G-code program structure in CNC Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this G-code program snippet?

Consider this G-code snippet for a CNC milling machine:

N10 G21
N20 G90
N30 G00 X10 Y10
N40 G01 X20 Y20 F100

What is the position of the tool after line N40 executes?

CNC Programming

N10 G21
N20 G90
N30 G00 X10 Y10
N40 G01 X20 Y20 F100

A The tool is at absolute position X20 Y20

B The tool is at relative position X30 Y30

C The tool is at relative position X20 Y20

D The tool is at absolute position X10 Y10

💡 Hint

G90 sets absolute positioning, G00 and G01 move the tool to specified coordinates.

G90 means absolute positioning, so coordinates are from the origin. Line N40 moves the tool to X20 Y20 at feed rate 100.

🧠 Conceptual

intermediate

Which line defines the program start in a typical G-code file?

In a standard G-code program, which line usually marks the start of the main machining commands?

A The line with M30

B The line with T1

C The line with G28

D The line with G00 or G01 after setup commands

💡 Hint

Look for the first movement command after setup.

G00 (rapid move) or G01 (linear feed move) lines after setup commands start the actual machining.

🔧 Debug

advanced

Identify the error in this G-code snippet

This G-code snippet is intended to move the tool to X50 Y50 and then start cutting:

N10 G90
N20 G01 X50 Y50 F200
N30 G00 X0 Y0
N40 M30

What is the problem with this program?

CNC Programming

N10 G90
N20 G01 X50 Y50 F200
N30 G00 X0 Y0
N40 M30

A The program lacks a spindle start command (M03 or M04)

B The feed rate F200 is missing a unit

C G90 should be after M30

D G00 cannot be used after G01

💡 Hint

Check if the spindle is turned on before cutting moves.

Without spindle start (M03 or M04), the tool won't cut even if it moves at feed rate.

🚀 Application

advanced

How many lines are in this G-code program excluding comments?

Count the number of executable lines in this G-code program (ignore lines starting with ';' which are comments):

; Program start
N5 G21
N10 G90
; Move to start
N15 G00 X0 Y0
N20 G01 X10 Y10 F150
N25 M05
N30 M30

CNC Programming

; Program start
N5 G21
N10 G90
; Move to start
N15 G00 X0 Y0
N20 G01 X10 Y10 F150
N25 M05
N30 M30

A 7

B 6

C 8

D 5

💡 Hint

Count only lines that do not start with ';'.

There are 8 lines total, 2 are comments, so 6 executable lines remain.

🧠 Conceptual

expert

What is the effect of the M30 command in a G-code program?

In a CNC program, what does the M30 command do when executed?

A Starts the coolant flow

B Pauses the program and waits for operator input

C Stops the spindle and ends the program, rewinding to start

D Moves the tool to the home position

💡 Hint

Think about program end and reset commands.

M30 stops the program, stops spindle and coolant, and rewinds program to start for next run.