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Old 06-13-2011, 04:27 AM
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Default A steaming Bowl

No, not that kind
Follow along for a second, opinionate at will:

Ok, so if you're going to do steam bending, we all probably know the basics. Heat and moisture make the wood supple, pliable, albeit briefly. And probably also because of the heat, the moisture gained dissipates fairly rapidly.
Bouncing around in my brain bucket is this thought that in the process, the wood has to relax. All the stresses of the day to day office drudgery must melt. If it still had those tensions, then bending it would have to be more of a challenge, no?

Ok, so the premise formed is, steaming the wood relieves stress. My follow on question is, to what degree, and for how long? If you did nothing to the board, would the stress return? I have no idea.

Not one to turn down the opportunity for an unscientific experiment, I decided the way, and the reason, to try this, was turning bowls. Now, how to dry your bowl blank correctly is probably as much a cause for war amongst turners as how to grind a gouge. I've heard of solutions, alcohol baths, wraps, bags, dehumidification kilns... ok. There's options.

So I got the idea that it may be possible, at least, to rough turn the blank, subject it to steaming, and thereby remove some of the stresses that would later lead to cracking and checking in the blank before final turning.

So today, I built a new steam box, squarish, and took a maple bowl blank about 16" dia and 1 1/2" wall thickness, and left it in there for an hour.
The moisture reading was back where it started an hour after coming out. There was not a lot of visible difference, save some bark areas I had left. Those distorted slightly.

I have no answers at this writing. I'm throwing it out so you can chime in if you like on what may or may not be rational, or likely. No idea what it will or won't do. For the moment, it will simply sit with the rest and continue drying.
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Old 06-13-2011, 05:17 AM
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Default Re: A steaming Bowl

Fun!

I'm guessing that during steaming the wood could relieve stresses by changing shape to compensate. Once dry, it'll retain the lower-energy state - cupped, warped, checked. Whatever.

It would be interesting to resaw a board that had a lot of internal stress (you know what I'm talking about - the ones that grab your blade as they go through); steam one board, and leave the other as is. Then compare their shapes. I'd bet the steamed one is significantly different.
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Old 06-15-2011, 08:25 PM
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Default Re: A steaming Bowl

Poto (the only one reading this ;-) )
go figure this one out. I got a hunk of pine off a tree that a neighbor downed on Saturday. Split it in half, rough turned it, and took a reading. Pin meter said 35%, which I know from experience, is about what it says when you submerge it. Its soaking. I took a shower while turning.
Ok, so its pine, sticky, sappy, full of knots (kind of pretty, actually) but absolutely the kind of thing that should just give one fits and crack and check all over. So I took both blanks and put them in the box for over an hour.
They bled so much sap it dripped out of the condensation drain holes like syrup. Two hours after I took them out, the pin meter read 24 on both.
What?
Its wet, you add water, and it loses 10%MC in 2 hours? 'splain dat!
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Old 06-15-2011, 08:42 PM
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Default Re: A steaming Bowl

I'm going to have to go with heat on that one, Randy. The heat melted the sap, allowing it to flow out, leaving the xylem and phloem relatively clean and empty - nothing hold the moisture in the tubes. Once out of the heat, the water evaporates out the ends of the tubes, and you get less moisture.

I'm making this up, of course. But it sort of makes sense - and is testable, and therefore science, not faith.
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Old 06-15-2011, 08:50 PM
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Default Re: A steaming Bowl

Quote:
Originally Posted by RWeber View Post

Poto (the only one reading this ;-) ) ...
Tain't so, RW, I've been following with interest. You drew me in with "Steaming Bowl".

I think pine syrup sounds pretty good, maybe on buttermilk pancakes.


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Old 06-15-2011, 11:25 PM
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Default Re: A steaming Bowl

Good thought Randy!

My gut (like yours I suppose) says it might be an improvement.
Allowing my brain to extrapolate from that I would leave it in there (on simmer?) for quite a while longer than you would for bending purposes and gradually allow it to cool in the the steamer. I think that would reduce internal stress.

Whether steaming would reduce the tendency to check as it dries is too far beyond me. I'd just keep putting it back into the bag of shavings you removed from the bowl during turning so it dries slowly.


As to the second experiment I won't get as specific as Peter but it clearly was the heat that prompted the excess moisture to leave. I doubt the loss of sap was anything more than coincident.

Last edited by MichaelKellough; 06-15-2011 at 11:28 PM.
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Old 06-16-2011, 12:03 AM
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Default Re: A steaming Bowl

I think it will relieve internal stresses. It'll do nothing about checking as that's a function of the endgrain drying considerably faster than the bulk of the stock. Granted, a case like the Pine losing moisture means less 'potential' for the checking, but I don't think the steaming will do it alone.

As for the resaw experiment, I kinda did one long ago. I had an 8/4 chunk of Walnut 5' long. Very very grumpy board. Pinched the blade on my last bandsaw to the point of stalling it. Left the boards for awhile and they were more curvy than Miss Megan. (Am I allowed to say that? )

Time passes, I'm grumpy at the board (this was waaaaay early in my woodworking adventure... in fact, resawing that 12" board was my first use of the bandsaw... ) I decide, like Randy, that maybe steaming it would release the stresses and let me get the board useably flat. Had it on the driveway and poured 3 liters of boiling water on it and covered it while a second 3 liter pot got to boil. Poured likely 12 liters of boiling water on it, both sides. I won't say it was very pliable, but it certainly was more than before. Stickered it and clamped it down to a bench with room for air.

It was significantly flatter the next day. By the time I did this experiment, it had been likely 2 years it was in the curvy state. I was better at resawing by then, definitely. It resawed very nicely; much like a normally behaved board.

Not scientific, but sure worked. YMMV
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Old 06-16-2011, 02:08 AM
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Default Re: A steaming Bowl

more curvy than Miss Megan. (Am I allowed to say that? )

I'm not sure. I think we need visual aids to be able to accurately assess the situation.
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