Nov 30, 2017 -- Although 3D CAD models are dominating the CAD design and manufacturing industry today, 2D drawings still haven’t lost their importance. Fabricators and manufacturers still delve in 2D CAD drawings to know part details, part information, assembly, and manufacturing process. And across the globe, industrial fabricators have adopted systems of specifying standards and symbols for mechanical CAD drafting.
Popularly, we call them ISO or ASME standards or more technically, we refer them as 1st angle project method or 3rd angle projection method. Typically, European countries use ISO standards while Americans, Brits, and even Australians prefer the ASME standards. Still there are divergent views between designers and manufacturers, when it comes to making a choice.
2D CAD draft of a valve with detailed views and sectional drawings
Though it’s an elementary concept for a CAD design engineer and a manufacturer, to know the two standards, here is a little different take on our conventional perception of the two.
1. ISO Standards: First Angle Projection Method
While drawing an object using 1st angle projection method, it gives you a feeling that you are making your drawings in an opaque box. The catch here is the fact that the projection plane lies behind the object. This makes the designer look at the object and makes him sketch its front view at the back of the object.
Alternatively, it can better be perceived as taking X-Rays of the objects, through the material and the output obtained is projected on the plane below or behind the object. This makes it difficult to understand and interpret the drawing since it involves heavy imagination and adjustment in drawings. Additionally, the 3D object and every feature aren’t easily understandable even, when all the views [top, front, side views and section drawings] are presented simultaneously.
2. ASME Standards: Third Angle Projection Method
While 3rd angle projection method is more like the popular jargon WYSIWYG – What You See Is What You Get. Since the projection plane is assumed to be transparent and in between the object and the observer, it gives a sense of putting the object flat on the drawing sheet or computer screen and traces the pencil or CAD jockey as the surface touches the drawing sheet or CAD interface.
As the drawings are exactly as the object appears, makes it easy to combine all the views of the object in drawing and imagine the entire object. There isn’t any sort of imagination or adjustment left for the manufacturer to have apart from decoding the hidden lines.
Choosing the one
Firstly, as already stated, different regions have their own set of requirement and their own tradition. As a consequence, it depends on the manufacturer: their location, practices of design standards and preferences, methods adopted by shop floor technicians and other factors on same lines. These are some of the questions you need to ask before drawing.
Secondly, there should be an ease in understanding the 2D drawing and interpreting it. By ease, it doesn’t only mean ‘which method one is acquainted with’; it means that how much information is warehoused in a particular drawing. It implies that there has to be a minimum number of hidden lines in the drawing. With hidden lines come uninvited interpretation, misconception and plethora of misleading information. So a common practice is to choose a drawing method that can depict a majority of information when all the views are projected with continuous lines, curves and arcs only.
As for the history concerns, both European and American engineers were pretty sure that they need to develop a universal standard for drawing. This idea became more widespread especially after World War I as the international trade became more frequent. However, they couldn’t reach a consensus and hence today, we, the modern day engineers, have adopted both the methods. Ideally, an engineering design support services provider or a consultant can help a manufacturer have both these methods with dexterity. And we also have 3D CAD models annotated with PMI and MBD approach which clears off our dilemma a bit.
A quick tip
A quick tip for CAD users who drafts multiple CAD drafts for a living and uses only one of these two methods: do set your default preference to that standard. In Autodesk’s Inventor you can do that by opening the IDW file you can find the set projections under ‘Styles’ editor located in General Tab. Save the styles to the library and save it in Inventor template folder. When you open a newly created template, changes will be reflected. [Thank Autodesk forum for the tip!]
Usha B. Trivedi is a Technical Writer at Hitech CADD Services - CAD Drafting Services. She is a qualified mechanical engineer and contributes in-depth articles for industrial equipment, processing plants and fabrication sector. Her contributions are primarily focused on enabling engineering professionals, fabricators and plant owners to accelerate design and improve project efficiencies through BIM, 3D CAD and CAE tools.