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EDT 300/ENGR 306 - Chapter 6 1
Dimensioning and NotationDimensioning and Notation
Chapter 6Chapter 6
Sacramento City CollegeEDT 300/ENGR 306
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2 EDT 300/ENGR 306 - Chapter 6
ObjectivesObjectives
Apply measurements, notes and symbols to orthographic views on a technical drawingUse ANSI standards for dimensioning and notesDifferentiate between size dimensions and location dimensions.Dimension a technical drawing using either the SI or US unitsDetermine appropriate sizes for precision fits between matching parts
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3 EDT 300/ENGR 306 - Chapter 6
ObjectivesObjectives
Specify geometric tolerances using symbols and notesDesignate appropriate surface textures
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4 EDT 300/ENGR 306 - Chapter 6
VocabularyVocabularyAligned systemAssembly drawingBasic hole systemsBasic shaft systemsBilateral tolerancesDatumsDetail DrawingDimension lineDimensioningDual-dimensioning system
Extension linesFinish markGeometric dimensioning and tolerancingLeaderOutline viewToleranceUnidirectional systemUnilateral tolerances
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5 EDT 300/ENGR 306 - Chapter 6
Goal of ChapterGoal of Chapter
This chapter discusses how to show the sizeof the objects you draw.
Dimensioning is Showing an object’s size
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6 EDT 300/ENGR 306 - Chapter 6
DimensioningDimensioning
Dimensioning - is the process whereby size and location data
Are shown for a technical drawing.
Notation - is the process whereby needed information not covered by dimensions is placed on technical drawings.
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7 EDT 300/ENGR 306 - Chapter 6
DimensioningDimensioning
ANSI Y14.5M is the most widely accepted dimensioning standard.
This standard applies in most instances where interchangeability of parts is a major consideration.Automobile parts - good example.
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8 EDT 300/ENGR 306 - Chapter 6
DimensionsDimensions
Three dimensioning formats are used in the US.
1. Decimal-inch dimensioning.Example: 1.375”
2. Fractional inches.Example: 1-3/8”
3. Metric SI units.Example: 1.375 mm
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9 EDT 300/ENGR 306 - Chapter 6
DimensionsDimensions
In the US system, measurements are given in:
1. Feet and Inches.40’- 6 1/2”
2. Inches and Fractions.6-1/2”
3. Decimal Divisions of Inches.6.5”Most commonly used.
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10 EDT 300/ENGR 306 - Chapter 6
DimensionsDimensions
Decimal divisions are Most commonly used throughout industry.Used exclusively in ANSI Y14.5 M (the drafting standard on dimensioning).
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11 EDT 300/ENGR 306 - Chapter 6
Dimensioning SystemsDimensioning Systems
Metric units are often used for engineeringdrawings.
Civil engineering drawings may be dimensioned in meters.
Architectural drawings may use both metersand millimeters.
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12 EDT 300/ENGR 306 - Chapter 6
Lines and Symbols for DimensioningLines and Symbols for Dimensioning
Dimensioning is standardized.
Professional and trade associations.Engineering societies.Certain industries.
have agreed upon the symbols so people who use the drawings can recognize their meaning.
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13 EDT 300/ENGR 306 - Chapter 6
Lines and Symbols for DimensioningLines and Symbols for Dimensioning
Organizations that publish dimensioning standards:
1. The American National Standards Institute (ANSI).2. The Society of Automotive Engineers. (SAE)
Automotive.3. The Military Standards. (MIL-Specs)
Military.4. The International Standards Organization (ISO).
Parts for international market.
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14 EDT 300/ENGR 306 - Chapter 6
Orienting DimensionsOrienting Dimensions
Dimension Formats:The aligned system.The unidirectional system.
Refer to page 167, 168.
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15 EDT 300/ENGR 306 - Chapter 6
Orienting DimensionsOrienting Dimensions
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16 EDT 300/ENGR 306 - Chapter 6
Placing DimensionsPlacing Dimensions
The aligned systemDimensions are place in line with the dimension lines. Once was the only system in use.See Figure 6-13.
Avoid placing dimensions in the shaded areas shown in Figure 6-14.
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17 EDT 300/ENGR 306 - Chapter 6
Placing DimensionsPlacing Dimensions
The Unidirectional SystemAll dimensions read from the bottom of the sheet no matter where they appear.Think “horizontal text”.See Figure 6-15. The Unidirectional System, has replaced the Aligned System in most industries.ANSI Y14.5M uses the unidirectional system exclusively.
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18 EDT 300/ENGR 306 - Chapter 6
Placing DimensionsPlacing Dimensions
Notes and dimensions with leaders ALWAYS read from the bottom of the drawing.
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19 EDT 300/ENGR 306 - Chapter 6
DimensioningDimensioning
Notes and symbolsShow
FinishMaterials, and other information needed to make a part
Are components of dimensioning.
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20 EDT 300/ENGR 306 - Chapter 6
Working DrawingWorking Drawing
A working drawing is used to build the part or building.includes
Shape description, MeasurementsNotes and Symbols.
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21 EDT 300/ENGR 306 - Chapter 6
Working DrawingWorking DrawingDimension precision
Show only as precise as necessary to allow the manufacturer to create the part.Example: Framing dimensions
40’-5.000330 inchesIs meaningless.TOO MUCH precision is shown.
Example: Auto engine partsPiston – diameter 5.2Cylinder – diameter 5.21Not ENOUGH precision is shown.Is meaningless.
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22 EDT 300/ENGR 306 - Chapter 6
Working DrawingWorking Drawing
Dimensions are given in FeetOnes TenthsHundredthsThousandthsTen-thousandths of an inch.
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23 EDT 300/ENGR 306 - Chapter 6
Complete Working DrawingComplete Working Drawing
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24 EDT 300/ENGR 306 - Chapter 6
Lines and Symbols for DimensioningLines and Symbols for Dimensioning
Lines and symbols show where the dimensions apply.
Measurements are shown on the drawings.The drawing is NOT scaled or measured !
Cannot measure a drawing accurately enough for many interchangeable parts that must fit closely together.
How would you measure 5.03456” on a drawing?
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25 EDT 300/ENGR 306 - Chapter 6
Lines and Symbols for DimensioningLines and Symbols for Dimensioning
Add size information to the drawing using a system of
LinesSymbolsNumerical values.
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26 EDT 300/ENGR 306 - Chapter 6
Lines and Symbols for DimensioningLines and Symbols for Dimensioning
Lines and symbols are used on drawings to show where the dimensions apply.
See Figure 6-2.
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27 EDT 300/ENGR 306 - Chapter 6
Figure 6Figure 6--22
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EDT 300/ENGR 306 - Chapter 6 28
Dimension ComponentsDimension Components
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29 EDT 300/ENGR 306 - Chapter 6
Dimension ComponentsDimension Components
1. Dimension LinesIs a thin lineShows where a measurement begins and where it ends.Show the size of an angle.
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30 EDT 300/ENGR 306 - Chapter 6
Dimension ComponentsDimension Components
1. Dimension LinesShow a break in it for dimension numbers.Be drawn about 0.38” from the drawing to allow for the dimension number.Be drawn about 0.25” from other dimensions.
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31 EDT 300/ENGR 306 - Chapter 6
Dimension ComponentsDimension Components
1. Dimension LinesMechanical Style
Start and end with arrowheads.Continuous line with gap in centerDimension value is centered in the gap.
Architectural StyleStart and end with “tic” marks.Continuous line with NO gap in center.Dimension value is centered over the dimension line.
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32 EDT 300/ENGR 306 - Chapter 6
Dimension ComponentsDimension Components
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33 EDT 300/ENGR 306 - Chapter 6
Dimension ComponentsDimension Components
2. Arrowheads and Tic MarksAre placed at the ends of dimension lines.Show where a dimension begins and ends.Are used at the end of a leader to show where a note or dimension applies.Can be open or solid.Should be one size and shape in any one drawing.See Figure 6-4.
Mechanical – arrowheads Architectural - tics
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34 EDT 300/ENGR 306 - Chapter 6
Dimension ComponentsDimension Components
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35 EDT 300/ENGR 306 - Chapter 6
Dimension ComponentsDimension Components
3. Extension Lines Are thin linesExtend the lines or edges of the views or part.Are used to locate center points.Are used to provide space for dimension lines (Figure 6-5).Are not part of the views and should not touch the outline.Start about 0.06” from the part.Extend to about 0.12” beyond the last dimension line.
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36 EDT 300/ENGR 306 - Chapter 6
Dimension ComponentsDimension Components
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37 EDT 300/ENGR 306 - Chapter 6
Dimension ComponentsDimension Components
4. Numerals and NotesCAPITAL LETTERS ARE PREFERRED.Vertical or Inclined letters.About 0.125” high.Must be easy to read.Draw light guidelines first.
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38 EDT 300/ENGR 306 - Chapter 6
Dimension ComponentsDimension Components
5. LeadersA thin lineDrawn from the note or dimension to the place where it applies.Drawn at an angle to the horizontal.
60o is preferred but 45o, 30o or other angles can be used.
Start with an 1/8” long dashEnd with an arrowhead.Use a dot if the leader is pointing to a surfacerather than to an edge (Fig 6-8).
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39 EDT 300/ENGR 306 - Chapter 6
LeadersLeaders
5. LeadersMany leaders drawn close togetherDraw them parallel to each other.Draw a leader to a circle or arc so that the arrowhead points to its center.Use one leader per dimension, (don’t try to economize).
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40 EDT 300/ENGR 306 - Chapter 6
LeadersLeaders
5. LeadersLeader “Don’ts”
Do not draw long leaders.Do not draw horizontally, vertically, or at a small angle.Do not draw leaders parallel to dimensions, extensions or section lines.
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EDT 300/ENGR 306 - Chapter 6 41
The Finish MarkThe Finish Mark
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42 EDT 300/ENGR 306 - Chapter 6
The Finish MarkThe Finish Mark
The finish mark or surface-texture symbol shows that a surface is to be machined
See Figure 6-7.The older symbol is still used but it is being replaced.The standard symbol now in general use is shown in Figure 6-7.The point of the symbol should touch the edge view of the surface.
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EDT 300/ENGR 306 - Chapter 6 43
Scale of A DrawingScale of A Drawing
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44 EDT 300/ENGR 306 - Chapter 6
Scale of A DrawingScale of A Drawing
The scale should be given near the drawing title.
If the drawing has views of more than onepart, and different scales are used,
Show the scale close to the views.
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45 EDT 300/ENGR 306 - Chapter 6
Units and Parts of UnitsUnits and Parts of Units
If parts require a great deal of accuracy use decimal dimensioning.
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46 EDT 300/ENGR 306 - Chapter 6
Units and Parts of UnitsUnits and Parts of Units
Decimal dimensioning is commonly used between
finished surfaces.center distances.pieces that must be held in a definite, accurate relationship to each other.
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47 EDT 300/ENGR 306 - Chapter 6
Units and Parts of UnitsUnits and Parts of Units
With customary measures, decimals are shown to two places where limits of +/- 0.01”are close enough.
Use decimals to three places where where limits smaller than +/- 0.01” are required.
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48 EDT 300/ENGR 306 - Chapter 6
Units and Parts of UnitsUnits and Parts of Units
Decimal dimensioning is used in most industries.
A dual dimensioning system is sometimes used in industries involved in international trade.
This system uses both the decimal inch and the millimeter.It is becoming more common to use the metric system alone.
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49 EDT 300/ENGR 306 - Chapter 6
Theory of DimensioningTheory of Dimensioning
Two kinds of dimensions existSize dimensionsLocation dimensions
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50 EDT 300/ENGR 306 - Chapter 6
Theory of DimensioningTheory of Dimensioning
Size dimensionsDefine the size of each piece.Show the dimensions of a number of simple shapes
Basic geometric formsPrismsCylindersPyramidsCones, etc.)
See Figure 6-16.
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51 EDT 300/ENGR 306 - Chapter 6
Theory of DimensioningTheory of Dimensioning
Location dimensionsShow the positions of each piece must also be given.Each piece is considered separately and then in relation to the other pieces.
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EDT 300/ENGR 306 - Chapter 6 52
Size Dimensions Size Dimensions -- PrismsPrisms
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53 EDT 300/ENGR 306 - Chapter 6
Size Dimensions Size Dimensions -- PrismsPrisms
The Prism is the first basic shape we will considerFor a rectangular prism, the width, height, and depth are needed.
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54 EDT 300/ENGR 306 - Chapter 6
Size Dimensions Size Dimensions -- PrismsPrisms
For any flat piece, give The thickness in the edge view.All other dimensions in the outline view.The Outline View is the one that shows the shape of the flat surface or surfaces.The front views in Fig 6-19 are outline views.
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55 EDT 300/ENGR 306 - Chapter 6
Size Dimensions Size Dimensions -- PrismsPrisms
Methods for dimensioning other prisms are shown in Figure 6-20.
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56 EDT 300/ENGR 306 - Chapter 6
Size Dimensions Size Dimensions -- PrismsPrisms
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EDT 300/ENGR 306 - Chapter 6 57
Size Dimensions Size Dimensions –– PrismsPrisms
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58 EDT 300/ENGR 306 - Chapter 6
Size Dimensions Size Dimensions -- CylindersCylinders
The cylinder requires two dimensionsthe diameter.the length.
For cylindrical pieces, give the diameter and the length on the same view.
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59 EDT 300/ENGR 306 - Chapter 6
Size Dimensions Size Dimensions -- CylindersCylinders
The symbol Ø is always placed with the diameter.Example: Ø 1.625”
The abbreviation DIA may be found on olderdrawings instead of the symbol Ø.Notes are used to give hole sizes, and are placed in the outline view.
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60 EDT 300/ENGR 306 - Chapter 6
Size Dimensions Size Dimensions -- CylindersCylinders
When parts of cylinders occur, such as filletsand rounds they are dimensioned in the view in which the curves show.
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61 EDT 300/ENGR 306 - Chapter 6
Size Dimensions Size Dimensions -- CylindersCylinders
The other shapes:ConeFrustumSquare pyramid Sphere
can be dimensioned in one view.
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EDT 300/ENGR 306 - Chapter 6 62
Location DimensionsLocation Dimensions
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63 EDT 300/ENGR 306 - Chapter 6
Location DimensionsLocation Dimensions
Location dimensionsShow the relative positions of the basic shapes.Locate holes, surfaces and other features.
Location dimensions are needed in three mutually perpendicular directions.
Up / down.Crossways.Forward and backward.
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64 EDT 300/ENGR 306 - Chapter 6
Steps In DimensioningSteps In Dimensioning
Two basic steps1. Apply the size dimension
This gives the overall size of the object and the various features which make up the object.
2. Apply the location dimensionLocation dimensions are dimensions which locate various features of an object from some specified datum or surface.
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65 EDT 300/ENGR 306 - Chapter 6
Location Dimensions Location Dimensions -- PrismsPrisms
Prisms are located bySurfacesSurfaces and axesAxesThree dimensions are needed
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66 EDT 300/ENGR 306 - Chapter 6
Location Dimensions Location Dimensions -- CylindersCylinders
Cylinders are located byAxes and bases.Three dimensions are needed
Refer to Fig 6-30.
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EDT 300/ENGR 306 - Chapter 6 67
Datum Dimensioning Datum Dimensioning
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68 EDT 300/ENGR 306 - Chapter 6
Datum DimensioningDatum Dimensioning
Datum are points, lines and surfaces that are assumed to be exact
Datum are used to compute other dimensions.
Location dimensions are given from datum.When positions of a part are given, they are all located from the same datum.
A datum must be clear.
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EDT 300/ENGR 306 - Chapter 6 69
Rules for DimensioningRules for Dimensioning
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70 EDT 300/ENGR 306 - Chapter 6
Rules for DimensioningRules for Dimensioning
1.Space dimension lines about 0.25” apart and 0.38” from the view outline.
2. Aligned system - dimensions read in line with the dimension lineRead aligned with part.Refer to Fig 6-12.
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71 EDT 300/ENGR 306 - Chapter 6
Rules for DimensioningRules for Dimensioning
3. Unidirectional system - dimensions read in line with the dimension lineRead left to right from bottom of sheet. Refer to Fig 6-14.
4.Machine drawingsUse decimal inches or millimeters.
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72 EDT 300/ENGR 306 - Chapter 6
Rules for DimensioningRules for Dimensioning
5.When all dimensions are in inches or millimeters, omit the symbol.
Add a note:“ALL DIMENSIONS ARE IN INCHES”.
6.Position all dimensions clearly.
7.Do not repeat the same dimension on different views.
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73 EDT 300/ENGR 306 - Chapter 6
Rules for DimensioningRules for Dimensioning
8.Do not give dimensions that are not needed.
9.Place overall dimensions outside the smaller dimensions
See Figure 6-31.See Figure 6-32.
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74 EDT 300/ENGR 306 - Chapter 6
Rules for DimensioningRules for Dimensioning
10. Avoid placing dimensions in the shaded areas when using the aligned system (Fig 6- 35).
11. Give dimensions from centerlines, finished surfaces or datums where needed.
12. Do not use a centerline or line of a view as a dimension line.
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75 EDT 300/ENGR 306 - Chapter 6
Rules for DimensioningRules for Dimensioning
13. Do not draw a dimension line that extends from a line of a view.
14. Avoid crossing a dimension line with another line.
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76 EDT 300/ENGR 306 - Chapter 6
Rules for DimensioningRules for Dimensioning
15. Give the diameter of a circle, not the radius. Use the symbol Ø before the dimension.
16. Place the abbreviation “R” before the dimension when giving the radius of an arc.
17. In general, dimensions should be placed outside the view outlines.
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77 EDT 300/ENGR 306 - Chapter 6
Rules for DimensioningRules for Dimensioning
18. Do not draw extension lines that cross each other or cross dimension lines if possible.
19. Avoid dimensioning to a hidden line if possible.
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78 EDT 300/ENGR 306 - Chapter 6
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EDT 300/ENGR 306 - Chapter 6 79
Dimensioning a Detail DrawingDimensioning a Detail Drawing
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80 EDT 300/ENGR 306 - Chapter 6
Dimensioning a Detail DrawingDimensioning a Detail Drawing
A detail drawing is a drawing for a single part that includes all the information necessary to make that part.
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81 EDT 300/ENGR 306 - Chapter 6
Dimensioning a Detail DrawingDimensioning a Detail Drawing
Dimension a detail drawing in the following order:1.Complete all views first before adding any
dimensions or notes2. Think about the part first, and its
characteristic views3. Think about the size dimensions and the
related location dimensions. Draw the dimension lines, leaders and arrowheads
4. After considering any changes, add any dimensions and notes that may be needed.
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EDT 300/ENGR 306 - Chapter 6 82
Dimensioning an Assembly DrawingDimensioning an Assembly Drawing
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83 EDT 300/ENGR 306 - Chapter 6
Dimensioning an Assembly DrawingDimensioning an Assembly Drawing
An assembly drawing shows parts of a machine in their relative positions.
If an assembly drawing needs a complete description of size, the rules and methods of dimensioning apply.
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84 EDT 300/ENGR 306 - Chapter 6
Dimensioning an Assembly DrawingDimensioning an Assembly Drawing
1. If the drawing is to show arrangement of parts or appearance only, leave dimensions off.
2. If a drawing is needed to show the space a product requires, give overall dimensions.
3. If parts can be located in relation to each other without giving detail dimensions, center-to-center dimensions are usually given.
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85 EDT 300/ENGR 306 - Chapter 6
AbbreviationsAbbreviations
Examples of abbreviations from ANSI are listed in Appendix C of the text.
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EDT 300/ENGR 306 - Chapter 6 86
Limit Dimensioning Limit Dimensioning
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87 EDT 300/ENGR 306 - Chapter 6
Limit DimensioningLimit Dimensioning
Parts are generally manufactured with a tolerance. A tolerance is an allowable variation in the part dimension
The tolerance may be stated in a note “DIMENSION TOLERANCE +/- 0.01 UNLESS OTHERWISE SPECIFIED”
Limit dimensions give the max and min dimensions allowed
The max limit is placed over the min limitFig 6-47B and C
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88 EDT 300/ENGR 306 - Chapter 6
Limit DimensioningLimit Dimensioning
Consecutive dimensions are listed one after the otherProgressive dimensions are all given from a single surface (Figure 6-47 C). This is called baseline dimensioning
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89 EDT 300/ENGR 306 - Chapter 6
Expressing SizeExpressing Size
Size is a designation of magnitude.When a value is given to a dimension it is called the size of that dimension
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90 EDT 300/ENGR 306 - Chapter 6
Expressing SizeExpressing Size
Nominal size - used for general identification.Basic size - is the size to which allowances and tolerances are added to get the limits of size.Design size - the size to which tolerances are added to get the to get the limits of size.Actual size - is the measured size.Limits of size - is the max and min sizes.
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91 EDT 300/ENGR 306 - Chapter 6
Expressing PositionExpressing Position
Locating round holesx-y coordinatespolar coordinates“equally spaced” holesDatum line dimensionsPoint-to-point or chain dimensioningDatum dimensioning
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92 EDT 300/ENGR 306 - Chapter 6
ToleranceTolerance
A tolerance is the total amount a given dimensions may vary.
Express in the same form as its dimension.Express in the same number of decimal places.
If the dimension is written as fraction, the tolerance should be also written as a common fraction.
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93 EDT 300/ENGR 306 - Chapter 6
ToleranceTolerance
In a chain of dimensions with tolerances, the last dimension may have a tolerance equal to the sum of the tolerances between it and the first dimension.
Tolerances accumulate (they are added together).
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94 EDT 300/ENGR 306 - Chapter 6
ToleranceTolerance
In a datum dimensioning, tolerances do NOTadd together.
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95 EDT 300/ENGR 306 - Chapter 6
TolerancesTolerances
Unilateral tolerancesAllow variations in only one direction from a design size.
Bilateral tolerancesAllow variations in both directions from a design size.
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96 EDT 300/ENGR 306 - Chapter 6
TolerancesTolerances
The Limit SystemOnly the largest and smallest allowed dimensions are shown .The tolerance is the difference between the limits.