An expandable forming tool has a body (10) with a mounting stem on its upper surface and a transversely extending channel in its lower surface in which is slidably seated a wedge-shaped actuator (12) for vertical sliding movement. The larger lower end normally depends from the body. A pair of slides (14) are slidably seated in the channel on opposite sides of the actuator, and they have angular surfaces slidably bearing on the sloping surfaces of the actuator (12). Springs bias the slides against the side surfaces of the actuator, and a spring biases the actuator outwardly of the body. The actuator is driven vertically inwardly of the channel by movement of its larger end against a workpiece, and this inward movement pushes the slide members outwardly in the channel to project beyond the periphery of the body. The tool can produce contours in the workpiece, or cut the workpiece, or both.