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Drafting

Today the mechanics of the drafting task has been largely automated, and greatly accelerated, through the use of CAD systems.

Drafting directly on paper

The basic concept of the mechanics of drafting is to place a piece of paper (or other material) on a surface with right-angle corners and straight sides - typically a drafting table. A sliding straight-edge known as a t-square is then placed on one of the sides, allowing it to be slid across the side of the table, and thus across over the surface of the paper.

Parallel lines can be drawn simply by moving the t-square and running a pencil along the t-square's edge, but more typically the t-square is used as a tool to hold other devices such as set squares or triangles. In this case the draftsman places one or more triangles of known angles on the t-square - which is itself at right angles to the edge of the table - and can then drawn lines at any chosen angle to others on the page. Modern drafting tables come equipped with a parallel rule that is supported on both sides of the table but can slide over the piece of paper. Because it is secured on both sides, parallel lines are guaranteed to be parallel.

In addition the draftsman uses several tools to draw curves and circles. Primary among these are the compass, used for drawing simple arcs and circles, and the french curve, typically a piece of plastic with complex curves on it. A spline is a rubber coated articulated metal that can be manually bent to most curves.

This basic drafting system requires an accurate table and constant attention to the positioning of the tools. A common error was to allow the triangles to push the top of the t-square down slightly, thereby throwing off all angles. Even tasks as simple as drawing two angled lines meeting at a point required a number of moves of the t-square and triangles, and in general drafting was a time consuming process.

A solution to these problems was the introduction of the "drafting machine", an application of the pantograph (sometimes referred to incorrectly as a "pentagraph" in these situations) which allowed the draftsman to have an accurate right angle at any point on the page quite quickly. These machines often included the ability to change the angle, thereby removing the need for the triangles as well.

In addition to the mechanics of drawing the lines onto a piece of paper, drafting requires the understanding of the engineering drawings. At one time, drafting was a sought-after job, considered one of the more demanding and highly-skilled of the trades. Today the mechanics of the drafting task has been largely automated, and greatly accelerated, through the use of CAD systems. Drafting is often accomplished by the engineer, architect, or machinist. Skilled CAD operators continue to be in demand for routine changes to drawings.

Common views of objects created by draftspeople include Orthographic projection, isometric projections, axonometric projections, cross sections, elevations, plan views, perspective drawings, bird's-eye views and worm's eye views.

Drafting is when one moving object gets close behind another moving object and gets into its slipstream, a region of reduced air pressure or even suction in the direction of the movement. As a result, the behind object uses less energy for moving because the front object blocks a significant amount of air resistance. See also: wake, race.

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