What each parameter controls
Confusing the two is the source of most parameter problems, because they respond to different symptoms.
| Parameter | Units | Governs | Raise it when |
|---|---|---|---|
| Cutting speed | m/min surface speed | Edge temperature, coating performance, tool wear rate | The material is soft and the tool is not wearing; built-up edge forms |
| Feed per tooth | mm per tooth | Chip thickness, whether the edge cuts or rubs, chip breaking | The edge rubs, work-hardens the material, or the chip is not breaking |
| Depth of cut | mm axial and radial | Load on the tool, number of passes, vibration risk | Fewer passes are needed and the setup is rigid enough |
| Engagement | arc of contact | Heat distribution, vibration, notch wear position | Consistent engagement can be maintained |
Cutting speed follows the material
Cutting speed is chosen from the workpiece material because it sets the temperature at the cutting edge, and the coating's ability to survive that temperature is what limits tool life. As a rough ordering, aluminium runs fastest, then brass and cast iron, then carbon steel, then stainless, then titanium, then nickel alloys, and hardened steel last.
The correct value is a range rather than a number, and the top of the range is where the tool wears fastest while the bottom is where built-up edge and work hardening appear. Starting in the middle and adjusting in the direction the symptom indicates is faster than searching for a published figure.
Feed per tooth decides whether the tool cuts
A cutting edge has a radius. If the chip thickness is smaller than that radius, the edge rubs the material rather than cutting it, which generates heat, work-hardens the surface and destroys the edge quickly.
This is why a feed that is too low is frequently more damaging than one that is too high. The minimum chip thickness is set by the edge radius, so a sharper tool can run a lighter feed, and a worn or blunt tool needs a heavier one to cut at all.
Reading the symptoms
Diagnosis is faster than calculation once the cut is running, because each failure mode points at one parameter.
- Built-up edge or a smeared finish: speed too low, or the edge is too blunt for the feed
- Rapid flank wear with a good finish: speed too high for the coating, or the coating is wrong for the material
- Chipping on entry or exit: feed too high for the edge preparation, or the setup is vibrating
- Chatter with a regular pattern: engagement or speed in resonance with the setup, not a parameter error as such
- Work-hardened surface on stainless: feed too low, so the edge is rubbing rather than cutting
- Chip not breaking: chip breaker wrong for the feed and depth, not the speed
Frequently asked questions
What is the difference between cutting speed and feed rate?
Cutting speed is the surface speed between the tool and the material and it sets the edge temperature, so it is chosen from the workpiece material. Feed rate is how fast the tool advances and it sets the chip thickness, which decides whether the edge cuts cleanly or rubs.
What happens if the feed is too low?
The edge rubs instead of cutting, because the chip thickness falls below the edge radius. That generates heat, work-hardens the surface in stainless and similar materials, and wears the tool faster than a heavier feed would. Too low a feed is frequently more damaging than too high a one.
How do I know whether to change speed or feed?
Read the symptom. Built-up edge or a smeared finish means speed is too low or the edge is too blunt. Rapid uniform wear with a good finish means speed is too high for the coating. Chipping means the feed is too high for the edge preparation or the setup is vibrating.
Why does my chip not break?
The chip breaker is matched to a feed and depth of cut range, and running outside that range will not break the chip regardless of speed. A finishing breaker at a roughing feed, or the reverse, is the usual cause.
Can you give me starting parameters for my material and tool?
Yes. Tell us the workpiece material and its condition, the tool geometry, the machine and the coolant condition, and we will give a starting speed and feed per tooth with the direction to adjust if the result is wrong. Where it matters we can confirm it in a cutting trial.