Steaming

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Giff

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Having some problems steaming.....not the sprouts for Christmas, but some 30mm x 35mm Ash. I have made up a steam tube from soil pipe and put a steam feed at one end and bunged up the other, and put a 6mm drain hole for water to escape. I left the piece in for about an hour and a half, but it may have cooled a bit in between as the water supply ran out and it shut down.When I took it out it seemed exactly the same as when it when in. I am trying to bend a fairly tight radius at one end of a 2 mtr length and have made up a former with clamps etc.

How long should it be in the steamer ? Any tips or suggestions ? Thanks Geoff
 
General rule of thumb is 1hr per inch of thickness.

What are you generating the steam with? is the steam actually getting to the wood or just condensing in the tube?
 
Giff":1172s1a4 said:
When I took it out it seemed exactly the same as when it when in.

it won't look any different, it'll just be soaking wet and too hot to pick up without gloves. Once it's out of the steam, speed is the essence. Once it cools you'll just snap it.
 
Once hot an hour and a half is in theory right. If it cools it wont work. If you run out of water it wont work. Its a straightforward process if you plan it properly If the moisture content of the timber is too low it will take longer. the tube should be insulated. I have steam bent 3/4" square oak recently and that has taken well over an hour for a 12" radius probably because it had been kiln dried which is not a good starting point.
hth
all the best
rob
 
I wrap my pipe in an old blanket for insulation. It is the heat, not the moisture which softens the wood.

If the wood is kiln dried success is unlikely too.
 
Also, overbend it slightly. It will most likely spring back a bit when it cools.

Trial & error really.
 
Thanks everyone. I am trying again today. I think the insulated tube might also be the answer as I have the pipe outside and maybe it isn't getting hot
I am using a " Propress steamer, which is used for steaming clothes, but has a 1/1/2 litre tank and a hose that (now) screws on to the pipe.. Geoff
 
If the steam has cooled before it's around the wood, you'll never bend it.
 
You're trying to get the very core of your workpiece as close to 100 degrees C as possible, you certainly want it up to at least 93 degrees C.

This isn't easy and gets harder the thicker the workpiece, by doing the job outside in winter you're not really setting yourself up for success. The "1 hour per inch" is only a very rough rule of thumb for steaming, your 1 1/4" workpiece may well need two hours steaming even under ideal conditions, and you'll struggle with a 1 1/2 litre tank as the workpiece will cool right down every time you re-fill, even with an insulated box and topping up with boiling water you might be better aiming for 2.5 or 3.0 hours steaming.

Once the workpiece is bent around the former you need to dry it right out before cutting it loose, for example getting down from 25% to 10% moisture content in 1" stock will probably take about a week inside your home, longer in your shed. Don't rush this.

Forget steam bending tropical timbers or most softwoods (Yew is a bit of an exception to that rule), and personally I wouldn't bother steaming kilned timber. It's not that kilned wood is impossible to bend to typical windsor chair type radii, it's just that the failure rate can easily top 80%. Personally I'm not prepared to put all that time and effort into something that might only deliver one success out of five attempts. My experience has been that air dried timber is almost as good for steam bending as freshly cut timber, however I seem to recall reading that James Mursell says freshly felled is significantly better than air dried, so I guess there's still room for debate on this one.

Good luck!
 
Thanks Custard, really helpful advice..I still haven't had much success and have reverted to my previous method for this particular job of laminating and gluing 6 mm strips. I think I will practice a bit more on the steaming though as I have quite a bit of air dried beech ( milled from a felled tree in our garden) which I will give a try. Geoff
 
I have bent a lot of wood in my time building & repairing boats. One thing i learnt early on told to me by an old Shipwriright was that you can easily over cook timber. We used green oak if possible or if the timber was dry & possibly kilned we would soak it for a few days first in the creek.
You need lots of wet steam & a steambox can be made from wood, yellow gas pipe or alloy pipe, dont use iron pipe with oak as it will stain the oak black
A typical rib for a sailing dinghy would be approx 3/4" wide by 5/8" thick & would be in the steam box for about 10 minutes.
A bigger rib say 1 1/2" x 1" yacht or workboat size would be in the steambox for about 20 minutes. I never understood the one hour per inch of thickness rule, probably written by someone who hadnt done a lot of it. If you leave them too long they get very brittle & the rate of breakages soars. Always have the ribs well sanded on all four corners, the slightest nick in the grain will cause a stress point from which a crack or split will propagate. Its useful to wrap a sack round the end of the pipe to keep the heat in. Good gloves too!
 
There is a trick for steaming stuff inside a polythene sheath instead of in a steamer box; that lets you clamp it into the bending form while still steaming it, so you can take your time during the bend. I found that made the process a bit easier for me. And it worked on kiln-dried walnut about half the time.

https://www.youtube.com/watch?v=50uXPPt8-VI
 
Keith 66":1q1whsyd said:
One thing i learnt early on told to me by an old Shipwriright was that you can easily over cook timber.

Interesting, because my experience is the exact opposite! When making windsor chairs I might have a dozen arm bows in the steamer, after giving them a couple of hours to heat up it might then take me another few hours to get them all processed. Not a problem, with the last one out steamed for maybe five or six hours. And that's bending to the 8"-12" radius that's typical for windsors.

As for soaking kilned stock, I also disagree with you there. Unfortunately once you take wood below the 12-14% you might achieve with air drying, and down to the 8% or so you'll get with kilning, then there's a permanent change in the cell structure that limits its ability to take up moisture in the future and also introduces additional brittleness.

However, let's not fall out over this, as Andy T sensibly pointed out, you might sometimes have two woodworkers from two completely separate contextual situations, and they end up with very different conclusions. Maybe what works for boat building doesn't work for windsor chair making and vice versa.
 
MarkDennehy":1hbq4y09 said:
There is a trick for steaming stuff inside a polythene sheath instead of in a steamer box; that lets you clamp it into the bending form while still steaming it, so you can take your time during the bend. I found that made the process a bit easier for me. And it worked on kiln-dried walnut about half the time.

https://www.youtube.com/watch?v=50uXPPt8-VI

Very ingenious!
 

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