A blowout preventer milling assembly for milling a gasket surface in a blowout preventer. The blowout preventer assembly can have legs, a support frame mounted to the legs, and a pair of support frame rails mounted to the support frame located on opposite sides of the gasket surface. The blowout preventer milling assembly can have a support frame actuator to move a bridge frame on support frame rails. The bridge frame can have bridge rails and a bridge frame actuator for moving a spindle holder on the bridge rails. A pneumatic spindle for calibrating and cutting the gasket surface is provided. A portable controller communicates through a network with the support frame actuator, the bridge frame actuator, a power supply, and a client device to control the movement of the pneumatic spindle to mill the gasket surface of the blowout preventer.