Drafting is the process of creating realistic drawings of a part, usually showing dimensions and details. Drawings may also show how various parts are put together, these are called assembly drawings. Hand drafting tries to create the illusion of a three dimensional object on a two dimensional page. Computer drafting creates a simulated three dimensional model.
It is said that a picture is worth a thousand words. Words alone may not be as accurate at making sure many people have the same image in mind. When designing, a sketch can often help explain a concept better. Drawings can also be used to help make parts, it is like picture instructions, telling how to bend, cut, and drill the the material to create a part. Assembly drawings show how multiple parts get put together. Assembly drawings may also include a parts list, this is called a Bill of Materials or BOM.Technical drawings, by hand or computer, are as close to the real item as possible, because the more detailed the drawing the easier it is for someone to make the part accurately. Technical drawings can be drawn to look 2D or 3D. 2D means two dimensions, which means an X and Y axis making a flat plane. 3D means three dimensions, which adds a third Z axis making the drawing appear to have depth. This is called using perspective. To get large objects onto a small page, drawings use a scale; that means that a smaller size is used to represent a bigger one. For example, 1/4 inch on the drawing might equal one foot on the machine. Technical drawings also usually include physical dimensions or measurements: length, width, height, angles, circumferences, distances between objects, etc.
Technical drawings look differently depending on the purpose for the drawing. A single part may be drawn in a variety of views. A view is the angle you are looking at the object. For instance, think of a rectangular box with a hole in the top (see drawing 1). If you were going to create a drawing of this box so that another person could make one exactly like it you might start with a picture that looks at one corner, then make separate drawings of the top and two of the sides, the short and the long. The view from the corner is called Isometric. The three views of the sides are called Orthographic projections (see drawing 1).
There are many other types of views. Some for special purposes. For instance, on an assembly, you may see an exploded view. This shows parts that are inside another part stretched out, showing how they go together (see drawing 2). Another special view is a Sectional view, which shows the part as if it has been sliced open so you can see inside. Think of cutting open an apple so you can see the seeds – that is a sectional view. A pattern view is used when making parts out of sheet metal (see drawing 3). This shows the part unfolded, which makes a pattern for cutting, which can then be bent into the desired shape.
CAD is a very useful drafting tool. Once a part is created as a digital model, the program can show it in a variety of views, and that part can be used in many different assemblies. Click here to see an example of a CAD drawing. Digital parts can be animated and tested in a computer simulation to see if they perform as desired. Often problem areas can be identified prior to actually manufacturing the parts. This allows modifications to be made before building.
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Click here for link to drawing learning activity: Technical Drawing learning activity by Living Children Multimedia