Manual G-code modifications in 3D Printing - Mini Project: Build & Apply

Manual G-code Modifications for 3D Printing

📖 Scenario: You have a 3D printer and a G-code file that controls how your printer makes a small object. Sometimes, you need to change the G-code manually to fix small issues or customize the print.For example, you want to change the print speed or add a pause at a certain layer.

🎯 Goal: You will learn how to open a G-code file, find specific commands, and manually edit them to change print speed and add a pause command.

📋 What You'll Learn

Open a G-code file as plain text

Identify lines that control print speed

Modify the speed value in those lines

Add a pause command at a specific layer

💡 Why This Matters

🌍 Real World

3D printing often requires tweaking G-code manually to fix print issues or customize behavior without re-slicing the model.

💼 Career

Understanding manual G-code editing helps technicians and makers troubleshoot prints and optimize printer performance.

1

Load the G-code file content

Create a variable called gcode_lines that contains the following lines exactly as a list of strings:
";Start G-code",
"G1 F1500",
"G1 X50 Y25.3 E22.4",
";Layer 1",
"G1 F1200",
"G1 X60 Y30 E25"

3D Printing

# Create the variable gcode_lines with the exact lines given
# Your code here

Hint

Use a list of strings with the exact lines given, including the semicolons and spaces.

2

Set the new print speed

Create a variable called new_speed and set it to the integer 1800 to represent the new print speed in mm/min.

3D Printing

gcode_lines = [
    ";Start G-code",
    "G1 F1500",
    "G1 X50 Y25.3 E22.4",
    ";Layer 1",
    "G1 F1200",
    "G1 X60 Y30 E25"
]
# Set the new_speed variable to 1800
# Your code here

Hint

Just assign the number 1800 to the variable new_speed.

3

Modify print speed commands in G-code

Use a for loop with the variable index to go through gcode_lines. If a line starts with "G1 F", replace that line with "G1 F" followed by the value of new_speed as a string.

3D Printing

gcode_lines = [
    ";Start G-code",
    "G1 F1500",
    "G1 X50 Y25.3 E22.4",
    ";Layer 1",
    "G1 F1200",
    "G1 X60 Y30 E25"
]
new_speed = 1800
# Loop through gcode_lines by index and replace lines starting with 'G1 F' with 'G1 F' + new_speed
# Your code here

Hint

Use range(len(gcode_lines)) to get indexes and startswith("G1 F") to check lines.

4

Add a pause command after layer 1 comment

Find the index of the line ";Layer 1" in gcode_lines. Insert a new line "M0 ; Pause for user" immediately after it.

3D Printing

gcode_lines = [
    ";Start G-code",
    "G1 F1500",
    "G1 X50 Y25.3 E22.4",
    ";Layer 1",
    "G1 F1200",
    "G1 X60 Y30 E25"
]
new_speed = 1800
for index in range(len(gcode_lines)):
    if gcode_lines[index].startswith("G1 F"):
        gcode_lines[index] = f"G1 F{new_speed}"
# Insert 'M0 ; Pause for user' after the line ';Layer 1'
# Your code here

Hint

Use the index() method to find the line and insert() to add the pause command.

Practice

1. What is the main purpose of manually editing G-code in 3D printing?

easy

A. To increase the printer's physical size

B. To change the filament color automatically

C. To customize printer actions beyond slicer settings

D. To update the printer's firmware

Solution

1. Step 1: Understand what G-code controls

   G-code commands tell the printer how to move, heat, and print.

2. Step 2: Identify the effect of manual edits

   Editing G-code manually lets you change these commands beyond what slicer software sets.

3. Final Answer:

   To customize printer actions beyond slicer settings -> Option C

4. Quick Check:

   Manual G-code editing = Customizing printer actions [OK]

Hint: Manual edits change printer commands directly [OK]

Common Mistakes:

• Thinking it changes physical printer parts
• Confusing G-code editing with firmware updates
• Assuming it changes filament color automatically

2. Which of the following is a correct G-code command to pause a print?

easy

A. M104 S0

B. G28

C. G1 X10 Y10

D. M25

Solution

1. Step 1: Identify pause commands in G-code

   M25 is commonly used to pause SD card printing.

2. Step 2: Check other commands

   M104 S0 sets temperature to 0, G28 homes axes, G1 moves the nozzle.

3. Final Answer:

   M25 -> Option D

4. Quick Check:

   Pause command = M25 [OK]

Hint: Pause print with M25 command [OK]

Common Mistakes:

• Confusing M104 (temperature) with pause
• Thinking G28 (home) pauses print
• Using movement commands to pause

3. Given this G-code snippet:

G1 X50 Y50 F1500
M104 S210
G4 P2000

What does the command G4 P2000 do?

medium

A. Moves the nozzle to X=2000

B. Pauses the print for 2 seconds

C. Sets the temperature to 2000°C

D. Homes all axes

Solution

1. Step 1: Understand G4 command

   G4 is a dwell command that pauses the printer for a set time.

2. Step 2: Interpret parameter P2000

   P2000 means pause for 2000 milliseconds, which equals 2 seconds.

3. Final Answer:

   Pauses the print for 2 seconds -> Option B

4. Quick Check:

   G4 P2000 = 2-second pause [OK]

Hint: G4 with P value pauses in milliseconds [OK]

Common Mistakes:

• Thinking G4 moves the nozzle
• Confusing temperature commands with G4
• Assuming G4 homes axes

4. You want to slow down the print speed by editing the G-code. Which line correctly changes the feedrate to 1200 mm/min?

medium

A. G1 F1200

B. M220 S1200

C. G28 F1200

D. M104 F1200

Solution

1. Step 1: Identify feedrate command

   G1 with F sets the feedrate (speed) for moves.

2. Step 2: Check other commands

   M220 changes speed multiplier, G28 homes axes (no feedrate), M104 sets temperature.

3. Final Answer:

   G1 F1200 -> Option A

4. Quick Check:

   Feedrate set by G1 F value [OK]

Hint: Use G1 F to set move speed directly [OK]

Common Mistakes:

• Using M220 which is a speed multiplier, not direct feedrate
• Trying to set feedrate with G28 or M104
• Confusing feedrate with temperature commands

5. You want to add a pause at layer 5 in your print by inserting a manual G-code command. Which approach is best?

hard

A. Insert M25 after the layer 5 start comment in the G-code file

B. Replace all G1 commands with M25 in layer 5

C. Add M104 S0 at the start of layer 5

D. Delete the commands for layer 5 to pause printing

Solution

1. Step 1: Identify how to pause at a specific layer

   Layer changes are usually marked by comments; inserting M25 pauses the print.

2. Step 2: Evaluate other options

   Replacing all G1 commands breaks movement, M104 S0 turns off temperature, deleting commands stops printing.

3. Final Answer:

   Insert M25 after the layer 5 start comment in the G-code file -> Option A

4. Quick Check:

   Pause at layer = Insert M25 at layer start [OK]

Hint: Insert M25 at layer start comment to pause [OK]

Common Mistakes:

• Replacing movement commands with pause command
• Turning off temperature instead of pausing
• Deleting commands which stops print instead of pausing