| 摘要 |
The present invention generally provides a system and method for stiffening a cutting tool assembly used in cutting laterally relative to a wellbore axis to reduce stresses and cyclical bending of the cutting tool assembly during cutting. The system includes a cutting tool attached to a shaft such as an output shaft of a motor or a drill string. A sleeve is disposed in an annular space, known as a box relief, defined between the shaft and a peripheral wall of the cutting tool. The sleeve is preferably fixed in the annular space by a sleeve ring surrounding a recess in the shaft, but can be coupled to the peripheral wall and/or shaft by, for example, a threaded engagement. As the cutting tool attempts to bend at a connection with the shaft during cutting, creating stresses at the connection, the stresses are distributed throughout the increased contact area of the sleeve with the cutting tool, causing less stress per unit area and distributing at least a portion of the stress away from the threaded engagement between the shaft and the cutting tool. The reduced stresses cause less fatigue and thus lower failure rate of the members. Also, the walls of the cutting tool surrounding the shaft are lengthened to engage even more surface area of the sleeve and further reduce the bending stresses. Also, the distance between the cutting portion of the cutting tool and an engagement portion between the cutting tool and the shaft can be shortened to reduce stresses on the engagement portion by forming a shorter cutting tool.
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