| 摘要 |
Section mills have been invented that have one or more blades one or more of whose tops are pivotably extendable outwardly from a mill body as bottoms of the blade(s) rotate about a fixed point, and one or more blades whose bottoms are pivotably extendable outwardly from the mill body, the blades pivotably secured to the mill body so that, in one aspect, in response to a downwardly moving wash tube contacting the blades, the blades move out from the mill body. In one aspect certain of the blades have a milling surface which is of such an outward extent and which is parallel to a central longitudinal axis of the mill body when the blades are fully extended so that "full sweep" milling is achieved.
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