Orthographic Projection PDF

Chapter 2 ORTHOGRAPHIC PROJECTION Unit 1: Orthographic Projection Introduction Orthographic projection is the graphic representation of the true shape of a given object using two or more views on planes which are at right angles to each other. It shows the views of an object in two-dimen...

Chapter 2 ORTHOGRAPHIC PROJECTION Unit 1: Orthographic Projection Introduction Orthographic projection is the graphic representation of the true shape of a given object using two or more views on planes which are at right angles to each other. It shows the views of an object in two-dimensional forms. In this method of representing the views of the object the observer is assumed to be directly in front of each side of the object, thus his line of sight is perpendicular to the view being projected. Specific Objectives At the end of the lesson, the students should be able to: - Explain orthographic projection. - Identify the planes of projection. - Describe standard line practices to orthographic projection. - Apply standard line practices to orthographic projection. - Draw the necessary views of assigned object taking into consideration the theories and principles involved in orthographic projection. Lesson Proper A. Planes of Projection A plane of projection is an imaginary plane assumed to be between the observer and the object. It is a flat plane where the object’s image is projected and drawn. Three Planes of Projection 1. Frontal Plane – is the plane in which the front view of the object is projected. 2. Horizontal Plane – the plane of projection in which the top view is projection. 3. Profile Plane - the plane on which the side views are projected. B. Regular Views of an Object An object has six regular views namely: 1. Front view – is the view that shows the characteristic shape of the object. Views with irregular shape or outline must be selected as front view. 2. Top view - is the view that is found over the front view. 3. Right side view – is found at the right of the front view. 4. Left side view – is found at the left of the front view. 5. Rear view - is the view found at back of the front view. 6. Bottom view – is found below the top view. An object likewise has three principal views namely the front, top, and right-side view. C. Three Space Dimensions 1. Width – is measured from left to right and is measured between two profile planes. 2. Depth – is measured from front to rear and is measured between two frontal planes. 3. Height – is measured from bottom to top and is measured between two horizontal planes. Any view in orthographic projection will only show two of the space dimensions (example: Front Figure 1. Three Space view will show the width and height dimensions Dimensions only.) D. Principles of Orthographic Projection An object is composed of points (corners), lines (edges) and surfaces (planes). The following principles apply to the above-mentioned parts of the objects. 1. A point is projected as a point in all planes of projection. 2. Lines parallel to a plane of projection appear as lines in their true lengths. 3. Lines perpendicular to a plane of projection become points. 4. Lines inclined to a plane of projection become foreshortened. 5. No lines can be projected longer than its true length. 6. Surfaces parallel to a plane of projection appear in their true sizes and shapes. 7. Surfaces perpendicular to a plane of projection are shown as edges. 8. Surfaces inclined to a plane of projection appear as surfaces but smaller in size and retaining its shape. 9. The top view is drawn directly over the front view. 10. The top and front views are vertically aligned. 11. The front and side views are aligned horizontally. 12. The depth of the top and side views is the same. Figure 2. Principles of Orthographic Projection E. Selection of Views The main purpose of orthographic projection is to provide an accurate description of the shape of an object using two or more views. Generally, an object has six views, but not all of them are used in describing the shape of the object. It is the overall characteristics of an object that indicates the views required to describe its shape. The following pointer will be of help in selecting what view or views to draw: 1. Consider the part that have a characteristic view by which it can be recognized (e.g. irregular shapes or outlines, circular parts, curves). This should be drawn as the front view. 2. Consider the normal position of the part when it is in use, whether it is vertically or horizontally aligned or is positioned upwards or downwards. 3. Views with the least hidden lines are east to read and understand and is less-time consuming to draw. Objects made of flat surfaces or parts having uniform thickness can be described using one-view drawings. A cylinder can be drawn using one-view, provided that a note or explanation is added to provide the missing part of feature. Two-view drawings can be made for objects that are generally cylindrical, conical or pyramidal. For objects of a more complex shape, three-view drawings are sufficiently enough for their description. Figure 3. Proper Selection of Views F. Arrangement of Views Two possible arrangements of views on the drawing sheet can be made on the angles of projection in orthographic drawing. This angle of projection divides the drawing space into four quadrants which are called angles. The division is made through the intersection of the vertical and horizontal planes which are at right angles. The first angle of projection has the vertical and horizontal planes rotated on to a single plane. The resulting view arrangement makes the front view drawn above the top view and the left side view to the right of the front view. In the third angle of projection the arrangement will show the top view drawn over the front view and the right-side view drawn to the right of the front view. The second and fourth angles of projection are not used in technical drawings. It is recommended, that beginners use the third angle of projection for clarity and ease in visualization of the views.  Figure 4. First and Third Angle Projections G. Conventional Lines Used in Orthographic Projection 1. Visible or Object line - a thick line used to show visible parts of an object. (Use 0.5- or 0.6-mm technical pen) 2. Invisible or Hidden line – thin line consisting of 3mm long dashes with 1mm gaps and is used to show features or parts hidden from view. (Use 0.2- or 0.3-mm technical pen) 3. Center line – alternate long and short dashes used to show the axes of symmetrical objects like cylinders, drilled holes and circles. Long dashes measure 12mm and short dashes about 3mm with 1mm gaps. Center lines are thin lines. (Use 0.2- or 0.3-mm technical pen) Figure 5. Conventional Lines Used in Orthographic Projection Figure 6. Procedure in Drawing Orthographic Views References/Additional resources/Readings Bertoline, G. and Weibe, E, (1995). Fundamentals of Graphic Communication. McGraw-Hill B00k Co. Giesecke, Frederick, et. al. (1990). Technical Drawing 13th Edition. Pearson Education South Asia Pte. Ltd. Giesecke, Frederick et. al. (2016). Technical Drawing with Engineering Graphics 15th Edition. Pearson Education, Inc., publishing as Prentice Hall. Tadeo, Frederick G., et. al. (2002) Engineering Drawing Workbook. ACTIVITY SHEET________________ UNIT TEST/QUIZ #3 Name: _______________________________ Date: _____________ Course/Year & Section: __________________ Score: ____________ Direction: Write the word/phrase that best describes the following statements. Write your answers on the blanks before each item. ____________________ 1. It is a graphic representation of an object in two or more views on planes that are at right angles with each other. ____________________ 2. What view of the object shows the characteristic shape of an object? ____________________ 3. The dimension that is measured between two horizontal planes. ____________________ 4. The plane of projection where the side views are projected. ____________________ 5. What object or parts can be described using only one view? ____________________ 6. It is a thick line used to show the visible parts or outlines of an object. ____________________ 7. It is used to show surfaces perpendicular to a plane of projection. ____________________ 8. Which of the views is found below the top view? ____________________ 9. Which of the views are vertically aligned in an orthographic drawing set-up? ____________________ 10. It is the imaginary plane located between the object and observer where the image is drawn. ____________________ 11. Which of the views have the same depth? ____________________ 12. The angle of projection with the top view is drawn over the front view. ____________________ 13. Lines made up of short dashes and used to represent edges hidden from view. ____________________ 14. Why should the front and side views be aligned horizontally in the orthographic drawing set-up? ____________________ 15. The view found at the back of the front view. Unit 2: Dimensioning Introduction Drawing of objects, machines and structures for fabrication or construction will not be complete without adding size descriptions called dimensions. Dimensions are the numerical value that defines the size, location, or geometric characteristics of an object or feature. Dimensions provide the fabricator, workman or builder the necessary sizes needed for completing the object or feature. The size descriptions are indicated on the drawing by using a system of lines, symbols and numerical values is called dimensioning. Size descriptions on a drawing are arranged on a drawing in a definite manner to ensure accuracy and efficiency. Specific Objectives At the end of the lesson, the students should be able to: - Describe dimensioning - Describe the lines and symbols used in dimensioning. - Differentiate between size and location dimension. - Describe the systems of placing dimensions - Apply the rules for dimensioning drawings. Lesson Proper A. Lines and Symbols Used in Dimensioning 1. Dimension line A dimension line is a thin line that has a break in the middle for the dimension numerals. It is drawn parallel to the edge that is measured. It ends with arrowheads that point outwards. Figure 1. Dimension Line 2. Extension line An extension line is a thin line that projects from the views to indicate points or surfaces to be dimensioned. A gap of 1 mm shall be provided between the view and the start of the extension line and must extend about 3 mm from the last dimension line. The extension line limits the dimension line. Figure 2. Extension Line 3. Arrowheads The arrowheads are used at the ends of a dimension line to show the limits of the dimension. Arrowheads may be open or solid and should be carefully drawn to a uniform size in a given drawing. Figure 3. Arrowhead 4. Numerals and Notes Numerals and notes must be made carefully so that they will be easy to read and not be too large. Generally, numerals and notes should be about 3 mm in height and must be done with the aid of guide lines. Figure 4. Numerals and Notes 5. Leader line Leaders are thin lines drawn from a note to the part of the drawing it applies. It is drawn to a preferred angle of 60O (45O, 30O, or any angle maybe used). A leader starts with a short horizontal line about 3 mm long, called the note end and ends with an arrowhead indicating the part being dimensioned (pointing end). When a number of leaders are close together, they should be drawn parallel. A leader drawn from a circle or arc should be in a radial direction. Figure 5. Leader Line 6. Diameter symbol A symbol that precedes a numerical value to indicate the size of a circle. It is represented by the Greek letter phi Ø. 7. Radius symbol A symbol that precedes a numerical value to indicate the radius of a circle or arc. It is represented by capital letter R. B. Systems of Placing Dimensions 1. Aligned System The aligned system of placing dimensions has the dimension numerals in line with the dimension lines. The horizontal dimensions always read from the bottom of the sheet and vertical dimensions read from the right-hand side of the sheet. 2. Unidirectional System In the unidirectional system of placing dimensions, all dimension numerals are placed to be read from the bottom of the sheet. It was brought into use by automotive and aircraft companies and is gaining acceptance by other industries. Figure 6. Aligned and Unidirectional System for placing dimensions C. Basic Kinds of Dimensions a. Size dimensions They are dimensions that provide the following: Width is the distance measured from left to right and is the only dimension placed horizontally. Depth is the distance measured from front to rear. Height is the distance measured from bottom to top Diameter is the full distance across a circle, measured through the center. Radius is the distance from the center of an arc to any point on the arc. b. Location dimensions They are dimensions used to specify relative positions of parts or shapes of an object. Figure 7. Size and Location dimension D. General Rules in Dimensioning 1. Provide a minimum distance of 10 mm between the object and the first-dimension line and between succeeding dimension lines. 2. Provide at least a 2 mm space between the outline of the object and the extension line. Extension lines should extend about 3 mm beyond the last dimension line. 3. Group dimensions on a view or drawing that most clearly describe the feature being dimensioned (contour dimensioning). Generally, dimensions are placed between views. 4. Extension lines should not cross dimension lines but may cross other extension lines. 5. Center lines can be used as extension lines in locating center to center distances of circles or edge to center distances of circles. 6. Stagger dimension on parallel dimensioning. Figure 8. General Rules of Dimensioning: Rule 1 – 6 7. Dimension arcs by giving the radius. 8. Dimension circles by giving their diameters. 9. Dimension chamfers by giving either an angle, a linear distance or two linear distances. 10. Dimension slots by using two linear distances, by their centerlines and required radius of the arc, and by using an explanatory note on a leader line describing two linear distances and radius of arc. 11. Angular dimensions are shown in decimal degrees, or in degrees, minutes and seconds and must be read horizontally. 12. Numerical values placed on dimensions must be actual sizes regardless of the scale used in the drawing.  Figure 9. General Rules of Dimensioning: Rule 6 – 11 References/Additional Resources/Readings Bertoline, G. and Wiebe, E. (1995). Fundamentals of Graphic Communication. McGraw-Hill Book Co. Giesecke, Frederick et. al. (2009). Technical Drawing 13th Ed. Pearson Education South Asia Pte. Ltd. Olivo, C. Thomas and Olivo, Thomas P. (1999). Basic Blueprint Reading and Sketching 7 th Ed. Delmar Publishers http://engineeringessentials.com>dim http://quizlet.com>the-16 rules of dimensioning ACTIVITY SHEET_______________________________ UNIT TEST/QUIZ #4 Name: _______________________________ Date: _____________ Course/Year & Section: __________________ Score: ____________ I. Fill in the blanks: Fill in the blanks with words or phrases to complete the sentences. ____________________ 1. The symbol used to indicate the diameter of a circle. ____________________ 2. A system of placing dimensions where the numerals are all read from the bottom of the drawing sheet. ____________________ 3. Dimensions that indicate the position of parts or features of an object. ____________________ 4. A thin, solid line usually broken in the middle for inserting dimension numerals. ____________________ 5. It is the numerical value that describes the size, location and geometric characteristics of an object. ____________________ 6. It is found at both ends of a dimension line. ____________________ 7. The distance that is measured from left to right. ____________________ 8. It is the full distance across a circle measured through the center. ____________________ 9. The preferred angle for leader lines. ____________________ 10. It limits the dimension lines. II. Direction: Write T, if the statement is correct and F if it is wrong. Place your answers on the blanks before each item. _____ 11. Dimension lines must be parallel with the edge being measured. _____ 12. The arrowheads at both ends of a dimension line shall point inwards. _____ 13. The gap or space between the object and the extension line should be at least 3 mm. _____ 14. Aligned system of dimensioning have the dimension numerals read from the bottom of the sheet. _____ 15. The same dimension can be repeated in different views. _____ 16. Dimension lines can cross each other. _____ 17. Contour dimensioning has the dimension figures placed on the view that clearly describes the feature. _____ 18. Overall dimensions are placed outside the smaller or detail dimensions. _____ 19. The numerical value in the aligned system of dimensioning are placed parallel to the dimension lines. _____ 20. It is good practice to omit one dimension in a row of dimensions. Unit 3: Scaling Drawings Introduction Scaling is the indication of relationship between measurements on a drawing and that of the object, machineries and parts, buildings and structure and everything that is fabricated for use. It is the method of drawing an object proportionately on paper. It takes into consideration the actual sizes of everything to be fabricated or constructed and the size of the drawing sheet. A few objects may fit a drawing sheet but most cannot fit the drawing sheet thus the need to scale drawings. Specific Objectives At the end of the lesson, the students should be able to: - Describe scaling. - Identify the methods of drawing an object to scale. - Draw given objects using assigned scale - Possess skill in using the triangular scale. Lesson Proper A. The Metric Scale The metric scale is used to create scaled technical drawings using SI units. It is divided into centimeters, with centimeters divided into millimeters (10 divisions) 0r into half millimeters (20 divisions). A metric triangular scale is used to lay out measurements on technical drawing and offers a combination of several scales on each side. Triangular scales are usually 15 or 30 centimeters long. B. Methods of Scaling Drawings The methods of scaling to be used shall take into consideration the actual sizes and the size of the drawing sheet. 1. Reduction scales These scales are used when the item to draw is of a large size compared to the drawing sheet like house plans, working drawings of machines, automobiles, airplanes, ships, household equipment and the like. The following reduction scales can be seen on triangular scales: 1:100, 1:80, 1:75, 1:60, 1:50, 1:40, 1:30, 1: 25, and 1:20. The number on the left side of the scale represents the drawing size while the number on the right represent actual sizes. In case, you may want to compute scaled sizes mathematically, just divide given actual sizes by the number on the right side of a given scale. Example: Given size/measurement = 3.50 meters Selected drawing scale = 1:100 Solution: 3.50 / 100 =.035 or 3.5 centimeters 2. Enlargement scales These scales are used when the item to draw is relatively small compared to the drawing sheet. It is where the actual sizes are multiplied by a preferred number of times to make details clearer. Enlargement scales are expressed like the following: 2:1 (double size), 3:1 (triple size) and soon. Notice that the drawing size (number on the left) is greater than the number on the right. These scales cannot be seen on triangular scale as all scales in the triangular scale are reduction scales.  3. Reproduction Scales/Full-Sizing This particular method of scaling has the object or item drawn in its actual size. The scale is expressed on the drawing sheet either as 1:1 or FULL SIZE. This is used when the item or object is comparatively small in relation to the drawing sheet. C. How to Read a Metric Scale Example 1: Given measurement = 0.44 m (44 cm or 440 mm) Given scale = 1:20 Step: align the zero mark with the left end of the line and read which mark on the scale is aligned closest to the right end of the line. For this example, assume a assume a line with the right end is closest to the mark past 400. The end of the line is 0.44 cm or 440 mm. Example 2: Given measurement = 4.20 meters Given scale = 1:100 The given scale means that 1 cm = 100 cm or 1.00 meter. One centimeter as represented by the number 1 on the triangular scale is divided into ten equal parts. Each part is equivalent to 10 centimeters. To layout 4.20 meters on a given line, align the zero mark of the scale with the left end of the line, read past the number 4 mark with 2 divisions to come up with the required 4.20 meter distance. References/Additional Resources/Readings Bertoline, G. and Wiebe, E. (1995). Fundamentals of Graphic Communication. McGraw-Hill book Co. Giesecke, Frederick et. al (2009). Technical Drawing 13th Ed. Pearson Education South Asia Pte. Ltd. ACTIVITY SHEET_______________________________ UNIT TEST/QUIZ #5 Name: _______________________________ Date: _____________ Course/Year & Section: __________________ Score: ____________ I. Direction: Write the word/phrase that best describes the following statements. Write your answers on the blanks before each item. ____________________ 1. It is used to create scaled technical drawings using SI units ____________________ 2. It is the method of drawing an object proportionately on paper. ____________________ 3. It is used to lay out measurements on technical drawing and offers a combination of several scales on each side. ____________________ 4. It is used when the item to draw is relatively small compared to the drawing sheet. ____________________ 5. Triangular scales are usually __________________ long. ____________________ 6. This particular method has its objects drawn on its actual size. ____________________ 7. It represents the number on the right side of the scale. ____________________ 8. It is used when the object or item to draw is in large size. ____________________ 9. It represents the number on the left side of the scale. ____________________ 10. The formula for computing scale sizes. II. Direction: Compute the scale sizes of the following given sizes/measurements. Use the formula for computing scale sizes. Write your answers in the form of centimeters. ____________________ 11. Given Size : 8.75 meters Selected Scale : 1:50 ____________________ 12. Given Size : 4.25 meters Selected Scale : 1:20 ____________________ 13. Given Size : 9.75 meters Selected Scale : 1:30 ____________________ 14. Given Size : 32.50 meters Selected Scale : 1:50 ____________________ 15. Given Size : 12.50 meters Selected Scale : 1:40