Depth of cut and step-over in CNC Programming

Introduction

Depth of cut and step-over control how much material a CNC tool removes in one pass. They help make cutting safe and efficient.

When setting up a CNC milling operation to remove material layer by layer.

When adjusting the tool path to avoid overloading the tool or machine.

When planning finishing passes to get a smooth surface.

When optimizing machining time by balancing speed and tool wear.

Syntax

CNC Programming

Depth of cut: The vertical distance the tool cuts into the material per pass.
Step-over: The horizontal distance the tool moves over between passes.

Depth of cut is usually set based on tool size and material hardness.

Step-over is often a percentage of the tool diameter to ensure proper surface finish.

Examples

The tool cuts 2 mm deep each pass and moves 1 mm sideways between passes.

CNC Programming

Depth of cut = 2 mm
Step-over = 1 mm

Using imperial units, the tool cuts half an inch deep and moves a quarter inch sideways.

CNC Programming

Depth of cut = 0.5 inch
Step-over = 0.25 inch

Sample Program

This simple script calculates and shows depth of cut and step-over based on tool diameter.

CNC Programming

TOOL_DIAMETER = 10  # mm
DEPTH_OF_CUT = 2     # mm
STEP_OVER = TOOL_DIAMETER * 0.5  # 50% of tool diameter

print(f"Tool diameter: {TOOL_DIAMETER} mm")
print(f"Depth of cut per pass: {DEPTH_OF_CUT} mm")
print(f"Step-over per pass: {STEP_OVER} mm")

Important Notes

Choosing too deep a cut can break the tool or damage the machine.

Too small a step-over increases machining time but improves surface finish.

Always check manufacturer recommendations for your specific tool and material.

Summary

Depth of cut controls how deep the tool cuts each pass.

Step-over controls how far the tool moves sideways between passes.

Balancing these helps make CNC machining safe and efficient.