Lesson 8, Topic 4
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# Steps in Orthographic Projection & Worked Illustration:

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### Illustration:

Draw the Isometric drawing object shown below, with the given dimensions, in first & third angle orthographic projection. The dimensions are in mm (1cm = 10mm).

First Angle Projection:

Steps:

a. Draw both the vertical and the horizontal axis to intersect midway.

b. Draw a 45° projection line from the intersection as shown below.

c. Next step is to put spaces in both the horizontal and vertical axis.

Add a 10 mm space to the left and a 10 mm space to the right side of the vertical line. Then draw lines parallel to the vertical line

Add a 10 mm space to the top and 10mm space to the bottom of the horizontal line. Then draw parallel lines to the horizontal line.

Make sure that the lines are very faint.

This is shown below.

d. Determine the placement of the views and label the diagram accordingly.

This is a first angle projection so It should be noted that the left side elevation is usually placed at the right-hand side and the right-hand side is placed at the left-hand side.

In the diagram we can see that the side view is on the left, so we will label it on the right of the front view.

The plan is located below the front view in first angle projection.

e. Front View: First you measure 60mm up and 60mm to the left. From the diagram, the other sides are 30mm. So from the top, we will draw 30mm to the left, 30mm down, 30mm to the left again and finally 30mm to complete the front view.

f. Add dimensions to the front view.

g. Next, we need to draw the plan view. To do this the first thing we do is project all the vertical lines from our Front view to our plan view, as shown below.

h. Plan View: This view is obtained by looking vertically down on the given object from above. The length of the object at the top is 60mm. So we will draw 60mm down. We can also see that the shape is divided into two halves of 30mm. The plane view is drawn as shown below.

h. Add dimensions to the plan view.

i. Next step, we will draw faint horizontal lines going from our front view to the left end elevation.

We will also draw horizontal lines from our plan view to the 45° horizontal, then up to the left end.

j. Left end elevation view: Next step is to draw the left end elevation view (on the right). From the diagram above, the left-end view is basically done. What we have to do now is make visible lines.

k. Add dimensions to the left end elevation view.

The job is complete!

Third Angle Projection:

To Draw a third angle projection, the placing of the views is different. The 45° projection line is also placed differently. Remember, what is viewed on the left-hand side is drawn on the left-hand side. This is shown below;

We followed the exact same steps as we did for the first angle projection. Starting with the front view, etc.

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