Orthographic projection

In orthographic projection, the front face is always parallel to the picture frame and the projectors are perpendicular to the picture frame (see Figure 2.9). This means that one only ever sees the true front face that is a 2D view of the object. The receding faces are therefore not seen. This is the same as on an oblique projection but with the projectors perpendicular rather than at an angle. The other faces can also be viewed if the object is rotated through 90 degree .There will be six such orthographic views. These are stand-alone views but if the object is to be 'reassembled' from these six views there must be a law that defines how they are related. In engineering drawing there are two laws, these are first or third angle projection. In both cases, the views are the same; the only thing that differs is the position of the views with respect to each other. The most common type of projection is third angle projection.
Engineering Drawing for Manufacture by Brian Griffiths Publisher:
Elsevier Science &
Technology Books

Oblique projection

In oblique projection, the object is aligned such that one face (the front face) is parallel to the picture plane. The projection lines are still parallel but they are not perpendicular to the picture plane. This produces a view of the object that is 3D. The front face is a true view (see Figure 2.7). It has the advantage that features of the front face can be drawn exactly as they are, with no distortion. The receding faces can be drawn at any angle that is convenient for illustrating the shape of the object and its features. The front face will be a true view, and it is best to make this one the most complicated of the faces. This makes life easier! Most oblique projections are drawn at an angle of 45 ~ and at this angle the foreshortening is 50%. This is called a Cabinet projection. This is because of its use in the furniture industry. If the 45 ~ angle is used and there is no foreshortening it is called a Cavalier projection. The problem with Cavalier projection is that, because there is no foreshortening, it looks peculiar and distorted. Thus, Cabinet projection is the preferred method for constructing an oblique projection. An oblique drawing of the bearing bracket in Cabinet projection is shown in Figure 2.8. For convenience, the front view with circles was chosen as the true front view. This means that the circles are true circles and therefore easy to draw. The method of construction for oblique projection is similar to the method described above for isometric projection except that the angles are not 30 ~ but 45 ~ . Enclosing rectangles are again used and transposed onto the 45 ~ oblique planes using 50% foreshortening. Engineering Drawing for Manufacture by Brian Griffiths Publisher: Elsevier Science & Technology Books

Structural foam molding

Structural foam molding is a modified version injection where conventional molding plastic products consist of a dense outer surface of the skin that surrounds the inside (foam). This process is suitable for large-scale production, the product is relatively thick. Foam cores are produced from this process is suitable for bending applications. If the skin has the highest tensile strength and compressive stress, then the neutral axis of the work on the weaker parts of the inner foam. This process offers several advantages from the manufacturing process because it is able to produce products that are complex and have a low voltage so that the tendency for reduced bending or distorted. Then the clamping force is required of this process is lower than conventional injection molding process. This process is widely used for the production of large-sized plastic such as engine housings, chassis, computer housings, bin-bin storage, pallets and others. Polymers are often used for this process is the HOPE, PP, ABS and PC. Resins used in the Low Pressure is applied to this process consists of a small amount of blowing or foaming agent, this type of Chemical Blowing Agent (CBA) decomposition temperatures approaching the temperature of the resin. During the CBA process is decomposed in a large volume of gas as the beginning of a foaming process. Then injected into the cavity short shot. The skin is formed when the gas pressure near the surface of the collapse due to the mold surface. Furthermore, the gas spreads pressing short shot to complete filling cavity. After filling the gas continued to press with the uniform in all directions, pressing the dense skin on the mold surface, effectively also eliminate sink marks. Compared with the conventional injection process, voltage and much reduced shrinkage due to pressure on the cavity is relatively uniform. Before the ejection process must be ensured that the product starts cold and dense. Besides the advantages mentioned above there are a number of disadvantages when compared with conventional injection molding process, namely because the thickness of the walls are made then the cycle time achieved the longer, the consumption of the material also becomes more and more. For this type of process better position the gate at the thinnest part, is to facilitate filling the cavity thick sections. Unlike in conventional injection molding process on the premature solidification of a thin section of a thicker section and the gate does not occur. (Bid / multiple sources)

Isometric projection

In isometric projection, the projection plane forms three equal angles with the co-ordinate axis. Thus, considering the isometric cube in Figure 2.4, the three cube axes are foreshortened to the same amount, i.e. AB = AC = AD. Two things result from this, firstly, the angles a = b = 30 ~ and secondly, the rear (hidden) corner of the cube is coincident with the upper corner (corner D). Thus, if the hidden edges of the cube had been shown, there would be dotted lines going from D to F, D to C and D to B. The foreshortening in the three axes is such that AB = AC = AD = (2/3) o.5 = 0.816. Since isometric projections are pictorial projections and dimensions are not normally taken from them, size is not really important. Hence, it is easier to ignore the foreshortening and just draw the object full size. This makes the drawing less complicated but it does have the effect of apparently enlarging the object by a factor 1.22 (1 + 0.816). Bearing this in mind and the fact that both angles are 30 ~ it is not surprising that isometric projection is the most commonly used of the three types of axonometric projection. The method of constructing isometric projections is shown in the diagrams in Figures 2.5 and 2.6. An object is translated into isometric projection by employing enclosing shapes (typically squares and rectangles) around important features and along the three axes. Considering the isometric cube in Figure 2.4, the three sides are three squares that are 'distorted' into parallelograms, aligned with the three isometric axes. Internal features can be projected from these three parallelograms. The method of constructing an isometric projection of a flanged bearing block is shown in Figure 2.5. The left-hand drawing shows the construction details and the right-hand side shows the 'cleaned up' final isometric projection. An enclosing rectangular cube could be placed around the whole bearing block but this enclosing rectangular cube is not shown on the construction details diagram because of the complexity. Rather, the back face rectangle CDEF and the bottom face ABCF are shown. Based on these two rectangles, the construction method is as follows. Two shapes are drawn on the isometric back plane CDEE These are the base plate rectangle CPQF and the isometric circles within the enclosing square LMNO. Two circles are placed within this enclosing square. They represent the outer and inner diameters of the bearing at the back face. The method of constructing an isometric circle is shown in the example in Figure 2.6. Here a circle of diameter ab is enclosed by the square abcd. This isometric square is then translated onto each face of the isometric cube. The square abcd thus becomes a parallelogram abcd. The method of constructing the isometric circles within these squares is as follows. The isometric square is broken down further into a series of convenient shapes, in this case five small long-thin rectangles in each quadrant. These small rectangles are then translated on to the isometric cube. The intersection heights ef, gh, ij and kl are then projected onto the equivalent rectangles on the isometric projection. The dots corresponding to the points fhjl are the points on the isometric circles. These points can be then joined to produce isometric circles. The isometric circles can either be produced freehand or by using matching ellipses. Returning to the isometric bearing plate in Figure 2.5, the isometric circles representing the bearing outside and inside diameters are constructed within the isometric square LMNO. Two angled lines PR are drawn connecting the isometric circles to the base CPQE The rear shape of the bearing bracket is now complete within the enclosing rectangle CDEE Returning to the isometric projection drawing of the flanged bearing block in Figure 2.5. The inside and outside bearing diameters in the isometric form are now projected forward and parallel to the axis BC such that two new sets of isometric circles are constructed as shown. The isometric rectangle CPQF is then projected forward, parallel to BC that produces rectangle ABST, thus completing the bottom plate of the bracket. Finally, the web front face UVWX is constructed. This completes the various constructions of the isometric bearing bracket and the final isometric drawing on the right-hand side can be constructed and hidden detail removed. Any object can be constructed as an isometric drawing provided the above rules of enclosing rectangles and squares are followed which are then projected onto the three isometric planes. 

Engineering Drawing for Manufacture by Brian Griffiths 

Publisher: Elsevier Science & 

Technology Books