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Boat Forum / Building / June 2007Newbie trying to Steam Bend Oak 1" thick x 3" wide
Hi, I am new to the concept of steam bending and am experimenting with very little success. In easy terms to understand how flexible would a piece of oak that is 1" thick x 3" wide become? How tight of radius can be formed before breaking the piece? I experimented with laying a short piece on top of a boiling pot of water with a lid above the oak for 1.5 hours and could not tell any difference between before and after. It was still very rigid. How flexible should the wood be if using a steam box? I understand how to build the steam box. I just don't have a bench mark to estimate how much or little force is needed to bend. I have heard people say that it turns the wood into a noodle for a short amount of time. Based on my limited experiment...I find this hard to believe. One more question is how much of the integrity is lost after application of the steam? I have heard that the steam destroys the cell structure of the wood. My alternate is to saw the wood from thicker to make the frames needed. thanks, marshall > I am new to the concept of steam bending and am experimenting with > very little success. <snip> Before getting into the nitty gritty, what are you trying to do. Lew > Hi, > [quoted text clipped - 27 lines] > thanks, > marshall Try posting on the rec woodworking NG there has been a lot of posts on steaming wood over the years there. If you can find the archives for that group you should be able to find you answers and more. Jim > Hi, > [quoted text clipped - 24 lines] > My alternate is to saw the wood from thicker to make the frames > needed. First off, the way you're doing it is not going to cut it. Make a real steam box. Secondly, the type of wood (green, air-dried, kiln-dried) makes a substantial difference. Kiln-dried wood is much more difficult to bend. Third, define "short". If you're talking about a 12" piece of 1x3 oak, you're never going to notice any difference in stiffness as you don't have enough leverage to bend it. Stock that size is not going to get limp, no matter what you do with it and it will require considerable force to bend it. Start with stock that's at least 24" long and you'll see the difference. > > Hi, > [quoted text clipped - 39 lines] > > - Show quoted text - Yeah, make a real steam box and figure 15 minutes for each 1/4 inch. You will need to leave the board long so you have enough leverage to do this. If you don't steam long enough, it will snap, if you steam too long it can get mushy and basically tear. I use a big box and a turkey frier to steam wood. I made a top for the pan and put a radiator hose from it to the box. >>> Hi, >>> I am new to the concept of steam bending and am experimenting with [quoted text clipped - 37 lines] > turkey frier to steam wood. I made a top for the pan and put a > radiator hose from it to the box. A good alternative steam source is a Wagner Wallpaper Steamer. They're ~$50 and produce enough steam to run a decent sized box, at least big enough for the stock the poster is asking about. ... >A good alternative steam source is a Wagner Wallpaper Steamer. They're >~$50 and produce enough steam to run a decent sized box, at least big >enough for the stock the poster is asking about. Talking of alternatives - nobody mentioned the cold water method in tihs incarnation of the wood bending thread - which is reputed to turn planks to spaghetti: add ammonia - soak overnight. Disclaimers: 1) not tried it. 2) may take some of the beef out of the wood. Brian Whatcott Altus OK > ... > [quoted text clipped - 12 lines] > > Brian Whatcott Altus OK They do not recover full strength after ammonia... >> ... >> [quoted text clipped - 14 lines] > > They do not recover full strength after ammonia... And it's noxious to work with. No thanks. A piece of 1" red oak can be bent to radius of 1" if supported by a metal strap and 11.5" unsupported according to "wood Bending Handbook" published by Woodcraft Supply. That sounds about right to me as long as the strap is fixed at both ends so that the neutral axis is pushed to the outer radius. Also, remember that it is primarily the heat that plasticizes wood and that you do not gain any additional softening by heating the wood beyond the boiling point of water. Luthiers use dry heat as did barrel makers. I have never had very good results from simply getting the work piece wet, it must get hot. If you need to do further testing for your application before building a steam box you can try boiling the piece of wood or wrapping the section that you need to bend in rags and pour lots and lots of boiling water over the rags. Leverage helps but does not prevent breaking or crushing the grain on the inner radius. Bending over matched male and female forms with plenty of clamps does help. > A piece of 1" red oak can be bent to radius of 1" if supported by a > metal strap and 11.5" unsupported according to "wood Bending Handbook" > published by Woodcraft Supply. I think you meant that one inch oak can be bent to a radius of one foot! I am sure most caught that though. That sounds about right to me as long > as the strap is fixed at both ends so that the neutral axis is pushed > to the outer radius. Also, remember that it is primarily the heat that > plasticizes wood and that you do not gain any additional softening by > heating the wood beyond the boiling point of water. Exactly, if you heat it to much it either crushes, or tears. Like I said, a general rule is 15 min/quarter inch of thickness. Luthiers use dry > heat as did barrel makers. I have never had very good results from > simply getting the work piece wet, it must get hot. [quoted text clipped - 3 lines] > section that you need to bend in rags and pour lots and lots of > boiling water over the rags. I don't think you could get enough consistancy with rags on 1 inch thick oak. I think the benefit of wet wood is transfering heat more evenly thorough the piece. > Leverage helps but does not prevent breaking or crushing the grain on > the inner radius. Bending over matched male and female forms with > plenty of clamps does help. A note. Once wood has been steamed once, the cells will not soften again with heat. Also, when you remove the part from the steam, you have literally seconds, maybe 7-10 to get the part bent or it will cool and lose it's ability to bend, it will most likely crack. Always make your radius a little smaller, it is much easier to open up a radius part later that way, than to try to bend it more closed on installation. You must also leave an extra foot or more on each end of 1 inch oak so you have some leverage, even after steaming, 1 inch oak is no party to bend. Lastly, always wear protective eyewear and optional other safety gear when working with steam, wood, fire, etc. Good luck and move quickly and in a predetermined manner and you should be fine. On Jun 25, 10:03 am, justwaitafrekinmin...@gmail.com wrote: > > A piece of 1" red oak can be bent to radius of 1" if supported by a > > metal strap and 11.5" unsupported according to "wood Bending Handbook" > > published by Woodcraft Supply. > > I think you meant that one inch oak can be bent to a radius of one > foot! I am sure most caught that though. Nope, the book says 1" or 25 millimeters. Unsupported it's 11.5 inches. (My experience is that a radius of 1 foot is achievable with out the metal strap support.) I'll grant you that it seems impossible and I'm looking for another source in my office but I can't put my hands on it just now. I know that Thonet did some very impressive bending in the chairs he made. The book states that these are the results of tests done on air-dried steamed material 1 inch (25.4 mm) thick. Part of the "support" they refer to is that the work piece is attached to a metal strap on the outer surface that is clamped to the work piece by applying clamping pressure on the ends of the pieces, i.e. the clamp faces are pressing on the end grain face of each end, this is critical for this kind of bending. It is not just having a "backing" strap. Clamping pressure must be applied to the end grain faces as the piece is bent. > On Jun 25, 10:03 am, justwaitafrekinmin...@gmail.com wrote: > [quoted text clipped - 19 lines] > "backing" strap. Clamping pressure must be applied to the end grain > faces as the piece is bent. Sounds like some pretty serious control of several aspects of the process would be necessary. Don't think I could get better than one foot radius with much consistancy on 1 inch thick oak with the setup I have. snip--- > Sounds like some pretty serious control of several aspects of the > process would be necessary. Don't think I could get better than one > foot radius with much consistancy on 1 inch thick oak with the setup I > have. I can imagine a 12" Radius or possibly bending to a 24" dia. Based on my test...I can not imagine a 1" radius though I read the same in my research. Anyone have hands on? thanks marshall >> A piece of 1" red oak can be bent to radius of 1" if supported by a >> metal strap and 11.5" unsupported according to "wood Bending Handbook" >> published by Woodcraft Supply. > > I think you meant that one inch oak can be bent to a radius of one > foot! I am sure most caught that though. No the original post is correct. > That sounds about right to me as long >> as the strap is fixed at both ends so that the neutral axis is pushed [quoted text clipped - 4 lines] > Exactly, if you heat it to much it either crushes, or tears. Like I > said, a general rule is 15 min/quarter inch of thickness. Nope. If you get it too WET, it will crush and/or tear. If you heat it too much, it drives off the moisture in the wood and it becomes brittle. The typical failure mode it a sharp break. > Luthiers use dry >> heat as did barrel makers. I have never had very good results from >> simply getting the work piece wet, it must get hot. The whole point of using steam is that it heats the wood quickly and evenly to a consistent temperature, the boiling point of water (100C/212F). The moisture helps to carry and transfer heat more efficiently than dry air does. >> If you need to do further testing for your application before building >> a steam box you can try boiling the piece of wood or wrapping the [quoted text clipped - 3 lines] > A note. Once wood has been steamed once, the cells will not soften > again with heat. Not exactly. As long as it has been steamed, it can be re-steamed. If you heat it any higher, such as is done during kiln drying, it alters the lignin in the wood and make bending it more difficult. However, I've seen good bending results with kiln-dried oak that was subsequently steamed, but you can't achieve as small a bend radius with it. > Also, when you remove the part from the steam, you > have literally seconds, maybe 7-10 to get the part bent or it will > cool and lose it's ability to bend, it will most likely crack. This is a common myth that is pure bunk. It takes ~1 hour to heat 1" thick wood sufficiently in a steam box, so there's no way that it can cool enough in a few seconds to make any difference in how it bends. In fact, one of the biggest causes for failures/breakage during steam bending is rushing it. It takes a little time for the fibers in the wood to slip and the thicker the wood, the more time it takes. Bending should be done smoothly, deliberately and as quickly as the wood will allow, but you have a LOT more than a few seconds to bend it. > justwaitafrekinmin...@gmail.com wrote: > >> A piece of 1" red oak can be bent to radius of 1" if supported by a [quoted text clipped - 54 lines] > should be done smoothly, deliberately and as quickly as the wood will > allow, but you have a LOT more than a few seconds to bend it. Now I will disagree with you. I have several steam boxes and have steamed a lot of oak and other lumber... But I will let the OP make the call. Nice to see you again Brian. >A piece of 1" red oak can be bent to radius of 1" if supported by a >metal strap and 11.5" unsupported according to "wood Bending Handbook" [quoted text clipped - 14 lines] >the inner radius. Bending over matched male and female forms with >plenty of clamps does help. Back when I lived on the coast of Maine I helped with the rebuilding of a 40 ft. dragger under the supervision of an 80 years old boat builder. We were replacing 4 X 4 inch ribs. The ribs were made from green oak or at least not seasoned for years and years. They were sliced down the middle for all but the butt where they mortised into the keel timbers. Then they were boiled. A long piece of large pipe sat at an angle with one end in a fire. The pipe held three or four ribs and was full of soapy water (I have no idea why soapy water was better). We boiled them for a while and then bent them into the forms. If they didn't seem limber enough we took them out and boiled them some more. It was all new to me but the 80 year old boat builder didn't seem to think it was anything out of the ordinary. Bruce in Bangkok (brucepaigeatgmaildotcom)  SignaturePosted via a free Usenet account from http://www.teranews.com |
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