Tuesday, February 17, 2009

Building up a head of steam

I just discovered that while you get the nifty little "pointy-link-finger" as you mouse over the pictures here at McKennawerks, it seems that double-clicking doesn't always open a larger view of the picture. I have no idea why not. Until I can it figure out and fix it, if you can't make out a detail you need in a picture, drop me an email and I'll send you the larger version.

We're getting ready to move on to steam, but that may be delayed a few days. It's gotten cold again, and I'm not sanguine about how successful I'd be in a frigid shop. Wood is bent with steaming by heat and moisture making plastic the hemicelluloses in the wood fibers. As soon as you remove the piece from the steam box is instantly begins to lose malleability as a function of cooling. Since these are long pieces, requiring many clamps, and shaping into a complex compound curve, I'm concerned that in a cold shop I won't have adequate working time to bend the poles without cracking.

I've made some test pieces and we'll give those a shot first.

(Later on...)

Man, I'm tickled pink! I got so pleased with the way the poles are turning out I had to drag Gen down to the McKennawerks in her jammies just so I could share with somebody. I thought the shop was still too cold for steaming, but I went ahead and built, scratch that, cobbled together, the bending jig. As you can see from the below pictures, the first pole I cut is nearly perfect just cold clamped in the jig, and the second pole is very nearly there, too.

Of course, at this point the wood is still green and springy, and as soon as I pull the clamps off it springs back too far to be useful. But this means that when I steam them they should conform to the blocking fairly easily. I didn't pull the left pole all the way into the block for fear of over-stressing and cracking it, but I was able to get this much conformity from both of them without and sign of cracking at all.
I think this strengthens the argument that bent poles are a possibility. It shows that with careful selection of the trees to be cut steam bending would not have been required, in that I feel strongly that I could clamp both poles to the blocking and let them dry in place for 6 months or so and they would be satisfactory.
However, I have a deadline, so steaming it must be.
BTW those of you thinking of building a dog-cart who want to skip steaming could produce the same effect with glued laminations, though it's not a period practice.

Here is a close-up of the end of the right-hand pole. You can see that the blocking for the jig is built up of odds and ends of scrap. The "C" clamp is hooked on the bottom to a super heavy duty clothes rod mount. I pulled a bunch of them out of the MBR closet 7 years ago when working on remolding the MBR--never throw anything away, that's what I always say (Gen always says, "Whatinthehell are you going to do with that old thing!).


1 comment:

  1. Ooo, exciting. I am looking forward to details of the steamer. There are several projects on my list that a steamer would be good for.