Contour milling with line segments in CNC Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of a simple contour milling G-code segment

What is the final position of the tool after executing this G-code snippet for contour milling a rectangle?

CNC Programming

G00 X0 Y0
G01 X50 Y0 F100
G01 X50 Y30
G01 X0 Y30
G01 X0 Y0

A X50 Y30

B X0 Y0

C X50 Y0

D X0 Y30

💡 Hint

Trace the tool path step by step, noting the last move command.

The tool starts at (0,0), moves along the rectangle edges, and ends back at the start point (0,0).

🧠 Conceptual

intermediate

Understanding line segment direction in contour milling

In contour milling with line segments, why is the direction of the toolpath important?

A It controls the machine power supply

B It changes the spindle speed automatically

C It determines the coolant flow rate

D It affects the surface finish and tool wear

💡 Hint

Think about how tool movement affects cutting quality.

The direction influences chip removal, surface finish, and tool wear by controlling cutting forces.

📝 Syntax

advanced

Identify the correct G-code for a line segment in contour milling

Which G-code line correctly moves the tool in a straight line to X=100, Y=50 at feed rate 200?

A G01 X100 Y50 F200

B G00 X100 Y50 F200

C G03 X100 Y50 F200

D G02 X100 Y50 F200

💡 Hint

G01 is linear interpolation with feed rate; G00 is rapid move without feed rate.

G01 moves linearly at the specified feed rate; G00 is rapid positioning without feed rate; G02 and G03 are arcs.

🔧 Debug

advanced

Find the error in this contour milling G-code snippet

What error will occur when running this G-code? G01 X20 Y10 F150 G01 X40 Y10 G01 X40 Y20 G01 X20 Y20 G01 X20 Y10 F-100

A Syntax error due to negative feed rate

B Tool will move too fast causing damage

C No error, code runs fine

D Machine will ignore last command

💡 Hint

Feed rate must be positive in G-code.

Negative feed rates are invalid and cause syntax or runtime errors in CNC controllers.

🚀 Application

expert

Calculate total distance moved in contour milling path

Given this contour milling path with line segments: Start at (0,0) Move to (30,0) Move to (30,40) Move to (0,40) Move to (0,0) What is the total distance the tool travels?

A 120 units

B 100 units

C 140 units

D 80 units

💡 Hint

Add lengths of all four line segments.

Each horizontal segment is 30 units, vertical segments are 40 units. Total = 30+40+30+40 = 140.

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