MOLD FOR ROTATING CYLINDER OF ROTARY HEAD ASSEMBLY FOR MAGNETIC RECORDING/REPRODUCING DEVICE

PURPOSE:To mold a rotating cylinder of high-roundness by making the radius of the cylindrical molded surface which forms the outer peripheral face of a rotating cylinder, larger in the portions farther from a molding material injection gate than to those closer. CONSTITUTION:The radius R1 of every portion 112 farther from a gate 12 is made larger than that R2 closer to the gate, and the radius of a cylindrical molding surface 111 A is gradually increased from the radius R2 in every portion 113 to that R1 in portions 112 contiguous to the former. A large quantity of molding material is injected from the portions 113 into the portions 112. As a result, although the amount of shrinkage due to the cooling in the portions 504 of the outer peripheral face 501 of a rotating cylinder 5 corresponding to the portions 112 is larger than that due to the cooling in the portions 503 of the outer peripheral face 501 of a rotating cylinder 5 corresponding to the portions 113, it is compensated by the difference in the quantity of injection material, the radius of the peripheral face 501 of an obtained rotating cylinder 5 is equal and the roundness of the peripheral face 501 of rotating cylinder 5 is improved.