichever way the bridge tried to warp, the fibers on one side would resist the tension on that side, preventing warpage.

Does that make sense?

 

 

Yes, that is correct.  The carbon fibers should be on the outside surfaces to prevent bending to the front or back.  

I've made a very light balsa wood bridge that had the unidirectional carbon fiber tape on the outside surfaces with a vertical fiber direction.  I thought it worked well but apparently the VSA judges didn't like it. 

The traditional maple bridges have the grain going in the horizontal direction with a low bending stiffness which is the worst way of avoiding bending in the front or back directions.  There must be an acoustical reason for this choice that is more important than bridge deformation.

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23 hours ago, Brad Dorsey said:

On another bridge thread, Dwight Brown said:

"A maple bridge with a laminate in the middle might be interesting to stabilize bridges from warping. Especially student ‘cello bridges which were the bane of my existence as a school orchestra director!"

We have all seen warped bridges, and they are especially a problem on student cellos.

My first thought was that Dwight's idea is interesting.  My next thought was that it wouldn't work.  A laminate in the middle would lie along the neutral axis of the bridge, where it wouldn't be subject to either tension or compression, so it wouldn't act as a reinforcement.

Is my analysis correct?

In trying to imagine how a warp-free bridge could be designed, I imagined a bridge with carbon fibers running vertically on the outer faces of both sides.  I assume that when a bridge warps one side is subject to tension and the other to compression.  So whichever way the bridge tried to warp, the fibers on one side would resist the tension on that side, preventing warpage.

Does that make sense?

Maybe not, because maybe when a bridge warps it is entirely due to the concave side being compressed and not at all to the convex side lengthening.

Am I over-thinking this?

And the carbon fibers would make fitting the feet and cutting the height difficult, and they would make planing the thickness impossible.

How would you design a warp-free cello bridge?

 

Like this, with 2mm carbon fiber rods.Tried and tested. Never warps, no negative effect on the sound. Detailed description how to do it in the Strad magazine, April 2021.904DFF2C-AF4E-4C14-B95C-103FD240A521.thumb.jpeg.a93ecce6c7e6febf1b3c8c99913f4e78.jpegB2A57F49-F86E-43A3-B51D-E8D5EEA5D35D.thumb.jpeg.2c4b84dbecf1b4d956be2721090919b4.jpeg

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18 hours ago, Don Noon said:

I'd go with the basic design, but use higher density maple, and torrify it.  Torrefied maple ribs are really tough to bend, so it seems this should work, and it's not terribly complicated.

Good bridge maple is already a kind of torrefied, the reason why the blanks are not white. 
 

This helps to stabilize the wood but is no recipe for musicians who don’t look regularly at the bridge and pull it back in the right position when necessary. 

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13 hours ago, jacobsaunders said:

Last night, I dreamt of going to a meeting of the VÖG (Austrian vm assn.) after having introduced plywood cello bridges to the Austrian market. The piss-taking was of such an intensity that I woke up with a shudder:)

Sounds like Austrian violin makers assassination. :lol:

Plywood bridges are too heavy and therefore don’t sound. 

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2 minutes ago, Brad Dorsey said:

Does it work?

Very well. Needs initially a bit training. I drill from the top of the bridge because, no matter how, the drill does not go through perfectly on the same level. 
 

Tried the same on violin bridges but the success rate is too low with thin drills in thin material.

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11 hours ago, Brad Dorsey said:

Do you do this to all your cello bridges?

For my own cellos, yes. (The joke here is that I don’t make cellos:D)

For clients I have a reasonable surcharge for the ‘magerarenai’ (jap: unbendable) bridge and try to convince my clients to choose it because it saves A LOT OF MONEY long term. Currently 50 percent of clients go for it. 

My attempts to offer it as an afterwards reinforcement to an existing bridge didn’t work well. Technically it is too difficult to drill a hole in a surface which has just a little more width than the diameter of the hole. 

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