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Improving steam bending
Hi. I tried steam bending a fairly sizeable piece of blue gum yesterday. Results were OK, in the sense that the wood is now bent, but the process was painful. Could some of the benders on this board please clarify...
1. Would you expect to steam bend 21mm x 200mm blue gum.
2. how much steam do you use. I know it is a very subjective question, but how much steam is coming out of the box?
3. What heat source do you use. I borrowed a gas burner, but dont have one of my own. I can buy a little burner fairly cheaply that will put out 7500 btus, is that enough. If you know the btu rating of your burner, can you let me know what you have found to be the minimum.
4. how imporant is it to have a close fit between the timber and the steambox. My steambox has quite a bit of space around the timber, should I resize it to make it more closely fit the timber?
cheers
Arron
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As I am in the middle of making an 18th century french sleighbed (bloody daunting project!) and will be having curved head and foot, this is of much interest to me..... have seen some bending done, but always thought it was beyond my building-stuff-in-the-garage-capacity..... what are you making with bent wood?
success
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Bending wood
Try a search on this forum with the keywords bending and steam and you will have a lot of responses. One has a series of links for the same subject.
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A couple of years ago I made some landing nets and made a steamer to bend the laminated handle/frame.
It consisted of an empty 4lt olive oil tin, a leangth of plastic tubing and a length of 4" PVC pipe.
The hose fed midway into the PVC pipe which was capped both ends with a small hole at the base to let water escape.
The can was placed on a portable gas burner (the $30 units with disposable cartridges, about $1.60 each from Asian grocery stores) and the water was brought to the boil, heat was then turned down and water kept at a rolling boil while the steam did its work.
Took about one hour and the thin sections were like overcooked spaghetti.
Very flexible.
I imagine that you could increase the size of the tube for what you want and a little trial and error depending upon the thickness of the timber.
I was using yellow box and ash about 1/4" thick.
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Steve, I'm making a carver-type chair. I'm trying to put a graceful curve in the back. I have a fairly crude homemade setup and will post some images of it in posts to follow this one. In retrospect I am thinking that there was not enough volume of steam, and probably too much airspace around the object inside the steambox. Also, maybe blue gum is just not meant to be bent.
Marc, I searched this site before posting, finding lots of posts but no real help. I have also searched the internet at large and have read every word I can find on steam bending. Nowhere have I read answers to my fundamental questions - how much steam do you need and can blue gum be bent. In fact, I can't find anywhere someone trying to put a decent quantitative value to the temperature, btu, steam output measure, ratio of object to free-space in the steambox, or relationship between timber properties and bending characteristics.
Iain, I hadnt thought of looking in an Asian grocery. They may have all kinds of burners. Strange oversite considering I live in Epping.
regards
Arron
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Steam bending setup
This is my rough-and-ready steam bending setup.
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Something bent
And this is the bent chair back, in its form. Note the curve is not really very good. Also, the damage done to the surface by using a trolley jack as a hydraulic ram.
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Arron (should that be Aaron?)
I am no expert in steam bending but there are a few chaps here who posted extensively on the subject, and I remember reading those posts that were rather detailed. One guy in particular comes to mind ... what's his name .. Mm forgot, he is rather obnoxious and likes boat building.. Mm anyway, he may turn up with this.
I think that from what you are showing here, your problem is the way you press the timber against the mould. It seems that the steam did its job since you bent it what it seems to be at a guess some 15 degrees. Yet if you want it to follow that particular curve, you must use a couple of good F clamps every 4 inches pressing on a series of 2"x3" across the board to even out the pressure. Also you must be extremely quick since the wood will stop being plastic in matter of minutes. The best is to align some help to get the clamps in place as quick as possible.
There is a formula that gives you the time to submit the wood to steam according to dimensions. Again do not remember but suppose it is one hour, the comment was that there is no point going beyond the time necessary.
Another observation from a non expert, I would keep the steam box horizontal and not vertical to even the temperature (Top hot bottom not so hot)
I remember as a kid playing in a boat-building yard and the old timers would bend the boat parts by boiling it in an open container built from two bent corrugated iron roof sheets, riveted together
filled with water and an open fire under it. They bent all sort of timber but mainly Lapacho, an Amazonian hard wood that bent very nicely.
If your google search came up with not much, try your local library, you may find a book about just what you want.
Good luck.
PS
May be Mr Obnoxious will turn up and give as all a lecture about bending and steaming and make fun about what I have to say in the process, you never know !
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Mr Obnoxious is no longer with us.
He commited E suicside some time ago, thats why you cant find his posts, he deleted himself and his posts.
But I'm sure he's lurking some where.
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I thought Christopha was his reincarnation? I could be and usually am wrong :D
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Thanks Marc. The point about the steambox being vertical is a good one. I did notice that most of the references mentioned their boxes were horizontal as well. I didnt think much about it but I will try it horizontal next time.
Actually, the photo of the bent item was taken some time after the exercise when the other clamps had been removed. We bent it on the inside of the mould (after unsuccessfully trying to bend it around the outside) because that allowed us to use a trolley jack as a hydrualic ram - we couldnt think of any way to do that when bending around the outside. I think if we were steaming things properly and getting good results the thing would be much more supple and we wouldnt need the ram.
The point about boiling is interesting as well. Why not just boil the timber, why bother with steam at all. I might try boiling next time.
Its a pity we cant have open fires here in Sydney.
cheers
Arron
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Hum e-suicide eh ... pity he had still skill to share regardless of emm... manners.
Now that I want to build a boat and need to ask lots of questions. Bummer!
Horizontal box yes, also use the outside of the mould, much easier to clamp. Try increasing the ammount of steam production and the time of exposure, and reduce the clamping time to as little as you are able to ... one minute?
No open fires? Why not? unless there is a total fire ban, you can have a barbaque on coals and you can have a bagne marie for you timber, use offcuts from the shop and keep the smoke to a minimum.
Keep us posted with your progress.:D
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I think that this will answer most of your Questions.
http://www.wcha.org/tidbits/steamfaq.html
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Be careful...
You need to be very careful with steam. It is actually invisible - what you see coming out of a kettle is condensed water vapour (that is still very hot and dangerous). With the stream of water vapour also comes steam (water as a gas) and that carries a tremendous amount of energy.
It's the energy that'll burn you.
