STEP (.stp) input — step_io.py reader: bent parts unfold, flat parts deliver direct (builds 139/140/151)

kerfmaster pin list · Input formats

recordStates what the code does today. Auditable against the code — this is the only type that can go stale.

Content last changed 2026-08-28 — computed from the item itself, not typed.

Reader (step_io.py, 2026-08-26): pure Python, no OCC kernel. ISO 10303-21 / AP214 MANIFOLD_SOLID_BREP: face/edge/vertex topology plus evaluable geometry -- planes, cylinders, lines, circles, ellipses, rational B-splines (complex multi-inheritance entities folded). Built for the unfold work; this pin records it as the general STEP front-end, which the 036-era step_sheet.py toolchain (step-unfold-calibration) predates.

Two paths

• Bent part → unfold.py: skin shell found by adjacency from the largest plane through tangent bend cylinders; exact development maps (isometry for planes, neutral-axis unroll for bends), BA = θ·(R_inner + K·t), K = 0.33 a stated assumption until the shop rules a value (open with Jordan). Builds 139 (BNM78651 unfold, t=0.075, 4×90°) and 140 (its meshed nest).
• Already-flat solid → direct profile (build 151, first): no bend cylinders, so no unfold -- the top Z-normal planar face's FACE_OUTER_BOUND + FACE_BOUND loops project by dropping Z, and every edge converts EXACTLY (this file: 100% LINE + CIRCLE; full circles as two half-arcs). Nothing is healed -- STEP carries true curves, the polyline disease cannot occur.

Units

Inventor exports CONVERSION_BASED_UNIT('inch') = LENGTH_MEASURE(25.4) over SI mm — coordinates are then NATIVE INCH and must not be rescaled (unfold.py's /25.4 is for mm-native NX exports). The flat deliver script asserts inch-based or refuses; detection is stated in the build stats per the units house rule.

Build 151 (2026-08-28, Jordan: 'DXF and PDF please')

8VACUSEPRNG0001_FLAT.stp (VAC SEPR LOCK RING FLAT A, Motor City Wash Works, Inventor 2026 via ST-Developer): 37.156 × 3.000 × 0.0625" (thickness measured from the solid; material not stated in the file — answered by Jordan 2026-08-28: 16 ga 304 stainless (.060"). Note the solid is modelled at 0.0625" (1/16 nominal) vs the .060" stock — flat geometry unaffected. The Rev2 master table already carries the row: GX 10K / Stainless / 0.060, M100[SS304,N2,ZHL,S25,GX,0.0600], offsets .003 on #108/#107/#106, min_gap 0.2 — nothing to type. Jordan same day: MetaCam has NOT been updated with the M100s they gave us, so MetaCam title-bar codes (SUSN7, 3015LVPlusII-45CFR) are the shop’s stale naming; the Rev2 sheet is the master), 7 loops (6 holes ø0.281). QC clean. Audited by re-reading the delivered DXF through dxf_io.parse (the same reader every customer DXF goes through) against the STEP-parsed source: max deviation 0.00005" both directions = 4-decimal emit rounding only. MetaCam census POLYLINE/VERTEX/SEQEND/CIRCLE, PASS. Deliver script: deliver_step151_8vacuseprng.py.