Sunday, July 20, 2008
History Of Engineering Drawing
An engineering drawing is a type of drawing that is technical in nature, used to fully and clearly define requirements for engineered items, and is usually created in accordance with standardized conventions for layout, nomenclature, interpretation, appearance (such as typefaces and line styles), size, etc. Its purpose is to accurately and unambiguously capture all the geometric features of a product or a component. The end goal of an engineering drawing is to convey all the required information that will allow a manufacturer to produce that component.
Engineering drawings are often referred to as "blueprints" or "bluelines". However, the terms are rapidly becoming an anachronism, since most copies of engineering drawings that were formerly made using a chemical-printing process that yielded graphics on blue-colored paper or, alternatively, of blue-lines on white paper, have been superseded by more modern reproduction processes that yield black or multicolour lines on white paper.
The process of producing engineering drawings, and the skill of producing them, is often referred to as technical drawing, although technical drawings are also required for disciplines that would not ordinarily be thought of as parts of engineering.
posted by yjlevia at 1:54 AM
The layout of an engineering drawing
It is important that you follow some simple rules when producing an engineering drawing which although may not be useful now, will be useful when working in industry.
All engineering drawings should feature an information box. An example is shown below.
Common information recorded on an engineering drawing
- TITLE
- The title of the drawing.
- NAME
- The name of the person who produced the drawing. This is important for quality control so that problems with the drawing can be traced back to their origin.
- CHECKED
- In many engineering firms, drawings are checked by a second person before they are sent to manufacture, so that any potential problems can be identified early.
- VERSION
- Many drawings will get amended over the period of the parts life. Giving each drawing a version number helps people identify if they are using the most recent version of the drawing.
- DATE
- The date the drawing was created or amended on.
- SCALE
- The scale of the drawing. Large parts won't fit on paper so the scale provides a quick guide to the final size of the product.
- PROJECTION SYSTEM
- The projection system used to create the drawing should be identified to help people read the drawing. (Projection systems will be covered later).
- COMPANY NAME
- Many CAD drawings may be distributed outside the company so the company name is usually added to identify the source.
posted by yjlevia at 1:46 AM
Orthographic projection
The aim of an engineering drawing is to convey all the necessary information of how to make the part to the manufacturing department. For most parts, the information cannot be conveyed in a single view. Rather than using several sheets of paper with different views of the part, several views can be combined on a single drawing using one of the two available projection systems, first angle, and third angle projection.
The diagram below demonstrates how the projection systems work
posted by yjlevia at 1:41 AM
Hatching
On sections and sectional views solid area should be hatched to indicate this fact. Hatching is drawn with a thin continuous line, equally spaced (preferably about 4mm apart, though never less than 1mm) and preferably at an angle of 45 degrees.
Hatching a single object
When you are hatching an object, but the objects has areas that are separated, all areas of the object should be hatched in the same direction and with the same spacing.
Hatching Adjacent objects
When hatching assembled parts, the direction of the hatching should ideally be reversed on adjacent parts. If more than two parts are adjacent, then the hatching should be staggered to emphasise the fact that these parts are separate.
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| Reverse hatching | |
Hatching thin materials
Sometimes, it is difficult to hatch very thin sections. To emphasise solid wall the walls can be filled in. This should only be used when the wall thickness size is less than 1mm
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Hatching large areas
When hatching large areas in order to aid readabilty, the hatching can be limited to the area near the edges of the part.
posted by yjlevia at 1:38 AM
Sectioning - Introduction
Sections and sectional views are used to show hidden detail more clearly. They are created by using a cutting plane to cut the object.
A section is a view of no thickness and shows the outline of the object at the cutting plane. Visible outlines beyond the cutting plane are not drawn.
A sectional view, displays the outline of the cutting plane and all visible outlines which can be seen beyond the cutting plane. The diagram below shows a sectional view, and how a cutting plane works.
posted by yjlevia at 1:37 AM
Which Sectional View?
Before proceeding, consider the diagrams below and select the correct sectional view.
posted by yjlevia at 1:37 AM
Types of sectioning
Sectional View in a single plane
The example below shows a simple single plane sectional view where object is cut in half by the cutting plane. The cutting plane is indicated on a drawing using the line style used for centre lines, but with a thick line indicating the end of lines and any change in the direction of the cutting plane. The direction of the view is indicated by arrows with a reference letter. The example below shows a sectional view of the cutting plane A - A.
Sectional View in two planes
It is possible for the cutting plane to change directions, to minimise on the number of sectional views required to capture the necessary detail. The example below shows a pipe being cut by two parallel planes. The sketch shows where the object is cut.
Half Sectional views
Half sections are commonly used to show both the internal and outside view of symmetrical objects.
Part Sectional views
It is common practice to section a part of an object when only small areas need to be sectioned to indicate the important details. The example above shows a part sectional view to indicate a through-hole in a plate. Notice that the line indicating the end of the section is a thin continuous line.
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posted by yjlevia at 1:34 AM