Creating Contoured and Plastic Parts - Autodesk Inventor 2010: No Experience Required - page 374

14. Right-click the Bottom solid in the Browser, and select Hide Others
from the context menu. See Figure 8.9.
15. Create a new sketch on the work plane you created to split the solid.
16. Using construction lines, project the edge of the cylindrical face and
the edge highlighted in Figure 8.10.
17. Turn off the visibility of the work plane.
FIGURE 8.9 It's easy to isolate which body you want to work on.
FIGURE 8.10 Project the edges to align the sketch to.