Dimensioning Chapter 10
Dimensioning What is the purpose of dimensions? Geometric shapes ANSI To locate features To specify sizes Geometric shapes ANSI Skill & Practice
Dimensioning The ability to create good dimensions requires: Technique of dimensioning Appearance for lines, spacing, and arrowheads, placement of text Placement of dimensions Easy to read, easy to find, logical Choice of dimensions Affect how a design is manufactured
Technique of Dimensioning
Technique of Dimensioning
Technique of Dimensioning
Technique in Dimensioning Arrowheads indicate the extent of dimensions They should be uniform in size and style throughout the drawing
Technique in Dimensioning
Placing Dimensions
Placing Dimensions Shorter dimension lines are nearest the object outline Dimension lines should not cross extension lines A dimension line should never coincide with or extend any line of the drawing Avoid crossing dimension lines when possible
Placing Dimensions
Placing Dimensions
Placing Dimensions
Placing Dimensions
Placing Dimensions
Placing Dimensions Avoid placing duplicate dimensions AVOID SUPERFULOUS DIMENSIONS
Placing Dimensions
Placing Dimensions - angles Dimension angles by specifying the angle in degrees and a linear dimension
Placing Dimensions - arcs A circular arc is dimensioned in the view where you see its true shape by giving the value for its radius preceded by the abbreviation R Individual fillets and rounds are dimensioned like other arcs If there are only a few and they are obviously the same size, giving one typical radius is preferred Fillets radii can also be given in a general note
Placing Dimensions - holes Show symbols when dimensioning holes Place leader line in view where hole is shown as a circle Arrowhead should appear as if it can extend through the center point Arrowhead should touch the outside of circle
Placing Dimensions - curves Done by giving group of radii Dimensioning the outside envelope, with radii being self-locating
Placing Dimensions - curves Coordinate method locating points along the curve Give chordal dimensions as shown below
Placing Dimensions – round shapes Method used depends on level of accuracy needed Accuracy may depend on manufacturing method
Dimension Units Dimension values are lettered horizontally, should read from the bottom of the sheet Exception – ISO, Architectural dimensions Engineering drawings – metric or decimal inches Omit mm and inch designations on drawings and note the units in the title block Units noted somewhere on the drawing ALL MEASUREMENTS IN MILLIMTER unless otherwise Noted
Dimension Units Where the metric dimension is a whole number, do not show a decimal point or a zero (Example 25) Where the metric dimension is less than 1mm, a zero precedes the decimal point (Example 0.25) Where the decimal-inch dimension is used, a zero is not used before the decimal point of values less than 1 (Example .25)
Dimension Units - rounding Preference is to round values to an even number If the number following the rounding position is less then 5, make no change If the number following the rounding position is more than 5, round up If the number following the rounding position is a 5, round to an even number
Dimensioning Units - dual Dual dimensioning is used to show metric and decimal inch dimensions on the same drawing Position method mm placed over inches separated by dim line or they break the dim line and are separated by a slash Bracket method mm dimension enclosed in parentheses
Dimension Units - symbols
Dimension Units - tolerance When a finished part is measured it may vary slightly from the exact dimension specified Tolerance is the total amount that the feature on the actual part is allowed to vary from what is specified by the dimension