Tolerancing Chapter 10

2 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Objectives Describe nominal size, tolerance, limits, and allowance of two mating parts Identify a clearance fit, interference fit, and transition fit Describe the basic hole and basic shaft systems

3 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Objectives (cont.) Dimension mating parts using limit dimensions, unilateral tolerances, and bilateral tolerances Describe the classes of fit and give examples of each Draw geometric tolerancing symbols Specify geometric tolerances

4 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Understanding Tolerance Tolerancing is an extension of dimensioning It allows you to specify a range of accuracy for every feature of a product so the parts will fit together and function properly when assembled

5 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Understanding Tolerance To provide tolerances in CAD, you must: Understand the fit required between mating parts Have a clear picture of how inspection measurements are performed Be able to apply tolerance symbols to a drawing

6 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Tolerance Tolerance is the total amount a specific dimension is permitted to vary Use generous tolerances when possible because increased precision makes parts more expensive to manufacture

7 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Quality Control Large batches of parts may use statistical methods to control quality where a sample of parts are inspected Specific tolerances are based on the part’s function and fit

8 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Variations in Form Acceptable parts must not extend beyond boundary limits

9 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Implied 90 Degree Angles When lines intersect on a drawing at angles of 90 degrees, it is customary not to dimension the angle Implied 90 degree angles have the same general tolerances applied to them as any other angles covered by a general note

10 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Implied 90 Degree Angles

11 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Fits Between Mating Parts Fit is the term for the range of tightness or looseness resulting from the allowances and tolerances in mating parts

12 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Clearance Fit

13 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Interference Fit

14 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Transition Fit

15 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Definitions for Size Designation Nominal size – used for general identification and usually expressed in decimals Basic size (basic dimension) – the theoretically exact size from which limits of size are determined

16 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Actual size – the measured size of a finished part Allowance – the minimum clearance or maximum interference specified to achieve a fit between two mating parts Definitions for Size Designation

17 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Basic Hole System Toleranced dimensions are commonly determined using the basic hole system in which the minimum hole size is taken as the basic size

18 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Basic Shaft System In this system, the maximum shaft is taken as the basic size and is used only in specific circumstances

19 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Specifying Tolerances The primary ways to indicate tolerances in a drawing are: A general tolerance note A note providing a tolerance for a specific dimension A reference on the drawing to another document that specifies the required tolerances

20 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Specifying Tolerances (cont.) Adding limit tolerances to dimensions Adding direct plus/minus tolerances to dimensions Geometric tolerances

21 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. General Tolerance Notes

22 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Limit Tolerances

23 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Plus-or-Minus Tolerances

24 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Tolerance Stacking

25 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Tolerances and Machining Processes

26 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Metric System of Tolerances and Fits The preceding material on limits and fits applies to both systems of measurement The ISO has a system of preferred metric limits and fits The system is specified for holes, cylinders, and shafts and has similar definitions of terms

27 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Geometric Tolerancing Geometric tolerances state the maximum allowable variations of a form or its position from the perfect geometry implied in the drawing The term “geometric” refers to forms such as planes, cylinders, squares, etc.

28 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Geometric Tolerancing Tolerances of form and position (or location) control such characteristics as: Straightness Flatness Parallelism Perpendicularity (squareness) Concentricity Roundness Angular displacement, etc.

29 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Geometric Characteristics and Modifying Symbols

30 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Symbols for Tolerances of Position and Form

31 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Symbols for Tolerances of Position and Form

32 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Datum Surfaces and Features Datum surfaces and features are used as references to control other features

33 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Maximum Material Condition Maximum material condition (MMC) means that a feature of a finished product contains the maximum amount of material permitted by the toleranced dimensions for that feature

34 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Tolerances of Angles Bilateral tolerances have traditionally been given on angles

35 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Using Geometric Dimensioning and Tolerancing Geometric dimensioning and tolerancing (GDT) considers an individual part’s dimensions and tolerances and that part’s relation to its related parts GDT also simplifies the inspection process

36 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education, Upper Saddle River, NJ All Rights Reserved. Using Geometric Dimensioning and Tolerancing Applying GDT principles requires: Defining the part’s functions Listing the functions by priority Defining the datum reference frame Control selection Calculating tolerances