Wood bending: using steam in a PVC pipe


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Old 02-15-13, 10:27 AM
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Wood bending: using steam in a PVC pipe

I want to bend some small pieces of wood, 1/8x4x21. I purchased the Earlex Steam Generator to create the steam and plan to use 4" PVC pipe for the steam box. One end of the PVC pipe will have a cap glued to the PVC. I will put a water faucet on the cap to allow steam to exit. The other end will have some kind of 'door' or cap that can be removed easily. I have seen someone using just a handful of rags to stuff the end.

The PVC is 4" by 24". I am trying to find out if I need to add release holes along the PVC pipe, if yes, how many, what size or will the water faucet on the end, when open, be sufficient for keeping the pressure inside the PVC pipe at a safe level.
 
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Old 02-15-13, 10:56 AM
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You don't need any pressure to steam wood for bending. You don't need the caps on the pipe and you most certainly do NOT want to pressurize the PVC pipe to any degree whatsoever.

All you really needed was a teakettle on a camp stove with a piece of metal downspout over the spout of the teakettle. Stuff a rag LOOSELY in the other end of the downspout, or in your case, the PVC pipe.

Many years ago I worked in a couple of wooden boat shops. I DO know a thing or two about steam bending.
 
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Old 02-15-13, 04:44 PM
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We used a similar setup when I was going to school. I will tell you this, that PVC pipe will expand a lot when it heats up. Trying to tightly seal either end is probably going to be a problem. I can't recall exactly how the ends were on the pipe I used, but they were wooden plugs made from plywood. I think the one end was screwed on and the other was held on with rubber bands so you could gain access to the pieces. Both ends let steam by. You want 0 psi in this thing when steaming.
 
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Old 02-15-13, 06:31 PM
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Thanks for your replies and information. My post was not clear and bit confusing. I'm not wanting to create or add pressure to the process. Just the opposite. I want to be sure that if there is any pressure that it is low and within safety guidelines. I will use your suggestions since you have done this before.
 
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Old 03-04-13, 07:36 AM
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Question

So, what's a brief outline of the process? Place the wood pieces inside the pipe, I assume. How do you know when they are ready to bend? Is it an iterative process, bend a little, re-steam, bend some more? What kinds of wood are best for this? Would it work better if the steam were introduced via a tee fitting in the middle of the pipe?
 
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Old 03-04-13, 04:05 PM
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I think the rule of thumb is 1 hour per inch of thickness. There is a feel for getting it right and there are some other variables like the type of wood and the radius it is to be bent to.

You will want your steam box (or pipe) to be slightly tilted up from the opening. Introduce the steam as close to the side that opens as possible. It will rise to the back end and condense. The condensation will then run back down into the pipe that brings in the steam.
 
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Old 03-04-13, 11:53 PM
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Most common species of wood will take to steam bending. Red Oak is an excellent wood for bending. White Oak a bit less tolerant. Alaska Cedar is also excellent. Droo is correct that about an hour per inch of thickness works well. Also, if possible slightly tilt the steam containment so that the condensed water drains back to the steam source or at least out of the containment. Don't stack multiple pieces without leaving plenty of space for the steam to fully engulf the wood.

You need to work fast as the wood will cool off quickly once you remove it from the steam box. Use lots of clamps and / or other fasteners to hold it to the mold. Let it set overnight before removing the clamps, a little spring back is to be expected.

Most important is to use green wood if at all possible. Next best is air dried but avoid kiln dried wood at all costs.
 
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Old 03-11-13, 08:03 AM
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Thanks for the tips! I have a lot of eucalyptus down here, may give it a try.
 
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Old 11-20-13, 06:01 PM
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You shouldn't aim to have any pressure, we used to pipe steam in at the back of the box and have a lose fitting door at the front, there should be a constant supply of steam otherwise it will just condense. Also you want to get your wood as close to the top of the box as possible as this is where the steam will be, lay it on some wooden fillets, this will also ensure it is getting steam penetration on the bottom instead of sitting in condensed water. I would always make your mold a bit tighter than your intended radius as you will get some spring, it is easier to flatten a piece than to put more curve in it. Timing is dependent on type of wood and thickness, I think we used to do soft woods like pine for at least an hour. You pretty much have to experiment but so long as your not trying too tight a radius It should be ok.
 
 

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