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Expert builders: let's talk about gluing and clamping

OK - now I have your attention :)

I've been thinking recently about all of the conflicting advice I've seen about how long you need to clamp wood glue while its drying. Let's take it as read that I'm talking about white glue (Titebond, I currently have Titebond 3)

When I first started making CBGs (almost a year ago) I had literally no woodworking experience. The glue I bought said the curing time was 24 hours so I clamped the piece for that time. It was always a frustrating part of the build process.

A few months later I spoke to a joiner friend of mine and he said this was a bit daft. 24 hours is the curing time, but it doesn't need to be clamped that long. He said he usually leaves gluing as the last job of the day and will clamp overnight. At a push about 6 hours would do as long as the join is not stressed until the glue has cured.

I posed the same question to a couple of experienced builders on Ted's site, and they said 18-24 hours to clamp. I asked another and he said about 2-3 hours.

I asked a couple of guys on CBN and they said 4-6 hours.

For my last 5 of so builds I have been clamping for roughly 6 hours. For my design I need to glue the headstock, the heel and the fretboard, and by the time I'm ready to start carving, let alone string up (which I guess would 'stress the join') the glue will have well and truly cured. No bad side effects so far.

So... the question I'm asking, or the discussion I'm instigating, is how long should glued joints be clamped for making instruments? And hopefully when others come along in the future with the same question I had, they can have a good read of this topic and come away with a bit of insight.

Rick

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Permalink Reply by John Sawyer on May 4, 2014 at 6:17am

There's a trick to polyurethane glues: They cure with moisture. When gluing foam (R/C Planes) a trick is to drop a blob on a piece of cardboard or whatever, wet a toothpick with a miniscule drop of water and stir like it's epoxy. The result is a fast-curing foamy expanding goo... Clamping is required, but it gets 90% hard in less than 2 hours, if I remember right...

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Permalink Reply by Better Trees on May 4, 2014 at 7:35am

That's freaking awesome! I'm going to see if I can find any info on if it affects the strength of the finished product.

Just looked it up; it does not weaken it, as long as you use the glue the way it is intended. For very dry wood you should wipe water on one side of the joint anyway; it requires water to cure.

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Permalink Reply by Sawbones on May 4, 2014 at 8:16am

Thats funny,I used to build RC planes too and CA was what the whole club used.Light,dry quick and strong.

But I just like Elmers wood glue for these CBG thangs!

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Permalink Reply by John Sawyer on May 4, 2014 at 8:28am

Ply glue works for foamies... not so much for balsa...

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Permalink Reply by ChickenboneJohn on May 4, 2014 at 8:36am

Only come across polyurethane glue when working on another makers build..awful stuff, soft as sh*ite and goes everywhere.

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Permalink Reply by John Sawyer on May 4, 2014 at 8:41am

It is definitely a different beast. It's slippery as hell until it cures, too... I had a heck of a time when I first decided to use it on a scarf joint... (never again)

I mostly use water based glues, but the poly's work well when the surfaces aren't perfectly even. Once cured, I've never had a problem.

Since it foams up, you do have to clamp it, (and use less than normal) if you don't clamp it well, it WILL shift.

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Permalink Reply by Uncle John on May 4, 2014 at 8:44am

CBJ, that makes me laugh and mildly offends me! Oh well, maybe the truth hurts a bit.

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Permalink Reply by ChickenboneJohn on May 4, 2014 at 9:05am

Well..I judge all glues by the classic old-fashioned hot hide glue. It's so easy to repair an instrument made with hide glue, and it dries as hard as glass. If you've got the time to make up a batch, it really is the best stuff to work with.

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Permalink Reply by Uncle John on May 4, 2014 at 9:23am

I hear good things about the old hide glue. The repair part is a huge bonus.

CBJ, I think you look at cbg building from the perspective of an expert craftsman/luthier who is also a good musician. That is fine perspective.

I view cbgs from a traditional perspective. I want an old timey much played look. I want them to look like a poor person scrounged up parts and built the 'instrument' with rudimentary tools and skills - and was in a bit of a hurry to get it done and play it.

We both want good players. I think you achieve that consistently. I do it less consistently, but I have a lot of fun. And sometimes frustration.