Finishing strategies (contour, scallop) in CNC Programming

Introduction

Finishing strategies help make the final surface smooth and accurate after rough cutting. They remove small amounts of material to get the perfect shape.

After rough cutting a part to clean up the edges and surfaces.

When you need a smooth finish on curved or complex shapes.

To improve the surface quality before painting or coating.

When tight tolerances are required on the final part.

To remove tool marks left by previous machining steps.

Syntax

CNC Programming

FINISHING_STRATEGY(strategy_type, parameters)

# strategy_type: 'contour' or 'scallop'
# parameters: dictionary with keys like 'stepover', 'feedrate', 'depth_of_cut'

Contour follows the outline of the part to clean edges.

Scallop moves in a pattern to smooth curved surfaces.

Examples

This sets a contour finishing pass with a small stepover and shallow cut for smooth edges.

CNC Programming

FINISHING_STRATEGY('contour', {'stepover': 0.1, 'feedrate': 100, 'depth_of_cut': 0.05})

This uses a scallop finishing pass to smooth curved surfaces with fine detail.

CNC Programming

FINISHING_STRATEGY('scallop', {'stepover': 0.05, 'feedrate': 80, 'depth_of_cut': 0.02})

Sample Program

This script simulates running two finishing strategies: contour and scallop. It prints the parameters used and confirms completion.

CNC Programming

# Simple CNC finishing strategy example

def FINISHING_STRATEGY(strategy_type, parameters):
    print(f"Starting {strategy_type} finishing with parameters:")
    for key, value in parameters.items():
        print(f"  {key}: {value}")
    print(f"{strategy_type.capitalize()} finishing completed.\n")

# Run contour finishing
FINISHING_STRATEGY('contour', {'stepover': 0.1, 'feedrate': 100, 'depth_of_cut': 0.05})

# Run scallop finishing
FINISHING_STRATEGY('scallop', {'stepover': 0.05, 'feedrate': 80, 'depth_of_cut': 0.02})

Important Notes

Always choose smaller stepover values for smoother finishes but expect longer machining time.

Feedrate should be adjusted based on material and tool to avoid damage.

Depth of cut in finishing is usually very shallow to avoid removing too much material.

Summary

Finishing strategies improve surface quality after rough machining.

Contour finishing cleans edges by following the part outline.

Scallop finishing smooths curved surfaces with a special tool path.