Steam bending question

[Garrett Lowell]

If you steam a piece of wood, say 1.25" thick by 6" wide, and bend it so that the width of the wood is on the flat, and the curve follows the thickness (like a curved molding for a window), is it advisable to resaw this piece? Or should it be resawn first, and then the three pieces individually steamed and bent?

[David Tabor (sailordave)]

Garrett: just to clarify, you are bending the the 1.25" dimension of the wood? It just happens to be 6" wide...
It would help to rip the wood if it isn't critical to be one piece, but longer steaming would offset that...
Just for your info... Stiffness of a beam is affected more by depth, than width.

Stiffness= x^3 E y Although this may not be the EXACT equation, it is pertinent in that you have a Cubic function versus a single multiple of the other dimension...

where "x" is the depth of the beam (1.25) E is the modulus of Elasticity and "y" is the width (6")

[David Tabor (sailordave)]

And if you're just comparing apples to apples you only need to know the dimensions..
IE if you have a piece of wood a true 1 inch x 1 inch you can see that if you make the depth 5/4 and keep the width at 1 inch you have basically made it twice as stiff...

1^3 times 1 equals 1

5/4^3 times 1 equals 125/64 times 1= 1 61/64 or almost 2...

Not real important to your question but the bottom line is while width affects the amount of steaming necessary to bend, the more critical factor is the thickness of the material being bent.

Note, the above is why 2x12 joists are so much stiffer than 2x10's ...and why when you use them as a ramp to walk up they don't feel much stiffer than 2x10's!!

[ 03-23-2005, 12:27 PM: Message edited by: David Tabor (sailordave) ]

[Bruce Hooke]

Garrett, I am confused about the two options you are considering. It is clearly going to be VERY hard to get much of a bend in the 6" direction, but I don't understand what the two options are that you are considering.

[Garrett Lowell]

"Garrett: just to clarify, you are bending the the 1.25" dimension of the wood? It just happens to be 6" wide... "
Thanks David, that's it exactly. Basically, I need 3 pieces of wood, 3/8" thick each, with the same sweep to them. I was planning on getting all 3 pieces from the same plank. So my question was, should I resaw the wood after steaming and bending, or should I just resaw first, and then steam? These pieces are not structural in any way.

[Bruce Hooke]

I think I get where you are going now. I would probably bend and then resaw, but I doubt you are going to be able to get much of a bend into a 6" wide piece of wood. This will not be much easier than bending a 6x6! Well, the force required will be less but the maximum bend achievable should be about the same.

[Garrett Lowell]

I figured as much, Bruce. It's not much of a sweep, and I was hoping to minimize the waste, as I've got a beautiful piece of khaya. I suppose the time honored "cut the angle/glue up/shape the curve" method may have to serve here.

[Garrett Lowell]

Actually, it's only going to be 4" wide. I suppose that won't change matters much, though.

[Bruce Hooke]

It all depends on what sort of radius you are trying to achieve...

[ssor]

If you saw it into strips with a thin kerf blade and keep track of the places for the pieces and match the grain you will be able to laminate the curve and have it appear as a natural bend.

[Mrleft8]

Good luck getting any bend out of that! In my experience, you'll rupture the outer grain and crush the inner grain, and kink the whole shebang. Better to laminate it up out of 1.25" strips. Why would you want to steam bend this hunk of wood anyway?

[Garrett Lowell]

Doug, I'm just trying to minimize the waste. I wanted the advice of all you gurus so that I could do the right thing. Thanks everyone for your input.

[Mrleft8]

Originally posted by Garrett Lowell:
Doug, I'm just trying to minimize the waste. I wanted the advice of all you gurus so that I could do the right thing. Thanks everyone for your input.OK. But you might end up with the whole thing as waste instead of 20% waste...

[Garrett Lowell]

Yes, and that would be bad. So I'll probably end up laying out the curve, end-cutting the angles, gluing up and then cutting out the curve, like you would do if you were making the frame for a round mirror.

[Mrleft8]

Don't forget to spline your joints.

[ssor]

I once saw a steam bent 1x3 oak chair seat frame on a kitchen chair. The wood on the inside fo the bend was accordian folded. It was too tight a bend for that width of wood. The chair had a leather seat tacked over the wood so that the bend was only visible on the outer perimeter, Until you looked at the underside.