I am working on a chair project that SHOULD have steam bent components. I am aware that this requires Air Dried wood and a Lee Valley steam bending restraints. But – still I have problems. I am on the verge of reverting to glued-up, bent laminations. Does anyone have any encouragement to offer me – or suggestions to make the process easier.
Thos project should be fun, but so far, the fun aspect eludes me.
Jerry
Replies
Jerry, it would be helpful it you can describe exactly what you are trying to accomplish, where you are in the process and where you are having difficulty.
The chair will have 11 bent components (4 legs, 4 rails, 2 lumbar supports and a crest rail) Most components require 3/4' or 1" thick material (quarter sawn white oak, air dried, moisture content 20%, bent to a 30" or 36" radius. The lumbar supports are thinner and will reqire a tighter radius. Should be easy, right?I have a Lee Valley compression strap package and have steamed at up to 1 3/4 hours for the 1" stuff. Steaming in 4" plastic pipe, covered woith insulation. Pipe is about 4' long with steamer entry into a Tee at midpoint. Enclosure temp is a little over 200 degrees.I've read that the stuff should bend like spaghetti but I grunt on a long lever arm and reach to slip on a clamp. Then go again. The last one (trial) is still drying down from the 20% MC but I fear a LOT of springback.Laminations in a vacuum bag now seems so simple compared to this hassle.Jerry
I have limited steam-bending experience, so take my comments with a grain of salt.
An hour/inch is pretty typical and, based upon my limited experience (frames for a boat), 1" stock should have bent like spaghetti. Based upon the info you have supplied, the only thing I can offer is I wonder if your steam box was too tight. If the box doesn't leak there's no place for the hot steam to go...
sorry you are having such a hard time. just finished my first steam bend project using 3/4 kiln dried white oak. I agree with geraldartman that the turkey fried is a great steam generator. Yes it takes some muscle but nothing outlandish ( I had back reconstruction surgery 9 months ago so the days of bullying with muscle power are over). I used clamps to draw the pieces to the forms. I found that it was not the race that all the literature referred to. The wood remained pilable for at least 10 minutes as the clamps drew the piece to the form. I would think that a 30 inch radius would be relatively easy. By the way do not put the piece into the chamber until it has reached 200 degree mark. placing the board in a cold chamber and bringing it up to temperature is a major no-no that I found when researching the subject.Attaching some pictures. The one for the resulting table leg looks a little wierd because it is upside down. Thickness was from glue laminating 3 pieces of stock after bending and drying.
Nice! Really cool design. There certainly could not have been much, if any, bend-back the way you laminated the three pieces.What I find interesting is your use of kiln dried wood. Everthing I have read says that you CAN'T bend kiln dried stuff - that the lignin has already been plasticised and set in the drying process. That is why I use air dried. I'm glad you had good luck.Thanks for the post and photos.Jerry
spring back about 2-3 inches for individual piece but the form was made to overbend so the spring back was close to shape I wanted. lamination did allow the final tweakingkiln dried because I had it on hand and it had extremely straight grain. wood is bunch of polymer so a repeatly taking it to its glass state will eventually weaken the polymer but it does not destroy it. I might have gotten lucky - stupidity trumps knowledge occasionally.
Jerry, Sorry I am so late getting in to offer help, I have been away. One of the mistakes that I made was to not use a big enough heat source. I could boil water, but not at a rapid enough rate. If you also are just making a small stream of steam, You may not be generating enough heat to get it hot all of the way to the middle of the wood. Ask around if any of your friends have a really good fish cooker that you can try.I moved up to a propane fish cooker, which worked fine but then a friend gave me one that his dad had left him that looks like it may be army-surplus, that is a lot hotter. I am using a canning pressure pot that I drilled and tapped for a 1/4" flair copper tubing fitting. I am also using a plastic pipe that I rolled up in packing foam to insulate it for long thin parts, but I also have used a ply-wood box with holes cut into the sides to closely match the size of parts to be bent, so only the part that will be bent is being steamed. This allows me to more easily cycle parts through at a rate that I can work them on the forms, and it eliminates the tendency to reverse bend toward the strap on the ends.I don't have enough experience to say for sure, but some of the wood that I have used seemed to work better with less than the 20% that you are using. I had great results with some 2" thick walnut at 12% and then had some fail at 20%.It sounds like you are getting a good start, and I hope your fears are unjustified.
Thanks for the encouragement. Perhaps it is the heat source. I use a 1200 watt steam kettle which seemed adequate - but to be sure, that is why I took the temp.Jerry
If you checked the temperature early in the steaming process, and were able to maintain over 200*, It doesn't sound like you have a heat problem to me now. If it take a long time to get there though it would have doubts.Have you taken the parts off of the form yet, and know whether you are getting spring-back?
Jerry,
Do an advance search (Knots) under my screen name Jackie Chan (or jackiechan) and the subject of Steam Bending. I've described in detail the process along with some tips and technique.
If you have any question, please feel free to ask.
Dan Kornfeld, Owner/President - Odyssey Wood Design, Inc.
Steam bending is too complicated. My Scout troop built a dog sled and 18 pairs of show shoes. The dog sled started from an Ash tree and we split and rived it to components and steam bent 1" thick runnings 90 degrees and half to three quaters 180 on about 18" radii. The next year's project was snow shoes with 3/4 squares and compound radii. But these we milled out of commercial stock. We lost a lot (20%+) of sticks due to grain run out.The steam box was simple OSB lined with foil skinned insulation board. The best steam generator we found is a turkey fryer with a 5 gal galvanized can. We used 4" metal dryer flex pipe to the box. For a small project just use a 5" or 6" hvac pipe with reducer. I made a web of wire or dowels to support stock and enhance steam flow.You should plan on some test to check out the time needed to soften the stock to fit your project.
I think you ment this post for Jerry. I incorporate steam bending into many of the pieces that I design and fabricate.
Dan Kornfeld, Owner/President - Odyssey Wood Design, Inc.
Edited 10/10/2005 6:01 pm ET by jackiechan
Hi Jerry
Have you tried Green Woodworking? If you start with a fresh cut tree of a specis that bends well- like Red Oak & Ash. In Green woodworking you work the wood with the grain to the dimension you need then put into a steamer for 1 hour per inch of wood. Then remove the piece and quickly bend around a form. I build Windsor Chairs using this method and have good results. There are several books on Green Woodworking. The one I use is by Drew Langster -- How to make a Windsor Chair -- that should give you lots of detail. -- using for a Windsor Chair is optional.
Good Luck
Compton
Thanks to all of you. I've put steam bending on hold - I've got to get on with the chair.
Some of the bends are minor (no problem with shortgrain) therefore I'll bandsaw the shape , the rest I'll laminate. I have not abandoned the idea of steam bending - just for this project.I'll let you know in a later post how the repeat process works. Thanks again.Jerry
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