The invention relates to a method and a forming machine for working a workpiece, for example by deforming it or fixing it in another workpiece, in which the workpiece is fitted over a mandrel, at least a part of the mandrel is expanded so as to fix the workpiece, the workpiece and at least one tool, such as a forming roller, are rotated about an axis relative to each other and the workpiece is worked by means of said tool. Less than half of the expanded or expandable part of the mandrel engages portions of the workpiece that are being worked with the tool.