I'm a hobbyist builder and I'm re-gluing a bridge on a 12 string guitar. I know the basics and have done it before: scrape the surfaces clean, use hot hide glue, etc. However, when I removed the old bridge there was a lot of damage to the spruce top under the bridge. It seems that I must route out the damage and inset an inlay. Does this sound like a good idea? What else could I do? The problem in the first place was that the bridge was glued over a large perimeter of finish. I will rectify this by making it full contact all the way around. Thanks for your help.
Amen to all of your thoughts Hesh. The learning process never ends I hope.
I can understand routing a .005" rabbet around the perimeter of the bridge with the proper fixture, but how in the devil do you mark the perimeter of the bridge on the top of the guitar (without scoring it) and remove finish to within .005"? Seems pretty tricky. Or, do you mask it before finishing? Still a pretty tricky masking job.
Jack we do score the finish, always and yes it's a bit tricky and requires some decent vision as well..... I'm 56 and have more trouble doing this than my shop mate who is 36 and still can see.... ;) When he's not looking I have been known to increase the inset to perhaps .010 which is still not very much but I can at least see where I am going...
Much of the stuff that we talk about on this very fine forum has to also take into account that not everyone here does Lutherie as their day job. Many folks just want to fix up a project and come to us for decent ideas and advice. OTOH (on the other hand) many of the members here are pros and we benefit greatly too from exchanging ideas. One of the down sides of Lutherie in my personal view is that since it's often a solitary pursuit sharing information was back in the day not as easy as it is these days with the Internet and more interest in the subject from lay folks too.
With that said some of the stuff that I offer may not be the best solution for the person who just wants to fix up a project guitar and be done with it. It's true that one has to be jigged-up to rabbit the bridge and it may not be a good approach for someone who does not want to spend their life making jigs to simply glue on one bridge.
For these folks simply cutting back the finish closer to the bridge perimeter, being sure to remove old glue and finish from the top and clean it up well too, and with some fitting, proper glue usage for the glue that you decide to use, and appropriate clamping, cauls, curing time, etc. and Bob's your uncle. After all only about a zillion guitars have been made by the f*ctories with their bridge slapped on over a less than ideal gluing surface and they usually last long enough.
Again there are lots of ways to do most anything that we do - A-men to that! Personally I am always fascinated by how things were done in the past, now, and perhaps in the future too. So I can get carried away at times and bring up stuff that perhaps has more academic value for those so inclined than the practical value of solving a real and present real world problem. So here's an apology from me for getting carried away and not staying focused on your project and what would best serve you going forward.
I don't know what finish is under tha lacquer but it's very hard to scrape off.
Poly can be pretty tenacious but it does chisel up well. Lacquer usually is far less tenacious... We don't scrape the bridge patch and instead use a uber sharp chisel to slice away unwanted finish after we score the boundaries with a single edged razor blade.
If you give this a try reading the top for the run-out direction is important here too as we don't attempt to chisel into the direction that the run-out is pointed and inadvertently lift fibers.
Be sure too to clean up the old glue off the bottom of the bridge (I use a belt sander for the heavy lifting part) and then be sure to give the bridge bottom a fresh scrape just prior to gluing. A freshly scraped surface results in more "joint energy" than a surface that has not been scraped. Chiseling or scraping the bridge patch on the top is the other half and then you should be good to go.