I've been steam-bending kiln-dried redwood, oak, walnut and iroko since forever. It's perfectly OK to do as long as the section you're bending is as close-grained and perfect as possible, and is also 100% free from splits, knots, shakes or any unusual, uneven patterns in the grain. You need to double (or preferably triple) the tank time - which for me has always been one hour of steaming for every 10mm of material thickness. I absolutely wouldn't recommend using green timber for any type of decorative joinery. Once it starts to dry out, it will contract and move like you wouldn't believe.
Also - most importantly of all - the radius of your bend former needs to be at least 10-15% smaller than the radius of the finished bend. No matter how many clamps you use whilst the timber cools and dries - it
will spring back by around this amount. It's easy to push out and expand a smaller radius to fit the work, but almost impossible to make an under-bent radius tighter, as you'll be fighting against the linear solidity of the material. To start with = it's always better to go tighter than you need, at least 15%. Think of it like making a cut = you can always take a little more off, but you can't put it back on. Plus - wear gloves when you take it out of the steamer, and get it on the former, bend it around slowly but firmly, pressing it hard against the former, and get it clamped up as quickly as you possibly can. Until you're comfortable with the process and you've got your available timescales figured out - a buddy tightening the clamps as you bend it is a great asset. It cools and starts to firm up very quickly, but don't stress or panic. If it goes badly = just put it back in the steamer, wait, and try it again.
Here's a matching pair of sash window frames I made for a Georgian rectory built in 1799. The astragal (glazing) bars were pre-machined to shape, bent through 180 degrees in one hit, then trimmed to size. The main section of the window frame was made in four pieces, with the curved section at the top, plus the two vertical jambs spliced onto it, then fixed to the sill using mortise & tenon joints. The rest of the frame consisted of various additional thinner decorative sections also bent in one piece, and fixed to the frame.
Good luck with the curves !! Pictures - or it didn't happen.
Kevin
