Bridge moved during gluing

[Danny Seamon]

During gluing the bridge on my number 4 guitar I did a stupid thing. In retrospect I believe that tightening the clamp caused the bridge to rotate and I didn't notice it until the glue was already dry. (see photo) I'm looking for recommendations. Here is the info: The top is cedar and has been french polished with shellac. The bridge is ebony. The bass side of the bridge moved toward the headstock 1.5mm. The treble side of the bridge moved away from the headstock .5mm. The distance of the center of the saddle slot to the nut is still good. The scale is 25.4. Bridge was glued with titebond II. The saddle will be 2.5 mm wide. The bridge pin holes have not been drilled through the top/bridge plate but of course they are drilled through the bridge.

As I see it, I have the following choices:

1) Leave it as is and live with the intonation problems. I am thinking that this isn't a good option but let me know what you think.
2) Try to correct the intonation by filing the top of the saddle at an angle away from the headstock on the bass side and toward it slightly on the treble side.
3) Remove the bridge and reglue it. I am a little hesitant here because of the cedar being softer and just not wanting to make things worse....but am gain if this is the only acceptable option. Concerning removing the bridge I have two repair books that list different recommended ways of doing this. One says use a artist's pallet knife that has been sharpened and don't use heat. The other says use heat but doesn't really describe how to apply the heat.

Lastly, I would appreciate any recommendations on how to prevent this from happening in the future. The method I used was to measure the location thrice and scribe around the bridge lightly with an exacto knife, then build tape dam. I've also included a picture of the clamping method.

As always I appreciate your good advice.
Danny

[Danny Seamon]

Additional info: The 1.5 mm shift on the bass side and .5mm shift on the treble side as described above is measured from the fret at the body joint to the corner of the bridge. I believe that the actual linear distance would be a little less.

[Danny Seamon]

Correction: I used regular Titebond. I must be getting senile.

[Mark Swanson]

Glad you made the correction, Titebond II has no use on a guitar.It causes problems.
I don't know how long ago you glued it on, but if the glue is fairly fresh it will release pretty easily with heat. I'd remove and re-glue it, why live with it at this point? It's easy enough to get it off. Make a piece of metal such as aluminum, to fit the top of the bridge with good contact all over. Then heat it up and clamp it on there, or if you have a way to clamp it on and then heat it, all the better. Get it good and warm, and the glue will release with a long thin knife worked in there. Easy does it, it'll work off, and if it's too difficult then it isn't hot enough. If you mess up your finish, French Polish is easily fixed.
When dry-fitting the bridge, drill the two outside pin holes. Then use pins in the holes when you glue the bridge, and it won't move.

[Robert Russell]

I would agree with Mark, Remove it and re-glue. As he said, if the glue isn't very old it should come off pretty easily.

To protect the finish from heat I use a ceramic blanket. I have a couple of them, one for bridges and one for fretboard extensions. I have replaced many bridges (have been reparing guitars for over 20 years) and I have an old cloths iron that I use, Just lay the ceramic blanket over the bridge, lay a damp shop towel over the bridge and then the iron. Let it sit for a few minutes and the glue is ready to go.

The ceramic blanket will literally block out heat up to 2500 degrees and will protect the finish and top. The only heat you will feel on the top is from the bridge heating up and not through the blanket.

You can get the ceramic at an outlet that installs wood stoves. It is what they use behind the heat shields so it doesn't get the walls hot. It is soft and pliable and easily cut with scissors. Works better than anything I have tried in the past and I wouldn't be without it now.

Cheers,
Bob

Here is a picture of mine.

[Danny Seamon]

Thanks for all the info. I made an aluminum block and ground a gradual sharp end to a flexible putty knife (see picture). Wasn't sure about this next part but heated the aluminum block in the oven at 350 then used it and the putty knife to slowly get it off. In retrospect I don't think I got the glue to loosen properly and I got a little tear out on the top. The tear out is all under the outline of the bridge. I glued the tear out down. A little section of cedar came off on the bottom of the bridge also. Any way I have two further questions now:

1) Since the top has some unevenness now with the tear outs, should I still use titebond? One book mentioned to use epoxy in this situation to help fill the voids.
2) I should have asked this before gluing the bridge on the first time...but here goes. The top is domed with a 28 ft radius. Should I try to scrape the bottom of the bridge to match this radius or leave it flat?

Thanks again for the excellent help.
Danny

[Danny Seamon]

Picture of top after bridge removal

[Peter Wilcox]

2) I should have asked this before gluing the bridge on the first time...but here goes. The top is domed with a 28 ft radius. Should I try to scrape the bottom of the bridge to match this radius or leave it flat?

The bridge should match the top radius. I lay a sheet of 220 sandpaper on the top (grit up, of course) over the bridge area, and sand the bottom of the bridge to match. This may be why your bridge moved in the first place, as it had better contact in the center than at the edges and was prone to pivot.

[Mark Swanson]

Yes, shape it to the top. glue in filler pieces of cedar or spruce to fill your gaps, and use titebond or hot hide glue if you know how. Sand all the old glue off of the top before you re-glue.
Robert, the ceramic blankets are a great idea! Thanks for that.

[Robert Russell]

Danny,

You probably didn't get the glue hot enough and that is why you got tearout. Either that or your putty knife was too sharp or you sharpened on the wrong side. I have gone through about 3 putty knives and have somewhat perfected the tool for how I use it.
If you look at the picture I posted you will see that I bend it to get the handle up off the soundboard and I round off the corners so there are no sharp edges to grab. I also thin the end of the blade making sure the bottom (the soundboard side) has most of the taper. That keeps the blade from digging into the soundboard and if anything gets damaged it will be the bridge. I also do not make the end of the blade sharp but smooth it off so it doesn't really cut anything. It is just thinner so it will slide between the top and bridge.

Also I usually find I need to heat the bridge up about 3 times to keep the glue soft. If I hear any wood tearing I come in from the opposite side because it probably means you are going against the runout.

Hope this helps you on your next one....(I am sure there will be one)

Mark,
No problem, happy to share the knowledge. That ceramic is pretty inexpensive and really works. I bought it a few years ago, I think I only paid about $15 for a 36" X 24" piece of it. If you get some of it I think you will be impressed how well it works. I got mine at an outlet that sells firebrick.

Cheers,
Bob

[Danny Seamon]

Mark, Bob and Peter,

Thanks you very much!. I did use the sharpened putty knife upside down - should have had the beveled side down toward the top. I should have heated the aluminum block more times. I also have learned that I pushed the putty knife from the wrong side (considering the grain runout concept) on the bass side where the tear out happened.

This time I radiused the bridge to match the 28 ft radiused top with sandpaper on top. I repaired the tearout gaps with the original piece where possible and since the remaining gap was so small I filled it with cedar sawdust/titebond mixture. (I hope that this is acceptable. If it ever comes loose due to this, I'll route out that section and put in a piece of cedar.) I also used the plastic pins in drilled holes in the first and sixth bridge pin holes. I saw where someone had drilled holes in the clamping caul to accomodate the plastic pins so that's what I did. (see picture) It stayed put this time!

Thanks again for all the great help!!!!
Danny

[Mark Swanson]

Good job!