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Good Dimensioning Practices

Good Dimensioning Practices

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Good Dimensioning Practices

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  1. Good Dimensioning Practices Goals • Review the principles of good dimensioning • Introduce additional dimensioning techniques Reference • Technical Graphics Chapter 6

  2. Dimensioning • Orthographic and Isometric Views define the shape and general features of the object • Dimensioning adds information that specifies • Size of the object • Location of features (e.g. holes) • Characteristics of features (e.g. depth and diameter of hole) • Dimensions also communicate the tolerance (or accuracy) required P. 2

  3. Some General Guidelines • Start by dimensioning basic outside dimensions of the object. • Add dimension for location and size of removed features • Add general and specific notes – such as tolerances P. 3

  4. Dimensioning Basic Shapes -Assumptions • Perpendicularity • Symmetry P. 4

  5. Dimensioning Shows: A) Size B) Location and Orientation • ALWAYS give DIAMETER “ “ for full circles (360 degrees) and RADIUS “R” for arcs (less than 360 degrees) P. 5

  6. Dimensioning - Terminology P. 6

  7. Principles of Good Dimensioning • The overriding principle of dimensioning is CLARITY • Principles – not an infallible rule set, need to apply good judgment. P. 7

  8. Each feature dimensioned once and only once Dimensions should suit the function of the object Principles of Good Dimensioning P. 8

  9. Principles of Good Dimensioning • Attach dimensions to most descriptive view P. 9

  10. Principles of Good Dimensioning • Angles as Right Angles Assumed 90o unless otherwise noted • Dimensions outside of object whenever possible P. 10

  11. Principles of Good Dimensioning • Dimension lines aligned and grouped to promote uniform appearance P. 11

  12. Principles of Good Dimensioning Correct Incorrect • Dimension and Extension Lines Outside the Body • Do not have Extension Lines cross Dimension lines. P. 12

  13. Principles of Good Dimensioning • Dimension lines should be unbroken except for the number between the arrowheads • Space (at least) • 3/8 in. from object to 1st line • 1/4 in. from line to next line P. 13

  14. Gap – object to extension line = 1/16 in. Extension lines 1/8 in. beyond dimension line Extension lines broken for crossing Principles of Good Dimensioning P. 14

  15. f1.50 f1.50 Incorrect Correct Principles of Good Dimensioning • Leader lines used to dimension circles and arcs should be radial P. 15

  16. Principles of Good Dimensioning • Positive Cylinder in longitudinal view, Holes in Circular View, n symbol before value P. 16

  17. Principles of Good Dimensioning • Internal and external radii should be dimensioned with numerical value preceded by the symbol R (Note small cross for center.) P. 17

  18. Principles of Good Dimensioning • Do a final check! • Every feature has been dimensioned once and only once • Make sure the numerical values are correct P. 18

  19. Extension Lines Practices P. 19

  20. Dimensioning Basic Shapes • Cylinders Positive (solid) Negative (hole) • Avoid dimensioning to a hidden line P. 20

  21. 1.00 2.00 .500 .500 1.25 .325 .250 Dimensioning Example Step 1. Dimension basic outside dimensions Step 2. Location and Size of Removed Features (Notch) LOCATION OF THE NOTCH SIZE OF THE NOTCH P. 21

  22. General considerations in dimensioning • Fillets and rounds can be dimensioned in a “NOTE” e.g. “ALL FILLETS AND ROUNDS R1.000 UNLESS OTHERWISE NOTED” • When there are multiple identical rounds or holes, dimension one and include the number of holes e.g. 4 X R1.000 or 2 X Ф1.000 and so on. NOTE: You may see older drawings with letters TYP after the dimension. This indicates that all similar un-dimensioned features have the same dimension P. 22

  23. Dimension Repetitive Features - Use the Symbol “X” P. 23

  24. Dimensioning Circular Center Lines • Circular Pattern Centerlines (Bolt Circles) P. 24

  25. Special Surface Features Countersink Counterbore Spotface Boss P. 25

  26. Symbols for Drilling Operations P. 26