Cutting values
What Are Cutting Values?
Cutting Values are parameters used in machining that define how a cutting tool and machine tool operate in relation to the material being machined. These parameters influence chip formation, heat load, mechanical stress on the tool, as well as the achievable surface roughness and dimensional accuracy.
In a machine shop, Cutting Values are not just theoretical values—they form the foundation of the entire production process's efficiency. Correctly chosen values enable controlled cutting, consistent tool loading, and predictable tool life. On the other hand, incorrectly set parameters can lead to vibration, built-up edge, pitting, thermal cracking, or premature edge failure.
Cutting Values are closely related to concepts such as cutting speed, feed per tooth, average chip thickness, and material removal rate. Mastering these is essential for professional CNC machining.
Cutting Values in the Manufacturing Industry
In machine shops, Cutting Values are always set as a whole, taking into account the material being processed, the tool, the machine, and the fixturing solution. Structural steels, stainless steels, aluminum, ductile iron, and superalloys each behave differently during machining, directly affecting cutting speeds and feeds.
The tool material—such as carbide, high-speed steel (HSS, HSCo), CBN, or PCD—determines the allowable temperature and load. Tool coatings, like TiN, TiAlN, TiCN, as well as CVD and PVD coatings, also influence optimal machining parameters.
The rigidity of the machine tool, spindle power, speed range, and tool holder type (SK, BT, HSK, or Capto) set practical limits on achievable values. Additionally, using cutting fluids and high-pressure cooling can enable higher cutting speeds and better heat management.
Key Terms in Machining Parameters
- Spindle speed (n): Spindle speed indicates how many revolutions a rotating tool or workpiece makes per minute. The correct spindle speed depends on the material, tool size, and cutting speed. Excessively high spindle speed can lead to faster tool wear and poor surface finish, while too low a speed can reduce efficiency and cause built-up edge formation.
- Cutting speed (vc): Defines how fast the tool’s cutting edge moves across the surface of the material being machined. The unit for cutting speed is meters per minute (m/min), and it affects the efficiency of the machining process, product quality, and tool life.
- Feed (fn): The distance the tool moves relative to the machine table per revolution. In turning, this value is usually given in millimeters per revolution (mm/r).
- Table feed (vf): The distance the tool moves relative to the machine table per minute. Table feed directly affects machining efficiency and quality. Higher table feed reduces machining time, but excessive feed rate can shorten tool life and deteriorate surface quality.
- Feed per tooth (fz): Very important in milling; it is the distance the tool’s cutting edge moves per revolution per tooth. Optimal feed per tooth depends on the workpiece material, tool type and material, and the width of cut.
- Material removal rate (Q): Indicates how much material is removed from the workpiece within a given time. Higher material removal rate means more efficient stock removal. Optimizing the material removal rate can significantly improve the cost-effectiveness and quality of machining processes.
- Average chip thickness (hm): Used to determine the actual chip thickness, especially in side milling. Optimizing average chip thickness helps achieve efficient and economical machining, improving surface quality and tool life.
Most Commonly Used Quantities in Machining Parameters
- Dc = Cutter diameter, mm
- ap = Depth of cut, mm
- ae = Width of cut (step-over), mm
- vc = Cutting speed, m/min
- n = Spindle speed, 1/min
- zc = Number of teeth, pcs
- fn = Feed, mm/r
- fz = Feed per tooth, mm
- vf = Table feed, mm/min
- Rɛ = Nose radius, mm
- hm = Average chip thickness, mm
- Q = Material removal rate, cm³/min
- Ra = Average surface roughness deviation, µm
Cutting Values and Chip Formation Control
Machining parameters directly affect chip geometry. Too small a feed per tooth can cause plastic deformation of the material without efficient chip breakage, resulting in built-up edge and poor surface finish. Too large a feed increases mechanical loading and the risk of vibration.
In side milling, the importance of average chip thickness is emphasized, as the actual chip thickness depends on the engagement angle and width of cut. In dynamic milling and trochoidal milling, higher cutting speeds are possible when average chip thickness is controlled.
In turning, using a constant cutting speed allows for a consistent cutting velocity as the diameter changes, improving surface finish and predictability of tool wear.
Optimizing Cutting Values in CNC Machining
In modern CNC machining, Cutting Values are often set using CAM software, but final optimization is done in the shop based on hands-on experience. Tool supplier recommendations serve as a starting point, but actual values are fine-tuned according to the machine, fixturing, and part geometry.
Systematic development of machining parameters increases the material removal rate, shortens machining time, and reduces unit costs. At the same time, it ensures tolerance and surface roughness requirements are met.
Summary
Cutting Values are the key values in machining that control cutting speed, feed rate, depth of cut, and material removal efficiency. Choosing the right parameters directly impacts surface finish, tool durability, production speed, and shop cost-effectiveness. Professional machining is based on comprehensive management of Cutting Values, balancing material, tool, machine, and cutting conditions as a cohesive whole.
