上海交通大学：《现代机械工程图学》教学资源_教学课件_Lec05_GD&T2

GEOMETRIC DIMENSIONING TOLERANCING (GD T) ME 250:Design Manufacturing I School of Mechanical Engineering Shanghai Jiao Tong University 1

Shanghai Jiao Tong University 1 GEOMETRIC DIMENSIONING & TOLERANCING (GD & T) ME 250: Design & Manufacturing I School of Mechanical Engineering

Outline Tolerance Definitions Datums ■Form Controls Rules for Tolerancing Location Control Orientation Controls ■Runout Controls Profile Controls ■Surface Finish Shanghai Jiao Tong University 2

Shanghai Jiao Tong University 2 Outline n Tolerance n Definitions n Datums n Form Controls n Rules for Tolerancing n Location Control n Orientation Controls n Runout Controls n Profile Controls n Surface Finish

Rules for Tolerancing RULE-1:For features-of-size,where only a size dimension is specified,the surfaces shall not extend beyond a boundary (envelope)of perfect form at MMC. a“perfect form”means perfect flatness, straightness,circularity,cylindricity Shanghai Jiao Tong University 3

Shanghai Jiao Tong University 3 Rules for Tolerancing n RULE-1: For features-of-size, where only a size dimension is specified, the surfaces shall not extend beyond a boundary (envelope) of perfect form at MMC. n “perfect form” means perfect flatness, straightness, circularity, cylindricity

Rule-1 for Tolerancing 10.8 10.6 INTERPRETATION PER RULE#1 ⑦1O.8 BOUNDARY PART SIZE-010.7- OF PERFECT FORM 0.1 FORM ERROR ALLOWED AT MMC 14.0 BOUNDARY OF PERFECT FORM AT MMC 146 14.0 HOLE SIZE-014.6 0.6 FORM ERROR ALLOWED Shanghai Jiao Tong University 4

Shanghai Jiao Tong University 4 Rule-1 for Tolerancing

Rule-1 for Tolerancing Rule-1 applies to all feature-of-size (and only to feature-of-size)on a drawing. Rule-1 says that a feature-of-size must have perfect form if the feature-of-size is at MMC. If the part was at less than MMC,a form error equal to the amount of departure would be permissible. If the part was at LMC,a form error equal to the amount of departure would be permissible. Shanghai Jiao Tong University 5

Shanghai Jiao Tong University 5 Rule-1 for Tolerancing n Rule-1 applies to all feature-of-size (and only to feature-of-size) on a drawing. n Rule-1 says that a feature-of-size must have perfect form if the feature-of-size is at MMC. n If the part was at less than MMC, a form error equal to the amount of departure would be permissible. n If the part was at LMC, a form error equal to the amount of departure would be permissible

The Term of RFS The Regardless of Feature Size(RFS)is when a geometric tolerance (or datum) applies independent of the feature size. That is,the geometric tolerance is limited to the stated amount regardless of the size of the feature-of-size. Shanghai Jiao Tong University 6

Shanghai Jiao Tong University 6 The Term of RFS n The Regardless of Feature Size (RFS) is when a geometric tolerance (or datum) applies independent of the feature size. That is, the geometric tolerance is limited to the stated amount regardless of the size of the feature-of-size

Rules for Tolerancing RULE-2:For tolerance of position,S,L,or M must be specified on the feature control frame,with respect to the tolerance value,datum reference,or both. 0.5D H E S,L.OR M MUST BE SPECIFIED IF THE DATUM IS A FEATURE-OF-SIZE Shanghai Jiao Tong University 7

Shanghai Jiao Tong University 7 Rules for Tolerancing

Rules for Tolerancing RULE-3:For other than tolerance of position,RFS applies with respect to the tolerance,datum reference,or both,if no modifier is specified. 0.12 (RFS applies) 0.6 (RFS applies) 0.1 M A (MMC is specified) Shanghai Jiao Tong University 8

Shanghai Jiao Tong University 8 Rules for Tolerancing

Exercise in Class If the block was at MMC,what would its straightness be limited to? the flatness of surface A be limited to? If the block was at LMC,the flatness of surface A would be limited to and the flatness of surface B would be limited to Could both of these flatness conditions exist simultaneously?Why? If the block was at LMC and the flatness of surface A was 0.3. what would the flatness of surface B would be limited to? SURFACE A- 12.2 16,2 118 16.0 SURFACE B Shanghai Jiao Tong University

Shanghai Jiao Tong University 9 Exercise in Class n If the block was at MMC, what would n its straightness be limited to? n the flatness of surface A be limited to? n If the block was at LMC, the flatness of surface A would be limited to and the flatness of surface B would be limited to . Could both of these flatness conditions exist simultaneously? Why? n If the block was at LMC and the flatness of surface A was 0.3, what would the flatness of surface B would be limited to?

Location Control Position and concentricity controls Controls locations of features such as holes,slots,bosses,etc.from datum features Controls center distances between such features Positional tolerances defines a zone within which the center,axis or center plane of a feature of size is allowed to vary from the theoretical (exact)position Shanghai Jiao Tong University 10

Shanghai Jiao Tong University 10 Location Control