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Discussion Starter #1
Hi!
I have been scrolling this forum for years, but never signed up. Now that I have a new project however, I could need some help.
I also beg you to forgive any wrongspelling etc, I´m Norwegian and thus English isn´t my native tounge. Anyway:
I am trying to make a chair. I have made some earlier, but in my own design and therefore I have never had big problems solving it. This time, I am going to make a kind of “replica” of Arne Norells “Inca” chair:

As you see, this is not a very complicated construction! Whats complicated however, was finding cylinder-poles in the preferred wood. Wanted beech, but all I can find is mahogany, teak or oak. The reason I wanted beech was simply because it seems like the two longest poles have to be bent. Now, I have done some kerfing earlier, but never on round poles, and never this thick. Never tried steam-bending, and I hope there is a chance that I won´t need to do that – the winter is already setteling in here, and I don´t have a proper place to execute the project.
As you also can see – the bended poles have to carry some weight. Not a lot, but it needs to be strong enough for a person to lean back in the chair. I have never put any weight on stuff i have kerfed before, but I suppose that with glue, it should be pretty solid?
SO. My questions are: Do you think it is enough to kerf the wood? It is not that much of a bend. Is it even possible to use kerfing on these poles? Possible with mahogany? This is the softest of the woods I have access to. I would be so grateful for answers.
 

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The heat in the steam heats the bound water in the wood. That is water stuck into the sides of the wood fibers. That heats the part of the wood which is not fiber, makes it soft like plastic. Only then will the wood bend.

It is important to try to get "air-dried" wood because it has more bound water in it. "Kiln-dried" wood is almost too dry.

I helped my father steam oak keels for wooden boats. He used a long piece of metal rainwater pipe and an electric kettle at the bottom. At the top of the pipe was a cloth rag that controlled how much kettle steam came all the way up the pipe. It took a whole day.
 

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Discussion Starter #3
Hi,

Thank you for your reply! I did not think of the dryness in the wood, but yes, that must be crucial. I am a little worried that the poles I found might be a little to dry, made for indoor use as they are...

But you say then, that kerfing will not work? Have yet to find images of large pieces, but this one illustrates my thoughs:



This is however smalle than my poles, and nor circular. The circular-issue might make the kerfing impossible?
 

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Discussion Starter #5
I guess you are right. I just think it´s a hassle getting started with it: requires some more outdoor space than what I have. Never done it before either, but that of course, would be another opportunity to learn...I suppose both mahogany and oak is bendable thogh.

I checked with the salesman and he told me that all the poles they sell are indeed very dry. Do you think it would work still?

And I suppose noone are in favor of kerfing?
 

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Scotty D
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I checked with the salesman and he told me that all the poles they sell are indeed very dry. Do you think it would work still?
Yes, I think you could get that bend. Slap together a steam box and cook it for an hour and see what you get. :smile:
 

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I might disagree slightly with Robson Valley on the physics of steam bending, but his point about dry wood is definitely valid and he may be correct on the physics. My understanding of steam bending is that the wood absorbs the moisture and becomes flexible again. Based on my understanding, very dry wood could still be bent, but it would take a very long time for it to absorb enough moisture. There could be some other results from kiln drying besides just the dryness level that make kiln dried wood harder to steam bend.

I would strongly recommend against kerf bending. A kerf bend does not have any structural integrity. If works because of solid joinery on either side of the bend, which would not be the case in this chair. (If you can cut out the kerf section and not change the structural integrity of the piece it is safe to use kerf bending.) In the chair you are building, the bend is in the middle of a structural pole and it is pretty easy to see that removing the curved section would have greatly reduce chair's structure.

In general, I would not recommend kerf bending on poles, because of how it would look (you cannot hide the kerfs) and because the section of the pole where you didn't cut would be very small compared to the section of the pole you did cut.
 

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To add to the above- from what I have read mahogany is much more suitable to bent lamination then steam bending. Oak would be more suitable. PS- I also agree on the kerfs- it will be very weak where it needs strength.
 

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While it would be a great deal of hand work, you could start with a square lamination of very thin strips, bend and glue as desired, then shape them round by hand - draw knife, spoke shave, etc.
 

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Kiln drying sets the wood such that it makes it much less pliable even when steamed. If kiln dried is all that is available it will have to laminated.
 

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Discussion Starter #11
Thank you all so much for your replies!

I talked to the salesman again...The oak has been dried with heat (we call it forced drying, I suppose that´s kiln drying) before it was made into a pole, and then dried naturally after that.

I am seriously considering to laminate-bend a square pole, and then shape it, but I am a little worried about the finish? Don´t think glue looks too good.

I think I am just going to try to build a box and use it as a steamer. And then see what happens....! Not going to kerf, I totally agree with those who spoke against that.
 

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I steam bent boat parts in my living room. I built a 6 foot long by 3 inch by 6 inch "box" out of insulating foam and duct tape that had two hinged "doors" at the ends. Put a rubber tube from a standard tea kettle to one end and slide the wood in from the opposite end. My pieces were on the order of a 1/2 inch diameter at the largest or for flat pieces 3/8 inch thick by 1 inch wide. I built a form with the right bend radius and an old leather belt "backer" that helps prevent tear-out and I took my time. I steamed pieces on the order of 1-3 minutes. For something as thick as you're looking for, I'd suggest longer. You can also pre-soak the wood in a bathtub for a day or two and that will help a lot.
 

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Discussion Starter #13
Ah,

A tea kettle and insulating foam, what a wonderful idea! I will most def go for the kettle solution, and I think my school has some foam for sale. (I´m an architecture student, so I have plenty of things I could borrow, and I can make the form at the shop there..)

I am really curious if steaming will work. It´s such large pieces, I think the diameter is 4,4 centimetres. That should be...1,7 inches? Well, the image above speaks for itself...
 

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The real issue with steam bending is the grain. Riven wood, stock that was split from the log, rather than sawn, is preferred. If the grain doesn't run straight along the piece, it's likely to break or split. You should have a form/mold that matches the chair shape for the back legs. It has to be solid and something you can load and clamp the work piece to within a minute or less. The plasticity of the wood starts to leave as soon as the work comes out of the steam box. In order to successfully "soften" the lumber, you need to generate a significant amount of hot billowy steam. A tea kettle isn't going to do it for your application. Once the parts make it into the form, they are left for months. Some will break when you first try to bend them, others will move when taken out of the form. With steam bending, you have to plan on some failures. I know folks like simple solutions but there aren't any when it comes to bent chair parts.
 

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I would think if your strips are sawn thin enough, they could be bent onto a jig without steam. I can bend 1/4" X 1-1/2" pine in a 4 foot semicircle without any problem. Even black walnut 1/16- 3/32" thick can be bent into a 4 inch circle dry. The bend shown in the OP isn't much. Take 1/8" X 3" or whatever size needed and see if it wont bend to the angle needed. Just keep layering them up with a good (Titebond II?) glue until you get to the size wanted. If you were really clever, start the first layer something like 1/8 or so X 1", next piece 1/8 X 1-1/2, etc, keep increasing until half diameter is reached, then reverse the sizes. Would save a lot of whittling to get it round.
 

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Discussion Starter #16
Hi,

I did not realie that the pieces had to be in the form for that long. Would be inteesting to try steam bending anyway, jus because I think it would introduce a new world of working with wood - but - maybe I should try to lamnate these parts instead. I am fond of having long projects and learning as I go, but I nedd the chair to be finished during December.

I am worried thoug, that with strips, the glue will be visible and it won´t look too good? But I supose it´s all about praktice. Thank you for you advice on the sizes. I am however nood good at inches, so do you men thickness or width? There is some hassle beiing used to the metric system on an American forum! If you mean different with, don´t I also need to make a form that fit?
 

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Hi,
I am worried thoug, that with strips, the glue will be visible and it won´t look too good? But I supose it´s all about praktice. Thank you for you advice on the sizes. I am however nood good at inches, so do you men thickness or width? There is some hassle beiing used to the metric system on an American forum! If you mean different with, don´t I also need to make a form that fit?
Perhaps this will help:
 

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Steam bending can be hit or miss, and there will be springback. For that chair the curved section is fairly short. I might make it from solid stock. I would use three sections (maybe two depending on the boards available). The curved section can be joined by doweled half laps. The profile can be done when complete. Curves done similar to these...
http://www.woodworkingtalk.com/f13/mahogany-bar-update-23653/





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I think everything that could be usefully suggested has already been said, but I'm posting a comment simply to ask that you come back to the forum with info on how the project worked out (even if it was not good) !

Look forward to hearing about the results.
 
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