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The position errors in the axis direction of a vertical machine center have been measured by means of the VM101 linear encored measurement system. The character of the backlash error is discussed; results show that the backlash error has great influence on the position error. The position accuracy is enhanced after the backlash errors are compensated

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Some broken end mills with many brittle breakage sections were collected, and the geometry features of these sections were summed up. As for minor breakage, the breakage sections were narrow planes parallel to the tool edge, and the depths of breakage were shallow. As for severe breakage, it likely occurred near the edge tip; its breakage sections were approximate planes perpendicular to the bottom of tool and tilted approximately 35°to the bottom edge; moreover, the broken degree of section side near the rake face was heavier, while that near the flank face was slighter. By taking these geometry features into account, mathematical instantaneous expressions of cutting force for broken end mills were amended correspondingly. Then, with these expressions, it could be analyzed that, on one hand, the amount of material removed by broken edge segment declined and, on the other hand, its coefficient of cutting force rose; therefore, the instantaneous cutting force might be in reverse relation with broken degree, and in positive relation with feed, and also the removed material by the tooth following the broken one would rise. These results indicate that, if a tooth is brittle broken, there exist two kinds of possibility as rise and decline for its cutting force-the cutting force of slightly broken tooth would rise, while that of heavily broken tooth would decline, the cutting force of tooth following the broken one would always rise, and that of other teeth would remain the same. Using artificial tooth breakage, cutting tests of broken end mills were taken; the test results agreed with above conclusions. Conclusions of this study may be used in modifying indices of monitoring brittle breakage for end mills.

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