DSTV NC1 marking data: layout marking, scribing and punch marks

Holes and copes get most of the attention in a DSTV file, but the marking data is what turns a cut beam into something a fitter can assemble without a tape measure. Layout lines show exactly where a stiffener, gusset or clip lands. The piece mark identifies the member in the yard. Get the marking wrong and the part is still dimensionally correct — it just costs an hour of setting out at the fit-up bay.

DSTV carries marking in three separate blocks, and they mean genuinely different things. This guide covers what each one contains, how to read the coordinates, and what typically goes wrong.

The three marking blocks

The distinction that matters on the shop floor: SI produces characters, while PU and KO produce geometry. A machine that can scribe a line may have no ability to write text, and vice versa. Two files can be equally valid DSTV and still be completely unusable on a given beam line depending on which of the three blocks the detailer chose.

SI — piece marks and hard stamping

Each data line places one string:

SI
  v  100.00  150.00  0.00  10.00  B-104

Reading left to right:

Two optional extras appear in real files. An additional single letter may sit between the face and X as a dimension reference, changing which edge the coordinates are measured from — it is recognisable because it does not begin with a digit or sign. A short flag token of letters such as x or z may also appear immediately before the text, controlling rotation reference and parameter handling. Both are easy to mistake for part of the text if you are parsing by hand.

PU — powder and scribe layout marking

PU uses the same line format as the contour blocks (AK and IK): one vertex per line, giving face, X, Y and a radius.

PU
  v  1200.00  0.00  0.00
  v  1200.00  300.00  0.00
  v  1500.00  300.00  0.00

That is a three-point polyline on the web — the kind of thing that shows a fitter exactly where a stiffener plate sits. Two properties trip people up:

• Marking polylines need not be closed. Unlike an AK outer contour, which is a closed loop by definition, a marking run is usually an open path. A parser that insists on closing marking contours will invent a segment that was never intended.
• The radius column works here too. A non-zero radius bulges the segment arriving at that vertex, so marking is not restricted to straight lines — circular layout for a base plate or a curved gusset is expressible.

One structural rule is worth knowing if you are writing an exporter: a new block header always terminates the current marking run. Two consecutive PU blocks are two separate polylines, no matter how the coordinates line up. If you emit one header and then pile every polyline underneath it, a conforming reader is entitled to join them into a single path — and it will.

KO — punch marks

KO takes the same line format as PU. The difference is intent: these are locations to be centre-punched rather than drawn. A single-point KO run marks one spot; a multi-point run marks a series.

Punch marking is often used to pre-locate holes that will be drilled in a second operation, or to mark a layout on material too rough for a scribed line to survive handling and blasting.

Where marking coordinates live

Every marking coordinate is two-dimensional and belongs to the plane of the face named on its own line. The face code decides how X and Y are interpreted:

• v — the web, viewed from the front
• h — the reverse side of the web
• o — the top flange, viewed from above
• u — the bottom flange, viewed from below

X always runs along the member length. Y runs across the face — through the profile height on v and h, across the flange width on o and u. Because h is the mirror of v, stamped text placed on the back of the web reads correctly from that side and mirrored from the other. Handed pairs of members are where this bites: a left/right pair whose marking was copied rather than mirrored produces two parts stamped on the same physical side.

Some exporters also emit marking on custom planes rather than the four standard faces, using numbered block variants alongside a plane definition. If you open a file and the marking appears to be missing, plane-scoped blocks are one thing to check for before assuming the detailer omitted it. See the block codes reference for the full list.

Machine support varies more than the format does

DSTV is a common language, but the marking hardware behind it is not uniform. Beam lines and plate processors from the major vendors — Peddinghaus, Voortman, Kaltenbach, HGG and others — differ in which marking methods they carry, and the same machine model is often configurable with or without a given unit:

• Scribing cuts a fine permanent line and survives blasting and painting, which makes it the preferred method where the layout must still be visible at fit-up.
• Powder or inkjet marking is fast and legible but can be lost to surface preparation later in the process.
• Hard stamping is permanent and readable but is restricted to text, and deforms the surface — which is why specifications sometimes forbid it in tension zones or on architecturally exposed steel.
• Centre punching is nearly universal, which is part of why KO shows up as a fallback in files aimed at mixed equipment.

The practical consequence: a file that marks correctly at one fabricator can arrive effectively blank at another. If you are sending NC1 out to a subcontractor, it is worth asking which marking blocks their line actually consumes before assuming the layout data will be used at all.

What usually goes wrong

• Marking exported for the wrong face. Layout lines on h when the fitter works from v. Dimensionally valid, practically useless.
• Text height left at a default that the machine cannot produce, so the piece mark is silently dropped.
• Copied rather than mirrored handed pairs, putting the piece mark on the wrong side of half the members in a set.
• Marking outside the part. Nothing in the format prevents a marking coordinate beyond the profile bounds; a Y value larger than the profile height means the detailer's reference edge did not match the one the exporter assumed.
• Layout that contradicts the holes. When a connection is revised, hole positions and marking lines are sometimes regenerated separately. If a scribed line and a bolt group disagree, trust neither until the drawing is checked.
• Marking dropped in translation. Round-tripping a file through an intermediate tool frequently preserves geometry and quietly discards PU/KO runs.

Checking marking data before it reaches the machine

Marking problems are cheap to catch on screen and expensive to catch at fit-up. The check is visual: open the file, look at each face, and confirm that the layout lines land where the connection detail says they should, on the face the fitter will be looking at.

NC1-Viewer.com renders SI, PU and KO alongside holes and contours on dimensioned 2D face views and in 3D, so a marking run that sits on the wrong face or outside the part is obvious immediately. Files are parsed locally in your browser and never uploaded, which matters when the geometry belongs to a client.

Check your marking data now →

Related guides

• DSTV block codes explained — every block in the format, including the plane-scoped variants.
• How to open and check an NC1 file — the full pre-production checklist.
• What is a DSTV NC1 file? — where the format comes from and what else it carries.