A tool for forming an annular workpiece, such as a gear, is provided. The tool has a cylindrical inner form member that has a perimeter that is surrounded by the gear. Driver moves axially along a central axis of the inner form member and gear. A plurality of outer form members rest on a support and are slideable with respect to the support. Each outer form member is provided with a tapered surface that corresponds with and engages with a tapered surface of the driver. Axial movement of the driver causes the tapered surfaces to engage, sliding the outer form members radially inwardly toward the gear. The outer form members are provided with surface features that form teeth onto the gear when the driver presses the outer form members against the gear.