There is no mystery in steam bending. There is only a phase transition in a structural polymer, managed with heat, moisture, and a piece of steel strap.
That's the whole mechanism. Everything else — species selection, blank prep, form geometry, overbend calculation — is just knowing which variable you're adjusting and why.
Six posts back, this arc started with the premise that steam bending looks more complicated than it is. Here's the proof: the box is a tube, the form is a jig, and the blank is lumber with good grain. The window is 90 seconds. You've worked in tighter windows than that.
What lignin does is simple. It's a polymer, and polymers soften under heat. Wet the blank to carry heat uniformly into the cell walls. Steam it to about 100°C until the lignin is plastic. Bend it over the form before it cools. When the lignin re-hardens, the new geometry is permanent.
The strap goes on the tension face — the outside of the curve — because that face would otherwise be in tension during the bend, and tension splits wood. With the strap bearing the load, both faces go into compression. The wood deforms instead of failing.
Springback happens when moisture releases and the elastic strain recovers. You planned for this when you calculated the overbend. That's why the overbend table exists. It's not a correction for bad technique. It's physics, acknowledged in advance.
None of this is unique to steam bending. It's the same material science as every post in the wood movement arc. Wood moves when it dries, expands when it wets, creeps under sustained load. Steam plasticizing is what happens when you take that fourth behavior — expansion under heat and moisture — and do something with it instead of working around it.
That's the shift this arc was trying to make. Wood movement as constraint is what you manage to avoid cracking panels and sticking doors. Wood movement as capability is what you use to build a Windsor bow.
The Windsor is the right integration test because it requires everything. Sharp tools for the spindles. Good joinery for the leg-to-seat connections. Sound understanding of movement for the seat slab. The bow requires the steam bending arc specifically — the right species, the right blank, the right session protocol.
You don't need to master all of it before you start. You need enough competence in each area to complete the piece. The bow goes first. Once the bow comes off the form and stabilizes for 24 hours, you know whether your blanks, your box, and your form are all working. If they are, the rest of the chair is furniture-making you already know how to do.
The sequence from this arc back to the beginning: sharp tools allow clean surfaces; clean surfaces allow tight joints; tight joints allow structural furniture; structural furniture eventually includes a chair; a chair with a bow requires understanding wood as a material that yields under the right conditions.
That is not a metaphor. That is the actual sequence of skills.
Build the box. Build the form. Mill the blank correctly and mark the tension face before it goes in. Do the session. Come off the form and leave it alone for a day.
The Windsor is waiting. So is every other bent piece you've been putting off because you thought it required something you didn't have.
You have it.