Planchard Copyright 2012 Drafting and Dimensioning Standards Instructors Name Course Number

Planchard Copyright 2012

Drafting and Dimensioning Standards

Instructors Name

Course Number


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:


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.



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.


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).



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.


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.


ANSI Drafting Standards - Dimensions

A dimension in a drawing consist of the following items: dimension arrow, dimension line, dimension value, and extension line.



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).



Insert a gap so people are not confused between the Feature line andthe extension line (ANSI standard).

Extension Line - extended from the view to indicate the edges referenced with the dimension line.

Dual Dimensions – Primary units – IPS; Secondary units (MMGS) .



Remember - a location dimension locates holes or other part features. A size dimension provides a radius, diameter, length, width, thickness, etc.



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.



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.



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.



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.



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.


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.


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


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


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 [ ].


ANSI Drafting Standards - Dimensions Hole dimensions are used to denote drilled hole

information by a bent leader line as illustrated.


ANSI Drafting Standards - Dimensions Hole dimensions are used to denote drilled hole

information by a bent leader line as illustrated.


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.



• 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.



• Linear Dimensioning – Dimensioning from feature to feature is known as Chain

Dimensioning. Chain Dimensioning is commonly used and easy to insert.



• 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!



• 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.



• 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.



• 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.



• 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

Documents

Planchard Copyright 2012 Drafting and Dimensioning Standards Instructors Name Course Number