What tool is primarily used to trim a rivet's length?

The primary tool used to trim a rivet's length is a rivet cutter. Rivet cutters are specifically designed to cut rivets cleanly and accurately without causing undue damage to the surrounding material. Using a rivet cutter allows for a precise cut, ensuring that the rivets are trimmed to the desired length for proper fastening in metal structures, which is essential for maintaining the integrity and safety of an aircraft.

Other tools listed, such as drill presses, angle grinders, and bench saws, are not suited for this specific task. A drill press is used for drilling holes and may not provide the control needed for cutting rivets. An angle grinder, while versatile for cutting and grinding, can cause heat distortion and is not ideal for precision trimming of rivets. A bench saw is typically used for larger cuts on wood or metal and is not practical for the precise, small-scale task of trimming rivets. Therefore, the rivet cutter is the correct and most effective tool for this purpose.