Angle Constraint Works in the Opposite Direction

Problem

Parts constrained with an angle constraint may sometimes rotate in the wrong direction, meaning the angle is applied with the “wrong sign.”

Solution

Always define angle constraints by also specifying the rotation axis, which can be a line or a cylindrical surface. If the rotation axis is not specified (the program does not require it), the angle may have multiple possible solutions, and often the wrong one is chosen.

When you define an angle constraint with a rotation axis, the program will highlight three objects: two planes/lines and the cylindrical surface/rotation axis.