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.