What is an NC1 file? The DSTV NC1 file format explained

NC1 files and the DSTV NC format

An NC1 file is a text file in the DSTV NC format. DSTV stands for Deutscher Stahlbau-Verband, the German Steel Construction Association, which published the standard for exchanging numerically controlled (NC) data of steel parts. Each NC1 file describes exactly one part – a rolled steel profile or a plate: its material, dimensions, outline, holes, cut-outs and markings.

The file normally has the extension .nc1 (older systems also use .nc). It is plain text, so any text editor can open it – but the numbers only make sense once you know the structure explained below. To see the part instead of the numbers, use the free online NC1 viewer.

NC1 file structure: the blocks

An NC1 file is a sequence of blocks. Each block starts with a two-letter code on its own line, followed by data lines. Lines that start with ** are comments.

ST – the header block

The first block of every NC1 file is ST. After the line ST and an optional comment line, the header values follow, one value per line, in a fixed order. Dimensions are in millimetres, written with a decimal point.

For profiles other than I-sections the dimension fields are filled according to the profile type; fields that do not apply are zero.

Profile type codes

Faces and coordinates: v, o, u, h

Every contour, hole and marking is assigned to a face of the part by a letter at the start of its line:

X runs along the length of the part from its start; Y runs across the face. For angles, channels, tubes and plates the standard defines which surface each letter means. A viewer shows the result at once; the NC1 Viewer can also turn the part about the X axis to look at it from the back.

AK and IK – outer and inner contours

AK is the outer contour of a face: a closed polygon given by points, each with X, Y and optionally a corner radius. For a beam cut square it is a simple rectangle; mitred ends, copes and notches appear as additional points.

IK is an inner contour: a closed cut-out inside a face – a window, a slot or a larger opening. A part can have several AK and IK blocks, one per face and contour. In plates, holes meant for laser or plasma cutting are sometimes written as circular IK contours instead of BO holes.

BO – holes, slots, countersinks and threads

Each BO line describes one hole: the face (v, o, u or h), the X position along the length, the Y position across the face and the diameter. Letter codes mark special holes:

• s – countersink;
• g – thread;
• l – slotted hole (oval / elongated hole), with further values for the slot.

Because holes are the part of an NC1 file that a drill line actually uses, the hole table is the first thing to check in a viewer.

SI, PU, KO and KA – marking and bends

SI holds marking text: face, X, Y, rotation angle, text height and the text itself – typically the piece mark and other identification. PU and KO are marking contours (powder and punch marking): lines applied to the surface, for example the outline of a mating part that will be welded on. KA describes bend lines for folded plates and bent parts.

NC1 file example: a minimal file, line by line

This simplified example describes four HEA200 beams, 2000 mm long, with two holes and a marking text:

ST
** example.nc1
  1001
  D-12
  1
  B1
  S355J2
  4
  HEA200
  I
    2000.00
     190.00
     200.00
      10.00
       6.50
      18.00
      42.300
       1.140
       0.000
       0.000
       0.000
       0.000
AK
  v      0.00      0.00     0.00
      2000.00      0.00     0.00
      2000.00    190.00     0.00
         0.00    190.00     0.00
         0.00      0.00     0.00
BO
  v    150.00     95.00    22.00
  v   1850.00     95.00    22.00
SI
  v     50.00     30.00     0.00   15   B1
EN

• ST – order 1001, drawing D-12, phase 1, piece mark B1, grade S355J2, quantity 4, profile HEA200 of type I, length 2000 mm, height 190 mm, flange 200 mm wide and 10 mm thick, web 6.5 mm, radius 18 mm, 42.3 kg/m, 1.14 m²/m and four zero cut angles (square ends).
• AK – the outline of the web face (v): a 2000 × 190 mm rectangle, closed by repeating the first point.
• BO – two Ø22 holes in the web, 150 mm from each end (X = 150 and 1850), centred across the web (Y = 95).
• SI – the text “B1” on the web.
• EN – end of file.

Who creates NC1 files, and how are they made?

You do not create NC1 files by hand. They are generated from the 3D model by an NC export in steel detailing and CAD software such as Tekla Structures, Advance Steel, SDS2, Bocad, HiCAD, StruCAD and ProSteel. Add-ins for other CAD programs can export DSTV as well.

If you only have a 2D drawing of a part as a DXF file (a DWG can be saved as DXF first), the planned CutForge Converter creates the NC1 file from it.

Who reads NC1 files?

NC1 files are read by CNC machines for steel fabrication: beam drill lines, drilling and sawing lines, coping and profile-cutting machines, and plate drilling and cutting machines – from many manufacturers, for example Ficep, Voortman, Kaltenbach or Peddinghaus. The machine's software turns the geometry in the file into tool paths.

Other software reads NC1 files too: production-planning and nesting systems, and cutting-plan tools such as CutForge, which takes profiles, lengths and quantities straight from the files. And there are viewers such as the free NC1 Viewer.

How to open an NC1 file (DSTV) without Tekla

1. Text editor. Notepad or any editor opens the file and shows the structure – but not the part.
2. Free online NC1 viewer. Open the viewer page, drag the file in and see every face of the part as a 2D drawing with its holes and cut-outs – in your browser, without uploading anything. The free desktop NC1 Viewer adds measuring and PDF printing.
3. The system that created the file. Tekla, Advance Steel and similar programs can show it, but you do not need them just to look at an NC1 file.

Variants and pitfalls

• The DSTV format exists in several editions, and not every system writes exactly the same dialect – header details, optional values, number of decimals. Strict machine software may reject a file that a viewer displays correctly, so cut a test part first.
• Holes in plates are sometimes written not as BO but as circular inner contours (IK), a convention used for laser and plasma cutting.
• A part drawn from the other side can come out mirrored on the machine. Compare the NC1 drawing with the order drawing before cutting.

NC1 vs DXF: can you convert NC1 to DXF?

DXF is a general exchange format for 2D and 3D CAD drawings: lines, arcs, circles and text. It knows nothing about steel profiles, grades or faces. An NC1 file is a part description for production: profile designation, grade, quantity, faces and holes.

NC1 to DXF: the free online NC1 Viewer shows NC1 files (the desktop NC1 Viewer for Windows also measures and prints them) but does not write DXF. Exporting plates to DXF at 1:1 for laser or plasma cutting is part of the planned CutForge Converter. DXF to NC1: the program has to recognise the profile, the faces and the holes in the drawing – the Converter is built for this as well.