Learn · File formats · NC1 / DSTV
What is an NC1 file?
An NC1 file is a plain-text CNC file that describes one structural-steel part — its outline, holes, cutouts, and markings — in a format defined by the German Steel Construction Association’s DSTV standard. The name comes from the file extension, .nc1. Detailing software writes them; CNC machines and nesting software read them.
That’s the whole idea: one part per file, written in text a machine can follow and a person can read. A steel job arrives at the shop as a folder full of them.
Sec. 01 · Where it sits
Who uses NC1 files, and where they come from
NC1 files are the handoff between the detailing office and the shop floor. They carry the part geometry from the 3D model to the machine that cuts it.
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Stage 01
Detailing
Detailing software — Tekla, SDS2, Advance Steel — models the job, then exports one NC1 file per part: plates, beams, connection pieces.
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Stage 02
File prep & nesting
Someone checks the files against the job plan, fixes what the machine won’t like, and nesting software arranges parts onto stock for cutting.
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Stage 03
The machine
CNC plate machines and beam lines read the file directly — cut the outline, drill or punch the holes, scribe the marks. What’s in the file is what gets made.
Because the machine trusts the file, the file-prep step matters more than it sounds. A wrong quantity, a shifted header field, or a units mix-up doesn’t look like much in a text editor — but it becomes real steel.
Sec. 02 · Anatomy
Inside an NC1 file, line by line
The format is line-oriented: a two-letter code starts each block, and the lines that follow belong to it. Here is a small plate, annotated. Coordinates are millimeters — the standard is metric.
STHeader block starts. Identity and material for this one part.** sample plate — demo jobA comment — lines starting ** are notes, not data. DEMO-JOB-001Order — the job this part belongs to. 104-BDrawing number. 1Phase of the job. P104Piece mark — the part’s name on the drawings. S355JRSteel grade. 4Quantity — how many of this part the job needs. PL10Profile — here, 10 mm plate. 400.00 250.00 …Dimensions — the part’s sizes, in mm. The header fields sit in a fixed order, which is why order matters so much.AKOuter contour. The part’s outline. v 0.00 0.00 0.00One corner point: face code v, then x and y in mm. The outline walks point to point back to the start. v 400.00 0.00 0.00Next point — 400 mm along the bottom edge. ……and so on around the plate.IKInner contour. A cutout — same point-by-point walk, inside the part.BOHoles. v 40.00 40.00 18.00One hole: x, y, diameter. Slotted holes carry extra fields on the same line.SIScribed text — the piece mark written onto the steel.ENEnd of file.A few more codes show up in real files: PU and KO carry powder- and scribe-marking geometry, and the face code (v, o, u, h) says which face of the part a point sits on — for a flat plate, everything is on v.
Sec. 03 · In the wild
Common problems with NC1 files
The standard is old and the exporters are many, so real job folders are messier than the spec. These are the ones that actually cost time.
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01
Detailer dialects
Different detailing packages fill the header fields differently — a value you expect in one field turns up shifted into another. Two files can describe identical parts and still not match line for line. Anything that reads NC1 files by position has to be checked against the files your detailer actually sends.
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02
Comment lines
Exporters drop ** comment lines into files — harmless notes, until a strict reader on the machine side treats one as data and refuses the file, or worse, misreads it.
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03
Millimeters vs. inches
The standard is metric: values are millimeters. But imperial shops and mixed toolchains produce inch-valued files, and a units mix-up doesn’t announce itself — the file looks fine right up until the part comes off the machine 25.4× the wrong size.
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04
Quantities that don’t match the job
Each file carries its own quantity field — and it can disagree with the job plan. Over-cutting wastes steel; under-cutting is discovered at fit-up. Reconciling file quantities against the plan before cutting is tedious by hand, which is exactly why it gets skipped.
Sec. 04 · FAQ
NC1 questions, answered plainly
How do I open an NC1 file?
Two ways. Because it’s plain text, any text editor opens it — Notepad works — and you’ll see the blocks described above. To see the part rather than the numbers, use a viewer: our free NC1 viewer runs in your browser, draws the outline, holes, and marks, and never uploads your file anywhere.
Is NC1 the same as DSTV?
Effectively, yes. DSTV is the standard — from the German Steel Construction Association — and NC1 is the everyday name, taken from the .nc1 file extension. People say “DSTV file” and “NC1 file” interchangeably.
What’s the difference between NC1 and DXF?
An NC1 file describes one steel part with its fabrication data attached — grade, quantity, piece mark, holes, markings — in a form CNC steel machinery reads directly. A DXF is a general CAD drawing exchange format: geometry, but no notion of a steel part. If the machine is a beam line or plate processor, it wants NC1; general drawing work travels as DXF.
What software creates NC1 files?
Steel detailing software — Tekla Structures, SDS2, and Advance Steel are the common ones. They export one NC1 file per part from the 3D model. On the consuming side: CNC plate and beam machines, and nesting software.
Are NC1 files metric or imperial?
The standard is metric — coordinates and dimensions in millimeters. Inch-valued files do circulate in imperial shops, and they’re a classic source of scale errors, because nothing in the file loudly declares which one you’re holding. If a 10 ft part parses as 120 mm, you’ve found one.
Can I edit an NC1 file by hand?
You can — it’s text. For one field in one file, a careful text-editor edit is fine. The trouble is scale and stakes: the header is positional, so a line accidentally deleted or shifted changes the meaning of everything after it, and the mistake surfaces as a cut part. Hand-editing a 300-file job is where it really breaks down.
Sec. 05 · Try it
See your own file, right now
Drop an NC1 file into our free viewer and see the part — outline, holes, cutouts, scribed marks, and the header decoded into a table. It runs entirely in your browser: nothing is uploaded, because there is no server to upload to.
We build tools that batch-process files like this — john@curioustech.org