Definition
An adjustable hand or machine reamer used to enlarge a hole to a precise diameter. The cutting blades are seated in tapered slots in the body, and turning an adjusting nut moves the blades outward or inward, allowing the reamer to be set to a specific size within a small range.
Plain English
A finishing tool that smooths and slightly enlarges an existing hole to an exact size. Unlike a fixed-size reamer, its cutting edges can be adjusted outward in small steps so one tool covers a small range of diameters.
Context Anchor
Seen in aircraft maintenance and repair work when holes in metal parts must be finished accurately for a close-fitting bolt, pin, or part.
Derivation
‘Expansion’ comes from the Latin expandere, ‘to spread out.’ ‘Ream’ comes from the Old English ryman, ‘to widen or make room.’ Together the name describes the tool’s action: a reamer whose cutting edges spread outward to widen the hole to size.
Why Pilots Care
Produces holes with the precise diameter needed for interference or slip fits, avoiding stress risers or loose joints that could lead to in-flight failure.
Intuition Check
An expansion reamer does not force the hole wider by pressure. It cuts the hole slightly larger after the tool itself has been adjusted.
Example Sentence 1
The mechanic used an expansion reamer to bring the bushing hole to the exact diameter called for in the maintenance manual.
Example Sentence 2
After drilling, the technician finished the hole with an expansion reamer to achieve the proper interference fit for the bolt.