Direct Answer
Verify NC1 files by opening them in a text editor or DSTV viewer, checking header values (profile, length, rotation) against the shop drawing, and confirming that every bolt hole record (BH line) matches the drawing hole pattern by X/Y position and diameter. Run the first member, measure all holes with a bolt gauge, and compare to the drawing before approving the batch.
Full Explanation
Common NC1 errors: wrong section rotation (member machined upside down — holes drilled in flange instead of web), hole diameter mismatch (metric vs. imperial units), missing operations (cope record absent — member shipped without a cope), extra operations (holes drilled on the wrong face — profile rotation error in the Tekla model). Most of these errors are visible in the NC1 text file without running the machine. Free DSTV viewer applications (available from CNC manufacturers) display a 3D preview of the machined member from the NC1 file.
What This Means for Your Shop
A file-level error check takes 5 minutes per file type; a machine-level error discovered mid-production requires scrapping the member and re-running. The 5-minute check is always worth it.
Common Mistakes
Trusting that the detailer's NC1 files are correct without verification. Even excellent detailers occasionally export with wrong settings — a quick verification on the first run of each member type is standard practice.
Recommended Process
For each new project, establish a 'first article' protocol: the CNC operator verifies the NC1 file in the viewer before running, runs one member, measures all holes and operations against the drawing, and signs a first-article form. Subsequent members in the same batch run without individual verification.