Dimensioning Study Guide (Study Chapter 11 in Technical Drawing) 1. In addition to a complete shape description of an object... a drawing of the design must also give a complete ; that is, it must be. 2. Dimensions should not be duplicated or superfluous. Only those needed to produce and inspect the part against the design specifications should be given. Students often. These are not necessarily. There is much more to the, as we will see. 3. What 3 principles must be learned to dimension properly? Explain each principle. a. b. c. 4. Explain FIGURE 11.2 5. Explain FIGURE 11.3 6. Explain FIGURE 11.4 7. How long should an arrowhead be? In the space below draw several arrowheads next to each number a. b. c. d. e. 1
8. What is a dimensioning Leader? What angle should they be drawn? (Study fig. 11.8) 9. What system of measurement is used in Architectural and Structural drawings? Why? 10. Why are decimal and metric units used in mechanical drawings? 11. Using the rounding rules, round 3.34324 to 3 places. 12. The last figure to be retained in rounding a number should be increased by 1 when 13. State the rule for rounding when the last figure to be retained is followed by exactly 5. Give an example. 14. When do you place numbers and arrows outside the extension lines? 15. When do you place the numbers inside the extension lines and the arrows outside? 16. How tall should the dimension text be? mm Inch. (Study fig. 11.11 & 11.12) 2
17. Study the last half of paragraph 11.11 and list the rules for placing zero's for both metric and decimal inches. a. Metric Rules 1. 2. 3. b. Decimal inch Rules 1. 2. 18. Explain FIGURE 11.14. 19. What does unidirectional mean when talking about dimension text? When is this method used? 20. What does aligned mean when talking about dimension text? When is this method used? 21. Show two methods of dimensioning angles? 3
22. Define and illustrate a finish mark using FIGURE 11.20 b. 23. Give two examples of when it would be appropriate to place dimensions on top of the actual drawing object instead of on extension lines. 1. 2. 24. Define contour dimensions. Give an example. 25. Define and illustrate: 1. Size dimensions 2. Location dimensions 4
26. Cylinders are dimensioned where they appear as. Dimension the cylinder below. 27. Study paragraph 11.23 and FIGURE 11.30 and then draw and label each of the ANSI/ASME symbols in the space below. 28. Holes should be dimensioned where they appear as a. 29. What is a bolt circle? How is it dimensioned? Sketch an example below? (Figure 11.37) 30. Location dimensions should lead to where ever possible because. 5
31. Study FIGURE 11.44 and explain why the dimension that is lined out should be left off each part. a. b. c. d. e. f. g. h. i j. k. l. 6
Dimensioning Rules The overriding principle of dimensioning is CLARITY 1. Each feature of an object is dimensioned once and only once. 2. Dimensions should be placed in the most descriptive view of the feature being dimensioned. 3. Dimensions should specify only the size of the feature. The manufacturing method should only be specified if it is a mandatory design requirement. 4. Angles shown on drawings as right angles are assumed to be 90 degrees unless specified otherwise and need not be dimensioned. 5. Dimensions should be moved outside the boundaries of the object whenever possible. 6. Dimension lines should be aligned and grouped where possible to promote clarity and uniform appearance. 8. Crossing dimension lines should be avoided whenever possible. 9. The space between the first dimension line and the object should be at least 3/8 inch (.375). The space between all other dimension lines should be at least 1/4 inch (.250). 10. There should be a visible gap between the object and the origin of the extension line. 11. Extension lines should extend 1/8 inch (.125) beyond the last dimension line. 12. Extension lines should be broken if they cross or are close to arrowheads. 13. Leader lines should be oriented to be read from the bottom of the drawing. 14. Diameters are dimensioned with a numerical value preceded by the diameter symbol. 15. Radii are dimensioned with a numerical value preceded by the radius symbol. 16. Cylinders should be dimensioned in the Rectangular view where possible. 17. When a dimension is given to the center of an arc or radius a small cross is shown at the center. 18. The diameter and depth of holes that are counter-bored, spot faced, or countersunk, should be specified in a note. 19. The depth of a blind hole may be specified in a note, and is the depth of the full diameter from the surface of the object. 7