Constrain
Constrain To Screen, Constrain Free, Constrain To X Axis, Constrain To Y Axis, Constrain To Z Axis, Constrain To XY Plane, Constrain To XZ Plane, Constrain To YZ Plane
 

Description:

      The Constrain commands are not listed in the program menus but can be assigned to keyboard shortcuts, image buttons, or mouse buttons via their respective customization dialogs.  These commands work with whatever manipulator is currently active (Move, Scale, Rotate, etc), and calling each command will allow you to perform the manipulator's actions in the specified axis or plane.  If the move manipulator is active and you press a keyboard shortcut assigned to Constrain To XZ Plane, then dragging your mouse (you can click or not) will move your selection in the manipulator's XZ plane.  You can click or release the mouse to complete the operation.
    If you grab the manipulator by its y axis and press a keyboard shortcut assigned to Constrain To X Axis, the effect will be to constrain to the plane defined by these two axes, in this case the xy plane.


Notes:

- Working with the Constrain commands can allow you to work completely or almost completely without the main manipulator being visible.

- You can use the different manipulator orientation options (Auto Orient and Orient) in conjunction with these constraints to transform your selection precisely how you want it.