Definition
A sheet metal forming tool, also called a leaf brake or bar folder, used to make straight-line bends across the full width of a sheet of metal. The sheet is clamped between an upper jaw and a lower bed, and a hinged leaf is then lifted to bend the exposed portion of the sheet to the desired angle.
Plain English
A workshop machine that grips a flat sheet of metal along a line and folds the rest of it upward to make a clean, straight bend.
Context Anchor
Seen in airframe maintenance and repair when forming aluminum sheet parts, edges, covers, or replacement panels.
Derivation
The word 'cornice' comes from Italian for the decorative molding along the top of a wall. The tool got its name because it was originally used to bend long, straight sheet metal cornices for buildings. The same machine is now used in aircraft sheet metal work for the same kind of straight bends.
Why Pilots Care
Maintenance technicians use cornice brakes to form repair patches and replacement skin sections. A bend made on the wrong type of brake, or with the wrong setup, can produce a part that does not fit or that cracks in service.
Intuition Check
Do not read brake here as something that slows or stops an aircraft. In sheet-metal work, a brake is a machine that bends metal in a controlled way.
Example Sentence 1
The technician used the cornice brake to bend a 90-degree flange along the edge of the aluminum repair patch.
Example Sentence 2
After calculating bend allowance, the mechanic used the cornice brake to shape the fuselage skin panel.