A hemming machine having a nest adapted to support a part to be hemmed. A hold down is movable between a retracted position in which the hold down is spaced from the part and an extended position in which the part is sandwiched between the hold down and the nest and a guide surface is formed around the periphery of the hold down. A hemming head having a roller hemmer assembly and mounted to and manipulated by a robotic arm. The roller assembly includes a first roller which engages the guide surface during a roller prehemming operation of the part performed by the robotic arm and a second roller which prehems the part.
