Warped Bridge Woes...

[Andrew]

Hey guys, Im in the middle of a bridge reglue on a somewhat local (to me) handcrafted acoustic, quite a nice guitar. The guitar had been subjected to some undesirable temperatures at the hands of a previous owner, I suspect, and the bridge began to pull up at the back edge as will happen. Anyway the bridge came off without issue. Upon removal it was obvious that the bridge had cupped across the grain. I tried FFs method of submerging the bridge in boiling water as he described it on FRETS.COM, to no avail. This is the second time Ive tried it and the second time it didnt work for me. So heres my first question: if/when this does not work, what is to be done? Are the only options sanding the bottom flat or replacing the bridge? In this case sanding would be objectionable to me with the amount of cupping that needs to be corrected - the middle of the bridge wings would end up substantially thinner than the edges.

Issue number 2: in attempting to address this cupping I boiled the bridge again then clamped it to a flat piece of wood with cauls on the top that are concave enough so as to press the edges down, hoping to coax it back into shape. I got some minimal results after a couple hours clamped up, so I tried again. Except this time I over did it and clamped to hard, as indicated by a small crack sound. In the following picture you will see a hairline crack running from the bottom treble side of the saddle slot to about halfway out the bridge wing. Is this bridge pooched? Can this crack be glued? Normally I would say no, but this crack still closes up invisibly with very little finger pressure, so I must ask. And even if it can be glued, what then is to be done about the cupping?

Any help would be great, I really wasnt expecting to be making a new bridge here, but if I have to eat my mistake on this one, so be it.

[Andrew]

The crack

[Robbie Collins]

Am I seeing this correctly ... the wing of the bridge is concave?

I think you might have more luck with continuous heat, like a silicon heating blanket set to 250°f. 

I think you can wick some #10 SM superglue into that crack after flexing it open. Might want to do it from the bottom to keep glue out of the saddle slot. Keep a q-tip and acetone handy in case.

[Andrew]

The wings of the bridge sweep up from the front edge about 3/16", if thats what you mean. I think that exacerbated the warp, or at least makes it harder to correct. And the warp results in the tops of the wings being concave. The crack doesnt seem to go to the bottom of the bridge, at least I cant see it. Ill check that out in the morning. I could certainly close it up tight with thin superglue, but that area is under a lot of stress as Dave has stated below. If I didnt also have the warp to deal with Id feel more certain about gluing such a fine crack.

[Dave Richard]

Given the warp, and the crack, I would make a new one. That cracked area is under a lot of stress, and it would be frustrating to have it open up again( once strung up) after all that work.

Dave

[Russell Vance]

Hi Andrew,

It's a policy issue: the bridge was probably not able to be saved because of the bad set it had taken.  Appropriate methods of repair failed to correct the problem and a last ditch effort to save the bridge resulted in damage.  However, the bridge was cactus anyway so it was going in the bin if it didn't respond.  You did not make a mistake here so do not "eat" someone else's problem. 

A motor mechanic would not do work for free if he found the loose fanbelt he quoted for was actually a broken crankshaft.  If you do charity work for your customers they will expect charity work in the future, which doesn't pay the bills.

So the customer should be advised of the situation and billed for the manufacture of a new bridge.

Both Professionals and tradesmen do not assume responsibility for an existing problem that cannot be fixed by normal process.  It is the customers responsibility to accept unforeseen problems that are pre-existant, regardless of a quote or indication made beforehand.  

Rusty.

[Andrew]

I just meant Ill have to eat it in the sense that it wasnt something I expected to need to do, and I have no ebony blanks on hand, so Ill have to order some, wait three days, a day or so to make another bridge, etc. A pain since Im not set up to make bridges quickly. This particular customer has an "extended guitar budget" as he says and is very easy to work with. I just dont like being caught off guard so Im a bit grumpy.

[David Farmer]

Andrew, I think I would bail on the bridge because the crack goes into the saddle slot and it's off the guitar anyway. I don't like the boil method because of all the water that must be removed before re-gluing and I never had much luck with it.

In the future a method that has worked for me is a 1/2" thick piece of aluminum that I shaped in a 25' hollow form so it is domed. I heat the aluminum up to 350 degrees on a hot plate. wet the bridge with a sponge and clamp. The aluminum cauls on the wings have cork on the bottom and the wood block is arched so it puts pressure on the outside edges.  You can feel the wood softening as you clamp so you won't crack it. It's like bending a side and it's fast. unclamp in a few hours. When I made the first domed caul I figured I would make a more arched one in a 15' hollow form if 25' wasn't enough. I've never needed to.

[Joshua Levin-Epstein]

If the guitar is local (to you) why not contact the maker for a new bridge? He/She is probably tooled up to turn out parts more easily than you doing a one-off.

[Andrew]

Well, local as in three hours from here, and Im not sure what his methods are, so if the bridge wasnt made with drill guides for the pin holes then a direct replacement might not be an exact fit, especially with it being an irregular shaped bridge, and I would still have to rout the saddle slot, so Id feel better if I made it here. Might as well improve that skill anyway.

David, i like your aluminum plate thing, Ill have to add that to my 'tools to make' list. Rougly how much pressure do you apply when you clamp a bridge on it?

[David Farmer]

I bring the pressure down over maybe 30 seconds depending on how warped it is. Once it's down making contact there's no need for more pressure. The rigid set up allows you to feel how much resistance there is. The heat really softens it. It's a little exciting when the moist bridge hits the aluminum for just a few seconds. It can kind of sizzle around but it quickly pulls the heat out of the block.

I actually like the challenge of making replica bridges. It hones the eye and hand skills.

[Andrew]

Indeed. After a nights sleep Im no longer frustrated over it, should be an interesting challenge.

It sounds like your hot caul works pretty well. Ill definitely be making one in the future.

[Paul Breen]

I'm using the same method as David to flatten bridges, works quite well. If you have a local machine shop, it would be a good source for some Aluminum scrap. I have been using mostly 3/4" stock but keep 1/2" around for this or that as well. Cuts easily in my band saw and is useful other heating applications too. I have a D93 Martin in for a lifting/warped bridge R&R and took these images a few days ago. (*beware if you work on one of these, it's a Poly finish!)

Same as David, I wet the bridge and clamp it onto the Aluminum that has been heated to 350 degrees and let it sit until cold. The 3/4" thickness shown holds the heat longer than a thinner stock but obviously 1/2" is working just fine for David. 1/4" cork contact cemented onto plywood makes great clamping pads. I'll lay up a few square feet of it and then cut out pieces as needed.

I have made heater cauls out of Aluminum for bridges, bridge plates, finger board extensions, heal caps and just about anything else where you might use a heating blanket. Unlike the heater blanket, these heaters are indestructible. A hot plate, one of these little thermometers pictured and some Aluminum scrap and you're in business.

Good luck with the bridge re-do, that really is your best recourse as the others have mentioned.