The part script¶

One script per part, at parts/<name>/<name>.py. It is ordinary build123d Python with a few conventions, so every tool (and every agent) knows where to find the dimensions, the variants and the checks.

from dataclasses import dataclass
from build123d import Align, Box, Cylinder, Mode, Part
from b123d_print import View, Wall, hole_comp

BED = (Align.CENTER, Align.CENTER, Align.MIN)

@dataclass(frozen=True)
class Dims:                      # every dimension named, in mm, with its source
    W: float = 30.0              # typed measurement
    H: float = 8.0
    HOLE_D: float = 3.4          # M3 clearance, target printed size
    CBORE_D: float = 6.5
    CBORE_DEPTH: float = 3.0
    HOLE_COMP: float = hole_comp(__file__)   # from YOUR config, default 0

VARIANTS = {"": {}, "wide": dict(W=40.0)}   # overrides only

def build(d: Dims) -> Part:      # print orientation, bed at Z=0
    p = Box(d.W, d.W, d.H, align=BED)
    p -= Cylinder((d.HOLE_D + d.HOLE_COMP) / 2, 50, mode=Mode.PRIVATE)
    p -= Cylinder((d.CBORE_D + d.HOLE_COMP) / 2, d.CBORE_DEPTH, align=BED, mode=Mode.PRIVATE)
    return p

def views(d):                    # sections saved with every export
    return [View("XZ", 0.0, "through the hole")]

def checks(d):                   # how much material is left around the counterbore?
    return [Wall("", "XY", d.CBORE_DEPTH / 2, near=(0, 0), radius=d.W, label="around the counterbore")]

if __name__ == "__main__":
    from b123d_print import run
    run(__file__)

What a script defines¶

Name	Required	What
`Dims`	by convention	frozen dataclass; every dimension an UPPER_CASE field in mm with a comment saying where it came from; derived values as `@property`
`VARIANTS`	no (default: only the standard part)	`{"": {}, "140": dict(PLATE_W=140.0)}` — overrides only; `""` is the standard part; output files get the key as a suffix
`build(d)`	yes	the printable part, or `{"name": part}` for several, in print orientation, bottom face on Z=0
`assembly(d)`	no	`[(part, color, label), ...]` in assembled position, plus simple stand-ins for what the parts mate with (a board, a sensor, a screw); the overlap check uses it
`views(d)`	no	`[View(...)]` cross-sections saved with every export
`templates(d)`	no	`[Template.slice(...), Template.face_of(...), Template.crop(...)]` fit-test templates written with every export (arguments)
`checks(d)`	no	`[Wall(...), Overhang(...), Probe(...), ...]` — see Checks API
`original(d)`	no	for a remix: the original model placed as the remix is; default: what `build(d)` loaded with `import_model`. The automatic checks also run on it, so its findings are labeled inherited, and `before_after` and export compare the remix with it

A script with only a module-level part = ... (no Dims) also works, without variants.

For the design review¶

Optional names the design review reads, in Dims (so a variant can override them) or at module level:

Name	Example	What
`STYLE`	`STYLE: str = "modern"`	`functional`, `modern`, `least_cost`, `rugged` or `soft`; `""` (the template's) uses the workspace's `style`, else functional
`SHOW`	`SHOW = ["+Y", "+Z"]`	the sides seen in use, in print orientation; surface findings are limited to them
`UP`	`UP = "+Y"`	the side that points up in use (print orientation), for the water-trap check; default `+Z`
`EDGES`	`EDGES = "chamfer"`	the edge language: `chamfer` or `fillet`; functional with `chamfer` is the industrial look

Values from the user's config¶

Helper	Use
`hole_comp(__file__)`	`HOLE_COMP: float = hole_comp(__file__)`; add it to hole diameters when cutting (Hole compensation)
`clearance(__file__)`	`CLEARANCE: float = clearance(__file__)`; the default mating gap (0.2 mm)
`printer(__file__)`	the active printer profile, or `None` in generic mode

Starting from an existing model¶

Helper	Use
`import_model(path, scale?, max_triangles?, merge?, script?)`	an STL, 3MF or STEP as a solid to change: `base = import_model("ref/bracket.stl")`; paths are relative to the script's folder (`ref/`) or the workspace (`refs/`). See Remixing a part

Never hard-code a hole compensation from somewhere else; keep hole fields at the size you want printed.

new_part / b123d-print new start from a template with all of this in place. The rules for agents (and humans) writing scripts are in Workflow rules; the modeling API itself is in the build123d docs. For real parts, see the Examples.