Naming Conventions for Revised CNC Files
CNC file naming should incorporate the piece mark and revision letter as mandatory fields. A file named 'C-101.nc1' is not reliably distinguishable from its prior revision. A file named 'C-101_RevB.nc1' is — and the machine operator knows immediately whether the file on the machine is the current one.
- Include piece mark in the file name — e.g., W14-132_B-104
- Include revision letter — e.g., B-104_RevA, B-104_RevB
- Include issue date if the shop workflow uses dates for versioning
- Never reuse file names across revisions — archive the old file, issue the new one with a new name
Linking CNC File Releases to Drawing Releases
CNC files should be issued simultaneously with shop drawing revisions — not separately or later. A drawing release package for PKG-02 should include the PDF drawing files and the NC files for all members in that package, labeled with matching revision identifiers. If the NC file folder contains files at a different revision than the drawings in the package, the package is incomplete and should not be released.
Machine-Side Controls
On the machine side, establish a protocol that the CNC operator must verify the revision of the NC file on the machine against the revision register before running any production batch. A 60-second check before a 4-hour production run is an excellent trade. Some shops implement a locked NC file directory where only the current revision is accessible — older files are moved to an archive folder that requires a supervisor override to access.
The CNC File Revision Register
The same discipline applied to drawing revision registers should be applied to CNC files. A CNC file revision register should contain: piece mark, current NC file name including revision identifier, file issue date, the revision of the associated shop drawing, and confirmation that the file has been verified on the machine. This register becomes the tool the shop supervisor uses to confirm the production floor is running from current files — not from files issued two revision cycles ago that were never replaced.
- Piece mark — must match the shop drawing piece mark exactly
- NC file name with revision identifier — e.g., B-204_RevB.nc1
- Issue date — date the file was sent to production
- Associated drawing revision — the drawing revision this NC file was generated from
- Machine verification — confirmation by operator that the correct file is loaded
- Prior revision disposition — archived, deleted, or overwritten
What Triggers a CNC File Revision
Any change to the shop drawing that affects machined geometry requires a revised CNC file. Changes that trigger NC file regeneration include: hole pattern changes (new holes, deleted holes, relocated holes), member length changes, cope dimension changes, and material section changes that affect section geometry. Changes that do not affect machined geometry — weld symbol changes, drawing notes, connection plate callout revisions — do not require a revised NC file. The detailer should communicate clearly with the shop when issuing revised drawings whether the revision affects the NC files, so the CNC operator knows whether to pull new files or proceed with existing ones.
Audit Process — Confirming the Floor Is Running Current Files
A spot-check audit of CNC file currency should be part of the shop's QA/QC process during active production. The audit selects 5–10 members currently in production or queued for machining, verifies the NC file revision on the machine against the revision register, and confirms the revision on the NC file matches the current drawing revision for that piece mark. Any mismatch is an immediate stop-work for that member pending file replacement and an investigation of how many other members may be affected. The audit should be performed at the start of each new drawing package release and at any time a drawing revision is issued during active production.