Which tool is typically used to deburr the interior surfaces of an assembly?

The tool that is typically used to deburr the interior surfaces of an assembly is the flat file. Deburring is the process of removing rough edges and imperfections from materials after they have been machined or cut. A flat file has a smooth cutting surface and is designed to effectively shave off material, making it ideal for achieving a clean edge and a smooth finish on the internal surfaces.

Using a flat file allows for precision and control, making it easier to work within the confines of an assembly without removing too much material, thereby preserving the intended dimensions and integrity of the parts. It provides the ability to finely manipulate the surface, ensuring that any sharp or jagged edges are eliminated, which is critical for both safety and the proper function of the assembly.

While other tools may serve specific purposes, such as a sanding block for flat surface finishing or a countersink cutter for enlarging hole entrances and chamfering edges, they are not traditionally used for deburring interior surfaces effectively like a flat file is. A drill bit is primarily used for making holes, which does not directly aid in deburring. Therefore, the flat file stands out as the most appropriate tool for this specific task in assembly processes.