FAA Aviation Mechanic Airframe (AMA)Airframe StructuresEasy
A technician is preparing to install rivets in a thin 0.020-inch aluminum skin where a flush surface is required, but the skin is too thin to safely countersink. What process should be used instead?
- AUsing a universal-head rivet instead of a flush rivet
- BMachine countersinking the rivet hole
- CIncreasing the rivet diameter to compensate
- DDimpling the skin around the rivet hole
Show answer & explanationAnswer & explanation
Correct answer: D. Dimpling the skin around the rivet hole
Dimpling forms a cone-shaped depression in thin sheet metal to accept a flush rivet head without removing material, which is required because thin skins are too fragile to machine-countersink without breaking through the material.
Why the other options are wrong
- A. This does not achieve the required flush surface.
- B. Countersinking removes material and would be too deep for very thin skin, risking a knife-edge or breakthrough.
- C. Changing rivet diameter does not solve the flushness requirement and doesn't address sheet thinness.
Dimpling vs Countersinking
Both create a depression for a flush rivet head, but dimpling stretches/forms thin sheet metal (no material removed) while countersinking cuts away material and is used on thicker sheet.
- Dimpling used when skin thickness is less than the rivet head height.
- Countersinking used on thicker skins, typically 0.040 inch or greater.
- Coin dimpling and radius dimpling are common dimpling methods.
Memory trick: Thin skin? Dimple it, don't cut it — 'Dimple for the Delicate'