Seam seperation

[thistle3585]

I was carving a top plate last night and noticed a small seperation in the seam about 1" long. Would a proper repair be to glue in a brace or just wick some CA into the seperation? The seperation location starts about 2" in from the tailblock.

[labraid]

I'd cut down your seam to separate the two for good, then rejoin and reglue.
er, unless they're already fully carved.....

[Chris Burt]

What type of glue did you use?

[thistle3585]

They are fully carved and I used titebond.

[sunburst]

OK, you have a carved top with a center seam separation -all the way through(?)- about 2" inboard of the tailblock?
My guess is, that will be a problem after the mandolin is strung up for a while no mater how you glue it now. The best "repair" would probably be a new top.

Titebond is hard to glue to. In other words, there's dried glue in there, and you can't really clean it out so that you can re-glue the wood. You'd be glueing the titebond, and that doesn't hold very well.

There are "heroic" ways to reglue top and back seams when it's important to preserve the originality of valuable instruments, but it's a poor substitute for a good original joint. If you heat that joint and take the plate apart, you'll have to re-joint the seam, and you'll loose top width. If there's still plenty of width, that's not a problem.
Also, carved plates invariably change shape when separated, so that the arch doesn't line up any more when you put the two halves together. I've built jigs to force the plated into alignment for regluing, so it can be done.
And, it's hard to clamp the joint in a top or back that is already cut to shape. I have a jig for that too, but it's still not the best clamping arangement.

So, while it's possible to reglue a seam in a top that's already carved, it isn't easy, and I never trust the glue joint as much as one made in a more normal way.

[labraid]

How about this, take two violin clamps, the ones with wing nuts and cork on the clamp faces, and tighten them tight at the base of the top near the separation, about 1" apart. Open your joint as much as you can to get glue in but without cracking down the glue line, then clamp with two other clamps against these violin clamps, pulling the separation together to dry.

[thistle3585]

I don't know if it goes all the way through. And I don't truly know if its seperated or not, in that when I hold it up to a light I get a bright line from where the light is coming through. As far as I know, there is glue in there that is filling the gap. I think I will put my air nozzle, from my compressor, against the area and see if I can feel air coming through. Honestly, it sucks to have to recarve a top, but I'm not opposed to doing it. No point in putting something together thats going to fall apart. Guess I'll need to do a search on joining or just use one piece top and backs. http://www.mandolincafe.net/iB_html/non-cgi/emoticons/biggrin.gif

[PaulD]

Thistle; if you had glue filling the gap you would not see the light coming through... especially not a "bright line". Titebond ends up being fairly opaque when it's dry.

My take on it as a woodworker is that if the gap starts 2" in and runs for 1" you would be hard pressed to get enough clamping pressure to close it up. You might be able to fill it, but Titebond is not very strong as a gap filling glue and I would worry about future failure (especially between the bridge and the tailblock... from what I've read I would want that area to be sturdy).

If it were mine and I wanted to save it I would probably try a variation on what John suggests: heating the plate and taking it apart (less material loss than sawing it apart). I would set a jack or jointer plane to take a whisper-thin shaving and rejoint the halves. If that was going to leave me too narrow that I couldn't hide the difference in the binding ledge, I would consider gluing a thin veneer of the topwood cut from scrap into the joint. The downsides of gluing the veneer in are that you're more likely to have a visible line unless you have no grain runout along the joint, and that you have two glue joints that could potentially fail.

I would also seriously consider making a new top and saving that one for another project.

I'm sure someone will tell us both if I'm way off base here. http://www.mandolincafe.net/iB_html/non-cgi/emoticons/wink.gif

[labraid]

Sounds scrap. You could make a neat mailbox with it though!
I've never used a shooting board for joining, I do it upright in my vise, the plane tells me when things are flat. But you need a _good_ plane for that. I save my Lee Neilson miniature scraping plane for the finishing touches on a top or back join. Then when you clamp it on the table, it should hold tight all the way down the line with _one_ clamp only. Move the plate ends, if they're stuck tight, test complete, then you glue up as usual.

[Michael Lewis]

Listen to John Hamlett. It would be easier to make a new top than to re glue the center seam in a manner that you could be confident using.

To Fix: make 2 plaster or bondo casts of the outside of the top. Make sure they cover the entire top and around the edges. One will be used to hold the shape of the top when gluing, and the other will be sawed in half along the centerline to use as "holders" for the halves of the top when jointing. Take miminal material off or you will have to use a shim to replace the lost material.

I think you can get the idea from what I put up here. If you need more help just ask.

[thistle3585]

Thanks everyone for your assistance. The seperation doesn't go through, in that there is glue filling the "gap". The gap does have an opaque apperance so it must have glue in it. Anyhow, I am going to just carve a new one. Maybe I'll make a clock or something out of this one.

Andrew