Definition
A sheet metal forming process used to prepare a rivet hole in thin aluminum skin so that a flush (countersunk) rivet will sit smoothly with the surface. A male and female die press the metal around the hole into a smooth, rounded depression matching the shape of the rivet head, rather than cutting the metal away. Used on skin too thin to be safely countersunk by machining.
Plain English
A way of pressing a smooth, rounded dent around a rivet hole in thin metal so the rivet head sits flush with the surface instead of sticking out.
Context Anchor
Seen in aircraft sheet-metal repair, especially when installing flush rivets in thin aircraft skin.
Derivation
Dimple comes from Middle English meaning a small natural hollow or depression, like the dimple in a cheek. Radius refers to the smooth curved (rather than sharp-edged) shape of the depression. Together they describe a small, rounded indentation pressed into the metal.
Why Pilots Care
Produces aerodynamically smooth surfaces and prevents stress risers that could lead to fatigue cracks in flight-critical structure.
Analogy
It is like pressing a neat, rounded seat into thin metal so a screw head can sit level with the surface, rather than simply denting the metal with a hard point.
Intuition Check
Do not read “dimpling” here as accidental denting. Radius dimpling is a controlled forming process used around a prepared rivet hole.
Example Sentence 1
The mechanic used radius dimpling to prepare the rivet holes in the wing skin because the aluminum was too thin to countersink.
Example Sentence 2
Radius dimpling works well on thin aluminum where a countersink cutter would risk cracking the material.