I've been doing a lot of work on steam bending tech lately. It started with an issue with my air dried white oak. The posts for my rockers are too thick to make out of green wood, the drying would take too long and be very likely to check. I had some problems even with the air dried stuff, until I learned to cover the stock right after getting it in the form so that the moisture didn't evaporate to quickly while the piece was steaming hot. It worked great. Then, I moved the wood to my new drier shop, and the wood checked up terribly regardless...bummer. I think that the wide, flat sawn boards just stressed too much in the heated/ dry shop. So with all my ruined oak, and many chairs to build, I had to try new stuff.
The first thing that I did, was to supercharge my steamer. I turned to insulated pvc pipe to keep all the moisture going to the workpiece and not the wood steam box. Two heaters insure uninterrupted heat and quick recovery of temp after opening the box. It's amazing how much condensation runs out the back weep hole.
Then, I turned to trying kiln dried wood. My first board was flat sawn white oak 8/4" thick. I turned and steamed the piece for 2 hours. It bent perfectly...too perfectly in fact, I can't get the bend to relax into the final form, it took the overbend too well! I covered the piece with foil when it was in the form and later wrapped it in newspaper.
Next, I tried wrapping the piece in cling wrap right when I pulled it from the steamer. It was a revelation in that the piece stayed so hot for so long. Now I can really take my time and the piece keeps cooking in the form, which I think helps it relax into the shape and may set it better.
Then I switched to shrink wrap tubing from ULINE. I seal one end of a section of tubing by folding it over a couple times and exposing it to the exhaust from the steamer, it shrinks right up. Then, drop the workpiece in, shove out the air and the piece shrinks right up to the steaming piece. The cooling now takes place through conduction through the plastic, which is way slower than through the evaporation of the steam. This works amazingly well and is super quick to do.
I even used this on a comb back arm and found that I could move so slowly during the bend (because the heat is staying put) that the piece relaxed into the bend much more evenly and without twisting. It's much flatter than I was getting before, saving me the job of trying to fix the twist without getting the arm too thin.
I've been experimenting with quarter sawn kiln dried white oak, hoping that the stress on the tangential face would be less intense. Even though the board is showing some checking on the edges, I cut the edges about 1/2" in and found that the wood was fine. More to come, as I fail more....