I have a question on steam bending wood.
If I can remember, there was a formmula for the length of time a piece should stay in the steamer…..I think it was 1/2hr per half in of stock…..I need to bend a piece of wood probably oak approx. 1 1/2″ X 2″ X 3′ long…..What’ s the length of time this piece should stay in if my formula is right, 1 1/2 hrs, 2 hrs, or 3 1/2 hrs?
Replies
I don't remember either. But Lee Valley has a free downloadable booklet on steambending on their website. Don't forget use air-dried material that hasn't been sitting around indoors.
Meg',
The wood needs to be steamed for 1 hour for every inch of thickness at a constant temperature of 212 degrees F. Other variables will come into play that could extend the steam time.
I do extensive amounts of steam bending in the custom furniture that I design and fabricate. If you have any questions, please feel free to ask.
Dan Kornfeld, Owner/President - Odyssey Wood Design, Inc.
Dan, I am fooling around with some steam bending also. The tables in the only reference material that I have only give the "minimum bending radius" for various species at one inch of thickness. I am wanting to bend about 3" of thickness, and can't find anything to guide me there. Do you have any info to share?
Keith,
What species of wood are you trying to bend, and what radius are you trying to achieve?
Each species of wood reacts differently to steam bending, but there are only a few that do it well. The best benders are Oak, Beech, Hickory, and Ash that is straight grained with no run out (a grain pattern that does not run parallel to the edge of the piece being bent). Other species can be bent, but not easily, and carry a high failure rate. 3" thick stock can definitely be bent using the proper technique and wood species. The wood will have to be in the steam box for over three hours under a constant temperature of 212 degrees.
The bending radius is based upon the thickness of the wood, the actual radius of the bend being attempted, and the wood species itself. A successful bend boils down to the ability to control both the forces of compression and tension being exerted upon the wood. The wood fibers on the inside of the curve are being compressed and can actually crush, the fibers on the outside are trying to stretch and will rip apart when pushed to their limit. The best way to control these adverse forces is by using a compression strap on the wood being bent.
What type of wood are you trying to bend, what is the length of the piece, and what will it be used for? Let me know, and I can address the specific situation (tips, techniques, etc...).
If you do an advance search of "steam bending" under my name jackiechan you can find a whole series of my previous postings that may be helpful.
Send along any questions that you've got.
Dan Kornfeld, Owner/President - Odyssey Wood Design, Inc.
Edited 8/23/2005 2:14 am ET by jackiechan
this is my thread i replied to someone in breaktime but you can get the idea of what I'm trying to accomplish...thanks for the advice
this is just standard oak from my shop....the piece I am bending is real simple (as far as the finished description goes) 3' long, at 2' there's a 45 degree bend, that's about it. I have done bending before. Nothing fantastic just messing around. Mostly small stock just to see how it works. I'm pretty much the fly by night guy, trial and error. This is my first piece where I'm actually going with demensions.....although this is not a drastic piece for my woodwork...I'm actually repairing an outdoor toy for my daughter. I made the steambox a while ago and the thing has been sitting there since those trial days......One thing that is new though, I've never heard of the fabric softner bit.
Thanks, Dave
Dave,
Oak has the best bending properties, and is an excellent choice for your project. But (and there always is one), trying to steam bend a piece of wood 3" square by 3' long with a 45 degree bend at the 2' mark will be difficult at best. Bending wood, even after being appropriately steamed takes some force and leverage. A steam bent piece of wood has an inherent amount of spring back (trying to go back to its original straight configuration). Because of this, a 20% over bend must be factored into the form that the wood is bent around.
For your project, and what I would recommend, is a combination of steam bending and laminate bending. Thinner sections of wood are much easier to bend, and when bonded (glued) together, produce a very strong piece with very little spring back. This also allows you to build a bending form to almost the exact final dimensions that you are trying to achieve (no 20% over bend).
Assuming that you have enough wood, resaw (table saw or band saw), the three foot long by 3" thick stock into manageable planks 3/8" to 1/2" thick (thinner is better). Once you have enough layers to add up to a three inch thickness, set them up in the steam box on edge (note: the wood inside the steam box must be raised up off of the bottom of the box on thin wood dowels or battens to allow full circulation of the steam) leaving enough space between the pieces for the steam to circulate.
Because each piece is now 1/2" or less thick, the entire group of pieces only needs to be in the steam box for a half hour or less (1 hour for every inch of thickness). Once they have steamed sufficiently, pull them out of the box, stack them on top of each other, and then as a group, bend and clamp them over your bending form. Let them cool overnight. Once they are finished cooling, use an appropriate outdoor adhesive, an epoxy would work best here, glue the layers together, and then just re-clamp it back onto the form until the glue fully sets up.
What you'll end up with is a very strong final piece that will produce little to no spring back.
Regarding your question about using fabric softener. The technique does work - somewhat, but I wouldn't recommend it. The 3" thick stock you're using would have to sit submerged for days, and would most likely spring back more than an acceptable amount. It can cause real problems when trying to apply a finish to the wood.
If you have any questions, please feel free to ask!
Dan Kornfeld, Owner/President - Odyssey Wood Design, Inc.
Edited 8/23/2005 10:28 pm ET by jackiechan
Edited 8/24/2005 12:36 am ET by jackiechan
great descrition dan
Thanks Dan, Very informative. I will probably try the laminating method.I'll let you know how it works out
thanks
45 degree bend.. DAMN!EDITZ:: I wish I could!
Edited 8/26/2005 1:50 pm ET by WillGeorge
Dan, Thanks for trying to help. I am bending some walnut right now, and will probably use some cherry, elm and oak later. If you failed to notice, what I am after, is tables which show " Minimum Bending Radii for various species of thick wood with steam".If you are not aware of any tables, or charts, do you know off-hand if there is a certain amount or percentage of compression before collapse per species, then i could figure out the rest with the ratios between the inside / outside ratios relative to thickness and radius.I did do a search, and have read a number of your responses to questions. I did not find any photos of your work, have you posted any here? I would like to see some examples of how you are using this in you work.Just so you will know where I am with my progress, I have managed to bend up to 2.25" T X 2.75" W X 57" long around a 6.5" radius. The last few pieces were at 18* MC, and under restraint, and drying, however last weekend I bent a 1.75" piece with 10* MC to the same radius and left it unrestrained to judge the spring-back, and it has only relaxed 1" after one week.
The pieces above were bent past 90*.
Edited 8/26/2005 4:04 pm ET by KeithNewton
"...If you are not aware of any tables, or charts, do you know off-hand if there is a certain amount or percentage of compression before collapse per species, then i could figure out the rest with the ratios between the inside / outside ratios relative to thickness and radius."
I haven't come across any specific compression to collapse ratio tables per se. For myself, I will choose an alternate bending process for wood species that are notoriously poor bending candidates. A piece may end up bent, but the amount of wood lost to milling out the defects afterwards doesn't justify the effort. Another issue is that all steam bending candidates are not good or bad 100% of the time. Issues such as the total amount of time the wood was allowed to steam in the box, how was the piece bent - using a compression strap or unassisted, all factor into the success or failure of a bend. As an example, I have seen Cherry crush at 10" to 12" of radius, but using a compression strap, I have gotten a 1"x1"x24" long piece of cherry bent to an 8" radius. Technically is shouldn't have worked so cleanly, but it managed to hold its structure.
The best thing to do would be to experiment with each species that you potentially would like to steam bend. You will find out readily that tropical and exotic hardwoods bend poorly, as does woods like Cherry and most definitely any soft woods. As a general guideline I have found that a 1"x1" blank of any of the aforementioned wood will begin to show inside face compression at around a 10" radius.
The photo below is an experimental/prototype design created out of Maple, Birch, and White Oak. The legs are steam bent White Oak that originally started as a 3"x3" bending blank. They were shaped after a day and a half of being clamped to the bending form. After shaping one of the legs with a spoke shave, I realized that the arc had stayed the same, but that it was now twisted about 1/2" to one side. Most likely caused by the release of some internal stresses.
The enclosed photo shows another prototype of my design that was created using laminate bending techniques with Maple. Each bent piece was kept in the order that it came off the bandsaw, and after the bending/gluing process was complete, the grain all matched and the seams were practically invisible. Each rib of the cradle is one solid piece that starts on one side, goes down, traverses the bottom, and comes up the other side. They were created by laminating 3, 1/16" layers together, flitch cut from the same piece. All the pieces were clamped using a vacuum press.
View ImageView Image
Dan Kornfeld, Owner/President - Odyssey Wood Design, Inc.
Edited 8/27/2005 3:42 am ET by jackiechan
Edited 8/27/2005 3:45 am ET by jackiechan
WOW! For some reason I LOVE them tables!
If you are bending for the first time, start here.
http://www.leevalley.com/wood/page.aspx?c=1&p=31161&cat=1,45866,45867
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