grindstone

Grindstone

A showcase piece, not an example. A procedural grindstone: a sandstone wheel, a timber A-frame trestle, iron shoes, axle, hubs and crank, and an open trough. The piece then runs the shipped pipeline: unique-cell UVs, a Cycles high-to-low normal bake, an LOD chain, a convex collider, and a Unity glTF export.

Each A-frame is a king post with two diagonals tenoned 12 mm into its faces and into a fatter sill. It is not two sticks meeting at a point. The sills stand in iron shoes, cups one 6 mm reveal proud of the sill on every side. The trough is one manifold basin seated into the sills and carried on two end stretchers, which it bites by 4 mm. Every timber and iron edge is chamfered. The stone is 48 smooth segments with hard chamfer rings, in a mottled sandstone material. Stated size is a 0.50 m × 0.095 m stone in a 0.72 × 0.42 × 0.61 m frame.

It asserts budget conformance of the generated result. It does not witness an API contract. "It rendered without error" is not a check.

Composes skills mesh-editing-and-bmesh, bake-high-to-low, depsgraph-and-evaluated-data, engine-export-presets, and snippets bake_normal_high_to_low.py, setup_bake_target_image.py, lod_chain.py / decimate_to_budget.py, convex_hull_collider.py, export_preset_unity.py (helpers copied, not imported as a package).

Budgets

Declared as named constants; every gate recomputes from the mesh, materials, UVs, evaluated LOD, collider, or export file.

Axis	Declared	Measured (4.5.11 / 5.1.2 / 5.2.1)
Base triangles	1560–1780	1668 / 1668 / 1668
LOD1 ratio	0.32–0.62 of base	0.5000 / 0.5000 / 0.5000
LOD2 ratio	0.10–0.35 of base	0.2194 / 0.2194 / 0.2194
Materials	exactly 3 distinct; ≥ 280 wood, ≥ 190 stone, ≥ 260 metal faces	3 slots; 400 / 240 / 364
UVs	in 0..1, AABB overlap ≤ 1e-5	in range, overlap 0
Outer AABB	(0.722, 0.419, 0.610) m ± 0.015	(0.7220, 0.4185, 0.6100), zmin 0
Collider tris	≤ 320	304
Bake texels	smallest UV cell ≥ 12 px at the baked resolution	29.44 px at 1024 px
Export	written, size > 0	152272 / 152272 / 152260 bytes

The collider ceiling moved from 240 to 320 with the stone. 48 segments put more of its rim on the hull (198 → 304 triangles).

Hygiene

Recomputed from the generated mesh, not asserted about the script.

Axis	Declared	Measured (all three)
Non-manifold edges	0	0
Loose verts / edges	0 / 0	0 / 0
Doubles merged at 1e-5	0	0
Zero-area faces	0	0
N-gons	0	0
Coplanar cross-shell face pairs	0	0
Grounded: zmin	within 1e-4 of 0	0.0000
Named supports: 4 shoes	each zmin ≤ 1e-3	4, shoe_z 0.00000
Stone size	0.500 m dia × 0.095 m thick ± 0.02 / ± 0.015	0.5000 × 0.0950
Edge treatment	manifold edges within 5° of 90° = 0	0 wood, 0 stone, 0 iron

The coplanar budget counts pairs from different shells within 0.05 m, using hay-bale's constants. The first build matched only faces whose centres fell within 0.1 mm of each other, and no real overlap ever does. It reported 0 while the shoes shared three planes with every sill end, seen as a lit slit in each foot close-up.

Joint fit and seat

Axis	Declared	Measured (all three)
Crank-axle gap	≤ 0.008 m	0.00376
Shoe-wood BVH gap	≤ 0.008 m (overlap is 0)	0.00000
Trough-sill per-side gap	≤ 0.008 m (overlap is 0)	0.00000
Stone dip into trough	0.015–0.045 m	0.02416
Trough floor zmin	≥ 0.040 m	0.05800
Trough bearing	2 end stretchers, each biting the trough floor 0.002–0.008 m	2, [0.00400, 0.00400]

DECIMATE COLLAPSE triangle counts can differ across series, so the gate is a ratio band, not an exact count. Bake pixels are stochastic. The gate is has_data plus operator FINISHED plus the texel floor, not byte-identity. Per-member wood tone comes from random.Random(TONE_SEED), so it is identical run to run. Export byte counts differ by 12 B on 5.2.1 (glTF serializer), which is not a gated axis.

Falsifiers

Each violates one named budget. All thirteen were run on 4.5.11, 5.1.2 and 5.2.1 and returned the same code on each.

Flag	Budget violated	Exit
--skip-decimate	LOD1 ratio band	9
--stray-vert	loose vertex count is 0	15
--flush-shoes	coplanar cross-shell pairs: shoes sized to the sill and flush with its end (0 → 4 pairs)	15
--lift-z	bounding box zmin is 0	16
--short-legs	named shoe supports at Z=0	16
--float-crank	crank-axle gap	17
--float-legs	shoe-wood join	17
--narrow-trough	trough-sill seat	18
--no-dip	stone dip band	18
--low-stretchers	trough bearing: stretchers back at sill height, 5.9 mm under the trough	18
--sharp-handle	edge treatment: the crank handle's rims left square (20 right-angle edges)	20
--low-bake	bake texel density: 256 px bake (7.36 px per cell)	21

--flush-shoes moves the shoe envelope 12 mm inside BBOX_TOL (15 mm), so the AABB gate cannot steal it. --sharp-handle leaves the triangle count inside its band, so only the edge budget sees it.

Run

blender --background --python grindstone.py --
blender --background --python grindstone.py -- --skip-decimate
blender --background --python grindstone.py -- --stray-vert
blender --background --python grindstone.py -- --flush-shoes
blender --background --python grindstone.py -- --lift-z
blender --background --python grindstone.py -- --short-legs
blender --background --python grindstone.py -- --float-crank
blender --background --python grindstone.py -- --float-legs
blender --background --python grindstone.py -- --narrow-trough
blender --background --python grindstone.py -- --no-dip
blender --background --python grindstone.py -- --low-stretchers
blender --background --python grindstone.py -- --sharp-handle
blender --background --python grindstone.py -- --low-bake
blender --background --python grindstone.py -- --output grindstone.png

Smoke passes no flags.

Exit codes

File-local. 9 is a valid check code. 10 is reserved for gallery_framing.check_framing on the --output path. 15–19 are the hygiene and joint-fit family.

Code	Meaning
0	Success
1	Uncaught exception (FATAL wrapper)
2	argparse / usage
3	Mesh did not build / no UV layer
4	Base triangle count outside range
5	Material count ≠ 3 distinct slots, or a face-count floor missed
6	UVs outside 0..1
7	UV AABB overlap above tolerance
8	World AABB off declared outer size
9	LOD ratio band (--skip-decimate lands here)
10	Framing gate (render path only)
11	Collider triangle count above ceiling
12	Bake did not finish or image has no data
13	Export file missing or empty
14	--output produced no file
15	Mesh hygiene: loose, non-manifold, zero-area, doubles, n-gons, coplanar cross-shell pairs
16	Not grounded: bounding box zmin off 0, or a named shoe floats
17	Joint fit: crank-axle gap, or shoe-wood join
18	Seat: trough-sill gap, stone dip band, trough on the dirt, or trough not bearing on its stretchers
19	Stone diameter or thickness off the stated real-world size
20	A right-angle edge survived the chamfer passes (--sharp-handle lands here)
21	Bake texel density below the floor (--low-bake lands here)