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Reading Technical Drawings

Learn about U.S. dimensioning systems, reading scales, decimal rounding rules, metric conversions, and blueprint essentials. Includes quizzes for practice.

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Reading Technical Drawings

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  1. Reading Technical Drawings Foundations of Manufacturing

  2. Dimensioning Systems • Four different systems of dimensioning used in U.S. • Fractional inch • Decimal inch • Dual dimensioning • SI Metric

  3. Dimensioning Systems

  4. Dimensioning Systems

  5. Dimensioning Systems

  6. Dimensioning Systems

  7. Dimensioning Systems

  8. Fractional type steel rules divided into units of: • 1/16 • 1/32 • 1/64 • Major graduation accentuated by longer lines • Some have small numbers printed adjacent to lines

  9. Scale Reading Quiz 1 • 3/4 Record the scale length identified by 1

  10. Scale Reading Quiz 1 • 1 5/8 Record the scale length identified by 2

  11. Scale Reading Quiz 1 • 2 7/16 Record the scale length identified by 3

  12. Scale Reading Quiz 1 • 3 3/16 Record the scale length identified by 4

  13. Scale Reading Quiz 1 • 3 15/16 Record the scale length identified by 5

  14. Decimal Scales • Subdivided into units of 1/10, 1/20, 1/50, or 1/100 in. • 1/50 is sufficient for most applications

  15. Decimal Scales • Closer measurements require using micrometer, vernier or dial calipers • Major graduations are accented by longer lines-usually every 1/10 in. • Popular scales graduation style has .04 and .06 increments slightly longer than .02 and .08 • Reads faster, more recognizable

  16. Decimal Scales

  17. Decimal Scales

  18. Decimal Scales

  19. Decimal Scales

  20. Scale Reading Quiz 2 • .80 Record the scale length identifiedby... 1

  21. Scale Reading Quiz 2 • 1.60 Record the scale length identifiedby... 2

  22. Scale Reading Quiz 2 • 2.50 Record the scale length identifiedby... 3

  23. Scale Reading Quiz 2 • 3.32 Record the scale length identifiedby... 4

  24. Scale Reading Quiz 2 • 3.86 Record the scale length identifiedby... 5

  25. Decimal Dimensioning • Drawing may be dimensioned using two- or three-place decimals • Amount of tolerance is determined by number of decimal places

  26. Decimal Dimensioning • .50 may have tolerance of ± .01 • .500 may have tolerance of ± .001 • .5000 may have tolerance of ±.0001

  27. Decimal Dimensioning • Converting fractions to decimals-results in too many decimal places • Need to round off those numbers to desired places

  28. Decimal Dimensioning • Rule #1-When the figure following the last digit to be retained is greater than 5---increase the last number by one • .016 becomes .02 • .047 becomes .05 • .078 becomes .08

  29. Decimal Dimensioning • Rule #2-When the figure following the last digit to be retained is less than 5---retain the last number • .031 becomes .03 • .062 becomes .06 • .093 becomes .09

  30. Decimal Dimensioning • Rule #3-When the figure following the last digit to be retained is exactly 5 and the figure to be retained is odd---increase the last number by one • .375 becomes .38 • .875 becomes .88

  31. Decimal Dimensioning • Rule #4-When the figure following the last digit to be retained is exactly 5 and the figure to be retained is even---retain the last number • .125 becomes .12 • .625 becomes .62

  32. Decimal Dimensioning

  33. Decimal Rounding Quiz • .109 = • .125 = • .156 = • .234 = • .438 = • .547 = • .562 = .11 .12 .16 .23 .44 .55 .56

  34. Decimal Rounding Quiz • .641 = • .797 = • .875 = • 1.056 = • 1.672 = • 2.205 = • 2.454 = .64 .80 .88 1.06 1.67 2.20 2.45

  35. Decimal Rounding Quiz • 3.335 = • 3.767 = • 5.555 = • 6.665 = • 7.045 = • 8.885 = 3.34 3.77 5.56 6.66 7.04 8.88

  36. Metric Dimensioning • Metric increment of measure is millimeter • Will be noted if different • Convert a metric dimension to inches by multiplying it by .03937

  37. Metric Dimensioning • Conversion charts are available to provide converted dimensions • Metric scales are available and can be used-eliminating need for conversion

  38. Metric Dimensioning • Metric scales • Have graduations every millimeter of half-millimeter • Designated “mm” or “1/2 mm” • Every fifth millimeter is accentuated by a longer line • Every tenth millimeter is identified by a number

  39. Metric Dimensioning

  40. Scale Reading Quiz 3 • 20 mm Record the scale length identified by 1

  41. Scale Reading Quiz 3 Record the scale length identified by 2 • 35 mm

  42. Scale Reading Quiz 3 Record the scale length identified by 3 • 51 mm

  43. Scale Reading Quiz 3 Record the scale length identified by 4 • 77.5 mm

  44. Scale Reading Quiz 3 Record the scale length identified by 5 • 93.5 mm

  45. Blueprints • Blueprinting-Term can be interpreted as • Drawing • Picture • Contains information • Required sizes • Tolerances • Essential requirements • Notes and instructions

  46. Engineering Drawings • Original drawing made by drafter or engineer • Prints are referred to as engineering drawings • Also referred to as blueprints (more common term)

  47. Engineering Drawings • Standardized drawings • “A” size is 8 ½ x 11 inches • “B” size is 11 x 17 inches • “C” size is 17 x 22 inches • “D” size is 22 x 34 inches • “E” size is 34 x 44 inches

  48. Engineering Drawings

  49. Title Blocks • Each drawing contains a Title Block • Drawing number is most prominent lettering in title block • Lettered larger to stand out • Scale determines the size of the object drafted

  50. Title Blocks • Mechanical drawings may be reduced to • Half size • Quarter size • One eighth size

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