Leave some finish under the bridge?

rodmbds · #1 03-30-2018, 11:49 AM

Hi there! I'm off to attempt my second bridge reglue on an acoustic guitar, to be more specific, classical guitar strung with nylon.

Last time I successfully reglued it and when removing material for the new bridge to fit, I did it exactly the same size having as much wood-to-wood contact as possible.

A friend of mine told me I should leave a thin strip of finish but couldn't really understand why. Could someone shed some light on this?

Thanks!

cobalt60 · #2 03-30-2018, 12:35 PM

Your friend is 100% incorrect. Wood-to-wood only. There are no exceptions.

(Exception: If hide glue and only hide glue was used in the original glue-up, the glue is able to reflow and melt into newly-added glue, but even that is usually only done for repairs where the bridge is not fully removed. To clarify, I mean you can re-flow the GLUE not FINISH, so this isn't really an exception at all)

I'd wonder why you're removing a bridge more than once. While a classical bridge removal is certainly a thing that might occur in a guitar's lifetime, I'd say it's a once-every-30-years type thing...

Looburst · #3 03-30-2018, 12:38 PM

Yep, you don't want any finish to wood when gluing the new bridge in place.

Alan Carruth · #4 03-30-2018, 12:50 PM

With glue lines thinner is usually better. Leaving a line of finish on the top makes a 'spacer' that holds the bridge up, usually higher than the thickness of a good glue line. Also, since it's the surface area of the glue line, and particularly the distance from the front of the bridge to the back, that holds it down, why would you want to reduce that? Leaving finish under the bridge is asking for trouble.

The only reason to do it is cosmetic: it makes it easier to do a neat job. Some of the manufacturers rout a rabbet around the edge of the bridge that is the same height as the thickness the finish is supposed to be, to allow for better wood contact and a thinner glue line.

rodmbds · #5 03-30-2018, 03:37 PM

Great, thanks! Sorry I didn't make myself clear, it's the second time I'm doing it but I mean, in two different guitars... The first one is still there, now I got another guitar with the same problem.

Well I guess I'll go wood-on-wood without the thin strip of finish.

redir · #6 03-30-2018, 07:24 PM

If it's a French Polish finish it's probably okay since it's so incredibly thin. I always strive to make it a perfect footprint but in doing so sometimes you can see marks. As mentioned some will rout a rabbet around the bridge to ride over the finish others will simply sand off a rounded edge to rise above it. In either case we are talking thousands of inches here.

HOF dad · #7 03-31-2018, 07:51 AM

Quote:

Originally Posted by cobalt60

Your friend is 100% incorrect. Wood-to-wood only. There are no exceptions.

(Exception: If hide glue and only hide glue was used in the original glue-up, the glue is able to reflow and melt into newly-added glue, but even that is usually only done for repairs where the bridge is not fully removed. To clarify, I mean you can re-flow the GLUE not FINISH, so this isn't really an exception at all)

I'd wonder why you're removing a bridge more than once. While a classical bridge removal is certainly a thing that might occur in a guitar's lifetime, I'd say it's a once-every-30-years type thing...

Sorry but I had to chuckle at "There are no exceptions" then you launched right into an exception! (even though you disclaimer it)