Official Luthiers Forum!

I have recently been using hide glue, with good results. However, I just tried using it for the first time to glue a back to the sides. I did OK, but it was definitely slower than my usual joint --- lots of go bars just take more time than a clamp or two.

So the question is, how do I test the joint? If it won't hold up over time, I would rather find out now.

Kelby...I don't know of any non destructive direct way you can QC the joint short of pulling it apart.

There may be some indirect ways to evaluate whether you got the 2 surfaces properly glued. Did you get uniform squeeze out? If so, then you probably got the plate clamped down before the glue gelled. How long was your open time...if you warmed the surfaces and got it clamped within 60 seconds then you should ne OK. In that case it's probably as good as any joint you would have with any adhesive.

Another suggestion...tap around the joint area with your fingernail. If you hear any hollow areas then you might have a void where the joined surfaces did not make the proper contact. Before I ever apply glue, I make sure that the braced plate drops in place and makes good contact all the way around. Not only is it important for a quality joint, it also makes the gluing operation go faster.

Also, when you route for bindings, you will be able to visually inspect the joint under magnification for any voids.

These are the things I have looked for...I've done 6 guitars with HHG and have not yet found voids nor have I had any joints fail after as long as 4 years. Knock on wood!

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JJ
Napa, CA
http://www.DonohueGuitars.com

Kelby, have you heard of the way that some of the old Spanish builders glued the back on using animal glues? They spread the glue on the linings and the braces (Braces were set into the linings rather than glued to the backplate) the back was then set in place. Then, they spread alcohol on the back directly above the glued areas. The alcohol was then ignited and the heat generated softened the glue so that the back could be firmly clamped in place.

Now if you want to ensure the joint is good you could always .....

Colin

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I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

[QUOTE=Colin S] Kelby, have you heard of the way that some of the old Spanish builders glued the back on using animal glues? They spread the glue on the linings and the braces (Braces were set into the linings rather than glued to the backplate) the back was then set in place. Then, they spread alcohol on the back directly above the glued areas. The alcohol was then ignited and the heat generated softened the glue so that the back could be firmly clamped in place.

Now if you want to ensure the joint is good you could always .....

Colin[/QUOTE]

Yup, or just run an iron around the edge and heat everything up again and clamp as you heat. That is appearantly how the factories did it before they switched to PVA's and AR's.

Shane

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Canada

Heat gun?

Something about setting my guitar on fire with alcohol doesn't sound good.

Kelby I used a heat gun on the edges when I used HHG for this, you can get the wood plenty hot with one and it should liquify any gelled areas (just make sure you clamp before you heat), that's the best I can suggest. I use PVA's for this now because it's a pain to do this with HHG...

Cheers

-Paul-

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-Paul-

Patriot Guitars

Thanks, everyone!

My intuition must be getting better. When I finished clamping, I ran a heat gun around the last section that got clamped to re-melt the glue in that area.

I pulled on the joint a little to test it --- not too much, but probably more stress than that joint will ever get --- and it held fine.

I'll keep my fingers crossed.

one way to speed things up is to use a radiused gluing caul which matches the radius of your plate: then the sequence is spread glue, place the plate in position, place the caul on the plate, then apply a sizable weight. the caul will distribute the weight evenly over the edges of the plate and the sequence is quick and simple.