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Fill wood missing from under bridge?
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Author:  cdn-bigfoot [ Mon Nov 10, 2014 1:34 pm ]
Post subject:  Fill wood missing from under bridge?
Help me save my old guitar from the dump!
I have a 40 year old Japanese Martin knock-off that I got as a kid. It is a decent spruce plywood top acoustic that was ignored for many years. As such the top bellied below the bridge and the bridge partially pulled off. I brought it in to a local reputable guitar shop and their "Luthier" glued the bridge back on and said it was cracked. BUT.... he didn't replace it, only glued it back down. Aaaagh!!!!
Of course it was quickly deemed unplayable as the bridge crack opened up to much larger than before. I have removed the bridge using heat from a travel iron and a couple thin blade putty knives. I don't know what kind of glue he used but it seemed pretty permanent. Some of the wood seems to be previously missing from under the bridge and some more of it came up attached to the bridge. So now I am faced with gluing down a new bridge with an uneven surface and obviously thinner top wood to attach it to. The spruce is now as low as 1mm from the top finish under either end of the bridge.

Question: Should I try to level out the wood under the bridge? It is mostly smoothed to a good gluing surface by scraping the glue down and removing as little of the wood fibres as possible. Since the spruce is now as low as 1mm from the top finish under either end of the bridge, can I fill that with wood or other material to bring it up to the surface of the finish or should I just glue down the new bridge? I was planning on using Fish Glue. Can I trust my old bridge plate or should I add to it?

I have ordered a new Martin style belly bridge from an actual Luthier who makes them by hand. The new bridge will have the pin holes arranged in a slight arc. I have also bought a Luthiers bridge clamp from him. He suggested filling the original holes with wood dowel pieces cut to match and then flattened and drilling new pin holes using the new curved bridge holes as a guide. I've bought and plan on using a JLD Bridge Doctor to help hold the top more flat and maybe the screw can help hold down the new bridge.

I will do this repair myself, as much for a learning experience as anything, but would like a playable and aesthetically good job. I am very handy although not very experienced with guitar repair.

Thanks for any advice. Barry.
Author:  WudWerkr [ Mon Nov 10, 2014 2:23 pm ]
Post subject:  Re: Fill wood missing from under bridge?
Pictures Please
Author:  cdn-bigfoot [ Mon Nov 10, 2014 2:48 pm ]
Post subject:  Re: Fill wood missing from under bridge?
As you can see it's a poor excuse for a bridge plate. May be worth replacing.
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Author:  WudWerkr [ Mon Nov 10, 2014 4:39 pm ]
Post subject:  Re: Fill wood missing from under bridge?
Im not a Pro ok ! That having been said , what I would do is replace the bridge plate underneath making it a bit larger . It appears that they used a spruce for the bridge plate. Or im seeing somthing wrong . I tend to use a harder wood to hold up better against the strings . Anyway , I would then fill the top to level or really close with wood filler , and reapply the bridge . Option #2 replace the Bridge plate and then purchase an oversized bridge ,mill down the edges of the bridge so it fits in the offset and reglue.
Option #3 mixture of both , replace bridge plate , fill top , buy oversize bridge and glue down.
Just my 2 cents worth

Have Facebook ? https://www.facebook.com/wudwerkr/media ... 065&type=3

forgot to add pic of it level before bridge applied , but yes I filled it level
Author:  Hesh [ Mon Nov 10, 2014 5:37 pm ]
Post subject:  Re: Fill wood missing from under bridge?
Another way to go would be to "cap" the bridge plate making your cap about 1/2" longer than the pin hole spacing, about 1/2" wide and I make mine about .060" thick out of maple. I predrill the pin holes and then use the outer two holes to position the cap and then clamp it in place with a caul (covered in waxed paper) and a couple of clamps. Once everything is dried, usually the next day for me I drill out the holes with a 3/16th drill and then ream with a 5 degree reamer. The pin fitting and drilling out the holes should wait for the new bridge to be installed first though as should gluing up and clamping the bridge plate cap if you go this route.

As for the top damage looks like a lot of wood is missing.... not good. And when you have such a ledge from the finish to the wood where the transition is from finish to wood will be useless in terms of wood-to-wood contact as well.

Frank Ford has an excellent article on this kind of a repair on his site, FRETS.com where he removes a "scoop" of top (for lack of a better word at the moment) and then inlays a replacement scoop. It's not an easy operation but if you want to gain some experience and are not in a rush it's about the best method that I have ever seen for this kind of damage.

Lastly a word about cleaning up under a removed bridge. Had the top not been damaged the goal is to remove ALL old glue and have freshly scraped wood available for the glue-up. Typically additional finish is removed too expanding the wood-to-wood surface area. The glues that we typically use, HHG, Titebond Original should not have surfaces prepared with keying.... As such you want uber clean, smooth wood under the bridge except in rare circumstances where "appropriate for the instrument" comes into play and perhaps it's an Ov*tion.... :D Seriously though I use a very sharp chisel to clean up old glue and crud and it's also important to be mindful of runout direction in the top wood to so that your chisel tends to remove the crud and not dig into the top.

Check out FREST.com and Franks article on remaining top damage under a bridge.
Author:  WudWerkr [ Mon Nov 10, 2014 5:42 pm ]
Post subject:  Re: Fill wood missing from under bridge?
Quote:
Frank Ford has an excellent article on this kind of a repair on his site, FRETS.com where he removes a "scoop" of top (for lack of a better word at the moment) and then inlays a replacement scoop. It's not an easy operation but if you want to gain some experience and are not in a rush it's about the best method that I have ever seen for this kind of damage.



which is basically what my Face book Pics show [:Y:]
Author:  cdn-bigfoot [ Tue Nov 11, 2014 1:01 am ]
Post subject:  Re: Fill wood missing from under bridge?
Thanks to all for their suggestions. I looked at Fred's technique for replacing the wood under the bridge on Frets.com. I also agree that a new harder wood bridgeplate is in order. Especially since my new bridge has a different pin configuration (curved).
I will take pics as I go.

If anyone has suggestions in the meantime please post!

Thanks.
BF
Author:  Bill Braske [ Wed Dec 10, 2014 11:02 pm ]
Post subject:  Re: Fill wood missing from under bridge?
How's this been going? I'm curious to see how you handled the missing wood under the old bridge.
Author:  jfmckenna [ Thu Dec 11, 2014 10:54 am ]
Post subject:  Re: Fill wood missing from under bridge?
On a cheap guitar like that you can just scrape and sand down to the next ply, probably a luan play, and glue the bridge on or just get it close and use something like Smith's epoxy and be done with it. The bridge plate doesn't look that bad imho you can just keyhole slot that and get to some fresh wood, but it's not too difficult to cap it either. Wood filler won't help because it's not really a bonding type material. But epoxy is gap filling. I would not use such techniques on a Martin but on plywood top guitars it's appropriate again... imho ;)
Author:  Ruby50 [ Thu Dec 11, 2014 9:13 pm ]
Post subject:  Re: Fill wood missing from under bridge?
Since the top is plywood to begin with, and since the repair will not be visible, and since you want a nice smooth wood surface to glue onto, how about routing out a layer of the plywood - say 1/3 the thickness of the top - then glue in a piece to fill. Not my idea, but seems simple and ideal. I think the 'scoop" technique that Frank is using is for valuable instruments.

Ed
Author:  cdn-bigfoot [ Mon Jan 12, 2015 9:41 pm ]
Post subject:  Re: Fill wood missing from under bridge?
Ruby50 wrote:
...how about routing out a layer of the plywood - say 1/3 the thickness of the top - then glue in a piece to fill.

Ed


Ed, that's basically the solution I've decided on. I used a straight blade razor to get the surface flat and down 1mm below surface finish. I kept the blade flat and vertical as I scraped. This seemed to get a clean flat finish. Now to fill with some spruce to bring it slightly higher than the top. Then I can sand it perfectly flat. Project was sidelined by work and is now back on track. I will post more pics as I go. Thanks


PS. I don't know why pics posted upside down they are correct on my computer. I hope you get the idea.
Author:  cdn-bigfoot [ Mon Mar 02, 2015 10:25 pm ]
Post subject:  Re: Fill wood missing from under bridge?
Finally back on the project.
Finished taking the rough wood down to .8mm deep.
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I also added a hardwood cap to the bridge plate.
drilled new bridge pin holes with 3/16" bit and tapered with an Easyout bit (approximates a 5 degree taper) spun in reverse on a drill.

Just going to wait a few more days and then install a JLD Bridge Doctor, new bone saddle and restring.

Final pics to follow.
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