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Orthographic Projection Part-1 engineering108.com

PROJECTION METHOD engineering108.com

Line of sight is an imaginary ray of light between an observer’s eye and an object. There are 2 types of LOS : parallel and converge Parallel projection Perspective projection Line of sight Line of sight engineering108.com

Plane of projection is an imaginary flat plane which the image is created. The image is produced by connecting the points where the LOS pierce the projection plane. Parallel projection Perspective projection Plane of projection Plane of projection engineering108.com

Disadvantage of Perspective Projection Perspective projection is not used by engineer for manu- facturing of parts, because 1) It is difficult to create. 2) It does not reveal exact shape and size. Width is distorted engineering108.com

Orthographic Projection engineering108.com

MEANING Orthographic projection is a parallel projection technique in which the parallel lines of sight are perpendicular to the projection plane Object views from top 1 2 1 5 2 3 4 5 3 4 Projection plane engineering108.com

ORTHOGRAPHIC VIEW NOTES Orthographic projection technique can produce either 1. Multiview drawing that each view show an object in two dimensions. 2. Axonometric drawing that show all three dimensions of an object in one view. Both drawing types are used in technical drawing for communication. engineering108.com

Axonometric (Isometric) Drawing Advantage Easy to understand Disadvantage Shape and angle distortion Example Distortions of shape and size in isometric drawing Circular hole becomes ellipse. Right angle becomes obtuse angle. engineering108.com

Multiview Drawing Advantage Disadvantage Example It represents accurate shape and size. Disadvantage Require practice in writing and reading. Example Multiviews drawing (2-view drawing) engineering108.com

IT IS A TECHNICAL DRAWING IN WHICH DIFFERENT VIEWS OF AN OBJECT ORTHOGRAPHIC PROJECTIONS: IT IS A TECHNICAL DRAWING IN WHICH DIFFERENT VIEWS OF AN OBJECT ARE PROJECTED ON DIFFERENT REFERENCE PLANES OBSERVING PERPENDICULAR TO RESPECTIVE REFERENCE PLANE Different Reference planes are Horizontal Plane (HP), Vertical Frontal Plane ( VP ) Side Or Profile Plane ( PP) And Different Views are Front View (FV), Top View (TV) and Side View (SV) FV is a view projected on VP. TV is a view projected on HP. SV is a view projected on PP. engineering108.com

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Defining the Six Principal Views or Orthographic Views Orthographic Projections are a collection of 2-D drawings that work together to give an accurate overall representation of an object. Defining the Six Principal Views or Orthographic Views engineering108.com

Auxiliary Vertical Plane (A.V.P.) Auxiliary Inclined Plane (A.I.P.) PLANES PRINCIPAL PLANES HP AND VP AUXILIARY PLANES Auxiliary Vertical Plane (A.V.P.) Auxiliary Inclined Plane (A.I.P.) Profile Plane ( P.P.)  A.V.P. A.I.P.  to Hp &  to Vp  to Vp  to Hp &  engineering108.com

PICTURE PLANE Object Observer engineering108.com

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Glass Box Approach The object, whose orthographic projection needs to be drawn, is enclosed in a glass-box engineering108.com

Glass Box Approach Project points on the front view of the glass-box engineering108.com

Glass Box Approach Project points on the the top view of the glass-box, just as done for front engineering108.com

Glass Box Approach Project points on the right view of the glass-box, just as done for front and top engineering108.com

Glass Box Approach Unfold the glass box, see how the views align engineering108.com

Glass Box Approach Unfold the glass box, see how the views align engineering108.com

First and Third Angle Projections First-angle Projection Instructor: Third angle projection is normally used in the US while Europe uses the First Angle projection. Note the symbols at the bottom of each one which tell you which projection that you are viewing. These can be confusing to students. We are only highlighting the fact that there are different ways to represent projections. It is not expected for students to fully understand the differences. From Fundamentals of Graphic Communications by Bertoline, McGraw-Hill First Angle Third Angle engineering108.com

Conventional Orthographic Views Height Depth Width Front View Top View/Plan Right Side View engineering108.com

Line Thickness Line Styles Lines on an engineering drawing signify more than just the geometry of the object and it is important that the appropriate line type is used. Line Thickness For most engineering drawings you will require two thickness', a thick and thin line. The general recommendation are that thick lines are twice as thick as thin lines.                                               A thick continuous line is used for visible edges and outlines. A thin line is used for hatching, leader lines, short centre lines, dimensions and projections. Line Styles Other line styles used to clarify important features on drawings are:                                              Thin chain lines are a common feature on engineering drawings used to indicate centre lines. Centre lines are used to identify the centre of a circle, cylindrical features, or a line of symmetry.                                               Dashed lines are used to show important hidden detail for example wall thickness and holes.. engineering108.com

Precedence of Lines Visible lines takes precedence over all other lines Hidden lines and cutting plane lines take precedence over center lines Center lines have lowest precedence 0.6 mm From: Bertoline, Figure 2.40/ Pg 43 Note the thickness specified for given three types of lines The precedence of lines governs which lines are drawn when more than one line occupies the same position on a drawing. For example the figure above shows that while a visible line takes precedence over all other lines, hidden line and cutting plane line take precedence over center lines. Standard engineering drawing practices requires the use of standard linetypes, which are called the alphabet of lines. The sizes show the recommended line thicknesses. 0.3 mm 0.6 mm engineering108.com

For Example: 1. Visible 2. Hidden 3. Center From Bertoline: Figure 2.38 / Pg 42 In engineering and technical drawing, it is important that hidden features be represented, so that the reader of the drawing can clearly understand the object. Thus we need hidden lines to emphasize that those features exist and are hidden in that particular view. We also need center lines to understand how the features defined in the 2D views translate into 3D. NOTE: It must be emphasized that hidden lines and center lines are used only on Orthographic projection drawings, never on isometric drawings Q: Do we need a convention for what line to show if two lines fall on top of each other? A: Yes! Otherwise features which are more important (eg: visible lines) would be overridden by less important features (eg: hidden lines) and the resulting drawing would be interpreted inaccurately. The next slide shows the convention followed. 2. Hidden 3. Center engineering108.com

Dimensioning A dimensioned drawing should provide all the information necessary for a finished product or part to be manufactured. An example dimension is shown below.                                                                                                                                                                                                         Dimensions are always drawn using continuous thin lines. Two projection lines indicate where the dimension starts and finishes. Projection lines do not touch the object and are drawn perpendicular to the element you are dimensioning. All dimensions less than 1 should have a leading zero. i.e. .35 should be written as 0.35 engineering108.com

Types of Dimensioning Parallel Dimensioning Parallel dimensioning consists of several dimensions originating from one projection line. engineering108.com

Superimposed Running Dimensions Superimposed running dimensioning simplifies parallel dimensions in order to reduce the space used on a drawing. The common origin for the dimension lines is indicated by a small circle at the intersection of the first dimension and the projection line. engineering108.com

Chain Dimensioning Combined Dimensions A combined dimension uses both chain and parallel dimensioning. engineering108.com

Dimensioning of circles (a) shows two common methods of dimensioning a circle. One method dimensions the circle between two lines projected from two diametrically opposite points. The second method dimensions the circle internally. (b) is used when the circle is too small for the dimension to be easily read if it was placed inside the circle. engineering108.com

Dimensioning Radii All radial dimensions are proceeded by the capital R. shows a radius dimensioned with the centre of the radius located on the drawing. (b) shows how to dimension radii which do not need their centres locating. engineering108.com

Tolerancing It is not possible in practice to manufacture products to the exact figures displayed on an engineering drawing. The accuracy depends largely on the manufacturing process. A tolerance value shows the manufacturing department the maximum permissible variation from the dimension. Each dimension on a drawing must include a tolerance value. This can appear either as: a general tolerance value applicable to several dimensions. i.e. a note specifying that the General Tolerance +/- 0.5 mm. or a tolerance specific to that dimension engineering108.com

values read from bottom and Right side Unidirectional System Aligned System values read from bottom and Right side Unidirectional System values read from bottom only (Preferred when?) engineering108.com

INCORRECT CORRECT engineering108.com

Dimensioning a circular arc. engineering108.com

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Omit unnecessary dimensions. engineering108.com

Use of enlarged view to clarify dimensions. engineering108.com

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