Nibbler

A nibbler is a tool for cutting sheet metal with minimal distortion. It may be used for "nibbling": cutting a contour by producing a series of overlapping slits or notches.
One type of nibbler 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 wide. Another type operates similar to tin snips, but shears the sheet along two parallel tracks apart, rolling up the waste in a tight spiral as it cuts.
Nibblers may be manual or powered. 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.