Chip load and feeds#
Formula#
chip load = feed ÷ (RPM × flutes)
Units: mm per tooth (feed in mm/min).
Gauge bands#
| Reading | Actual ÷ target | Means |
|---|---|---|
| 🔴 rubbing · too hot | below 0.75 | Too slow a feed for the RPM |
| 🟢 sweet spot | 0.75 – 1.4 | Good |
| 🔵 chips too large | above 1.4 | Too fast a feed for the RPM; risk of breaking |
What sets the target#
| Factor | Effect |
|---|---|
| Material | Softer takes a thicker chip |
| Bit diameter ≥ 1/8" | Chip grows with diameter, up to 2× a 6 mm bit's |
| Bit diameter < 1/8" | Chip shrinks faster than the bit (1/16" ≈ ⅓ of 1/8") |
| Bit type | V-bits, ball noses and bull noses take less |
| Rated chip load | Ceiling. Never exceeded |
| Rigidity | Trims it |
When max feed is too low#
The app slows the spindle to keep the chip load, rather than taking shallower passes.
Related: Why chip load matters