# The Form Hewn Shop Notes · https://hewn.build/shop-notes/the-form AI-drafted, not yet checked: Drafted by Chip, the writing system Hewn runs on Claude, from Hewn's craft corpus. Jonathan Salomons has not read this note yet, and no outside reader has checked it. Read it as a shop note: check a number before you cut to it. Cite as: "The Form." Hewn Shop Notes, hewn.build/shop-notes/the-form. Drafted 2026-05-02; AI-drafted, not yet checked. --- Most failed bends aren't steam failures. The temperature was right. The time was right. The blank went soft. And then something went wrong on the form — wrong radius, wrong position, clamps not where they needed to be — and the part came out wrong or not at all. The form is where you actually make the bend. Steam just opens the window. The form is what you put in it. --- ## Build the form before you touch project stock The form tells you whether the bend is achievable before you've committed anything expensive. Can you clamp it in time? Is the radius actually what the design calls for? Is the form somewhere you can reach in 90 seconds with wet hands? Answer those questions with cheap test blanks, not with the cherry you milled last week. **Material.** Two or three layers of 3/4" MDF, glued and screwed. It machines cleanly on the bandsaw, takes clamp pressure without compressing, and doesn't warp. Solid wood works but can absorb moisture over repeated sessions and shift the radius on you. MDF is the reliable choice. **Height.** The form needs to be at least as tall as the part is wide. A 1.5" back rail needs a form face at least 1.5" tall. Shorter than the part and the overhanging edge springs out under clamping. You can't fix that in the session. **Clamping.** You need three clamp positions: start, middle, end of the bend. Build a small reference block at the start so the blank seats against something instead of sliding when you're moving fast. Moving fast is what you'll be doing. **Bench attachment.** The form mounts to the bench and stays there for the session. Clamp it, bench-dog it, screw it to a backing board — doesn't matter, as long as it can't move. Bending force is real. An unsecured form will shift the moment you need it not to. --- ## The overbend Every steam-bent part springs back. The form needs to account for this before you build it. Run three test blanks from the same species and section you'll be bending for the project. Measure the springback on each. Average them. Build the form to that radius tighter than your target. If you have no data yet, start here: - Cherry and ash: 10–15% tighter than target radius - Hard maple: 15–20% - White oak (quartersawn only): 20–25% These are starting points. Don't skip the test blanks. A form built to the wrong radius produces parts at the wrong radius, and there is no correction after they're cut and assembled. --- ## Clamping sequence The blank comes out of the box soft. You have 90 seconds. The sequence matters. Start at the center of the bend, not at one end. Clamping end-to-end drives the unsupported portion off the form face. Center first, then work out toward both ends. Pressure: firm enough to pull the part flush to the form. If it's lifting off, tighten. If the wood is visibly crushing, back off. "Firm and flush" is the standard. Pad the clamp faces — thin cork or leather between the jaw and the wood. The inside of the curve (against the form) is unprotected and that's where local crushing happens. The rehearsal before the session isn't optional. It's not about learning the motions. It's about making them automatic so you're not thinking when the clock is running. --- ## Setting Leave the part in the form overnight — minimum 12 hours in a heated shop, 24–36 in a cold one. Before pulling all the clamps, release one at the far end of the bend. If that end springs back significantly, it's not set. Leave it another 12 hours. Once it's out of the form, give it 24 hours before any final dimensioning or joinery layout. A freshly released bend continues to move as residual moisture equalizes. Mark your reference face after it settles. --- A well-built MDF form handles dozens of sessions. Check the face periodically for moisture absorption — enough sessions and the radius drifts. If you're building a form for a one-off, you can build it simpler. Five bends is a different proposition than fifty. The form is the geometry. Get it right before the first blank goes in the box.