What type of cutter is used to chamfer holes for fillet relief?

The open countersink is specifically designed to create a beveled edge or chamfer on the inside of holes, which is essential for fillet relief in aerospace applications. This type of cutter provides a larger and more controlled chamfer compared to other options, allowing for easier assembly and reducing stress concentrations around the hole. By facilitating the smooth transition between surfaces, the open countersink ensures better load distribution and enhances the strength of the assembly, which is critical in aerospace components where safety and performance are paramount.

In contrast, standard countersinks do not provide the same size or adaptability as open countersinks for larger or specific fillet relief geometries. Flat-end mills are typically used for surface milling and making flat-bottomed cavities rather than for creating chamfers. Drill bits are designed primarily for creating cylindrical holes and cannot effectively create the necessary beveled edge within the material. Thus, the open countersink stands out as the most suitable tool for this task.