Guitar break (Full Version)

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El Burdo -> Guitar break (Oct. 27 2012 11:32:49)

Hello

I played the (unfinished) guitar I made last night at a gig playing Bossa Nova - so lots of chordal plucking rather than rasqueo. The build is shamefully inept and an expensive learning curve but worth it - I'm looking forward to doing the next one, the proper one!).

Then this happened. It wasn't just the string breaking, the bridge detached wholesale from the s/b mid G13/Ab, requiring me to play percussion on the remains until a replacement guitar was located. Needless to say, the band were suitably helpful with 'nice guitar break', 'you pick your time' , 'take it to the bridge' etc...

I'm a bit confused as to the reason for the break as it seemed to have been properly glued along the length; there is some Rosewood attached still, but at the edges, pine has been torn out of the s/b. Are there any (less than) obvious conclusions that I can guard against as I'm now worried that this can happen on any guitar I make. I glued the bridge on, after the body assembly, with Titebond using the go-bar deck method as I don't have long clamps and I'd read that one shouldn't apply too much pressure in any case.

Any help gratefully etc etc.

(I have also really been enjoying the photographs of Anders' #100. It's very instructive and inspiring so thanks from a neophyte. I didn't realise how easy is was to build a side press (if you can afford the blankets), and I like the short plane used for the head. I've done everything with a fore-plane up to now!).

Thanks.



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Stephen Eden -> RE: Guitar break (Oct. 27 2012 14:30:43)

From the looks of it, the glue has struggled a bit to get onto the underside of the bridge. Two reasons for that could be that the underside of the bridge was greasy from handling or there was not enough clamping pressure on the center of the bridge.

Sand both the underside of the bridge and the sound board and make sure you have good clamping pressure.

I have seen it happen a few times and these were both the reason it happened



Andy Culpepper -> RE: Guitar break (Oct. 27 2012 14:45:55)

quote:

I glued the bridge on, after the body assembly, with Titebond using the go-bar deck method as I don't have long clamps and I'd read that one shouldn't apply too much pressure in any case.


I think this method is problematic because of the flexibility of the soundboard when you are pressing the bridge onto it. Even if you have a perfect fit on the bridge, the joint gets distorted when you apply downward pressure on the whole thing I would think.
I know a bridge can be glued with external pressure only as I have seen a picture of the Ramirez shop doing it with rope and wedges, but I think those kinds of methods would require hot hide glue and VERY little pressure. As far as I know HHG is the only glue capable of creating a very strong joint with very minimal pressure.



Morante -> RE: Guitar break (Oct. 27 2012 14:53:57)

If you use go bars you must support the tapa underneath. Otherwise the tapa sinks and the bidge does not connect well.



El Burdo -> RE: Guitar break (Oct. 28 2012 22:28:00)

Thanks peeps - everything you say chimed with what I was thinking! (Still needed to be told though).

I'll try and make some long clamps to keep the shape of the curved tapa.

I'm also going to try and keep the remaining spruce on the bridge rather than sand it off as I'd rather have wood than filler, but I take your point, SEden.

Again, thanks.



constructordeguitarras -> RE: Guitar break (Oct. 29 2012 3:44:49)

The only way I have glued on well over 100 bridges is with Titebond and two cam clamps outside, on the wings. I have never had one come loose--in fact, once I glued one on upside down and a minute later had a lot of trouble getting it off (along with some spruce splinters). If the soundboard is domed or arched at all, there will be pressure in the middle.

There may have been too little clamping pressure in your case. Do some test glue-ups with scrap wood. I use so much pressure that I flatten the doming while gluing on bridges; then it springs back later when the clamps are removed, bending the bridge. When using Titebond to make furniture, people use tremendous amounts of pressure, to good effect.



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Anders Eliasson -> RE: Guitar break (Oct. 29 2012 7:38:59)

Andy is right. Dont use synthetic glues without a good deal of pressure. meaning dont use a go bar without have an inside clamping caul AND some inside clamps. But thats not the way to go.
Buy some long clamps. Its a must.

Hide glue has this strange capacity of dragging things together. Its a lot stronger than what you think. Even when gluing the tentellones to the top and sides, where you dont put any pressure you can see it the next day. The tentellones might even slightly pull the soundboard out of shape if they have less angle than the sides/soundboard.



El Burdo -> RE: Guitar break (Oct. 29 2012 8:25:48)

Thanks, I'll bite the bullet and buy some clamps. You learn by your mistakes!

Should I clean up the bottom of the bridge prior to re-gluing and 'fill' the tapa or keep the spruce (and the film of old glue) on the bridge and stick that on? They are both bodges/hacks but the wood seems the better bet to me. I guess I could try using pumice rather than wood filler.



johnnefastis -> RE: Guitar break (Oct. 29 2012 9:08:48)

Did you pin it too ? I never new thats what you luthiers did and enjoyed reading about bamboo / rosewood pins etc on Anders' guitar 100 thread. I imagine it makes a big difference to something like this happening.

http://www.foroflamenco.com/tm.asp?m=209908&mpage=4&p=&tmode=1&smode=1&key=guitar%2C100



Stephen Eden -> RE: Guitar break (Oct. 29 2012 9:15:17)

If it was the grease or even polish under the bridge that stopped the glue taking to it then even with good clamping pressure the bridge will not stick. Cleaning the underside would then be the only way to go. This is what happened when I was asked to glue the bridge on for someone else. The bridge popped off with almost straight away under string tension. I cleaned the under side of the bridge and the sound board and re glued and it was perfect.

If you feel it was the clamping pressure then you might get away with it. Although the extra spruce on the under side of the bridge may also prevent you getting a good join.



Anders Eliasson -> RE: Guitar break (Oct. 29 2012 9:26:15)

When using sinthetic glue, you should ALWAYS remove all the old glue from both the bridge and the soundboard. If not you get a weak glue joing.
Hot Hide glue doesnt have to be removed, but will interact perfectly with fresh hhg.

Pinning a bridge doesnt help in cases like this. Its only for positioning the bridge. And pins should only be used if you have a bridge patch or strap with the grains running 90 degrees to the soundboard and where the pins go through the soundboard AND the patch/strap. If not done like this and the bridge start moving just a little bit because of the glue creeping, the pins will start splitting the soundboard along the grain.



El Burdo -> RE: Guitar break (Oct. 29 2012 10:24:14)

quote:

Did you pin it too ?


No, that's just a little too sophisticated for where I'm at right now. Actually that was why I chose go-bars to clamp the bridge as I then found that locating it accurately was quite easy. The longitudinal pull of clamps has been a problem for me in the past so I might use pins next time. I tried pins when locating the fingerboard but getting a pin to penetrate into ebony wasn't easy (for me). I might try the strip beneath though as it seems to be a nice way of keeping top curveture as well.

quote:

Hot Hide glue doesnt have to be removed, but will interact perfectly with fresh hhg.


One day I'd like to use hhg but at the moment it has to be Titebond all the way. I made this last guitar in my flat and my wife had enough to put up with!

quote:

Cleaning the underside would then be the only way to go


I'll clean the surfaces before re-attaching. But..I'll still have some missing spruce. Any suggestions how I could fill the hole? I guess I could also make a spruce/glue paste first?

Thanks again.



Blair Russell -> RE: Guitar break (Oct. 29 2012 14:46:01)

quote:


No, that's just a little too sophisticated for where I'm at right now.


El Burdo, it couldn't be simpler. Locate the bridge position, clamp, drill 2 holes through the saddle slot and put a toothpick in each hole. If I didn't do this I'm sure my bridges would be sliding around everywhere during glueing.



estebanana -> RE: Guitar break (Oct. 29 2012 17:59:21)

I use hide glue for bridges and if I take time to make the fit prefect I only have to hold the bridge down with my fingers for three minutes and it is not going to move, then I slip clamps on it for a few hours to allow it to dry. But I wait until the next day to put full string tension on the bridge. Hide glue is wonderful stuff.

The only other thing you need to make sure of when you glue bridge is that the relative humidity is the same as it was, close or less, as when you braced the top. If there is a radical difference between the gluing of the bridge and the natural arch of the top you could have trouble.

If you were to glue the bridge on and the humidity were very high the top would be more swelled up. If that guitar goes to a really dry room or place the bridge and the top braces/arch will fight each other. In some cases the bridge might even lift off or pop off.

The bridge is the component that marries the strings to the top and facilitates driving the top, but it is also a brace for the top. The bridge adds stiffness across the grain in the area it is glued down so the rule of gluing cross grain joints at lower humidity applies here; the bridge in essence is another brace that needs to be treated like a brace, it also happens to be the brace which the strings tie to.



El Burdo -> RE: Guitar break (Oct. 30 2012 14:19:16)

Thanks everyone for these observations - it really is very useful.

There's only one remaining problem - how should I deal with the holes in the soundboard produced when the bridge tore off? I'm thinking of spruce glue mix but there's a coloration there.



Stephen Eden -> RE: Guitar break (Oct. 30 2012 14:40:23)

theres not much you can do with spruce. you can try and sand it out but you run the risk of thinning your sound board too much. Or hope the bridge covers it up. When ever you try and cover up something in spruce you will see it.

Perhaps just glue it on and fill the left over stuff with polish it won't look brilliant though.



El Burdo -> RE: Guitar break (Oct. 30 2012 15:03:55)

Thanks. No problem - it doesn't look brilliant now! [:D]



El Burdo -> RE: Guitar break (Oct. 30 2012 15:06:09)

Hello Ethan - that looks fierce! Why don't you use a cawl across the top of the bridge?



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