Select any sketch entity on Central
Arm-1, drag the block adjacent to the left point in the base, and
then click 
.
Connect the base to the central arm using relations. This allows the arm to pivot.
Select any sketch entity on Central
Arm-1, drag the block adjacent to the left point in the base, and
then click .
Click Zoom
to Area 
(View
toolbar) and zoom in to the top of the base and the bottom of the central
arm.
Click Add
Relations 
(Dimensions/Relations
toolbar).
Select the point on the base, and the center point of the arc for Selected Entities.
If the pointer does not allow
you to select the center of arc, use Zoom
to Area to
magnify the image.
In the PropertyManager,
under Add Relations, select Coincident 
, and click
.
