Welding symbol diagram

About welding symbols

A welding symbol tells a fabricator exactly how to weld a joint: what kind of weld, on which side, how big, how long, and how to finish it. The notation is a reference-line skeleton — a horizontal line, a leader arrow pointing at the joint, and a small weld-symbol glyph snapped above or below the line — standardised by AWS A2.4 (US) and ISO 2553 (international). Schematex draws the skeleton correct-by-construction: you describe the weld, the engine places every glyph, dimension, and supplementary symbol.

This is a fixed-skeleton notation, not a graph — there is no layout to solve, so it renders deterministically every time.

1. Your first weld

The smallest useful callout: a header, one joint, one arrow-side weld.

welding "Bracket"
joint "bracket to plate" {
  arrow: fillet size=8
}

Three rules cover most usage:

1. Start with welding, optionally standard: aws | iso-a | iso-b (default aws) and a quoted title.
2. Each joint is a joint "label" { … } block. Put a weld on arrow: (arrow side) and/or other: (other side).
3. A weld spec is a type followed by key=value dimensions — fillet size=8, vgroove angle=60 root=3.

2. Sides — arrow, other, both

A joint is welded on the arrow side, the other side, or both.

joint "double fillet" {
  both: fillet size=6        # same weld on both sides
}
joint "asymmetric" {
  arrow: fillet size=8       # arrow side only
  other: vgroove angle=60    # different weld on the other side
}

• AWS (default): the arrow-side glyph draws below the reference line, the other-side glyph above.
• ISO-A (standard: iso-a): a dashed companion line appears; the arrow-side weld attaches to the solid line, the other-side weld to the dashed line. A symmetric both: weld suppresses the dashed line.

3. Weld types

Aliases: v→vgroove, u→ugroove, j→jgroove, flare-v→flarev.

4. Dimensions

Dimensions read along the reference line in fixed slots.

joint "groove" {
  arrow: vgroove angle=60 root=3 throat=12 len=50 pitch=150
}

5. Supplementary symbols

joint "post base" {
  arrow: fillet size=10
  around            # weld-all-around — open circle at the junction
  field             # field / site weld — filled flag pointing to the tail
  tail: "GTAW; WPS-12"   # process / spec / NDE method
}

6. Standard compliance

Schematex welding diagrams implement AWS A2.4:2020 (single reference line) and ISO 2553:2019 Systems A (dual solid+dashed line) and B.

• ✅ Full glyph catalog — fillet, square / V / bevel / U / J / flare-V / flare-bevel grooves, plug, slot, spot, seam, back, backing, surfacing, edge
• ✅ Dimension slots — size, throat (E), length, length-pitch, count×length, groove angle, root opening
• ✅ Supplementary — weld-all-around circle, field-weld flag, tail process/spec/NDE, contour + finish
• ✅ Arrow / other / both sides with per-standard convention
• ✅ AI-readable validation of illegal type/side/dimension combinations
• ⏳ Combined weld + NDE symbols (NDE is tail text today)
• ⏳ Arrow-break for the prepared member; staggered intermittent offset; melt-through / consumable-insert glyphs

References:

• American Welding Society (2020). AWS A2.4: Standard Symbols for Welding, Brazing, and Nondestructive Examination.
• ISO 2553:2019. Welding and allied processes — Symbolic representation on drawings — Welded joints.

7. Grammar (EBNF)

document  = "welding" ( "standard:" std )? title? NEWLINE joint*
std       = "aws" | "iso-a" | "iso-b"
joint     = "joint" title? "{" directive* "}"
directive = ( "arrow:" | "other:" | "both:" ) weldspec
          | "around" | "field"
          | "tail:" quoted-string
weldspec  = type ( WS key "=" value )*
type      = "fillet"|"square"|"vgroove"|"bevel"|"ugroove"|"jgroove"
          | "flarev"|"flarebevel"|"plug"|"slot"|"spot"|"seam"
          | "back"|"backing"|"surfacing"|"edge"
key       = "size"|"len"|"pitch"|"count"|"angle"|"root"|"throat"|"contour"|"finish"

Authoritative source: src/diagrams/welding/parser.ts.

Related examples