PURPOSE: To obtain various runners which are low in their costs, and different in aerodynamic performance in such a way that when manufacturing runners for centrifugal fans, blade-shaped slits are formed on the conical face which is formed in conical trapezoid by means of rawing, and then these blade parts are made into the determined shapes by extruding them from the direction of the conical trapezoid axis.

CONSTITUTION: A conical trapezoid 2 is formed by drawing a sheet metal, and then slits 6 are provided in response to the blade shapes to be formed on the conical face 5. Blades 7 are set up by pushing the parts 7b to their outsides. At this moment, the blades 7 are set up by making narrow parts 8a, 8b between the slits into the fulcra. Their sizes in mm unit are noted as the embodiment in the figure. In conformity with this method, if the blade set-up strokes are made variable, angles at outlet and inlet of the blades can be freely slected, so that various runners which are different in aerodynamic performance by only one metal mold.