Importance

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Abstract

A downhole cutting tool for use in a wellbore, the cutting tool having a mandrel and a cylindrical knife body slidably mounted coaxially on the mandrel. The mandrel can be attached to or suspended from any type of workstring. The upper ends of a plurality of knife blades are pivotably mounted at fixed points on the knife body. The knife blades are suspended therefrom over a plurality of ramps formed on the exterior of the mandrel. A pressure chamber is formed between the knife body and the mandrel. Fluid from the work string can be directed through the mandrel to the pressure chamber, to drive the knife body downwardly relative to the mandrel, causing the lower ends of the knife blades to contact the ramps on the mandrel and kick or pivot outwardly to cause the lower tip of the blade to contact the downhole material to be cut. As the mandrel is rotated, the knife blades rotate with it and cut into the material. The point at which the lower end of the blade contacts the ramp is a fulcrum point which is closer to the lower tip of the blade than to the upper end of the blade. This creates a mechanical advantage causing the lower tip of the blade to be more forcefully urged into the material to be cut.

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First Claim