Wednesday, January 5, 2011

A little support goes a Long way

"Have you ever used straps while steam bending?" It's a question that I've gotten countless times, and I've always had a simple "nope" for an answer. The reason being that I avoided the types of work that call for strap support. The riven, green, ring porous hardwoods that I work with and the shapes that I make from them have never been a problem to work out. But times change, and two broken crests made of kiln dried, sawn walnut later, I decided to take the plunge.

The first question was what to use for the actual strap. I've read about it and it seemed to me that the advice was a bit of overkill. In my usual, whatever's around kind of way, I use a piece of heavy flashing that was left over from the ridge cap of my shop. The strap needs to easily conform to the shape of the workpiece but without stretching or tearing.

Which brings me to the concept of why straps work and what they do. The straps really do two things, one is that they support any fibers that might have exposed endgrain on the surface and keep them from breaking away, but more importantly, by restraining the length of the expanding surface, it actually shifts the neutral point closer to the outer surface. This neutral point normally lies somewhere near the center of the piece where the expansion switches to compression. Hopefully I haven't mangled the science of this too badly. Truthfully, you don't need to understand it, just know what parts of the process are non negotiable!

In making the form, I decided to attach one end of the strap and create a stop for the workpiece, that way, I only have to wrangle one end of the rig while bending. I sandwiched the steel between a plywood block and the form and screwed through with 5 screws. I also folded over a flap on the end and screwed it as well.

Besides securing the strap to the form and handle firmly, the next most important detail is that the length of the strap is slightly shorter than the workpiece. This insures a tight grip on the outer surface. Below you can see that without pressure on the handle, the stop doesn't sit flat on the end of the walnut.

Here is the piece bent after one hour of steaming. The strap worked like a charm, actually too well. There was a small knot in the middle of the compression face and it formed a small kink in the bend, which, left unattended would have led to some marring that I might not have been able to shave out. So as soon as I saw the kink, I threw another clamp in the middle of the bend to contain it. Lesson learned, watch the bend!

The tight grip of the strap is very reassuring.

Now that I see how effective this can be, I might just find some other uses for it, but frankly, I still like bending riven oak better.

Here is the next spoon available in my Spoons for Hunger project. Thanks for all of you who participated in the first drawing. This one is apple wood and while delicate looking, will be very useful and durable in the kitchen. It's one of my favorite shapes and works well sauteing as well as serving.

This one is $40 plus $6 shipping and as before, all proceeds will be donated to charity. I will take names for the next 3 days at and then pick one from a hat to choose the winner.

There are some lovely dark streaks and details in the bowl and handle.

I have another large ladle drying as well as some smaller offerings!


John Scott said...

I was taught that it wasn't possible to successfully bend kiln dried wood. Myth busted.

Peter Galbert said...

I'll keep you posted on the results, but they seem to show that kiln dried bends fine, with a little help. Actually, my favorite way to get the thicker bends for my chairs is to use air dried wood, it sets in the bend quickly and is ready to go with no surprises,
thanks for the comment,

Linden said...


Is that piece of steel for the strap galvanized?.. will that be non-staining?



Andrew Jack said...

kiln dried can work, within reason. the strap plays an increasingly important role, the further you get from green or even air-dried. we are not talking c-arms or anything... but a strap can go a long way on single-plane bends. i forgot what other numbskull comment i had. enjoy.

i just called marc (afro) about this white oak, and he reminded me that it was sold as 'air-dried,' but it was still 30% or so. we both got ripped off.

Peter Galbert said...

the strap is galvanized and didn't show any staining on the walnut, but I suppose it might on a lighter wood.

you looked so much younger then!
thanks for chiming in,

John said...

I heard about you on the Craftsman Path... Glad to find your page. Looks like you have some great insights and do some incredible work.

Peter Galbert said...

thanks and welcome to Chair Notes!