CNC Downtime Tracking: Reason Codes and a Shift Log

A useful CNC downtime log records the machine, affected job, start and end time, elapsed minutes, reason and review owner for each stop. “Machine stopped” is an observation; it does not establish why production stopped.

Agree the reporting boundary first. State the scheduled operating window, treatment of planned breaks and changeovers, and whether short stops are recorded individually. Keep those definitions consistent when comparing shifts.

Use a small, clear reason-code set

Make the reason specific enough to act on without asking operators to guess a root cause. An alarm description can support investigation; it is not automatically the final mechanical diagnosis. Preserve the original observation when a reviewer later updates the classification.

Record and reconcile one stop

In this illustrative example, CNC-02 stops at 10:05 and resumes at 10:17 during job WO-104. The elapsed time is 12 minutes. The initial reason is “material wait”; the review records that the correct blank was unavailable at the workstation.

For a stop crossing midnight, record full dates and times. Split reporting at the shift boundary if needed, while retaining the original event identity so the same minutes are not counted in both shifts.

Handle overlapping reasons explicitly

If a machine waits for material and a tool issue is discovered during the same 12-minute interval, do not add two 12-minute stops for that machine. Keep one time interval with a primary classification and supporting notes, or split it into non-overlapping intervals when the evidence supports that split.

Reconcile stop minutes against the defined shift window. Review gaps, impossible negative durations, repeated event IDs and an end time that precedes the start. Keep planned non-production time separate according to the agreed definition.

Check machine signals before trusting automatic totals

A missing network update should remain a data gap until it is resolved. It does not prove a breakdown. Confirm which signal means running, stopped or disconnected, and compare a sample of recorded intervals with operator observations. Check clock alignment and the process for adding a reason.

ERPNext’s downtime-entry documentation describes a straightforward manual record of machine downtime in minutes. A reliable manual log can establish the definitions before any machine connection is introduced.

Use the downtime improvement guide to choose investigations from the reviewed log. For availability, performance and quality together, see the worked OEE calculation. In an Optiwise IoT discussion, ask which signals and manual inputs your proposed configuration needs.

Questions from manufacturing teams

What should a CNC downtime log contain?

Record machine, job, full start/end times, elapsed minutes, planned or unplanned class, observed reason, evidence, recorder and review owner.

Can one stopped interval have more than one reason?

Yes, but overlapping reasons must not duplicate the same machine minutes. Keep supporting reasons on one event or split the interval using documented boundaries.

Does a missing machine signal mean downtime?

It means data is missing. Investigate connectivity, signal definitions and clock alignment before classifying the interval as a production stop.