Short answer
Design rules
- Count
- 15–25 reasons, 7–8 groups; remove what nobody uses after a month
- Two kinds
- Breakdown (fault; alerts; cleared by supervisor) vs Pause (operator-controlled stop)
- Wording
- What the operator sees, not the engineering cause — 'spindle noise', not 'bearing wear'
- Where
- Picked at the machine at the moment of the stop, one tap
- Root cause
- Recorded later on breakdowns by supervisor/maintenance; never the operator's job
The list
| Group | Reason | Use it when |
|---|---|---|
| Breakdown (Breakdown) | Tool breakage | Tool or insert broke mid-cut |
| Spindle / noise / vibration | Spindle fault or abnormal noise | |
| Machine alarm / fault | Control alarm the operator cannot clear | |
| Hydraulic / pneumatic | Pressure, chuck, tailstock, turret faults | |
| Electrical | Drive, servo or power-supply fault | |
| Coolant system | Pump failed, no flow, leak | |
| Setup (Pause) | Job changeover | Fixture, jaws, tools, offsets for the next job |
| First-piece approval | Waiting for inspection of the first piece | |
| Program edit / proving | Editing or proving the program | |
| Tooling (Pause) | Tool / insert change | Planned change at end of tool life |
| Tool not available | Waiting for a tool from the crib or supplier | |
| Tool setting / offset | Measuring and setting a tool | |
| Material (Pause) | Waiting for material | Raw material or blanks not at the machine |
| Wrong / rejected material | Material found wrong or defective | |
| Material handling | Loading, unloading, crane waiting | |
| Quality (Pause) | In-process inspection | Waiting for the inspector or measuring |
| Dimension issue | Stopped to correct a dimension | |
| Rework | Reworking pieces on the machine | |
| Utilities (Pause) | Power cut | Grid failure; generator changeover |
| Air pressure low | Compressor or line pressure | |
| Coolant top-up / change | Planned fluid change | |
| Operator (Pause) | Break | Tea, lunch, personal |
| No operator | Machine idle, nobody assigned | |
| Training / meeting | Operator away for training or a meeting | |
| Planning (Pause) | No job assigned | Machine has no work scheduled |
| Waiting for drawing / instruction | Waiting for information | |
| Planned maintenance | Scheduled maintenance window |
Why grouped, and why so few?
A report is only as good as the reason column. With sixty codes, operators tap the first plausible one and the top reason becomes “other”. With eight groups and two or three reasons each, the choice is obvious at a glance — and the weekly report can be read at the group level (setup vs tooling vs material) before drilling into a reason.
Word every reason the way the operator experiences it. The operator hears spindle noise; the engineer later finds a bearing. Ask for the noise; record the bearing as root cause afterwards.
Breakdown vs pause — why the distinction matters
A pause is the operator's call and ends when they tap resume. A breakdown is a fault: it should alert the supervisor and owner immediately, hold the machine in the down state until someone clears it, and carry a root cause and corrective action afterwards. That gives every breakdown a start, an end and a person who confirmed it — which is what makes a downtime report believable. This is how downtime tracking in OpeEye treats the two.
Reading the report: the first fix is the top line
Rank the week's minutes by reason. The top line is next week's project — usually a setup group reason or “waiting for material” in a job shop. Fix it, watch the ranking for two weeks, take the next line. OEE moves because availability moves; availability moves because the top reason shrank.
Put this list on a tablet at every machine — this week.
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Questions shop owners ask
How many downtime reason codes should a CNC shop have?
+
Between 15 and 25, grouped into 7 or 8 families. Fewer than that and 'other' swallows the truth; more than that and operators tap the first one they see. Start with the list on this page and remove what your floor never uses after a month.
What is the difference between a breakdown reason and a pause reason?
+
A breakdown is a fault that stops production and needs someone to fix or clear it — tool breakage, alarm, spindle. A pause is a stop the operator controls — break, waiting for material, inspection. Breakdowns should alert a supervisor and stay open until cleared; pauses just need a reason.
Should setup be a downtime reason?
+
Yes. Setup is time the machine is not producing, so it counts against availability. Track it as its own group — job changeover, first-piece approval, program proving — because it is the loss job shops can shrink fastest.
Where should the operator pick the reason?
+
At the machine, at the moment of the stop, in one tap. A reason recalled at the end of the shift is a guess. A tablet with big buttons and a short list is enough; a register with a code column is not.
Should I record root cause as well?
+
For breakdowns, yes — after the fact, by the supervisor or maintenance: what actually failed and what was done. Keep it separate from the operator's reason so the operator's job stays one tap.
Related
- Downtime trackingOne-tap stop reasons, breakdown alerts in seconds, hours lost by cause.
- How to calculate OEEThe formula, a worked example on a turning centre, and a calculator.
- Daily production report formatThe columns that matter, a filled example, and how to automate it.
- OEE softwareAvailability × performance × quality, computed from real floor events.