What are the two methods of countersinking?

The two methods of countersinking in aircraft metal structural repair are machine (or drill) countersinking and dimpling (or press countersinking).

Machine countersinking involves using a special countersink bit in a drill to create a conical recess in the material. This method is precise and is ideal for achieving a specific depth and angle consistently across multiple parts. It allows for smooth and even recesses that can accommodate flush mounting of rivets, ensuring structural integrity and aerodynamics.

Dimpling, on the other hand, is a process where a tool is used to create a shallow dimple in the metal, allowing for a rivet head to sit flush with the surface of the material. This is often done using a press, making it a quick and efficient method for preparing sheet metal for riveting. Dimpling provides strength to the joint while maintaining a smooth surface finish.

Both methods serve the same purpose of creating a surface that allows rivets to sit flush, improving the overall performance and aesthetics of the aircraft structure. Understanding these methods is critical in ensuring proper assembly and repair of aircraft metal components.