What the Detailer Needs from Your Shop
- Equipment make and model — e.g., Ficep Tipo 1001, Peddinghaus FDB-1500, Voortman V807
- NC file format — DSTV NC1, proprietary DXF, or machine-specific format
- Section library — the section profile database the machine uses (European, AISC, custom)
- Hole tolerance — the diameter tolerance programmed into your drill line for each bolt diameter
- Coping machine parameters — corner radius requirements, minimum cope dimensions
- Test procedure — whether a test file and dry run are required before production files are issued
The Section Library Compatibility Issue
The most common CNC compatibility problem is a section profile mismatch between the detailing model and the machine's section library. Tekla Structures uses its own section naming convention (e.g., W14X132 vs. W14x132 vs. W360X197). If the machine's library uses a different naming convention or profile geometry, the NC file will error or produce incorrect output. The fix is a one-time mapping table that translates model section names to machine section names — typically a 2–4 hour setup task per machine type.
Testing Before Production
For a new shop-detailer relationship, always test CNC files on a pilot member before committing to production. Select a member with holes, a cope, and a non-standard cut end. Verify the NC file runs correctly on the machine, the holes are in the right locations, and the cope dimensions match the drawing. Document the test result and keep it as the baseline for future NC file generation on that equipment.
Hole Diameter and Tolerance in NC Files
One of the most common CNC file errors is programming hole diameters equal to bolt diameter rather than to the required hole clearance. AISC Table J3.3 specifies standard hole sizes — a 3/4" bolt requires a 13/16" hole (standard), 15/16" (oversized), or slotted dimensions as required. The NC file must program the drill to the hole size, not the bolt size. In Tekla, this is set in the bolt properties for each connection component. If the Tekla model was built by a detailer who set bolt diameter and relied on the fabricator to adjust for clearance, the NC files will drill holes that are 1/16" undersize — producing bolt installation problems throughout the project.
- Standard holes: bolt diameter + 1/16" for bolts up to 1"
- Oversized holes: bolt diameter + 5/16" — requires EOR specification
- Short-slotted holes: 1/16" over bolt diameter in width, bolt diameter + 5/16" in length
- Long-slotted holes: 1/16" over bolt diameter in width, bolt diameter + 1-3/8" in length
- Confirm Tekla bolt catalog has hole clearance configured, not just bolt diameter
Multi-Machine Shops and File Management
Fabrication shops with multiple CNC machines — separate drill lines, coping machines, and saw stations — may require different NC file formats for each machine type even within a single DSTV output. Some shops run a Ficep drill line that requires DSTV NC1 and a separate plasma table that requires DXF. The detailer must understand which members go to which machine and generate the correct file type for each. At project kickoff, collect a complete equipment list from the shop: make, model, and required NC format for each machine. Build a file routing table that maps member types to machines, and confirm with the shop before the first production release.
Revision Management for CNC Files During the Project
Once production begins, revised CNC files must be managed with the same rigor as revised drawings. When a drawing is revised to Rev B, the NC file for that member must be regenerated from the updated Tekla model and re-issued as Rev B. The shop must retire the Rev A NC file and replace it on the machine. Establish a CNC file revision log that mirrors the drawing revision register: piece mark, current NC file revision, date issued, and machine confirmation of receipt. A single outdated NC file running on the drill line can produce incorrectly drilled holes on dozens of members before the error is caught during assembly inspection.