1. C H A P T E R E L E V E N TOLERANCING

2. 2 Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. OBJECTIVES 1.Describe the nominal size, tolerance, limits, and allowance of two mating parts. 2. Identify a clearance fit, interference fit, and transition fit. 3. Describe the basic hole and basic shaft systems. 4. Dimension mating parts using limit dimensions, unilateral tolerances, and bilateral tolerances. 5. Describe the classes of fit and give examples of each. 6. Draw geometric tolerancing symbols. 7. Specify geometric tolerances. 8. Relate datum surfaces to degrees of freedom.

3. 3 Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. UNDERSTANDING TOLERANCE To effectively provide tolerances in your drawings and CAD models, 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 or model. Apply functional tolerancing to individual features of the part. Tolerance is the total amount a specific dimension is permitted to vary. Tolerances are specified so that any two mating parts will fit together. The inner workings of a watch are an example of parts that must fit precisely to work. (Courtesy of SuperStock, Inc.)

4. 4 Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. Quality Control Before paying for parts, most companies have a process to quality certify (QC) the parts against the drawing or model. A tolerance must be specified for each dimension so that it can be determined how accurately the part must be manufactured to be acceptable. The tolerances that you specify are based on the part’s function and fit.

5. 5 Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. Definitions for Size Designation Feature Feature of size Actual local feature Nominal size Nominal size Allowance Allowance Definitions of size designation terms that apply in tolerancing.

6. 6 Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. Variations in Form and Envelope You can sometimes notice variations in form by placing a machinists’ scale along the edge of the part and checking to see whether you can slip a feeler gage between the scale and the edge of the part. You can think of tolerance as defining a perfect form envelope that the real produced part must fit inside in order to be acceptable. Actual minimum material envelope This envelope is the counterpart to the actual mating envelope.

7. 7 Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. Material Envelope continued… Actual mating envelope The envelope toward the outside of the material, in which the acceptable actual feature must fit. For external parts, like cylinders, this is the perfect feature at the largest permissible size; for internal features, like holes, this is the perfect feature at the smallest permissible size.

8. 8 Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. Implied Right Angles Implied 90° angles have the same general tolerances applied to them as do any other angles covered by a general note. The exception is when a geometric tolerance is used for that feature. When geometric tolerances are specified, implied 90° or 0° angles between feature centerlines are considered basic dimensions to which no tolerance applies outside that stated by the geometric tolerance. The tolerance of plus or minus 1° applies to the implied 90° angles as well as to the dimensioned angles in the drawing.

9. 9 Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. Fits between Mating Parts Fit is the range of tightness or looseness resulting from the allowances and tolerances in mating parts. The loosest fit, or maximum clearance, occurs when the smallest internal part (shaft) is in the largest external part (hole),

10. 10 Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. Fits between Mating Parts continued… Clearance Fit A clearance fit occurs when an internal part fits into an external part with space (or clearance) between the parts. Interference Fit An interference fit occurs when the internal part is larger than the external part, so the parts must be forced together.

11. 11 Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. Specifying Fit Using Limit Dimensions Limit dimensions are a method of directly specifying tolerance by providing dimensions for the upper and lower limits of the feature’s size. The high limit (maximum value) is placed above the low limit (minimum value) in place of the dimension value.

12. 12 Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. Selective Assembly In selective assembly, all parts are inspected and classified into several grades according to actual sizes, so that “small” shafts can be matched with “small” holes, “medium” shafts with “medium” holes, and so on. Selective Assembly… Difference between the sizes of mating parts is exaggerated for visibility.

13. 13 Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. Hole System Toleranced dimensions are commonly determined using the hole system. (Lockhart, Shawna D.; Johnson, Cindy M., Engineering Design Communication: Conveying Design Through Graphics, 1st, © 2000. Printed and electronically reproduced by permission of Pearson Education, Inc., Upper Saddle River, New Jersey.)

14. 14 Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. Shaft System In some industries, such as textile machinery manufacturing, which use a great deal of cold- finished shafting, the shaft system is used. (Lockhart, Shawna D.: Johnson, Cindy M., Engineering Design Communication: Conveying Design Through Graphics, 1st, © 2000. Printed and electronically reproduced by permission of Pearson Education, Inc., Upper Saddle River, New Jersey.)

15. 15 Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. GENERAL TOLERANCE NOTES General notes are usually located in the lower right corner of the drawing sheet near the title block. Often, general tolerance notes are included in the title block itself. “ALL TOLERANCES ±1 mm UNLESS OTHERWISE NOTED. ANGLES 1 DEGREE.” “ALL TOLERANCES ±1 mm UNLESS OTHERWISE NOTED. ANGLES 1 DEGREE.”

16. 16 Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. LIMIT TOLERANCES Limit tolerances state the upper and lower limits for the dimension range in place of the dimension values. Method of Stating Limits Note: The upper value is always placed above the lower value. Note: The upper value is always placed above the lower value.

17. 17 Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. PLUS-OR-MINUS TOLERANCES Unilateral when the tolerance applies in only one direction so that one value is zero; or, Bilateral when either the same or different values are added and subtracted.

18. 18 Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. Angular tolerances Angular tolerances are usually bilateral and given in terms of degrees, minutes, and seconds, unless geometric dimensioning and tolerancing is used. Plus/Minus–Toleranced Decimal Dimensions

19. 19 Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. TOLERANCE STACKING A Chained dimension uses the end of one dimension as the beginning of the next. Tolerance stacking refers to the way the tolerance for one dimension is added to the next dimension in the chain and so on from one feature to the next, resulting in a large variation in the location of the last feature in the chain. Baseline dimensioning locates a series of features from a common base feature. Tolerances do not stack up because dimensions are not based on other toleranced dimensions.

20. 20 Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. USING AMERICAN NATIONAL STANDARD LIMITS AND FIT TABLES Portion of RC8 Fit Table. The International Organization for Standardization (ISO) publishes a similar series of fit tables for metric values. The American National Standards Institute has issued ANSI B4.1, Preferred Limits and Fits for Cylindrical Parts, defining terms and recommending preferred standard sizes, allowances, tolerances, and fits in terms of the decimal inch. This standard gives a series of standard classes of fits on a unilateral-hole basis so that the fit produced by mating parts of a class of fit will produce approximately similar performance throughout the range of sizes.

21. 21 Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. TOLERANCES AND MACHINING PROCESSES Tolerances Related to Machining Processes

22. 22 Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. METRIC SYSTEM OF TOLERANCES AND FITS Terms Related to Metric Limits and Fits. (Reprinted from ASME B4.2-1978, by permission of The American Society of Mechanical Engineers. All rights reserved.)

23. 23 Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. GEOMETRIC DIMENSIONING AND TOLERANCING Geometric tolerances state the maximum allowable variations of a form or its position from the perfect geometry implied on the drawing. The term “geometric” refers to various forms, such as a plane, a cylinder, a cone, a square, or a hexagon.

24. 24 Technical Drawing with Engineering Graphics, 14/e Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman © 2012, 2009, 2003, Pearson Higher Education, Upper Saddle River, NJ 07458. All Rights Reserved. Tolerances and CAD 3D models Tolerances can be added directly to a 3D model so that it can be used as the digital product definition. (Reprinted from ASME Y14.41-2003, by permission of The American Society of Mechanical Engineers. All rights reserved.) SolidWorks software makes it easy to select surface finish symbols. (Courtesy of Solidworks Corporation.)