3d-print-model-splitting

# 3D Print Model Splitting This skill turns a single complex sculpted STL into multiple Bambu-ready, physically assemblable parts. ## Core rule Do not confuse printable with assemblable. Also do not confuse a material-selection preview with a split part. - MeshFix/slicers can make parts watertight and printable. - They do not guarantee that interfaces have clearance. - The validated workflow succeeds because it treats part interfaces as the core problem. - A face-selection preview is only a semantic preview. It is not a valid part preview until every split part has its open contact boundary capped/filled. ## Mandatory preview gates For interactive demos or human-guided annotation, proactively generate previews; do not wait for the user to ask. - After preparing the annotation `.blend`: render a quick source/annotation preview so the user can confirm scale, orientation, and material slots. - After the user saves material-face annotation: render an annotation preview/contact sheet with clear part colors and face counts. - Before claiming “拆件完成” / “split complete”: generate a **capped split preview**, not just a face-selection preview. - In previews, label colors explicitly. If possible, show cap/interface faces in a distinct color. - If any part is still open at the cut/contact surface, say so clearly and call it “annotation preview only”, not “split preview”. ## Split-surface capping hard rules Every part created by material splitting must have its cut/contact surfaces filled before baseline export. - Deleting the other material groups leaves shell openings at the interface. This is expected but not acceptable as a split baseline. - Cap/fill all boundary loops introduced by the split before exporting baseline STLs. - Validate capping with boundary-edge counts per part. Target: `boundary_edges = 0` for each baseline part, unless a known intentional opening is documented. - If automatic hole filling leaves residual boundaries, retry with a more robust method or explicitly report the residual count; do not present it as final. - Lock the first accepted baseline only after it is “split + capped”; never lock a raw material-isolated shell as baseline. ## Scope boundaries Good fit: - figurines, statues, toys, decorative sculpts, and similar triangle-mesh STL files; - human-guided semantic part boundaries; - glue-fit or lightly finished assemblies; - Bambu-ready 3MF/STL handoffs. Poor fit unless explicitly requested: - fully automatic semantic recognition; - precision mechanical snap-fits; - automatic locator pins/magnets without human-confirmed anchors; - CAD-grade tolerance guarantees. ## Dependencies Common tools/libraries: - Blender for STL import, face/material annotation, rendering, and optional interference checks; - Python packages as needed by scripts: `trimesh`, `numpy`, `manifold3d`, `pymeshfix`, `Pillow`; - Bambu Studio or another slicer for final slicing/print review; - project-local folders for generated STL/3MF/Blend/PNG outputs. Do not write generated model outputs into the skill directory. ## Progressive references Read only what the task needs: - `references/sop.md` — generic workflow from STL to assemblable 3MF. - `references/clearance-lessons.md` — Boolean/MeshFix/clearance failure modes. - `references/blender-material-annotation.md` — human Blender annotation instructions. - `references/versioning.md` — project versioning and status conventions. - `references/case-study-v13.md` — optional validated example for a 5-part figurine. ## Standard workflow 1. **Prepare annotation file** - Create a Blender `.blend` from the input STL. - Add material slots for intended parts. - Use a project-local output folder. 2. **Human material-face annotation** - Human selects triangle faces in Blender Edit Mode. - Assign each face to a material slot. - Material assignment is geometry metadata (`polygon.material_index`), not texture paint. 3. **Split by material and lock a baseline** - Use material indices to export parts. - Clean tiny islands, cap open boundaries, export STL, render preview. - Lock a baseline that is only “split + capped”, with no clearance/pins/experimental Boolean. - Never overwrite the baseline. 4. **Repair only before clearance** - Use MeshFix when needed to make baseline parts watertight before clearance. - Treat MeshFix as a printability repair, not an assembly solution. 5. **Normalize winding before Boolean** - Ensure each STL has outward / positive-volume winding. - If volume is negative, invert before expanding cutters. - Wrong winding can reverse the clearance direction. 6. **Apply interface clearance** - Decide the real remaining assembly interfaces. - Define a responsibility table: which part subtracts which expanded neighbor. - Use robust manifold Boolean difference for interface allowance. - Choose clearance based on printer, scale, material, and finishing expectations. 7. **Do not MeshFix after clearance** - After clearance, use only tiny manifold simplify/sliver cleanup. - Strong MeshFix can fill intentional clearance cavities and recreate interference. 8. **Validate the deliverable, not only source STL** - Export the final 3MF/STL set. - Re-read 3MF objects and validate watertight/non-manifold properties. - Run pairwise interference checks on adjacent parts. 9. **Slicer and physical test** - Use Bambu Studio or another slicer for import/slicing/support/print preview. - Do not treat “no overlap warning” as assembly proof. - Physical assembly test is the final gate. ## Interface-clearance hard rules - Start from an un-clearanced baseline when changing the part plan. - Do not directly merge parts that already had clearance cut between them; this leaves internal cavities/seams. - Keep clearance work localized to real assembly interfaces. - If assembly is tight, create a new version and increase clearance locally; do not repair a failed branch blindly. ## Deliverables checklist For a final handoff, include: - final Bambu 3MF or slicer-ready project; - final STL parts; - preview/contact sheet; - version note; - validation summary; - 3MF object validation report; - pairwise interference report; - notes on failed/disallowed routes. ## Script organization Scripts in `scripts/` are reusable helpers with parameterized paths and part definitions. Keep new scripts project-agnostic: no user-specific absolute paths, no private names, and no hardcoded part schema unless the script clearly accepts a config/CLI override.