Moldings: Steaming the bentside hitchpin molding

I finally got around to working on the bentside molding at soundboard level, which I decided had to be steam-bent. Kerfing with a test piece of walnut looked rather ugly, even though it did allow the piece to bend. The problem is that this molding needs to be bent along its thick dimension, and doing so makes it twist out of flatness against the soundboard. My handscrews don't seem able to clamp the molding while it's trying to twist at the same time.

The steaming apparatus is a consolidation of information from numerous web pages discussing the art of bending wood. I used a 1.5"-diameter PVC pipe 7.5 feet long, capped on both ends with threaded covers. On one end I put a Y-junction into which steam flows from a boiling kettle. In several places I drilled through holes and installed a 2" bolt to act as a shelf on which the wood sits while inside the pipe. At the far end I drilled a small drain hole to allow condensed moisture to exit the pipe.

Here's the setup:


At the far end, the kettle spout nestles into the Y-junction and the connection is wrapped with aluminum foil to prevent the steam from escaping. Bricks keep the whole thing from tipping sideways onto the floor, while at the near end a tray collects condensed water from the drain hole.

After putting my molding into the pipe, it was simply a matter of filling up the kettle, plugging it in and letting it steam for about 20 minutes. The general rule of thumb for steaming is 1 hour per inch of wood thickness, regardless of width. My piece is not even 1/4" thick, but the bare minimum steaming time seems to be about 15 minutes for thin pieces. I gave it a little extra to be sure, then uncapped the near end of the pipe, pulled out the molding and quickly rushed it over to the clamping jig:


This is largely the same as that used to bend the bridge, except that the clamping blocks have notches marginally larger than the width and thickness of the molding. These contain the molding and keep it from twisting out of flatness as it is bent.

I'll let this sit in place for a day or so, then I'll see how it looks when it's unclamped. I screwed my clamping blocks along a tighter curve than when I bent the bridge. The bridge needed a little extra bending at gluing time and I want to minimize that with this piece of molding.

WARNING: in case anyone is thinking of trying to steam-bend wood at home, make sure your steam pipe isn't completely air-tight, or it might burst after it fills up thoroughly with steam. My drain hole provides some pressure relief, and I also have a few unused bolt-holes that I plugged with plumber's putty. In an over-pressurized situation the putty would get forced out and excess steam would safely escape.