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The spindle is not turning at the speed it was commanded, and the difference is larger than allowed for longer than allowed. The drive reads that as loss of spindle control and cuts out. It can be because the load is winning, because the transmission is slipping, or because the speed feedback it receives is not good.
For reference only: alarms change with the manufacturer, the control and the machine PLC. Check the full code in the official manual before doing anything. Legal notice.
If it appears with no load, when orienting or at low rpm.
Reset with the spindle stopped and after removing the load.
Choose the manual matching your control series, software version and machine builder. A support portal is a starting point; it does not establish applicability to every model.
The spindle drive works in a closed velocity loop: it takes the command from the CNC, measures actual rpm with the motor or spindle encoder, and adjusts current so the two match. That loop has a supervisor comparing command against measurement; while the difference is small or brief it is considered normal, because every acceleration produces a transient deviation. When the difference stays above the threshold for longer than expected, the supervisor trips SP9002. There are three routes there. First: the load is more than the spindle can overcome at that speed, so the drive commands maximum torque and the rpm still fall; this is what happens when a drill jams, when you enter material abruptly, or when you work well below the power curve. Second: the motor really is turning at the correct speed but the spindle is not, because there is a slipping belt, a loose coupling or a gear range clutch that never engaged between them; depending on where the encoder sits, this shows up as deviation or goes unnoticed until the part comes out wrong. And third: there is no real deviation at all and the measurement is what has failed: a dirty or damaged spindle encoder, a degraded feedback cable, a loose connector. That third route is the one that gives strange alarms with no load, sometimes during spindle orientation or at start-up.
In order, from the fastest and cheapest check to the most expensive.
01Compare the commanded S against the actual rpm on screen
The control displays both. If the actual figure sits clearly below the command while cutting, it is load or transmission. If the actual figure jumps, oscillates or shows nonsense values even with the spindle nearly stopped, suspect the measurement: encoder or cable.
02Test in air, in steps
With no tool cutting and the machine safe, command several speeds from low up to working rpm and watch whether it reaches and holds each one. If it follows every command in air with no deviation, the problem appears under load and it is process or transmission. If it already fails in air, it is the drive, the motor or the measurement.
03Look at the operation where it trips
Abrupt entries into material, deep drilling with packed chips, tapping with a worn tap or an aggressive change of cut will all collapse the rpm suddenly. If the alarm always comes up at the same point in the program, look at that specific move: it is almost certainly too aggressive an entry or a tool that no longer cuts.
04Check the transmission
If the spindle is belt driven, check belt condition and tension against the machine manual, with the machine stopped and locked out. A loose or glazed belt slips exactly when torque rises, and the symptom is precisely this: perfect in air, collapsing under load. On machines with gear ranges, check that the range really changes and that the screen reflects the correct one.
05Listen to the spindle on orientation and on stopping
An encoder with problems usually also causes orientation faults or abrupt stops during tool change, because orientation depends directly on that measurement. If alongside SP9002 the tool changer is complaining or the spindle does not orient the same way every time, the diagnosis is practically made and it is a maintenance job.
06Note the drive's own code before you call
The spindle amplifier has its own alarm number on the control's spindle diagnostic screen. That number separates deviation caused by load from a feedback failure, which is exactly the question that has to be answered. Collecting it before calling saves half a visit.
A slipping belt, a gear range that did not engage, or load above the capacity at that speed. Confirm it by repeating the pass with half the feed: if it no longer collapses it was load; if it collapses just the same it is the transmission and maintenance checks it.
Feedback: encoder or cable. It is confirmed because the actual speed on screen is unstable or inconsistent without cutting. That is a maintenance diagnosis; do not keep starting the spindle over and over.
A very high momentary torque from packed chips or a worn tap. Confirm it by checking the tool and chip evacuation, and by trying a peck cycle or more retracts. Fix it in the process: tooling, coolant and evacuation strategy.
Belt and transmission inspection inside the periodic plan, at the tension the machine manual specifies. Ramped entries into material instead of full engagement. Life control on taps and drills, which are the tools that collapse rpm most suddenly. Through-tool coolant or peck cycles on deep holes so chips get out. And an alarm log with time and operation: separating the ones that appear under load from the ones that appear in air is what steers the whole diagnosis afterwards.
The Fanuc spindle does not maintain the commanded speed within tolerance. It is an alarm from the Spindle area, and in the catalog it is listed as “Spindle speed deviation”. On the machine you notice it like this: Actual rpm does not follow the setpoint, Alarm when accelerating or cutting, There may be loss of torque.
On the shop floor it almost always comes from one of these causes: Cutting overload, Spindle encoder, Belt or transmission slipping, Spindle drive. Rule out the most likely one on your machine first, before touching parameters or swapping anything.
Reset with the spindle stopped and after removing the load. Resetting without fixing the cause first only hides the problem: SP9002 trips again and, in the meantime, you keep working with the machine in bad shape.
With the machine stopped and in a safe state, start with these checks: Compare the commanded S with the actual rpm, Check transmission and cutting load, Write down the spindle amplifier code. That alone will tell you whether it is the program or whether you need to raise a maintenance job.
With SP9002 active, avoid this: Do not bypass safety devices, Do not manipulate energized electrical cabinet, Do not continue producing if the alarm reappears. Skipping any of these points is what turns a minor stop into an expensive breakdown.
If it appears with no load, when orienting or at low rpm. If you are not sure how far it goes, stop the machine and report it: a repeat alarm always works out cheaper than a crash.
It is critical: there is a real risk of damage to the machine, the tool or a person. Leave the machine stopped, do not keep resetting it to see if it goes away, and call maintenance before producing again. Guidance reference. Always confirm the full text in the exact machine/control manual.
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