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I recently began building my first OM style guitar. Everything has been progressing nicely however I seem to have run into my first problem and I am feeling a bit discouraged.

The backs I purchased have a little warp and I sprayed them with a little water and then clamped them for about a week between sheets of MDF and wax paper to straighten them out prior to joining.



I recently used a router jig to join both halves of my rosewood back. I verified a tight seem with a light box and then joined both halves and a backstrip together with Titebond.



After the glue dried I removed the back and moved it to my work bench where I placed it between 2 pieces of MDF to make sure it remained flat.

I joined the backs on Wed and tonight I went to show my dad, who was visiting, my progress the left halve became loose. The backstrip is still firmly attached to the right side but the left side is complete loose.

What is the best way to go about reattaching? Can I just cleanup both edges and re-glue re-join?

Any ideas and/or help is greatly appreciated. Terrible timing; these types of problems have a tendency to consume my thoughts and ruin my mood. It turns out that is a terrible combination on Valentines Day. The wifey is not very happy...

Thanks,

Chris

I seem to think maybe the backs weren't completely dry when I joined them so the wood probably shrank just enough to weaken the joint an separate.

Think I'm going to flat sand each edge and rejoin tomorrow.

Any thoughts?

I would imagine re-cutting the joint faces would be much better than sanding them, and old titebond should be removed completely.
Personally I use a plane to joint, but there have been several discussions on this on the forum already.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

my first thought was along the lines that using a router to straight line an edge is only as good as the guide you use, but you used a light box to verify...

moisture might have been the problem but I wonder...did the dried up glue line turn chalky? the glue itself might be bad...you do need to recut the joints as wood glues work by making a mechanical bond when they soak into the wood grains and dry creating little 'tendrils' of hardened material...the point being you have to get back to a fresh wood edge and any remaining glue in the woods has to be removed for a proper gluing surface.

If the back strip is a piece of marquetry I would sand the edge lightly to remove the glue residue and reglue. If it is just a plain stick of contrasting wood Then rerouting the edges might be quicker.
The back seam is much stronger with a back graft, especially when a back strip is used, but usually it will stand up to a moderate amount of handling after the glue has dried.
Don't let this small stuff get to you - there will probably be more to come.

I agree with Clay, and as someone else has suggested maybe a new bottle of glue if the other is old. Less water on any surface the better. Looks like your gluing board with wedges should work fine. As Clay said don't let the small stuff get to you, and it's mostly small stuff.

The joint you described should be quite strong. I've taken to wiping my rosewood with Denatured Alcohol or acetone to remove oils before gluing and really can't say if that's a factor - I read it on the internet somewhere - but perhaps?

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Thank You and Best To All

Nice shop!

What goes in the shop, stays in the shop. Keeps the lady friends happy.

Did you glue your back panels and center strip at the same time? Never heard of that.

Did you insert the back strip full depths between the panels, or did you rout partway through and inlay it?

I would cut the panels apart, rejoint it, and re glue it without center strip. Then I would inlay the center strip, cutting only halfway through the panel.

Routers always seem to leave behind a surface that isn't as smooth as needed for joining purposes -- are you absolutely certain that no light is showing through the joint? I personally feel that you would be better served by using your router method and then following up by sanding or you could just using a plane for the whole procedure (which is ideal). If you have a jointer with a perfectly flat bed, you can get some 320 grit adhesive sandpaper (like Stikit Gold) and place it on the jointer and use the fence to lightly swipe the surface after you routed the joint. A 320 grit or even a 220 grit surface works plenty good for glue joints.

Also, I would recommend inlaying the centerstrip rather than sandwiching it between the two back halves -- in fact, that may be the source of your problem.

Best Regards,
Simon

Just a thought, is it possible you over clamped it and starved the joint?

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Lance@LuthiersForum.com

Or, if you have a jointer, you can joint it using the jointer...

Thanks everyone for the advice and encouragement. I'm going to start with new clean edges and then rejoin the back. I'll update my progress later.

I'd also suggest that if you want to flatten out top or back halves, using stickers is better IMO than clamping as you did. With the wax
paper and MDF clamping arrangement, it's very hard for any moisture to escape the wood.

Good Luck!! These small setbacks seem big in the moment, but they really don't mean much in the overall art of building a guitar.

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Gene

Politicians and diapers must be changed often, and for the same reason- Mark Twain

Just to add another thought: Might it be possible that the that the router left a burnished surface?

Yeah, that was my first thought.

Backs successfully replaned and and joined including a new backstrip. Thank you everyone for your advice. I appreciate it.

Good stuff!