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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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Replies to This Discussion

Permalink Reply by Bad Finger (Eric) on May 5, 2014 at 3:18am

I think the trim and moulding glue is OK for the fret board to neck. The excess cleans off easy with a chisel or plane. I find that sanding warms up the glue and makes it harder to clean off as it stretches and smears a little. Best to clean off the extra with a cutting operation first.

I may have used it on a scarf joint, but I prefer the yellow glue for that. I arrange my scarf joints to the fretboard is glued over the joint so there is probably plenty of strength either way with wood and glue on both sides. But if ya got the yellow stuff, use it. :)

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Permalink Reply by 14 buck bass (aka antonio) on May 5, 2014 at 2:56am

oh yeah and i just clamp in the evening and work on my other cbg. i usually just work on two at a time twice the fun and excitement. and open the package after coffe and donuts in the morning .

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Permalink Reply by Wichita Sam on May 5, 2014 at 2:43pm

Used to be my only build time was early morning or late evening. Typically got 6-8 hours cure that way. Seemed to work ok for me. I would stretch it out it I was working a joint, like drill machine head posts on paddle head glue lines.

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Permalink Reply by ChickenboneJohn on May 5, 2014 at 6:26pm

Wayfinder - the fretboard to neck joint is a stressed joint, and a critical one at that. The neck is being bent by 60-80lb of string tension on a 3 string guitar, so it's subject to a fairly rigorous loading in shear at the joint face. That's why gluing on a fingerboard helps to strengthen a neck, it's taking a lot of the compression load as the neck is being bent by the strings.

One factor that nobody has considered is that most of these woodworking glues have a fairly high moisture content. Deep in a thin joint, that water can't simply evaporate, some of that moisture will migrate into the wood. It takes quite a while for that moisture to dissipate through the timber and settle back to pre-gluing levels, so one important part of leaving glue joints such as a neck to fretboard for long time is to allow the moisture to dissipate and reduce the risk of warping.

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Permalink Reply by ChickenboneJohn on May 5, 2014 at 6:51pm

The risk with unclamping before all the moisture has dissipated, is that the moisture will move into the timbers, possibly cause it to bend or twist the neck, and then when the glue joint really does fully cure, it will have developed a permanent distortion. The reason I mention this is because I have made this mistake myself, it's not just a theoretical situation. What the manufacturer tells you won't necessarily cover unusual situations like this.

No matter how you "design" the neck, simply gluing a fretboard onto it will affect the way it acts under stress...usually in a good way in terms of increasing it's resistance to bending. Although the fretboard is maybe only 1/4" (6mm thick) it's taking almost ALL of the compressive loading under string tension. That may seem counter intuitive, but when neck bends, the front (ie fingberboard) is in compression and the back of the neck is in tension...without going all technical on the loading, stress and neutral axis etc...glueing a thin fingerboard onto a relatively weak neck will probably double its resistance to being bent by the strings.

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Permalink Reply by Rob (Uker) Porras on May 8, 2014 at 6:38am

I do overnight and that's airing on the side of caution. I have never had a glue joint fail.

Oops. I just jinxed my self.

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Permalink Reply by Wichita Sam on May 9, 2014 at 3:37am

One thing not mentioned (and not asked, except in the title gluing and clamping) is a fairly comment mistake of clamping directly on top of the fretboard.. The use of a patten board to spread the load strsses will keep board for getting wavy from the force of individual clamps. And, single frets can be distorted by the force of a clamp placed full force on it.

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Permalink Reply by AGP # on May 9, 2014 at 10:09am

As you say ideally the best way is to glue and clamp as the last job of the day, and leave overnight, but at times this does not fit into the time frame, I currently use GORILLA (white) WOOD GLUE, and take the clamps off an hour or so later, this then allows me to shape, route & sand etc; so far have not had any problems, but again as you say the join probably should not be stressed.