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MFGT 124Solid Design in ManufacturingGD&T : 

Copyright 2003 Joseph Greene All Rights Reserved 1 MFGT 124Solid Design in ManufacturingGD&T

GD&T : 

Copyright 2003 Joseph Greene All Rights Reserved 2 GD&T Topics Introduction History Feature Control Frames Material Condition Modifiers Form Tolerances Datums Orientation Tolerances Runout Profiles Position Tolerances Applications

GD&T vs. Coordinate Measuring : 

Copyright 2003 Joseph Greene All Rights Reserved 3 GD&T vs. Coordinate Measuring What is a quality drawing? Compare two drawing styles Figure 1. GD&T example. Figure 2. Coordinate dimensioning example of same part. Part straightness Both drawings specify a part thickness of 0.25 inches +-0.010”. How straight must the part be? Fig 1 has GD&T straightness symbol applied to thickness (Area A) Symbol on part means that the part must be straight enough to pass between two parallel plates spaced 0.260” Fig 2 has coordinate version says nothing about straightness. Part could be within thickness tolerance, yet significantly bowed . Note needs to be added to drawing to require straightness.

GD&T vs. Coordinate Measuring : 

Copyright 2003 Joseph Greene All Rights Reserved 4 GD&T vs. Coordinate Measuring What is a quality drawing (continued) Unwanted tolerance accumulation Fig 1 includes several dimensions (B) called basic dimensions which identify exact locations from which tolerances are specified. Fig 2 has no corresponding term and tolerances can accumulate. Another note needs to be added “Dimensions are gage dimensions. Part inspection Figure 3. Different inspection points and procedures can lead to different measurements. GD&T establishes an order of measurement sequence. Coordinate measuring does not. Two inspectors can get totally different results from same part. GD&T system Specifies measurement sequence. Parts intended to contact gage are datums. (C Fig 1) Geometric tolerance controlling hole locations defines the sequence in which part surfaces must touch the gage surfaces. (D) Reading from left side of positional tolerance callout, the letter sequence lists the order in which the part touches the gage. A, B, C Coordinate measuring system has no equivalent system and as such requires a note.

GD&T vs. Coordinate Measuring : 

Copyright 2003 Joseph Greene All Rights Reserved 5 GD&T vs. Coordinate Measuring What is a quality drawing (continued) Hole location GD&T system (D) contains a symbol (circle with slant in it) that denotes the shape of the tolerance zone as a diameter. Same geometric tolerance includes a circled M symbol (Maximum material condition) that permits the location tolerance to increase for larger holes. Coordinate measuring system show two ways in which is inadequate: Uses square tolerance zones, Fig 4, which allow more tolerance for hole centers diagonally than vertically or horizontally. Round tolerance zone is better. Requires tolerance zone for hole location to remain fixed in size, regardless of hole size. Small holes have same tolerance zones as larger diameters. Notes have to be added for round tolerance.

GD&T vs. Coordinate Measuring : 

Copyright 2003 Joseph Greene All Rights Reserved 6 GD&T vs. Coordinate Measuring What is a quality drawing (continued) Counterbore location GD&T specifies counterbore diameter, depth, and location. Includes position symbol under counterbore, E. Specifies location relative to small diameter Coordinate version only specifies bore diameter and depth, allowing user to choose between Following smaller diameter location, or Locating by tolerance dimension for both diameters. Note must be added to ensure proper location. Equivalent information on Coordinate Measuring drawing Fig 6

GD&T Standards : 

Copyright 2003 Joseph Greene All Rights Reserved 7 GD&T Standards ANSI Y14.5 The ANSI standard was revised in 1982. In 1994, the standard was moved form ANSI to the American Society of Mechanical Engineers (ASME) and the name changed to ASME Y14.5. The standard was also revised into its current form of ASME Y14.5-1994. Geometric Dimensioning and Tolerancing (GD&T) Establishes the standard by which designers can communicate the intended function of the part to the machinist making the part and the inspector checking the part. This standard lets the designer inform the machinist, toolmaker or fabricator what are the important features of the design when they are making the part. The standard also lets the inspector know what are the important features to inspect form. GD&T uses symbols to communicate the information to those involved in making the part to eliminate any misunderstanding. Word explanations can be confusing especially with the global market and the translations of words into different languages. A simple layout of the symbols used in GD&T can be found in below.

GD&T Definitions and Terms : 

Copyright 2003 Joseph Greene All Rights Reserved 8 GD&T Definitions and Terms Feature Control Frames Geometric Tolerance Geometric Characteristic Symbol The feature control frame helps to organize the various symbols into a sentence. This sentence communicates the information in an organized manner. The first is the Geometric Tolerance is the total tolerance band for that feature. This means that it is not a +/- tolerance. An example of this is if we have a dimension of 1.00 and a Geometric tolerance of .005, we can interpret this as 1.000 +/-.0025. Figure 3a-1 Simple Feature Control Frame Geometric Characteristic Symbol Geometric Tolerance

GD&T Material Condition Modifiers : 

Copyright 2003 Joseph Greene All Rights Reserved 9 GD&T Material Condition Modifiers Material Condition Modifiers Indicate at what material condition the tolerance is applicable. There are three different types of material condition modifiers Regardless of Feature Size (RFS) Used if the tolerance is to be met at all possible sizes of the feature to be produced. In the current standard, this is assumed if one of the other modifiers is not specified. In the older standards, the symbol ? was placed in the feature control frame to designate the RFS condition.

GD&T Material Condition Modifiers : 

Copyright 2003 Joseph Greene All Rights Reserved 10 GD&T Material Condition Modifiers Maximum Material Condition (MMC) External Indicates that the tolerance given applies only at the maximum amount of material for that feature. For holes, it is the smallest diameter-Max material The key words in this modifier are maximum material. When working with external features the MMC is at the largest limit or maximum amount of material, as shown in Figure 3b.ii.1. Maximum Material Condition (MMC)- Internal When working with internal features the MMC is at the smallest limit, or maximum amount of material, as shown in Figure 3b.ii.2. The feature control from the symbol o represents MMC

GD&T Material Condition Modifiers : 

Copyright 2003 Joseph Greene All Rights Reserved 11 GD&T Material Condition Modifiers Least Material Condition (LMC) External Indicates that the tolerance given applies only at the least amount of material for that feature. For diameters, it is the smallest diameter. For holes, it is the biggest diameter-Min material When working with external features the LMC is at the largest limit or least amount of material, as shown below. Least Material Condition (LMC) Internal LMC is at the smallest limit, or least amount of material, as shown The feature control from the symbol ? represents LMC

GD&T Form Tolerances : 

Copyright 2003 Joseph Greene All Rights Reserved 12 GD&T Form Tolerances Form tolerances The control the variations of individual features of a part. Such features include straightness, flatness, circularity and Cylindricity. Form tolerances do not control the relationship between features. Straightness The straightness tolerance controls all the elements along a theoretical straight line on a surface or axis. The tolerance given for straightness specifics how close to perfectly straight the feature must be created. Depending on the way straightness is defined on the drawing, determines whether surface elements or an axis is to be controlled. The symbol for straightness is ?

GD&T Straightness : 

Copyright 2003 Joseph Greene All Rights Reserved 13 GD&T Straightness Straightness Note that straightness is applied only to the view that it is defined on a drawing The placement of the feature control frame is very important.

GD&T Flatness : 

Copyright 2003 Joseph Greene All Rights Reserved 14 GD&T Flatness Flatness A perfectly flat surface must contain all elements in one plane. The flatness tolerance establishes a set of parallel planes that must contain all elements of the surface. The flatness tolerance is not used in conjunction with a material modifier or datum reference it is a stand-alone tolerance. The symbol for flatness is ?. Example, gives the different representations of how flatness tolerance is used in conjunction with a feature control frame.

GD&T Circularity : 

Copyright 2003 Joseph Greene All Rights Reserved 15 GD&T Circularity Circularity Controls the roundness of any feature with circular cross section. The circular cross-section must be taken perpendicular to the axis of the cylinder or cone, or through a common center of a sphere. Circularity tolerance is also referred to as the roundness tolerance. The symbol for Circularity is c. The tolerance zone for a circularity tolerance is bounded by two concentric circles. The tolerance value is determined by the radial distance between the circles, not the distance between the diameters. Example gives a typical call-out for circularity tolerance.

GD&T Cylindricity : 

Copyright 2003 Joseph Greene All Rights Reserved 16 GD&T Cylindricity Cylindricity Controls the surface of a cylinder. This tolerance can be applied to a shaft or a hole. Cylindricity is identified by a radial tolerance zone that establishes two perfectly concentric cylinders. The surface of the cylinder that the tolerance is applied to must lie within this tolerance zone. The cylindricity tolerance also controls the parallelism of the sides of the cylinder to prevent the part form being tapered. Example gives a typical call-out for cylindricity tolerance.

GD&T Datums : 

Copyright 2003 Joseph Greene All Rights Reserved 17 GD&T Datums Datums Theoretically perfect planes, surfaces, points, lines or axes that are derived form a datum feature. Datums are used by designers to specify important features of reference by which toolmakers and machinists create the part and inspectors check the part to the print. Datum features are actual features of the part, such as a surface, that establish the datum. The feature control frames that define tolerances based on datum features include datum references. Datums are used to establish an inspection point from a surface. Checking jigs and fixtures are built based upon datums to inspect parts.

GD&T Datum Identification : 

Copyright 2003 Joseph Greene All Rights Reserved 18 GD&T Datum Identification Datum Identification A datum feature is identified by using the datum symbol combined with a datum feature triangle. A datum target symbol is a circle with a horizontal line across it, with the bottom half of the circle used to identify the datum target and the top is empty except when specifying the diameter of a datum target area.

GD&T Orientation Tolerances : 

Copyright 2003 Joseph Greene All Rights Reserved 19 GD&T Orientation Tolerances Orientation tolerances Control the relationship of features to one another. Orientation tolerances include parallelism, perpendicularity and angularity. Orientation tolerances are datum related and may be applied with material modifiers MMC or LMC. RFS material modifier is always implied unless otherwise stated. Parallelism Defined as two parallel planes of cylindrical zones that are parallel to a datum plane where the surface or axis of the feature must lie. The symbol for parallelism is ? Parallelism Tolerance Feature Control Frame

GD&T Parallelism : 

Copyright 2003 Joseph Greene All Rights Reserved 20 GD&T Parallelism Parallelism There are three main types of parallelism call-outs, surface, axis and line. When a surface is to be parallel to a datum, the feature control frame is either connected by a leader to the surface or directly connected to the extension line of the dimension.

GD&T Parallelism : 

Copyright 2003 Joseph Greene All Rights Reserved 21 GD&T Parallelism Parallelism When parallelism is applied to an axis the axis of the hole may be specified within a tolerance zone that is parallel to a given datum. The feature control frame is place with the diameter dimension Parallelism to line elements. When it is desirable to control only individual line elements, rather than the entire surface, the note “EACH ELEMENT” or “EACH RADIAL ELEMENT” Parallelism Applied to Line Elements

GD&T Perpendicularity : 

Copyright 2003 Joseph Greene All Rights Reserved 22 GD&T Perpendicularity Perpendicular geometric tolerance Two parallel planes of cylindrical zones that are a basic 90? to a datum plane where the surface or axis of the feature must lie. The symbol for perpendicularity is ?

GD&T Perpendicularity : 

Copyright 2003 Joseph Greene All Rights Reserved 23 GD&T Perpendicularity The examples below give different applications of perpendicularity geometric tolerance. Figure 1 is the application of perpendicularity to a surface. Figure 2 is the application of perpendicularity to an axis. Figure 3 is the application of perpendicularity to a center plane. Figure 4 is the application of perpendicularity of line elements. Perpendicularity to an Axis Perpendicularity to Line Elements

GD&T Angularity : 

Copyright 2003 Joseph Greene All Rights Reserved 24 GD&T Angularity Angularity geometric tolerance A surface, center-plane or axis at a specified angle (other than 90?) form a datum plane or axis. The symbol for angularity is ? Figure 1 the application of angularity to a surface. Figure 2 is the application of angularity to an axis. Figure 3 is the application of angularity to a center plane. Angularity to a Center Plane Angularity to a Surface Angularity to an Axis

GD&T Runout Tolerances : 

Copyright 2003 Joseph Greene All Rights Reserved 25 GD&T Runout Tolerances Runout Combination of geometric tolerances used to control the relationship of one or more features of a part to a datum axis. The geometric tolerances associated with Runout Form, Orientation and Location tolerances. The features that may be controlled by Runout are surfaces around, or perpendicular to, a datum axis. There are two types of Runout error, Circular Runout and Total-Runout. Of these two types of Runout, Circular Runout is the less complex.

GD&T Circular Runout : 

Copyright 2003 Joseph Greene All Rights Reserved 26 GD&T Circular Runout Circular runout Is the error on a single circular element and provides the control of these elements on a surface. The surface must have circular cross sections that are controlled relative to an axis of rotation. Typical surfaces that are controlled by circular runout include cylinders, cones, spherical surfaces and flat surfaces. The symbol for circular runout is ?. Circular Runout Tolerance Feature Control Frame

GD&T Circular Runout : 

Copyright 2003 Joseph Greene All Rights Reserved 27 GD&T Circular Runout Circular runout The following three examples give some of the different applications of circular runout. Figure 1 gives the application of circular runout as applied to a cylindrical surface. Figure 2 gives the application of circular runout as applied to a non-cylindrical feature. Figure 3 gives the application of circular runout as applied to face surfaces.

GD&T Total Runout : 

Copyright 2003 Joseph Greene All Rights Reserved 28 GD&T Total Runout Total runout Is the variation across the entire surface of a cylindrical feature or perpendicular face surface. Total runout is used to control the combined variations of circularity, straightness, coaxiality, angularity, taper and profile when applied to surfaces around and at right angles to a datum axis. The symbol for total runout is ?.

GD&T Total Runout : 

Copyright 2003 Joseph Greene All Rights Reserved 29 GD&T Total Runout Total runout Note that total runout cannot be applied to conical or curved surfaces as can circular runout. The following two examples give some of the different applications of total runout. Figure 1 gives the application of total runout as applied to a cylinder. The total runout feature control frame, in this figure, references a compound datum of A and B. When checking the feature that references a compound datum both datum’s A and B must be used together to establish an axis of rotation. Figure 2 gives the application of total runout as applied to face surfaces. Total Runout Applied to a Cylinder with Compound Datum Total Runout Applied to a Face Surface

GD&T Profile Tolerances : 

Copyright 2003 Joseph Greene All Rights Reserved 30 GD&T Profile Tolerances Profile tolerance The outline of an object represented either by an external view or by a cross section through the object. Profile tolerances may be used to control form, orientation and location. The manner in which the profile tolerance is applied, How it is dimensioned, and How datum’s are utilized all effect the level of control desired by using profile tolerances. There are two profile tolerance types, Profile of a line and profile of a surface. Note: when the profile is other than flat, basic dimensions must be used to describe the profile. A basic dimension is depicted with a box around the dimension and is considered an exact dimension

GD&T Profile Tolerances : 

Copyright 2003 Joseph Greene All Rights Reserved 31 GD&T Profile Tolerances Profile of a Line A two-dimensional cross section tolerance that extends along the length of the feature. The line profile tolerance is used where parts have changing cross section along their length and do not have to be along the entire feature. The symbol for profile of a line is e. Figure shows the feature control frame for profile of a line geometric tolerance. Profile of a Line Feature Control Frame

GD&T Profile Tolerances : 

Copyright 2003 Joseph Greene All Rights Reserved 32 GD&T Profile Tolerances Profile of a Line Many automobile companies use an exact profile to gage sheet metal parts that have changing cross sections. The hood of an automobile is a good example of such a cross section that has a changing profile. The profile tolerance is assumed a bilateral tolerance, which is the tolerance both above and below the true profile line. The following examples give usage of the profile of a line tolerance. Figure. Cross section of a simple contour that is controlled by line profile tolerance. Figure 2. Uses profile of a line to control all around a cross section of a wing. Figure 3 is a special case of using profile of a line for a unilateral specification.

GD&T Profile Tolerances : 

Copyright 2003 Joseph Greene All Rights Reserved 33 GD&T Profile Tolerances Profile of a Surface Used to control all the elements of a surface and treats them as a single entity. Profile of a surface, as its definition states, covers all points on a surface in three dimensions. The symbol for profile of a surface is f. Figure shows the feature control frame for profile of a line geometric tolerance. Profile of a Surface Feature Control Frame

GD&T Profile Tolerances : 

Copyright 2003 Joseph Greene All Rights Reserved 34 GD&T Profile Tolerances Profile of a Surface As with profile of a line, profile of surface can be measured with a mater gage to control features of the surface or profile. The following examples give usage of the profile of a surface tolerance. Figure 1 is a cross section of a plate with a slot. The slot is controlled by a profile of a surface tolerance. That means that the depth of the slot as well as it’s cross sectional profile is controlled. Figure 2 uses profile of a surface to control the surface of a part similar to that seen in figure 3g.i.2.

GD&T Positional Tolerances : 

Copyright 2003 Joseph Greene All Rights Reserved 35 GD&T Positional Tolerances Position tolerances Locate features from datum’s or for establishing coaxiality or symmetry. Positional tolerances define A zone where the center, axis or center plane of a feature of size is permitted to vary form true position. The true position is the theoretically exact position of the feature. Basic dimensions are used to establish the location of the feature in relationship to datum features. When using positional tolerances MMC and LMC must be specified in the feature control frame after the tolerance otherwise RFS is assumed. Positional tolerances are also applied only to features of size; they are not applied to features of form. The format for the positional feature control frame is given below. Position Tolerancing Feature Control Frame

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