| 摘要 |
The procedure consists of extruding a metal blank (1) having a basic inverted U-section with hollow side chambers (5, 6) between inner (7, 8) and outer (9, 10) walls, and reinforced lower edges (12, 13). The inner walls of the side chambers are substantially thicker than the outer ones, which are convex in shape. The blank is machined by removing material to form a platform (15) to support a boot, drilling holes (23, 24) for wheel axles, and cutting away parts of the side walls so that the remaining portions of the inner side walll are visible through the gaps in the outer one. In the finished frame the remaining portions of the side walls extend at an oblique angle between the platform and the reinforced lower edges.
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