Abstract: A downhole tool mechanism for applying a driving force, such as a cutter tool for cutting a line captured within the tool, comprises a resiliently compressible member for storing a compressive force; a retaining device for maintaining storage of the compressive force until released; a trigger mechanism for releasing the compressive force when the trigger mechanism is activated. In one form the resiliently compressible member comprises a plurality of concentrically arranged spring washers each having a radial slot therein for receiving a line along the length of the resiliently compressible member. In the cutter form, there is a cutter arranged to cut the line when the trigger mechanism is activated, and the trigger mechanism is activated when the tool receives a shock force to one or both ends.