How to open and check an NC1 file

You have been handed a set of .nc1 files — from a detailer, a customer, or your own CAD export — and you need to look at them before anything gets cut. Here are your options, and a checklist worth running every time.

Option 1: a text editor (fine for a quick peek)

NC1 files are plain ASCII text, so Notepad, VS Code, or any editor opens them. You can read the ST header directly: piece mark, steel grade, profile, quantity, length. That is often enough to answer "is this the right part?". But holes and contours are coordinate lists — checking a bolt pattern by mentally plotting X/Y values per face is slow and error-prone. If a file will not open as readable text at all, it is not a DSTV file, whatever its extension says.

Option 2: desktop viewers and CAD software

Detailing packages (Tekla Structures, Advance Steel) can re-import NC files, and machine vendors ship free desktop viewers with their CAM software. These work well if the software is already installed on the machine in front of you — less well when you are on a laptop in the yard, on a tablet, or on a locked-down office PC where you cannot install anything.

Option 3: open it in your browser

A browser-based viewer needs no installation and works on anything. NC1-Viewer.com parses files locally in your browser — nothing is uploaded — and renders each part as dimensioned 2D face views plus an interactive 3D model:

Go to nc1-viewer.com.
Click Open file (or drag and drop) and select one or more .nc1 / .nc files.
Click through parts in the list; switch between face views and 3D; hover holes for exact positions and diameters.

Open your NC1 files now →

The pre-production checklist

Whichever tool you use, these are the checks that catch real-world fabrication errors before they cost material:

Header sanity: piece mark matches the drawing; steel grade is what the job specifies; quantity is right; profile name and dimensions agree (a HEA200 that claims a 300 mm height is a red flag — see profile types).
Length: compare the header length against the cut list. Watch for detailing in a different unit convention — DSTV is millimetres.
Hole count and pattern: count holes per face against the connection detail. Verify gauge (cross-member spacing) and pitch (along-member spacing) on at least one bolt group per face.
Hole sizes: bolt holes are typically drilled 2–3 mm over the bolt diameter (metric practice; imperial jobs use 1/16″ over) — an 18 mm hole for an M16 bolt is expected, an 16 mm hole is a problem. Slots should show their full length and width, not just a diameter.
Copes and end cuts: check the outer contour (AK) at both ends — cope depth and length, bevel angles, and that the cope is on the correct flange for the connection orientation.
Openings: internal contours (IK) for web penetrations should match the service-opening schedule.
Markings: piece-mark numbering (SI) present and on a visible face; layout lines (PU/KO) where fit-up needs them.
Mirrored parts: for handed pairs (left/right members), confirm the holes really are mirrored and not just copied — the classic NC1 mistake.

When a file looks wrong

Exporters have quirks — non-standard slot syntax, plane-numbered blocks, reference-edge suffixes (see block codes). If geometry renders unexpectedly, compare the raw text of the suspicious block with the drawing before blaming the file. If NC1-Viewer.com itself misreads a file, send it to us — exporter quirks we can reproduce get fixed in the parser.

Need to fix a file, not just view it?

Small corrections — a hole position, a piece mark, a steel grade — do not have to go back through the detailing office. NC1-Viewer.com's Pro tier lets you edit hole positions and header fields in place and export a clean NC1 file back out.