10 Dimensioning

Explain why dimensions and notes are needed on drawings. Identify, explain, and accurately use the two systems of linear measurement to dimension drawings. Describe the difference between unidirectional and aligned dimensioning. © Goodheart-Willcox Co., Inc.

Identify and explain the three basic types of dimensions. Apply the general rules for dimensioning inch and/or metric drawings. Dimension circles, holes, arcs, and angles. Explain the methods used in the conversion to metric dimensioning from conventional inch dimensioning. © Goodheart-Willcox Co., Inc.

Explain how dimensions are generated in computer-aided drafting. Describe the basic principles of geometric dimensioning and tolerancing. Explain how dimensions are generated in computer-aided drafting. © Goodheart-Willcox Co., Inc.

Dimensioning Used to communicate the size and shape of the product Shown with dimensions and notes Drafter defines what information is pertinent for assembly of product © Goodheart-Willcox Co., Inc.

Systems of Measurement US Customary system Used to measure in inches and feet Measurements are made in decimal inches in mechanical drafting Measurements are made in fractional inches in architectural drafting SI Metric system Used to measure in metric units (e.g., millimeters) Drawings are dimensioned using one or both systems © Goodheart-Willcox Co., Inc.

Dimensioning Methods Unidirectional dimensioning Aligned dimensioning Preferred method Aligned dimensioning © Goodheart-Willcox Co., Inc.

Lines Used in Dimensioning Dimension line Thin, black Capped with arrowheads or other terminator Extension line Leader Angular with shoulder Capped with arrowhead © Goodheart-Willcox Co., Inc.

Lines Used in Dimensioning (Cont.) © Goodheart-Willcox Co., Inc.

Leader Placement © Goodheart-Willcox Co., Inc.

Correct Leader Shoulder Placement © Goodheart-Willcox Co., Inc.

Arrowheads © Goodheart-Willcox Co., Inc.

Types of Dimensions Overall dimensions Location dimensions Size dimensions © Goodheart-Willcox Co., Inc.

Basic Rules of Dimensioning 1. Dimension views showing true shape. © Goodheart-Willcox Co., Inc.

Basic Rules of Dimensioning (Cont.) 2. Do not dimension within or on top of views. Extend primary centerlines and use as extension lines © Goodheart-Willcox Co., Inc.

Basic Rules of Dimensioning 3. Group dimensions in an orderly manner. Avoid extending extension lines more than halfway across any given view © Goodheart-Willcox Co., Inc.

Basic Rules of Dimensioning (Cont.) 4. Dimensions must give complete information. No measurements or scaling should be necessary. 5. Draw dimension lines parallel to direction of measurement. Stagger numerals to reduce crowding. © Goodheart-Willcox Co., Inc.

Basic Rules of Dimensioning (Cont.) 6. Do not duplicate dimensions unless necessary. Omit dimensions when using chain dimensioning if needed. © Goodheart-Willcox Co., Inc.

Basic Rules of Dimensioning (Cont.) 7. Extension lines should not cross dimension lines. Place smallest dimensions nearest the view. © Goodheart-Willcox Co., Inc.

Basic Rules of Dimensioning (Cont.) 8. Do not use inch symbol (″) if all dimensions are in inches. Include note stating “UNLESS OTHERWISE SPECIFIED, ALL DIMENSIONS ARE IN INCHES” (or MILLIMETERS). 9. Draw numerals and fractions to proper height relative to one another. © Goodheart-Willcox Co., Inc.

Rules for Inch Dimensioning 1. Do not place zero before decimal point for values of less than 1″. 2. Express dimensions to same number of decimal places as their tolerance. 3. Reduce fractions to lowest common denominator. © Goodheart-Willcox Co., Inc.

Dimensioning Circles and Arcs Dimension circles by giving diameter Dimension arcs greater than 180° by giving diameter Indicates drilling process Dimension arcs equal to or less than 180° by giving radius Indicates cutting process © Goodheart-Willcox Co., Inc.

ASME Standard Callouts Diameter = Ø (Greek letter phi) Radius = R Place callout before size Ø4 = diameter of 4 R4 = radius of 4 © Goodheart-Willcox Co., Inc.

Diameter Dimensioning Guidelines © Goodheart-Willcox Co., Inc.

Dimensioning Holes Use abbreviation THRU when necessary to indicate hole goes through entire part Provide hole depth when hole does not go through entire part © Goodheart-Willcox Co., Inc.

Dimensioning Holes (Cont.) Use symbols to indicate common manufacturing processes Countersink Spotface Counterbore © Goodheart-Willcox Co., Inc.

Dimensioning Holes (Cont.) © Goodheart-Willcox Co., Inc.

Dimensioning Cylinders Dimension diameter and length on same view (secondary view) May be more convenient to show diameters of concentric circles on longitudinal view © Goodheart-Willcox Co., Inc.

Placing Leaders for Diameter Dimensions Leaders point at or intersect primary center of diameter Arrow tip never touches primary center point © Goodheart-Willcox Co., Inc.

Radius Dimensioning Guidelines © Goodheart-Willcox Co., Inc.

Location and Size Dimensions on Cylindrical Parts © Goodheart-Willcox Co., Inc.

Dimensioning Holes in Radial Patterns © Goodheart-Willcox Co., Inc.

Dimensioning Angles Express value in degrees and decimal parts of a degree or in degrees (°), minutes (′), and seconds (″) Locate vertex of angle and give size Dimension angles to extension lines, not object lines Locate angles with respect to original edges of object © Goodheart-Willcox Co., Inc.

Angle Dimensioning Conventions © Goodheart-Willcox Co., Inc.

Dimensioning With Limited Space © Goodheart-Willcox Co., Inc.

Methods for Adapting US Customary Conventions to Metric Dimensioning Dual dimensioning Dimensioning with tabular chart Metric dimensioning with conversion chart Metric dimensioning (metric units only) Undimensioned master drawings © Goodheart-Willcox Co., Inc.

Dual Dimensioning Two methods of presentation Most complicated system Position method Bracket method Most complicated system Seldom used today © Goodheart-Willcox Co., Inc.

Dimensioning with Tabular Chart Dimensions are labeled with letters Letters are listed in chart Chart shows metric and inch equivalents © Goodheart-Willcox Co., Inc.

Dimensioning with Conversion Chart When part is designed to metric standards, drawing is labeled “Metric” Some drawings provide conversion chart showing metric dimensions and inch equivalents © Goodheart-Willcox Co., Inc.

Metric Dimensioning (Metric Units Only) Drawing is labeled “Metric” No conversion values given © Goodheart-Willcox Co., Inc.

Undimensioned Master Drawings Drawing is made without dimensions Dimensions are added in different formats on different prints Notes and details are added in appropriate language © Goodheart-Willcox Co., Inc.

Rules for Metric Dimensioning 1. When millimeter dimension is a whole number, decimal point and following zero are not shown 125, not 125.0 2. When dimension is less than one millimeter, zero is shown to left of decimal point 0.5, not .5 3. Drawings must be clearly identified as METRIC with note © Goodheart-Willcox Co., Inc.

Rules for Metric Dimensioning (Cont.) 4. Space (or comma) is not used to separate digits into groups 20500, not 20 500 5. When dimension exceeds whole number by a decimal fraction, zero does not follow last digit to right of decimal point 125.5, not 125.50 © Goodheart-Willcox Co., Inc.

Geometric Dimensioning and Tolerancing (GD&T) Highly accurate definitions of tolerances for form and position are needed to design products today GD&T system uses geometric characteristic symbols to specify form and positional tolerances © Goodheart-Willcox Co., Inc.

Datum Used to indicate an exact point, axis, plane, or surface Identified by a datum feature symbol © Goodheart-Willcox Co., Inc.

Feature Control Frame Indicates geometric tolerance Contains geometric characteristic symbol Typically shown with dimension © Goodheart-Willcox Co., Inc.

Dimensioning in CAD Saves time drawing dimensions manually Created with dimensioning commands Dimension styles control format and appearance © Goodheart-Willcox Co., Inc.

Dimension Style Specifies unit format Must incorporate correct scale setting Provides controls for various elements Extension and dimension line format Dimension spacing Text placement Tolerancing method © Goodheart-Willcox Co., Inc.

Types of CAD Dimensions Linear Aligned Angular Diameter Radius Leader © Goodheart-Willcox Co., Inc.

CAD Dimensioning Rules used in manual drafting apply Dimension styles are created based on drafting discipline used Dimension styles should observe ASME, school, or company standards © Goodheart-Willcox Co., Inc.

What information is provided by dimensions? Dimensions define the size and location of the features (geometric features) of an object and give overall size of the object. © Goodheart-Willcox Co., Inc.

The basic unit of measurement in the SI Metric system is the _____. millimeter © Goodheart-Willcox Co., Inc.

_____ dimensioning requires that dimensions be placed parallel to the dimension lines. Aligned © Goodheart-Willcox Co., Inc.

Dimensions can be classified as _____, _____, or _____ dimensions. overall, location, size © Goodheart-Willcox Co., Inc.

When dimensioning, _____. A. group dimensions together B. place dimensions within object lines of views C. duplicate dimensions in multiple views D. give the size of features in secondary views © Goodheart-Willcox Co., Inc.

True or False? When dimensioning a metric drawing, the distance 45 and one-half millimeters should be shown as 45.50 mm. False © Goodheart-Willcox Co., Inc.

True or False? When dimensioning an arc that is greater than 180°, the radius should be specified. © Goodheart-Willcox Co., Inc.

D. Dimensions are not labeled. When dimensioning with a tabular chart, dimensions are labeled with _____. A. symbols B. numbers C. letters D. Dimensions are not labeled. © Goodheart-Willcox Co., Inc.

What is a datum? A datum is an exact point, axis, plane, or surface from which features of a part are located. © Goodheart-Willcox Co., Inc.

A dimension _____ provides controls for elements such as extension line and dimension line format and dimension spacing. style © Goodheart-Willcox Co., Inc.

Aligned dimensioning Chain dimensioning Counterbore Countersink A method of dimensioning in which dimensions are placed parallel to the dimension line and read from the bottom and right side of the drawing. Chain dimensioning Placing several dimensions in a straight line along an object to describe successive features. Counterbore A deep recess at the end of a smaller hole used to provide a bearing surface for the head of a bolt or nut. Countersink A chamfered recess at the end of a smaller hole used to receive the head of a fastener. © Goodheart-Willcox Co., Inc.

Geometric characteristic symbols Datum An exact point, axis, plane, or surface from which features of a part are located. Dimensions Lettering or text on a drawing defining object sizes and locations. Feature control frame A rectangular compartment that contains a divided series of symbols identifying geometric tolerance. Geometric characteristic symbols Symbols used in GD&T to specify and explain form and positional tolerances. © Goodheart-Willcox Co., Inc.

Geometric dimensioning and tolerancing (GD&T) A standard system devised to control interpretation of the form, profile, orientation, location, and runout of features on drawings. Leader An angular dimension line used to point out special characteristics of objects. © Goodheart-Willcox Co., Inc.

Location dimensions Overall dimensions Size dimensions Spotface Dimensions that indicate where particular object features lie along or within an object. Overall dimensions Dimensions that provide the overall size of an object. Size dimensions Dimensions that specify the size of particular features within an object. Spotface A recess at the end of a smaller hole used to provide a bearing surface for the head of a bolt or nut. © Goodheart-Willcox Co., Inc.

Unidirectional dimensioning Tolerance An allowable variance from the original dimension. Unidirectional dimensioning A method of dimensioning in which dimensions are placed horizontally on the drawing sheet and read from the bottom of the drawing. © Goodheart-Willcox Co., Inc.