Bor A nibbler is a tool for cutting sheet metal with minimal distortion. One type operates much like a punch and Die, with a blade that moves in a linear fashion against a fixed Die, removing small bits of metal and leaving a kerf approximately 6 mm wide. Another type operates similar to tin snips, but shears the sheet along two parallel tracks 3–6 mm apart, Rolling up the waste in a tight spiral as it cuts. Nibblers may be manual (hand operated) or powered.
http://sjfiremuseum.org/style.php Power nibblers are often powered by compressed air, though electrical types also exist. A common DIY nibbler tool is an electric Drill attachment, which converts the rotary motion of the Drill into a reciprocating motion of the jaw.