Although many students today have a variety of digital tools to help identify and visualize their designs, orthographic drawing is still a useful way to determine the dimension, shape, and parameters of an object without actually having to draw freehand.
Also called orthographic projection, orthographic drawings present different perspective points of a 2D image of an object to allow for a clearer visualization than isometric drawing, which is a 3D rendering that only uses one point of perspective. Orthographic projection is a necessary component of technical drawing and helps provide useful information on the proportions, structure, and appearance of a drafted object. Read on for more information about orthographic drawing.
The Basics of Orthographic Drawing
Imagine for a moment that you have an object inside a glass box. There are six principal ways to see this object through each pane of glass: from the top, the bottom, left, right, front, and back. Now take the object’s appearance from each of the six sides and project it onto the glass panes, as if making its shadow. In an orthographic drawing, this imaginary box is then unfolded until all the projected views are laid out on the same plane, so each view is a flat image of one perspective, making it a 2D rendering.
All six sides generally aren’t needed when considering the dimensions and shape of an object, however, and typically only three are used. These are known as the plan, or top, front, and side views, and build what is considered the ideal perspective viewing positions, the first and third angle projections, which are important to know in a career in engineering design technology.
These are based on the planes formed by a right angle. The first angle is comprised of the frontal view of an object, the side view, and the plan view, which is how it’s seen from above. The only difference between first and third angle projections is the positioning of the viewer, as well as the fact that first angle projection is preferred in Europe and third angle projections are the standard in the United States and Canada.
Line Precedence and Sketching Techniques
Lines on an engineering drawing involve more than just outlining the geometry or shape of the object. For those with an engineering technicians diploma, they also are a valuable tool that identifies specific areas of an object.
Different lines indicate different use or type of space. A thick continuous line is used for visible edges and outlines, while a thin line signifies dimensions and projections. There is also a kind of hierarchy involved, where visible lines take precedence, followed by hidden lines and cutting plane lines, and finally centre lines, which have the lowest precedence.
Visible lines are denoted by solid, thick lines, while hidden and cutting plane lines are dashed. Hidden lines are used to depict elements which are not visible from the current angle, while centre lines are chain-dotted and used for symmetric objects and to note the axes of minor components such as circles or cylinders. The dimensions of an object are always drawn in a continuous, unbroken line to indicate its shape and parameters.
Dimensioning in an Engineering Design Technology Program
The goal of any orthographic projection is to provide accurate information on the dimension and detail of an object. Dimensioning is the process of measuring area or volume and helps students in an engineering design technology program know the exact specifications of their project.
There are a few different types of dimensioning in orthographic projection. Dimensions primarily use tolerance values to indicate specifications such as length, width, or height. Parallel dimensioning measures all of the tolerance values in the same continuous line, while progressive dimensioning involves the same values but shorter lines to cut down on space. Combined dimensioning uses many different dimensioning styles into one, including parallel and progressive, and coordinate dimensioning makes drawings easier to read by using an additional coordinate table with the tolerance values.
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