Contour milling with line segments in CNC Programming

Introduction

Contour milling with line segments helps cut shapes by moving the tool along straight lines. It is simple and precise for making edges and outlines.

Cutting a rectangular pocket in a metal plate.

Tracing the outline of a part with straight edges.

Removing material along a straight path on a flat surface.

Creating a frame or border with straight sides.

Machining a simple polygon shape with straight edges.

Syntax

CNC Programming

G01 Xx Yy Ff

G01 means move in a straight line at a controlled feed rate.

Xx and Yy specify the end point coordinates of the line segment.

Ff sets the speed of the tool movement.

Examples

Move the tool in a straight line to X=10, Y=0 at feed rate 100.

CNC Programming

G01 X10 Y0 F100

Move diagonally to X=10, Y=10 at feed rate 150.

CNC Programming

G01 X10 Y10 F150

Move straight to X=0, Y=10 using the last feed rate set.

CNC Programming

G01 X0 Y10

Sample Program

This program mills a rectangular contour 50mm wide and 30mm tall by moving the tool along four straight line segments.

CNC Programming

G21 ; Set units to millimeters
G90 ; Use absolute positioning
G00 X0 Y0 ; Move quickly to start point
G01 X50 Y0 F200 ; Cut line to X=50, Y=0
G01 X50 Y30 ; Cut line to X=50, Y=30
G01 X0 Y30 ; Cut line to X=0, Y=30
G01 X0 Y0 ; Cut line back to start
M30 ; End program

Important Notes

Always set the correct units (G20 for inches, G21 for millimeters) before contour milling.

Use absolute positioning (G90) to make coordinates easier to understand.

Feed rate (F) controls how fast the tool moves; too fast can damage the tool or part.

Summary

Contour milling with line segments uses straight moves (G01) to cut shapes.

Coordinates specify where the tool moves next.

Set units and positioning mode before starting the contour.

Practice

1. What does the G01 command do in contour milling with line segments?

easy

A. Sets the tool to a circular interpolation mode

B. Moves the tool in a straight line at a set feed rate

C. Moves the tool rapidly without cutting

D. Stops the machine immediately

Solution

1. Step 1: Understand G-code commands for movement

   The G01 command is used for linear interpolation, meaning the tool moves in a straight line at a controlled feed rate.

2. Step 2: Differentiate from other movement commands

   G00 is rapid move without cutting, G02/G03 are circular moves, and M00 stops the machine.

3. Final Answer:

   Moves the tool in a straight line at a set feed rate -> Option B

4. Quick Check:

   G01 = straight cutting move [OK]

Hint: G01 always means straight cutting move [OK]

Common Mistakes:

• Confusing G01 with rapid move G00
• Thinking G01 is for circular moves
• Assuming G01 stops the machine

2. Which of the following is the correct syntax to move the tool to X=10, Y=20 using linear interpolation in CNC code?

easy

A. G01 X10 Y20

B. G00 X10 Y20

C. G02 X10 Y20

D. G03 X10 Y20

Solution

1. Step 1: Identify the command for linear interpolation

   G01 is used for linear moves with cutting at a set feed rate.

2. Step 2: Check the coordinate format

   Coordinates are given as X10 Y20 to specify the target position.

3. Final Answer:

   G01 X10 Y20 -> Option A

4. Quick Check:

   Linear move syntax = G01 X10 Y20 [OK]

Hint: Use G01 for cutting moves with coordinates [OK]

Common Mistakes:

• Using G00 which is rapid move without cutting
• Using circular move commands G02 or G03 incorrectly
• Omitting the G-code command before coordinates

3. Given the CNC code snippet:

G21
G90
G01 X10 Y0 F100
G01 X10 Y10
G01 X0 Y10
G01 X0 Y0

What shape will the tool cut?

medium

A. A square with 10 units sides

B. A circle with radius 10

C. A diagonal line from (0,0) to (10,10)

D. A triangle with vertices at (0,0), (10,0), (10,10)

Solution

1. Step 1: Analyze the coordinate moves

   The tool moves from (0,0) to (10,0), then to (10,10), then to (0,10), and back to (0,0).

2. Step 2: Visualize the path

   These points form the four corners of a square with sides of length 10 units.

3. Final Answer:

   A square with 10 units sides -> Option A

4. Quick Check:

   Coordinates form square corners [OK]

Hint: Trace points step-by-step to visualize shape [OK]

Common Mistakes:

• Assuming circular shape from linear moves
• Ignoring the return to start point
• Confusing coordinate order

4. Identify the error in this CNC code snippet for contour milling:

G21
G91
G01 X10 Y0 F150
G01 X0 Y10
G01 X-10 Y0
G01 X0 Y-10

medium

A. Feed rate (F150) is missing

B. Coordinates must be absolute with G90, not incremental

C. Using incremental positioning (G91) causes incorrect final position

D. Negative coordinates are not allowed

Solution

1. Step 1: Understand positioning modes

   G91 sets incremental positioning, so each move is relative to the current position.

2. Step 2: Check if moves form a closed contour

   Contour milling typically uses absolute positioning (G90); G91 leads to incorrect final position relative to absolute expectations.

3. Step 3: Identify the error

   Using incremental mode without adjusting coordinates causes unexpected tool path.

4. Final Answer:

   Using incremental positioning (G91) causes incorrect final position -> Option C

5. Quick Check:

   Incremental mode changes move reference [OK]

Hint: Check G90 vs G91 for coordinate reference [OK]

Common Mistakes:

• Confusing incremental and absolute positioning
• Ignoring feed rate presence
• Believing negative coordinates are invalid

5. You want to mill a rectangular contour 50 units wide and 30 units high starting at the origin (0,0). Which CNC code sequence correctly uses line segments (G01) to cut this shape with absolute positioning and feed rate 200?

hard

A. G21\nG90\nG01 X0 Y50 F200\nG01 X30 Y50\nG01 X30 Y0\nG01 X0 Y0

B. G21\nG91\nG01 X50 Y0 F200\nG01 X0 Y30\nG01 X-50 Y0\nG01 X0 Y-30

C. G20\nG90\nG01 X50 Y0 F200\nG01 X50 Y30\nG01 X0 Y30\nG01 X0 Y0

D. G21\nG90\nG01 X50 Y0 F200\nG01 X50 Y30\nG01 X0 Y30\nG01 X0 Y0

Solution

1. Step 1: Confirm units and positioning mode

   G21 sets millimeters, G90 sets absolute positioning as required.

2. Step 2: Check the coordinate moves for rectangle

   Moves go from (0,0) to (50,0), then (50,30), then (0,30), and back to (0,0), forming a 50x30 rectangle.

3. Step 3: Verify feed rate and command correctness

   Feed rate F200 is set on first move, and all moves use G01 for linear cutting.

4. Final Answer:

   G21 G90 G01 X50 Y0 F200 G01 X50 Y30 G01 X0 Y30 G01 X0 Y0 -> Option D

5. Quick Check:

   Absolute moves with G90 and correct coords [OK]

Hint: Use G21 + G90 + G01 with correct coords for rectangle [OK]

Common Mistakes:

• Using incremental mode instead of absolute
• Setting wrong units (G20 instead of G21)
• Incorrect coordinate order or values