Reading G-code for troubleshooting in 3D Printing - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is G-code in 3D printing?

G-code is a set of instructions that tells a 3D printer how to move, where to move, and what actions to perform during printing.

intermediate

What does the command G1 X50 Y25.3 E22.4 mean?

It tells the printer to move the print head to position X=50, Y=25.3 while extruding 22.4 units of filament.

beginner

Why is reading G-code important for troubleshooting?

Reading G-code helps identify where the printer might be making mistakes, such as wrong movements, missing extrusion, or incorrect temperatures.

intermediate

What does the command M104 S200 do?

It sets the extruder temperature to 200°C without waiting for it to reach that temperature before continuing.

intermediate

How can you spot a problem with filament extrusion by reading G-code?

Look for E values in movement commands. If E values don’t increase when the print head moves, filament may not be extruding.

What does the G-code command G28 usually do?

A Home all axes

B Set extruder temperature

C Pause the print

D Move to X=0 Y=0

G28 tells the printer to move all axes to their home positions, usually the origin point.

If the printer is not extruding filament but moving correctly, which G-code part should you check?

A X and Y coordinates

B M104 temperature settings

C E values in movement commands

D G28 homing commands

The E values control filament extrusion. If they don’t increase, no filament is pushed out.

What does M140 S60 command do in G-code?

A Set extruder temperature to 60°C

B Set bed temperature to 60°C

C Move print head to Y=60

D Pause the print for 60 seconds

M140 sets the heated bed temperature, here to 60°C.

Which G-code command waits for the extruder to reach the target temperature before continuing?

A M109

B M104

C G1

D M140

M109 sets extruder temperature and waits until it is reached before moving on.

If you see G1 X100 Y100 E0 repeatedly without increasing E, what might be wrong?

A The printer is paused

B The print head is not moving

C The bed temperature is too low

D The filament is not extruding

Since E is not increasing, filament is not being pushed out during moves.

Explain how reading G-code can help you find why a 3D print is failing.

Think about what each part of the G-code controls in the printer.

Describe what the E value in a G1 command represents and why it matters.

Focus on the role of extrusion in printing.

Practice

1. What does the G-code command G1 X50 Y25 instruct the 3D printer to do?

easy

A. Move the print head to coordinates X=50 and Y=25

B. Set the temperature to 50°C and 25°C

C. Start the print job from layer 50 to 25

D. Pause the printer for 50 seconds and then 25 seconds

Solution

1. Step 1: Understand the G1 command

   The G1 command is used to move the print head to a specific position.

2. Step 2: Interpret the coordinates

   X50 and Y25 mean move the print head to X=50 units and Y=25 units on the print bed.

3. Final Answer:

   Move the print head to coordinates X=50 and Y=25 -> Option A

4. Quick Check:

   G1 moves print head = Move to X=50 Y=25 [OK]

Hint: G1 moves print head to given coordinates [OK]

Common Mistakes:

• Confusing G1 with temperature commands
• Thinking G1 pauses the printer
• Assuming G1 controls print speed only

2. Which of the following is the correct syntax to set the extruder temperature to 210°C in G-code?

easy

A. G1 T210

B. G28 S210

C. M104 S210

D. M109 X210

Solution

1. Step 1: Identify the temperature command

   M104 is the G-code command used to set the extruder temperature without waiting.

2. Step 2: Check the syntax

   S210 means set temperature to 210°C. So, M104 S210 sets extruder temperature to 210°C.

3. Final Answer:

   M104 S210 -> Option C

4. Quick Check:

   M104 sets temp with S value = M104 S210 [OK]

Hint: M104 sets extruder temp; S is temperature value [OK]

Common Mistakes:

• Using G28 which is for homing axes
• Confusing M109 which waits for temp
• Using wrong letter like X or T for temperature

3. Given this G-code snippet:

G28
M104 S200
G1 X100 Y100 E10 F1500
M109 S200

What does the command G1 X100 Y100 E10 F1500 do?

medium

A. Homes all axes and waits for temperature 200°C

B. Moves the print head to X=100, Y=100 while extruding 10 units of filament at speed 1500

C. Sets the extruder temperature to 100°C and moves at speed 1500

D. Pauses the print for 10 seconds at position X=100, Y=100

Solution

1. Step 1: Understand the G1 command with parameters

   G1 moves the print head. X100 Y100 sets position. E10 means extrude 10 units of filament. F1500 sets movement speed.

2. Step 2: Combine all parts

   The command moves the head to X=100, Y=100 while pushing 10 units of filament out at speed 1500 mm/min.

3. Final Answer:

   Moves the print head to X=100, Y=100 while extruding 10 units of filament at speed 1500 -> Option B

4. Quick Check:

   G1 with X,Y,E,F moves and extrudes at speed [OK]

Hint: G1 with E extrudes filament while moving [OK]

Common Mistakes:

• Thinking E means temperature
• Confusing F as filament amount
• Assuming G1 only moves without extruding

4. You see this G-code line causing a print error:
M104 S-10
What is the problem and how to fix it?

medium

A. Temperature cannot be negative; change S-10 to a positive value like S210

B. M104 cannot be used for temperature; replace with G1 command

C. The command is missing a wait; add M109 before M104

D. S-10 means wait 10 seconds; replace with S10 to fix

Solution

1. Step 1: Identify invalid temperature value

   Temperature values must be positive. S-10 is invalid because temperature cannot be negative.

2. Step 2: Correct the temperature value

   Change S-10 to a valid positive temperature like S210 to fix the error.

3. Final Answer:

   Temperature cannot be negative; change S-10 to a positive value like S210 -> Option A

4. Quick Check:

   Temperature must be positive = fix S-10 to S210 [OK]

Hint: Temperature values must be positive numbers [OK]

Common Mistakes:

• Thinking negative temperature means wait time
• Confusing M104 with movement commands
• Adding wrong commands instead of fixing value

5. You want to troubleshoot a print where the filament is not extruding properly. Which G-code command should you check first to verify the extrusion amount?

hard

A. M109 commands waiting for temperature

B. M104 commands setting temperature

C. G28 commands for homing axes

D. G1 commands with the E parameter

Solution

1. Step 1: Identify extrusion control in G-code

   The E parameter in G1 commands controls how much filament is pushed out (extruded).

2. Step 2: Focus on G1 commands with E values

   Checking these commands helps verify if the printer is instructed to extrude filament properly.

3. Final Answer:

   G1 commands with the E parameter -> Option D

4. Quick Check:

   Extrusion controlled by G1 E values = check G1 E commands [OK]

Hint: Extrusion amount is set by E in G1 commands [OK]

Common Mistakes:

• Checking temperature commands instead of extrusion
• Confusing homing commands with extrusion
• Assuming M109 controls extrusion amount