Modeling with Radial Symmetry in SketchUp

By Aidan Chopra

In SketchUp, you can model objects that exhibit radial symmetry just as easily as those with bilateral symmetry; you just start slightly differently. The only thing you have to decide before you start is how many wedges — how many identical parts you need to make the whole object.

To model something with radial symmetry, start with one wedge, make it into a component, and then rotate copies around the center. Follow these steps to get the hang of it:

  1. Draw a polygon with as many sides as the number of segments you need for the object you’re modeling.

    Here’s the easiest way to draw a polygon in SketchUp:

    1. Choose Tools→Polygon to select the Polygon tool.

    2. Click once to establish the center (you might want to do this on the axis origin), move your cursor, and then click again to establish the radius.

      Don’t worry about being accurate right now.

    3. Before you do anything else, type the number of sides you want your polygon to have and press Enter.

      image0.jpg

  2. Draw edges from the center of your polygon to two adjacent vertices (endpoints) on the perimeter, creating a wedge.

    To find the center of a polygon (or a circle), hover your cursor over the outline for a couple seconds and move the cursor toward the middle; a center inference point appears.

  3. Erase the rest of your polygon, leaving only the wedge.

    The first three steps in this list are all about making sure that your wedge is the correct angle; if it isn’t, this technique won’t work.

  4. Turn your wedge into a component.

  5. Make copies of your wedge component instance with the Rotate tool.

    image1.jpg

    As with the Move tool, you can use the Rotate tool to make copies. You can even make an array (more than one copy at a time). Here’s how:

    1. Select your wedge’s edges and select the face, too.

    2. Choose Tools→Rotate to select the Rotate tool.

    3. Press the Ctrl key (Option on a Mac) to tell SketchUp you want to make a copy.

      A plus sign (+) appears next to your cursor.

    4. Click the pointy end of your wedge to set your center of rotation.

    5. Click one of the opposite corners of your wedge to set your rotation start point.

    6. Click the other corner to make a rotated copy of your wedge.

    7. Type the number of additional wedges you want, followed by the letter x, and then press Enter.

  6. (Optional) Test your setup.

    Follow the steps to test whether updates to a single component in your new object updates all instances of the component.

Hiding the edges in your component instances makes your finished model look a whole lot better.