Creating Contoured and Plastic Parts - Autodesk Inventor 2010: No Experience Required - page 391

FIGURE 8.28 Setting up the sketch's construction geometry
FIGURE 8.29 Create a sketch on the bottom surface.
18. Finish the sketch on the top and create a new one on the right surface.
19. In the new sketch, project the endpoints of the arcs that contact the
right surface.
20. Draw a line between the two projected points. See Figure 8.31. Finish
the sketch.