Making some wooden cartop roof rack cross beams

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?

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RE: Making some wooden cartop roof rack cross beams

If you call it springback, there's formulas out there for it for metal and wood. Try this one for wood.




RE: Making some wooden cartop roof rack cross beams

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.

RE: Making some wooden cartop roof rack cross beams

   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.

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