tailieunhanh - Dimensioning and Tolerancing Handbook Episode 1 Part 5

Tham khảo tài liệu 'dimensioning and tolerancing handbook episode 1 part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 5-6 Chapter Five items as Sheetrock windows bathtubs and air conditioning ducts will fit in the spaces between his frame members. Good fits are important to conserve space and money. It also means that when electrical outlet boxes are nailed to the studs 12 up from the slab they will all appear parallel and neatly aligned. Remember that it all derives from the flatness and squareness of the slab. By now readers with some prior knowledge of GD T have made the connection The house s concrete slab is its primary datum. The slab s edges complete the datum reference frame. The wooden framing corresponds to tolerance zones and boundaries that must contain features such as pipes ducts and windows. Clearly the need for precise form and orientation in the slab and framing of a house is driven by the fixtures to be used and how precisely they must fit into the framing. Likewise the need for GD T on a part is driven by the types and functions of its features and how precisely they must relate to each other and or fit with mating features of other parts in the assembly. The more complex the assembly and the tighter the fits the greater are the role and advantages of GD T. Fig. 5-4 shows a non-GD T drawing of an automobile wheel rotor. Despite its neat and uniform appearance the drawing leaves many relationships between part features totally out of control. For example what if it were important that the bore be perpendicular to the mounting face Nothing on the drawing addresses that. What if it were critical that the bore and the OD be on the same axis Nothing on the drawing requires that either. In fact Fig. 5-5 shows the shanty that could be built. Although all its dimensions are within their tolerances it seems improbable that any fixtures could fit it. In Fig. 5-6 we ve applied GD T controls to the same design. We ve required the mounting face to be flat within .005 and then labeled it datum feature A. That makes it an excellent slab from which we can .