Definition
A hand-operated drill featuring a curved plate at the upper end against which the operator presses their chest to apply forward pressure while turning the crank handle to drive the drill bit. Used in aircraft maintenance for drilling holes when powered tools are unavailable, impractical, or where fine control is required.
Plain English
A manual drill you push against with your chest while you turn its crank by hand. The chest plate lets you lean your body weight into the work to push the bit through the material.
Context Anchor
Seen in aircraft maintenance and repair work, especially older tool lists or procedures for making small holes without an electric drill.
Derivation
Named for the breast plate at the top of the tool, which the operator's chest pushes against to provide drilling pressure. The name describes how the tool is used rather than what it drills.
Why Pilots Care
Mechanics and owner-operators may encounter this tool during sheet metal repairs or in older shop inventories. Knowing the name prevents confusion when reading maintenance manuals or ordering tools.
Intuition Check
Do not read “breast” as referring to the front of the airplane. In “breast drill,” it refers to the user’s chest, which is used to push the tool steadily into the work.
Example Sentence 1
The mechanic used a breast drill to bore a clean hole through the aluminum bracket where the powered drill couldn't fit.
Example Sentence 2
In vintage aircraft restoration, breast drills remain useful for precise, low-speed drilling operations.