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#### Orthographic Projection and Isometric Drawing Orthographic Projection

Orthographic Projection is to observe a 3-Dimensional object in a perpendicular direction and the representation of this 3-Dimensional object in to a 2-Dimensional drawing on drawing sheet or drawing paper. It is a form of parallel projection in which all the projection lines are orthogonal to the projection planeresulting in every plane of the scene appearing in affine transformation on the viewing surface. The obverse of an orthographic projection is an oblique projection, which is a parallel projection in which the projection lines are not orthogonal to the projection plane.In Engineering Graphics, the projection of one face of an object usually will not provide an overall description of the object; other planes of projection must be used. To create the necessary 2D views, the point of sight is changed to project different views of the same object; hence, each view is from a different point of sight. If the point of sight is moved to the front of the object, this will result in the front view of the object. And then move the point of sight to the top of the object and looking down at the top, and then move to the right side of the object, as the case may be. Each additional view requires a new point of sight.

Planes of Orthographic Projection

1. HP (Horizantal Plane)- It is the reference plane of projection shows the top view of an object.

2. VP (Vertical Plane)-It is the reference plane of projection shows front view of an object.

3. Auxolary Plane.-It is the extra plane of projection shows the view of an object, the views are not shown in HP and VP.

In Orthographic Projection the 3-dimensional object is lies in quadrant system, in this system there are four quadrants but our syllabus only first and third quadrant system is used for projections. the second and fourth are not used because when we are convert the 3-dimensional object in to a 2-dimensional drawing at that time the HP plane is rotate 900 in  Clockwise direction then HP and VP are overlap or interconnected that’s why we are not used second and fourth quadrant system.

After completing of this topic students should able to know what is mean by orthographic projection. we are clear this topic and basic concepts related to this topic in our college Pimpri Chinchwad Polytechnic Nigdi it is the topmost college in pune division.

Methods of Projection

 SR.NO First Angle Projection Third Angle Projection 1 Object lies in 1st quadrant Object lies in 3rd quadrant. 2 F.V lies on above XY line. FV lies on below XY line. 3 TV lies on below XY line. TV lies on above XY line. 4 LHSV lies right of the FV. LHSV lies left of the FV. 5 RHSV lies left of the FV RHSV lies right of the FV. 6 Used in INDIA. Used in ASIAN Countries. Isometric Drawing

Engineering Graphics is the language of engineers. The concepts of Engineering Graphics are used to develop, express the ideas, and convey the instructions which are used to carry out jobs in the field Engineering. The course illustrates the techniques of graphics in actual practice. This preliminary course aims at building a foundation for the further course in drawing and other allied subjects. This subject is useful in developing drafting and sketching skills of students. Develop ability to differentiate between isometric view and isometric projections. Isometric drawings are a type of pictorial drawings that show the three principal dimensions of an object in one view. The principal dimensions are the limits of size for the object along the three principal directions. Pictorial drawings consist of visible object faces and the features lying on the faces with the internal features of the object largely hidden from view. They tend to present images of objects in a form that mimics what the human eye would see naturally. Pictorial drawings are easy to understand since the images shown bear resemblance to the real or imagined object. Non-technical personnel can interpret them because they are generally easy to understand. Pictorial drawings are excellent starting point in visualization and design and are often used to supplement multiview drawings. Hidden lines are usually omitted in pictorial drawings, except where they aid clarity. An isometric drawing is one of three types of axonometric drawings they are created based on parallel projection technique. The other two types of axonometric drawings are dimetric and trimetric drawings. In isometric drawings, the three principal axes make equal angles with the image plane. In dimetric drawing, two of the three principal axes make equal angles with the image plane while in trimetric drawing; the three principal axes make different angles with the image plane. Isometric drawings are the most popular.

Isometric Projection and Scale

There are number of nonconventional machining process which are combines with the CNC to give more advancement in the manufacturing

Isometric Projections-

It is the type of axonometric projections, representation of a 2-Dimenstional drawing in to 3-Dimensional object. An isometric projection is a representation of a view of an object at 35o 16’ elevation and 45o azimuth. The principal axes of projection are obtained by rotating a cube through 45o about a vertical axis, then tilting it downward at 35o 16’ (35.27o) as shown in Fig. 1a. A downward tilt of the cube shows the top face while an upward tilt shows the bottom face. The 45o rotation is measured on a horizontal plane while the 35o 16’ angle is measured on a vertical plane. The combined rotations make the top diagonal of the cube to appear as a point in the front view. The nearest edge of the cube to the viewer appears vertical in the isometric view. The two receding axes project from the vertical at 120o on the left and right sides of the vertical line as shown in Fig. 1b. The three principal axes are therefore inclined at 120o and are parallel to the cube edges in the isometric view. These three principal axes are known as isometric axes. The two receding axes are inclined at 30o to the horizontal line while the vertical axis is at 90o to the horizontal line. The three visible faces of the cube are on three planes called isometric planes or isoplanes. The Lines in an object parallel to the isometric axes are referred to as isometric lines while lines not parallel to them are known as non-isometric lines. Isometric projection is not the most pleasant to the human eye but it is easy to draw and dimension. Types of Isometric Projections-

1. Isometric View (True Scale)-

Isometric View (True Scale)-Isometric view is the type of isometric projections to draw the isometric drawing by using true scale of the drawing.

2. Isometric Projections(Isometric scale)-

Isometric Projection is the type of isometric projections to draw the isometric drawing by using isometric scale of the drawing.

Difference between the these two types of isometric projection is that the isometric view is drawn by the true dimensions menas drawing drawn at 300 and isometric projection is drawn by isometric scale means first the true dimensions is take on 450 then these dimensions are take on 300 angle and draw the isometric drawing.On the behalf of above subject the orthographic projection and isometric projection on this topic our college PIMPRI CHINCHWAD POLYTECHNIC NIGDI it is TOP COLLEGES IN PUNE region organize the technical event every year of a academic calendar .

Prof.T.V.Inde

Mechanical Department