What is depth of cut?

Short Answer:

Depth of cut is the thickness of the material layer removed by a cutting tool in one pass during a machining operation. It is the perpendicular distance between the machined surface and the surface of the workpiece before machining. Depth of cut is usually expressed in millimeters (mm).

It plays an important role in determining the rate of material removal, tool life, and surface finish. If the depth of cut is too high, it may cause excessive tool wear and power consumption, while too small a depth of cut can reduce productivity and increase machining time.

Detailed Explanation :

Depth of Cut

Depth of cut is a key parameter in machining processes such as turning, milling, drilling, and shaping. It determines how deep the cutting tool penetrates into the material during each pass. In other words, it is the distance between the uncut surface of the workpiece and the final machined surface, measured perpendicular to the surface being cut.

The depth of cut directly affects the volume of material removed, the power required for machining, and the quality of the surface produced. It must be carefully selected according to the machine capacity, tool material, and workpiece hardness to achieve efficient machining and desired accuracy.

Measurement of Depth of Cut

The depth of cut is denoted by the symbol “t” and is measured in millimeters (mm). In a turning operation, it can be calculated using the formula:

Where,

  • t = Depth of cut (mm)
  • D₁ = Diameter of workpiece before machining (mm)
  • D₂ = Diameter of workpiece after machining (mm)

This formula shows that the depth of cut is half the difference between the original and the final diameters of the workpiece. In milling or shaping, it represents the vertical distance between the top of the uncut layer and the machined surface.

Importance of Depth of Cut

  1. Material Removal Rate (MRR): The depth of cut is a major factor determining the rate at which material is removed from the workpiece. Increasing the depth of cut increases MRR and reduces machining time.
  2. Tool Life: Greater depth of cut increases cutting forces and temperature, leading to faster tool wear. Therefore, an optimum depth of cut ensures longer tool life.
  3. Surface Finish: Shallow depths of cut produce smoother surfaces, while deep cuts may cause roughness and vibration.
  4. Power Requirement: As depth of cut increases, the power required for machining also increases because more material is being removed at once.
  5. Dimensional Accuracy: Proper selection of depth of cut helps in maintaining the desired dimensions of the machined component.

Factors Affecting Depth of Cut

  1. Material of Workpiece: Hard materials require smaller depths of cut to prevent tool damage. Softer materials can allow deeper cuts.
  2. Cutting Tool Material: Tools made from high-speed steel (HSS) or carbide can handle greater depths of cut compared to carbon steel tools.
  3. Type of Operation: In roughing operations, a larger depth of cut is used to remove more material quickly. In finishing operations, smaller depths of cut are used to achieve better surface finish and accuracy.
  4. Machine Power and Rigidity: The capacity and stiffness of the machine limit how much depth of cut can be applied without causing vibration or chatter.
  5. Cutting Speed and Feed Rate: These parameters are interrelated with the depth of cut. Increasing all three simultaneously can cause excessive tool wear and poor quality.

Effects of Improper Depth of Cut

  • Too High Depth of Cut:
    • Causes high cutting forces and tool breakage.
    • Produces rough surface and vibration.
    • Increases heat generation and power consumption.
  • Too Low Depth of Cut:
    • Reduces material removal rate and productivity.
    • May lead to rubbing instead of cutting.
    • Wastes time and increases machining cost.

Selection of Depth of Cut

Choosing the right depth of cut depends on the machining stage and work requirements:

  • Rough Cutting: A large depth of cut (2 mm to 6 mm) is used to remove more material quickly.
  • Finishing Cutting: A smaller depth of cut (0.1 mm to 0.5 mm) is used to improve accuracy and surface finish.

Manufacturers usually provide recommended depth of cut values for different materials and tool types. These are based on experimental data and machine capabilities.

Role in Metal Cutting Operations

Depth of cut works together with cutting speed and feed rate to determine the overall machining performance. These three parameters are interdependent and must be optimized for efficient cutting. Increasing depth of cut increases material removal rate, but it should not exceed the machine or tool’s limit. Balancing these parameters helps to achieve maximum productivity and tool efficiency.

Example:

If a cylindrical steel rod has an initial diameter of 50 mm and is turned down to 48 mm in one pass, then:

Hence, the depth of cut is 1 mm. This value indicates how deep the tool has penetrated the surface during machining.

Conclusion:

Depth of cut is the thickness of the material removed by a cutting tool in one pass during machining. It plays a vital role in determining tool life, surface quality, and material removal rate. Selecting an appropriate depth of cut is important for balancing productivity and tool wear. Using the correct value according to the material, tool, and machine condition ensures efficient, economical, and precise machining operations.