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Dimensioning and Tolerancing Handbook Episode 3 Part 2

Tham khảo tài liệu 'dimensioning and tolerancing handbook episode 3 part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 18-10 Chapter Eighteen 18.6.1.3 Composite Positional Tolerance Verification Composite positional tolerancing is a unique tolerance used in controlling patterns of two or more features. In this tolerancing method the location of the entire pattern is less important than the relationship of features within the pattern. Verifying a composite positional tolerance using a fixed-limit gage would require the development of two separate gages one for each requirement. However with the paper gage both requirements may be easily verified from a single set of measurements. Fig. 18-8 illustrates a composite position specification for the four-hole part used in previous examples. Figure 18-8 Four-hole part controlled by composite positional tolerancing As in the previous examples the inspector would set up the part extract the measurements and record the data on the Inspection Report as shown in Table 18-3. Note that the report reflects two allowable tolerances for each hole. The larger tolerance represents tolerance allowed by the upper segment of the feature control frame with the smaller tolerance representing the tolerance allowed by the lower segment of the feature control frame. Table 18-3 Inspection Report for composite position verification LAYOUT INSPECTION REPORT NO. FEATURE FEATURE SIZE ALLOW TOL. X LOCATION Y LOCATION ACCEPT REJECT MMC ACTUAL DEV. BASIC ACTUAL DEV BASIC ACTUAL DEV 1 .312 .003 .309 .310 .001 0.011 1.500 1.506 .006 2.500 2.503 .003 X 0.005 X 2 .312 .003 .309 .315 .006 0.016 1.500 1.505 .005 1.000 1.006 .006 X 0.010 X 3 .312 .003 .309 .313 .004 0.014 4.500 4.506 .006 2.500 2.499 -.001 X 0.008 X 4 .312 .003 .309 .312 .003 0.013 4.500 4.501 .001 1.000 1.005 .005 X 0.007 X Paper Gage Techniques 18-11 Verification of the upper segment is accomplished as in previous examples. A polar coordinate system representing the round positional tolerance zones is laid over the coordinate grid with the centers of both aligned as shown in Fig. 18-9. The inspector then