Drafting and Dimensioning Standards.ppt - Vanier Tech Ed

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Drafting and Dimensioning
Standards
Instructors Name
Course Number
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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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 Y14.5-2009.
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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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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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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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ANSI Drafting Standards Dimensions
 Hole dimensions are used to denote drilled hole
information by a bent leader line as illustrated.
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ANSI Drafting Standards Dimensions
 Hole dimensions are used to denote drilled hole
information by a bent leader line as illustrated.
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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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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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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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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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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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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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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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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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