Editing Technical drawing (section)

==Methods==
===Sketching===
[[File:Architekturskizze Verwaltungsgebäude Biel.jpg|thumb|right|[[Sketch (drawing)|Sketch]] for a government building]]

A [[Sketch (drawing)|sketch]] is a quickly executed, freehand drawing that is usually not intended as a finished work. In general, sketching is a quick way to record an idea for later use. Architect's sketches primarily serve as a way to try out different ideas and establish a composition before  a more finished work, especially when the finished work is expensive and time-consuming.

Architectural sketches, for example, are a kind of [[diagram]].<ref name="BoCo04">Richard Boland and Fred Collopy (2004). ''Managing as designing''. Stanford University Press, 2004. {{ISBN|0-8047-4674-5}}, p.69.</ref> These sketches, like [[metaphor]]s, are used by architects as a means of communication in aiding design collaboration. This tool helps architects to abstract attributes of hypothetical provisional design solutions and summarize their complex patterns, thereby enhancing the design process.<ref name="BoCo04"/>

===Manual or by instrument===
[[File:Zeichenmaschine.jpg|thumb|left|A drafting table]]
[[File:Technical drawing instruments 1.jpg|thumb|right|Old-fashioned technical drawing instruments]]
[[File:Stencils01.jpg|thumb|right|Stencils for lettering technical drawings to DIN standards]]
The basic drafting procedure is to place a piece of paper (or other material) on a smooth surface with right-angle corners and straight sides—typically a [[drawing board]]. A sliding [[straightedge]] 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 over the surface of the paper.

"Parallel lines" can be drawn by moving the T-square and running a pencil or [[technical pen]] along the T-square's edge. The T-square is used to hold other devices such as [[set square]]s or triangles. In this case, the drafter 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 draw lines at any chosen angle to others on the page. Modern drafting tables are equipped with a [[drafting machine]] that is supported on both sides of the table to slide over a large piece of paper. Because it is secured on both sides, lines drawn along the edge are guaranteed to be parallel.<ref>{{cite book|last=Bhatt|first=N.D|title=Machine Drawing|publisher=Charotar Publication}}</ref>

The drafter uses several [[technical drawing tools]] to draw curves and circles. Primary among these are the [[Compass (drafting)|compasses]], used for drawing arcs and circles, and the [[French curve]], for drawing curves. A [[Flat spline|spline]] is a rubber coated articulated metal that can be manually bent to most curves.

Drafting templates assist the drafter with creating recurring objects in a drawing without having to reproduce the object from scratch every time. This is especially useful when using common symbols; i.e. in the context of [[stagecraft]], a lighting designer will draw from the [[USITT]] standard library of lighting fixture symbols to indicate the position of a common fixture across multiple positions. Templates are sold commercially by a number of vendors, usually customized to a specific task, but it is also not uncommon for a drafter to create his own templates.

This basic drafting system requires an accurate table and constant attention to the positioning of the tools. A common error is 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 require a number of moves of the T-square and triangles, and in general, drafting can be a time-consuming process.

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

In addition to the mastery of the mechanics of drawing lines, arcs and circles (and text) onto a piece of paper—with respect to the detailing of physical objects—the drafting effort requires a thorough understanding of geometry, [[trigonometry]] and spatial comprehension, and in all cases demands precision and accuracy, and attention to detail of high order.

Although drafting is sometimes accomplished by a project engineer, architect, or shop personnel (such as a [[machinist]]), skilled drafters (or designers) usually accomplish the task, and are always in demand to some degree.

===Computer aided design===
{{Main article|Computer-aided design|Product and manufacturing information}}

Today, the mechanics of the drafting task have largely been automated and accelerated through the use of [[computer-aided design]] systems (CAD).

There are two types of computer-aided design systems used for the production of technical drawings: [[2D computer graphics|two dimensions]] (2D) and [[3D computer graphics|three dimensions]] (3D).
[[File:Construction drawing autocad.jpg|thumb|right|An example of a drawing drafted in [[AutoCAD]]]]
2D CAD systems such as [[AutoCAD]] or [[MicroStation]] replace the paper drawing discipline. The lines, circles, arcs, and curves are created within the software. It is down to the technical drawing skill of the user to produce the drawing. There is still much scope for error in the drawing when producing first and third angle [[orthographic projection]]s, auxiliary projections and [[Multiview orthographic projection#Section|cross-section view]]s. A 2D CAD system is merely an electronic drawing board. Its greatest strength over direct to paper technical drawing is in the making of revisions. Whereas in a conventional hand drawn technical drawing, if a mistake is found, or a modification is required, a new drawing must be made from scratch, the 2D CAD system allows a copy of the original to be modified, saving considerable time. 2D CAD systems can be used to create plans for large projects such as buildings and aircraft but provide no way to check the various components will fit together.

[[Image:cad crank.jpg|thumb|left|View of a CAD model of a four-[[Cylinder (engine)|cylinder]] [[Straight engine|inline]] [[crankshaft]] with [[piston]]s]]
A 3D CAD system (such as [[KeyCreator]], [[Autodesk Inventor]], or [[SolidWorks]]) first produces the geometry of the part; the technical drawing comes from user defined views of that geometry. Any orthographic, projected or sectioned view is created by the software. There is no scope for error in the production of these views. The main scope for error comes in setting the parameter of first or third angle projection and displaying the relevant symbol on the technical drawing. 3D CAD allows individual parts to be assembled together to represent the final product. Buildings, aircraft, ships, and cars are modelled, assembled, and checked in 3D before technical drawings are released for manufacture.

Both 2D and 3D CAD systems can be used to produce technical drawings for any discipline. The various disciplines (electrical, electronic, pneumatic, hydraulic, etc.) have industry recognized symbols to represent common components.

[[British Standards|BS]] and [[ISO]] produce standards to show recommended practices but it is up to individuals to produce the drawings to a standard. There is no definitive standard for layout or style. The only standard across engineering workshop drawings is in the creation of orthographic projections and cross-section views.

In representing complex, three-dimensional objects in two-dimensional drawings, the objects can be described by at least one view plus material thickness note, two, three, or as many views and sections that are required to show all features of object.

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