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layout: post title: “OpenSCAD Lesson: Rotate Extrude Function” date: 2023-05-05 last_modified_at: categories: [OpenSCAD] tags: [Coding, 3D modeling, Rotate Extrude] —

Learning Objectives

By the end of this lesson, students should be able to:

  1. Understand the concept of rotational extrusion in OpenSCAD.
  2. Know how to use the rotate_extrude function and its parameters.
  3. Understand how transformations can affect the extrusion process.
  4. Create simple 3D shapes using rotational extrusion.



Understanding Rotational Extrusion in OpenSCAD

Rotational extrusion is a key concept in 3D modeling that allows you to create symmetrical solids by spinning a 2D shape around the Z-axis. Think of a potter’s wheel; the clay object being shaped on the wheel is the 2D shape you’re feeding into the rotate_extrude function. Here, OpenSCAD acts as your virtual potter’s wheel, rotating your shape about the Z-axis to create a 3D solid.

It’s important to note that rotate_extrude works on the projection of the 2D polygon onto the XY plane, and any transformations applied to the 2D polygon before extrusion can change the final 3D object.




How to Use rotate_extrude Function

The rotate_extrude function spins a 2D shape around the Z-axis to form a solid. Here’s a basic example of its usage:

rotate_extrude(convexity = 10)
translate([2, 0, 0])
circle(r = 1);

In this example, a circle of radius 1 is translated 2 units along the X-axis and then extruded rotationally to form a torus.

This function also accepts several parameters:

  • angle (default is 360): Specifies the number of degrees to sweep, starting at the positive X-axis.
  • convexity (default is 2): Helps with rendering non-trivial 2D shapes.
  • $fa, $fs, and $fn: Control the minimum angle, minimum circumferential length, and fixed number of fragments in 360 degrees, respectively.




Improving Mesh Quality

We can improve the quality of our 3D shapes by increasing the number of fragments that make up the 2D shape and the extrusion.

rotate_extrude(convexity = 10, $fn = 100)
translate([2, 0, 0])
circle(r = 1, $fn = 100);

However, keep in mind that increasing these values can also increase render times.


Review

In this lesson, you learned:

  • The concept of rotational extrusion in OpenSCAD and how it’s like a potter’s wheel.
  • How to use the rotate_extrude function to create 3D objects from 2D shapes.
  • How transformations can affect the projection of the 2D shape and the final 3D object.
  • How to control the quality of the 3D shape by adjusting fragment values.


Resources