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The Technological World. Drafting Symbols And Techniques. Symbols and Legends.
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The Technological World Drafting Symbols And Techniques
Symbols and Legends • Everything we use has symbols and legends for us to follow. The most common ones to us all are the ones found on maps. The symbols we find there help us to locate a hospital, washroom, telephone or airport with a simple glance at the map. But we would never know what the symbols meant unless we had a Legend.
Common Symbols You Should all Recognize • You should recognize this one as: • DON’T WALK!
You should know this one as: • NO SMOKING! (DUH!)
This one should be obvious! NO CELL PHONES PLEASE!!!!
Basic Drafting Symbols • Line Types • Construction lines: Light lines used as a guideline in construction visible lines. (lines you can erase)
Visible Lines: The lines that you leave on your paper the lines that you will see when you are looking at the object.
Hidden Lines: Are lines that go through the object but are not visible from the point that you are drawing from. (Normally drawn as a broken line.)
Cutting Plane Line: Show where a drawing was cut to pull out a detail.
Manual drafting • 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 drafting table. 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 simply by moving the t-square and running a pencil or technical pen 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 draw lines at any chosen angle to others on the page. Modern drafting tables (which have by now largely been replaced by CAD stations) come equipped with a parallel rule that is supported on both sides of the table to slide over a large piece of paper.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.
In addition, the draftsperson uses several tools to draw curves and circles. Primary among these are the compasses, 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. • Drafting templates assist the draftsperson consistently recreate 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 typically 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 draftsperson to create their own templates.
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 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. • 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.
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 even by shop personnel such as a machinist - skilled drafters (and/or designers) usually accomplish the task and are always in demand to some level
Computer-aided design • Computer-Aided Design (CAD) is the use of computer technology to aid in the design of a product. Current software packages range from 2D vector base drafting systems to 3D solid and surface modellers.
CAD originally meant Computer-Aided Drafting or designing because of its original use as a replacement for traditional drafting. Now, CAD usually means Computer Aided Design to reflect the fact that modern CAD tools do more than just drafting. CAD is sometimes translated as "computer-assisted", "computer-aided drafting", or a similar phrase. Related acronyms are CADD, which stands for "computer-aided design and drafting", CAID for computer-aided industrial design and CAAD, for "computer-aided architectural design". All of these terms are essentially synonymous, but there are a few subtle differences in meaning and application.
CAD is used to design, develop and optimize products, which can be goods used by end consumers or intermediate goods used in other products. CAD is also extensively used in the design of tools and machinery used in the manufacture of components, and in the drafting and design of all types of buildings, from small residential types (houses) to the largest commercial and industrial structures (hospitals and factories). • CAD is mainly used for detailed engineering of 3D models and/or 2D drawings of physical components, but it is also used throughout the engineering process from conceptual design and layout of products, through strength and dynamic analysis of assemblies to definition of manufacturing methods of components. • CAD has become an especially important technology, within the scope of Computer Aided technologies, with benefits such as lower product development costs and a greatly shortened design cycle. CAD enables designers to lay out and develop work on screen, print it out and save it for future editing, saving time on their drawings.
Examples of CAD • Digital Multi-CAD Mock-up
History of CAD • Designers have long used computers for their calculations. Initial developments were carried out in the 1960s within the aircraft and automotive industries in the area of 3D surface construction and NC programming, most of it independent of one another and often not publicly published until much later. Some of the mathematical description work on curves was developed in the early 1940s by Isaac Jacob Schoenberg, Apalatequi (Douglas Aircraft) and Roy Liming (North American Aircraft). Robert A. Heinlein in his 1957 novel The Door into Summer suggested the possibility of a robotic Drafting Dan. However, probably the most important work on polynomial curves and sculptured surface was done by Pierre Bezier (Renault), Paul de Casteljau (Citroen), Steven Anson Coons (MIT, Ford), James Ferguson (Boeing), Carl de Boor (GM), Birkhoff (GM) and Garibedian (GM) in the 1960s and W. Gordon (GM) and R. Riesenfeld in the 1970s. • It is argued that a turning point was the development of the SKETCHPAD system at MIT in 1963 by Ivan Sutherland (who later created a graphics technology company with Dr. David Evans). The distinctive feature of SKETCHPAD was that it allowed the designer to interact with his computer graphically: the design can be fed into the computer by drawing on a CRTmonitor with a light pen. Effectively, it was a prototype of graphical user interface, an indispensable feature of modern CAD.
First commercial applications of CAD were in large companies in the automotive and aerospace industries, as well as in electronics. Only large corporations could afford the computers capable of performing the calculations. Notable company projects were at GM (Dr. Patrick J.Hanratty) with DAC-1 (Design Augmented by Computer) 1964; Lockheed projects; Bell GRAPHIC 1 and at Renault (Bezier) – UNISURF 1971 car body design and tooling. • One of the most influential events in the development of CAD was the founding of MCS (Manufacturing and Consulting Services Inc.) in 1971 by Dr. P. J. Hanratty[6], who wrote the system ADAM (Automated Drafting And Machining) but more importantly supplied code to companies such as McDonnell Douglas (Unigraphics), Computervision (CADDS), Calma, Gerber, Autotrol and Control Data. • As computers became more affordable, the application areas have gradually expanded. The development of CAD software for personal desk-top computers was the impetus for almost universal application in all areas of construction.
Capabilities of CAD • The capabilities of modern CAD systems include: • Wireframe geometry creation • 3D parametric feature based modelling, Solid modelling • Freeform surface modelling • Automated design of assemblies, which are collections of parts and/or other assemblies • create Engineering drawings from the solid models • Reuse of design components • Ease of modification of design of model and the production of multiple versions • Automatic generation of standard components of the design • Validation/verification of designs against specifications and design rules • Simulation of designs without building a physical prototype • Output of engineering documentation, such as manufacturing drawings, and Bills of Materials to reflect the BOM required to build the product • Import/Export routines to exchange data with other software packages
Output of design data directly to manufacturing facilities • Output directly to a Rapid Prototyping or Rapid Manufacture Machine for industrial prototypes • maintain libraries of parts and assemblies • calculate mass properties of parts and assemblies • aid visualization with shading, rotating, hidden line removal, etc. • Bi-directional parametric association (modification of any feature is reflected in all information relying on that feature; drawings, mass properties, assemblies, etc.) • kinematics, interference and clearance checking of assemblies • sheet metal • hose/cable routing • electrical component packaging • inclusion of programming code in a model to control and relate desired attributes of the model • Programmable design studies and optimization • Sophisticated visual analysis routines, for draft, curvature, curvature continuity.
Software to Consider • The best software used by most companies such as: Nike, DeBeers, Bayliner, General Motors, and most major engineering firms is: • Rhinoceros 4.0 • Note: all CAD images in this slide show where modeled and rendered on Rhino • Note: Billings is one of the only High Schools in Canada to have this program!
