## ENG 004 Lecture 13, Nov 8, 2012

### Announcements

• Homework #5 due Tuesday, Questions?
• Read Chapter 9 (through 9.5)

• Teamwork
• Dimensions

## Dimensioning

### Dimensions

They define the size and/or location of a feature.

All features must have a dimension associated with it.

### Datum

A point or origin of a reference frame.

### Units of Measure

You must specify the units of measure: inches, millimeters, degrees, radians, etc.

### Tolerances

An allowable deviation in size, location, and/or geometry of a feature.

All dimensions must have a tolerance associated with it.

## Dimension Guidelines

• Each dimension shall indicate the allowable variation in size, i.e., a tolerance, unless the dimensions is a reference dimension or a basic dimension
• 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.

## Dimension Units

### 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 non-zero:
• Neither commas nor spaces shall be used to separate digits into groups:

## Dimension Units

### US Customary Units (decimal inches)

• A zero is not used before a decimal point for values less than one inch:
• 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 necessary:
• All decimal points used in the above must be clearly visible

Cell Shearer

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