Definition
A method of inspecting a honeycomb sandwich structure for disbonds by pressing the edge of a coin against the skin and tapping or sliding it across the surface while listening to the sound. A solid, sharp ring indicates the skin is properly bonded to the honeycomb core; a dull or flat sound indicates the skin has separated from the core underneath.
Plain English
A simple way to check if the thin outer skin of a composite panel is still glued to the honeycomb material inside. You tap the surface with a coin and listen — a clear ring means it's still stuck together, a dull thud means it has come unstuck.
Context Anchor
Seen in aircraft maintenance and metal repair discussions, especially when describing how small, accurate shapes are formed in aircraft metal parts.
Derivation
Named for the tool used: an actual coin. The technique relies on the fact that a bonded panel transmits the tap as a clean, high-pitched sound, while an unbonded area sounds dead because the skin can vibrate freely above the void.
Why Pilots Care
Disbonded honeycomb panels lose much of their strength and can fail in flight. Coin pressing is a quick, no-equipment check a mechanic or pilot can use during a walkaround or preflight on suspect areas.
Analogy
Like tapping a wall to find a stud — solid backing sounds different from a hollow space behind the surface.
Intuition Check
Coin pressing does not mean pressing coins or using money as a tool. In this context, it means a controlled metal-forming process that works like coin stamping.
Example Sentence 1
The mechanic used coin pressing along the trailing edge of the rudder and found a dull spot indicating a small disbond.
Example Sentence 2
When the proper dimple dies were unavailable, the mechanic relied on coin pressing to finish the repair.