bridge lifting off

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brad barron
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bridge lifting off

Post by brad barron »

Hi guys

I finished my first guitar about a month ago - it is fantastic. I built the Stewmac 000 kit with a LR Baggs ibeam and have been playing it all month. I am completely hooked and already planning the next build. Thx to the forum members that helped me with my nut issue - the bone dust / sg repair is working great.

However, .....

This morning I was playing and saw that the bridge is separating - the glue joint did not hold. I will reglue but am interested in tips and tricks to get a better bond before i do.

I used Titebond glue , brushed on to the bridge, and clamped in place with three cam clamps and hand made cauls. Let the glue dry for 24 hrs before unclamping. Also, the guitar has a french polish finish - i scraped it down with alcohol before gluing under the bridge to what looked like bare wood to my eye (and no more residue coming on the chisel i was scraping with).

Some questions in my mind

1) maybe more glue? I did have some squeezeout but not a terrible lot as i tried to minimize cleanup. Do i need to goop it on?
2) better clamping? My hand carved cauls fit well but not perfectly. Also, the clamps were almost too short so were a bit off center.
3) some other kind of cleanup before gluing?
4) I live in Beijing and it gets pretty dry in the winter. I do humidify the guitar room but it swings 30-50% RH as it is tough to control (have a few small cracks already - damn!)

Let me know your thougths and ideas. I am a but bummed but on the other hand, looking forward to tackling this. I can also post pics if it helps.

tx

brad

Also - what is the best way to get the bridge off without damaging the top? Thin knife and patience? Heat? I don't know with titebond.

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Mark Swanson
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Re: bridge lifting off

Post by Mark Swanson »

Heat is the best way to loosen the Titebond, then when it's hot and the glue begins to soften, work a thin blade under there, a little at a time. Patience here will help you. Make sure you protect your shellac finish, the shellac will also soften with the heat.
Then clean all the old glue off the surfaces. Make sure your fit is as good as you can get it, if there are gaps they will be the weak places in the bond because Titebond is not a good gap filler, it likes wood-to-wood contact.
If you have cracks and your room dries out then I suspect that you had a drying out event and that's what popped the bridge loose.
  • Mark Swanson, guitarist, MIMForum Staff

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Bob Gramann
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Re: bridge lifting off

Post by Bob Gramann »

Mark got in there while I typed. He said about what I did but I said it differently so I'll still post:

Wait a while to do anything until you get a few replies and understand what you want to do.

To remove a Titebond glued bridge, make a corrugated cardboard and foil mask to protect the finish around the bridge from heat, then heat the bridge with a small iron while carefully working a thin knife through the glue joint. Figure out the grain direction on each side of the top so that you don't carve into the top with the thin knife. Titebond will totally release with heat and patience and very little prying. If you get impatient, you risk lifting some top wood with the bridge.

To replace the bridge, first clean all of the glue from the bridge bottom and the footprint on the top. It's likely that some shellac remained and helped your joint to fail. It took me a while when I started to learn how to make the bridge fit perfectly. Now, I put a bridge-shaped piece of sticky-backed sandpaper on the bridge footprint. I mark the bottom of the bridge all over with pencil lines. I then sand the bottom of the bridge, with very short (1/4 inch) strokes until the pencil is sanded off everywhere. After I remove the sandpaper, I check the fit using a piece of paper as a feeler gauge (a piece of 20 pound copy paper is .003" thick). If I can't slide a paper edge under anywhere when I'm pressing the bridge to the top, I consider it a good fit. Over clamping can distort the bridge or guitar top shape and leave a gap. Test your clamping setup and pressure dry with the paper.

Humidity changes can make a perfectly fitted glue joint fail. The grain direction of the bridge is at right angles to the top. So, the top can move quite a bit across the grain while the bridge won't change it's length. When the movement is drastic, you're lucky when it's the bridge to top joint that fails. So, control the humidity.

Good luck.

Brad Heinzen
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Re: bridge lifting off

Post by Brad Heinzen »

When I'm removing the shellac from the bridge footprint prior to gluing, I use a sharp razor blade to scrape down to the bare wood. It sounds harder and scarier than it actually is, and you can get the surface of the top totally clean and ready for gluing without much effort. I'd bet that washing with alcohol didn't remove all the shellac.

Dick (DT) Trottier
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Re: bridge lifting off

Post by Dick (DT) Trottier »

Hi Brad,
Sand the underside of the bridge as well right before gluing. The glue will penetrate better.
Good luck...

Steve Senseney
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Re: bridge lifting off

Post by Steve Senseney »

I agree with all of the above, and would offer that all of us have had to reglue a bridge.

John Hamlett
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Re: bridge lifting off

Post by John Hamlett »

Did you do anything to the underside (glue surface) of the bridge before gluing it on? I ask because, especially with ebony, rosewood, and other dense woods, a freshly prepared glue surface (withing 15 minutes of gluing) is important for a good glue joint. If you didn't scrape, sand, or otherwise refresh the glue surface of the bridge and top right before gluing, there's a good chance that you did everything else right and the failure could have been entirely due to lack or preparation. If you did prep the surfaces right before gluing, ignore all that.
A tip for removing Titebond to clean up for re-gluing: http://de-gluegoo.com/

Alan Carruth
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Re: bridge lifting off

Post by Alan Carruth »

About the only thing I'd add is that it helps to get the bottom of the bridge _very slightly_ concave from the front to the back before you glue it down. You want to just barely see light in the middle when you hold a straightedge across it. Partly this is to get a 'sprung' joint, and partly it's to make up for the fact that the water in the glue makes the underside of the bridge swell a little, so that your flat dry surface becomes a convex one when the glue hits it.

It never hurts on critical joints to put glue on both surfaces. That way you _know_ it's there... Extra squeeze out is less of an issue than a lifting bridge.

Alan Carruth / Luthier

brad barron
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Re: bridge lifting off

Post by brad barron »

Outstanding advice guys. I did not prep the underside of the bridge. Maybe that plus poor clamping and a bit of humidity swing was enough to cause the issue. My brother is coming in a few weeks - ill have him bring a stewmac care kit with a longer throat clamp and ill reglue then.

Keep the ideas coming - it will be the end of the month before he is here and the next week is crazy busy so I have some more time.

Brad

Bill Snyder
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Re: bridge lifting off

Post by Bill Snyder »

Brad, do you have any hide glue. For bridges you might want to consider it to avoid problems with the joint creeping over time.

Michael Lewis
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Re: bridge lifting off

Post by Michael Lewis »

One clamp is not sufficient in my estimation. I generally use 3 bridge clamps, one at each end and one in the center of the bridge, and 2 spool clamps threaded through the outboard pin holes. The spool clamps help locate the bridge as well. I made those clamps from some bolts that just fit a 3/16" hole, and T nuts glued into the "spools". It really helps to have some plastic washers on them so things don't get glued in place. And always place clamping cauls inside and outside so you have something you can reef the clamps against without damaging the instrument.

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Mark Day
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Re: bridge lifting off

Post by Mark Day »

I'll give a second vote for hide glue as well. I'm pretty green and if I can do it, anyone can. My first from-scratch build was done using nothing but hide glue and that is all I have used since. If a joint does fail, at least you don't have to clean off all the old glue as hide glue "reactivates". Titebond may still be easier, but hide glue is no biggie. Like I said; if I can do it, anyone can.
On the humidity issue, I have what must amount to the cheapest humidifier out there. I have a couple bathtub toys that are made of some type of space age polymer foam that expands when you soak it. One is an octopus and the other is a stingray. You simply soak them until they grow to about twice their dry size, then wipe them dry and put them in your case. You know when they have dried out and need re-soaking because they shrink! It may sound stupid, but they work well, are probably a lot cheaper than official "guitar humidifiers" and they are good for a laugh when people see them. The sting ray goes in my vihuela case and the octopus goes in the 8 course lute case because 8 courses, octopus, 8...well alright enough of that...
Have fun building, and have fun in Beijing!

Zaijian!

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Woodrow Brackett
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Re: bridge lifting off

Post by Woodrow Brackett »

I'm an avid hot hide glue user, but if a bridge glued with titebond lifts in a month it would have lifted if glued with hide glue. I suspect there was some shellac left on the top under the bridge.
I need a signature here.

Chuck Tweedy
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Re: bridge lifting off

Post by Chuck Tweedy »

I'm with Woodrow - I think there was finish on the top still. Because of the OP's description of how he cleaned the bridge footprint with alcohol. That is just going to seal everything back up again.
Likes to drink Rosewood Juice

brad barron
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Re: bridge lifting off

Post by brad barron »

Chuck Tweedy wrote:I'm with Woodrow - I think there was finish on the top still. Because of the OP's description of how he cleaned the bridge footprint with alcohol. That is just going to seal everything back up again.
So - chuck - how would you clean the finish off? I used alcohol and a chisel - scraping and wiping on a cloth until there was no visible residue on the chisel. What would you do? Should I sand as well? Suggestions welcome.

brad barron
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Location: Beijing

Re: bridge lifting off

Post by brad barron »

Woodrow Brackett wrote:I'm an avid hot hide glue user, but if a bridge glued with titebond lifts in a month it would have lifted if glued with hide glue. I suspect there was some shellac left on the top under the bridge.
Ok. I admit that this is a bit weird but I have been a vegetarian for 25 years. Hide glue just seems wrong..... I realize this is heresy but my work is hide free.....

Steve Senseney
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Re: bridge lifting off

Post by Steve Senseney »

Being vegetarian, do you use shellac?

Alan Carruth
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Re: bridge lifting off

Post by Alan Carruth »

The best way to clean the top before gluing the bridge is to dry scrape it. As has been said, using alcohol just dissolves the shellac, and spreads it around on the surface, so you never get it all off. Remember that a glue joint is primarily a chemical bond, not a physical one.The glue bonds to both surfaces, and if there's anything on the surface that interferes with the bond, the joint is weaker. Also, if the 'surface energy' of the bridge bottom or the top is low the bond won't be as good. You get a high surface energy by removing a little bit of material, and the energy starts to drop off pretty quickly once you stop scraping. I was told the Forest Products Lab found that the best glue joints are produced when the pieces are glued within fifteen minutes of working the surfaces. Even if the glue can penetrate into the pores of the wood, the shellac is still preventing it from bonding properly. The glue itself is not as strong as the bond with the surface, which is why you want only a minimal amount of glue, between .002"-.006" in the glue line. Clamps are used to squeeze out the excess glue: if the parts fit well, you can get the glue out some other way, and they won't shift around, you don't need any clamps. I use 'rub joints' with HHG on fiddle and archtop plates all the time, and I've heard of folks who rub on the bridge with hide glue, although I've never tried that myself.

Alan Carruth / Luthier

Chuck Tweedy
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Re: bridge lifting off

Post by Chuck Tweedy »

Brad, you can clean off the bridge area by scraping off the finish - dry (as suggested earlier in the thread).
I have a special scraper I've made for this purpose and I also use single-edge razor blades.
I position the bridge and scribe around it with a very sharp awl.
I then tape off the top outside the scribe line (so I don't slip and scrape the good stuff).
My specialty scraper is a 3/4" wide by 0.040" thick piece of 1095 blue spring steel that I roll a good scraper burr on.
The special scraper takes off finish VERY fast, but is too aggressive once I get down to bare spruce, so I switch to the single-edge razor once I'm most of the way there.
I scrape as close to the scribe line as I can and leave it bare and dry. I do this right before gluing down the bridge - leave the tape in place to help with cleanup.
Likes to drink Rosewood Juice

Steve Senseney
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Re: bridge lifting off

Post by Steve Senseney »

On a new build, I lay down a single layer of blue masking tape. I position the bridge, scribe lightly with a new edge on a disposable utility knife.

I peel up the tape where the bridge will be glued, scrape with a 1/4 or 3/8 inch sharp chisel, held at 90 degrees to the surface. I work each line to the center, then work the center last.

If it feel like it needs a little more "cleaning" or smoothing, I use some sand paper.

I always put 2 pins in to hold the bridge in position while I glue.

I use hot hide glue.

I place the guitar in the go bar deck, with little jacks inside the body supporting the bridge area. I use the go bar deck to press the bridge down.

After I use the hot hide glue, I wait about 5 minutes, clean up the squeeze out while it is soft, and then pull the tape. This is all while the in the go bar deck.

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