Definition
A short, stiff, two-ended drill bit used to start a precisely located hole in a workpiece. It has a small pilot tip and a 60-degree tapered shoulder, and is used in a lathe or drill press to produce an accurate starting point that keeps a longer twist drill from wandering off center.
Plain English
A short, sturdy drill bit used to make a small, accurate starter hole so that a longer drill bit will go in straight and exactly where you want it.
Context Anchor
Seen in aircraft maintenance and sheet-metal work when a mechanic needs a hole to begin exactly on a marked point.
Derivation
Called a 'center' drill because its job is to establish the exact center point of a hole before the main drilling is done. The starter hole locates the center; everything else follows from it.
Why Pilots Care
An accurately started hole helps protect aircraft parts from misplaced holes, poor fit, and unnecessary damage during maintenance.
Analogy
Like making a small dimple with a nail and hammer before driving a screw -- the dimple keeps the screw tip from skating across the surface.
Intuition Check
A center drill is not simply any drill used near the center of something. It is a specific starter tool used to make a hole begin accurately.
Example Sentence 1
The mechanic used a center drill to start the hole before switching to a larger twist drill for the final size.
Example Sentence 2
Select the proper center drill size so the pilot hole matches the rivet or bolt diameter called for in the repair drawing.