2D ESSENTIALSInstructor: Laura Gerold, PECatalog #10614113Class # 22784, 24113, 24136, & 24138Class Start: January 18, 2012Class 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.
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/IndPro d/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 architectural and structural drawings are similar in many ways to those for dimensioning manufactured parts, but some practices differ. Refer to the following standards: • ANSI/ASME Y14.5-2009 Dimensioning and Tolerancing • ASME Y14.41-2003 Digital Product definition Data Practices Automatically Generated Dimensions. • ASME B4.2-1978 (R1999) Preferred Metric Limits and Fits Views and dimensions can be generated automatically from a solid model. (Courtesy of Robert Kincaid.)
Three Aspects of Good Dimensioning Technique 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. ALL TOLERANCES ±.02 INCHE UNLESS OTHERWISE NOTED.XAMPLES A Title Block Specifying Tolerances. (Courtesy of Dynojet Research, Inc.)
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.theswg eek.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 LINESa. 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
Guidelines for USING DIMENSION AND EXTENSION LINESDimensions should be lined up and grouped togetheras much as possible.
Guidelines for USING DIMENSION AND EXTENSION LINESa) Extension and Centerlines must cross visible lines of an object in many cases.b) When this occurs, do not leaves gaps
ARROWHEADS • 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 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.
LEADERSA leader is a thin, solid line directing attention to a note or dimension andstarting with an arrowhead or dot. For the Best Appearance, Make Leaders • near each other and parallel • across as few lines as possible Don’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 Drawing scale is noted in the title block. The drawing should not be scaled for dimensions. (Courtesy of Dynojet Research, Inc.)Many standard title blocks include anote such as: DO NOT SCALE DRAWING FOR DIMENSIONS
DIRECTION OF DIMENSION VALUES AND NOTESAll dimension values and notes are lettered horizontally to be read from the bottom of thesheet, as oriented by the title block.
DIMENSION UNITSA note stating ALL MEASUREMENTS IN MILLIMETERS or ALL MEASUREMENTS ININCHES UNLESS OTHERWISE NOTED is used in the title block to indicate themeasurement units… (Courtesy of Dynojet Research, Inc.)
MILLIMETER VALUES The 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 thethousandths of an inch. In two-place decimals, the second placepreferably should be an even digit.
RULES FOR DIMENSION VALUESGood hand-lettering is important for dimension values onsketches. The shop produces according to the directions on thedrawing so to save time and prevent costly mistakes, make alllettering perfectly legible.Make all decimal points bold, allowing ample space. When themetric dimension is a whole number, do not show either a decimalpoint or a zero. When the metric dimension is less than 1 mm, azero precedes the decimal point.When the decimal-inch dimension is used on drawings, a zero is notused before the decimal point of values less than 1 in.
DUAL DIMENSIONING and COMBINATION UNITSDual dimensioning is used to show metric and decimal-inch dimensions on the samedrawing. 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 LEGIBLYRules for the placement of dimensions help you dimension your drawings sothat they are clear and readable… Fitting Dimension Values in Limited Spaces (Metric Dimensions)
PLACING AND SHOWINGDIMENSIONS 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)
Dimensioning by Size (Geometric Breakdown)• 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
Dimensioning by Size (Geometric Breakdown)• 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
Dimensioning by Size (Geometric Breakdown)• 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 • 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: FILLETS R6 AND ROUNDS R3 UNLESS OTHERWISE SPECIFIED or ALL CASTING RADII R6 UNLESS NOTED or simply ALL FILLETS AND ROUNDS R6.
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 MARKSA 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 finishmark means that allowance of extra metal in the rough workpiece must beprovided 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?
SIZE DIMENSIONING HOLES• 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
SIZE DIMENSIONING HOLES• 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• 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. Use “Ø” to indicate circular shape
SIZE DIMENSIONS: CYLINDERSDimensioning 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 giveunnecessary 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 HomeworkChapter 10 Review Questions: 2, 4, 5, 7, 8, 10, 13Chapter 10 Exercises: 10.1 (a) – use any scale, justdefine it.