Tekla fabrication handoff: standardise it before the project starts

The two-day iteration tax

You have been there. The fabricator opens the drawing package, finds a cope depth wrong on the main beam, fires off an RFI, and the clock starts. Back at the detailer's desk, the correction is three model picks and a regenerate — ninety seconds of work. But now begins the cycle: the revised drawing needs to clear the internal check, go back to the engineer of record for re-sign-off, get re-exported to PDF, renamed, uploaded to the CDE folder, then emailed to the fabricator's project manager who forwards it to the shop planner who checks it against what is already on the floor. By the time the corrected information reaches the cutter operator, forty-eight hours have passed. If the fabricator had already programmed that beam into the CNC queue, add another round of NC file regeneration and another email thread.

Multiply that by eight or twelve drawing iterations per package — a completely normal number on a mid-size commercial building — and you have burned somewhere between two and three weeks of float on paperwork choreography that should take an afternoon. This is the two-day-per-iteration tax, and it is almost entirely a process problem, not a technical one.

The root cause is almost never the complexity of the correction. The cause is that the handoff package was not standardised before the project started. Folder structures were invented on the fly. File names carry no machine-readable revision suffix. Nobody agreed in advance on what constitutes a "superseded" NC file or where superseded files live. There is no single version number that ties the drawing revision to the NC file revision to the BOM row. When something changes, every stakeholder spends hours doing archaeology before they can act.

This guide is a working standard for the model-to-fabrication handoff. It covers what the package must contain and why, how to lay it out on disk and in your CDE, what a properly structured DSTV NC file looks like, how to configure Tekla Structures to produce it consistently, and the anti-patterns that silently add days to every revision cycle. The code and templates here are opinionated. You will need to adapt them to your firm's environment and to the preferences of the specific fabricators on each project. But they represent a defensible baseline — the kind of thing you agree to in the BIM Execution Plan before the first beam goes into the model.

If you adopt nothing else from this article, adopt one rule: the handoff package version number must appear in every filename, every folder name, and every NC file header. That single discipline eliminates more confusion than any other single practice.

One more contextual note before the detail: the principles here are not Tekla-exclusive. The drawing types, the NC file format, and the folder discipline apply equally if your team is working in SDS/2, Advance Steel, or any other detailing tool that produces DSTV output. But the workflow examples, the Open API code, and the specific settings paths are Tekla Structures. Adapt as needed for your toolchain, but do not let toolchain differences become an excuse to skip the process discipline.

What a fabrication handoff actually contains

A complete steel fabrication handoff is not just a folder of PDFs. It is a layered information delivery: drawings for human communication and sign-off, machine-readable files for CNC programming, quantity schedules for procurement and tracking, and optionally a federated model for coordination and clash review. Each layer has a specific audience and a specific purpose. Conflating them — or omitting one — creates predictable failure modes.

Erection drawings (GA drawings)

Erection drawings — called General Arrangement (GA) drawings in Tekla's terminology — are the contract documents between the structural engineer, the detailer, and the erector. In Tekla Structures, GA drawings are created from one or more model views and associated schedules, placed on a project title sheet. They are the primary means by which consulting structural engineers communicate structural intent to the site team, the costing team, and the erector's foreman.

GA drawings typically show:

• Grid lines and levels. Column grid letters and numbers with centreline dimensions. Floor and beam soffit levels at key points.
• Member positions. The centroid location of every primary beam, column, brace, and truss, keyed to position marks.
• Connection callouts. Bolted or welded connection types referenced to a detail sheet. On straightforward frames these may be abbreviated; on complex frames every node type gets its own callout.
• Sequence or zoning notes. Lift sequence, erection stage numbers, temporary bracing requirements.
• Revision cloud and delta triangle. Every change since the previous issued revision is enclosed in a revision cloud, with a delta triangle pointing to the change description in the title block.

Erection drawings are issued to the fabricator for approval before shop drawings are produced. The fabricator checks that the frame geometry matches their own detailing model, that connection sizes are achievable, and that any site constraints (crane pick zones, access routes) are correctly reflected. Only after GA approval does detailed shop fabrication drawing production begin.

In Tekla, GA drawings remain always up to date because they reference live model data as associative objects. When a beam shifts position in the model, the GA view regenerates automatically. Revision clouds, however, must be placed manually or via a revision management workflow — Tekla can highlight changed objects, but the actual cloud boundary and delta triangle still require a human decision about what constitutes a revision-worthy change.

Single-part drawings

Single-part drawings (also called detail drawings or piece-mark drawings) are workshop fabrication drawings for one individual piece of steel. In Tekla's classification, a single-part drawing "shows fabrication information for one part, usually without welds." They are the primary documents a shop welder or operator uses to understand what to do to a specific piece of steel that has come off the saw table.

A single-part drawing for a column stub might show:

• The overall profile and length with saw-cut or cope geometry.
• All hole patterns on every face, dimensioned from the beam end and from the centreline.
• End preparation: saw perpendicular, cope, weld bevel angle and root gap.
• Any paint or surface treatment instructions.
• The piece mark (position number) and the assembly mark it belongs to.
• Material specification, grade, and heat number tracking requirement.

Single-part drawings are typically printed on A4 or A3 and physically travel with the steel through the shop. Many fabricators now display them on tablets at each workstation. The piece mark printed on the drawing must exactly match the mark stamped or painted on the physical piece after cutting — this is the chain of identity that allows the erector to find the right piece on a crowded laydown yard.

In Tekla, single-part drawings are generated automatically from the model after numbering. The master drawing catalog stores template settings for each profile type, so a W310×97 beam template can be pre-configured with the correct view orientation, weld symbol preferences, dimension style, and title block fields, and every W310×97 in the model will get a consistent drawing. This automation is where the time savings are: a project with 600 unique part marks should take three hours to produce drawings for, not three days.

Assembly drawings

Assembly drawings show how multiple parts are assembled into a shipping unit — what Tekla calls an "assembly." The main part (usually the primary beam or column section) is shown with all its secondary parts (connecting plates, stiffeners, shear tabs, end plates) welded to it, with weld symbols, fit-up dimensions, and the position of each secondary part relative to the main part's datum.

The key distinction: a single-part drawing tells the shop what to do to an individual piece of steel; an assembly drawing tells the shop how to join those pieces together into a sub-assembly before it leaves for site. Assembly drawings are used at the fitting-up and welding stations.

For typical rolled-section frames, the assembly drawing carries:

• The main member in its dominant view, with all attached secondaries shown in correct position.
• Weld symbols at every connection, with size, type (fillet, CJP, PJP), and length.
• Fit-up dimensions from the main part datum to each secondary part's attachment face.
• Shop-bolted and site-bolted connections distinguished clearly — shop bolts shown solid, site bolts shown open or in a different layer colour.
• The assembly mark (distinct from the piece marks of the constituent parts).

In Tekla, assembly drawings are generated in the same workflow as single-part drawings but for the assembly object. The master drawing catalog contains separate templates for assembly drawings. Because the assembly contains multiple parts, the sheet format is typically larger — A2 or A1, or multidrawings that gang several small assemblies onto one sheet.

NC files (DSTV format)

NC files are the machine-readable instructions that drive CNC equipment in the fabrication shop: drilling machines, punching lines, coping robots, angle-cutting saws. They encode the geometry of every hole, cut, cope, bevel, and slot as Cartesian coordinates referenced to the steel member's own coordinate system.

The dominant format is DSTV-NC, defined by the Deutscher Stahlbau-Verband (German Steel Construction Association) and now used globally. Virtually every structural CNC machine — Peddinghaus, Voortman, FICEP, PythonX, Ocean, Controlled Automation — accepts DSTV-NC files natively or with a post-processor. The file extension is .nc1, though .nc and .dat extensions are also used by some machine configurations.

NC files are covered in exhaustive detail in the dedicated section below.

Bill of materials (BOM)

The BOM is the structured tabular record of every part in the package: piece mark, profile, grade, length, quantity, weight, surface treatment, and any user-defined attributes (fire rating zone, erection sequence number, paint specification code). In Tekla the BOM is generated as a report using a template file (.rpt or via the Organizer), and it is output as XLS, CSV, or PDF.

The BOM serves multiple downstream functions simultaneously:

• Procurement. The mill order or service centre order is built from the BOM. Errors in profile designation or grade here propagate to the wrong steel arriving on site.
• Material tracking. In fabrication management systems (ERP tools like Tekla PowerFab, Strumis, or FabTrol), the BOM is the seed data for the job. Each row becomes a work order item.
• NC file correlation. The piece mark in the BOM must exactly match the piece mark in the NC file header. This is the join key. If the NC file carries a mark from a previous numbering run and the BOM reflects the current run, the shop planner cannot correlate them.
• Erection sequence. Zone or sequence attributes in the BOM allow the erection contractor to sequence bolt-up work.

The BOM is not a drawing substitute and should not be used to resolve dimensional ambiguity. If a fabricator is making a measurement decision based on the BOM rather than the drawing, something has gone wrong upstream.

In Tekla, the BOM is generated via the Report tool (Drawing & Reports → Reports) using a template file (typically with a .rpt extension). The report template defines which model attributes appear as columns, how they are sorted, and what filtering applies. For a fabrication BOM, the standard practice is to sort by zone, then by sequence, then by part mark — this matches the erection team's programme and makes the BOM directly useful for planning.

A separate "material take-off" report sorted by profile type and grade is useful for procurement, but it is a different document for a different audience. Do not try to serve both purposes with a single BOM layout — a report that tries to serve the shop planner and the estimator simultaneously usually serves neither well.

Two BOM columns that are frequently omitted but consistently requested by fabrication project managers: actual weight per piece (not theoretical weight from the profile table — Tekla calculates this from the actual modelled geometry including copes and cutouts) and surface treatment specification code. The surface treatment code ties the piece to the painting or galvanising specification and determines which queue it enters in the shop's workflow after fabrication. Omitting it means a phone call or email for every piece.

IFC model

The IFC (Industry Foundation Classes) export provides a neutral geometry file that coordination teams can federate into a common data environment for clash detection and coordination review. Tekla Structures supports IFC2x3, IFC4, and IFC4.3 export. For fabrication handoffs, the standard practice is:

• IFC2x3 Coordination View 2.0 for clash detection import into Navisworks, Revizto, or BIM Track.
• IFC4 Design Transfer View when the receiving party needs parametric properties and full material attributes preserved.

In IFC export from Tekla, beams oriented between 20° and 70° from horizontal are classified as IfcMember (bracing) rather than IfcBeam. This is correct classification behaviour per the IFC schema, but it can confuse coordination teams expecting all linear steel members to appear as IfcBeam. Brief the coordination lead before the first IFC issue.

For fabrication-to-erection coordination specifically, the IFC is not a contract document — it is a coordination aid. The drawings and NC files are the deliverables that carry legal weight under the fabrication contract.

CIS/2 (optional)

CIS/2 (CIMsteel Integration Standards, Release 2) is a product model and electronic data exchange format for structural steel that predates IFC and was developed specifically for the steel supply chain. It enables information exchange among design, structural analysis, detailing, and fabrication software packages. AISC promoted CIS/2 as the foundation for their interoperability initiative for the structural steel industry.

CIS/2 remains in use by some North American fabricators who have integrated it with their ERP systems, and by analytical software (RISA, ETABS, SAP2000) that reads CIS/2 for model back-check. For most modern projects, IFC4 has superseded CIS/2 for coordination purposes, but a small subset of larger fabricators — particularly those running integrated detailing-to-ERP pipelines — still request CIS/2 in the handoff package. Check this in the BIM execution plan.

The standard handoff package

The most persistent source of handoff confusion is not technical — it is organisational. Someone created a folder called drawings_FINAL at week four, and by week twenty there are three folders called drawings_FINAL, drawings_FINAL_v2, and drawings_FOR_FABRICATION_USE_THIS_ONE. The NC files live in a different location than the drawings they correspond to. Nobody can tell which revision of the BOM matches which revision of the drawings.

The solution is a folder structure and naming convention defined in the BIM Execution Plan before the first drawing is issued, and enforced by the detailing lead from day one.

Recommended folder structure

[PROJECT_CODE]/
├── 00_BEP/
│   └── BIM-Execution-Plan.pdf
├── 01_Model/
│   ├── Tekla/                     ← model backup snapshots
│   └── IFC/
│       ├── CURRENT/
│       └── SUPERSEDED/
├── 02_Drawings/
│   ├── GA/
│   │   ├── CURRENT/
│   │   └── SUPERSEDED/
│   ├── Shop/
│   │   ├── SinglePart/
│   │   │   ├── CURRENT/
│   │   │   └── SUPERSEDED/
│   │   └── Assembly/
│   │       ├── CURRENT/
│   │       └── SUPERSEDED/
│   └── Erection/
│       ├── CURRENT/
│       └── SUPERSEDED/
├── 03_NC/
│   ├── Profiles/
│   │   ├── CURRENT/
│   │   └── SUPERSEDED/
│   └── Plates/
│       ├── CURRENT/
│       └── SUPERSEDED/
├── 04_BOM/
│   ├── CURRENT/
│   └── SUPERSEDED/
├── 05_Transmittals/
│   └── [YYYYMMDD]_TX[nnn]/
└── 06_RFI/

The CURRENT / SUPERSEDED split within each document type is the most important structural decision. It means a fabricator always knows where the live files are. The SUPERSEDED folder is an archive, not a bin — it must be retained for the project record and for resolving disputes about what information was current at a given time.

File naming convention

Every file in the handoff package must carry four pieces of information in its name:

1. Project code — the same short alphanumeric code used across all project documents.
2. Document type prefix — GA, SP (single-part), AS (assembly), ER (erection), NC, BOM.
3. Sheet or part identifier — the drawing sheet number or the piece mark.
4. Revision suffix — a two-character code: A0, A1, B0, B1, etc., or ISO 19650 convention P01, P02, C01 (preliminary / contracted).

[PROJECT]-[TYPE]-[IDENTIFIER]-[REV].[ext]

Examples:

BLD42-GA-E01-A0.pdf          ← GA erection drawing, sheet E01, revision A0
BLD42-SP-B42-B1.pdf          ← single-part drawing, piece mark B42, revision B1
BLD42-AS-BA42-B1.pdf         ← assembly drawing, assembly mark BA42, revision B1
BLD42-NC-B42-B1.nc1          ← NC file for piece mark B42, revision B1
BLD42-BOM-PKG03-A2.xlsx      ← BOM for package 03, revision A2
BLD42-IFC-COORD-A1.ifc       ← coordination IFC, revision A1

The critical rule: the revision suffix on the NC file must always match the revision suffix on its corresponding single-part drawing. They are generated from the same model state. If they diverge, it means either the NC file was regenerated without a drawing regeneration or vice versa — both indicate a process breakdown.

Revision marking protocol

Revision discipline follows a two-tier system:

• Preliminary revisions use sequential numbers within a letter series: A0 → A1 → A2. These are issued for coordination and review, not for fabrication.
• Issued-for-fabrication revisions advance the letter: B0 → B1 → C0. The letter advance signals a fabrication-status change. If you move from B1 to C0, it means a scope or contract change drove the revision, not just a correction.

Within drawings, every change since the previous issued revision must be enclosed in a revision cloud with a delta triangle pointing to the change description in the title block revision table. The revision table must record:

• Revision code.
• Date of issue.
• Brief description of what changed.
• Initials of the checker and approver.

Changes that do not affect the fabricated geometry (e.g., a corrected note reference, a changed specification clause) can be marked as minor and noted without a cloud if the firm's QA procedure permits it — but this must be a written policy, not an ad-hoc judgment.

Package versioning

Beyond individual drawing revisions, the handoff package itself has a version: the transmittal. Each transmittal is a formal issue event, documented in a transmittal record that lists every file included, its revision, its issue purpose (IFC = Issued for Coordination, IFF = Issued for Fabrication, IFR = Issued for Review, IFA = Issued for Approval), and the recipient.

The transmittal folder (05_Transmittals) contains one subfolder per issue event, named [YYYYMMDD]_TX[nnn] (e.g., 20260415_TX003). Inside each transmittal folder: a transmittal cover sheet (PDF) listing every file in the issue, and a copy or hard link of every file issued.

Define the folder structure and naming convention in the BEP.

Write it down before the model starts. Include it in the contract document set.

Create the folder structure in the CDE before the first file is issued.

Do not create it retrospectively. Projects that create folders ad-hoc always end up with inconsistencies.

Perform a numbering check in Tekla before every transmittal.

All changed parts must be renumbered and all affected drawings and NC files regenerated before packaging.

Move superseded files to SUPERSEDED immediately when CURRENT files are updated.

Do not leave old and new versions in the same CURRENT folder, even temporarily.

Issue via transmittal every time, including for minor corrections.

A transmittal takes five minutes to produce and is the permanent record of what was communicated and when.

The supersede convention

When a revised file is placed in CURRENT, the previous version moves to SUPERSEDED. The naming convention must be preserved — do not rename files when superseding them. The date of supersession and the reason should be recorded in the project transmittal log (a simple spreadsheet or a CDE audit trail).

For NC files specifically, the supersede must happen atomically: the new NC file should not be placed in CURRENT/NC/Profiles until the corresponding new drawing is also placed in its CURRENT folder and the old NC file has been moved to SUPERSEDED. If a fabricator's shop planner opens the NC file and the drawing at the same time and they are from different model states, the result can be a machined part that does not match the drawing issued for approval.

NC file standardisation

NC files are where the precision of the Tekla model meets the physical capability of the fabrication shop. Getting this layer right eliminates the largest class of RFIs: dimension discrepancies between drawings and machined parts.

The DSTV standard: what it is

DSTV (Deutscher Stahlbau-Verband, the German Steel Construction Association) defines a neutral ASCII text file format for transmitting the geometry of fabricated steel members to CNC machinery. The standard is version-controlled; SDS/2 and other detailing software expose the choice between DSTV v5.0 and DSTV v7.0. Version 7 introduced additional block types and improved handling of complex geometries. Tekla Structures produces DSTV-format NC files by default, with the .nc1 extension, regardless of underlying DSTV version — the version is selected in the export settings.

The format is ASCII, human-readable, and deliberately simple. A typical NC1 file for a drilled column stub is around 50–150 lines. The design goal was neutrality: one standard description drives multiple different machine brands without post-processor modification.

The .nc1 extension is the most common, but fabricators may request .nc or .dat depending on their machine post-processor configuration. This is a filename extension change only — the file content format is identical. Establish which extension each fabricator requires in the BEP.

NC1 in depth: the format

Every DSTV NC1 file has a structured header followed by machining blocks. The header identifies the part; the blocks define what to do to it.

Header fields (representative subset):

ST
  1.0                             ← DSTV version
  B42                             ← Part (piece) mark / position number
  W310X97                         ← Profile designation
  S355JR                          ← Material grade
  1450.0                          ← Part length (mm)
  4.0                             ← Flange thickness (mm)
  9.9                             ← Web thickness (mm)
  308.0                           ← Overall height (mm)
  166.8                           ← Flange width (mm)
  0.0                             ← Angle 1 (saw cut angle at start, degrees)
  0.0                             ← Angle 2 (saw cut angle at end, degrees)
  BLD42                           ← Project identifier
  B1                              ← Revision
  20260415                        ← Issue date
EN

Following the ST (start) block is a series of machining blocks, each beginning with a two-letter code identifying the face and operation type:

Face orientation codes reference the cross-section of the profile as viewed from the start end:

For plate parts (B profile type), the face codes reference the flat faces.

A minimal NC1 file snippet — W310×97 column with two flange holes:

ST
  1.0
  B42
  W310X97
  S355JR
  1450.0
  4.0
  9.9
  308.0
  166.8
  0.0
  0.0
  BLD42
  B1
  20260415
EN
BO
o
  100.0    83.4    24.0    0    0
  300.0    83.4    24.0    0    0
EN
BO
u
  100.0    83.4    24.0    0    0
  300.0    83.4    24.0    0    0
EN

In the BO block: the first value is X (distance from the start end along the part), the second is Y (lateral position measured from the part centreline), the third is the hole diameter in millimetres. The fourth and fifth values are tolerance class and depth override (0 = full thickness).

NC1 vs NC2 vs NC4: what the designations mean

This is a point of common confusion. In the DSTV standard, the NC number does not refer to different file formats — it refers to the machine type the file targets within the older, pre-DSTV machine numbering systems. In modern usage, the terms are often used to distinguish operational categories:

Tolerance class codes in BO blocks

The fifth field in a BO block row — the depth override — is often left at zero by default, meaning the machine drills full thickness. But the fourth field (tolerance class) is frequently misunderstood and left at zero as well, when it should carry meaningful values for the fabricator's machine:

The consequence of leaving all tolerance class values at 0 when some holes should be 3 (punched): the fabricator's CNC management system may route the part to the drill line rather than the punch line, or the machine operator may punch holes that should have been drilled, producing a surface finish and edge condition incompatible with the connection specification.

Tekla derives the tolerance class from the bolt standard defined in the connection component. High-strength structural bolts (ASTM A325, A490, or EN equivalent 8.8 / 10.9) in bearing connections use standard drilled holes; turn-of-nut or direct-tension-indicator connections may require specific hole preparation. Verify the tolerance class export mapping in the NC settings against the project's connection specification before the first issue.

NC file header customisation for traceability

The hard stamp block (SI) in a DSTV NC file drives the machine's labelling function — typically a centre-punch dot matrix or carbide scribing tool that marks the piece mark and optionally the project code directly onto the steel web or flange. This stamp is the physical identity of the part on the shop floor and at the laydown yard.

Tekla's NC file header and hard stamp configuration allow the following fields to be included:

<<MARK>>          ← Piece mark (position number from Tekla numbering)
<<ASSEMBLY>>      ← Assembly mark
<<PROFILE>>       ← Profile designation
<<GRADE>>         ← Material grade
<<LENGTH>>        ← Part length in mm
<<WEIGHT>>        ← Calculated weight in kg
<<PROJECT>>       ← Project number (from project properties)
<<REVISION>>      ← Revision suffix (from user-defined attribute)
<<DATE>>          ← Export date (system date at time of export)

For the revision field to work correctly, it must be driven by a project-level UDA that is updated before every export run. If it is left as a static string in the header template (e.g., the detailer types B1 directly into the template), it will not update when the revision changes and will produce NC files with wrong revision stamps for every subsequent export.

The recommended pattern: create a Tekla user-defined attribute called HANDOFF_REVISION at the model level (not the part level), set it to the current package revision before each export run, and reference it as <<HANDOFF_REVISION>> in the NC header template. This takes 30 seconds per export run and eliminates revision stamp errors entirely.

When each fabricator prefers which format

Different shop configurations produce different NC preferences. Understanding these preferences before the first issue eliminates a whole category of re-export requests:

High-volume structural shops with integrated drill-saw-cope lines (e.g., Peddinghaus FDB or Voortman V630): These shops run NC1 for profiles through a single machine that performs all operations in one pass. They prefer a single NC1 file per part, with all BO, AK, and IK blocks included. They do not want separate drill-only and cope-only files.

Shops with separate operations (saw first, then manual drill, then cope robot): These shops may prefer NC files that have been pre-filtered by operation type, so the saw operator only sees the saw parameters and the drill operator only sees the hole pattern. Some Tekla configurations support outputting operation-specific NC files, but this requires custom post-processing or a CNC management system like Graitec CMS.

Tube and hollow section specialists: Round hollow sections (RU profile type) are a special case. Tekla does not export standard DSTV NC files for round tubes — it exports XML files instead, because the tube geometry requires a different coordinate system. Fabricators running tube coping and saddle-cutting machines (e.g., HGG profiling machines) accept these XML files directly. If you have a mix of open sections and RHS/CHS in the same package, the NC export produces .nc1 files for the open sections and .xml files for the tubes — the transmittal must make this explicit.

Shops with legacy punching lines: Older punching lines (pre-2005 equipment common in smaller regional fabricators) may not support DSTV v7.0 and require DSTV v5.0 files. The block structure is the same, but the header format differs slightly. Tekla's NC export does not have a version toggle directly in the UI — the version is controlled via the DSTV export settings file. SDS/2 explicitly exposes a v5.0 / v7.0 toggle. If you are producing NC files from Tekla for a v5.0-only shop, verify with a test export and a single accepted first article before running the full package export.

Laser and plasma cutting shops for plates: These machines typically prefer the AK (external contour) and IK (internal contour) blocks to define the cut path, with BO blocks only for pre-drill operations. The machine's own nesting software (e.g., Lantek or Sigmanest) typically imports the NC1 plate files and re-nests them onto sheet stock, so the individual part NC file just needs accurate geometry — the nesting optimisation happens downstream.

Fabricators using proprietary machine software with post-processors: Machines from Ficep or Kaltenbach that use their own control software may perform NC1-to-proprietary conversion internally. In these cases, the DSTV NC1 file is still the correct deliverable — the machine's post-processor handles the translation.

Tekla NC export configuration

In Tekla Structures, NC files are created from File → Export → NC files. The dialog contains two primary export rows: DSTV for profiles and DSTV for plates. Each can be enabled independently and each has its own settings template.

Navigating the settings:

Open the NC files dialog.

File → Export → NC files. If a template has been pre-configured for the project, load it from the settings file list before making changes.

Configure the Files and Part Selection tab.

Set the output folder path. For profiles, the convention is 03_NC/Profiles/CURRENT. For plates: 03_NC/Plates/CURRENT. Set the file extension to match the fabricator's requirement (.nc1 is the universal safe default).

Configure the Holes and Cuts tab.

For each profile type, set the maximum drill diameter (typically the machine's maximum — e.g., 76 mm for a heavy drill line). Set slot handling: most shops prefer "internal contours" for slots rather than "four corner holes." Confirm flange clearance distance with the fabricator — this prevents the machine from attempting to drill too close to a fillet radius.

Configure the Hard Stamp tab.

The hard stamp is the piece mark punched into the web or flange face by the machine. Include: project code, position mark, profile, length, revision. Match the stamp field order to the fabricator's labelling convention.

Configure the Advanced tab.

Set the number of decimal places (0 for whole millimetres if the fabricator's machines are calibrated to 1 mm; 1 decimal for shops with 0.1 mm resolution equipment). Enable curve detection with an appropriate chord tolerance (0.5 mm is a reasonable default for hot-rolled profiles).

Save the settings file with a project-specific name.

Name the settings file [PROJECT_CODE]-NC-profiles.ncx and check it into the 00_BEP folder so any team member can reproduce the same export.

Tekla Open API: automating NC export

For projects with repeated partial re-issue events (a common scenario on phased projects where floors 1–10 are issued for fabrication while floors 11–20 are still in detailing), automating NC export via the Tekla Open API eliminates manual re-export errors.

The core method is Operation.CreateNCFilesFromAll in the Tekla.Structures.Model.Operations namespace:

using Tekla.Structures.Model.Operations;
using Tekla.Structures.Model;
using System;
using System.IO;
 
namespace BimMobius.FabricationExport
{
    /// <summary>
    /// Exports NC files for all model parts using the project-standard
    /// NC settings templates. Targets both profiles and plates in one pass.
    /// Requires the model to be fully numbered before calling.
    /// </summary>
    public class NcExporter
    {
        private readonly string _projectCode;
        private readonly string _outputRoot;
        private readonly string _revision;
 
        public NcExporter(string projectCode, string outputRoot, string revision)
        {
            _projectCode = projectCode;
            _outputRoot  = outputRoot;
            _revision    = revision;
        }
 
        public void ExportAll()
        {
            // Resolve timestamped output subfolder so each run is auditable.
            // Files are placed in a staging folder; the caller is responsible
            // for moving them to CURRENT and archiving the previous CURRENT.
            var timestamp    = DateTime.Now.ToString("yyyyMMdd_HHmmss");
            var stagingRoot  = Path.Combine(_outputRoot, "03_NC", "_STAGING", timestamp);
            var profilesOut  = Path.Combine(stagingRoot, "Profiles");
            var platesOut    = Path.Combine(stagingRoot, "Plates");
 
            Directory.CreateDirectory(profilesOut);
            Directory.CreateDirectory(platesOut);
 
            // Export profiles
            bool profileSuccess = Operation.CreateNCFilesFromAll(
                NCFileSettings:                  $"{_projectCode}-NC-profiles",
                DestinationFolder:               profilesOut,
                CreatePopMarks:                  true,
                PopMarkSettingsFileName:         "standard",
                CreateContourMarking:            true,
                ContourMarkingSettingsFileName:  "standard"
            );
 
            if (!profileSuccess)
                throw new InvalidOperationException(
                    "Profile NC export failed. Check that numbering is up-to-date " +
                    "and that the NC settings file exists: " +
                    $"'{_projectCode}-NC-profiles'");
 
            // Export plates
            bool plateSuccess = Operation.CreateNCFilesFromAll(
                NCFileSettings:                  $"{_projectCode}-NC-plates",
                DestinationFolder:               platesOut,
                CreatePopMarks:                  false,
                PopMarkSettingsFileName:         "",
                CreateContourMarking:            false,
                ContourMarkingSettingsFileName:  ""
            );
 
            if (!plateSuccess)
                throw new InvalidOperationException(
                    "Plate NC export failed. Check numbering and settings file: " +
                    $"'{_projectCode}-NC-plates'");
 
            Console.WriteLine(
                $"[{_projectCode}] NC export complete. " +
                $"Staging: {stagingRoot}. " +
                $"Revision: {_revision}. " +
                $"Review and promote to CURRENT when verified."
            );
        }
    }
}

The method signature from the official Tekla Developer Center documentation:

public static bool CreateNCFilesFromAll(
    string NCFileSettings,
    string DestinationFolder,
    bool   CreatePopMarks                  = false,
    string PopMarkSettingsFileName         = "",
    bool   CreateContourMarking            = false,
    string ContourMarkingSettingsFileName  = ""
);
// Returns: true if successful.
// Throws:  ArgumentException  if NCFileSettings is not defined.
//          ArgumentNullException if NCFileSettings is null.
// Note:    Returns false (does not throw) if numbering is not up-to-date.

BOM correlation with NC files

The BOM must be generated from the same model state as the NC files. In Tekla, the safest practice is to export them in the same session, using a script or macro that runs: (1) numbering check, (2) NC export, (3) BOM report export, in sequence. If the BOM and NC files are generated in different Tekla sessions without an intervening numbering check, part additions or connection changes may have caused mark reassignment — a newly added part may have stolen a mark from an existing part that was reprogrammed.

Sample BOM column structure (CSV):

ProjectCode,PkgRev,AssemblyMark,PartMark,Profile,Grade,Length_mm,Qty,Weight_kg,Zone,Sequence,Finish,NCFile
BLD42,B1,BA42,B42,W310X97,S355JR,1450,1,207.8,L3,3A,2B SA2.5,BLD42-NC-B42-B1.nc1
BLD42,B1,BA42,B43,PL200X12,S355JR,650,2,12.3,L3,3A,2B SA2.5,BLD42-NC-B43-B1.nc1
BLD42,B1,BA43,B44,W460X74,S355JR,9200,1,681.0,L3,3B,2B SA2.5,BLD42-NC-B44-B1.nc1
BLD42,B1,BA43,B45,PL300X16,S355JR,480,4,18.1,L3,3B,2B SA2.5,BLD42-NC-B45-B1.nc1
BLD42,B1,BA44,B46,HSS203X203X9.5,S355JR,3600,1,197.2,L3,3B,2B SA2.5,BLD42-NC-B46-B1.nc1

Key columns:

• PkgRev — the package revision. Every row in a given BOM issue has the same value. This is the join key that ties the BOM to a specific transmittal.
• NCFile — the filename of the corresponding NC file. Enables a fabrication management system to auto-associate the NC file when importing the BOM.
• Zone and Sequence — erection sequence attributes. The erector's team uses these to plan the lift sequence without needing to read every drawing.

Holes vs cuts: coding correctly in Tekla

The most common class of NC file errors is misclassified geometry: a notch that should be an AK (external contour cut) gets exported as a series of BO (holes) because the Tekla component used to create it did not generate a fitting or cut object. The NC file output then asks the machine to drill a series of holes in a line rather than drive a coping robot along a contour.

To avoid this:

• Use fittings (not line cuts) for beam-end copes. Fittings modify the part length and are correctly exported to the AK block. Line cuts do not affect the beam length in the NC file.
• Use contour cuts for web openings with non-circular geometry. These export to IK blocks.
• Use standard Tekla components (shear tab, moment end plate, column base plate) rather than manual geometry cuts where possible. Standard components have been validated against NC export.
• After export, open a sample NC1 file in a text editor and verify that copes appear as AK blocks and holes appear as BO blocks before transmitting. A five-minute visual check eliminates the most common shop-floor RFI.

Anti-patterns

Anti-patterns are the practices that seem harmless or convenient in the moment but compound into serious problems by the third revision cycle. These are the ones most frequently encountered on projects that are struggling with fabrication RFI volume.

Mixing NC file revisions in a flat folder

What happens: The CURRENT NC folder contains BLD42-NC-B42-A0.nc1, BLD42-NC-B43-B0.nc1, and BLD42-NC-B44-A1.nc1 — three different revisions from three different export runs, all in the same folder.

Why it happens: The detailer only changed beam B44 in the latest model session, so they only re-exported B44 and dropped it into the folder without moving B43 to SUPERSEDED.

Why it is catastrophic: The fabricator's shop planner imports the entire folder into the CNC management system. The system's file-by-file import cannot tell which revision the planner expected. If B43 had been corrected between A0 and B0 (say, a hole diameter changed from 22 mm to 24 mm), the A0 version of B43 is still in the folder and will be programmed.

Fix: Every NC export run — even a single-part re-issue — must atomically move all affected part NC files from CURRENT to SUPERSEDED and replace them with the new versions. The revision suffix in the filename must always increment; two files with the same part mark but different revisions must never coexist in CURRENT.

Ad-hoc folder structure invented mid-project

What happens: The project started with drawings in one shared drive folder. Three months in, a new sub-contractor joined and created their own _FROM_FABRICATOR folder. The fabricator started emailing NC files directly to the project manager who stored them in Downloads. Nobody can tell which NC files are the ones actually loaded into the CNC system.

Why it is costly: When the engineer issues a correction, they have no reliable way to tell the fabricator which specific file to replace. The fabricator has to manually search their system for every instance of the affected part mark.

Fix: The folder structure defined in the BEP must be the only structure that exists. CDE access controls should prevent any participant from creating folders outside the defined structure. Any file that arrives outside the structure must be moved into it before being acted on.

Manual revision marking on NC file headers

What happens: A detailer regenerated the NC file for a corrected part but forgot to update the revision field in the Tekla NC file header template. The NC file header still reads A0 while the drawing has been issued at B1.

Why it is dangerous: The fabricator's CNC system uses the header revision field to determine whether to reload a part. If the header says A0 and the system already has A0 loaded, it will silently skip the import — the correction never reaches the machine.

Fix: The revision field in the NC file header template must be driven by a Tekla user-defined attribute (UDA) set at the project level, not typed manually per export. The Tekla NC file header customisation dialog supports template variables. Set the revision field to <<REVISION>> where REVISION is a UDA updated programmatically or via a QA checklist before every export.

No supersedes archive

What happens: Old NC files are deleted when new ones are issued. Three months later, there is a dispute about what information the fabricator had at the time they cut a beam that was subsequently found incorrect on site.

Why it matters: Without the supersede archive, there is no way to establish what was current at any given time. The legal and commercial exposure is significant.

Fix: Never delete. Move to SUPERSEDED. This costs approximately 50 MB of disk space per 100 parts per revision cycle — completely negligible. CDE platforms like Trimble Connect retain version history automatically, which is an additional reason to issue via a proper CDE rather than bare file shares.

BOM issued without NC correlation column

What happens: The BOM is a flat list of part marks and profiles. The fabricator imports it into their ERP system and manually links each row to the corresponding NC file by searching the NC folder.

Why it fails: If part marks have been renumbered between model sessions (which Tekla does when numbering series overlap or when the model is partially reorganised), the manual search will link the wrong NC file to a BOM row. The shop planner has no way to detect this without opening every file.

Fix: Include the NC filename as a BOM column. Include the Tekla model's last-run numbering date as a header field in the BOM. If the BOM date and the NC file export date do not match, the package is not ready to issue.

Case studies

These are representative composite engagements drawn from patterns seen across multiple fabrication handoff projects. Identifying details have been generalised.

Case study 1: multi-storey commercial frame, four fabrication packages

A seven-storey office building in a central business district, structural steel frame, 1,200 unique part marks across four fabrication packages issued over eight months. The project started without a defined handoff standard. By the third week of package one fabrication, the shop planner had received three different versions of the NC file for a column splice detail — two by email and one via a shared drive — with no clear indication of which was current. The column had been cut from the A0 NC file; the B0 revision carried a changed bolt gauge that had been issued as "minor" without a formal transmittal. The result: 24 column splice plates recut and 11 columns re-drilled in the shop at the detailer's cost. Direct cost to the detailing firm: approximately two days of shop time plus the re-work coordination labour.

For packages two through four, the handoff standard was formalised. A BIM Execution Plan addendum defined the folder structure, naming convention, and revision protocol. The Tekla NC export was scripted using the Open API CreateNCFilesFromAll method, and the BOM was generated from the same script run to guarantee correlation. Transmittals were issued via Trimble Connect with version history enabled. Packages two through four produced a combined total of three NC-related RFIs across 800 parts — compared to 17 in package one alone.

Case study 2: industrial building, overseas fabricator

A large-span industrial shed, 2,400 tonnes of structural steel, fabricated by a shop with a beam drill line set up for DSTV v5.0 files with .dat extension, no KO (etching) block support, and a maximum drill diameter of 38 mm.

The initial NC export was configured for Tekla's default settings: DSTV v7.0, .nc1 extension, KO blocks included. The fabricator's machine controller rejected every file at import because the extension did not match and the v7.0 header format was unrecognised by their older controller firmware.

Resolution required:

1. Changing the file extension setting in Tekla's NC export dialog from .nc1 to .dat.
2. Setting the DSTV version to v5.0 in the export template.
3. Removing KO blocks by disabling contour marking and etching in the NC settings.
4. Splitting any connection with holes larger than 38 mm diameter into a separate "flame cut" detail, since those holes had to be manually burnt and were not NC-cuttable on that machine.

The total delay from first export to accepted first article: nine days. Had the fabricator's machine capability been captured in the BEP and the NC settings pre-configured against it, this would have been zero days of delay.

The lesson: always obtain the fabricator's NC specification sheet before the first export. Machine brand, controller firmware version, DSTV version preference, accepted file extension, maximum drill diameter, maximum part length, and whether the shop runs separate drill and cope operations or an integrated line — all of these affect NC configuration and should be documented.

Case study 3: phased issue, tight erection schedule

A mixed-use development with structural steel on levels one through twelve, issued in three packages aligned to the erection programme. Package one covered levels one through four; package two covered levels five through eight; package three covered levels nine through twelve. Each package was issued for fabrication before the previous package was fully erected.

The challenge: part marks in levels one through four were in series B1–B310. When levels five through eight were detailed, new connection geometry at the inter-level joints produced six new connection plate marks that fell within the B1–B310 series under Tekla's numbering algorithm. Running a full renumber resolved the collision but changed the marks of 14 parts in package one that were already being fabricated.

The correct resolution was to pre-define separate numbering series in Tekla's numbering settings for each package (e.g., P1 series: B001–B399; P2 series: B400–B799; P3 series: B800–B1199). This is a three-minute configuration change at project start that eliminates the risk of mark collision between packages entirely.

When the mark collision occurred anyway on this project, the remediation required issuing a package one revised BOM and NC supersede for the 14 affected parts, re-transmitting to the fabricator, and providing a change notice to the shop floor. Two affected parts had already been cut; their marks had to be physically re-stamped. The total delay to the erection programme: half a day.

Case study 4: Trimble Connect as the single source of truth

A hospital expansion project, structural steel and composite deck, approximately 900 part marks, three subcontractors involved (steel fabricator, metalwork subcontractor for stairs and balustrades, concrete subcontractor for embedment plates). The project BIM lead insisted on Trimble Connect as the single CDE for model and document sharing before the project started.

The result: the detailing firm published every transmittal directly to Trimble Connect, with folder permissions configured so that the steel fabricator could see GA, shop drawings, NC files, and BOM, but not the structural analysis model or the unreleased coordination drawings. The metalwork subcontractor had a separate permission set covering only the stair and balustrade drawings. The concrete subcontractor could access only embedment plate drawings and the GA.

Three outcomes stood out:

First, the Trimble Connect version history made the "what revision was current at a given time?" question answerable in seconds. When a dispute arose about whether a revised base plate drawing had been current at the time the fabricator cut the base plates, the platform's audit log showed the exact timestamp of both the upload and the fabricator's confirmed download. The dispute was resolved in a single meeting rather than three weeks of email archaeology.

Second, the fabricator's project coordinator set up email notifications for the NC file folder. Every time a new NC file was published, an automatic notification went to the shop planner. The shop planner confirmed receipt directly in Trimble Connect, creating a timestamped acknowledgement record that the drawing team could see. This replaced the email "please confirm receipt" loop that had been the previous workflow.

Third, because the IFC was also published to Trimble Connect, the clash detection coordinator could federating the structural IFC with the mechanical and electrical models in the same environment. Three pipe-steel clashes were found before fabrication of the affected beams — web penetrations were added to the model, NC files regenerated, and the revised NC files issued with a two-day turnaround. Without the federation step, those clashes would likely have been found during erection, requiring field remediation at 3–5× the cost of a shop modification.

The additional setup time for the Trimble Connect project structure: approximately four hours at project start. The time saved across the project lifecycle: conservatively estimated at two to three weeks of total coordination and rework time.

Limits and caveats

International fabricators and non-metric units

The DSTV standard is metric throughout. Coordinates are in millimetres, angles in degrees, weights in kilograms. For North American fabricators accustomed to imperial units (inch-fraction dimensioning, pounds per linear foot for profile weights), the NC file itself does not need to change — CNC machines universally work in metric even in imperial-unit environments — but the drawings must carry both unit systems or exclusively the units the fabricator's shop workforce is comfortable reading. A fabricator whose shop floor reads exclusively in inches will be slower to detect a dimension error on a millimetre-dimensioned drawing.

In Tekla, drawings can be configured with imperial, metric, or dual-unit dimensioning. The NC export is always metric regardless of the drawing dimension setting.

For profile designation, North American shapes (W, HP, S, MC, L, HSS per AISC) map to DSTV profile codes differently from European shapes (HEA, HEB, IPE, UB, UC). Verify that the Tekla model's profile catalogue matches the fabricator's source database. A mismatched profile catalogue is a common cause of NC files with slightly wrong flange or web thickness values in the header — which does not affect the CNC program (the machine measures the actual part) but does create confusion in the fabricator's ERP system when the header dimensions do not match the material delivery tag.

MEP-steel integration

Steel fabrication handoffs typically do not include MEP coordination deliverables, but the absence of steel-MEP coordination from the handoff process creates a downstream problem: web penetrations for services. If the structural detailer has been asked to pre-cut web openings for mechanical or electrical runs as part of the fabrication scope, those openings must appear in the model before the NC files are generated — an opening added after the NC files have been issued requires a re-issue of the affected part.

The appropriate protocol is to include a "web penetration freeze" milestone in the project programme: all confirmed MEP route penetrations are modelled in Tekla by a specified date, the NC files are not exported until that date passes, and any penetration added after that date is classified as a variation. This requires coordination with the mechanical, electrical, and plumbing engineers who are typically working on a different schedule and a different model.

Trimble Connect supports multi-discipline model federation and can display steel and MEP models in the same viewer, allowing clashes to be identified before the NC freeze date. Establishing a Trimble Connect project early — before the first NC export — and inviting MEP coordinators to it is the minimum viable integration step.

The limits of automation

The Tekla Open API CreateNCFilesFromAll method automates export, but it cannot automate judgment. The automated export will faithfully reproduce every error in the model: a cope created with the wrong component will produce a wrong AK block; a bolt in the wrong location will produce a BO block at the wrong X coordinate. Automation removes the risk of export process error (wrong settings file, wrong folder, wrong extension) but does not remove the need for a model QA review before every transmittal.

The minimum QA step before any NC export: open the model, run the numbering check, filter for changed parts since the previous transmittal date, review each changed part's connections visually, and if in doubt, open the generated NC1 file for that part in a text editor and verify the hole positions against the drawing.

Dealing with RFI after NC files have been issued

Even a well-run handoff generates RFIs. The question is not how to eliminate them entirely but how to handle them without losing two days per incident.

When an RFI arrives that requires a model change:

1. Confirm scope before touching the model. Is this a correction to the detailer's work, or is it a design change initiated by the engineer of record? If the latter, a variation order or site instruction must exist before any model change is made. Making the change before the instruction is formalised removes the record of what the original scope was.

2. Make the model change and re-run numbering. Check what marks have changed. If the RFI affects only one part and the numbering change is confined to that part, the scope of the re-issue is clear. If the numbering change propagates (because the changed part's mark is shared by identical parts elsewhere in the model), every affected part needs a re-issued NC file.

3. Re-generate only the affected NC files and drawings. In Tekla, use the "selected parts" workflow (CreateNCFilesFromSelected) rather than the "all parts" workflow. Export to a staging folder, review, then promote to CURRENT and move the previous version to SUPERSEDED atomically.

4. Issue via a revision transmittal, not an email attachment. An email attachment has no audit trail. The transmittal creates the record. Even for a single-part re-issue on an urgent basis, the transmittal can be generated in five minutes and uploaded to the CDE.

5. Communicate what changed. The transmittal should identify the specific part marks, the specific change, and whether the fabricator needs to check whether the original version has already been cut. If it has been cut, the fabricator needs to know whether the change requires a re-cut or whether it can be accommodated by a field bolt tolerance.

The two-day cycle only persists when the process is ad-hoc. A defined protocol converts a two-day event into a four-hour event.

Sources and further reading

This article draws on the following primary sources, all verified accessible at time of writing:

1. Trimble / Tekla User Assistance — NC files (2025). Configuration and export documentation for Tekla Structures NC file creation, including DSTV format specification, block types, and settings tabs. https://support.tekla.com/doc/tekla-structures/2025/int_create_nc_files

2. Trimble / Tekla User Assistance — DSTV file description (2025). Block-level reference for the DSTV NC format as implemented in Tekla Structures. https://support.tekla.com/doc/tekla-structures/2025/int_nc_dstv_file_description

3. Trimble / Tekla Developer Center — CreateNCFilesFromAll method (2024). Official API reference for programmatic NC export, including method signature and parameters. https://developer.tekla.com/doc/tekla-structures/2024/create-nc-files-all-method-string-string-boolean-string-boolean-string-29058

4. Trimble / Tekla User Assistance — Quick start to Tekla Structures drawings (2026). Reference for drawing types: GA, single-part, assembly, cast unit, multidrawings. https://support.tekla.com/doc/tekla-structures/2026/dra_quick_start_to_ts_drawings

5. AISC — BIM & VDC for Structural Steel (F201-19). AISC's guidance document on BIM implementation for structural steel, covering model review and approval workflow, IFC exchange, and fabrication model requirements. https://www.aisc.org/globalassets/aisc/publications/references/f201-19.pdf

6. Graitec / StrucSoft — CMS DSTV NC1 Software overview. Practical reference on DSTV block types (AK, IK, BO, KO, SI, KA), machine compatibility (Peddinghaus, Voortman, FICEP, PythonX, Ocean), and NC1 format behaviour. https://strucsoftsolutions.com/blog/connecting-design-to-fabrication-how-graitecs-cms-dstv-nc1-software-powers-smarter-steel-fabrication/

7. Trimble — From Model to Metal: Eliminating Steel Fabrication Data Silos. Case study material and workflow analysis for Tekla Structures — Tekla PowerFab integration, Trimble Connect collaboration, and detailer-fabricator data exchange. https://www.trimble.com/blog/construction/en-US/article/connected-steel-data-workflows

8. NIST / ITcon — Details of the Mapping Between the CIS/2 and IFC Product Data Models for Structural Steel (Lipman et al., 2009). Definitive reference for the CIS/2 to IFC relationship, data model differences, and translation considerations for structural steel. https://itcon.org/papers/2009_01.content.09082.pdf

9. SDS/2 Technical Support — DSTV Options. Reference for DSTV v5.0 vs v7.0 version selection, file extension options (.nc1, .nc, .dat), and machine-specific configuration parameters. https://techsupport.sds2.com/sds2_2023/Topics/cnc_dstv.htm

10. Klietsch GmbH — DSTV NC Data / NC1 Data. Profile type code reference (I, U, L, B, M, RU, RO, C, T, SO) and block type overview for the DSTV standard. https://klietsch.com/?m=page&action=240827&lang=en