Finishing strategies (contour, scallop) in CNC Programming - Mini Project: Build & Apply

Finishing Strategies: Contour and Scallop CNC Paths

📖 Scenario: You work in a small CNC workshop. Your job is to create toolpaths that finish parts smoothly. Two common finishing strategies are contour and scallop. Contour follows the edge of the part exactly. Scallop removes small leftover material in a wavy pattern.Understanding these helps you make parts look nice and fit well.

🎯 Goal: Build a simple CNC program script that defines a part shape, sets finishing parameters, generates contour and scallop toolpaths, and outputs the final G-code commands.

📋 What You'll Learn

Create a dictionary called part_shape with exact points defining a square: (0,0), (0,10), (10,10), (10,0)

Create a variable called finishing_params as a dictionary with keys 'stepover' set to 1.0 and 'tool_diameter' set to 2.0

Write a function called generate_contour_path that takes part_shape and returns a list of G-code strings following the contour

Write a function called generate_scallop_path that takes part_shape and finishing_params and returns a list of G-code strings for scallop finishing

Print the combined G-code commands from both finishing strategies

💡 Why This Matters

🌍 Real World

CNC machinists use finishing strategies like contour and scallop to produce smooth, precise parts. Automating G-code generation saves time and reduces errors.

💼 Career

Understanding and scripting finishing toolpaths is essential for CNC programmers and manufacturing engineers to optimize machining quality and efficiency.

1

Define the part shape points

Create a dictionary called part_shape with these exact points as keys and values: 1: (0, 0), 2: (0, 10), 3: (10, 10), 4: (10, 0)

CNC Programming

# Create the part_shape dictionary with points 1 to 4
# Your code here

Need a hint?

Use a dictionary with keys 1 to 4 and tuple values for coordinates.

2

Set finishing parameters

Create a dictionary called finishing_params with keys 'stepover' set to 1.0 and 'tool_diameter' set to 2.0

CNC Programming

part_shape = {1: (0, 0), 2: (0, 10), 3: (10, 10), 4: (10, 0)}
# Create finishing_params dictionary
# Your code here

Need a hint?

Use a dictionary with the exact keys and values.

3

Write functions to generate finishing paths

Write two functions: generate_contour_path(part_shape) that returns a list of G-code strings moving along the points in order, and generate_scallop_path(part_shape, finishing_params) that returns a list of G-code strings simulating scallop passes inside the shape using the stepover parameter

CNC Programming

part_shape = {1: (0, 0), 2: (0, 10), 3: (10, 10), 4: (10, 0)}
finishing_params = {'stepover': 1.0, 'tool_diameter': 2.0}

# Define generate_contour_path function
# Define generate_scallop_path function
# Your code here

Need a hint?

Use loops to create G-code lines moving along points and scallop passes.

4

Print the combined finishing G-code

Call generate_contour_path(part_shape) and generate_scallop_path(part_shape, finishing_params), combine their results into one list called final_gcode, then print each line in final_gcode

CNC Programming

Need a hint?

Print each G-code line from the combined list.