ENG 004 Lecture 13, Nov 8, 2012
- Homework #5 due Tuesday, Questions?
- Read Chapter 9 (through 9.5)
They define the size and/or location of a feature.
All features must have a dimension associated with it.
A point or origin of a reference frame.
Units of Measure
You must specify the units of measure: inches, millimeters, degrees,
An allowable deviation in size, location, and/or geometry of a feature.
All dimensions must have a tolerance associated with it.
Adopted from ANSI Y 14.5M-1994
- Each dimension shall indicate the allowable variation in size, i.e., a
tolerance, unless the dimensions is a reference dimension or a basic
- All features must be fully dimensioned so that there is no ambiguity of
the feature's size, location, and form (geometry or shape)
- All dimensions required to document the design are necessary, however,
only a necessary set of dimensions should be used. That is, no redundant
dimensioning. All dimensions should be directly referenced to the view with
the most detail of the feature.
- Dimensions shall be selected and arranged to suit the function of the
feature or its relationship to other features and shall not be interpreted
to more than one interpretation.
Dimension Guidelines Continued
- The drawing shall not specify the method of manufacture. If this
information is required, it shall be specified in a specification document
referenced on the drawing
- Dimensions shall be shown in true size using orthographic multi-views
and/or auxiliary views.
- Wires, cables, sheets, etc. shall be specified by linear dimensions
indicating the object's diameter or thickness.
- A 90° angle is implied at locations shown on a drawing at right angles
and no angle is specified.
- All dimensions are applicable at 20° C.
SI Units (mm)
- If the dimension is less that 1 mm, a zero precedes the decimal point:
- If the dimension is a whole number, neither the decimal point nor a
zero is shown:
- If the dimension exceeds a whole number by a decimal fraction of one
millimeter, the last digit to the right of the decimal point shall be
- Neither commas nor spaces shall be used to separate digits into groups:
US Customary Units (decimal inches)
- A zero is not used before a decimal point for values less than one
- A dimension is expressed to the same number of decimal places as its
tolerance. Zeros are added to the right of the decimal point where
- All decimal points used in the above must be clearly visible
Most Descriptive Views
Extension Lines Not Object Lines
Dimensions Outside Object
Dimensioning Center Lines