Air dried wood, at about 15%MC, is the preferred material for both steam and hot pipe bending, because the lignin has not been dried out excessively in the kiln and still plasticizes easily in the presence of heat. Since we are not blessed with a reliable source of air dried hardwoods in Arizona, it’s good to know that kiln-dried wood will also bend — though not so easily, and with a higher expected failure rate and a more unpredictable spring-back factor.
Bending kiln-dried wood is only possible with the use of a compression strap — a stiff but flexible steel strap with stop blocks bolted in place that precisely capture the length of the stick to be bent. The strap forces nearly the full thickness of the stick into compression, allowing only a bit of tension stress on the convex side of the bend. Wood stretches under tension only a small amount before failing (i.e., breaking rather dramatically), while it can be compressed very substantially before buckling. We bent 42″ (107cm) long sticks, 3/4″ x 1-1/4″ (19mm x 32mm) in cross section, into a ‘U’ shape around a 6-1/2″ (165mm) radius form. The most agreeable sticks made the trip with no discernible tension or compression stress whatsoever. Measured after cooling, the outside (convex) face of the stick was still 42″ (107cm), while the inside (concave) face of the stick averaged 39-3/4″ (101cm), a difference of 2-1/4″ (57mm)!
In the workshop we made these 42″ (107cm) bends using kiln-dried ash, hickory, walnut, cherry, maple and alder. We saw minor tension and compression stress evidence in some pieces of virtually all the species used, but several pieces bent perfectly. Ash is a predictable performer, as is hickory, and the oaks are fairly reliable. Our favorite on the day was the walnut (easiest to bend, least stress evidence, no failures). A couple of pieces of cherry also fared very well. When choosing pieces to be steamed and bent, use only the straightest grain stock you can find.
Bent (cold) lamination is arguably the most direct and effective way for most woodworkers to bend wood. The material is sawn into thin sections – typically 1/8″ (3mm), more or less – that are individually pliable enough to be bent cold to the intended form. Stacked up with glue between each layer, the stack is progressively clamped firmly to the form and remains clamped until the glue has thoroughly set. Preferred glues for bent lamination are the urea formaldehyde types because they cure hard, are not thermoplastic, and do not ‘creep’ (i.e., allow the laminates to ‘slip’ in reaction to the laminates’ tendency to try to spring back to an unbent condition).
Please peruse the following gallery of images from the workshop to get an idea what we were doing. If you’re interested in learning more about bending wood, considering signing up for my workshop the next time it comes on the schedule.
Thanks for sharing your knowledge. I recently built three toboggans in my ill equipped workshop. One I built from naturally dried ash, and the other two from kiln dried, quarter sawn ash. Regular sawn kd didn’t work. I didn’t use a compression strap for any of them, and 6 out of 27 failed, and most were the k.d. The slats were 1 1/2″ x 3/8″ thick.
Thanks for the comments, Carter. I hope the toboggan project(s) worked out OK in the end, and that you’re happily sliding down the hills now. I think you’d find that the compression strap would save at least some of those failures, were you to do it again. I’d be interested to know the radius of the bends you were making, how long you steamed the stock and what you used for a steam box sand steam generator. Any pictures of the completed work?
I am trying to bend a shepherd’s crook on a walking stick. I am using small trees ( 1 to 2 inches in diameter). I have tried steam bending without a compression strap. I have been able to get a 90 degree bend but nothing beyond that.
Is steaming bending with a compression strap the way to go or is there another method. I have searched the internet but have not been able to find anything on how people did it before “modern” times.
Hi Jim — thanks for posting. I’d like to know a little more about precisely what you’re doing: Using green, fresh-cut saplings? What kind of form and restraints are you using? I don’t have much experience bending round stock, instinctively I would say that using a strap certainly can’t hurt. But the strap would only be in contact with a very small portion of the tension side of the workpiece. I don’t have much experience steaming very green wood, either — it seems to me I’ve heard that it can be a good idea to dry the wood somewhat before working it. Water doesn’t compress, so if the piece is really wet when you put it in compression, bad things can happen. Here’s a link to Ed Peck’s 1957 USDA work “Bending Solid Wood To Form”:
http://www.fpl.fs.fed.us/documnts/usda/ah125.pdf
It may have some useful information for you. I’ll poke around a little and see if I can find any other pertinent info on this. Feel free to email me (or post again here): david@dfcabinetmaker.com
Good luck!
Hello Dave, Your insight on bending kiln dried Cherry has my keen attention. For a Maloof style cradle I am making I need to bend the cherry on a 31cm radius. It is 8cm wide, 25mm thick at the point where it enters my mold, and being 60 cm long it tapers dowm to 15mm. I want to bend it to form a 90 degree arc, and have prepared for over bending at the ends. If you see my video on Facebook: https://www.facebook.com/photo.php?v=10203126919034721&set=vb.1259212818&type=2&theater
you will see my setup.
The wood has soaked for three days. It is hard for me to believe that an hour steaming per inch of thickness is sufficient. I know that over steaming created compression problems. My strap is built into my comealong chain tensioner setup, I can achieve 212 degrees of heat, and steam all night if needed. Having read all that the Woodenboat Forum guys have suggested, I still come up shy on Kiln Dried Cherry.
May I ask you for suggestions. Specifically, how long should I steam and would vinegar added to my water help?
Thanks for sharing and any wisdom you may have for me.
Sincerely,
Greg Niederhaus
dakengreg@gmail.com
Hoping you’re still out there. Used to live in Arizona (18 yrs.) now in Savannah, GA. I’m wanting to bend some legs for a table I’ve been commissioned to build. All of reclaimed lumber, air dried for a century or more, roughly 12%. I’ve done a lot with glued up laminations but only one venture into steam bending and that was years ago, while still in Phoenix, and simple compared to what I’d like to try. Stickley chair rockers as compared to what’s in the picture. The problem I see offhand, width references seem never to be more than 1 1/2″. I’d need to be about 3″. Thickness no matter, I’ve even considered glue laminating to the steam bend. The steam bend becomes the form, so to speak. Can I get a 3″ strap? I know I can get the steel at a local metal shop but the stops seem pretty important. I’m sending a couple photos to the above email address. A couple mock ups. Don’t know which yet but the legs are pretty much the same. If you’re still there, thank you so much.
Chris LaReau
Hi Chris — Still here, indeed (thanks for the reminder that I need to update my site and blog more regularly, so it doesn’t seem as though I’ve disappeared! :-)). I received your images via email, and I’ll send a more complete reply there. You didn’t say what species of wood you’re using for the bends, and I’m curious? Some woods bend easier than others. If the stuff is truly air dried (never in a kiln) and has been in a humid environment like Savannah all these years, the lignin may still be viable (i.e., may respond favorably to steam bending). I’m assuming (hoping) you have enough of this stuff to do some testing and trial runs. Lee Valley is the only company offering strap kits of which I’m aware. Their straps are either 1-1/4″ or 2″ wide. You could try combining a 2″ with a 1-1/4″ to get your width. Otherwise a local steel supplier might be able to provide what you need (I think the stuff is spring steel, which would not stretch as easily under load as mild steel). The stops are extremely important — the combination of strap and stops is what forces the wood into almost 100% compression — it’s very handy to have one stop be adjustable, as in the Lee Valley setup, to be able to relieve pressure as the bend is formed. I’ll send you an email directly, and we can continue the conversation here or there. Good luck! – David
Hi,
Im trying to bend a small piece, about 6″ long, and 3/8 thick in a 2″ area and only about 30-45 degrees. The wood is ziricote, kiln dried. What would you suggestion be on bending that small area?
Hi Cameron,
6″ x 3/8″ x …. what?
I have not bent ziricote, and as a rule tropical hardwoods are not the most easily bent. Regardless, for pieces of that size and cross-section, hot-pipe bending would be the ticket. This involves soaking the workpieces in water for 2-3 hours, typically. The pipe setup is 2″ black (not galvanized!) pipe, threaded, about 6″ long. The threaded end is screwed into a flange, which is in turn screwed to a board concentric to a 2″ hole in the board. Fiberglass insulation is placed between the flange and the wood for safety. Fixing the board in a bench vise, a propane torch (lighted) is directed into the pipe through the flange end, heating the pipe up to a moderate temperature (water dances for a bit before evaporating). The soaked workpiece is then presented to the hot pipe surface and heated up (moving back and forth as necessary to prevent burning) until it is limber enough to bend. Have a form handy as a model to bend the piece to.
Hope that helps.
Regards,
David
Hi David,
I want to build a 4″ toboggan made of Ash and cannot manage to bend the wood properly. I do not have a woodshop and am using basic tools plus handheld power tools.
Do you know of anywhere I can buy the bent wood from or do you know of someone who is willing to do that piece of the project for me for payment? I live in Los Angeles and cannot find anywhere.
Thanks man,
Shawn
Hi Shawn,
Thanks for the inquiry. Bending wood successfully is not difficult, but neither is it simple. A bit of specialized equipment (often shop-built), some decent wood chosen expressly for bending, and a little knowledge of what you can (or can’t) get away with is all that’s needed. A toboggan could be a fairly easy place to start, depending on the actual curve you’re trying to get, especially since the thickness of the bent pieces will typically be relatively thin. I’ll send you an email with some information and suggestions. Good luck with your project!
Regards,
David
I am in Durango CO making wooden snowshoes. I have my jigs and steam box built. Kiln dried white ash fails each time. Do you know any sources where I can get air dried white ash? Thanks
Hi Jim,
Thanks for the inquiry. I’m a big fan of wooden snowshoes, having broken many miles of trail on them, made countless repairs, and even made a couple pairs (long ago).
I’m not surprised you’re having trouble with kiln dried material for this project. Even sawn, air dried stock will misbehave unless it’s very straight grained, shaved down to minimal thickness (in areas of severe bend), and preferably supported by a strap of some kind. But, I’m wandering off into how it’s done, and you asked about sources.
My Canadian friend and bending mentor, Michael Fortune, has recommended A&M Wood Specialties, near Toronto, as a good source of AD material. I have just written to him to ask if he has any additional suggestions, and will post his reply here and via email when I get it. You really have to dig to find possible sources, and then contact them to see if they can supply what you’re after. Here’s a couple other possibilities:
My friend Alf Sharp and his partner specialize in furniture grade, air dried wood at Stones River Hardwoods in Woodbury, TN. Searching around the internet for sources comes up with possible sources such as G.W. Green, in Indiana (worth checking out, but I have never done business with G.W. Green, so it’s not a recommendation). Small sawyers, specialty sawyers, sawyers supplying boatbuilders, and similar small yards are all possibilities. You have to dig, and do some calling — AD stuff is not that easy to find. Hearne Hardwoods in PA air dries all their stuff, but usually gives it a minimal blast in the kiln to kill bugs before shipment, you might talk with them.
That brings up one point of concern regarding ash, in particular: the emerald ash borer has been devastating ash forests in the US, so it’s very possible that will make it more difficult to obtain air dried lumber by shipment. There may be restrictions in place to help prevent the insects’ spread. Haven’t researched it, but something to keep in mind.
Hope the above info helps a little, and if Michael has any good suggestions I will post them here. Anyone else reading this, if you know of good sources of supply for air dried timber of any kind, please share here if you can.
Good luck – and let me know if you find some good stuff!
Regards,
David
Michael Fortune reports that A&M is still a good source, and they are familiar with shipments to the US (may not be cheap). He suggests, as I did above, beating the bushes to find small sawmills and/or distributors out east who might cater to the AD market.
Again, if anyone reading this knows of or discovers a source worth trying, please post here. Thanks ….
David
Thanks a lot Dave for your comprehensive info. I’ll let you know what I find. Happy New Year.
Hi, I am a novice in woodworking and I am wanting to specialise in creating artistic pieces incorporating slightly curved surfaces, for example the horizontal top of a Japanese lantern that incorporates a slight curve towards one or two corners. Typically I am interested in knowing if the steam bending method could be used curve a 200x200x10mm square wood? I can see a lot of information on bending long narrow pieces of wood but I haven’t come across bending wider pieces. Thank you for your input.
Cecilia
Hi Cecilia,
Thanks for your interest and inquiry. You should be able to bend 200x200x10mm piece, using steam or perhaps the hot pipe as the heating medium, especially if the bends are mild. 10mm is about the functional maximum thickness for using the hot pipe, but it might be worth a try. As with any bending operation, air dried (12%-20% mc) material is preferred. You may find it easier to bend a longer piece — say, 200x10x400mm — because it gives you more leverage, trimming it down to the desired length after the bending. The 200mm width may present some challenges, but it should be doable. If you like, send me a drawing and details of your proposed project (david@dfcabinetmaker.com) and I may be able to make more specific recommendations. Also, look for any of the articles and videos on steam and hot pipe bending that Michael Fortune produced for Fine Woodworking Magazine over the past 25 years or so. He is the master. Good luck, let me know if I can be of help.
Regards,
David
Hi, I need to bend a top rail for two driveway gates. Being 3 inches thick and square it’s a big piece to try to steam bend. With the right wood, and a curvature of 10- 20 degrees along 2.5 metres, is this the way to go. Or should I go with lamination or try cutting from a single piece of stock? Cutting the piece will show a lot of end grain (it’s external use). Bending may not create the same curve on each gate.
Really appreciate your thoughts. Thanks
Hi Phil,
With good material — straight grained, a species amenable to bending, ans air dried — you should be ble to make the kind of bends you describe. I confess you’ve sent me back to my (dusty) math books to try to figure the radius of 10-20 degrees of curvature over a chord of 2.5 meters, but on the face of it I don’t think that’s very severe. I once saw nearly 4″ thick AD walnut successfully bent to 90 degrees of curvature over a chord of about 28″ (20″ radius), yours is mild by comparison. The form must be very stout to withstand the force and leverage required to bend heavy stuff, and of course a full width strap and end blocks are recommended. Air dried stuff is essential. Typically air dried material exhibits minimal ‘springback’, so getting two pieces bent to the same shape, or nearly so, is not a problem.
Cold lamination has it’s charms, most especially in terms of controlling the resulting shape as precisely as possible. As long as possible glue line exposure is not an issue, with a waterproof, no-creep glue such as resorcinol or epoxy, lamination is a perfectly good way to go.
Curves formed by joining sawn segments are always a last resort, in my opinion.
I hope that helps.
Regards,
David
I have been looking into doing some steam bending for the first time and came across this article. I know you wrote it a long time ago but I wanted to know if steam bending a small cabinet door would be a bad idea. I am not quite sure how it will react over time. Thank you for your time
Thanks for the inquiry. In order to answer your question, I need more information about what you’re hoping to do. I think you would find that most curved cabinet doors are fabricated by lamination, rather than steam bending. But it’s possible you could incorporate steam bending into your construction — is the intended door a solid panel? Frame and panel? What kind of material? What size? What approximate radius of curvature? If you let me know more about your project, I can hopefully give you some information that will be of use. Feel free to post here, or send me details via email.
Regards,
David