Đang chuẩn bị nút TẢI XUỐNG, xin hãy chờ
Tải xuống
Tham khảo tài liệu 'dimensioning and tolerancing handbook episode 1 part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 5-56 Chapter Five 5.8.7 Circularity or Cylindricity Tolerance with Average Diameter The thin-wall nylon bushing shown in Fig. 5-45 is typical of a nonrigid part having diameters that fit rather closely with other parts in assembly. If customary diameter size limits were specified no matter how liberal their inherent circularity control would be overly restrictive for the bushing in its free state unassembled . The part s diameters in the free state cannot and need not stay as round as they ll be once restrained in assembly. We need a different way to control size-in-assembly while at the same time guarding against collapsed or grotesquely out-of-round bushings that might require excessive assembly force or jam in automated assembly equipment. The solution is to specify limits for the feature s average diameter along with a generous circularity tolerance. Where a diameter tolerance is followed by the note AVG the size limit boundaries described in section 5.6.1 do not apply. Instead the tolerance specifies limits for the feature s average diameter. Average diameter is defined somewhat nebulously as the average of at least four two-point diameter measurements. A contact-type gage may deflect the part yielding an unacceptable measurement. Where practicable average diameter may be found by dividing a peripheral tape measurement by p When the part is restrained in assembly its effective mating diameter should correspond closely to its average diameter in the free state. Though we told you our nylon bushing is a nonrigid part the drawing itself Fig. 5-45 gives no indication of the part s rigidity. In particular there s no mention of restraint for verification as described in section 5.5.1. Therefore according to Fundamental Rule l a drawing user shall interpret all dimensions and tolerances including the circularity tolerance as applying in the free state. The standard .rDA_rr7S _ 02.262 02.268 02.235 02.243 AVtKAGL ------------------------------------------------ 4 .
