CHAPTER Dimensioning 10
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Objectives 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.
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Objectives 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.
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Objectives Understand and demonstrate tolerance dimensioning. Describe the basic principles of geometric dimensioning and tolerancing. Explain how dimensions are generated in computer-aided drafting.
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. 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
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Systems of Measurement US Customary system –Measure in inches and feet –Decimal inches used in mechanical drafting –Fractional inches used in architectural drafting SI Metric system –Used to measure in metric units (millimeters)
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Dimensioning Methods Unidirectional dimensioning –Preferred method Aligned dimensioning Goodheart-Willcox Publisher
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Lines Used in Dimensioning Dimension line –Thin, black –Capped with arrowheads or other terminator Extension line –Thin, black Leader –Thin, black –Angular with shoulder –Capped with arrowhead
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Lines Used in Dimensioning (Cont.) Goodheart-Willcox Publisher
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Leader Placement Goodheart-Willcox Publisher
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Correct Leader Shoulder Placement Goodheart-Willcox Publisher
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Arrowheads Goodheart-Willcox Publisher
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Types of Dimensions Goodheart-Willcox Publisher
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Basic Rules of Dimensioning 1. Dimension views showing true shape. Goodheart-Willcox Publisher
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. 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 Publisher
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Basic Rules of Dimensioning 3. Group dimensions in an orderly manner. –Avoid extending extension lines more than halfway across any given view Goodheart-Willcox Publisher
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. 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.
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Basic Rules of Dimensioning (Cont.) 6. Do not duplicate dimensions unless necessary. Omit dimensions when using chain dimensioning if needed. Goodheart-Willcox Publisher
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Basic Rules of Dimensioning (Cont.) 7. Extension lines should not cross dimension lines. Place smallest dimensions nearest the view. Goodheart-Willcox Publisher
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. 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.
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. 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.
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. 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
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. ASME Standard Callouts Diameter = Ø Radius = R Place callout before size –Ø4 = diameter of 4 –R4 = radius of 4
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Diameter Dimensioning Guidelines Goodheart-Willcox Publisher
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. 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 Publisher
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Dimensioning Holes (Cont.) Use symbols to indicate common manufacturing processes –Countersink –Spotface –Counterbore
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Dimensioning Holes (Cont.) Goodheart-Willcox Publisher
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. 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 Publisher
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Placing Leaders for Diameter Dimensions Leaders point at or intersect primary center of diameter Arrow tip never touches primary center point
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Radius Dimensioning Guidelines Goodheart-Willcox Publisher
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Location and Size Dimensions on Cylindrical Parts Goodheart-Willcox Publisher
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Dimensioning Holes in Radial Patterns Goodheart-Willcox Publisher
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. 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 visible lines Locate angles with respect to original edges of object
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Angle Dimensioning Conventions Goodheart-Willcox Publisher
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Dimensioning with Limited Space Goodheart-Willcox Publisher
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. 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
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Dual Dimensioning Two methods of presentation –Position method –Bracket method Most complicated system Seldom used today Goodheart-Willcox Publisher
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Dimensioning with Tabular Chart Dimensions are labeled with letters Letters are listed in chart Chart shows metric and inch equivalents
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Dimensioning with Tabular Chart (Cont.) Goodheart-Willcox Publisher
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. 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
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Dimensioning with Conversion Chart (Cont.) Goodheart-Willcox Publisher
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Metric Dimensioning Metric units only Drawing is labeled “Metric” No conversion values given
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. 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
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Rules for Metric Dimensioning 1. When millimeter dimension is a whole number, decimal point and following zero are not shown –125, not 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
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Rules for Metric Dimensioning (Cont.) 4.Space (or comma) is not used to separate digits into groups –20500, not When dimension exceeds whole number by a decimal fraction, zero does not follow last digit to right of decimal point –125.5, not
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Tolerancing Tolerance is an allowable variance from the original dimension Permit allowances in size that occur during manufacturing Tolerances added to basic size
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Limit Dimensioning Limits are absolute maximum and minimum sizes allowed –Difference between high limit and low limit is tolerance –High limit appears above or after low limit Goodheart-Willcox Publisher
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Plus-and-Minus Tolerancing Specifies variation in the positive and negative directions –Plus symbol (+) means positive direction –Minus symbol (−) means negative direction Unilateral tolerance in one direction only Bilateral tolerance in both directions –Equal bilateral uses plus-and-minus (±) symbol
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Plus-and-Minus Tolerancing (Cont.) Goodheart-Willcox Publisher
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. General Tolerances Apply a tolerance for all dimensions without a specified tolerance Included in title block, note, table, or separate document Goodheart-Willcox Publisher
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Geometric Dimensioning and Tolerancing (GD&T) Highly accurate definitions of tolerances for form, orientation, and position Needed to design products for precision applications Geometric characteristic symbols specify form, profile, orientation, location, and runout tolerances
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Geometric Characteristic Symbols Goodheart-Willcox Publisher
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Datum Used to indicate an exact point, axis, plane, or surface Identified by a datum feature symbol Goodheart-Willcox Publisher
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Feature Control Frame Indicates geometric tolerance Contains geometric characteristic symbol Typically shown with dimension Goodheart-Willcox Publisher
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. GD&T Interpretation Goodheart-Willcox Publisher
Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website. Dimensioning in CAD Saves time drawing dimensions manually Created with dimensioning commands Dimension styles control format and appearance Rules used in manual drafting apply Dimension styles should observe ASME, school, or company standards