What is Step Over in CNC Milling: Definition and Examples

In CNC milling, step over is the sideways distance the cutting tool moves between passes when machining a surface. It controls how much the tool overlaps the previous cut, affecting surface finish and machining time.

How It Works

Imagine painting a wall with a roller. Each time you move the roller sideways, you overlap a bit of the previous paint to avoid gaps. In CNC milling, step over works the same way: it is the horizontal distance the cutting tool moves over before making the next pass.

This distance determines how much the tool's cutting path overlaps the last one. A smaller step over means more overlap, resulting in a smoother surface but longer machining time. A larger step over means less overlap, which speeds up the process but can leave ridges or roughness.

Example

This example shows a simple CNC milling program snippet where the step over is set to 2 mm between passes to machine a flat surface.

gcode

G21 ; Set units to millimeters
G90 ; Absolute positioning
G0 Z5 ; Raise tool to safe height
G0 X0 Y0 ; Move to start position
G1 Z-1 F100 ; Lower tool to cutting depth

; First pass
G1 X50 Y0 F200 ; Cut along X axis

; Step over 2 mm to next pass
G0 Z5 ; Raise tool
G0 Y2 ; Move sideways by 2 mm
G1 Z-1 ; Lower tool
G1 X0 Y2 F200 ; Cut back along X axis

; Step over 2 mm again
G0 Z5
G0 Y4
G1 Z-1
G1 X50 Y4 F200

G0 Z5 ; Raise tool after finishing

Output

The tool moves along the X axis cutting at Y=0, then moves sideways 2 mm to Y=2 and cuts back, then moves another 2 mm to Y=4 and cuts again, creating overlapping passes with 2 mm step over.

When to Use

Use a smaller step over when you need a smooth surface finish, such as in finishing passes on molds or parts that require high precision. This reduces visible tool marks but takes more time.

Use a larger step over for roughing passes where speed is more important than surface quality. This removes more material quickly but leaves a rougher surface for finishing later.

Choosing the right step over balances machining time and surface quality depending on the part's purpose.

Key Points

• Step over is the sideways distance between tool passes in CNC milling.
• Smaller step over means smoother finish but longer machining time.
• Larger step over speeds up rough cuts but leaves rougher surfaces.
• It is important to balance step over for efficiency and quality.

Key Takeaways

Step over controls the sideways distance between cutting passes in CNC milling.

Smaller step over improves surface finish but increases machining time.

Larger step over speeds up roughing but reduces surface quality.

Adjust step over based on the desired balance of speed and finish quality.