compose_part_from_primitives
Build exact 3D-printable parts by combining geometric primitives with boolean operations. Generates deterministic STL files and automatically centers them on the build plate to prevent print errors.
Instructions
Build a functional part by composing geometric primitives with booleans.
The **CAD-aware generation path** -- instead of asking text-to-mesh AI
to guess at geometry, describe parts as a tree of primitives combined
with boolean operations. Produces exact, deterministic, functional parts.
**SAFETY DEFAULT (changed 2026-04-15):** ``center_on_bed=True`` is the
default. OpenSCAD primitives are natively centered on the model origin
(``cylinder(h,r)`` produces geometry centered on X/Y = (0,0), which
means half the geometry lives at NEGATIVE X/Y). Sending such an STL
to most FDM printers (Bambu, Prusa, Ender, Creality) — whose bed
origin is the front-left corner — causes the nozzle to drive off-bed
into the purge/wipe assembly on layer 1. This happened once on a
Bambu A1 (incident #0, 2026-04-15, nearly damaged the printer).
With ``center_on_bed=True`` the output STL is translated so it sits
centered on the build plate and its lowest point touches z=0. Set
``center_on_bed=False`` only if your downstream flow expects
origin-centered geometry (e.g. further CAD composition).
**Operation format** -- each item is either a primitive or boolean:
Primitive: ``{"type": "primitive", "shape": "<shape>",
"params": {...}, "translate": [x,y,z], "rotate": [rx,ry,rz]}``
Boolean: ``{"type": "boolean", "operation": "union|difference|intersection",
"children": [op1, op2, ...]}``
**Primitive shapes and params:**
- cube: ``{"size": [x,y,z]}`` or ``{"size": scalar}``
- cylinder: ``{"h": height, "r": radius}`` or ``{"h", "r1", "r2"}``
- sphere: ``{"r": radius}``
- cone: ``{"h": height, "r1": bottom_r, "r2": top_r}``
- torus: ``{"major_r": ring_radius, "minor_r": tube_radius}``
- wedge: ``{"width": w, "depth": d, "height": h}``
- hex_prism: ``{"r": radius, "h": height}`` -- hexagonal (for nuts)
- text: ``{"text": "string", "size": 10, "depth": 2}``
- rounded_cube: ``{"size": [x,y,z], "radius": 1}``
- pipe: ``{"h": height, "outer_r": 10, "inner_r": 8}``
Requires OpenSCAD installed on the system.
:param operations: List of operation dicts (primitive/boolean tree).
:param output_path: Output path (defaults to temp file).
:param center_on_bed: Translate output to bed-center (default True).
:param bed_x_mm: Build plate X dimension for centering (default 256).
:param bed_y_mm: Build plate Y dimension for centering (default 256).
:param printer_id: Optional supported printer model id. When
provided, printer intelligence supplies the bed size.
:returns: Dict with result path, SCAD code, triangle count, and
(if centered) ``bed_centered=True`` + applied translation.INLINE 3D STAGE: on success this tool also opens Kiln's interactive 3D stage — an inline viewer panel the user can orbit, zoom, and turn over — in hosts that render MCP Apps panels (Kiln's hosted connection attaches a browser stage link for hosts that don't). Oversized meshes are decimated automatically for the stage; the PNG preview is the floor, not the whole experience.
Input Schema
TableJSON Schema
| Name | Required | Description | Default |
|---|---|---|---|
| bed_x_mm | No | ||
| bed_y_mm | No | ||
| operations | Yes | ||
| printer_id | No | ||
| output_path | No | ||
| center_on_bed | No |