tailieunhanh - Dimensioning and Tolerancing Handbook Episode 3 Part 6

Tham khảo tài liệu 'dimensioning and tolerancing handbook episode 3 part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Floating and Fixed Fasteners 22-15 - 1 4 A B I c I Rivets 2X .OO4 fo 0 .D12 a I BI c 4 D 2X X 100 .OO4 fo 0 .D12 a I BI c 4 D 0 PLACES Floating nut plate nut Figure 22-14 Positional tolerance for clearance holes and nut plate rivet holes Projected Tolerance Zone When using fixed or double-fixed fasteners a projected tolerance zone should be used regardless of whether the design is using threaded fasteners or alignment pins. Variation in the perpendicularity of the screw or pin could cause assembly problems. If a threaded fastener was out of perpendicular by the total amount of the positional tolerance of an interference problem could occur see Figs. 22-15 and 22-16 . by Tapped hole out of perpendicular Figure 22-15 Tapped hole out of perpendicular by Tapped hole -------- out of perpendicular by would cause assembly fit problem Figure 22-16 Variation in perpendicularity could cause assembly problems 22-16 Chapter Twenty-two Fig. 22-17 shows how a projected tolerance zone corrects the interference problem shown in Fig. 2216. The projected tolerance zone is applied to the threaded fastener or the pressed pin. The tolerance zone for the tapped hole extends through the mating parts clearance hole thereby assuring the mating parts will fit. THIS ON THE DRAWING MEANS THIS Cylindrical tolerance zone .250 28 UNF-2B Cylindrical tolerance 250-28 UNF-2B UNF-2B 180 Figure 22-17 Projected tolerance zone example Comparison of Positional Tolerancing With and Without a Projected Tolerance Zone This section compares two position tolerancing methods to locate size features for fixed fasteners. In the first method we use a projected tolerance zone and calculate the functional tolerance zone using the fixed fastener formulas as shown previously. We consider this a functional method for the case of a fixed fastener. In the second method we convert .