[family] clevis_fork_head: DIN 71752 fork head

[TimPetrillo]

Family

• Family: clevis_fork_head
• Closes [family] clevis_fork_head #51
• What the part is: A parametric DIN 71752 steel clevis fork head without pin or retaining hardware, covering the coupled short and long catalog variants.

Checklist

• uv run bench2 validate clevis_fork_head passes locally; CI will re-run it.
• I ran bench2 preview clevis_fork_head, inspected every generated image, and committed preview.png, preview_views.png, and preview_extremes.png. The sampled tiers and both extremes are sane.
• This is a single-solid family, so family.json correctly omits a solids count.
• Every PARAM_SPEC source and check() constraint cites the Ganter table, a physical geometry rule, a documented shop convention, or an explicitly labeled proportion.
• The PR touches only designs/clevis_fork_head and contains only the allowed family package files.
• The commit is DCO-signed.
• This contribution is AI-assisted; I reviewed every line and stand behind the sources and constraints.

Sources used

• Ganter DIN 71752 Fork Heads, Steel, without Pin drawing and article table:
  https://www.ganternorm.com/en/products/3.6-Moving-Transferring-Connecting-with-Joints-Couplings-and-Gears/Fork-joints-Fork-heads/DIN-71752-Fork-heads-Steel
• Official Ganter DIN 71752-4-8-M4 STEP reference, SHA-256:
  484D00DB511133380BDCD87B676816C8A1798173320C8B047955E0D635972018
• Issue [family] clevis_fork_head #51 scope: standard right-hand coarse metric thread, with a simplified cylindrical thread-core passage.
• ISO metric coarse-pitch values and the documented tap-drill shop approximation d_core = d2 - pitch.
• The two end chamfers use the documented proportion c = 0.1*d2, fitted to the official M4 STEP's 0.4 mm chamfers.

Verification

• All 16 catalog size/length combinations build as one valid solid and survive STEP export/import.
• The M4 short model and the official STEP have zero bidirectional boolean difference after axis alignment, within CAD-kernel tolerance.

[github-actions]

Welcome, and thanks for the family PR! Three things that answer most questions:

• No checks running? A maintainer must click Approve workflows once for your first PR — pending, not ignored.
• Red gate? The message tells you the fix: click Details, or read the bench2 validate report comment posted after each run. Reproduce locally with uv sync && uv run bench2 validate <family> (debug help).
• Scope: designs/<family>/ holds only the package files (reference drawings/photos go in the family issue), and the PR checklist must be fully ticked. Not done yet? Mark the PR as a Draft.

中文:红 ✗ 点 Details 或看 validate 报告评论;本地 uv run bench2 validate <family> 复现;参考图放 issue 不放 PR;没做完用 Draft。入门 → GETTING_STARTED.zh

[github-actions]

bench2 validate

clevis_fork_head

  ✓ family.json: keys + base_plane valid
  ✓ pieces: build(10 params) + PARAM_SPEC + check present
  ✓ PARAM_SPEC: 10 params, all entries complete
  ✓ easy: 4/4 seeds sample+check+build+execute clean
  ✓ medium: 4/4 seeds sample+check+build+execute clean
  ✓ hard: 4/4 seeds sample+check+build+execute clean
  ✓ coverage: d1 reaches all 8 declared values (standard table fully covered)
  ✓ coverage: is_long reaches all 2 declared values (standard table fully covered)
  ✓ difficulty separation: difficulties produce distinct programs
  ✓ geometry novelty: 9/12 unique shapes (25% duplicate)
  ✓ solids: every instance non-degenerate, 1 solid(s) each
PASS — designs/clevis_fork_head

Previews: the previews artifact on this run.

[Copilot]

Pull request overview

Adds a new clevis_fork_head design family implementing a parametric DIN 71752 steel clevis fork head (without pin/retainer hardware), with coupled catalog-row sampling across short/long variants.

Changes:

• Introduces a catalog-row–coupled spec.py (PARAM_SPEC + refine + check) covering DIN sizes d1 = 4..16 and both length variants.
• Implements the CadQuery solid in part.py, including the clipped-sphere forged envelope, fork slot, pin hole, and simplified threaded bore + entry chamfer.
• Documents transcription, geometry derivations, and deliberate deviations in NOTES.md, and adds family.json metadata (plus committed preview images in the family directory).

Reviewed changes

Copilot reviewed 4 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
designs/clevis_fork_head/spec.py	Defines the sampling contract: coupled DIN row selection, refinement, and engineering/geometry checks.
designs/clevis_fork_head/part.py	Builds the CAD geometry for the fork head, matching the coupled parameters from the spec.
designs/clevis_fork_head/NOTES.md	Captures sources, transcription, and the geometric rationale for the model and proportions.
designs/clevis_fork_head/family.json	Declares family metadata for BenchCAD (standard, base plane, description, contributor).
designs/clevis_fork_head/preview.png	Rendered preview output for manual visual verification.
designs/clevis_fork_head/preview_views.png	Multi-view preview output for manual visual verification.
designs/clevis_fork_head/preview_extremes.png	Extreme-case preview output for manual visual verification.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[HaozheZhang6]

Highly recommend you to include the corrsponding img in issue and render img from your code

[TimPetrillo]

Thanks for the suggestion. The reference dimensional drawing, product photograph, and standard table are included in #51.

Below are the renders generated from this PR with uv run bench2 preview clevis_fork_head.

Multi-view render

Minimum and maximum catalog sizes

[Copilot]

Copilot was unable to review this pull request because the user who requested the review is ineligible. To be eligible to request a review, you need a paid Copilot license, or your organization must enable Copilot code review.

[HaozheZhang6]

lgtm

---

Thread-construction check (added 07-31): the M4-M16 internal threads are plain core-Ø passages (_thread_core_d, nominal − pitch, matching the official M4 STEP's 3.3 mm bore). Since the manufacturer's own STEP ships unthreaded, matching it is a defensible declared simplification — but note it in NOTES.md as a deliberate deviation (checklist §5) so the next reviewer doesn't re-litigate it. If the family is later held to modelled-thread standard, the framework's ring-thread construction drops in per bore.

[Copilot]

Copilot was unable to review this pull request because the user who requested the review is ineligible. To be eligible to request a review, you need a paid Copilot license, or your organization must enable Copilot code review.