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2D ESSENTIALS

Instructor: Laura Gerold, PE

Catalog #10614113

Class # 22784, 24113, 24136, & 24138

Class Start: January 18, 2012

Class End: May 16, 2012

Reminders

• Extra Credit (Write Exam Question) Due TODAY• Final Project is due in next week on May 9th.• Final Exam is in two weeks on May 16th.

QUESTIONS

How do you draw faster ellipses?• An ellipse template!

Can Architectural Standards be Used for Dimensions on Project?

• Architectural Standards can be used

How Do you Dimension a Corkscrew?

• Inside diameter• Outside diameter• Centerline of the screw diameter• Cut a section through the centerline, and put a vertical

dimension, or typical dimension on each…

CHAPTER 10 – DIMENSIONING

Why Do We Dimension Drawings?• Dimensions describe the size, shape, and material of

objects • Give detail on how to build an object from the designer to

the manufacturer

Source: http://www.design-technology.info/IndProd/page11.htm

UNDERSTANDING DIMENSIONINGThe increasing need for precision manufacturing and interchangeabilityhas shifted responsibility for size control to the design engineer or detail drafter.

Practices for dimensioning architecturaland structural drawings are similarin many ways to those for dimensioningmanufactured parts, but some practicesdiffer.

Refer to the following standards:• ANSI/ASME Y14.5-2009 Dimensioning and Tolerancing• ASME Y14.41-2003 Digital Product definition Data Practices• ASME B4.2-1978 (R1999) Preferred Metric Limits and Fits

Automatically Generated Dimensions. Views and dimensions can be generated automatically from a solid model. (Courtesy of Robert Kincaid.)

Three Aspects of Good DimensioningTechnique of dimensioning

Placement of dimensions

Choice of dimensions

Three Aspects of Good Dimensioning• Technique of dimensioning

• Standard appearance of lines• Spacing of Dimensions• Size of Arrowheads• Etc.

Three Aspects of Good Dimensioning• Placement of dimensions

• Logical Placement to make dimensions:• Legible• Easy to Find• Easy for the Reader to Interpret

Three Aspects of Good Dimensioning• Choice of dimensions

• Show how the design is manufactured• Dimension first for Function• Add dimensions for ease of manufacturing

ToleranceTolerance is the total amount that the feature on the actual part is allowedto vary from what is specified by the drawing or model dimension.

A Title Block Specifying Tolerances. (Courtesy of Dynojet Research, Inc.)

ALL TOLERANCES ±.02 INCHUNLESS OTHERWISE NOTED.E

XAMPLES

LINES USED IN DIMENSIONING• Dimension Line

• A thin, dark, solid line terminated by an arrowhead, indicating the direction and extent of a dimension

• Usually Perpendicular to extension lines• The distance is indicated numerically at the midpoint of the

dimension line, either adjacent to the dimension line, or in a gap provided for it.

• First Dimension Line should be at least 3/8” away from object

• Subsequent lines can be ¼” apart and should be uniform

LINES USED IN DIMENSIONING• Extension Line

• Thin, dark, solid line that extends from a point on a drawing to which a dimension refers

• Typically Perpendicular to Dimension Lines• A small gap (1/16”) should be left between the

extension line and the object• Extension line should extend 1/8” beyond the outermost

arrow• An extension line does not have arrows

LINES USED IN DIMENSIONING• Example Dimension and Extension Lines

Source: http://www.theswgeek.com/2008/05/29/hide-show-extension-and-dimension-lines/

LINES USED IN DIMENSIONING• Centerlines

• Thin dark line alternating long and short dashes

• Commonly used as extension lines in locating holes and other symmetrical features

• When extended for dimensioning, cross over the other lines of a drawing with no gaps

• End centerlines using a long dash

Guidelines for USING DIMENSION

AND EXTENSION LINES

a. Shorter dimensions are nearest the object outlineb. Do not place shorter dimensions outside, which result in

crossing extension linesc. Okay to cross extension lines, but they should not be

shortenedd. A dimension line should never coincide with or extend from

any line of a drawing


AND EXTENSION LINES

Dimensions should be lined up and grouped together as much as possible.


AND EXTENSION LINES

a) Extension and Centerlines must cross visible lines of an object in many cases.

b) When this occurs, do not leaves gaps

ARROWHEADS

When you are drawing by hand and using the arrowhead method in which both strokes are directed toward the point, it is easier to make the strokes toward yourself.

• Arrowheads• Should be uniform in size and style

throughout the drawing• Length and width should have a ratio of

3:1• Length of arrowhead should be about

1/8” long• Should be filled in to look better

LEADERSA leader is a thin, solid line directing attention to a note or dimension and starting with an arrowhead or dot.

For the Best Appearance, Make Leaders• near each other and parallel• across as few lines as possibleDon’t Make Leaders• parallel to nearby lines of the drawing• through a corner of the view• across each other• longer than needed• horizontal or vertical

Time to Mix up Groups . . . • Find a new person to form a group with that sits in a

different row the you• Look for someone that you have not previously teamed

with before• Form groups of 2 to 3 people.

Group Project• Look at the drawings on page 401 & 402 of the text• Identify the extension, dimension, center, and leader lines• Note the style and location of the arrowheads

• Dimension a simple block object. Label the lines as extension, dimension, and leader lines.

DRAWING SCALE AND DIMENSIONING

Many standard title blocks include a note such as:

DO NOT SCALE DRAWING FOR DIMENSIONS

Drawing scale is noted in the title block. The drawing should not be scaled for dimensions. (Courtesy of Dynojet Research, Inc.)

DIRECTION OF DIMENSIONVALUES AND NOTES

All dimension values and notes are lettered horizontally to be read from the bottom of the sheet, as oriented by the title block.

DIMENSION UNITS

A note stating ALL MEASUREMENTS IN MILLIMETERS or ALL MEASUREMENTS IN INCHES UNLESS OTHERWISE NOTED is used in the title block to indicate the measurement units…

(Courtesy of Dynojet Research, Inc.)

MILLIMETER VALUESThe millimeter is the commonly used unit for most metric engineering drawings. One-place millimeter decimals are used when tolerance limits permit. Two (or more)–place millimeter decimals are used when higher tolerances are required.

DECIMAL-INCH VALUESTwo-place inch decimals are typical when tolerance limits permit. Three or more decimal places are used for tolerance limits in the thousandths of an inch. In two-place decimals, the second place preferably should be an even digit.

RULES FOR DIMENSION VALUESGood hand-lettering is important for dimension values on sketches. The shop produces according to the directions on the drawing so to save time and prevent costly mistakes, make all lettering perfectly legible.

Make all decimal points bold, allowing ample space. When the metric dimension is a whole number, do not show either a decimal point or a zero. When the metric dimension is less than 1 mm, a zero precedes the decimal point.When the decimal-inch dimension is used on drawings, a zero is not used before the decimal point of values less than 1 in.

DUAL DIMENSIONING and COMBINATION UNITS

Dual dimensioning is used to show metric and decimal-inch dimensions on the same drawing. Two methods of displaying the dual dimensions are:

1. Position Method2. Bracket Method DIMENSIONS IN () ARE MILLIMETERS

DIMENSION SYMBOLSDimensioning symbols are used to replace traditional terms or abbreviations. (pg 373)

Form and Proportion of Dimensioning Symbols. (Reprinted from ASME Y14.5M-1994 (R2004),by permission of The American Society of Mechanical Engineers. All rights

reserved.)

PLACING AND SHOWING DIMENSIONS LEGIBLY

Rules for the placement of dimensions help you dimension your drawings so that they are clear and readable…

Fitting Dimension Values in Limited Spaces (Metric Dimensions)

PLACING AND SHOWING DIMENSIONS LEGIBLY continued…

Dimensioning by Size (Geometric Breakdown)

• Engineering structures are composed largely of simple geometric shapes, such as the prism, cylinder, pyramid, cone, and sphere. They may be exterior (positive) or interior (negative) forms.

• Positive = exterior (ex. Steel shaft)

• Negative = interior (ex. Round hole)


• Step 1: Consider the geometric features of the part and break them down.

• In this example, there are:• 2 positive prisms• 1 positive cylinder• 1 negative cone• 6 negative cylinders


• Step 2: Specify the size dimensions for each feature by lettering the dimension values as indicated

• Note that the four cylinders with the same size can be specified with one dimension


• Step 3: Locate the geometric features with respect to each other

• Check to ensure the object is fully dimensioned

LOCATION DIMENSIONS• After you have specified the sizes of the

geometric shapes composing the structure, give location dimensions to show the relative positions of these geometric shapes.

• (a) rectangular shapes located by faces• (b) symmetrical features located by centerlines

LOCATION DIMENSIONS

• Locate holes where the holes appear circular

LOCATION DIMENSIONS• Use the note 5X to note repetitive features

or dimensions• X means times• 5 means the number of repeated

features.• Put a space between the X and the

dimension• Use coordinate dimensions when you need

greater accuracy (c)

Group Project: Location vs. Size Dimensions

• Find an object around the room that has holes or is composed of two different geometric items together.

• Dimension the object first using size and then location• The dimensions do not need to be numerical, label them

as “size” or “location.”• Present

DIMENSIONING ANGLES• Angles are dimensioned by specifying the angle in degrees

and a linear dimension.• The coordinate method is better when a high degree of

accuracy is required• In civil engineering projects, ratios are used with one

member of the ratio equal to 1.

DIMENSIONING ANGLES – GROUP PROJECT

• Using a simple object with an inclined surface, dimension the angle

• Use both degrees and a linear dimension• Present

DIMENSIONING ARCS• A circular arc is dimensioned in the view where its true

shape in seen by giving the value for its radius preceded by the abbreviation R.

• The center is marked with small crosses to clarify the drawing (except when small, unimportant, or undimensioned arcs)

• When there is enough room, both the radius value and arrowhead are placed inside the arc

• If not, the arrowhead is left inside, but the value is moved outside or both are moved out

• False center may be indicated with dimension line jogged to it (f)

DIMENSIONING FILLETS AND ROUNDS

FILLETS R6 AND ROUNDS R3 UNLESS OTHERWISE SPECIFIED

orALL CASTING RADII R6 UNLESS NOTED

or simplyALL FILLETS AND ROUNDS R6.

• Dimensioned like other arcs• If there are few and they are obviously the same size, only

dimension one• If numerous and a standard size, use notes such as the

following:

Group Project – Dimensioning Arcs• Use a simple object with an arc that I have, that is around

the room, or that you brought with you• Dimension the arc using a couple of different methods

discussed• Present

FINISH MARKS

A finish mark is used to indicate that a surface is to be machined, or finished, as on a rough casting or forging. To the patternmaker or diemaker, a finish mark means that allowance of extra metal in the rough workpiece must be provided for the machining.

FINISH MARKS

• There are three styles of finish marks as shown on the figure below

• (c) shows a simple casting having several finished surfaces

• (d) shows on finish marks are indicated on the drawing.

• The finish mark is shown on the edge view of the finished surface and is repeated in any other view in which the surface appears as a line, even a hidden line

FINISH MARKS

• A finish mark point should be directed inward toward the body of the metal similar to a tool bit (a)

• It should be shown upside down (b)

FINISH MARKS GROUP PROJECT• Build a simple block item• Draw the necessary views• Apply finish marks • Compare your finish marks with another group• Present

SIZE DIMENSIONING HOLES

• The leader of a note should point to the circular view of the hole, if possible.

• Arrowhead should touch the outer circle• How would you read the dimensions on the

object below?


• When the circular view of a hole has two or more concentric circles (counterbored, countersunk, spotfaced, or tapped holes), the arrowhead should touch the outer circle.

• Draw a radial leader line, a line that would pass through the center of the circle if extended


• Countersunk, counterbored, spotfaced and tapped holes are usually specified by standard symbols or abbreviations.

• As a group, figure out the symbols on the above figures (see page 379 & 380 in text)

• Present

GROUP PROJECT - SIZE DIMENSIONING HOLES

• Draw one block with the center hole, or another object with a hole

• Dimension the hole• Present

DIMENSIONING CURVES• One way to dimension curves is to give a group of radii (a) • On (a), a jog is made in the dimension line if the radius is

inaccessible• On (b), the outline envelope of the curved surface is

dimensioned and the radii are self-locating from “floating centers”

• Both circular and noncircular curves may be dimensioned by using coordinate dimensions, or datums (c).

.

DIMENSIONING CURVES

• When angular measurements are unsatisfactory, you may give chordal dimensions (a)

• Or you can give linear dimensions on curved surfaces (b)

DIMENSIONING CURVES – GROUP PROJECT

• Sketch a simple curved surface• Practice using the different methods of dimensioning the

curved surface as discussed on the previous two slides (and as shown on page 382 & 383 of the text)

• Which method do you prefer?• Present

DIMENSIONING PRISMS• Height and width are usually given in the front view• Depth is given in the top view• Vertical dimensions are placed on the left or right, usually inline• Place the horizontal dimensions between views

DIMENSIONING PRISMS – GROUP PROJECT

• Draw the necessary views of a simple rectangular prism• Dimension the prism• Present

SIZE DIMENSIONS: CYLINDERS

Use “Ø” to indicate circular shape

• Cylinders are usually dimensioned by giving the diameter and length where the cylinder appears as a rectangle.

• The radius of a cylinder should never be given.

SIZE DIMENSIONS: CYLINDERS

Dimensioning a Machine Part Composed of Cylindrical Shapes

SIZE DIMENSIONS: CYLINDERS – GROUP PROJECT

• Sketch the necessary views of a simple cylinder• Dimension the cylinder• Present

CONTOUR DIMENSIONING PRINCIPLE

• Dimension features should be attached to the view where the feature’s shape is best shown

SUPERFLUOUS DIMENSIONSAll necessary dimensions must be shown, but do not give unnecessary or superfluous dimensions.

SUPERFLUOUS DIMENSIONS continued…

No unnecessary or superfluous dimensions.

Project Time!• Share your projects with your group.• Discuss dimensioning your project. • Do you have any final questions to finish your project?

What’s Next?

• Finish Lingering Questions from Chapter 8 and Chapter 10

• Review for Final Exam

Questions?

• On one of your sketches, answer the following two questions:• What was the most useful thing that you learned today?

• What do you still have questions about?• What specific items would you like to review next week before the exam?

LAST Homework

Chapter 10 Review Questions: 2, 4, 5, 7, 8, 10, 13

Chapter 10 Exercises: 10.1 (a) – use any scale, just define it.