GEOMETRIC DIMENSIONING AND TOLERANCINGCoordinate vs Geometric Tolerancing Methods 8.5 +/- 0.1 Rectangular Tolerance Zone 10.25 +/- 0.5 B 10.25 A 8.5 +/- 0.1 1.4 A B C Circular Tolerance Zone 10.25 10.25 +/- 0.5 C Coordinate Dimensioning +/- 0.5 Geometric Dimensioning 1.4 +/- 0.5 Rectangular Tolerance Zone Circular Tolerance Zone Circular Tolerance Zone 57% Larger Tolerance Zone Rectangular Tolerance Zone Increased Effective Tolerance PURPOSE OF GD&T ► ► ► TO AVOID SCRAPPING PERFECTLY GOOD PARTS. THE PARTS SHOULD PROPERLY FIT AND FUNCTION EVERY TIME. THE LARGEST AMOUNT OF TOLERANCE SHOULD BE AVAILABLE TO THE MANUFACTURER FOR PRODUCING THE PART AT MINIMUM COST, YET THE PART SHOULD BE FUNCTIONALLY ACCEPTABLE. GD & T COMMON SYMBOLS . GD & T COMMON SYMBOLS . COMPONENTS OF FEATURE CONTROL FRAME . Title block tolerances do not apply to basic dimensions. or plane derived from the true geometric counterpart of a specified datum feature. The tolerance associated with a basic dimension usually appears in a feature control frame or a note. ► Datum feature: A datum feature is an actual feature on a part used to establish a datum. profile. . A datum is the origin from which the location or geometric characteristics of features of a part are established. ► Datum: A datum is a theoretically exact point. or location of a feature or datum target.Terms in GD&T ► Basic dimension: A basic dimension is a numerical value used to describe the theoretically exact size. Basic dimensions are used to define or position tolerance zones. orientation. line. Tolerance zones are located at true position. ► Feature of size (also Size Feature and Feature Subject to Size Variations): Features of size are features that have a size dimension. hole. A feature of size takes four forms: Cylindrical surfaces Two opposed parallel surfaces A spherical surface Two opposed elements Cylindrical surfaces and two opposed parallel surfaces are the most common features of size. . or slot. tab. such as a flat surface.► Feature: A feature is a physical portion of a part. ► True position: True position is the theoretically exact location of a feature established by basic dimensions. pin. Material Conditions Regardless of feature size ► Maximum material condition ► Least material condition ► . RFS specifies that no bonus tolerance is allowed. the minimum shaft diameter or the maximum hole diameter. For example. the maximum shaft diameter or the minimum hole diameter Least material condition (LMC): ► The least material condition of a feature of size is the least amount of material within the stated limits of size. .Maximum Material Condition (MMC) ► The maximum material condition of a feature of size is the maximum amount of material within the stated limits of size. for example. Regardless of feature size (RFS): ► Regardless of feature size is a material condition modifier used in a feature control frame to indicate that a geometric tolerance or datum reference applies at each increment of size of the feature within its limits of size. 3-2-1 Principle A part always have Six degree of freedom (3 translational + 3 rotational) As per 3-2-1 principle . secondary datum should have 2 degree of freedom and tertiary only 1. . primary datum should have 3 degree of freedom . the limits of size of an individual feature of size prescribe the extent to which variations in its geometric form.RULES OF GD&T There are four rules that apply to drawings in general. Rule #3 The pitch diameter rule ► ► Each tolerance of orientation or position and datum reference specified for screw threads applies to the axis of the thread derived from the pitch diameter. MMC and LMC must be specified when these conditions are required. such as MAJOR DIA or MINOR DIA. and to GD&T in particular. ► Rule #1 states that where only a tolerance of size is specified. Rule #2 states that RFS automatically applies. to individual tolerances of size features and to datum features of size. the datum feature symbol. beneath the feature control frame. the datum applies at virtual condition with respect to orientation. . Exceptions to this rule may be specified by placing a note. ► Rule #4 The virtual condition rule Where a datum feature of size is controlled by a geometric tolerance and that datum is specified as a secondary or tertiary datum. or beneath or adjacent to. in a feature control frame. are allowed. as well as its size. . Bonus plus Geometric Tolerance equals Total Positional Tolerance.Bonus Tolerance ► ► Bonus equals the difference between the Actual Feature Size and MMC. Features specified with an LMC modifier also have a virtual condition.Virtual condition The virtual condition of a feature specified at MMC is a constant boundary generated by the collective effects of the MMC limit of size of a feature and the specified geometric tolerance. Virtual condition calculations: External Features (Pin) MMC Plus Geometric Tolerance @ MMC Internal Features (Hole) MMC Minus Geometric Tolerance @ MMC . 1) (ASME Y14.4.5M-1994. 6.4.4) .5M-1994.4.5M-1994. 6.4.5M-1994.Tolerances of Form Straightness Flatness (ASME Y14.3) (ASME Y14. 6.2) Circularity Cylindricity (ASME Y14. 6. 1 25 +/-0.25 0.5 0.5 Tolerance Straightness is the condition where an element of a surface or an axis is a straight line .1 Tolerance 0.Straightness 0. 75 min 0.0. All points on the surface must lie within the limits of size and the applicable straightness limit.5 Tolerance Zone 25.1 Tolerance Zone In this example each line element of the surface must lie within a tolerance zone defined by two parallel lines separated by the specified tolerance value applied to each view. The straightness tolerance is applied in the view where the elements to be controlled are represented by a straight line .25 max 24. 1 Tolerance Zone 0.75 min 25. The flatness tolerance must be less than the size tolerance.1 Tolerance Zone 24.1 25 +/-0. Flatness must fall within the limits of size. All points on the surface must lie within the limits of size and the flatness limit.25 max In this example the entire surface must lie within a tolerance zone defined by two parallel planes separated by the specified tolerance value. Flatness is the condition of a surface having all elements in one plane.Flatness 0. .25 0. 1 9 0 9 0 0.1 0.Circularity (Roundness) 0. Circularity is the condition of a surface where all points of the surface intersected by any plane perpendicular to a common axis are equidistant from that axis. The circularity tolerance must be less than the size tolerance .1 Wide Tolerance Zone In this example each circular element of the surface must lie within a tolerance zone defined by two concentric circles separated by the specified tolerance value. All points on the surface must lie within the limits of size and the circularity limit. Cylindricity is a composite control of form which includes circularity (roundness).Cylindricity 0. straightness.1 Tolerance Zone MMC In this example the entire surface must lie within a tolerance zone defined by two concentric cylinders separated by the specified tolerance value. and taper of a cylindrical feature. . All points on the surface must lie within the limits of size and the cylindricity limit.1 0. Cylindricity is the condition of a surface of revolution in which all points are equidistant from a common axis. 6. 6.6.4) Parallelism (ASME Y14.5M-1994 .4) .6.6.2) Perpendicularity (ASME Y14.5M-1994 .Tolerances of Orientation Angularity (ASME Y14.6.5M-1994. Angularity is the condition of the planar feature surface at a specified angle (other than 90 degrees) to the datum reference plane.3 A 30 o A 19.3 Wide Tolerance Zone A 0.5 min 20.5 max 30 o 30 o A 0.5 0. .Angularity (Feature Surface to Datum Surface) 20 +/-0.3 Wide Tolerance Zone The tolerance zone in this example is defined by two parallel planes oriented at the specified angle to the datum reference plane. within the specified tolerance zone. 3 A A 0.Perpendicularity (Feature Surface to Datum Surface) 0.3 Wide Tolerance Zone A A The tolerance zone in this example is defined by two parallel planes oriented perpendicular to the datum reference plane. within the specified tolerance zone.3 Wide Tolerance Zone 0. . Perpendicularity is the condition of the planar feature surface at a right angle to the datum reference plane. 3 Wide Tolerance Zone 0.5 min A A The tolerance zone in this example is defined by two parallel planes oriented parallel to the datum reference plane.Parallelism 0. within the specified tolerance zone.5 A 0.3 A (Feature Surface to Datum Surface) 25 +/-0. .5 max 24. Parallelism is the condition of the planar feature surface equidistant at all points from the datum reference plane.3 Wide Tolerance Zone 25. 7.1.Tolerances of Runout Circular Runout (ASME Y14.6.5M-1994 .1.2) .7.2.2.2) Total Runout (ASME Y14.5M-1994 .6. . With circular runout. angularity. and rotating the part about its central axis while measuring with a dial indicator its surface deviation from perfect roundness. coaxiality.Circular Runout Runout refers to the result of placing a solid of revolution on a spindle such as a lathe. and profile. taper. Total Runout Total runout involves moving the dial indicator along the length of the part while the part is rotated. cylindricity. Circular runout is therefore applied independently at each station along the length of the part as the part is rotated through 360 degrees. the dial indicator is not moved along the direction of the axis of the part. straightness. so that it controls the cumulative variations of circularity. 13) .12) Symmetry (ASME Y14.5M-1994.5M-1994. 5.5M-1994. 5.Tolerances of Location True Position (ASME Y14.2) Concentricity (ASME Y14. 5. 5.2) True Position Means This . or center plane of the feature may vary from true position (ASME Y14. axis.True Position A theoretical tolerance zone located at true position of the toleranced feature within which the center point.5M-1994. 05 15.5 Coaxial Tolerance Zone Derived Median Points of Diametrically Opposed Elements Within the limits of size and regardless of feature size.90 As Shown on Drawing Axis of Datum Feature A 0.35 +/. .5 A 6. The axis of the tolerance zone coincides with the axis of datum feature A. Concentricity can only be applied on an RFS basis.5 cylindrical tolerance zone.0.Location (Concentricity) Datum Features at RFS A 0.95 15. all median points of diametrically opposed elements must lie within a 0. 5 apart. all median points of opposed elements must lie between two parallel planes equally disposed about datum plane A. 0.5 A A 15.90 As Shown on Drawing Center Plane of Datum Feature A 0.0.35 +/.05 0.Location (Symmetry) Datum Features at RFS 6. Symmetry can only be applied on an RFS basis.95 15. .5 Wide Tolerance Zone Derived Median Points Within the limits of size and regardless of feature size. 5M-1994. 6. 6.5M-1994.2b) Profile of a Surface (ASME Y14.5.2a) .5.Tolerances of Profile Profile of a Line (ASME Y14. .Profile of a Line The profile of a line tolerance is a two-dimensional or cross-sectional geometric tolerance that extends along the length of the feature. .Profile of a Surface A profile of a surface tolerance is used where it is desired to control the entire surface as a single feature. THANK YOU .