2 ObjectivesDescribe the purpose of conventional tolerancing and its limitationsUse standard tables to specify an appropriate fit between two mating partsExplain the advantages of using geometric dimensioning and tolerancing (GD&T) over conventional tolerancing
3 Objectives (cont’d.)Recognize the datum reference frame on a drawing with geometric dimensions and tolerancesDescribe the tolerance zone shape for each geometric toleranceCorrectly read the feature control frames on a drawing with geometric dimensions and tolerances
4 Introduction Relationships between different parts Necessary to specify intended fit between partsProblems with inexperience in new engineersLack of knowledge in history, materialsInappropriate tolerance values
5 Formats for Tolerances Displayed in several common formatsFIGURE Formats for tolerance dimensioning in millimeters and inches.
6 Tolerance Buildup Problems Can be minimized depending on type of dimensioningChain: yields largest tolerance buildupBaseline: can eliminate some accumulationDirect: best way to eliminate tolerance accumulationSingle dimension placed between two key points
7 Statistical Tolerance Control Based on sound statistical practicesCan be applied only when appropriate statistical process control methods usedFIGURE Tolerancing with statistical process control.
8 Use of Tables for Fits Types of fits FIGURE Specifying a CLEARANCE FIT withlimit dimensioning.FIGURE Specifying an INTERFERENCE FIT with limit dimensioningFIGURE Specifying a TRANSITION FIT with limit dimensioning.
9 Fit Terminology FIGURE 16.11. Clearance fit terminology. FIGURE Interference fit terminology.
10 English Fits Running or sliding clearance Locational clearance Locational transitionLocational interference (see next slide)Force or shrink (see next slide)
11 English Fits (cont’d.)FIGURE Locational interference and force fits.
13 Fits TablesTo specify an inch fit between holes and shafts from a standard tableDetermine type of fit appropriate for the design and locate corresponding tableDetermine basic size of the partsFind size range on the tableDetermine tolerances for hole and shaftRemember that values on the English tables are in thousandths of an inch
14 Fits Tables (cont’d.)FIGURE A close sliding fit.
15 Fits Tables (cont’d.) To determine metric fits Determine type of fit appropriate for the design and locate corresponding tableDetermine basic size of the partsFind the size range on the tableDetermine the tolerances for the hole and the shaft
16 Conventional Tolerancing versus Geometric Tolerancing Feature with sizeCylindrical or spherical surface or set of two opposed elements or opposed parallel surfaces associated with size dimensionFeature without sizePlanar surface or a feature where the normal vectors point in the same direction
17 Conventional Tolerancing versus Geometric Tolerancing (cont’d.) FIGURE Conventional tolerance dimensioning of a block.
18 Conventional Tolerancing versus Geometric Tolerancing (cont’d.) FIGURE How conventional tolerancing controls surfaces.
19 Location of Holes and Pins with Conventional Tolerancing FIGURE Square tolerance zones from conventional tolerancing.
20 Geometric Dimensioning and Tolerancing (GD&T) GD&T is a 3-D mathematical system for describing the form, orientation, and location of features on a part within precise tolerance zonesBetter communication throughout design processAlmost nothing can be interpreted in more than one way
21 The Datum Reference Frame FIGURE Components of the theoretical datum system.
22 The Datum Reference Frame (cont’d.) FIGURE Datum terminology.
23 Geometry Characteristic Symbols and Feature Control Frames FIGURE Geometric characteristic symbols.
24 Geometry Characteristic Symbols and Feature Control Frames (cont’d.) Contains geometric characteristic symbol, the geometric tolerance, and the relative datumsFIGURE A featurecontrol frame with theperpendicularity tolerance.FIGURE A feature control frame with the position tolerance.
25 Order of Precedence for Datums FIGURE The sequence of datum features
26 Position Tolerances versus Conventional Tolerances FIGURE Geometric dimensioning and tolerancing of the PLATE.
27 Position Tolerances versus Conventional Tolerances (cont’d.) Basic dimensionsTheoretically exactMaximum material condition modifierSize of zone changes if size of hole changesSquare vs. cylindrical tolerance zonesFIGURE Cylindrical tolerance zones for the position tolerance.
28 Form Tolerances For individual features and not related to datums StraightnessFlatnessCircularityCylindricity
30 Profile Tolerances (cont’d.) Profile of a surfaceInspection of profile tolerancesOptical comparitorsOverlay chartsMechanical gagingUsed when datum reference frame applied
31 Orientation Tolerances Parallelism toleranceCan be used to control a surfaceFIGURE Parallelism tolerance used to control a surface.
32 Orientation Tolerances (cont’d.) PerpendicularityAngularityFIGURE Inspecting the angularity between two surfaces.
33 Location Tolerances Position Can be used to locate axis of a hole FIGURE Using the position tolerance to locate the axis of a hole.
34 Location Tolerances (cont’d.) ConcentricityApplied to cylinderSymmetryFIGURE Concentricity applied to a cylinder.
35 Runout Tolerances Circular runout Total runout Multiple datums Tolerances applied based on function, so careful specification of datums is necessary
36 Examples of Specifying Fits and Geometric Tolerances Specifying the fit between two partsFIGURE Coupling assembly.
37 Examples of Specifying Fits and Geometric Tolerances (cont’d.) FIGURE Limit dimensions for the STUD andBUSHING.
38 Adding Geometric Dimensions FIGURE PLATE ASSEMBLY.FIGURE Establishing the datums on the PLATE.
39 FIGURE 16.104. Controlling the datums on the PLATE.
40 FIGURE 16.105. Positioning the hole on the PLATE.
41 FIGURE 16.106. Controlling the other surfaces on the PLATE.
42 SummaryCovered basic information related to conventional tolerancing and GD&TDiscussed interchangeable manufacturing and explained why it is important to the way modern industry functions
43 Summary (cont’d.)Discussed conventional tolerancing, including how to specify fits and how tolerance dimensions control form and locationCovered the basics of geometric dimensioning and tolerancing
44 Summary (cont’d.)Discussed the advantages of geometric tolerancing over conventional tolerancingExplained the importance of the datum reference frame to establish a coordinate system for design manufacturing and inspectionExplained how to read feature control framesDescribed each geometric tolerance