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All,

I did a repair for a guy the other day and it's turned interesting. The bridge cracked through the pin holes. Mike Larrivee told the customer that it would be cheaper for him to have a local luthier repair it then to ship it back which of course is true. So he sent him a replacement bridge and I got her all set up. Now the question is why did the bridge crack? This is for warranty information. It was suspected that the guitar had dried out which could cause such a crack to happen. However I see none of the tell tail signs of drying out, no fret ends sticking out, binding and rosette are still flush, etc... There is finish checking though I'm not so sure that is something that happens when a guitar dries out but rather when it gets cold.

What I suspected immediately after inspecting the bridge was that it was not glued on properly. I took off the bridge with heat and a knife, a clean dis-assembly. The finish was fairly thick, I wish I measured it but I'd say it was 1/64th. There was about a 1mm border of finish around the perimeter of the bridge and bare wood elsewhere in the center. That means that the bridge was 'floating' over top of a bare wood surface equal to the thickness of the finish.

So I got to thinking that this glue joint could have creeped under stress as two different rates, the bridge to finish and the bridge to wood surface area's causing the bridge to give way.

That, or it was just a bad piece of ebony.

But when I glue a bridge I make sure that I have only wood to wood contact, no finish at all.

I just want to know from you all if first of all this is a common practice in gluing a bridge and second if my thinking seems reasonable. It's an extremely nice guitar, plays great and sounds wonderful BTW.

I re-glued a Collings bridge this summer that was also glued over a lip of finish with no relief cut in the bridge. I was really surprised because the rest of the guitar was put together so well.

That is certainly a potential cause of glue failure but I don't see how it could cause a split. Those splits just happen because there's a lot of force there and not a lot of wood. I suppose humidity could contribute if you had a bridge that shrank and pins that didn't. And ebony does move a lot.

At least they sent you a bridge! It's my understanding that the Martin warrantee for that calls for super glue in the split.

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JF my friend if you check out my web site you will see a small pic on the home page of a bridge reglue on a Laravee parlor. Same deal, very nice guitar, looks very well made, sounded great once I repaired it. I do work for a local Laravee dealer so he sends me his repairs.

This guitar had the bridge lift, also had about 1/8" of thick finish inside the bridge foot print and no ledge was routed on the bridge bottom... This is exactly what I described in the other current thread about gluing on bridges. A number of factories just smash/clamp the bridge over the finish that overlaps the bridge's foot print and hope for the best....

How I repair these is to cut the finish back so it's either not under the bridge or if I leave some I route a ledge around the bridge so that I have clean wood-to-wood contact.

I once asked David Collins about when there is tear-out to some degree how much wood-to-wood contact is a "best practice" when regluing a bridge. His answer was about 85% wood-to-wood contact is the minimum in his opinion. So that's what I shoot for too or more. And again this is for damaged tops and bridge reglues not new instruments.

Also on some of the Laravees that I have reglued bridges on and there have been several now I am noticing that the saddles are pretty high in the neighborhood of .6" measured from the bottom of the low e to the top at the face of the bridge. This makes a loud guitar but also is a lot of torque on the saddle and can lead to a split bridge. I have seen this happen on a Gallagher too that I repaired. Just a thought - if the action is high and the saddle much over .5" that could have contributed to the bridge split/lifting. Of course dryness as you suspected earlier is always our enemy.

And even though others have very good luck forcing the bridge to fit a top with clamps I won't do this on my own guitars or repairs. Instead I want the bridge to fit perfectly prior to gluing.

Bridge pins at thier worst are wedges. If six pins are in a line and close together they can generate a bit of force especially if they are forced. This usually happens with guitars that have slotted pins and the bridge is not slotted and ramped at the entrance. Some folks who don,t understand try to force the pins no matter what,not the only reason for failure but a big factor. Just to add a bit more if the holes are not reamed all the force can be focused on the top face of the bridge compared to reamed holes which spread the force over the whole depth of bridge and bridge plate. Just MHO of course.
Tom

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

I just reglue 2 Larivee bridges also.
No cracks-just big gaps between the bridge & top.
They flew off the top very easily!
There was a bunch of finish there!
Just NOT a good glue joint!

Cracks between the pin holes can be caused by using different size pins than the guitar was set up for-without reaming to fit .
Bad glue joint.
Bad string ramps that are not a soft curve or radius.
Forcing the pins in when the string ball &windings are not seating.

Mike

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Mike Collins

Look inside the guitar with a mirror. Are the ball ends of the strings pulling through the top to the underside of the bridge? You might have a worn bridge plate.

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Old growth, shmold growth!

i really like this original post, because,
the standard now is to glue the bridge on, after the finish.
i'm sure doing this properly is the best way to go, for a flawless finish.
i prefer to glue the bridge on first, then finish.
i'd rather have the bridge heck-for-stout glued on,
and the finish sealing the edges, and have a less than perfect finish around the bridge.
why? because the 2 most important things to me are, a great sounding box,
that won't break down.
moo, (my own opinion).

Ok thanks for your replies. I did indeed check out the guitar thoroughly. The balls ends of the strings were seated nicely on the bridge patch and the pins were not tight. I cut keyholes in the new bridge to make it even better. I'll chalk this one up to "stuff happens" and suggest that it should be a warranted repair.

FWIW on my guitars I make a tape foot print slightly smaller then the bridge and then finish the guitar. That way when I remove the tape I only need to scrape back a little bit of finish for a perfect wood/wood fit. And really it only takes ten minutes.

How thick did the glue appear after removal? If it was indeed bridging 1/64" do to the finish it could certainly play a role in the failure. I would also be curious to know if most luthiers and repair techs are wiping the gluing surface with acetone to remove oils and tannic acids that will impair adhesion.

Hugh I don't think I could get an accurate measurement of the glue thickness. Once removed with heat it's just a melted up mess. I didn't think it was necessary to treat ebony in that manor but maybe it should be?