Putting Things in Place with Assemblies - Inventor 2013 and Inventor LT 2013 Essentials - page 103

FIGURE 4.5 Applying constraints does not automatically restrict all
movement.
The Angular Constraint
There are three solutions for the Angular constraint, allowing the flexibility to,
for example, set the axis of rotation apart from the components, along with other
options that give less control. For this exercise, you will use the most precise
solution, the Explicit Reference Vector tool.
1. Verify that the 2013 Essentials project file is active, and then open the
c04-04.iam file from the Assemblies\Chapter​4 folder.
2. Launch the Constrain tool from the Assemble tab in the Position
panel or the marking menu.
3. Set Constraint Type to Angle, and make sure the solution type is set
to Explicit Reference Vector.
4. For the first selection, click the narrow face on the side of the
purple part.
5. For the second, click the face on the red part, as shown in Figure 4.6.