DSTV NC Files (Steel)

DSTV NC files (.nc1) are what steel fabrication machines read: beam drilling and sawing lines, plate drilling and punching machines, plasma and oxy-fuel plate cutters, and the steel CAM programs that feed them. The format is the German steel construction association's (DSTV) Standard Description for Steel Construction, its NC data interface (7th edition, 1998). Each file describes one piece: what it is (its order, drawing, piece mark, steel grade, quantity and profile), its outline, holes, inner cut-outs and markings.

To write them, use File › Export › Export… and choose DSTV NC Files (Steel). A drawing whose industry is Structural steel offers it among its first formats.

What is written

Each piece is cut out by the lines on the Cut layer: a closed outline, with whatever is cut inside it. Draw a plate's outline (the Base Plate and Gusset Plate tools, a library design, or lines and arcs of your own) on the Cut layer, and its holes with it.

Arcs are written as arcs: each point of a contour carries the radius of the arc to the next point, positive turning anticlockwise, an arc of more than 180° in two. Other curves become short lines within the Curve tolerance. Everything else (dimensions, notes, centre lines on other layers) is left out. Sizes are written in millimetres whatever the drawing's units, from the piece's lower left corner, on its front face (v).

A plate taller than it is long is turned a quarter, so its length runs along x as most machines expect (switch off Longer side along the length to keep it as drawn).

One file per piece

A drawing with one piece is written to the file you choose. With several, each goes to a file of its own beside it, named after the file and the piece's mark: exporting Plates.nc1 writes Plates-B1.nc1, Plates-B2.nc1 …, and the messages say how many were written. A piece's mark is its part mark (text on the Etch layer inside it); a piece without one takes the Piece mark in the options, numbered if there are several (G-1, G-2), or just a number. With Every page, the pieces of all the drawing's pages are written (a piece without a mark is named after its page).

The header: from the drawing's classification

Each file starts with the piece's header. The options start from the drawing's classification (File › Drawing Properties, or CLASSIFY in the drawing), so a drawing that says what it is needs nothing typed:

A plate's profile is written as PL with its thickness and width (PL20*300), its code B, its length and width, and its thickness; its weight and painted surface per metre are worked out from them.

Profiles: coped beams

Give a Profile (IPE 300, HEB 200 …) and each piece is a length of that profile: the drawing is its web seen from the front, its length along x and its bottom at the bottom, as the Beam Cope tool copes it. The outline is written as the web's contour (with its copes), holes in it as holes in the web, and for an I section the top and bottom flanges' contours where a cope cuts them back. The profile's code comes from its name (I for IPE, HE, UB, UC and W; U for channels; L for angles; M for square and rectangular hollow sections; RO for tubes); the sizes of IPE, HEA and HEB sections from a table, and those of any other from the options. The messages say if the drawing's height isn't the profile's.

Skew cuts

A profile sawn at an angle is drawn with that end as one straight line, the web's whole height, leaning: the angle it leans from square is written in the header as the web's start or end cut (and the end is in the web's contour as well, as the spec asks). The angle is in degrees, positive when the end's top is turned back anticlockwise (towards the start at the far end, past it at the start), as the contour's arcs are; square, coped or shaped ends are 0. The flanges' cuts are read the same way from the bottom flange's page (or the top flange's, if there is no bottom one; see Faces), as the spec gives them seen on the bottom face. A plate's ends aren't sawn: its cuts are 0.

A profile's faces

The DSTV file places what is cut, drilled and marked on each face of a profile: v the front (an I section's or a channel's web, an angle's upright leg), o the top flange, u the bottom flange (an angle's other leg), h behind (the web's far side). By the spec's figures, I sections, channels (U) and rectangular hollow sections (M) have all four, angles (L) v and u, and tubes and round bars (RO, RU) only v (their surface unrolled).

To give the other faces, draw the profile a face a page (pages), each page named after its face:

A name in any language ends with the face's letter in brackets: Ala superior (o), 上翼缘 (o). On each face's page draw the face as it is seen, with the piece's start on the left at the same x as on the web's page, so a hole 300 from the start is at x = 300 on every page. Its outline on the Cut layer (the flange's width high, cut back where the end is coped or notched) is written as the face's contour if anything is cut off it, and y is measured from its lower edge; a face with only holes needs no outline (y is then measured from the page's 0). Holes and cut-outs (Cut layer), drill holes (Drill layer), and text and lines on the Etch layer go on the face as they do on the web. A flange drawn on its own page is written as drawn, in place of the contour worked out from the web's copes.

The pages make one piece when the page you are working on is one of them, or when Every page is chosen (the drawing's other pages are then pieces of their own). A Profile must be given: a plate has only its front. The messages say if a page is a face the profile hasn't, or if the web's page has more than one piece on it (the faces are then left out).

Weld preparations

Plates (and profiles' contours) can be bevelled for welding by a plasma or oxy-fuel head that tilts. The DSTV spec gives a contour's point two more values after its radius, the angle of flamecutting (Phi) to the vertical and the distance Y, for the edge from that point to the next, and a second pair if we need a welding preparation on both sides. With Weld preparations as bevels (on unless you switch it off), a Weld Preparation on a straight edge of a piece's outline or of a cut-out in it is written there: its bevel angle (from square) as Phi and its root face (the land left square) as Y; a double (K) preparation writes the pair for both sides. Its bevel line, now part of the contour, isn't marked as well; its label is marked with the Etch layer's other lines. A preparation on a curved edge is marked only. Switched off, the bevel lines are marked like the Etch layer's other lines, for a fitter to grind to.

Machines differ in what they take from these values (some read Y as the bevel's depth rather than the land): check one bevelled piece in the machine's viewer before cutting a batch.

On the machine

• Copy the .nc1 files to the machine (or its CAM program's import folder) and import them as DSTV/NC1 files; most programs take a folder of them at once, one piece per file.
• Check the steel grade and the thickness against the machine's stock list: a plate is nested or loaded by them.
• A plate cutter cuts the inner contours (IK) before the outline (AK) and drills or punches the holes (BO) first; on a plasma table that cuts every hole, choose Round holes: Cut as contours.
• If a machine misreads the arcs of a contour (rounded corners come out wrong), switch on Arcs as short lines under Advanced.
• A machine without a bevelling head ignores the weld preparations and cuts the edges square; if it refuses the file instead, switch off Weld preparations as bevels.

Not written

Slots as slotted holes (they are written as inner contours, which every machine cuts), saw cuts given as the SC block (the skew cuts are in the header and the contours), the spec's weld-preparation notches (t and w points), and the DSTV's additional planes for a face that isn't one of the four are not written. A curved edge's weld preparation is marked, not bevelled.

See also: File Formats, Structural Steel, Drawing Properties.