I need to make some cross beams for my Jeep's roof rails. My plan is to create two cross beams, each one made of two 1x4x4 pieces of wood laminated together. I plan to create a little curvature in these cross beams by weighting the ends of the 1x4's after applying the glue for the lamination.
My question is this: How well will the glued pieces of wood retain the curvature? Should I expect all of the curvature to remain once the glue is dry and I remove the weight, or will the beam "bounce back" toward its original shape a bit? If so, is there any way to estimate the bounce-back?
If you call it springback, there's formulas out there for it for metal and wood. Try this one for wood.
Laszlo
Lazlo's link beat me to what I was going to suggest, that rather than 2 - 1x4's laminated you resaw them so you have four (or more) 'leaves', lessening the springback.
Too, weighing the center during glue-up likely won't be as effective as building a simple form against which you do your laminating, clamping the leaves from the center towards the ends once you start assembly.
For what you describe, which I see as a 4' long 'beam' deflected maybe 2" in the center once finished, I'd build a form with 3" deflection at center.
Using a form had the additional advantage that the curve doesn't have to be uniform either, it can curve more at the ends than in the middle.
Thanks for the useful info. It would be nice to be able to create a 4-ply beam, but I don't have access to the right tools to re-saw the lumber. But even with 2-ply I should be able to get some curvature.
Fairing the beams is another issue. I'll do most of the fairing before gluing, clamping, and bending. I'm thinking I should feather the trailing edge, as if making a long, thin daggerboard.