3dSynth

Tutorials / Custom G-code

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---
title: Tutorial 32 Non-planar Toolpaths
description: Printing on curved surfaces.
---

Tutorial 32 Non-planar Toolpaths

1. Lesson Header

2. Concept Introduction

The Z-Clearance Problem.
In Lesson 22, we made a simple wave.
Now we want to print on top of a complex object (e.g., a dome or a shoe sole).
The challenge: Collision.
The nozzle is a cone. The heater block is a rectangle.
If the surface slope > Nozzle Angle (usually ~45-60 degrees), the shoulder of the nozzle hits the print.

3. Machine State Explanation

Tool Geometry.
We need to model our tool.
- Nozzle Tip: Point (0,0,0).
- Nozzle Shoulder: Circle at Z=1mm, Radius=1mm (Example).
- Heater Block: Rectangle at Z=3mm, Width=20mm.

Algorithm:
For every point (x,y,z) on our target surface:
Check if (x,y,z) + Tool_Shape intersects with Existing_Print.

4. Command Breakdown

5. Minimal Working Example

The Dome Finish.
1. Print a standard stepped dome (Layer height 0.2mm).
2. Switch to Non-planar Mode.
3. Run the nozzle over the steps in a spiral to smooth them out ("Ironing").

6. Visual Representation

Interactive preview is available in the interactive reader.

7. Build Exercise

Task: Write a Python script to generate a Non-planar Ironing path for a Sphere (R=20mm).
Path: A spiral starting at Z=20 (Top) and winding down to Z=10.
Constraint: The nozzle angle is 45 degrees.
So we can only iron down to where the surface tangent is 45 degrees.
Slope = dz/dr = -r/sqrt(R^2 - r^2).
Find r where slope = 1.

8. Deep Insight Section

Slicing Software.
Standard slicers (Cura, PrusaSlicer) are starting to support "Non-planar Layers" (experimental).
But doing it manually teaches you the limits.
The "Fan" Trick:
You can print steeper angles if you have a pointy nozzle (Airbrush nozzle adapter).

9. Common Failure Modes

  1. Gouging: If your Z calculation is slightly too low, the nozzle digs into the plastic.
  2. Air Printing: If Z is too high, you are just extruding spaghetti in the air above the surface.

10. Real-World Application

Shoe Soles.
Printing tread patterns onto a curved shoe sole.
The sole is molded (or printed flat then bent), and the printer adds texture after.
This requires a 5-axis machine or very careful 3-axis non-planar paths.

11. Final Clean Version

The Ironing Script:

import math

filename = "dome_iron.gcode"
R = 20
start_angle = 0 # Top (0 degrees from vertical? No, let's say 0 is pole)
end_angle = 45 # Stop at 45 degrees
steps = 1000

with open(filename, "w") as f:
    f.write("G21\nG90\nG28\n")
    # Assume dome is already printed and centered at 100,100
    cx, cy = 100, 100
    
    # Lift Z to safe height
    f.write(f"G0 Z{R+5}\n")
    f.write(f"G0 X{cx} Y{cy}\n") # Go to center
    
    # Spiral Out
    for i in range(steps):
        # Current angle from pole (0 to 45 degrees)
        phi = (i / steps) * math.radians(end_angle)
        
        # Spiral angle (theta)
        theta = i * 0.5 # Winding speed
        
        # Spherical coordinates
        r = R * math.sin(phi)
        z = R * math.cos(phi)
        
        x = cx + r * math.cos(theta)
        y = cy + r * math.sin(theta)
        
        # Move
        # Note: We extrude very little, just to smooth/iron
        f.write(f"G1 X{x:.3f} Y{y:.3f} Z{z:.3f} E... F1000\n")

    f.write("G28 X0 Y0\n")

12. Stretch Challenge

Challenge: Write a script that detects collision.
Given a surface function Z(x,y), determine the maximum steepness your specific nozzle can handle.
Print a "Test Slope" object that increases angle until the nozzle hits.
Measure the angle where the finish gets ruined.