Steam Bending Tips
Expert info on grain, sawing, moisture content, and finishing concerns for steam bending wood. October 2, 2005
I'm about to embark on my first steam bending mission. I'm looking at white oak as the best wood. I'm using 2" x 2" and want to know if flat or quartersawn is best. Radius will be approximately 3-4 feet. I'm getting conflicting advice. Also, I'd like to know about finishing bent wood. Does it matter if it's not completely dry?
From contributor J:
I wouldn't use either. I've steamed several pieces for the bow on Windsor chairs. I always rived the piece out, making sure to follow the grain and even then, with a diameter of around one inch, I would get tearout about 25% of the pieces. The radius would be about a foot.
From contributor F:
According to my sources, there is little difference in bending properties between plain sawn and quartersawn material. Only in the case of severe (tight) bends was any difference noted, and then it was a slight difference. Very straight grained and very clear (little swirls and pin knots can cause problems) woods are the best for bending. Ash seems to be rated high as a good choice. Oak gets bent quite a bit, as there is a lot of it around. You will need to let the parts dry before sanding and finishing.
From Professor Gene Wengert
Moisture content at the time of bending is oftentimes more important than grain. But if you have the correct MC, then quarter grain will bend with much less defect than will flat grain with the ring porous species like oak, ash, hackberry, etc. So, use quarter white oak for sure. (Contributor F's comment is true for even grained woods like maple, alder, basswood, etc. but not for ring porous woods.) Once bent, the wood must be held in the bent position and dried fully. If it dries later, then it will try to come back to straight (or will unbend) somewhat. Do not finish it and then let it dry further.
From the original questioner:
Thanks for all the replies. Doctor, what would you consider optimum MC for steam bending? I'm having trouble finding a source for 2 x 2" x 12' white oak locally and time is of the essence. A local boat builder said the wetter, the better. If that is so, I do have some European copper beech that I cut up late last year. It has been stickered about 2 months, and must not have dried too much here in cold CT. I may try some of that and it would be a nice change from the oak.
From Professor Gene Wengert
For a severe bend, 25% MC is ideal... not too much wetter, however, as hydraulic pressure can develop and that will blow the wood apart. (Above 25% MC, there will likely be liquid water in the wood.) For gentle bends, no drier than 15% MC, with 18% MC being ideal.