What is a DSTV NC1 file?

If you work anywhere near structural steel fabrication, sooner or later someone sends you a folder full of files ending in .nc1. This guide explains what they are, where the format comes from, and how to read one.

The short answer

A DSTV NC1 file is a plain-text description of one structural steel part, written in a standard format that CNC machines understand. It tells a beam drill line, saw, or plasma/laser cutter everything it needs to make the part: the profile and its dimensions, the steel grade, the length, every hole with its exact position and diameter, any copes or cuts on the ends, internal openings, and layout markings.

"DSTV" comes from the Deutscher Stahlbau-Verband — the German Steel Construction Association — which defined the standard (formally, the Standard Description for Steel Structure Pieces for Numerical Controls). Because it is machine-neutral and dead simple (ASCII text, one part per file), it became the de facto interchange format between steel detailing software and shop-floor machinery worldwide.

Who produces NC1 files, and who consumes them

On the producing side, detailing and CAD software exports NC1 files, including:

• Tekla Structures (NC file export)
• Autodesk Advance Steel
• SDS/2 and other detailing packages
• Exporters and add-ins for Inventor, SolidWorks, and AutoCAD

On the consuming side:

• CNC beam drill lines and saw-drill lines (Ficep, Peddinghaus, Kaltenbach, Voortman, and others)
• Plasma, oxy-fuel, and laser cutting machines for plates and profiles
• MRP/production-control software that nests, schedules, and tracks parts
• Viewers — desktop tools, or a browser-based one like NC1-Viewer.com that renders the part in 2D and 3D without installing anything

Anatomy of an NC1 file

Every NC1 file is organized into blocks, each introduced by a two-letter code at the start of a line. Here is a real (simplified) example describing an I-beam with six holes and a marking line:

ST
    1
    TEST-I
    PHASE1
    POS1
    S235
    1
    I
    W14X90
    1000.00
    355.60
    368.30
    18.03
    11.18
    15.24
    ...
BO
  v  200.00  95.00  18.00
  v  400.00  95.00  18.00
  o  100.00  50.00  14.00
  u  900.00  150.00 14.00
SI
  v  500.00  50.00  10.00  0.00  TEST-I
PU
  v  300.00  50.00
  v  300.00  140.00
EN

Reading it top to bottom:

• ST (start / header) — one block per file, listing order number, drawing/piece identifiers, phase, position number, steel grade (S235), quantity, profile type code (I = I-section), profile name (W14X90), then the numeric dimensions: length, height, flange width, flange thickness, web thickness, fillet radius, weight per metre, and more.
• BO (holes) — one line per hole: the face code (v web, o top flange, u bottom flange, h rear), the X and Y position in millimetres, and the diameter. Extra fields describe slots and counterbores.
• SI (numbering) — where and how large to stamp or write the piece mark on the part.
• PU (powder marking) — points defining layout lines to be marked on the part, here a vertical line on the web.
• EN (end) — end of the part description.

Other common blocks include AK (outer contour — end cuts, copes, bevels), IK (inner contour — rectangular or curved openings), KO (punch marks), and KA (bend lines for plates). For the full list, see DSTV block codes explained.

Units and coordinates

Dimensions are in millimetres, angles in degrees. Coordinates are local to the part: X runs along the member length from the start end, and Y is measured within the face being described. That per-face coordinate system is why the same physical hole appears with different Y values depending on whether it is described on the web or a flange — and why a purpose-built viewer beats reading raw coordinates.

NC1 vs. other formats

• NC1 vs DXF: DXF is generic 2D/3D drawing geometry; NC1 is manufacturing data for one steel part with fabrication semantics (faces, holes, contours) that machines act on directly.
• NC1 vs IFC: IFC models a whole building with rich metadata; NC1 deliberately describes a single piece, which keeps it robust on the shop floor.
• NC1 vs proprietary CNC formats: Machine vendors have their own controller formats, but nearly all of them import DSTV — it is the common denominator.

See a file for yourself

The quickest way to build intuition is to open a file and compare the text with the geometry. NC1-Viewer.com parses the file locally in your browser (nothing is uploaded) and shows every face as a dimensioned 2D drawing plus an interactive 3D model.

Open an NC1 file in the free viewer →

Next up: DSTV block codes explained and DSTV profile types.