| 摘要 |
A single point turning tool has a tip including a cutting edge with a tip radius and a linear portion added on one side of and slightly behind the point to form a cutting edge with a linear portion and a protruding portion. The protruding extends beyond the plane of the linear portion which, in turn, extends normal to a longitudinal axis on which the tip radius is centered. During manufacture of a piston, the turning tool is positioned with the linear portion aligned generally with the plane of the finished outer surface. The piston is turned while the tool cuts a helical path or turn around the skirt surface by advancing the tool each turn a desired dimension or lead that is greater than the width of the protruding portion but not greater than the combined widths of the linear and protruding portions. The resulting skirt surface is a series of sequentially adjacent turns, each of which includes a shallow valley, preferably with slightly sloping sides, and each turn has a width equal to the width of the protruding portion of the tool and an adjacent flat or linear portion having a width equal to the difference between the lead of the helix and the width of the adjacent valley.
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