tailieunhanh - Geometric Dimensioning and Tolerancing for Mechanical Design Part 8

Tham khảo tài liệu 'geometric dimensioning and tolerancing for mechanical design part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Position Location Position Location 127 0 . ABC Figure 8-2 Floating fastener with a zero positional tolerance at MMC. available and give the machinist the maximum size flexibility in producing the clearance hole. The calculations could not be easier. The MMC hole size when toleranced with a zero positional tolerance is the same as the diameter of the fastener. H .250 .000 .250 What is the actual location tolerance in Fig. 8-2 The location tolerance for a given hole size at MMC is the same no matter what tolerance is specified in the feature control frame. If the clearance hole is actually produced at the total location tolerance is Geometric tolerance bonus total positional tolerance .020 .285 - .270 .035 or .000 .285 - .250 .035 If the machinist happens to produce the hole at and zero positional tolerance is specified the hole size is acceptable but the hole must be within a location tolerance of . No matter what tolerance is selected it is important to use the formula to determine the correct MMC hole diameter. If the MMC clearance hole diameter is incorrect either a possible no fit condition exists or tolerance is wasted. The next step is to determine the LMC clearance hole size the largest possible clearance hole. The LMC hole size is essentially arbitrary. Of course the clearance hole must be large enough for the fastener plus the stated tolerance and it cannot be so large that the head of the fastener pulls through the clearance hole. Some engineers suggest that the clearance hole should not be larger than the largest hole that will fit under the head of the fastener. If a slotted clearance hole Fig. 8-3A will fit and function then surely the .337 diameter hole in Fig. 8-3B will also fit and function. How is the clearance hole diameter in Fig. 8-3B determined The largest hole that will fit under the head of a fastener is the sum of half of the diameter of the fastener and half of the diameter of the fastener head or the .