If you use Solid Inspector 2, the extension can find and fix the reversed faces for you. To reverse a face, context-click it and select Reverse Faces. By default, the face fronts are white and face backs are dark gray. To check that the face fronts point outward in SketchUp, select View > Face Style > Monochrome to see whether the back sides of a any faces point outward.

(And thus, the backs of faces need to face inward.) Technically, making sure all your faces are oriented the correct way is called checking the normals.

Check that the fronts of faces point outward.

For example, if your model contains internal geometry, then your model is not a solid. (In SketchUp, select Window > Extension Warehouse, search for the extension, and click the red Install button.) This extension helps you analyze why your model isn’t solid and repair and holes or issues. If your group or component isn’t solid, download and install the Solid Inspector 2 extension created by Thomas Thomassen and available via the Extension Warehouse. If your model is a solid group, the Entity Info window tells you so in the upper left, also shown in the following figure. With your group or component selected, choose Window > Entity Info.

Make sure your model is a solid group.

For example, if you want to 3D-print a gear, rather than orient the gear vertically, place the gear on its side, as shown in the following figure. If your model juts out at the top, the 3D printer has nothing to build upon. Your 3D printer prints your model one layer at a time.

Orient your model so that the 3D printer has a base on which to build your model.

Here’s a quick overview of how to set up your SketchUp model for 3D printing: Before you print a model on a 3D printer, you need to make sure your 3D printer can understand your model data.

3d model sketchup