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How Do We Find Out Why Our CNC Machines Are Stopped When They Should Be Cutting?

CNC machines sit idle for reasons nobody records: waiting for material, tools, first off approval. We build stoppage logging that shows where spindle time goes.

Updated 3 min readBy SpiderHunts Technologies

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Quick answer — TL;DR

Idle machine time goes unexplained because stoppages are short, frequent and never written down, so the shop only sees the big breakdowns. We build stoppage logging that detects when a machine stops from its controller or a simple signal, asks the operator for a reason with one tap, and reports where the lost time actually goes by machine, shift and cause.

Busy people, quiet machines

Walk the shop at any moment and everyone looks busy. Yet when you add up the parts that came off the machines this week, it does not match the hours the machines were staffed. The five axis sat for most of Tuesday morning. Nobody is quite sure why. Someone thinks it was waiting for a first off to be signed. Someone else thinks the material was in the wrong size.

The breakdowns are remembered, because an engineer was called. The dozens of short stops are not.

Why the lost time stays invisible

Most stoppages in a machine shop are not faults. They are waiting: for material, for a tool, for the inspector, for a program edit, for a crane, for someone to finish a setup on the next machine. Each one is short and feels unavoidable, so nobody records it.

  • Only breakdowns are logged, in a maintenance book.
  • Operators have no quick way to say why they stopped.
  • Waiting for first off approval is treated as part of setup.
  • Machines left idle over lunch or at shift change are not counted.
  • Nobody compares staffed hours with cutting hours.

What the idle time costs

Spindle time is what you sell. Every hour a machine is staffed but not cutting is a cost with nothing to show for it. Without knowing the causes, the usual response is to buy another machine or add overtime, when the real fix might be presetting tools, moving an inspector, or getting material cut a day earlier.

The stoppage logging we build

  1. Each machine reports whether it is cutting. Newer controls do this through MTConnect or OPC UA. Older ones can use a current sensor on the spindle or a signal from the cycle light.
  2. When a machine stops for longer than a few minutes, a tablet at the cell asks the operator for a reason from a short list you choose: waiting material, waiting tools, waiting inspection, setup, program, breakdown, no operator, planned.
  3. One tap records the reason. If the operator is busy, the question waits until they come back.
  4. Stoppages are recorded with machine, job, shift and duration.
  5. A daily and weekly report shows cutting time against staffed time for each machine, and the lost time broken down by cause.
  6. A live screen in the office or on the shop floor shows which machines are cutting, set up or stopped, and why.
Stoppage reasonUsually fixed by
Waiting for materialCutting stock a day ahead
Waiting for toolsPresetting before the machine is free
Waiting for first off sign offInspector availability or operator sign off rules
Program editsMore prove out in CAM or simulation
No operatorShift cover or running one person across two machines

The list of reasons is yours. We keep it short, because a long list means operators pick whichever is at the top.

What the reports start to show

Within a few weeks you have a picture of where time goes that nobody could give you before. It is usually not what people expected. The fixes that follow are often small and cheap: a tool presetter, a second person trained to sign first offs, a change to when material is cut. The live screen also means the supervisor sees a stopped machine straight away rather than at the next walk round.

This is not the same as predicting breakdowns. It is about the ordinary waiting that makes up most lost time, which is where most shops have the most to gain.

Could your machines be cutting more?

  • You cannot say how many hours each machine cut last week.
  • Only breakdowns are logged.
  • Machines wait for first offs to be inspected.
  • Output does not match staffed hours.
  • The answer to idle machines has been overtime or another machine.

FAQ

Frequently asked questions

The questions readers ask us after this guide.

Still have a question?

Ask us directly — a senior engineer will get back to you.

Ask about your project

Do we need new machines for this?

No. Older machines can be monitored with a simple sensor. We look at each control before quoting.

Is this the same as OEE software?

It covers similar ground. Off the shelf OEE products are sometimes the right answer, and we will say so. We build custom when you want it tied to your own jobs and reasons.

Will operators feel watched?

That depends on how it is used. We suggest introducing it as a way to remove the things that make them wait, and showing them the reports.

Does it need network cabling to every machine?

Not always. Wireless sensors and tablets cover most shops, though a wired connection is more reliable for controller data.

Keep reading

More on Problems We Solve

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