Importance

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Abstract

A section mill for cutting through well casing, the mill including multiple sets of cutting blades which are selectively engaged to continue cutting operations as blades dull. The cutting blade sets are selectively indexable such that as a first set dulls or fails a succeeding set can be utilized following retraction of the first set. The section mill includes a central mandrel having offset cammed surfaces which engage the cutting blades and cause them to expand outwardly. The mandrel is axially displaceably by a piston affected by hydraulic pressure. As the mandrel is axially displaced the indexed cutting blades are expanded by the cammed surface. Indexing is accomplished by a cam drum which allows the mandrel to be rotated relative to the cutting blades in order to align the next cammed surfaces with their respective cutting blades. The cam drum includes a continuous slot within which an indexing pin travels to control longitudinal and rotational displacement of the mandrel relative to the outer assembly which retains the cutting blades. In a preferred embodiment, the section mill includes three longitudinally spaced sets of cutting blades and camming surfaces which are relatively displaced 40.degree..

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First Claim