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The spindle amplifier keeps count of how much current it is delivering and for how long, and it has reached the limit it can sustain. It is not a spike: it is sustained high load. In practice, the spindle is telling you the operation it is running is too much for it as programmed or with the tool it is carrying.
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 occurs without load or after reducing parameters and changing tools.
Reset after stopping, letting it cool if applicable and removing the load cause.
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.
A spindle has two different ratings that get confused all the time: continuous power, which it can deliver all day, and overload power, which it can deliver for a limited time. The amplifier polices that difference with a thermal model: it accumulates current over time while it is above the continuous rating and discounts when it drops below. When the accumulated figure hits the ceiling, it trips the overload alarm. The consequence is that the machine cuts out late relative to when the problem started: by the time it trips, the spindle has already been working hard for quite a while. There is also a detail that explains many apparently inexplicable cases: available power depends on rpm and on the gear range. Below a certain speed a spindle delivers considerably less continuous power than its nameplate suggests, because the torque and power curve falls away. That is why a roughing operation at low rpm can trip the alarm while the same pass at higher rpm does not. And it is why a machine with a mechanical gear change that stayed in high range when it should have shifted to low gives repeated overloads with nothing odd in the program. The other half of the cases is tooling: a worn edge does not cut, it rubs, and torque rises with nothing changed in the program.
In order, from the fastest and cheapest check to the most expensive.
01Watch the spindle load before it trips
The control shows spindle load percentage on its monitor screen. Repeat the operation watching that number: if it sits steadily above 80 or 90 % during the pass, the alarm is only a matter of time and you know it is real load. If it trips with the load low, the problem is not the cut and you should be looking at the drive or the cooling.
02Check the tool before the program
Take the tool out and look at the edges under a loupe: flank wear, a rounded edge, built-up edge or a broken tooth. A worn tool can double the torque required. Changing it and repeating the same operation is the fastest and cheapest test there is: if it does not trip with a new tool, the diagnosis is over.
03Check rpm and gear range
See what speed it is working at and, if the machine has gear ranges, which one it is in. A roughing operation programmed at low rpm is demanding torque in the region where continuous power is lowest. If the machine stayed in high range because the shift failed, the overload is constant and repeatable: it is confirmed because the gear change does not sound right or the screen shows a range that does not match.
04Compare the cutting parameters against the reality of the machine
Width of cut, depth, feed per tooth and material. Tool catalogue figures assume a rigid machine with power to spare; if your spindle is more modest, the numbers have to come down. Try halving the feed with the override and repeating the pass: if it stops tripping, it is pure process and the job needs reprogramming, not running permanently with the override turned down.
05Test the spindle in air
With the machine cooled down, run the spindle with no tool cutting, stepping the rpm up, and watch the load. A healthy spindle draws very little in air. If it already shows appreciable load or makes noise in air, you have a bearing, an over-tensioned belt or a motor problem, and that is maintenance.
06Check chip evacuation and coolant
Recutting chips spikes the torque instantly and is a common cause in deep pockets and in drilling. Check that coolant reaches where it has to, with flow and pressure, and that chips are getting out. If the alarm always appears in the same deep feature of the part, this is probably it, not spindle power.
Process overload: the operation is beyond what that spindle can sustain. The new tool only delays the moment. Confirm it by watching the load during the pass. Fix it by splitting the pass, reducing the width of cut, or raising rpm if the material allows.
Something changed that is not in the program: a harder batch of material, a different tool supplier, coolant at the wrong concentration, or a gear change that no longer engages. Confirm it by comparing against a part from the previous batch if any is left, and by checking coolant concentration and gear change operation.
It is not cutting overload: it is the drive, the amplifier cooling or the transmission. It is confirmed because the load percentage is low while cutting. Pass it straight to maintenance with that fact, because it is what steers the diagnosis.
Tool life control by cutting time or part count, instead of changing when you can already tell. Watch spindle load percentage as process data and leave headroom: an operation at 70 % absorbs material variation, one at 95 % does not. Avoid long roughing operations stuck in the low rpm region. Coolant with concentration and flow checked, and strategies that evacuate chips rather than recut them. And gear change and transmission inspection inside periodic maintenance if the machine has them.
The Fanuc spindle amplifier detects accumulated overload. It is an alarm from the Spindle area, and in the catalog it is listed as “Spindle overload”. On the machine you notice it like this: Alarm during cut, High spindle load, The spindle may stop.
On the shop floor it almost always comes from one of these causes: Worn tool, Excessive advance or depth, Harder material than expected, Ventilation or motor with problem. Rule out the most likely one on your machine first, before touching parameters or swapping anything.
Reset after stopping, letting it cool if applicable and removing the load cause. Resetting without fixing the cause first only hides the problem: SP9001 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: Check spindle load before alarm, Check tool and cutting parameters, Test the spindle with no load if it is safe. That alone will tell you whether it is the program or whether you need to raise a maintenance job.
With SP9001 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 occurs without load or after reducing parameters and changing tools. 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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