Every CNC control shows a spindle load meter, and most operators glance at it on a heavy cut. Read once, it says whether the motor is struggling. Read across hundreds of parts, it says how the tool is wearing.
Reading the load meter
Under 80%
- What it usually means
- Comfortable — within the motor’s continuous rating
80–100%
- What it usually means
- Working hard but sustainable
Brief peaks over 100%
- What it usually means
- Normal on entry or heavy cuts — short-time rating
Sustained over 100%
- What it usually means
- Overload risk — many controls alarm after a set time
| Reading (typical) | What it usually means |
|---|---|
| Under 80% | Comfortable — within the motor’s continuous rating |
| 80–100% | Working hard but sustainable |
| Brief peaks over 100% | Normal on entry or heavy cuts — short-time rating |
| Sustained over 100% | Overload risk — many controls alarm after a set time |
Thresholds and colours vary by control maker, so check the manual for the exact limits on a given machine.
What load trends tell you
A sharp tool cuts with less force than a worn one. On the same operation, the load climbs gradually as the edge wears (illustrative: 42% on the first part of a new insert, 55% by the end of its life). A sudden jump usually means a chipped edge, a harder batch of material, or a changed offset — a slow climb usually means it is time for a fresh edge.
Tracking spindle load per part
On controls that report it over the network, ThingConnect reads spindle load along with spindle speed on every poll. In tool life monitoring it is charted as the average load per part while each tool cuts, across that tool’s life — so you can see whether a tool is being changed too early or run too long.
Two cautions when reading it. Load only means something compared with the same tool on the same operation — a roughing end mill and a finishing insert will never read alike. And a reading taken while the spindle is accelerating or the tool is in air is noise, which is why the per-part average is taken only while that tool is cutting.