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AutoCAD
College of North Atlantic Qatar
Dimensioning Basics and Rules
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Dimensioning
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TOPICS
IntroductionDimensioning componentsDimensioning object s features
Placement of dimensions.
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Scaling vs. Dimensioning
Drawings can be different scales, but dimensions are ALWAYS at FULL
scale
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Standards of Measurement:1. Inch System
1. When all of the dimensions are expressed ininches, do not use inch mark () or theabbreviation for inches (in.)
2. values less that one inch should NOT be precededwith a zero.
2. Metric (ISO)1. For metric drawings, omit the use of the
millimeter (mm) notation following the numeral,as millimeters are the default units.
2. Values less than 1 mm SHOULD BE preceded witha zero
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DimensioningComponents
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Dimension elements
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Dimensioning Styles
UnidirectionalSystem
Aligned System
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THE BASIC CONCEPT
Dimensioning is accomplished by adding size and
location information necessary to manufacture
the object.
ClearCompleteFacilitate the- manufacturing method- measurement method
This information have to be
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General Guideline
To think that you would make an object and dimension it in
the most useful way. Put in exactly as many dimensions as are necessary for the
craftsperson to make it -no more, no less.
Do not put in redundant dimensions.
It is often better to measure from one end to various points.This gives the dimensions a reference standard. Repeatedlymeasuring from one point to another will lead toinaccuracies.
It is helpful to choose the placement of the dimension in theorder in which a machinist would create the part. Thisconvention may take some experience.
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Dimensioning Rules Basics 11. Dimension lines should never cross.
2. Dimension lines should NOT coincide or continue any line of the drawing.
3. Dimension lines should be lined up and grouped together.4. Extension lines may cross each other and over other lines on the part
5. Extension lines can be shared, and broken.
6. Dimension lines and extension lines are usually drawn at 90 degree
angles7. Centerlines can be used as a measurement location, but not as extension
lines.
8. Always place the first row of dimensions a minimum distance of3 text
heights away from the edge of the part. Additional stacks can be a
minimum of2 text heights away from each other.
9. The overall dimension should always be given. It should be placed
outside of smaller dimensions and be the furthest dimension from the
part.
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Dimensioning Rules Basics 2
10. If the measurement on the drawing is less than 5mm or 0.20
inches, then the arrows are placed outside the extension lines.11. Avoid placing any dimensions on the part (inside the view)
unless there is no other option.
12. Avoid dimensioning to hidden features
13. Always place the dimension where the characteristic shape is
shown in the most descriptive view. (This means dont place adimension on object lines making a T joint.)
14. Keep dimensions between the views whenever possible
15. Do not duplicate dimensions and avoid using unnecessary or
superfluous dimensions
16. Stagger horizontal dimensions to avoid contact or crowding of
values.
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Dimensioning Rules: Curved Features
17. Place the R in front of radius dimensions and, the diametersymbol () in front of diameter dimensions.
18. Always dimension holes in their circular view by stating thediameter of drilled holes.
19. Dimension cylindrical objects as diameters in their rectangularview
20. Dimension rounded corners and arc features as radii wherethey appear in their rounded views.
21. Leaders start at the beginning or end of a note. Point them
toward the center of circular features that they are specifying.
22. Dimension angles by specifying a) the angle in degrees and b)
a linear dimension.
23. Specify the hole depth of special features such as
countersinking with a note following the dimension.
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Dimensioning Rules: Advanced
24. If the same value is repeated many times, then
use a general note for the features.
25. Dimension repetitive features using the symbol
(x) [multiplication]26. The origin for baseline or ordinate dimensions
used as a datum should be extended from afinished edge of the part.
27. Conserve space and time by using abbreviationsand standardized symbols whenever possible.
28. Reference dimensions should be placed inparentheses or should include the abbreviationREF.
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Special Hole
Features
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Chain and Baseline Dimensioning
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Summary
What is Dimensioning?
Purpose of Dimensioning
Types of Dimensioning
Aligned
Unidirectional
Dimensioning Rules/Guidelines
Dimensioning styles
Chain
Baseline
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