Stepped Recess

To create a recess or protrusion adjacent to a curved shape:

Let's assume Z = 0.4 for the outer rectangle and that all but the Z = -0.2 notch is already drawn.

1. At the location of the notch draw a rectangle extending past the left edge of the outer rectangle and past the large arc.
2. Choose Edit | Select All.
3. Click the Repeat button.
4. Nudge the copy fully away from the original, using the arrow keys.
5. Choose Line | Intersect.
6. Remove all lines except the shape corresponding to the arced notch.
7. Group the lines of the notch.
8. Set Z to -0.2.
9. Delete the original notch rectangle.
   
10. Nudge the arced notch into place.
11. Choose View | 3D.