During the drilling process, the processing problems of the various types of bushings shown in Figure 1 are often encountered. If the inner hole of the bushing is large, the mandrel can be used to position the outer circle with the inner hole, and the coaxiality error of the outer circle to the inner hole is controlled within a small range. But when the inner hole of the drill sleeve is too small, for example, less than φ0.5mm, it is very processed.
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