I've done a bunch of hophornbeam with steam, by steaming the entire stave for one hour, another 15 minutes if it's really bad. Some staves have had a significant amount of twist from one end to the other, almost 90 degrees... although I try to avoid trees with that much twist. I do them while they still have a fairly high moisture content, but it may work if they're drier too. I bring them to about 1 3/4" wide end to end, 3/4" thick at the dips to 5/8" thick at the ends... bark removed, two coats of shellac on the back. I like to leave them clamped up until the next day if possible, but have removed them after they've cooled... doing 3-4 a day.