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

Shanghai Jiao Tong University GD & T Outline Dimensioning Principles Standards Tolerancing Definitions Datums Form Controls Shanghai Jiao Tong University

Shanghai Jiao Tong University Working Drawing Three orthographic views Auxiliary views, section views Dimensions Special lines/symbols/notations Tolerances Title block Bill of materials Other notes/labels Shanghai Jiao Tong University

Shanghai Jiao Tong University Working Drawing Shanghai Jiao Tong University

Shanghai Jiao Tong University Dimensioning Dimension is used to specify the object size and its location. Specify the exact theoretically values for the size,orientation and location of features. Shanghai Jiao Tong University

Shanghai Jiao Tong University Principles Show every necessary dimension. Never repeat a dimension. Locate dimensions that are linked to one another with respect to the same datum. If possible, avoid crossing two dimension lines. Arrange a series of dimensions in a continuous line. Place longer dimensions outside shorter ones so that extension lines will not cross dimension lines. Place dimensioning information outside the orthographic views if possible. Leaders note dimensions and information. Fillet are dimensioned with leaders or by an appropriate note. Shanghai Jiao Tong University

Shanghai Jiao Tong University Principles Shanghai Jiao Tong University

Shanghai Jiao Tong University Standards Extension Lines Dimension Lines Dimension Shanghai Jiao Tong University

Shanghai Jiao Tong University Threads Threads are specified by giving the nominal diameter and threads per inch. ANSI: ½-13UNC; ½-13UNF Metric: M8x1.25 Shanghai Jiao Tong University

Shanghai Jiao Tong University Schematic Symbols Shanghai Jiao Tong University

Shanghai Jiao Tong University Simplified symbols Shanghai Jiao Tong University

Shanghai Jiao Tong University Chamfer Shanghai Jiao Tong University

Shanghai Jiao Tong University Counterbore Shanghai Jiao Tong University

Shanghai Jiao Tong University Countersink Shanghai Jiao Tong University

Shanghai Jiao Tong University Title Block Shanghai Jiao Tong University

Shanghai Jiao Tong University Bill of Material Shanghai Jiao Tong University

Shanghai Jiao Tong University GD & T Dimensional tolerance is defined as the permissible or acceptable variation in the dimension (height, width, length, angle, etc.) of a part. Shanghai Jiao Tong University

Shanghai Jiao Tong University GD & T Why do we need the tolerance? Increasingly exact dimensions Interchangeable Manufacturing costs increase as tolerances become smaller A tolerance should be as lager as possible without interfering with the function of the part to minimize production costs. Shanghai Jiao Tong University

Shanghai Jiao Tong University GD & T In the U.S. GD&T standards are evaluated, updated and published by the sub-group Y14.5 of the American National Standards Institute (ANSI). Shanghai Jiao Tong University

Shanghai Jiao Tong University GD & T Per ANSI Y14.5 standard symbols are: used to define part features and tolerances on drawings. interpreted in a consistent way for manufacturing. Shanghai Jiao Tong University

Shanghai Jiao Tong University Definitions Feature is a general term applied to a physical portion of a part, e.g., a surface, hole, slot, etc. Feature-of-size is one cylindrical or spherical surface, or a set of parallel surfaces, each of which is associated with a size dimension. Shanghai Jiao Tong University

Shanghai Jiao Tong University Definitions Location dimension is a dimension which locates the centerline or centerplane of a part feature relative to another part feature, centerline or centerplane . Shanghai Jiao Tong University

Shanghai Jiao Tong University Definitions Shanghai Jiao Tong University

Shanghai Jiao Tong University Definitions Maximum Material Condition(MMC): When a feature-of-size contains the most amount of material it is said to be in its MMC. Shanghai Jiao Tong University

Shanghai Jiao Tong University Definitions Least Material Condition(LMC): When a feature-of-size contains the minimum amount of material it is said to be in its LMC. Shanghai Jiao Tong University

Shanghai Jiao Tong University Definitions An external feature-of-size is at MMC when it is at its largest size limit. An external feature-of-size is at LMC when it is at its smallest size limit. Shanghai Jiao Tong University

Shanghai Jiao Tong University Definitions An internal feature-of-size is at MMC when it is at its smallest size limit. An internal feature-of-size is at LMC when it is at its largest size limit. Shanghai Jiao Tong University

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

Shanghai Jiao Tong University Terminology Basic size: the exact theoretical size Actual size: the measured size of the finished part Tolerance: the difference between the limits prescribed for a single feature Limits of tolerance: the extreme measurements permitted by the maximum and minimum sizes of a feature Shanghai Jiao Tong University

Shanghai Jiao Tong University Fits Fit: the tightness between two assembled mating parts Clearance fit: the clearance between two assembled mating parts Interference fit: results in an interference between two assembled mating parts Transition fit: may result in either an interference or a clearance between two assembled mating parts Shanghai Jiao Tong University

Shanghai Jiao Tong University Fits Shanghai Jiao Tong University

Shanghai Jiao Tong University Datums A theoretically exact point, line, axis, or plane which indicates the origin of a specified dimensional relationship between a toleranced feature and a designated feature on a part. Datum feature is a part feature which contacts or is used establish a datum. Shanghai Jiao Tong University

Shanghai Jiao Tong University Datums Datums are used to locate a part in a repeatable manner for checking geometric tolerances. Shanghai Jiao Tong University

Shanghai Jiao Tong University Datums Shanghai Jiao Tong University

Shanghai Jiao Tong University Datums Shanghai Jiao Tong University

Shanghai Jiao Tong University Datums Shanghai Jiao Tong University

Five categories of ANSI symbols Shanghai Jiao Tong University

Shanghai Jiao Tong University Form Controls Flatness Straightness Circularity Cylindricity Does not use any datum surface Shanghai Jiao Tong University

Shanghai Jiao Tong University Straightness Shanghai Jiao Tong University

Shanghai Jiao Tong University Form Controls Each element of the feature controlled must lie between the stated tolerance zone. Additionally, each element of the feature must be within the specified limits of size. Shanghai Jiao Tong University

Shanghai Jiao Tong University Flatness Shanghai Jiao Tong University

Shanghai Jiao Tong University Circularity Shanghai Jiao Tong University

Shanghai Jiao Tong University Cylindricity Shanghai Jiao Tong University