What a Single-Part Drawing Shows
A single-part drawing is the lowest-level fabrication document — it shows one raw steel component before any assembly occurs. It includes: the member section size and grade (e.g., W14×132 A992), the exact cut length, all hole groups with locations from the work point, cope dimensions if applicable, bend information for curved or kinked members, and a quantity (how many identical members are required). It also shows the piece mark prominently — this is the ID that gets stenciled or tagged on the fabricated member.
Single-Part Drawings vs. Assembly Drawings
A single-part drawing shows one component. An assembly drawing shows how multiple components fit together — a column assembly, for example, may show the base plate, the column section, and all connection plates as a single fabricated unit. Assembly drawings are used by the fitter and welder who builds the assembly; single-part drawings are used by the saw operator and drill line operator who process each individual component before assembly begins.
When Both Are Required
Most structural steel projects require both. Simple bolted framing can sometimes be detailed with assembly drawings only — if each member has only shop-bolted or shop-welded components that can all be shown on one sheet. Complex built-up members (plate girders, built-up columns, trusses) require separate single-part drawings for each plate and component plus an assembly drawing showing how they are welded together.
Key Dimensional Information on a Single-Part Drawing
Dimensions on a single-part drawing follow a strict hierarchy. Work-point-to-work-point dimensions establish the member's theoretical position in the frame; detailing dimensions define the exact cut length accounting for end conditions (cope depth, beam setback, erection clearance). Hole group dimensions are given from a reference datum — typically the left end of the member or the work point — to the centerline of the first hole, then hole-to-hole spacing across the group. AISC Code of Standard Practice Section 6 governs dimensional tolerances: ±1/16" on member length for members under 30 feet, ±1/8" over 30 feet. Hole location tolerance is ±1/16" from the centerline of any bolt hole group. These tolerances must be understood by the saw operator and drill line operator before they can correctly interpret dimension callouts.
How Tekla Structures Generates Single-Part Drawings
In Tekla Structures, single-part drawings are extracted directly from the 3D model through the drawing extraction engine. Each unique model object — identified by its position number (the equivalent of a piece mark) — generates its own single-part drawing. The drawing includes automatically dimensioned views at predefined scales, hole group tables, and a material header populated from the model's object properties. When the model changes, drawings are flagged as 'not up to date' and must be updated before re-issue. This model-driven workflow eliminates the manual dimension errors that occur when drawings are produced independently from the 3D geometry. Detailers working in SDS/2 follow the same principle: single-part drawings are extracted from the model's single-part containers, not drafted manually.
Piece Mark Systems and Uniqueness Rules
The piece mark on a single-part drawing is the fabricator's primary production identifier. Mark systems vary by firm but follow consistent logic: W-prefix for wide-flange beams, C-prefix for columns (or sometimes W-prefix with a column designation in the description), PL-prefix for plates, HSS or TS for hollow structural sections, and L or A for angles. Marks must be unique within a project — no two different members may share a mark. If two members are truly identical in every respect (same section, same length, same hole pattern, same end conditions), they can share a mark and a single-part drawing, with the quantity on the drawing reflecting the count of identical pieces. Most detailing platforms enforce uniqueness automatically, but manual overrides can introduce duplicate marks — a QA check before drawing release should verify mark uniqueness across the entire set.
Shop Traveler Integration with Single-Part Drawings
In fabrication shops that use ERP systems such as FabSuite, Strumis, or Tekla EPM, single-part drawings are linked to shop travelers — production documents that travel with each member through the fabrication sequence: saw, drill, fit-up, weld, inspection, paint, and ship. The piece mark on the single-part drawing is the key that links the drawing to the traveler. When the CNC saw operator scans or enters the piece mark, the correct NC file is loaded from the server. When the inspector signs off on the drilled member, the traveler advances to the next operation. This integration makes the single-part drawing the anchor of the entire production tracking system — errors in the piece mark or dimensions on the drawing propagate through every downstream operation.