What factor allows machine countersinking when flush riveting?

Machine countersinking for flush riveting is primarily influenced by the relationship between material thickness and the rivet head. When preparing the surface for flush riveting, it is essential that the countersink is appropriately sized according to the thickness of the material being joined. This ensures that when the rivet is inserted and set, its head sits flush with the surface of the material.

If the material is too thick relative to the rivet head, it may not allow for the necessary countersink depth, leading to protruding rivets. Conversely, if the material is too thin, it may not provide enough surface area for the rivet head to properly support the structural integrity required for the joint. Thus, accurately assessing and managing the thickness of the material against the rivet head design is crucial for effective machine countersinking, ensuring that the finished surface remains smooth and aerodynamic, which is particularly important in applications such as aircraft structures.