| 摘要 |
A plurality of annular plates are machined to have substantially identical outer diameters equal to the inner diameter of the head to be made. A first annular plate is arranged as an annular base plate. The other annular plates are cut into four congruent arc portions of less than 90 DEG and braces are attached to each congruent arc portion. A plurality of the arc portions are mounted by a first end to the upper surface of the annular base plate in a substantially equally, circumferentially spaced arrangement. The second end of each arc portion is fastened to the outer surface of a central collar to form the hemispherical frame.
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