2. 10
Dimensioning

3. Explain why dimensions and notes are needed on drawings.
Identify, explain, and accurately use the two systems of linear measurement to dimension drawings.
Describe the difference between unidirectional and aligned dimensioning.
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4. Identify and explain the three basic types of dimensions.
Apply the general rules for dimensioning inch and/or metric drawings.
Dimension circles, holes, arcs, and angles.
Explain the methods used in the conversion to metric dimensioning from conventional inch dimensioning.
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5. Explain how dimensions are generated in computer-aided drafting.
Describe the basic principles of geometric dimensioning and tolerancing.
Explain how dimensions are generated in computer-aided drafting.
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6. Dimensioning Used to communicate the size and shape of the product
Shown with dimensions and notes
Drafter defines what information is pertinent for assembly of product
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7. Systems of Measurement
US Customary system
Used to measure in inches and feet
Measurements are made in decimal inches in mechanical drafting
Measurements are made in fractional inches in architectural drafting
SI Metric system
Used to measure in metric units (e.g., millimeters)
Drawings are dimensioned using one or both systems
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8. Dimensioning Methods Unidirectional dimensioning Aligned dimensioning
Preferred method
Aligned dimensioning
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9. Lines Used in Dimensioning
Dimension line
Thin, black
Capped with arrowheads or other terminator
Extension line
Leader
Angular with shoulder
Capped with arrowhead
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10. Lines Used in Dimensioning (Cont.)
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11. Leader Placement
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12. Correct Leader Shoulder Placement
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13. Arrowheads
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14. Types of Dimensions Overall dimensions Location dimensions
Size dimensions
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15. Basic Rules of Dimensioning
1. Dimension views showing true shape.
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16. Basic Rules of Dimensioning (Cont.)
2. Do not dimension within or on top of views.
Extend primary centerlines and use as extension lines
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17. Basic Rules of Dimensioning
3. Group dimensions in an orderly manner.
Avoid extending extension lines more than halfway across any given view
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18. Basic Rules of Dimensioning (Cont.)
4. Dimensions must give complete information. No measurements or scaling should be necessary.
5. Draw dimension lines parallel to direction of measurement. Stagger numerals to reduce crowding.
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19. Basic Rules of Dimensioning (Cont.)
6. Do not duplicate dimensions unless necessary. Omit dimensions when using chain dimensioning if needed.
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20. Basic Rules of Dimensioning (Cont.)
7. Extension lines should not cross dimension lines. Place smallest dimensions nearest the view.
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21. Basic Rules of Dimensioning (Cont.)
8. Do not use inch symbol (″) if all dimensions are in inches.
Include note stating “UNLESS OTHERWISE SPECIFIED, ALL DIMENSIONS ARE IN INCHES” (or MILLIMETERS).
9. Draw numerals and fractions to proper height relative to one another.
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22. Rules for Inch Dimensioning
1. Do not place zero before decimal point for values of less than 1″.
2. Express dimensions to same number of decimal places as their tolerance.
3. Reduce fractions to lowest common denominator.
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23. Dimensioning Circles and Arcs
Dimension circles by giving diameter
Dimension arcs greater than 180° by giving diameter
Indicates drilling process
Dimension arcs equal to or less than 180° by giving radius
Indicates cutting process
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24. ASME Standard Callouts
Diameter = Ø (Greek letter phi)
Radius = R
Place callout before size
Ø4 = diameter of 4
R4 = radius of 4
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25. Diameter Dimensioning Guidelines
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26. Dimensioning Holes
Use abbreviation THRU when necessary to indicate hole goes through entire part
Provide hole depth when hole does not go through entire part
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27. Dimensioning Holes (Cont.)
Use symbols to indicate common manufacturing processes
Countersink
Spotface
Counterbore
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28. Dimensioning Holes (Cont.)
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29. Dimensioning Cylinders
Dimension diameter and length on same view (secondary view)
May be more convenient to show diameters of concentric circles on longitudinal view
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30. Placing Leaders for Diameter Dimensions
Leaders point at or intersect primary center of diameter
Arrow tip never touches primary center point
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31. Radius Dimensioning Guidelines
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32. Location and Size Dimensions on Cylindrical Parts
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33. Dimensioning Holes in Radial Patterns
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34. Dimensioning Angles
Express value in degrees and decimal parts of a degree or in degrees (°), minutes (′), and seconds (″)
Locate vertex of angle and give size
Dimension angles to extension lines, not object lines
Locate angles with respect to original edges of object
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35. Angle Dimensioning Conventions
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36. Dimensioning With Limited Space
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37. Methods for Adapting US Customary Conventions to Metric Dimensioning
Dual dimensioning
Dimensioning with tabular chart
Metric dimensioning with conversion chart
Metric dimensioning (metric units only)
Undimensioned master drawings
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38. Dual Dimensioning Two methods of presentation Most complicated system
Position method
Bracket method
Most complicated system
Seldom used today
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39. Dimensioning with Tabular Chart
Dimensions are labeled with letters
Letters are listed in chart
Chart shows metric and inch equivalents
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40. Dimensioning with Conversion Chart
When part is designed to metric standards, drawing is labeled “Metric”
Some drawings provide conversion chart showing metric dimensions and inch equivalents
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41. Metric Dimensioning (Metric Units Only)
Drawing is labeled “Metric”
No conversion values given
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42. Undimensioned Master Drawings
Drawing is made without dimensions
Dimensions are added in different formats on different prints
Notes and details are added in appropriate language
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43. Rules for Metric Dimensioning
1. When millimeter dimension is a whole number, decimal point and following zero are not shown
125, not 125.0
2. When dimension is less than one millimeter, zero is shown to left of decimal point
0.5, not .5
3. Drawings must be clearly identified as METRIC with note
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44. Rules for Metric Dimensioning (Cont.)
4. Space (or comma) is not used to separate digits into groups
20500, not
5. When dimension exceeds whole number by a decimal fraction, zero does not follow last digit to right of decimal point
125.5, not
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45. Geometric Dimensioning and Tolerancing (GD&T)
Highly accurate definitions of tolerances for form and position are needed to design products today
GD&T system uses geometric characteristic symbols to specify form and positional tolerances
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46. Datum Used to indicate an exact point, axis, plane, or surface
Identified by a datum feature symbol
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47. Feature Control Frame Indicates geometric tolerance
Contains geometric characteristic symbol
Typically shown with dimension
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48. Dimensioning in CAD Saves time drawing dimensions manually
Created with dimensioning commands
Dimension styles control format and appearance
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49. Dimension Style Specifies unit format
Must incorporate correct scale setting
Provides controls for various elements
Extension and dimension line format
Dimension spacing
Text placement
Tolerancing method
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50. Types of CAD Dimensions
Linear
Aligned
Angular
Diameter
Radius
Leader
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51. CAD Dimensioning Rules used in manual drafting apply
Dimension styles are created based on drafting discipline used
Dimension styles should observe ASME, school, or company standards
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52. What information is provided by dimensions?
Dimensions define the size and location of the features (geometric features) of an object and give overall size of the object.
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53. The basic unit of measurement in the SI Metric system is the _____.
millimeter
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54. _____ dimensioning requires that dimensions be placed parallel to the dimension lines.
Aligned
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55. Dimensions can be classified as _____, _____, or _____ dimensions.
overall, location, size
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56. When dimensioning, _____. A. group dimensions together
B. place dimensions within object lines of views
C. duplicate dimensions in multiple views
D. give the size of features in secondary views
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57. True or False? When dimensioning a metric drawing, the distance 45 and one-half millimeters should be shown as mm.
False
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58. True or False? When dimensioning an arc that is greater than 180°, the radius should be specified.
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59. D. Dimensions are not labeled.
When dimensioning with a tabular chart, dimensions are labeled with _____.
A. symbols
B. numbers
C. letters
D. Dimensions are not labeled.
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60. What is a datum?
A datum is an exact point, axis, plane, or surface from which features of a part are located.
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61. A dimension _____ provides controls for elements such as extension line and dimension line format and dimension spacing.
style
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62. Aligned dimensioning Chain dimensioning Counterbore Countersink
A method of dimensioning in which dimensions are placed parallel to the dimension line and read from the bottom and right side of the drawing.
Chain dimensioning
Placing several dimensions in a straight line along an object to describe successive features.
Counterbore
A deep recess at the end of a smaller hole used to provide a bearing surface for the head of a bolt or nut.
Countersink
A chamfered recess at the end of a smaller hole used to receive the head of a fastener.
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63. Geometric characteristic symbols
Datum
An exact point, axis, plane, or surface from which features of a part are located.
Dimensions
Lettering or text on a drawing defining object sizes and locations.
Feature control frame
A rectangular compartment that contains a divided series of symbols identifying geometric tolerance.
Geometric characteristic symbols
Symbols used in GD&T to specify and explain form and positional tolerances.
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64. Geometric dimensioning and tolerancing (GD&T)
A standard system devised to control interpretation of the form, profile, orientation, location, and runout of features on drawings.
Leader
An angular dimension line used to point out special characteristics of objects.
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65. Location dimensions Overall dimensions Size dimensions Spotface
Dimensions that indicate where particular object features lie along or within an object.
Overall dimensions
Dimensions that provide the overall size of an object.
Size dimensions
Dimensions that specify the size of particular features within an object.
Spotface
A recess at the end of a smaller hole used to provide a bearing surface for the head of a bolt or nut.
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66. Unidirectional dimensioning
Tolerance
An allowable variance from the original dimension.
Unidirectional dimensioning
A method of dimensioning in which dimensions are placed horizontally on the drawing sheet and read from the bottom of the drawing.
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