Toolpath simulation and verification in CNC Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of a simple G-code toolpath simulation

What is the final position of the tool after running this G-code snippet in a simulation?

CNC Programming

G00 X0 Y0 Z0
G01 X10 Y10 Z-5 F100
G01 X20 Y5 Z-5
G00 Z10

A X0 Y0 Z0

B X20 Y5 Z-5

C X10 Y10 Z-5

D X20 Y5 Z10

💡 Hint

Remember that G00 is rapid move and G01 is linear feed move. The last command sets Z to 10.

The tool moves rapidly to X0 Y0 Z0, then feeds linearly to X10 Y10 Z-5, then to X20 Y5 Z-5, and finally rapidly moves Z to 10 while keeping X and Y at 20 and 5.

🧠 Conceptual

intermediate

Understanding toolpath verification errors

During toolpath verification, which of the following issues is most likely to cause a collision error in the simulation?

A Toolpath contains only G00 rapid moves

B Tool moves at a feed rate slower than programmed

C Tool moves below the workpiece surface without retracting

D Toolpath uses canned cycles for drilling

💡 Hint

Think about what causes the tool to hit the material unexpectedly.

If the tool moves below the surface without retracting, it can collide with the workpiece causing a collision error in simulation.

🔧 Debug

advanced

Identify the error in this toolpath simulation script

This Python script simulates a toolpath by parsing G-code lines. What error will it raise when run?

CNC Programming

gcode_lines = ['G00 X0 Y0 Z5', 'G01 X10 Y10 Z-1 F100', 'G01 X20 Y5 Z-1']
positions = []
for line in gcode_lines:
    parts = line.split()
    pos = {}
    for p in parts:
        if p.startswith(('X','Y','Z')):
            pos[p[0]] = float(p[1:])
    positions.append(pos)
print(positions[3])

A KeyError: 'Z'

B IndexError: list index out of range

C ValueError: could not convert string to float

D No error, prints last position

💡 Hint

Check the length of the positions list before accessing index 3.

The positions list has only 3 elements (indices 0,1,2). Accessing positions[3] causes IndexError.

🚀 Application

advanced

Calculate total machining time from toolpath feed rates

Given this simplified toolpath with feed moves and distances, what is the total machining time in seconds?

CNC Programming

moves = [
  {'distance': 50, 'feed': 100},
  {'distance': 30, 'feed': 60},
  {'distance': 20, 'feed': 80}
]
# Time = distance / feed rate (feed in mm/min, distance in mm)

A 75 seconds

B 50 seconds

C 55 seconds

D 60 seconds

💡 Hint

Convert feed rate from mm/min to mm/sec before calculating time.

Convert feed rates to mm/sec: 100/60=1.6667, 60/60=1, 80/60=1.3333. Then time = sum(distance/feed_sec) = 50/1.6667 + 30/1 + 20/1.3333 = 30 + 30 + 15 = 75 seconds.

💻 Command Output

expert

Output of a complex toolpath verification script

What is the output of this Python script that verifies if any tool moves exceed a safe Z height?

CNC Programming

toolpath = [
  {'X': 0, 'Y': 0, 'Z': 5},
  {'X': 10, 'Y': 10, 'Z': -2},
  {'X': 20, 'Y': 5, 'Z': 3},
  {'X': 15, 'Y': 15, 'Z': -1}
]
safe_z = 0
violations = [pos for pos in toolpath if pos['Z'] < safe_z]
print(len(violations))

A 2

B 3

C 0

D 1

💡 Hint

Count how many positions have Z less than 0.

Positions with Z < 0 are {'Z': -2} and {'Z': -1}, total 2 violations.

Practice

1. What is the main purpose of toolpath simulation in CNC programming?

easy

A. To clean the CNC machine after use

B. To physically cut the material faster

C. To write the CNC program code automatically

D. To visualize the cutting process before actual machining

Solution

1. Step 1: Understand toolpath simulation

   Toolpath simulation shows a virtual preview of the cutting process on the computer.

2. Step 2: Identify the main benefit

   This helps catch errors and understand the machining steps before actual cutting.

3. Final Answer:

   To visualize the cutting process before actual machining -> Option D

4. Quick Check:

   Simulation = Visual preview [OK]

Hint: Simulation means seeing the cut before it happens [OK]

Common Mistakes:

• Confusing simulation with actual cutting
• Thinking simulation writes code automatically
• Assuming simulation cleans the machine

2. Which of the following is the correct syntax to start a toolpath simulation command in a CNC script?

easy

A. START SIMULATION

B. TOOLPATH_SIM()

C. SIMULATE TOOLPATH START

D. RUN TOOLPATH SIM

Solution

1. Step 1: Identify typical CNC scripting syntax

   Commands often use function-like calls with parentheses in CNC scripting environments.

2. Step 2: Match syntax to options

   Only TOOLPATH_SIM() matches a valid function call style for starting simulation.

3. Final Answer:

   TOOLPATH_SIM() -> Option B

4. Quick Check:

   Function call syntax = TOOLPATH_SIM() [OK]

Hint: Look for function call style with parentheses [OK]

Common Mistakes:

• Choosing commands without parentheses
• Using incomplete or invalid command phrases
• Confusing natural language with code syntax

3. Given this CNC script snippet for toolpath simulation:

TOOLPATH_SIM()
MOVE X10 Y10
CUT Z-5
END_SIM()

What will be the output of the simulation?

medium

A. Syntax error due to missing parameters

B. Simulates moving to X10 Y10 but no cutting

C. Simulates moving to X10 Y10 and cutting 5 units deep

D. Simulates cutting at origin only

Solution

1. Step 1: Analyze the commands inside simulation

   The commands move the tool to X=10, Y=10, then cut down to Z=-5 depth.

2. Step 2: Understand simulation output

   The simulation will show this movement and cutting action as a preview.

3. Final Answer:

   Simulates moving to X10 Y10 and cutting 5 units deep -> Option C

4. Quick Check:

   Move + Cut commands = Simulated cut at X10 Y10 Z-5 [OK]

Hint: Look for MOVE and CUT commands inside simulation [OK]

Common Mistakes:

• Ignoring the CUT command effect
• Assuming syntax error without checking commands
• Thinking simulation cuts at origin only

4. This CNC script for toolpath simulation has an error:

TOOLPATH_SIM()
MOVE X20 Y20
CUT Z-10
END_SIM

What is the error and how to fix it?

medium

A. Missing parentheses in END_SIM; fix to END_SIM()

B. MOVE command missing Z coordinate; add Z0

C. CUT command depth should be positive; change to Z10

D. TOOLPATH_SIM() should be TOOLPATH_SIM_START()

Solution

1. Step 1: Check command syntax

   All commands use parentheses except END_SIM which lacks them.

2. Step 2: Correct the syntax error

   Add parentheses to END_SIM making it END_SIM() to fix the error.

3. Final Answer:

   Missing parentheses in END_SIM; fix to END_SIM() -> Option A

4. Quick Check:

   Function calls need parentheses [OK]

Hint: Check all commands have parentheses if others do [OK]

Common Mistakes:

• Ignoring missing parentheses on END_SIM
• Changing CUT depth sign incorrectly
• Adding unnecessary coordinates to MOVE

5. You want to verify a CNC program that moves the tool in a square path cutting 2mm deep. Which sequence correctly simulates and verifies this toolpath?

hard

A. TOOLPATH_SIM()
MOVE X0 Y0
CUT Z-2
MOVE X10 Y0
MOVE X10 Y10
MOVE X0 Y10
MOVE X0 Y0
END_SIM()
VERIFY_PROGRAM()

B. START_SIM()
CUT Z-2
MOVE X0 Y0
MOVE X10 Y0
MOVE X10 Y10
MOVE X0 Y10
END_SIM()
VERIFY()

C. TOOLPATH_SIM()
MOVE X0 Y0
CUT Z2
MOVE X10 Y0
MOVE X10 Y10
MOVE X0 Y10
MOVE X0 Y0
END_SIM()
VERIFY_PROGRAM()

D. SIMULATE_TOOLPATH()
MOVE X0 Y0
CUT Z-2
MOVE X10 Y0
MOVE X10 Y10
MOVE X0 Y10
MOVE X0 Y0
END_SIM()
VERIFY_PROGRAM()

Solution

1. Step 1: Check simulation command correctness

   TOOLPATH_SIM() MOVE X0 Y0 CUT Z-2 MOVE X10 Y0 MOVE X10 Y10 MOVE X0 Y10 MOVE X0 Y0 END_SIM() VERIFY_PROGRAM() uses TOOLPATH_SIM() and END_SIM() correctly to start and end simulation.

2. Step 2: Verify cutting depth and path

   Cutting depth is negative (-2) which is correct for downward cut; moves form a square path.

3. Step 3: Confirm verification command

   VERIFY_PROGRAM() is the correct command to check the CNC program after simulation.

4. Final Answer:

   The sequence has correct simulation, cutting depth, path, and verification commands -> Option A

5. Quick Check:

   Correct commands + negative cut depth + square path = TOOLPATH_SIM() MOVE X0 Y0 CUT Z-2 MOVE X10 Y0 MOVE X10 Y10 MOVE X0 Y10 MOVE X0 Y0 END_SIM() VERIFY_PROGRAM() [OK]

Hint: Check commands, cut depth sign, and path shape carefully [OK]

Common Mistakes:

• Using positive cut depth instead of negative
• Wrong simulation start/end commands
• Incorrect or missing verification command