There are two common reasons why objects are not immediately seen in your project.
- It’s possible that your polygon’s normals are facing the wrong direction. Try to select all of your model faces and make sure the normals are facing the right direction.
- Alternatively, your 3D object may be way too small or way too big which cannot fit in viewer. If too small, zoom in by grabbing the scale tool and scaling it up; eventually you will see it appear in the preview window.