How to bend wood like this - Outdoor furniture project

[Steve Demuth]

A couple of things:

First, I assume the maple was kiln dried, which makes it harder, as you know. Harder in this case means more springback, because the lignin is already set from the kiln. So that's part of it.

But, second, I suspect you've got a cooling problem. One challenge with steam bending thin strips is that they lose temperature very rapidly when you pull them out of the steam chamber, and with a large piece going in an elaborate bending setup, can easily below the resetting temperature of the lignin in the wood by the time you actually get them bent. When bending thin wood for glue lams, as you are, I would not even use your bending apparatus for any lams 1/8" or less in thickness - I'd just slip them out of the steam, lay them over a curved form of the right radius, and immediatel weigh them down, or clamp them at the ends. You're not trying at this stage with thin lams to get a perfect conformance to the final shape - you'll do that in your big form when you glue them up - but rather, get the lam approximately in shape, and you want to capture the bend when the wood is hot through - especially since you've got kiln dried, recalcitrant wood to go with.

You're elaborate mechanism will still be very useful on the glue up, by the way. It's not a waste. And it'll work great for steam bending too, if you decide to go with thick pieces that hold their heat.

Edited to add: The spalted maple probably didn't help either. Spalting is of course the beginning of wood breakdown. Wood that is losing it's structure doesn't bend as well, or hold a bend as well. So, depending on how far along it was, that could have contributed to your issue.