CNC Cutting Speed: Definition, Key Factors, and Its Impact on Tool Life
What is Cutting Speed?
Cutting speed is one of the most critical parameters in CNC machining. It refers to the relative surface speed between the cutting edge of the tool and the workpiece, usually measured in meters per minute (m/min) or feet per minute (ft/min). For CNC manufacturers, the cutting speed directly affects machining efficiency, surface finish, and tool life. Incorrect cutting speed may result in rough surfaces, excessive tool wear, or even machining failure. Understanding the definition of CNC cutting speed is essential to improve productivity and ensure machining quality.
Basic Formulas: Cutting Speed, Feed Rate, and Depth of Cut
Three fundamental parameters determine machining performance: cutting speed (Vc), feed rate (f), and depth of cut (ap). Their basic formulas are:
Cutting Speed Vc = (π × D × n) ÷ 1000
(D = tool diameter, n = spindle speed in RPM)
Feed Rate f = fz × z × n
(fz = feed per tooth, z = number of teeth)
Depth of Cut ap = thickness of material removed per pass.
Example 1: High-Speed Cutting of Aluminum Alloy
Tool: Ø20 mm carbide end mill, 4 flutes
Spindle Speed (n): 12,000 RPM
Feed per Tooth (fz): 0.05 mm/tooth
Depth of Cut (ap): 2 mm
Calculation:
Cutting Speed Vc = (π × D × n) ÷ 1000
= (3.14 × 20 × 12000) ÷ 1000
= 754 m/min
Feed Rate f = fz × z × n
= 0.05 × 4 × 12000
= 2400 mm/min
Depth of Cut ap = 2 mm
Suitable for high-speed machining of aluminum alloys, ensuring high productivity.
Example 2: Stable Cutting of Stainless Steel
Tool: Ø10 mm carbide end mill, 2 flutes
Spindle Speed (n): 3000 RPM
Spindle Speed (n): 3000 RPM Feed per Tooth (fz): 0.03 mm/tooth
Depth of Cut (ap): 1.5 mm
Calculation:
Cutting Speed Vc = (3.14 × 10 × 3000) ÷ 1000
= 94 m/min
Feed Rate f = 0.03 × 2 × 3000
= 180 mm/min
Depth of Cut ap = 1.5 mm
Suitable for medium-speed cutting of stainless steel, minimizing tool wear.
Example 3: Heavy Cutting of Mold Steel
Tool: Ø50 mm face mill, 6 inserts
Spindle Speed (n): 600 RPM
Feed per Tooth (fz): 0.08 mm/tooth
Depth of Cut (ap): 3 mm
Calculation:
Cutting Speed Vc = (3.14 × 50 × 600) ÷ 1000
= 94 m/min
Feed Rate f = 0.08 × 6 × 600
= 288 mm/min
Depth of Cut ap = 3 mm
Suitable for low-speed, heavy-load cutting of mold steel, balancing stability and tool life.
These formulas are simple, but achieving both efficiency and extended tool life requires careful adjustment according to tool type, workpiece material, and machine stability.
Key Factors Affecting CNC Cutting Speed
Several conditions influence the selection of cutting speed:
Workpiece Material: Aluminum allows high-speed cutting, while stainless steel or hardened steel requires slower cutting speeds.
Tool Type: Carbide tools withstand higher cutting speeds compared to HSS tools.
Cutting Depth and Feed Rate: Larger engagement increases load, requiring reduced speed to protect tool life.
Machine Condition & Tool Holder Stability: Insufficient rigidity may cause vibration, shortening tool life and reducing accuracy.
Therefore, CNC cutting speed should always be optimized according to real machining conditions rather than simply “faster is better.”
Practical Applications of Cutting Speed
For instance, when machining aluminum alloys with a Ø20mm carbide end mill, cutting speeds can exceed 300 m/min to achieve high efficiency. In contrast, stainless steel or tool steel typically requires cutting speeds in the range of 80–150 m/min to minimize tool wear. In cases involving thin-wall parts or long tool overhangs, cutting speeds should be reduced, and a high-rigidity tool holder should be used to suppress vibration and maintain dimensional accuracy.
CNC Cutting Speed and Tool Life
In CNC machining, cutting speed has a significant impact on tool life. Excessive speed causes the cutting edge to wear rapidly due to high-temperature friction, while overly slow speed may lead to chip buildup, work hardening, and reduced efficiency. The optimal CNC cutting speed should strike a balance between efficiency and tool life.
To maintain stability and precision under high-speed machining, we recommend using the PARFAITE HER collet high-rigidity tool holder. With excellent dynamic balance and strong clamping force, PARFAITE tool holders effectively extend tool life, making them particularly suitable for high-speed machining, deep cavity milling, and precision component manufacturing. For CNC manufacturers, selecting the right tool holder along with proper cutting speed is the best solution to improve machining performance and ensure product quality.
