Definition
A solid shaft, spindle, or form around which material is shaped, machined, or held during fabrication or repair. In aviation maintenance, a mandrel is commonly used to support tubing while it is being bent, flared, or formed, and to hold workpieces in alignment on a lathe or other machine.
Plain English
A solid rod or form that you slide a part onto, or work material around, to hold its shape while you bend, cut, or shape it.
Context Anchor
Seen in aircraft maintenance when a part must be shaped, supported, or held accurately during repair or fabrication.
Derivation
From the French 'mandrin', meaning a lathe chuck or shaft. The word entered English through the machining trades, which is why it still carries the sense of 'something that holds or supports a workpiece' in modern shop use.
Why Pilots Care
A part shaped or supported with the wrong mandrel can end up distorted or poorly fitted, which can make a repair unsafe or unreliable.
Analogy
Think of the cardboard tube inside a roll of paper towels. The tube gives the paper its shape and keeps it from collapsing. A mandrel does the same job for metal — it supports the part from the inside or underneath while the part is being formed.
Intuition Check
A mandrel is not usually the finished aircraft part. It is the tool used to hold or shape the part during the work.
Example Sentence 1
The technician slid the aluminum tubing onto a mandrel before bending it, so the tube would not kink or flatten at the bend.
Example Sentence 2
After installing new bearings, the team checked crankshaft runout while the shaft was supported on a mandrel.