The Critical Role of Cutting Speed In CNC Milling

DALIAN, China - Sept. 28, 2025 - PRLog -- What is Cutting Speed? (And Why It's Not RPM)

First, we must correct a common misconception. Cutting Speed is not the same as Spindle Speed (RPM).

Spindle Speed (RPM): Revolutions Per Minute simply measures how fast the machine's spindle is rotating. It is a machine-centric parameter.

Cutting Speed (CS): This is the relative surface speed between the cutting edge of the tool and the workpiece. It is a process-centric parameter, describing the physics of the cut itself. It is measured in Surface Feet per Minute (SFM) in the imperial system or meters per minute (m/min) in metric.

The central importance of cutting speed

Driving Efficiency: Material Removal Rate (MRR)

In a production environment, time is money. Material Removal Rate (MRR)—the volume of material removed per minute—is a key performance indicator. Cutting speed is a direct multiplier in the MRR formula.

MRR (in³/min)=Radial Depth of Cut (in)×Axial Depth of Cut (in)×Feed Rate (in/min)

Since feed rate is derived from cutting speed, a higher cutting speed allows for a higher feed rate, thus increasing MRR. However, this creates the central economic trade-off in machining: Speed vs. Tool Life. Pushing for the absolute maximum MRR will drastically reduce tool life and increase tooling costs. The goal is to find the economic balance point where the time saved in the cut outweighs the cost of more frequent tool changes.

Eg: When machining 6061-T6 aluminum alloy, increasing the cutting speed from 600 m/min to 1200 m/min can theoretically cut machining time in half, significantly increasing productivity.

The Decisive Impact on Tool Life

Cutting speed is arguably the single most significant factor affecting how long a tool lasts. The underlying principle is heat generation and management. The energy used to shear a chip is primarily converted into heat at the cutting zone.

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