Wednesday, August 12, 2009

An Embarrassing Cracked Rib

Today will be another day in the workshop. I visited the Parks artifacts on Monday and have been making the modifications on the reproductions since then. On Thursday I have another visit scheduled to compare the progress.

I suppose the most interesting thing happening at work right now are my problems with wood bending. These are kind of embarrassing pictures, but these things don't always go according to plan, so here it goes.

On Sunday I tried to steam bend the spruce board that I've been using for the kayak rib reproduction. I soaked it for a few minutes ahead of time and then steamed it for an hour. I came up with a jig that I thought would give me the curve that I needed, but when I tried to bend it, the wood cracked and split along growth rings. To me it seemed like the wood was still pretty dry inside.

It didn't break completely in half, so I took it with me to compare to the original artifact on Monday. One of the reasons that I chose this particular piece of wood to work is that there are no knots in the wood, except for a single tiny knot that matches a tiny knot in the original artifact. In the artifact, this knot is important because the weathering pattern of the wood is affected by it. Its a harder part of the wood so it has weathered like a little volcano around that knot. Its important that the reproduction have a similar knot in the same place. The knots that I'm talking about are the little black specks towards the right side of the pieces in the middle photo.

Coincidentally, the artifact kayak rib thins a lot at the same point that my reproduction rib split. I can remove the wood that cracked and still have enough mass left on that side to make the reproduction. Of course, the challenge now is to go back and try to bend the other end of the rib, which is thicker, without cracking the wood again.

To bend it next time, I plan to soak it in water for longer ahead of time, steam it longer, and use clamps to slowly bend it into shape, rather than try to wrench it into a jig.

Photo Credit: Tim Rast

Photo Captions:
Top, The cracked rib in the bending jig
Middle, Comparing the cracked rib to the artifact
Bottom, The crack conveniently lines up with a thinning in the artifact, so I can keep working on this piece.


  1. Hey Tim, did you see this?
    Nothing to do with steam-bending, though . . .

  2. Thanks for the link - I hadn't seen that before - that's much, much older than I would have guessed heat treating was being used. Interesting.

  3. Who knew wood bending would be such a problem? Based on your photos, I suspect the main problem is with the direction of the grain of the wood. It needs to be continuous throughout the length of the piece you want to bend, and not terminate within (crosscut) the piece.

  4. I think you are right about the crosscut grain being a problem - its certainly where this piece chose to break. Its on my list of things to watch for on the next attempt.

  5. Tim stumbled on this one and figured I'd add my 2 cents. I had a hard time steaming kayak ribs on my 2 SOF's I built. I found it much more productive to boil up somewater to a boiling roll. Then place the rib in the pot one end out to hold and pour the hotwater with a cup down the rib. I had read it in one arch document somewhere that this is how it was done sometimes up north along with chewing the rib to soften it.


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