Final answer:
A mechanic can determine whether the countersink for a flush rivet should be dimpled or drilled based on the type of material being used and the application requirements. Soft or thin materials like aluminum or fiberglass typically require a dimpled countersink, while hard or thick materials like steel require a drilled countersink.
Step-by-step explanation:
A mechanic can determine whether the countersink for a flush rivet should be dimpled or drilled based on the type of material being used and the application requirements.
In general, a countersink hole is used for flush rivets to provide a smooth and level surface. If the material is soft or thin, such as aluminum or fiberglass, a dimpled countersink is typically used. This involves creating a slight depression with a countersink tool without removing material.
If the material is hard or thick, such as steel, a drilled countersink is usually required. This involves using a drill bit to remove material and create a conical shape. The diameter of the countersink hole should be slightly larger than the rivet head to ensure proper installation.