1. Drafting and Dimensioning Standards
Instructors Name
Course Number
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2. Drafting Standards
In order for drawings to be dimensioned so people can understand them, we need to follow various drafting dimensioning standards. Below are a few:
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3. Drafting Standards Institutions
ANSI - American National Standards Institute - This institute creates the engineering standards for North America
ISO - International Organization for Standardization - This is a world wide organization that creates engineering standards with approximately 100 participating countries.
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4. Drafting Standards Institutions
DIN - Deutsches Institut für Normung - The German Standards Institute created many standards used world wide such as the standards for camera film.
JIS - Japanese Industrial Standard - Created after WWII for Japanese standards.
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5. Drafting Standards Institutions
BSI - British Standards Institute - The national standards organization for the UK and an influential member of the ISO.
GOST - Gosudarstvennye Standarty State Standard - Standards cover over 20 industries including Petroleum, Chemical, Mining & Mineral Resources, Power & Electrical Equipment, and Oil & Gas products. This body of standards has been adopted by the Commonwealth of Independent States (CIS) and is administered by the Euro-Asian Council of Standardization, Metrology, and Certification (EASC).
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6. Drafting Standards Institutions
GB - Guojia Biaozhun, Standards - A set of mandatory and recommended standards regulated by SAC (Standardization Administration of China). Each GB Standard has a GB Standard number followed by the year when it's issued.
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7. ANSI Drafting Standards - Dimensions
Dimensioning: is the process of defining the size, form and location of geometric features and components on an engineering drawing.
Two general types of dimensions are used in drawings:
Size dimensions - size of holes and size of features.
Location dimensions - location of holes.
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8. ANSI Drafting Standards - Dimensions
A dimension in a drawing consist of the following items: dimension arrow,
dimension line, dimension value, and extension line.
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9. ANSI Drafting Standards - Dimensions
Arrowheads are used to terminate dimension lines. The point of the arrowheads
on the leader line must make contact with the Feature line. The standard
size ratio for all arrowheads on Mechanical Drawings is ~2.5:1 (Length to width).
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10. ANSI Drafting Standards - Dimensions
Extension Line - extended from the view to indicate the
edges referenced with the dimension line.
Insert a gap so people are
not confused between the Feature line and
the extension line (ANSI standard).
Dual Dimensions – Primary units – IPS; Secondary units (MMGS) .
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11. ANSI Drafting Standards - Dimensions
Remember - a location dimension locates holes or other part features.
A size dimension provides a radius, diameter, length, width, thickness, etc.
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12. ANSI Drafting Standards - Dimensions
A leader dimension is a leader line
used to point toward a diameter or radius.
A linear dimension is a dimension that is either horizontal or vertical to the dimensioning plane.
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13. ANSI Drafting Standards - Dimensions
An arc is always dimensioned by its radius. ANSI
standards require a radius dimension to be preceded
by the letter (symbol) R as illustrated.
A angular dimension is used to specify the
amount of degrees between two lines.
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14. ANSI Drafting Standards - Dimensions
A point or a center of an arc or circle is generally measured from two finished
surfaces. The method of location the center is preferred to making an angular
measurement. As illustrated, the center of the circle and arc may be found easily
be scribing the vertical and horizontal center lines from the machined surfaces.
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15. ANSI Drafting Standards - Dimensions
If a number of holes are to be equally spaced on a circle, then the exact location
of the first hole is given by a location dimension. To locate the remaining holes,
the location dimension is followed by 1.) the diameter of the holes,
2.) the number of holes, and 3.) then the notation EQUALLY SPACED or “EQ SP” as illustrated.
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16. ANSI Drafting Standards - Dimensions
Holes are often dimensioned in relation to one another and to a finished surface.
Dimensions are usually given, in such cases, in the view which the shape of the
holes, that is, square, round, or elongated. The preferred method of placing
these dimensions as illustrated.
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17. ANSI Drafting Standards - Dimensions
There are basically two types of dimensioning systems use in creating parts and drawings
U.S. (IPS)
Metric (MMGS)
*Dimensioning standards based on ASME Y
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18. ANSI Drafting Standards - Dimensions
The U.S. system uses the decimal inch value. When the decimal inch system is used, a zero is not used to the left of the decimal point for values less than one inch, and trailing zeros are used as illustrated.
Leading zero
Trailing zero
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19. ANSI Drafting Standards - Dimensions
The Metric system is normally expressed in millimeters and is rounded to the nearest whole number - No trailing zeros as illustrated.
Leading zero
Trailing zero
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20. ANSI Drafting Standards - Dimensions
Working drawing are usually drawn with all U.S. or all metric dimensions. Sometimes the object manufactured requires both U.S. and metric measuring system. Dual dimensioning may be necessary. The optional secondary units are normally displayed in brackets [ ].
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21. ANSI Drafting Standards - Dimensions
Hole dimensions are used to denote drilled hole information by a bent leader line as illustrated.
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22. ANSI Drafting Standards - Dimensions
Hole dimensions are used to denote drilled hole information by a bent leader line as illustrated.
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23. ANSI Drafting Standards - Dimensions
Placement of Linear Dimensions - Order of Preference. When there is not enough room on the drawing view between the extension lines to accommodate either the dimension value or the dimension lines - located the outside extension lines as illustrated.
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24. ANSI Drafting Standards - Dimensions
Linear Dimensioning
Ordinate dimensioning is also known as Datum dimensioning or Baseline dimensioning
Used when the location of features must be controlled from a common reference point or plane.
Baseline dimensioning ensures the tolerance in manufacturing does not add up.
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25. ANSI Drafting Standards - Dimensions
Linear Dimensioning
Dimensioning from feature to feature is known as Chain Dimensioning. Chain Dimensioning is commonly used and easy to insert.
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26. ANSI Drafting Standards - Dimensions
Linear Dimensioning
Chains of dimension should only be used if the function of the object won't be affected by the accumulation of the tolerances.
View the two examples!
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27. ANSI Drafting Standards - Dimensions
Dimensioning Check List
Each dimension should be written clearly with only one way to be interpreted.
A feature should be dimensioned only once.
Dimensions and extension lines should not cross.
Each feature should be dimensioned.
Dimension features or surfaces should be done to a logical reference point.
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28. ANSI Drafting Standards - Dimensions
Dimensioning Check List
Dimension features on a view should clearly show its true shape.
Enough space should be provided to avoid crowding and misinterpretation.
Extension lines and object lines should not overlap.
Dimensions should be placed outside the part.
Center lines or marks should be used on all circles and holes.
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29. ANSI Drafting Standards - Dimensions
Dimensioning Check List
Extension lines do not cross unless situation is unavoidable.
Stagger dimension text.
Largest dimension placed farthest from profile.
Dimensions should be evenly spaced and grouped.
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30. ANSI Drafting Standards - Dimensions
Dimensioning Check List
Arrow heads do not overlap.
Break extension lines that cross close to arrowhead.
Flip arrows to the inside if needed for room.
Move dimensions to the view that displays the outline of the feature.
Insure that all dimensions are accounted for. DO NOT OVER OR UNDER DIMENSION
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