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whats your favorite way to remove the finish from the top to glue the bridge ?I have a french polished top, I tried taping off the bridge outline,was not happy with the results so I redid the top.I have heard of routing off the finish , my fear here is when I use a router to cut a channel, it seems to be rough on the bottom .I tried using a chisel, got a bit of chipping at the perimeter.I have also heard if using a paint stripper, which makes me nervous.. any ideas are greatly appreciated. thanks Jody

Jody,
I route mine off with a dedicated router and jig but if you don't want to take the time here's what I suggest:
1.Mask the bridge area
2.Mark the bridge outline and score
3. Remove masking tape on the area where the bridge will be leaving tape outside of that area to protect the finish.
4. scrape with a razor blade.

You can cut a razor blade in smaller sections to help you in the tighter places.
Should be an easy task.

Good luck,

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Peter M.
Cornerstone Guitars
http://www.cornerstoneukes.com

I route mine with the 56K rpm mini die grinder setup that John Hall and Dave Nichols sell , using a 1/8 inch bit - also use the rig to route a lip on the bridge bottom.. wouldnt do it any other way now (used to use a chisel, learned that from Serge DeJonge, and before that scraped with glass, both after scoring with an exacto knife)

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Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

Router here as well. Dremel in the StewMac holder with a 1/8" bit. Finish off with a sharp chisel. I also have adapted the same jig to rout the ledge in the bridge. About 1/32". I always rout the ledge in some short pieces of scrap first and push up against the finish edge to get the depth just right.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

I scrape it with a really sharp chisel. I don't see how you can rout without removing some wood and leaving a ledge.

When using a router, how would you go about routing a ledge into the bridge given that its base has been shaped to conform to the dome of the top? Some pictures would help!
Thanks
Pete

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Cheers
Pete

I appreciate everyones replies, I should add, this is not a conventional shaped bribge, it has some round areas , and a couple of sort of notches, or returns cut out of it that come to a point. jody

I kind of "de-bulk" it with the router Alan going almost down to wood, and then finishing off with the chisel. I do have a question for you though, I use shellac on my tops under the nitro. I usually try to scrape all the shellac off as well which involves removing a tiny amount of wood. I've always assumed that was necessary with hide glue. Is that right?
I've been doing a 1/32" ledge in the bridge with the setup below which I learned from a thread by David Collins a few years ago. I usually rout a ledge into scrap first to get the depth right so it just clears the finish. The little table on the dremel router is sanded to a 30'radius, same as my tops. I usually sand the bridge on the actual top to get as good a fit as possible. I put low tack drafting tape over the finish on the bridge area and stick sandpaper to that.

The picture below was taken a couple of years ago and I use a lot narrower ledge now

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It's not what you don't know that hurts you, it's what you do know that's wrong.

I doubt you'll be able to do that with a router - or rather it would mean a fairly complex set up.
You could try laying down masking tape and then carefully scribe around the bridge with a scalpel. Try it on scrap first. If it's such a complex shape I can't think of any other way of doing it. Scraping the finish is relatively easy on 'normal' bridges but I don't think I'd like to try it where notches are concerned.

You do want to remove the _surface_ of the wood, with any kind of glue. some research done at (I believe) the Forest Products Lab back in WWII showed that surfaces that were worked within 15 minutes of gluing yeilded stronger joints. But I don't want to take off any more wood than needed.

I've heard the arguments in favor of the 'ledge'. It _almost_ makes sense if you make the bridge that much bigger than 'normal' to preserve the length of the joint along the line of pull: does everybody do that? I'm afraid that this old dog just doesn't buy that new trick: I've seen too many bridges with finish left around the edges that peeled up. Possibly an absurd prejudice, but a hard-earned one.

Has anyone studied how this strength improvement decays with time, or, the typical max improvement if done right away? I remove the darker (oxidized?) surface wood, but often don't glue until the next day or, um... week.

Thanks, David

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David Malicky

i can't answer that question directly but if you are using Hide glue you can just go ahead and size the wood. You can probably glue it months after if it's well sized.

As for the chipping at the edge, make the masked area somewhat smaller than the actual bridge. Well, that's what I do. Who ever said you need 100% of the bridge bottom surface for a pefect bond? 1/16" inset all around provides suffient glue surface with no ill visual effects where the edges of the bridge meet the top.

Mike

You never want to use masking tape where you French polish. The alcohol will likely draw the adhesive out and into the surrounding shellac as you body over that area. This will lead to contamination of both the film and your muneca and will spread that contamination into the film elsewhere.

If French polishing IMO you have two good choices. Scrap or rout the finish off after the finish has cured or finish with the bridge in place.

I don't remember offhand (if I was ever told) how much stronger the fresh joint was. What happens is that, when you remove wood, you're breaking chemical bonds. It takes a while for the 'loose ends' to find something to latch onto, and if you give them some glue they latch onto that. It's genrally accepted (this week) that most of the stength of the glue bond is chemical, so improving the chemistry helps.

Mike wrote:
"As for the chipping at the edge, make the masked area somewhat smaller than the actual bridge. Well, that's what I do."

IMO that's just what you _don't_ want to do. A good glue bond is between .002" and .006" thick. If you use .005" of finish (which would be thin) then you've got that much of a 'spacer' all around the edge, even assuming you don't scrape away _any_ wood. The liklihood of ending up with a too-thick glue line this way is pretty high. It's also a stress riser just where you don't want one. I know some of the manufacturers have done it this way (including Martin), but I also know that I've re-glued a lot of those bridges. I think that, if you're going to do this, the 'ledge' rabbet around the edge of the bridge is an improvement, although I don't like that either.

Alan, thanks, I never thought about that. Very good point.

Mike

Alan, would my approach be OK if I took, say, 5 thous off the perimeter (as in the pic above, just less)?

Mike

I am probably the odd man out, but I like to scrape right out to the edges of the bridge and get full contact. It is fussy work to get a clean edge because any slip will show, but it allows me to sleep at night.

That's the way I do it. If you score the finish around the bridge with an exacto knife you don't have to worry about chips. Like others have said, a super sharp chisel is a must. I've tried routing, and that worked too. If I had a funny shaped bridge I'd route the finish off. It's not more delicate than doing an intricate inlay, you're just not routing as deep.

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I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

barry and woody......thats the way i have done it for years also......i did not think there was any other way lol

I'm with joe et al: I was aware of the 'other' ways mostly as things that turned up on the repair bench.

I'm with Barry ,Woody,Joe & Alan.
I've reglued 1000s of bridges in the last 30 + years .
The factory idea of leaving a small amount(1/16" or more) of finish under the edge is not good.
Just as Alan said -it's a good place for the joint to start coming apart.
Only wood to wood works !


Alan you would have liked the Woodstock show.

Mike

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Mike Collins

Jody, a thin shellac finish is pretty easy to scrape/sand off. The trick is removing the finish to the exact outline of the bridge, and removing all the finish without removing any wood. Carefully place the bridge in position, carefully score all the way around it with a sharp X-acto - don't cut into the wood. Then, if you want, you can mask the area around your scribed outline, right up to the line. Carefully scrape the finish away with a razor blade or other small scraper of your choice. You can also sand with a very small sanding block.

The two word answer to the question of how to do this procedure is the same as the answer to how every other operation in guitar making is done: very carefully.

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Todd Rose
Ithaca, NY

https://www.dreamingrosesecobnb.com/todds-art-music

https://www.facebook.com/ToddRoseGuitars/

Any reason not to zip-strip the majority of finish away and then scrape the rest?

I'm sure that works great.........but, I'd get stripper somewhere it wasn't supposed to be.

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I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/