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Engineering H191 Engineering Fundamentals and Laboratory I

Engineering H191 Engineering Fundamentals and Laboratory I. Lecture 19 - Week 06 Day 01 Review of Good Dimensioning Practices. Objectives. Review principles of good dimensioning Introduce additional dimensioning techniques. Dimensioning.

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Engineering H191 Engineering Fundamentals and Laboratory I

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  1. Engineering H191Engineering Fundamentals and Laboratory I Lecture 19 - Week 06 Day 01 Review of Good Dimensioning Practices

  2. Objectives • Review principles of good dimensioning • Introduce additional dimensioning techniques AU 2008

  3. 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 AU 2008

  4. 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 AU 2008

  5. Dimensioning Basic Shapes – Assumptions • Perpendicularity • Symmetry AU 2008

  6. 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) AU 2008

  7. Dimensioning – Terminology AU 2008

  8. Principles of Good Dimensioning • The overriding principle of dimensioning is CLARITY • Principles – not an infallible rule set, need to apply good judgment. AU 2008

  9. Each feature dimensioned once and only once Dimensions should suit the function of the object Principles of Good Dimensioning AU 2008

  10. Principles of Good Dimensioning • Attach dimensions to most descriptive view AU 2008

  11. Principles of Good Dimensioning • Assume angles that appear to be 90 degrees are unless explicitly stated otherwise • Place dimensions outside of object whenever possible AU 2008

  12. Principles of Good Dimensioning • Dimension lines aligned and grouped to promote uniform appearance AU 2008

  13. Principles of Good Dimensioning Correct Incorrect • Dimension and Extension Lines Outside the Body • Do not have Extension Lines cross Dimension lines. AU 2008

  14. 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 first line • 1/4 in. from line to next line AU 2008

  15. 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 AU 2008

  16. ∅1.50 ∅1.50 Incorrect Correct Principles of Good Dimensioning • Leader lines used to dimension circles and arcs should be radial AU 2008

  17. Principles of Good Dimensioning • Positive Cylinder in longitudinal view, Holes in Circular View, always use ∅symbol before value AU 2008

  18. Principles of Good Dimensioning • Internal and external radii should be dimensioned with numerical value preceded by the symbol R (Note small cross for center.) AU 2008

  19. Principles of Good Dimensioning • Do a final check! • Every feature has been dimensioned once and only once • Make sure the numerical values are correct AU 2008

  20. What are the dimensioning errors? AU 2008

  21. What are the dimensioning errors? Missing width dimension Move dimension from Line to shape Gaps too wide Dimensions not between views AU 2008

  22. Extension Lines Practices AU 2008

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

  24. 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

  25. 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 AU 2008

  26. Dimension Repetitive Features - Use the Symbol "X" AU 2008

  27. Dimensioning Circular Center Lines • Circular Pattern Centerlines (Bolt Circles) AU 2008

  28. Special Surface Features Countersink Counterbore Spotface Boss AU 2008

  29. Symbols for Drilling Operations AU 2008

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