Creating Contoured and Plastic Parts - Autodesk Inventor 2010: No Experience Required - page 392

FIGURE 8.30 Adding a sketch to the top surface
FIGURE 8.31 Draw a leading edge between the two points.
21. Create a new sketch on the left surface.
22. Project the points of the arcs that come in contact with the left
surface.
23. Create a short, vertical construction line to establish tangency from
the projected point at the top surface.
24. Draw a tangent arc between the points, as shown in Figure 8.32.