Why two types of drawings...

Dear

It depends on situation for which perpose you are using the drawings, Isometric drawings beside some other puposes are mainly used for production and true, scaled and accurate pictures of concerned object, while oblique views are mainly used in presentation purposes and its beauty depends on the selected angle of view.

Regards.

This is exactily right

At first reading I took this to be a question about first and third angle projection. Who'd like to explain that in words (of one syllable)?

A dimensioned 'oblique' view? Maybe with sections too!

Are you really looking for an explanation of 1st & 3rd angle projection, or are you just being facetious?

Wiki does:

http://en.wikipedia.org/wiki/First_angle_projection

Third angle: Imagine you are an artist at an easle in front of an object. You paint what you see. This is third angle. The features are projected toward the view from the front.

First angle: The canvas is behind the object. Features are projected toward the view from the back.

Americans prefer third angle, since we think it's easier to envision. Europeans prefer first angle and make the same claim for it. I don't know about the rest of the world.

Very good explanation. Do you perchance know why the angles were labeled as 1st and 3rd. Is there a 2nd angle projection?

I dont believe that I have ever seen an oblique view drawing. I probabley have without associating the description. Does anybody have an oblique drawing that can be posted for viewing. I would be interested to see one and then make comment about the pros and cons of isometric versus oblique.

Well done yesyen

Good job yesyen. I remember you are the `animation guy'.

Well regarding drawings , the oblique was a new one. All I receive from machine Manufacturers are:

1 . 2 - D (Top View) always

2 . Cut Sections on 2-D to highlight side view always

3 . Line Drawings - P & ID/ Schematic (detailing utility pipings) always

4 . Isometric - very rare

5 . Oblique - Never

6 . 3-D Very very rare.

Anyway thank you for the difference between the two.

I have read through all the comments to date of this posting, now, I will give you my comment(s). But first, you must understand my viewpoint. I am a retired principle mechanical designer who worked for a very large engineering corporation with extensive experience in the design and construction of refineries, chemical plants, off shore platforms, and nuclear and non-nuclear power plants. So, what does that title mean? It means I am supposed to be a know-it-all whether I do or not. Well actually, it means that I can usually tell you where to go to get the answers and how to do your job. The title is usually bestowed upon those of us who, through education and experience, have demonstrated the ability to be leaders and are capable of leading a large and diverse crew of engineers and technicians through any number of projects to a complete and successful end.

Now on to answer you question about drawings and their uses. You have often heard, I am sure; "A a picture is worth a thousand words." This is true as far as it goes. Most all engineering projects can be described in text alone. However, to use text alone would take volumes to describe this way for even the simplest of projects. Thus, we use drawing to illustrate the text and saving those "thousand words". The drawing is used to accurately give a mental picture to the craftsman. It is used to aid in translating engineering data into a language the craftsman and other lay people can understand. With any project, whether it is building a barn or a chemical plant, a set of drawings are required, beginning with a simple over all layout of the project and becoming more and more detailed as needed.

Before the advent of the computer, these drawing were all done by hand. Since time was important, too, a procedure and standard for producing the required drawings was established for each discipline and type of project. When it came to piping of a chemical or power plant, process diagrams, a mechanical flow diagrams, an overall layout called a plot plan(s), electrical diagrams, instrumentation diagrams, piping plans, and so on, until we come to "iso drawings".

Each drawing, regardless of the discipline, was in more specific detail for each and every part of the project, the "iso" drawing being one of the most specific detail, outlining the individual pipe, wiring, or instrument. It is important to note here that never was a drawing to be an accurate to exact scale drawing. It was to be an approximate representation of the work, a picture of the general location and shape, never exact. To be exact would be far too unacceptably time consuming. The important information for all drawings is the accuracy of the dimensions, angles, and text descriptions. These are the data points that translate the engineering to the language a craftsman can use for his work in construction.

When the computer aided drafting came to be accepted, none of the above procedures and standards were changed. Yes, the cad programs can make accurate planes to the micrometer and most plan drawings created with cad is that accurate. In some cases, such as in the aircraft and space industry, the digital information for the drawings is used as a template for the actual parts of an assembly. In the power and chemical industry, the digital data is what must be accurate, not the drawings. In fact, some of the drawings are either non-dimensional and some depend totally dimensions. One of the drawing types that are totally dimensional is the "iso" drawing. The "iso" drawing gives direction and length. It counts the connections to individual parts such as welds, splices and parts. It also contains a "bill of material". But in no case does it require pictorial dimension accuracy, a 500 meter straight piping run and be just 5 cm long on the drawing or a 5 mm straight run can be 5 cm long on the drawing. The important thing is that that segment of the pipe run describes in detail each part of the assembly and the dimensions are accurate and complete.

As far as I am concerned, all other "prospective" drawings, regardless of how they are made or what their use needs to fit the need and accurately convey the required information in a language the client, user, or craftsman can understand. Care must be taken that the information is not confusing or does not misrepresent.

"Care must be taken that the information is not confusing or does not misrepresent."

too many words do exactly the same thing.

That was great. Now every one should have understood. As an artist I can display a face as true as possible. It will not tell the unlearned who the person is or what that person is thinking. This (painting, plan) must be followed up by reading or listening about the face/plan. A small melanoma could be recognized just under the nose but it will take a surgeon to identify it. He is the one with the ability to read and interpret the object and go and fix it. A drawing of what ever kind, even 3D cad, can not be regarded as a true representation of function and position. The real thing is the only thing to go by. All else is speculation more or less sophisticated. Back to the drawing board. Ky.

Cant agree with you KY. If I recieve an isometric drawing of a piping system, that is an absolute true representation of the system that I have to manufacture and install.

OK, then, think Picasso, De Vinci, Michelangelo. How does one read their faces, especially Picasso's.

can somebody tell me what are the pros and cons in using

a)isometric b)oblique c)third angle d)1st angle