What's the best way to make curved parts? Here are a few options and opinions, courtesy of our friends at the Woodworker's Journal.
Q. I've been woodworking -- exclusively with oak - for about 11 years. My question is on bending wood. On a simple chair the back piece is curved with the spindles fastened to the seat and the back piece. Since a dry piece of oak can't be bent into a horseshoe shape without splintering, how do you prepare a strip of wood so it can be bent into shape and how long does the process take? If steaming is the solution, where would I find or how would I make a steam box?
A. Michael Dresdner: "Steaming is an excellent option, especially with oak, which steam bends quite nicely.
"You can make a box of any material, including wood, to fit the size board you need to steam, but the easiest way to make a steam box is with plastic sewer pipe, since most boards will fit inside its 4" diameter interior. Cap the pipe on one end, and make a removable cap for the other. Angle the pipe a bit, with a drain hole near the bottom so that any condensed water can drip out. Add an intake hole along the top edge, and run a high temperature hose from your steam generator to pipe steam into the tube. Insert the wood, cap the end, and turn on the steam. You can generate steam with a cappuccino maker or any water kettle.
"Let the board remain in the steam for about one hour per each inch of its thickness. Hence, a half inch thick board would take about 30 minutes before it is ready to bend. Wear gloves (the board will be hot), and get it bent and inserted into a holding form as quickly as possible, as it will only bend while it is still hot, and once you remove it from the steamer, it cools very quickly. Set it into the bending form or clamps, and leave it in there until it is cool and dry, which in some cases may take more than a day.
"This is merely a capsule summary, of course. You might want to check one of the many woodworking books on the market that cover steam bending in depth. A quick online search turned up 38,000 entries on the subject. Here's a link to one such online article, including a sketch of a sewer pipe steamer."
A. Rob Johnstone: "There are a few of ways to form the curved top rail or crest rail of a chair. One easy way is to glue up bent laminations. If you slice oak about 1/8" thick, you would be amazed at the radius your can achieve. Use a mold or form and clamp multiple layers of thin stock (dry, not steamed) and glue. Once the glue cures, the shape is set. You will have lamination lines (they will be minimized if you used sequentially sliced pieces from the same piece of wood) and you will waste as much stock in saw dust as you will end up with. But the overall results are very good.
"You can also just start with a really wide piece of wood and cut the curved rail out of it using a band saw or jig saw. (Logically, you can glue up a really big piece of wood with that process in mind.)
"Steaming wood is one method of creating a curved rail as well. There are a couple of things that I have learned about steam bending that I can share. You will break as much wood as you successfully bend. Thinner stock bends better than thicker stock. At some point in the process you will burn yourself. I hate steam bending. (Did I type that out loud.) There are a few books on the market that will instruct you in building a steaming box and provide clamping instructions. The good ones will include a chart that calls out the approximate time required for differing species of various thickness. (e.g., steam 8/4 white oak for 10,000 hours before you try to bend it.)"
From the Woodworker's Journal eZine 2004 archives