Overview of Technical Drawing

Drawing Tutorials Overview of Technical Drawing Tutor: Robin Sloan [email protected]

This tutorial is intended for use in CA0816 3D Illustration 1. Introduction to Technical Drawing This tutorial is a basic overview of three types of technical drawing; orthographics, isometrics (pictorial), and perspective drawings. There are many online tutorials, including video tutorials, which may help you with more advanced techniques. However, for the purposes of this module, all that is needed is an understanding of how to produce these types of drawing. You will want to pick which types of technical drawing to use based on the type of object you want to draw. For instance, if you aim to create a small and very organic object, you might find that isometric drawing is impractical. Instead, you might want to try a couple of different perspective drawings. Certain objects are more or less suited to the various perspective drawings, for instance tall objects are well suited to 3-point perspective, while 1-point perspective drawings often work best with objects which have fairly planar sides (for instance cuboid-like objects). 2. Preparation for Drawing Before you begin drawing, you will first want to find a large flat surface which you can secure your paper to, using either clips or masking tape. Note that there are drawing tables in White Space around the drawing area. You can also use the easels and boards in the Life Drawing room, which is available to use during the CA0816 class. You may also want to have a t-square and appropriate protractors to help you draw straight lines and specific angles. This is particularly important when projecting guidelines.

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However, your final drawings don’t need to be highly accurate. If you use this tutorial as a guide and try to use the drawing tools when appropriate, you should find that you can come up with orthographic, isometric and perspective drawings that will help you with the modelling phase of the project.


3. Orthographic Views To draw the main orthographic views, you’ll first want to draw in guides that define the areas where the plan, front, and side views will be drawn. In the image below, the top right area has an extra guide at 45 degrees to the horizontal guide. This guide line is important for projecting the plan on to the side view, and vice versa.

It is usually easiest to start with a front view. In the image below, a simple house has been drawn. The dotted lines indicate geometry that cannot be directly observed from this view.

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To project our plan view from the front view, we can draw guide lines straight up from the key points on the front elevation.

We can then use these guides to complete the plan drawing. This method can be used to draw multiple orthographic views that match up with each other exactly. Here, we can see that the hidden lines match up with an extension on the back of the house.

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We now have two views of the object. By projecting from both of these views, we can insure that the side view matches both the plan and front views exactly. Projection lines from the plan are taken as far as the 45 degree guide line, and then drawn down to meet the ground guide line from the front view.

This can look confusing initially. However,if you follow the projection lines back to the plan and front views, you will see that the side view is relatively easy to draw – especially if you used specific measurements to create the first two drawings.

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The finished orthographic drawings of the house object can then be used to create accurate ‘3D’ drawings, or even feed directly into a 3D package to help with the creation of a 3D model.

The same method can also be used to draw more complicated shapes that include curves. Consider the example below. In the front view, we can see that one element of the object has a curve.

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However, the plan view shows that this element is also intricately curved when observed from above.

Let’s concentrate on what the curved element will look like in the side view. Firstly, we can identify a few points on the curve in the plan view, and then project these to the side view (as shown in the image below)

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Next, we can project down from the points in the plan view on to the front view. We can then project from the front view across to the side view. Now we have overlapping projection lines that we can use to help us draw the curved element from the side.

By referring back to the plan and front views, we can see how the curved element should be drawn in the side view, as shown in the image below.

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To complete the side view drawing, we just need to make a few more projections from the plan and front views…

And now we have accurate drawings in the plan, front and side views.

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4. Isometric View Isometric views are pictorial drawings that, like standard orthographic views, do not use vanishing points. In other words, all adjacent lines are perpendicular – there is no apparent depth, so regardless of how big the object being drawn is it will not ‘vanish’ into the distance. Isometric views typically show the three main orthographic views – top, front and side - at once. This is achieved by drawing the object from an angle. For example, below is an isometric drawing of a box, with the orthographic views labelled.

Isometric drawings are usually drawn so that, if the object was box shaped, the width and depth lines would be drawn at 30 degrees to the horizontal, as shown below. Height lines are at 90 degrees to the horizontal.

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So, an isometric drawing that is fairly box like can be drawn very easily by using guidelines and taking measurements from orthographic views.

As you can see below, this isometric shape was based on the three orthographic views shown below. Measurements were taken from the various sides on the orthographic views, and these were mapped on to the sides of the isometric drawing.

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For more complicated or organic shapes, you can use bounding boxes to give you further guidelines. For example, the cylinder below can be drawn by drawing the bounding box (red lines) in the isometric view, then drawing the curves freehand.

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5. Perspective Views Perspective drawings make use of vanishing points to give an illusion of depth. Vanishing points are points on a defined ‘horizon line’ which are used as the point of origin for projection lines. There are three types of perspective drawing; 1-point, 2-point and 3-point perspective. Firstly, 1-point perspective drawings have a single vanishing point on the horizon, as shown below.

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With 1-point perspective drawings, you should first aim to draw a side that will face out from the drawing. This is effectively an orthographic view of one of the sides (typically the front or left/right side) as shown below.

You can now project guidelines out from the vanishing point to the corners of the front/side view.

Finally, you can complete the drawing by filling out the depth of the object.

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2-point perspective drawings, like 1-point perspective drawings, are fairly self explanatory! On your horizon line, you should have two vanishing points, usually placed towards the edge of your drawing area. 2-point perspective drawings are perhaps the most commonly used perspective drawing. You will probably find that 2-point perspective suits your design best.

Firstly, you might want to draw the corner ‘nearest’ to you using the vanishing points to help project the bottom edges, as shown below.

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You can then begin filling out more detail…

To draw lines that are not vertical and don’t exist on the vanishing point guidelines, you can use your orthographic drawings to help you create additional guidelines. For instance, to draw the sloping roof here, the green guideline is taken from the midpoint along the end of the house. The length of the green guideline could be taken from an orthographic drawing of the house. With the apex of the roof established, new lines can be drawn down to meet the top corners of the house walls.

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You may find that you need to use a combination of measurements, vanishing point guidelines, and (at times) estimation to plan your perspective drawing.

This house was relatively simple to draw in 2-point perspective. For more organic objects, you will often need to use a degree of freehand drawing (for instance to create curves) but you can usually project sufficient guidelines to help you.

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3-point perspective drawings are most often used to draw objects which are tall, as they can be used to create an illusion of height. The typical layout for a 3-point perspective drawing is shown below.

Guidelines are drawn into the centre of the page from all 3 points.

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As with 2-point perspective drawings, you usually want to start with the bottom corner, as shown below.

You can then project from the 3rd point to find the edges of the object.

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From there, objects can be planned out and completed in much the same way as 2-point perspective drawings.

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Overview of Technical Drawing

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