Work Smarter by Building Half a Bilaterally Symmetrical Model

By Aidan Chopra

Bilaterally symmetrical forms are everywhere. Most animals you can name, the majority of the furniture in your house, and your personal helicopter — they can all be modeled by building half, creating a component, and flipping over a copy.

Follow these steps to get the general idea of how to build a bilaterally symmetrical model in SketchUp:

  1. Make a simple box.

    You can do this however you want, but the easiest way is to draw a rectangle and push/pull it into 3D.

  2. Draw a diagonal edge on the corner of your box.

    The point of this step is to mark one side of your box so that when you flip it over, you don’t get confused about which side is which.

  3. Turn your box into a component.

  4. Make a copy of your new component instance.

    1. Choose the Move tool and then press the Ctrl key (Option on a Mac) to toggle from Move to Copy mode.

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

    2. Click your component instance, move your copy beside the original, and click again to drop it.

      Make sure that you move in either the red or the green direction; it makes things easier in the next step.

  5. Flip over the copy.

    To do this, right-click the copy and choose Flip Along from the context menu. If you moved your copy in the red direction in the preceding step, choose Flip Along→Component’s Red. Choose Component’s Green if you moved in the green direction.

  6. Stick the two halves back together.

    Using the Move tool (this time without Copy toggled on), pick up your copy from the corner and move it over, dropping it on the corresponding corner of the original. Take a look at the last image. Doing this precisely is important if you want your model to look right.

    image0.jpg

Now you’re set up to start building symmetrically. If you want, you can do a test to make sure things went smoothly. Follow these steps:

  1. With the Select tool, double-click one of the halves of your model to edit it.

  2. Draw a circle on the top surface and push/pull it into a cylinder.

    image1.jpg

If the same thing happens on the other side, you’re good to go. If the same thing doesn’t happen on the other side, it’s possible that:

  • You’re not really editing one of your component instances. If you aren’t, you’re drawing on top of your component instead of in it. You know you’re in edit mode if the rest of your model looks grayed out.

  • You never made a component in the first place. If your halves don’t have blue boxes around them when you select them, they’re not component instances. Start a new file and try again, paying particular attention to Step 3 in the previous steps.