1 Master object
Drop an STL here
or click to choose a file
FLASK works in millimetres. Everything downstream (walls, draft, shrink) assumes mm.
2 Pull direction & parting
Draft and undercuts are judged relative to this axis. Reorienting the pull is the first fix when the part locks.
Where the mold splits (two-piece) or where the open-face block is cut. Default is the part's mid-plane; the maximal cross-section is often better.
3 Mold type
Two-piece: part split along the parting plane into mating halves with keys, sprue and vents. For full 3D objects.
Casting: gravity-poured polyurethane. Halves named cope (upper) and drag (lower).
4 Shrink compensation
The cavity is scaled up so the cooled/cured part lands on size. Resin barely shrinks; semi-crystalline plastics shrink most.
5 Mold body
Wall is the minimum solid land around the part. The flange is the flat clamping land around the parting silhouette; the block footprint provides it.
6 Draft, keys, sprue, vents
Walls flatter than this against the pull are flagged. Automatic draft ADDITION on arbitrary meshes is a v1.1 target; v1.0 measures and flags (see Known Limitations).
One half gets bosses, the other sockets cut larger by this clearance so the halves seat without binding. The layout is asymmetric so they mate one way only.
Casting: a funnel at the cavity high point for gravity pouring; vertical risers vent trapped air upward, with small overflow reservoirs to feed shrinkage.
Injection: a tapered sprue feeds a runner on the parting plane, then a small edge gate into the cavity. The gate leaves the witness mark, so it enters on the part edge facing the gate side you choose here (put it on a non-functional face). Vents are thin slots on the opposite side, full depth on the cavity half, opening through the parting face so the split does not seal them. Vent depth 0.15 to 0.25 mm suits 3D-printed or CNC-aluminium tooling; go thinner only if you can machine it. Because the slots are so thin they are hard to see on the part, the viewport highlights the sprue, runner, gate and vents in colour (toggle "feed & vents"). Gate and vent LOCATION are CAD and flow-analysis calls, this places sensible defaults. See README.
Draft & undercut analysis
Load a part and set the pull direction. Analysis colours the mesh and reports the minimum draft.
Draftable toward pull (opens cleanly)
Draftable toward the opposite half
Low-draft wall (below threshold)
Undercut (traps the part in a rigid mold)
Result
No mold generated yet.
Export
STL is exported per mold piece, named by role. The session captures pull direction, parting and every parameter for re-import.