Bent lamination's glue up time

[glzahn]

I'm building the Coolest Cutting Board featured in FWW #233. See my cutting board post from last week.

I've never built anything with bent lamination's and have a question regarding glue time. I completed the first lamination and left it clamped for approx. 18 hrs. I clamped up the second lamination around 1000 this morning and probably wont get back to the project till tomorrow morning. I have one more lamination to do.

I've unclamped simple face frame to carcass glue ups after 2-3 hours without any issues, but this is an entire different animal considering the lamination is in a loose S shape. Lots of pressure working to pry it apart.

My question is what's the minimum time I should leave the lamination's clamped?

[John Mihich]

I have done a lot of bent laminations and have always left it for 24 hours. Mainly because I use PVA glue and it's putting much totally cured by that time. I figure not to take chances.

[R Clark]

I let mine go a full 24 hours.

[mound]

I usually let mine go overnight since other things usually pull me away.. but a while back I was curious and had extra strips in a project. Using PVA glue, a fairly tight curve, something like 5 or 6 layers, I put it in the vacuum press and pulled it out after an hour, just to see.. there was nothing to see, it held strong just like the "real part" I had let sit overnight.

of course a sample of 1 doesn't really mean much, just sayin'

[boblang]

Glue dries in stages. Dry enough to remove the clamps isn't the same as fully cured. With most woodworking glues I let an assembly sit for 12-24 hours before putting the assembly through any sort of stress; sending it though a machine or putting it under load. But I take it out of the clamps after an hour or two. Most assemblies (unless you really force it together with clamp pressure) don't have any built-in stress trying to pull them apart. Bent pieces on the other hand will try to straighten back out.

Bent laminations need a form, and if you need more than one or two, leaving them in the form for a day can stretch a project out too long. I remove them from the form after a couple of hours and put a bar clamp across the ends, and leave the clamp on overnight. That makes the form available for the next lam.

[KC]

boblang said:

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Glue dries in stages. Dry enough to remove the clamps isn't the same as fully cured. With most woodworking glues I let an assembly sit for 12-24 hours before putting the assembly through any sort of stress; sending it though a machine or putting it under load. But I take it out of the clamps after an hour or two. Most assemblies (unless you really force it together with clamp pressure) don't have any built-in stress trying to pull them apart. Bent pieces on the other hand will try to straighten back out.

Bent laminations need a form, and if you need more than one or two, leaving them in the form for a day can stretch a project out too long. I remove them from the form after a couple of hours and put a bar clamp across the ends, and leave the clamp on overnight. That makes the form available for the next lam.

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I know you've done a lot of woodworking over the years, but so have I... and more than I care to remember laminating things. My comment would be that you'll only take them out of the forms too quickly once, then you'll build more forms. And pick up some more clamps if necessary. Overnight at least, in my experience.

[GEB]

I used to follow Norm's New Yankee Workshop method of "letting it cook overnight " until I watched a high end cabinet maker glue his face frame on his cabinets and pull off the clamps 30 minutes later.
Bill

[iublue]

GEB said:

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I used to follow Norm's New Yankee Workshop method of "letting it cook overnight " until I watched a high end cabinet maker glue his face frame on his cabinets and pull off the clamps 30 minutes later.
Bill

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Face frames and bent laminations, two entirely different animals. There should be no built in tension when gluing face frames onto cases. Obviously bent laminations have tension. I go with the cook over night just like it says in the instructions for my UniBond.

[JGrout]

considering the adhesive (unibond) requires 4-8 hours dependent on the ambient temperature your conclusion is correct

For those of us who have worked with PVA glues doing bent work:2 hours in a vacuum bag and out works fine if you just clamp the ends to hold the shape for another two hours.

I've bent up to 6 units in a 10 hour day this way and in all the time I have been doing it (longer than I care to admit) I have had two units that failed to be acceptable for use