A calibration tool for fabricating disk springs. The tool includes a circular cylindrical tool body having an insertion bevel at its face end portion for receiving and centering a workpiece within an inner circumferential enveloping surface of the tool body. A tool surface at the inner circumferential enveloping surface aligns the workpiece relative to a forming tool disposed within the inner circumferential enveloping surface. The tool surface includes a first portion having an inner diameter that increases in size along the axial longitudinal direction of the tool body, and a second portion with an inner diameter that decreases in size along the axial longitudinal direction of the tool body.