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Bridge Warp After Removal
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Author:  klooker [ Tue Feb 06, 2018 8:25 pm ]
Post subject:  Bridge Warp After Removal
I had to pull the bridge on my current build - Martin belly style, BRW.

Before I glued it, I had radiused it so that the underside was concave to match the guitar top.

After pulling it with with heat, it's slightly convex on the underside. I suspect this is because the top side dried out more from the heat & shrank.

So those of you experienced with repairs, what do I do? Make a new bridge, let this one sit out for a few days to see if it returns to it's original shape? idunno

Thanks in advance.

Kevin Looker
Author:  Chris Pile [ Tue Feb 06, 2018 9:07 pm ]
Post subject:  Re: Bridge Warp After Removal
Wouldn't hurt to try bending it or re-hydrating it..... Experiment a little. You might save it, and have a new technique.
Author:  Hesh [ Tue Feb 06, 2018 11:35 pm ]
Post subject:  Re: Bridge Warp After Removal
Yep they curl in the removal process.

Flatten it on your belt sander and know you platen so you know where the flattest areas are.

Two schools of thought on the next step:

1). Use the biggest, baddest clamp that you have to clamp that puppy back on

2). We after flattening the bridge scrape the bottom to fit the dome of the top so that the wings and all other places are completely down with only finger tip pressure. We use clamp(s) but we look for an excellent fit first.

The rabbit thing is optional, we do it and value it, so does Collings, Taylor and many small builders but it's still optional.

Lastly watch the thickness of the wings when you flatten the bridge. If they were too thin to begin with this can be an issue on bridge designs that taper away to very little.
Author:  Clay S. [ Wed Feb 07, 2018 6:28 am ]
Post subject:  Re: Bridge Warp After Removal
You could clamp it to a caul that matches the shape it should be and let it rest for a week. This might help it regain it's shape and limit how much you have to rework it.
Author:  Greg Maxwell [ Wed Feb 07, 2018 8:42 am ]
Post subject:  Re: Bridge Warp After Removal
Here's a tip from Frets.com: Soak it in boiling water for a couple minutes then clamp flat until dry. I used this technique a few days ago on a badly twisted bridge from a 1918 Martin and it took about 85% of the distortion out. The rest I had to sand out.
Author:  Woodie G [ Wed Feb 07, 2018 8:54 am ]
Post subject:  Re: Bridge Warp After Removal
There are bridges we really do not want to significantly alter, so we gently heat to 160-170 degrees F or so, then clamp to a dead-flat surface and let it cool evenly (foil cover and some preheating of the granite helps prevent thermal shock). This can help minimize the curl and reduce leveling and top-of-wing reshaping. The temptation to shim under the center of the wing and apply pressure on the front and rear edges to rebend should be tempered with the knowledge that this can lead to some spectacular cracks.

This sort of heat can also dry the bridge enough to open cracks and cause previous repairs to fail, so having a moisture source in the oven can help - a ramekin filled with wet paper towels does the job here.
Author:  klooker [ Wed Feb 07, 2018 10:44 am ]
Post subject:  Re: Bridge Warp After Removal
Thanks folks!

I thought this would be a common problem.

Now I get to order one of those StewMac bridge plate repair things to repair the other half of the problem, $$$ gaah
Author:  david farmer [ Wed Feb 07, 2018 11:13 am ]
Post subject:  Re: Bridge Warp After Removal
I never had much luck with wetting and drying flat. Re-heating works great for me though. I think it's more like re-bending sides. You have to get to the re-forming temp.
I heat a chunk of 1/2" aluminum sanded convex in a 25' dish to 300-350, scrape the glue off the bottom, moisten, then clamp. A couple of pieces of wood put the pressure on the outside edges and the the bridge relaxes down just like bending. works great if there is no height to spare or if the distortion is large.
Author:  SteveSmith [ Wed Feb 07, 2018 11:41 am ]
Post subject:  Re: Bridge Warp After Removal
klooker wrote:
Thanks folks!

I thought this would be a common problem.

Now I get to order one of those StewMac bridge plate repair things to repair the other half of the problem, $$$ gaah


That bridge plate saver does work and where I can use it, it saves a lot of time/money.
Author:  Mike Collins [ Wed Feb 07, 2018 4:14 pm ]
Post subject:  Re: Bridge Warp After Removal
I clamp a large block of brass(can be any metal) 6" x 2"(clean any glue residue from the bridge!
I heat it with a propane torch -sprits some water on it to know if it hot!
Clamp the bridge on this block - walk away for hours-the bridge will be flat on the
gluing surface-now just readjust the curve you need to the bridge gluing service.

works every time!!!
Mike [:Y:]
Author:  Mike Collins [ Wed Feb 07, 2018 4:17 pm ]
Post subject:  Re: Bridge Warp After Removal
I clamp a large block of brass(can be any metal) 6" x 2"(clean any glue residue from the bridge!
I heat it with a propane torch -sprits some water on it to know if it hot!
Clamp the bridge on this block - walk away for hours-the bridge will be flat on the
gluing surface-now just readjust the curve you need to the bridge gluing service.

works every time!!!
if you working on a classical bridge with finish on it-be careful !
Mike [:Y:]
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