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Tham khảo tài liệu 'drilling and associated cutting tool technology industrial handbook_3', kỹ thuật - công nghệ, điện - điện tử phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Drilling and Associated Technologies 105 drilled hole tolerances. On turning centres this can be readily achieved by modifying the CNC cutting program to offset the drill with respect to the machine s centreline. Moreover for turning operations employing drilled features then the indexable insert s top surfaces must remain parallel to the X-axis of the machine tool. The arrangement of the inner and outer cutting edges of an indexable insert drill relative to each other together with the drill s position to the axis of rotation are vital for perfect drilling operations19 i.e. see Fig. 53a . The cutting inserts positions by possible X-axis adjustments are critical for the smooth running resultant cutting forces and will influence the drilled hole s alignment. Preferably the cutting edges are arranged in such a manner that the inner- SBI and outer-inserts SBA have identical cutting widths Fig. 53a - bottom left . When new insert cutting edges are utilised this results in a balance of the cutting forces in the Y-axis guaranteeing drilled holes of accurate size and surface texture without retraction striae 20. When selecting the appropriate adjustment angles Xi and xa the lines of force via feed forces Fa and Fi will coincide with the drill s axis in the centre of the clamping shaft Fig. 53a - top . Hence the clamping shaft must only transmit torque resulting from the cutting forces and the bending moment of the resultant cutting force which will be present. Typically the outer insert s resultant cutting force FA i.e. Fig. 53b is comprised of the following forces Remaining cutting force AFc - generated through greater wear rates at the periphery of the outer cutting insert Passive force Fp - generated by the corner radius of the outer cutting insert. With indexable drills the chip flute is selected so that the drill s profile from the tip up to the chip flute has its runout twisted by between 65 to 85 . In the vicinity of the chip flute the runout i.e. the longest lever
