Steaming wood

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I draw a line across before I saw the wood up and then glue it up so that the line is still there my reasoning is that there is more chance of it looking as if it was originally one piece of wood just bent.

Good point
 
@Cabinetman
here's a few pics of the pipe i use and a very rubbish drawing using winpaint

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Feed pipe.jpg


T connector.jpg


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It is all packed away unfortunately and not easy to get to but hope this gives you an idea of how I do it
 
That’s great thank you very much, my beloved has set her heart on a two seater bentwood where the back changes direction to form the arms And then back down again into the seat, so sort of a three-dimensional set of turns, half the battle will be making the former, its just as well I relish a challenge. Ian
 
Forgot to put in the drawing that there is a grid made from knackered shopping cart sides (wet wood weighs a lot) to keep the wood off the bottom of the box and help heat all round and a drain hole at the far end
 
Had a look for pics of the steam box but most of my woodworking pics seem to have gone awol on transfer to a new computer and the backup which should contain them doesn't. Really annoying.

Jim
 
Thought I would add to this thread, as I have recently noticed several people claiming success with steam bending kiln dried timber. Whilst I have done a bit of steam bending greenwood for chairmaking, often the limiting factor is sourcing green or air dried material and that seems to dissuade a lot of people from trying. So when no less a person than Peter Galbert says he is a converted to the practicality of steam bending kiln dried, I took notice though it seems he is holding his insights for his new video series. He did share on Instagram that he was bending kiln dries ash without a strap into double bent Windsor chair arms with "5 days soaking in the rough, then shaved , steamed for 2 1/2 hours "..... and an added advantage is that the resulting part dries much quicker than if it had been green to start with.

Another internet woodworker Philp Morley (@philipmorleyfurniture on instagram) details here his success (after much failure!) bending 2.125”x2.125” kiln dried walnut and says:
Here are several things that made this possible and these were the things I picked up from several people.
1 presoak the wood.
2 buy the Lee Valley strap thingy.
3 use shrink wrap.
4 get lots of steam.
5 don’t give up.

Look around the internet some more seems to offer the following:

1. Presoaking - 5-7 days seems to be the usual recommendation. Some Americans seem to be big on adding a couple of cup fulls of Downy fabric conditioner (which I believe is the same as Lenor) which acts as a surfactant and 'softens the fibres' or maybe just helps the water to penetrate ( veneer softeners contain surfactants like glycerine for similar reasons). My understanding is that water is good at absorbing and conducting the heat so getting some back into your timber will help even though is will only penetrate a little way.

2. Bending Straps - Basically wood is much stronger in compression than tension, therefore whilst not always essential, success rates are higher if you use one as it stops the outside of the bent wood being put into tension. Whilst you can source 16g or 18g stainless steel strip, I have had success with builders band (from screwfix). Wooden blocks and thin wedges are cheaper and simpler than adjustable end stops. The main thing is to ensure you have a strap that will not stretch and your timber fits tightly between solid end stops

3. Shrink wrap - this was a new one on me. Watching Philips video, you do see that when he cuts away the wrap after bending the wet wood surface quickly dries. So I assume by restricting water evaporation it helps retain the heat for longer.

4. Lots of steam - the old rule of thumb is 1hr for each inch of thickness, but it looks like kiln dried wood needs a lot longer, presumably because the dry core will conduct heat much slower than green wood at 20% moisture. Peter above was saying 2 1/2 hours for something that looks less than an inch. As others have said it is the heat that counts, so a meat or oven thermometer to confirm your steam box is at around 100C is a good check. I imagine over steaming is much less of an issue with dry wood. I have found one 2kw wallpaper stripper quite sufficient, though for big stuff I have had to refill from the kettle

5. Don't give up - True, trial and error plays it's part on the journey. My early tries were spoilt by hurrying. It is important to allow the wood to bend gradually so a strong steady force is best - you can manage without large levers or winches however these encourage/force you to apply the bend gradually in a controlled manner.

Finally I encourage anyone to experiment as it is a great process (when it works). There is a zero waste movement in sewing, designing patterns and approaches that minimise the wastage of material. Whilst wood does grow on trees, these days we need to make the most of a precious resource and see less of our lovely expensive wood end up in the vacuum extractor. Steam bending is such a process and once you have it makes laminating look such a waste.
 
I have a gentle curved window to make. The component to be bent is 2.4m of 58 x 95mm Accoya. Im intending to pre machine the timber ie - rebate. Do you think steam bending will work in this case? have never done it before!
 
This shows what is possible. the below beam is being bent on edge
 
It's not the water but the heat in the steam that softens the lignin to enable you to bend wood. The big one above has gone through a process where it is in a sealed container that applies hydraulic pressure to shrink the wood along its length. Once cooled it lets the wood bend more easily
 
Looking at the cad, it should be possible if the accoya is air dried. If it has been kiln dried, then it may not work as easily.
I've recently steam bent some 1.5m lengths of Oak in a steam box made from plywood. I used a Wagner wallpaper steamer which was perfect for an hour. However a 95mmx58mm piece needs steaming at 100c for possibly 2 hours. You also need a former to hold the wood in shape after steaming for a day or so while the wood dries and the lignin takes on the new shape.
I wouldn't machine the rebate before steaming but do it after it has dried in the former. The wood shrinks on the inner curve and stretches on the outer curve and this movement can alter the rebate.
Pictures of the steam box and former are attached.
 

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Thing is Accoya has gone through a chemical process to make it almost impervious to rot, I suspect that this will cause real problems trying to bend it,
If it were me I would laminate it, a simple gradual slow curve like that will only need 3 or 4 strips and is easy to do, then add the bit inside which forms the rebate afterwards, just pin and glue. Ian
 
Thing is Accoya has gone through a chemical process to make it almost impervious to rot, I suspect that this will cause real problems trying to bend it,
If it were me I would laminate it, a simple gradual slow curve like that will only need 3 or 4 strips and is easy to do, then add the bit inside which forms the rebate afterwards, just pin and glue. Ian
+1 for that.
 

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