Sheet metal, clinch hardware and blind rivets: the guides cad-agent builds from (2026-11-01)

For Valpatel/cad-agent#283. Before any rule is written down or any check is coded, this page finds the best existing design guides for bent sheet metal, self-clinching (PEM-type) hardware and blind rivets. It ranks them and picks one primary source per topic. Every later rule in research/process-profiles.yaml and every check in the domain packages is built from the guides chosen here and credits them by name. Where an open-source tool already does the job, cad-agent adopts or wraps it instead of writing its own.

How to read it:

• Every source is in research/references.yaml and is cited here as [ref:<id>]. That entry records what was opened and on which date.
• A source marked unread was named, but cad-agent has not opened it. That may be because it sits behind a form, is paid, or could not be reached. Nothing is taken from it. Such sources are listed under unverified: in the registry.
• Values are cited and condensed, never copied. No vendor PDF, table or figure is kept in this repo.
• All sources were read on 2026-11-01 unless the registry entry says otherwise.

The answer: which guide leads each topic

Each arrow below means "its rules are written down in". Each source box names its kind (shops, maker, makers and government), so the colours only repeat what the words say.

flowchart TD
    S["shops:<br/>SendCutSend,<br/>Protolabs,<br/>OSH Cut"] --> P["process-<br/>profiles.yaml:<br/>shop and<br/>generic rules"]
    H["maker: PEM<br/>handbook and<br/>bulletins"] --> C["clinch rules<br/>and check"]
    V["makers: POP,<br/>Marson, GESIPA;<br/>government:<br/>FAA, NASA,<br/>MIL-HDBK-5J"] --> K["rivet rules<br/>and check"]
    S --> C
    classDef here fill:#fffdf5,stroke:#173d3c,color:#173d3c
    classDef near fill:#eef1e4,stroke:#6f8a80,color:#173d3c
    classDef out fill:#ffe1cc,stroke:#bd3a12,color:#173d3c
    class S,H,V near
    class P,C,K out

How the guides were rated

Each guide's authority is one of:

• Maker: the company that makes the fastener (PEM, Stanley, Howmet, GESIPA).
• Shop: a fabricator's own process rules (SendCutSend, Protolabs, OSH Cut).
• Government: a US government publication (NASA, FAA, DoD). These are free to quote.
• Standard: a consensus standard (ISO, DIN, ASTM, ANSI, SMACNA). These are paid, and are cited by number and title only.
• Handbook: a reference book.

A maker or a government source outranks a shop's rule of thumb on the physics of the part. A shop outranks everyone on what that shop's machines can do.

flowchart TD
    M["maker: the<br/>part's physics<br/>(PEM, POP)"] --> R["a rule in cad-agent,<br/>with its source"]
    G["government:<br/>free to quote<br/>(FAA, NASA)"] --> R
    S["shop: what its<br/>own machines<br/>can do"] --> R
    R --> C["a check names the rule;<br/>a paid standard is<br/>cited by number only"]
    classDef here fill:#fffdf5,stroke:#173d3c,color:#173d3c
    classDef near fill:#eef1e4,stroke:#6f8a80,color:#173d3c
    classDef out fill:#ffe1cc,stroke:#bd3a12,color:#173d3c
    class M,G,S near
    class R here
    class C out

The terms column says how cad-agent may use each guide:

• cite means summarise it and cite it as facts with page references, but do not reproduce it;
• public means a US government work;
• by number means a paid standard, cited by number and title only.

1. Sheet-metal design guides

Choice. A named shop's own data comes first: for SendCutSend, its feed and guidelines. The generic default when no shop is chosen is Protolabs, cross-checked against OSH Cut and The Fabricator. The Protolabs one-pager sets the tolerances. SendCutSend's figures sit in research/process-profiles.yaml as a named shop profile. A project's style.suppliers (cad-agent#284) can select it later, and the generic rules stay supplier-neutral.

2. Self-clinching hardware (PEM and its equivalents)

Choice. The PEM handbook and bulletins are primary for every clinch rule. SendCutSend's catalogue is primary only for what it will install, and where; its K/N values per sheet are sometimes stricter than PEM's, and then the stricter one applies. PEM's terms allow personal, non-commercial use and forbid republishing. So cad-agent records the rules and a cited subset of common sizes as facts with page numbers. It never copies whole tables, and never commits PEM's PDFs or CAD models.

One rule the PEM bulletins alone supply: the hardest sheet each fastener material takes. Drawn by tools/process_profile_figures.py from the compare: sm-clinch-sheet-hardness rules in process-profiles.yaml; sheet-metal-joining.md reads it.

3. Blind rivets

Choice. POP is primary for industrial, non-structural rivets. Marson, Avdel and GESIPA cross-check the strength per rivet. FAA and NASA set the edge distance and pitch, and MIL-HDBK-5J sets when its allowables hold. A rivet check labels its result "typical values, not certified", because POP, NASA and FAA all say that pop rivets are not for critical structure.

Where the rivet guides agree and where they do not: edge distance and pitch in rivet diameters. Drawn by tools/process_profile_figures.py from the compare: sm-rivet-edge and compare: sm-rivet-pitch rules in process-profiles.yaml.

4. Joint strength, tolerance and corrosion references

5. Paid standards and handbooks (cited by number and title)

These are recorded so that a reader with access can check cad-agent's rules against them. Nothing is taken from their contents.

6. Where the sources disagree

Where two sources give different numbers, cad-agent records both, with the spread, and states which one it applies.

The data errors found in the feeds are listed with the rules that use them, in the sheet-metal and joining pages. For example, SendCutSend's feed labels SP-440-1 as #6-32, and prints "A236" where A286 is meant.

7. Open-source tools: adopt, wrap, borrow or build

The recommendation key follows CONTRIBUTING step 1:

• adopt: depend on it;
• wrap: call it as a separate process, for GPL or LGPL code or another language;
• borrow: take its ideas, structure or test cases, with credit;
• pass: not useful, or it has no licence;
• build: write it ourselves, because nothing fits.

flowchart TD
    N["what cad-agent needs:<br/>bent parts · clinch<br/>hardware · blind rivets"] --> A["adopt<br/>bd_warehouse"]
    N --> W["wrap<br/>FreeCAD SheetMetal ·<br/>open-mrp/dfm"]
    A ~~~ B["borrow<br/>Blueprints · AISIS100.jl ·<br/>ranf_thread_fast"]
    W ~~~ U["build<br/>PEM table · rivet part ·<br/>clinch and rivet checks"]
    N ---> B
    N ---> U
    classDef here fill:#fffdf5,stroke:#173d3c,color:#173d3c
    classDef near fill:#eef1e4,stroke:#6f8a80,color:#173d3c
    classDef out fill:#ffe1cc,stroke:#bd3a12,color:#173d3c
    class N near
    class A,W,B here
    class U out

Gaps that cad-agent must build:

• There is no open dataset of PEM specifications. cad-agent's table is built from the PEM bulletins, with a citation on every row.
• No open CAD library models a blind rivet.
• No open calculator checks a blind-rivet joint in thin sheet.

So the clinch check and the rivet check are both build work. Their golden vectors come from the PEM bulletins, NASA RP-1228, MIL-HDBK-5J and published worked examples.

8. Sources for a second supplier profile: Protocase

These pages could build a second named shop profile next to SendCutSend [ref:protocase-design-resources]. Each page was opened to confirm its title, but its rules were not read.

• Public pages:
  • bend radii and minimum flange and hole distances;
  • bend types, including hems, jogs and offsets;
  • manufacturing tolerances;
  • self-clinching fasteners (PEM brand);
  • blind threaded fasteners, countersinking and inserts;
  • a cut-out library.
• Gated: the 31-page sheet-metal design guide sits behind a form, so it is unread.
• Terms of use: not yet read. They must be read before anything is taken from Protocase.