steam bending al-fresco

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steam bending al-fresco

Postby pedder63 » Fri Feb 22, 2013 9:07 pm

Does anyone know of a simple, cheap, safe, portable way to steam bend over an open fire, I'm currently using a wall paper stripper, but would love to find a way of using the fire as a heat source.
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Re: steam bending al-fresco

Postby jrccaim » Sat Feb 23, 2013 7:44 am

pedder63 wrote:Does anyone know of a simple, cheap, safe, portable way to steam bend over an open fire, I'm currently using a wall paper stripper, but would love to find a way of using the fire as a heat source.


I see that you have a problem. I understand it perfectly. I'm there too. But "cheap, safe, portable" are in some conflict! One thing you have not told us is how wide or long the thing you want to steam is. Of all the solutions I have seen the following is the most reasonable.

(1) Procure a piece of PVC drain pipe. It could even be castoff iron drain pipe, but it must be large enough to accomodate whatever you are going to steam. Block off one end. If you have PVC they will sell you a piece to block the end. Otherwise whack a wooden plug into the end. This is not a boiler and it can be quite leaky. We are talking something like 4" or 10-15 cm drain pipe. Or even bigger.

(2) Drill a hole in t'other end of the pipe. It accomodates a hose. For the hose almost anything goes. Vinyl is easy to find. Diameter say 1cm - 2cm but it has to fit on your boiler. Seal hose into hole with "Red RTV" we call it here, may have another name in the UK. It is a forms-a-gasket red plastic compound, good to about 300C or so. Other end of hose must go into boiler.

(3) Now you need a boiler. One possibility is a discarded teakettle. Other is an equally discarded pressure cooker. Of the two I prefer the pressure cooker because it is easier to get the hose on to it. Use a hose clamp (may be called a "jubilee clamp" in the UK) to make sure it is reasonably tight, but do not be worried about minor leaks.

(4) Put lots of water into boiler. Put boiler on fire. Put steam victim into pipe. Stuff some foam rubber, or even tinfoil, or wood plug, into open end of pipe. Do not strive for a 100% seal. This would be dangerous because I did not specify a safety valve! Let steam escape all over the place. It does not matter. We are using HVLP as the techies call it. High Volume Low Pressure. We want steam leaks. They are our safety valve. Then you have to calibrate your system. How long should you steam? Dunno. Mike Abbot does something like 25 min with a similar contraption for a chair leg.

Such a contraption is extremely inefficient by industrial standards. Those people use High Pressure Low Volume steam and it is much quicker. But the equipment costs about 10,000 times more than the above contraption and we bodgers do not worry about efficiency. Plus if you run those rigs you will have to comply with the ubiquitous EU safety regs which no doubt mandate special clothing, boiler certification, and numerous fees that feed the bureaucracy. No! HVLP is your friend. Run at low pressure. Almost atmospheric. Escape the bureaucrats. Make chairs :)
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Re: steam bending al-fresco

Postby Brian Williamson » Sat Feb 23, 2013 8:46 am

I tried the following on the top of my wood burning stove. It should work on an open fire with care,

Take item to be steamed. Wrap in wet tea towel. Wrap in aluminium foil. Place over (or in!) heat source until done.

Admittedly, the item I steamed was small in section (a basket handle) but it worked a treat. It was clean, neat and efficient, and could probably be scaled up.

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Re: steam bending al-fresco

Postby gavin » Sat Feb 23, 2013 9:23 am

pedder63 wrote:Does anyone know of a simple, cheap, safe, portable way to steam bend over an open fire, I'm currently using a wall paper stripper, but would love to find a way of using the fire as a heat source.

When I lived in Australia, a re-creation of Batavia a 17th century Dutch sailing vessel was in Sydney harbour. They built this in Holland. The oak was bent over fires. The trick the re-creators only slowly learned was the exact point where the wood was flexible enough to bend without it burning. Since the beams bent were large in cross-section this was quite a feat, but they did it. The original was built in 7 months at the VOC shipyards, so they clearly had the technique well mastered years ago.
Image
More info: http://www.bataviaphotos.com
I cannot recall from my numerous visits aboard her if the image above has beams bent or hewn, but I do know they bent some of the components and over open fires. I recall reading there something about the temperature at which lignin (?) becomes liquid. Anyway, if they could bend thick oak, I bet you could bend thinner chair components without steam.

Does anyone know if you could reach wood-bendy temperatures in a domestic oven? Or must it be hotter than say 250 centigrade? Google advises "melting point of lignin is 482 to 527°F (250 to 275°C)."
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Re: steam bending al-fresco

Postby robin wood » Sat Feb 23, 2013 4:00 pm

Gavin the knees of the ships will be carved it is the outside planks which are bent though on a large vessel these can still be several inches thick. Whatever the melting point of lignin wood bends at much lower temp so it must become plastic long before it melts. When bending larger timbers I have used temp probe and looked to hold it above 95C for a while before bending. Obviously steaming worn't take you above 100C unless you are under pressure.
You certainly can heat bend over an open fire and all it needs is skill and practice no steaming equipment. You just need to get all the wood (or the part where you want the bend up to 95c or so. I have seen images of spanish basket makers hot riving chestnut by standing the billets in a pyramid over the fire and turning them regularly so they get an even heat. Keep feeling how springy it is by bending it over your knee and you'll feel when it changes from elastic to plastic.
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Re: steam bending al-fresco

Postby gavin » Sat Feb 23, 2013 9:30 pm

robin wood wrote:. Keep feeling how springy it is by bending it over your knee and you'll feel when it changes from elastic to plastic.

I like this idea - I will give a shot!
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Re: steam bending al-fresco

Postby steve tomlin » Sat Feb 23, 2013 11:57 pm

pedder63 wrote:simple, cheap, safe, portable way to steam bend over an open fire

i' started by putting kettles or pressure cookers over an open fire but you have only one point of contact with the heat source and are losing so much through the walls of the vessel that it's difficult to keep the steam up.
the best method i found for lots of steam is to get a small empty calor gas bottle, take the valve off and fill it full of water - this is to ensure it's really empty. then drill a fill hole (drill a circle of small holes and knock it out with a cold chisel) and fit your steam hose to where the valve was using parts of the valve, plumbing fittings or whatever.
dig a shallow pit for the fire and put the gas bottle over it, using the dug earth to make a wall around. the boiler then sits in the fire so you get more heat to it, putting a roof made from corrugated tin over the top to keep the heat in helps too.

the flexible hose used to take the heat out the back of dryer makes a good packable steambox, you can even sew a steambag out of ripstop nylon.

it depends what you're steaming; i've bent wood by ladling hot water over it, soaking in hot water in a length of metal guttering, using a box from 1" copper pipe for thin projects, holding the bend point in the vapour of a boiling kettle and even by poking the wood into a kelly kettle. you just want to get it hot, there's loads of ways

have fun experimenting
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Re: steam bending al-fresco

Postby jrccaim » Sun Feb 24, 2013 7:11 am

Fascinating thread. If you have a small enough piece may I recommend a pressure cooker. Indeed, if you have a medium-sized piece may I recomend a presssure canner. These vague sizes mean something like "if you can stuff the thing you are steaming inside the contraption" then use it. In fact I steam my miniatures in exactly the same pressure cooker I use to prepare chicken vindaloo. The chicken seems to have no objections to this multi-tasking usage :). These things run at about 4 bar, 4 times atmoshpheric pressure.

There is an enormous advantage to this. High Pressure Low Volume, HPLV in techspeak. Very quick; five minutes more than enough. Joy! Be sure to put lots of water in the canner/cooker. Do not run it dry.

But if you are doing a chair leg then this will not work, alas, because the leg is much too long, meter and a half or so. Can't stuff it into a pressure canner. This is when you resort to PVC or cast-iron drainpipe HVLP steamers per my last post.And you pay the price. It will ltake longer. But I know of no manufacturer that will make you a 2-4 bar pressure cooker for steaming chair legs. Unless you are willing to pay an ridiculous price for it. So for us bodgers HVLP is the way to go.
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Re: steam bending al-fresco

Postby Doftya » Mon Feb 25, 2013 1:14 am

I can't remember where I sawit, probably it was youtube, but I remember seeing a video of someone making a longbow, and after the basic tillering he bent in the recuve by just holding the wood over an open fire. He would pull it out before it would scorch and try bending it. If it wasn't ready, back into the fire it would go. It took about 1/2 hour. I believe he didn't use any steam because it was green wood.
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Re: steam bending al-fresco

Postby pedder63 » Tue Feb 26, 2013 10:19 am

Brilliant! Thanks guys. Lots to think about here. The gas bottle sounds like the best bet for what I am trying to do,

Many thanks,

Peter
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Re: steam bending al-fresco

Postby gavin » Tue Feb 26, 2013 10:36 am

Does it follow you can put DRY wood in an oven at 95 centigrade and bend it?

(yes I can imagine the replies: Try it Gavin, then report back so we all learn!

But if anyone with a better understanding of wood science could advise me, I'd appreciate it.
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Re: steam bending al-fresco

Postby SeanHellman » Tue Feb 26, 2013 6:53 pm

gavin wrote:Does it follow you can put DRY wood in an oven at 95 centigrade and bend it?


It is heat that makes wood soft enough to bend, steam is used as it easy and simple.

People making shaker boxes and guitars etc use an oval metal heated tube to bend there wood around, they are only bending a few mm thickness so applying direct heat like this is the best way
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Re: steam bending al-fresco

Postby Shankar » Tue Feb 26, 2013 11:22 pm

As we are talking food and cooking.

If its just the heat then to get even heat along a length of wood without using a steam tube and without risk of burning how about a pit cooker (as in Ray Mears cooking.)
Dig a long pit and insulate base with leaves, heat a load of stones(non-explosive) in fire. When really hot drop into length of pit and cover with some more leaves.
Place lengths of wood in pit, cover with more leaves and bury the whole lot for a couple of hours- when "cooked" pull out and bend.
The leaves will generate steam which will enhance the "tenderness" of the wood.

? Out of The (steam) Box thinking or is there a flaw in logic. And no, I've not tried it even with food.

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Re: steam bending al-fresco

Postby robin wood » Tue Feb 26, 2013 11:58 pm

This is almost certainly the standard form of steam bending throughout prehistory. On many sites in the UK and Europe I am told archaeologists find piles of "pot boilers" that is stones that have been in the fire. These are mostly by rivers and friends who are into nautical archaeology are sure they were used for steam bending boat timbers. A not disimilar method is still used in the pacific north west for expanding the big cedar dug out canoes.
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Re: steam bending al-fresco

Postby jrccaim » Wed Feb 27, 2013 6:02 am

robin wood wrote:This is almost certainly the standard form of steam bending throughout prehistory. On many sites in the UK and Europe I am told archaeologists find piles of "pot boilers" that is stones that have been in the fire. These are mostly by rivers and friends who are into nautical archaeology are sure they were used for steam bending boat timbers. A not disimilar method is still used in the pacific north west for expanding the big cedar dug out canoes.


Absolutely. No mystery to steaming. Expose steam to wood. It bends more easily; just as green wood bends more readily than dry. The steam is there to speed things up. You could soak your victim in cold water. It would take a long time (by modern standards) but you could do it. Some clever person back around the dark ages discovered that if you heated things up it worked much faster. So the recipe, as with so many fast foods these days, it "add water and serve." Steam just works faster than plain liquid water. The end result is the same, though. Put the water back in and the wood bends.

Only problem is the mechanics of the thing. Most of us these days have other things to do, for example a job at which we work to put food on the table which allows us to bodge in our "spare" time. And many places frown on your digging up your back yard to make a steamer. I find this deplorable and outrageous but there you are. Which brings me back to drain-pipe. Use it, then put it away. No one will be the wiser, and you will have a chair leg.
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