Regluing bridge - how to make the fit?

[Janne Koskela]

Dear Forumers,

The bridge of my second build (eben bridge on spruce top jumbo OM acoustic) came off the top (with my gentle help), and I'm about to glue it back. 

My question is: How do you make it fit well enough? Obviously the first fit wasn't good enough as it started "smiling". Scraper? Sandpaper? Testing? Please tell me what's your tried procedure!

Janne

[nathan clark]

Janne,

I use hand tools for this (no sandpaper) giving the bottom of the bridge an arch that's either the same as or (more typically) less pronounced than the arch of the top. I get lots of the old glue off the bottom of the bridge with a chisel, then I shape the bottom of the bridge with a block plane followed up by a scraper. I hold the bridge in my vice by using the stew mac outer bridge reglue clamping caul for planing and scraping (I'll try to post a picture of this). To clean up the top, I'll use a scraper, a razor blade with a burr as a scraper or a chisel as a scraper. I like hot hide glue for this job which seems to work best on splinter-free surfaces trued by edged tools rather than sandpaper.

There are some really good repair people who simply belt-sand the bottom of the bridge flat (no arching). So there's definitely lots of different and good ways to do this repair.

If your bridge doesn't have pin holes you can put an oversized saddle in the bridge and clamp the protruding saddle in your vise.

[William F.Eden]

First of all make sure that there is no finish were the bridge is going to be glued on the top .Then I sand the bridge to the shap of the top . If you have to much finish build up around were the bridge is trying to sit it my not be getting good contact with the bare top . If so then you will have to take a little bitt of wood off the first 1/8" around the eadges of the bridge so it can sit down into the glue. Good luck Bill."""""""""""""'

[griff]

I suspect gluing procedure before fit. What did you use to glue it down the first time, and how long did it last before it started to come up? It could be the glue was old, or it was hide glue from a bottle, or was insufficiently clamped, or there was too much glue, or not enough...

I also use a small scraper (you could use a razor blade with a burr or a glass slide) to scrape the top clean. I use a sanding board to clean and true the bottom of the bridge (I don't try to put an arch in), wipe the bottom of the bridge with naptha to remove sanding dust, and glue it up with yellow glue (I buy the smallest bottles I can get so it doesn't sit around long).

[Janne Koskela]

Thanks for responses!

The glue was (and is going to be) yellow Titebond, as I don't have acces to any hide glue at the moment. I believe the bridge was too thick the first time - it didn't give in at all to fit the top curvature. It started to come up pretty soon (within two months at most), but I only realised it later because the gap was so narrow and the bridge so stiff it did't warp at all. It turned out that the bridge had had only about 60% contact to top from the very start (dont't ask me how that happened!). So the issue could be clamping too. Anyway I'm shaving down the top of the bridge first to get some flex. And then try to get best possible fit and best possible gluing down...

[Jim Bancroft]

I don't worry about the top radius when gluing a bridge unless the radius is excessive, then I may shape the bottom of the bridge to match the top. Some Gibson's have excessive radius, but most guitars are basically flat in the bridge area.

I check the flatness of both the top and bottom of the bridge with a 6" straightedge(ruler) Next I will dry clamp the bridge in place with the same setup and pressure as if I was actually gluing it on. Now I take a thin feeler guage, .004", and work it around the perimeter of the bridge, trying to work it under the bridge. If it works under somewhere, while under clamp pressure, then I need to do a little better fitting. Once I get a good fit, and can't work the feeler guage in anywhere, then I glue it on.

I normally use hot hide glue, but original titebond will work.

Jim