A malleable shaft device for use in surgical procedures, having a tension fiber therein, whereby the malleable shaft transitions from a malleable state to a rigid state when a force is applied to the tension fiber, has a variable-pitch cam operatively connected to the tension fiber, and a lever operatively connected to the variable pitch cam for applying force. The mechanical advantage of the cam changes with displacement to accommodate increasing load, and to increase the rate of travel while loads are light. The force profile may provide for a constant input force to accomplish the full travel of the cam.