Provided are magnetically actuated wafer chucks that permit a wafer to be clamped or undamped at any time during a process and at any rotational speed, as desired. Such wafer chucks may include constraining members that are movable between open and closed positions. In a closed position, a constraining member aligns the wafer after wafer handoff and/or clamps the wafer during rotation to prevent it from flying off the chuck. In an open position, the constraining member moves away from the wafer to allow liquid etchant to flow from the wafer edge without obstruction. The constraining members may be, for example, cams, attached to arms or links of the chuck. The cams or other constraining members move between open and closed positions by self-balancing forces including a first force, such as a spring force, that acts to move a cam in a first direction, and a non-contact actuate-able force, such as a magnetic force, that acts to move the cam in the opposite direction. The resulting cam motion is smooth and continuous.