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baroquecello

Straightening a cello bridge

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I acquired a cello for student use. The bridge is quite warped, and, although in the long run I will have a new one made, I would like to straighten it. I've done this in the past using a water boiler, holding the bridge in the steam. however, this has the disadvantage that the pores of the wood open and the wood will look decidedly different afterwards. Also, I've heard that steam hurts the cell structure, leaving the wood less strength. So I wad wondering if there exists an alternative method for making the wood bendable, without steam. Would heating in an oven work? And, if yes, what temperature should I use? I believe I only want to soften the lignin, nothing more, right? Thank you for any advise! 

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To straighten a bridge, I just leave the bridge floating on a saucer of water overnight. The next day I cramp the bridge on a flat board (with some aluminium foil in-between, so it doesn‘t stick). On the third day you can re-touch it with some 600 sandpaper, and a rag damp with linseed oil.

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2 hours ago, jacobsaunders said:

To straighten a bridge, I just leave the bridge floating on a saucer of water overnight. The next day I cramp the bridge on a flat board (with some aluminium foil in-between, so it doesn‘t stick). On the third day you can re-touch it with some 600 sandpaper, and a rag damp with linseed oil.

Floating on a saucer of water: does this mean the bridge is placed into a bowl of water to be soaked? Put directly into the water?

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4 minutes ago, BassClef said:

Floating on a saucer of water: does this mean the bridge is placed into a bowl of water to be soaked? Put directly into the water?

Yes, just let it swim on the surface of the water, all day and night, and let it dry at it‘s own pace afterwards for 24 hours +. Lest haste, more speed.

 Bridges float, they don't sink.

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If the bridge is badly warped, usually one side is concave and the other is convex.  I float warped bridges with the concave side down, because expanding that side will straighten the bridge.  Usually the top (convex) side does not even get wet.  I find that floating the bridge concave side down for an hour usually straightens it, but I usually clamp it to a flat surface to dry overnight.

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I wet a paper towel, fold it to the dimensions needed to correct the problem as locally as necessary, put that on the microwave turntable with the bridge's concavity appropriately sitting on the wet towel, and nuke it in 15 second increments until the problem straightens out (which happens most of the time but not 100%). Then a few seconds of nuke of the bridge standing dries it out, and back it goes.

Warning: without adding water, a bridge will burn before you know it, and from the inside out, so by the time it's smoking, it's too late.

When this doesn't work, I follow by bending against a hotplate with a1/4" sheet of aluminum on it. 

Additionally, I have heard, many times, that a bridge that's straightened is weak and will bend again. I regard this as TOTAL NONSENSE. Bridges curl for two reasons, both usually correctable. The first is that the player has not properly kept on top of pulling it back, and that is not anything about the quality of the bridge. The second is that the feet were improperly cut, or the arching has tilted forward (very commonly excessively so on new instruments) and the resting angle of the bridge has become wrong relative to the top. In either case, recutting the feet so that the bridge sits at the correct angle to the top will correct the problem permanently. If you want the fix to be permanent, you MUST correct this or the bridge will bend again. But this, also, is not a bridge defect. Grotesquely cutting a bridge wrong (flat on the back, highly rounded on the front) will also usually result in a warped bridge, but again, not the bridge's problem. I have seen flat-back bridges that bend back at the top, then forward at the legs, in an s-curve! Again, not the bridge's fault, but of the person who cut it.

If you don't recut the feet, and do it right, the bridge will fail. If you have consistent bridge failures, you need to look at how you are cutting bridges. We have quite a few cellos in our subsidiary's rental program, and I don't think I have yet had to replace a bridge because of "failure" other than for the above reasons.

Regarding the resting angle of the bridge, I don't know how many people are aware that when a cello is put to tension the arching invariably tilts forward just a bit, towards the upper eyes, so the angle you cut with no stress doesn't stay. So cutting just a couple of degrees of backwards lean right from the start accounts for this in advance. The other thing that happens is that the post presses up on the back of the foot on that side immediately changing the fit, resulting in a twisting pressure of the legs relative to each other. I correct for that; you may or may not want to for your own reasons. You can satisfy yourself on this question by tilting the bridge backwards slightly and watching which foot lifts first on the front side, then doing the same in the other direction. 

Regarding the OP, there's no way to touch a bridge with water and not have the grain puff up a bit. The fix as noted, is to resand the side that was wet. Not too much to ask, I don't think.

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I had that problem. My luthier boiled the bridge for under ten minutes, and then stood it upright in the sun. He said it would dry straight, and it did,  but it warped again pretty quickly when I put it on again about a year later.

oh well...

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For a quick fix, I soak the bridge just a few minutes in a bowl of water. Then heat a skillet on low, lay the bridge convex side down, and use some utensil to press down flat, take it out when it stops steaming. Repeat until the bridge is flat. Usually a max of 3 times does the trick.

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10 hours ago, Michael Darnton said:

I wet a paper towel, fold it to the dimensions needed to correct the problem as locally as necessary, put that on the microwave turntable with the bridge's concavity appropriately sitting on the wet towel, and nuke it in 15 second increments until the problem straightens out (which happens most of the time but not 100%). Then a few seconds of nuke of the bridge standing dries it out, and back it goes.

Warning: without adding water, a bridge will burn before you know it, and from the inside out, so by the time it's smoking, it's too late.

When this doesn't work, I follow by bending against a hotplate with a1/4" sheet of aluminum on it. 

Additionally, I have heard, many times, that a bridge that's straightened is weak and will bend again. I regard this as TOTAL NONSENSE. 

“High temperatures may result in some permanent loss of strength, the extent depending on the temperature reached, the duration of heating, the heat source, and the moisture content of the wood.”

— Understanding Wood: A Craftsman's Guide to Wood Technology by R. Bruce Hoadley

“TOTAL NONSENSE” Does not square with available data, and it is my experience that bridges warp quicker after straightening this way if no other remedy is attempted.  However, heating wood without the moisture to close to ignition momentarily does not show reduced strength...... try quickly heating the bridge and bending it dry......not in a microwave!  This of course cannot fix the reduced strength from the compression of the wood.

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3 hours ago, Jerry Pasewicz said:

“High temperatures may result in some permanent loss of strength, the extent depending on the temperature reached, the duration of heating, the heat source, and the moisture content of the wood.”

— Understanding Wood: A Craftsman's Guide to Wood Technology by R. Bruce Hoadley

“TOTAL NONSENSE” Does not square with available data, and it is my experience that bridges warp quicker after straightening this way if no other remedy is attempted.  However, heating wood without the moisture to close to ignition momentarily does not show reduced strength...... try quickly heating the bridge and bending it dry......not in a microwave!  This of course cannot fix the reduced strength from the compression of the wood.

One doesn‘t need any heat at all to straighten a cello bridge. Blimey, you will be dovetailing it next!

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3 hours ago, jacobsaunders said:

One doesn‘t need any heat at all to straighten a cello bridge. Blimey, you will be dovetailing it next!

Yes Jacob, I suppose “one doesn’t need any heat” if the goal is to turn a 10 minute job into a 3 day ordeal.  I guess my brain is not set up to think of ways to take as much time as possible to do as little as possible.

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1 hour ago, Jerry Pasewicz said:

Yes Jacob, I suppose “one doesn’t need any heat” if the goal is to turn a 10 minute job into a 3 day ordeal.  I guess my brain is not set up to think of ways to take as much time as possible to do as little as possible.

 

On 12/30/2019 at 10:22 AM, jacobsaunders said:

To straighten a bridge, I just leave the bridge floating on a saucer of water overnight. The next day I cramp the bridge on a flat board (with some aluminium foil in-between, so it doesn‘t stick). On the third day you can re-touch it with some 600 sandpaper, and a rag damp with linseed oil.

Jacob's method would seem to take about 3 minutes - it's just spread over 3 days.

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The only "available evidence" I have in this regard is actual bridges showing that the best wood can warp if the bridge is cut wrong or not maintained and the worst wood can stay straight if the bridge is cut right and properly maintained even after heat straightening, so any theoretical evaluation of wood strength has very little to do with the issue, in my experience. This basically removes theoretical measurements from the question.

On the other hand. I have seen lots of violin bridges collapse straight down, which brings up some more questions. But not cello bridges. I'm in the middle of getting a handle on this for violins, but the evidence so far is indicating cutting errors, in that I'm seeing this in supposedly good wood from supposedly good shops, consistently. The examples I've seen I am pretty sure have never been subjected to straightening.

Actually, this brings up another question: I know that a lot of shops cook bridges as part of the cutting process to give them a bit of color. IF heating wood damages wood . . . but the people who do this maintain just the opposite. . . .

 

. . . an after-shower afterthought: If someone wants to attack the problem of wood integrity, they'd better not be using Aubert Deluxe bridges, which in my opinion exhibit more wood damage from whatever process they use than I could do with heat. But I think that quite a few people have decided that's not an issue, in that case, so I'm really not worried about heat.

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19 minutes ago, Michael Darnton said:

The only "available evidence" I have in this regard is actual bridges showing that the best wood can warp if the bridge is cut wrong or not maintained and the worst wood can stay straight if the bridge is cut right and properly maintained even after heat straightening, so any theoretical evaluation of wood strength has very little to do with the issue, in my experience. This basically removes theoretical measurements from the question.

On the other hand. I have seen lots of violin bridges collapse straight down, which brings up some more questions. But not cello bridges. I'm in the middle of getting a handle on this for violins, but the evidence so far is indicating cutting errors, in that I'm seeing this in supposedly good wood from supposedly good shops, consistently. The examples I've seen I am pretty sure have never been subjected to straightening.

Actually, this brings up another question: I know that a lot of shops cook bridges as part of the cutting process to give them a bit of color. IF heating wood damages wood . . . but the people who do this maintain just the opposite. . . .

I agree, if the bridge is cut correctly and maintained than none of the issues regarding strength is relevant. The strength issue has to do with the cellular structure collapsing and then never being able to fully "un-collapse.  The dry heat for cooking bridges might be an issue, although more research would be needed to be relevant to what we do.  As far as violin bridges, I have been working with this issue for a while because of bridges sinking at the e string kidney.  Moving the center-line between the kidneys toward the e string to equalize the downward pressure would certainly do the trick, but I do not know if having the pressure balanced at the kidneys is a good thing or a bad thing. 

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3 hours ago, martin swan said:

 

Jacob's method would seem to take about 3 minutes - it's just spread over 3 days.

Most high-level players I have encountered would vastly prefer to have their favorite instrument back in three hours, versus three days, if the faster job can be done without compromise.

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11 minutes ago, David Burgess said:

Most high-level players I have encountered would vastly prefer to have their favorite instrument back in three hours, versus three days, if the faster job can be done without compromise.

Tough luck

 

PS. the OP question was about a school cello

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11 minutes ago, David Burgess said:

Most high-level players I have encountered would vastly prefer to have their favorite instrument back in three hours

Most high level players dont let their bridge get bent.

Actually I can think of a violist who played quite well with a bent bridge. But I have never let a bridge get bent in my lifetime of playing. But I compulsively look at my instruments (setups)

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25 minutes ago, David Burgess said:

Most high-level players I have encountered would vastly prefer to have their favorite instrument back in three hours, versus three days, if the faster job can be done without compromise.

Depends what you're lending them while they wait ...:lol:

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It really depends on your definition of "high level" as well. I run into plenty of competent, full-time, professional players who are scared to pull their bridge back. Once you've snapped a cello bridge trying to pull it back . . . well, it's a serious negative reinforcement for a lot of people. But many of these also come in regularly for check-ups, and I pull their bridge back as part of that, so it doesn't really matter as much. More often I see problems from the non-serious, amateur musicians whose last visit to a violin shop was in 1993 when their parents bought them their instrument.

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If the player doesn't keep the bridge straight, it will warp, no matter how well feet are adjusted or how it is cut. It's just a question of mechanical forces. (Or a cello bridge would need to be 20mm thick at the feet and something like 7mm thick at the top)

Anyway bridges warping again after straightening were a good reason for me to erase the 'straighten bridge' item from my repair menu. If I can't give a warranty for at least a year it's not worth doing it. (Just my personal philosophy)

To prevent bending from the beginning as good as possible I make sure that 1. the 'feet resistance' in North South direction can be felt clearly when cutting a bridge and that 2. the notches are super 'greased' so that strings can't tear the upper portion of the bridge to one direction too easily. 

For customers I cut a cardboard fitted to the back side of the bridge so that the user can measure when the bridge starts to lean to one side even a fraction of a millimeter. I show how to move it back to 'zero position' and tell the customer to stop by if he/she is scared to do it. One of the few things I do for free (only on my own bridges)

I wished music schools for professionals would teach at least some fundamental of violin maintenance including bridge maintenance. 

Otherwise it seems that bridge material is not what it has been in the past, maybe caused by climate changes. Worldwide we can see as well a tendency going to slimmer bridges. Both contributing to the fact that we see more often warped bridges. 

(Besides, I had long time ago a cellist who asked me to cut a bridge with both sides completely flat. This bridge would have warped within weeks but didn't  because he was very meticulous to keep it straight. He was the type of guy who would dust off any dirt on his car even after a short drive)

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