Failed Bridge

[luke_lee]

Hi All
I finish this guitar about a month ago and today I noticed the treble side wing of the bridge had lifted.

So I removed the stings and had a look. I slid a ruler under the bridge and it came off easily. I have made several guitar before and all their bridges are fine after 10 years.

I wiped the bridge with acetone before gluing with titebond. The glue has not stuck to the rosewood at all.

Any ideas on what caused this and how to prevent it?
Your ideas will be greatly appreciated.

Thanks Luke

[kiwigeo]

Two possible reasons:

1. bad glue bond due to contamination or inadequate clamp up. Are you using a caul under the bridge plate?
2. bottom of bridge not profiled adequately to match doming of top. The fact the bridge is lifting at the wings rather than along the back suggests to me that this could be part of the problem.

I use Titebond on my IRW bridges without any use of solvent on the bridge and have never had any problems.

Clean up the top and bottom of the bridge. Check the profile of underside of the bridge and fine tune if possible (I rub bridge over sandpaper laid on the soundboard in bridge area). Reglue (use fresh glue if age of stuff you used is not determinable) and reclamp

[jeffhigh]

There are two schools of thought on the solvent wiping of rosewood
If you do it, you must keep wiping with a fresh cloth and fresh solvent until there is no more oil or colour coming off.
Personally I never wipe it, just use a freshly sanded or scraped surface immediately before gluing and as Martin says, a good fit is critical

[Nick]

Just to chuck another possibility in the pot apart from the valid suggestions made already, could it have been an old batch of glue? I looks like very little of the glue was actually doing the job it was designed to do. As with Jeff & Martin, I've never wiped off Rosewood before gluing up and I've never had any problems of gluing it with Titebond so to see such a clean seperation (you usually take a couple of small strands of Spruce with the bridge ) would indicate it never was sticking much in the first place. I also wonder (without any technical knowledge but a fair dollop of guessing) If the Acetone hadn't gassed off or dried out fully before applying the glue it may have broken down the glue as it was applied? Maybe somebody else could discredit or back up this theory?

[simso]

It looks to me like a bad batch of glue, there appears almost no residue on the two parts from a good bond

[J.F. Custom]

I've never personally had a "bad batch" of Titebond. However, it could be too old or have been kept in poor condition, ie - left open; direct sunlight; too hot; too cold etc. Given its relatively cheap, if I'm ever in doubt, I buy a new bottle.

I have also had the same thought as Nick though. I am no more knowledgable (read untested) but also wonder if the acetone is not left to fully dry, whether this would impact on the Titebond's ability to cure?

So aside from the points already mentioned such as bridge fit etc, perhaps too thin a glue coverage ? Or how did you clean the glue squeeze out - is it possible too much water via a damp rag was applied while the glue was wet and could have leached under the bridge and thinned it? Finally and don't take this personally as you suggest you have had many successful joints previously, but you were gluing direct to the timber, be it scraped/sanded or taped off - not to the lacquer right?

Jeremy.

[Tom West]

Luke: When I saw your first picture,I thought you had an ebony bridge. Quite obvious the Rosewood is a nice piece loaded wit resins. If it were me I would soak the bridge in acetone for a week or so, changing solvent when it appears dark.Be prepared for a lighter bridge both in weight and color. You may not be adventuresome enough for this but may be worth a try.
Tom

[Nick]

If it were me I would soak the bridge in acetone for a week or so

Acetone is a pretty 'hard' solvent (in that it will pretty much remove/break down anything), why leave the bridge in it for a week? Not knocking your technique as we all do things differently, I just can't see why the need for that long time, if any & am looking for enlightenment.
I've glued numerous IRW fingerboards & bridges and a good abrade with 100 grit is all I've ever done & to date none have come back with seperation issues so you can see why I would be puzzled by the thought of submerging the bridge in solvent.

[Tom West]

Somogyi wrote a section in an article about bridges. Think it was in an old Frets magizine. At that time it was one of the things he did to lighten the weight of a bridge. Art Overholzer was another person who did this but with the backs and sides to get the resins out and he claimed it enabled the wood to resonate easier. I think Art( who wrote a book on classical guitar construction)left the wood in the acetone much longer sometimes. The resins would gradually leach out,darken up,and then he would change the acetone. As far as I know he did not indicate any down grade due from the acetone bath.
Tom

[Nick]

Thanks Tom, guess I'm not that picky about remove milligrams or even micro grams from a bridge, I'd be more inclined to remove material from the bridge to acheive a weight target. Be an interesting experiment tho just to see how much you could 'dissolve' out. I have access to a four decimal place set of balances & plenty of Acetone, might sort out a bit of IRW & run it to see if it's worth the expense.

[kiwigeo]

Thanks Tom, guess I'm not that picky about remove milligrams or even micro grams from a bridge, I'd be more inclined to remove material from the bridge to acheive a weight target. Be an interesting experiment tho just to see how much you could 'dissolve' out. I have access to a four decimal place set of balances & plenty of Acetone, might sort out a bit of IRW & run it to see if it's worth the expense.

Ok for you...you've got a world class chemistry lab at your disposal to handle the gallons of waste acetone you'll end up with.

[Tom West]

Yeah It was a stupid idea after all.....!!
Tom

[charangohabsburg]

Yeah It was a stupid idea after all.....!!

Hmmm... not sure if it was a stupid idea. After all, it would be marketable!
There have been (and are) worse ideas around which made it to be great selling arguments.

Regarding the bridge of the OP: That picture looks very strange to me, Luke. I have seen a "couple" of bridges that had come off, but all of them had at least some spruce splinters left on them. I think that if nothing had been wrong with the contacting surface of the rosewood there should at least some glue be sticking to it. Maybe Nick is on to something when he mentions the possibility of remaining and interfering acetone, but I also have no idea what chemically or physically could happen between Titebond and acetone. Let's do some experiments or ask "Mr. Franklin".

[Trevor Gore]

The glue has not stuck to the rosewood at all.

Hmmm. There seems to be a whitish residue on the bridge and some rosewood "splinters" on the guitar top. Really hard to tell what happened without seeing it in the flesh. But one (of many) things that can go wrong is if you masked the bridge area with masking tape and then didn't clean up properly when you pulled the tape. It is easy just to get the tape adhesive residue soaking into the top as you try to remove it, giving you a really poor gluing surface. I don't bother masking, but just scrape the finish off the bridge area, leaving a clean, new surface.

[luke_lee]

Thanks for all of your comments and advice.

Just to clarify,
*The Radius on the bottom of the bridge was not 100% but with a light amount of pressure the joint closed and looked good.

*The glue was bought at Carbitec (Sydney) in March this year. Not sure what their stock turnover is like.

*I did use a wet brush an a fair amount of water to clean up the glue squeeze out.

*I didn’t use any tape to mask the bridge position, I chiselled the lacquer off (to bare spruce).


I did oil the bridge with fretboard oil (after 24 hour of glue drying time).
All the glue was left on the soundboard, nothing on the rosewood.

I have just glued up some test pieces, spruce to spruce, spruce to IRW wiped vs scraped and spruce on a different piece of IRW. I’ll let them dry and then try to prise it apart.

Thanks again Luke

[kiwigeo]

Thanks for all of your comments and advice.

Just to clarify,
*The Radius on the bottom of the bridge was not 100% but with a light amount of pressure the joint closed and looked good.

*The glue was bought at Carbitec (Sydney) in March this year. Not sure what their stock turnover is like.

*I did use a wet brush an a fair amount of water to clean up the glue squeeze out.

*I didn’t use any tape to mask the bridge position, I chiselled the lacquer off (to bare spruce).


I did oil the bridge with fretboard oil (after 24 hour of glue drying time).
All the glue was left on the soundboard, nothing on the rosewood.

I have just glued up some test pieces, spruce to spruce, spruce to IRW wiped vs scraped and spruce on a different piece of IRW. I’ll let them dry and then try to prise it apart.

Thanks again Luke

What was clamping arrangement?

[Trevor Gore]

I did oil the bridge with fretboard oil (after 24 hour of glue drying time).

I oiled a bridge once, with fretboard oil, the Dunlop stuff (Dunlop 02 Fretboard Deep Conditioner oil), probably a few months after I'd glued the bridge on. A while later, hard to say exactly when, but it's still getting worse, maybe 7 or 8 years on, there is a "Stain burst" around the bridge. All I can put it down to is oiling the bridge and the oil and wood colour permeating right through the bridge, through the glue line and into the guitar top. The bridge shows no signs of coming loose, but it would have been a fully cured glueline (Titebond) when the oil went on.

Now, with a fresher, not fully cured glueline and possibly more porous wood, one could believably expect what you got.

Here's a pic:

Bridge Burst.jpg (105.52 KiB) Viewed 26657 times

I felt bad about it until I saw a pic of (one of) Linda Manzer's Pikasso guitar(s) with the exact same problem, but a few times over! Moral of the story: If you want to oil anything on a guitar, use a drying oil, and especially NOT a "deep conditioner" non-drying oil.

So it was probably good that the bridge popped, Luke. At least you won't have a bridge burst to try to get rid of!

[J.F. Custom]

Gah! ^^^ Now that's frustrating...

I have used a tung oil based blend before and haven't had any issues with that. Despite being a penetrating oil, it is also meant to be a drying oil. I've also wiped some down with citrus (pure orange) oil too... Hope I don't find that giving any problems down the track.

Not an easy fix I'm thinking.


Oh and Luke - the reason I mentioned the water issue (cleanup) on the bridge is that water mixed with Titebond can leave a milky white residue. A couple of month old bottle of glue should not be a problem at all - still, a quick test on scrap as you have done should clarify that.

Jeremy.

[luke_lee]

Hi,

I just thought I would follow up on my bridge/glue tests. In the photo:

The top bridge is the one that came off, I wiped one half with Acetone until no more colour came out (Jeff’s suggestion) the other half I scraped. Then I glued a strip of spruce on, let it dry for 24 hours. After that I tried to prise it off using a chisel.

The bridge in the middle is a different piece of IRW (that is not as dark as the original), with the same process applied as above.

I think both test glued successfully.

The bottom piece is a test of the oil I used (Dunlop). I put a drop of oil on top and the photo is the opposite side after 24 hours. It is hard to see in the photo but a fair amount has come through to the bottom side.

I think it failed due to the oil and maybe the poor use of acetone.

Luke

[Tod Gilding]

I managed to get hold of a MSDS for one of the popular fretboard conditioning oils a couple of years ago,( the one that smells like Lemons) and was surprised to find that it was mineral oil (Baby Oil ) with a lemon essence added for the smell.
I now use the Howards Orange Tung oil which is basically just Tung Oil with orange oil added to thin it down it does not penetrate very deep, but is a drying oil and have found no problems.

[kiwigeo]

Oils aint oils

[Kim]

Looking at the white, dark and lighter patterns in this image has me wondering if the glue joint had been a good wood to wood mating when it was clamped. The white patches look like they may possibly be voids in the bottom of the bridge where glue had migrated during the clamping operation. The darker patches around the perimeter and pin holes, but especially the back edge and treble wing look to be areas into which oil had quite freely penetrated when applied the next day. For that to have happened would indicate a probability that there had never been a decent wood to wood bond where it was needed the most. What remains between the white and dark look to be areas that took the bond enough to hold things in place for a while. But it even there it looks like only 'just' because there is no real wood 'fibre' exchange between the components, rather the spruce looks to be only stained a little and this makes me question the glue as well and whether or not it had been out of date, or perhaps exposed to sub zero temperatures at some stage both of which do nothing whatsoever for the integrity of white and yellow glues.

Before I got too concerned about the oil, be it applied the day after or that which may be in the rosewood itself, I would be looking very carefully at the glue 'and' process. Because if it is not allowing a 'full' wood to wood mating of theses components there is potential for even greater disappointment should good glue be used and the bridge were to pull free taking divots of spruce with it. So glue aside I would still be looking carefuly at how the mating of the underside of the bridge to the surface of the top had been achieved, how long it had been left after the mating was done and then glue was applied, how well matched the bridge plate caul had been to the inner radius of the top, and how effectivly clamping pressure had been applied.

Back to oil, my own thoughts on wiping oily wood with acetone prior to gluing are that it can be a risky practice. I say this because I 'suspect' that acetone thins out the oils in wood 'too' much. What I am suggesting is that like most oils, these wood oils polymerise upon exposure to oxygen, and as the surface of the wood and that immediately below have the greatest exposure to oxygen, it is here that this reaction must have greatest effect. I think that perhaps this polymer hardened, 'stabilised' oil, effectively seals off the oils deeper in the wood from the effects of oxygen exposure leave them in a more fluid state ..I speculate that if you break down and wash away the polymer seal with something as astringent as acetone, those oils deeper in the wood will also be thinned allowing them to freely migrate toward the surface as the acetone evaporates and fill the voids, because with most things in nature its 'all' about achieving an equilibrium, and my thoughts are that this migration would be assisted by a wicking action potentially resulting in bond failure as those thinned, volatile wood oils move their way between the bonded components.

I don't 'know' any of that to be true. But my own experience tells me that only a light scrap to expose fresh 'surface' wood just prior to glue application works well. As for glue up process I mate the bridge plate caul to the top just after the bracing has been carved and the top is held securely by gobars into the radius dish. I also relieve the ends of the caul just a tad to be sure they will not crush the top later should it force the top back into the intended radius during bridge clamping. To avoid too much work taking place on the freshly glued top of the guitar, initially mating of the underside of the bridge is performed on a matching radius form to that of the top. This primary form is made by sanding a piece of mdf in the appropriate radius dish, its then sealed with thick shellac and fitted with 80 grit abrasive allowing the majority of that bridge wood which is not guitar to be quickly hogged off.

The bridge mating process is then completed with only a very light pressure sand being required on a sheet of abrasive taped in place on the guitar's top at the location of the bridge. The idea is to avoid the temptation to push hard during what can be a drawn out process as this will cause a deflection of the radius and a mismatch of the components. The mating process and the gluing of the bridge itself all take place at the very same RH at which the braces had been glued to the top. Just prior to application of glue, a freshly turned scraper is run along the underside of the bridge to freshen up the surface and take out any sanding marks left by mating.....and I've tried not to say it ....but.... ..........I use hide glue for this crucial joint because it's the best glue in the world...

Cheers

Kim

[Lillian]

If the glue is allowed to get close to freezing (below 45*F if I remember correctly) during transport it will break down and leave a chalky residue. And unfortunately there is no way to tell if it was or not. The only way to tell is to glue something up and test it.

[kiwigeo]

My theory is very simple....the acetone wipe thing is a carry over from the days when synthetic glues werent as sophisticated as they are now.

[Nick]

My little acetone bath experiment is still continuing but the interesting thing is the amount of water that the Acetone has pulled out of what I thought was nice dry wood! It's not much, probably 5-6mls worth (I'll measure it at the end of the experiment) & if I calculated it out it probably still falls within the 4-8% moisture content but still amazed to see it when it's collected in one place.