Parallel Lines and Planes Engineering Drawing
A three-dimensional object can be represented in a single airplane, such as on a sheet of paper, using projecting lines and planes. All projection theory is based on two variables: line of sight (projecting lines) and airplane of projection.
A line of sight (LOS) is an imaginary line betwixt an observer's eye and an object. A aeroplane of projection (i.eastward., an image or motion-picture show plane) is an imaginary flat plane upon which the image is projected. The project is produced by connecting the points where the lines of sight pierce the projection plane. As a result, the 3D object is transformed into a second view.
If the altitude from the observer to the object is space, then the projection lines are causeless to be parallel, and the projection is chosen a parallel projection. Parallel projection is orthographic if the plane of projection is placed betwixt the observer and the object, and the plane is perpendicular to the parallel lines of sight.
You lot can utilize parallel projection technique to create both multiview and pictorial (isometric and oblique) views.
- In multiview orthographic projection (run into details below), the object surface and the projection aeroplane are parallel, and you tin can meet only 2 dimensions.
- In isometric view (orthographic) the surface is no longer parallel to the projection plane, merely the latter is perpendicular to the lines of sight, with three dimensions existence seen.
- In oblique projection (not-orthographic) the object surface and the project plane are also parallel, merely the lines of sights are not perpendicular to the projection plane, and you tin see again three dimensions.
If the altitude from the observer to the object is finite, and so the projection lines are non parallel (since all lines of sight start at a single point), and the drawing is classified every bit a perspective projection. In perspective view the object surface and projection plane can be also parallel.
Multiview projection
By irresolute position of the object relative to the line of sight yous can create dissimilar views of the aforementioned object. Drawing more than ane face up of an object by rotating the object relative to your line of sight helps in agreement the 3D form. Having several views on one drawing you utilize the concept of multi-view projection, which is based on the orthographic (parallel) projection technique where
- the airplane of project is positioned betwixt the observer and the object,
- the plane of project is perpendicular to the parallel lines of sight, and
- the object is oriented such that only 2 of its dimensions are shown.
Main principles of creating multiview projections
The plane of projection tin can be oriented to produce an infinite number of views of an object. However, the most common views are the six mutually perpendicular views that are produced by six mutually perpendicular planes of projection:
- Front view – the ane that shows nearly features or characteristics.
- Left side view – shows what becomes the left side of the object afterward establishing the front view position.
- Right side view – shows what becomes the right side of the object after establishing the front view position.
- Summit view – shows what becomes the pinnacle of the object one time the position of the front view is established.
- Bottom view – shows what becomes the lesser of the object once the position of the front view is established.
- Rear view – shows what becomes the rear of the object in one case the position of the front end view is established.
The most informative (descriptive) view of the object to be represented is normally called as the principal view (front view). This is view A related to the corresponding management of viewing A and it usually shows the object in the performance, manufacturing, or mounting position.
View positions on drawings and corresponding viewing directions
Positions of the other views relative to the principal view in the drawing depend on the projection method.
The number of views and sections must be express to the minimum necessary to fully represent the object without ambiguity.
Unnecessary repetition of details must be avoided.
Conventional view placement
Generally, 3 views of an object are enough, still, a drawing must comprise as many views as necessary to illustrate the role, normally at correct angles to one another.
Frontal airplane of projection
In multiview projection, the object is viewed perpendicular to the main faces, then that but one face of the object is depicted in each view. The frontal plane of projection is the plane onto which the front view of a multiview drawing is projected.
In the front view you can come across height and width of the object, but you cannot see its depth.
Horizontal aeroplane of projection
The top view is projected onto the horizontal aeroplane of project, which is plane suspended in a higher place and parallel to the height of the object.
The top view of an object shows the width and depth dimensions.
Profile plane of project
In multiview drawings, the right side view is the standard side view. The right side view is projected onto the correct profile plane of projection, which is a airplane that is parallel to the right side of the object. However, yous can besides use the left side view if it is more descriptive and informative. Moreover, when needed, you lot can include both side views into ane drawing.
The side view of an object shows the depth and height dimensions.
The three-view multiview drawing is the standard used in engineering and technology, because frequently the other three common views are mirror images and practise not add to the knowledge virtually the object.
The standard views used in a three-view drawing are the
- elevation,
- front end, and
- correct side views,
arranged equally shown in the figure:
The width dimension is common to the forepart and peak views. The height dimension is common to the front and side views. The depth dimension is mutual to the top and side views.
For simple parts 1 or 2 view drawings will oft be enough. In one-view drawings the third dimension may be expressed by a note, or past descriptive words, symbols, or abbreviations, such as Ø, HEX, etc.
Square sections may exist indicated by light crossed diagonal lines, equally shown in a higher place, which applies whether the face is parallel or inclined to the drawing aeroplane.
Some other example of a ane-view drawing:
Additional views may be added if they meliorate visualization.
The views should also be chosen to avoid hidden feature lines whenever possible. That ways that the most descriptive view should be shown.
Besides, y'all should select the minimum number of views needed to completely describe an object. Eliminate views that are mirror images of other views.
Why multiview drawings technique is so important?
To produce a new product, it is necessary to know its truthful dimensions, and true dimensions are not adequately represented in most pictorial drawings. For example, the photo is a pictorial perspective paradigm. All the same, as you can see, the image distorts truthful distances, while the latter are essential for manufacturing and construction, and in this example the case in question is the width of the road, non the electrical pole!
In mechanical engineering perspective projections distort measurements.
Equally you can see, the two width dimensions in the front view of the cake appear different in length in the perspective projection. In other words, equal distances do non announced equal on a perspective cartoon.
Thus, since engineering and technology depend on verbal size and shape descriptions for design, the best approach is to apply the parallel projection technique (orthographic projection) to create multi-view drawings where each view shows only ii of the three dimensions (width, height, depth).
To summarize:
The reward of multiview drawings over pictorial drawings is that multiview drawings shows the truthful size and shape of the various features of the object, whereas pictorials distort true dimensions which are critical in manufacturing and construction.
1st & iiird angles (glass box)
What exactly you should place on the right side projection?
Is it that we can run into from the left side, or from the right side of the object?
To answer these questions there are two different ways, based on two different principles
- Kickoff-Angle Project
- Third-Angle Projection.
Third angle is used in Canada and the United States. Kickoff angle is used in Europe.
In third angle orthographic projection the object may be assumed to be enclosed in a glass box.
Each view represents that which is seen when looking perpendicularly at each face of the box.
The resulted views are identified by the names as shown.
The front end, rear, and side views are sometimes called eleva tions, e.chiliad., front elevation. The top view may be termed the plan.
If desired, the rear view may be shown both ways – at the extreme left or the extreme right. When this is not practical to show rear view at he extreme left or right due to the length of the office, particularly with panels and mounting plates, the rear view should not exist projected upwards or down, as this would outcome in its beingness shown upside down.
Instead, it should be drawn as if projected sideways, merely located in another position, and should exist conspicuously labelled REAR VIEW REMOVED.
In offset bending orthographic projections the object is considered every bit being rolled over to either side, so that the right side of the object is drawn to the left of the front height:
Information technology is mandatory to indicate the method of multiview projection by including the appropriate ISO (International Organization for Standardization) projection symbol – the truncated cone:
Yous should place this symbol in the lower right-hand corner of the drawing in or adjacent to the title block.
Axonometric projection
It is one of the pictorial cartoon projections, which are useful for illustrative purposes, educational aids, installation and maintenance drawings, design sketches, and the like.
The Greek give-and-take axon means axis and metric means to mensurate. Axonometric project is a parallel projection technique used to create a pictorial drawing of an object by rotating the object on an centrality relative to a plane of projection.
Axonometric projections such as isometric, dimetric, and trimetric projections are orthographic, in that the projection lines are all parallel, but the angle of views is so chosen that three faces of a rectangular object would be shown in a single view.
Axonometric drawings are classified by the angles betwixt the lines comprising the axonometric axes. The axonometric axes are axes that meet to form the corner of the object that is nearest to the observer.
When all three angles are unequal the drawing is classified every bit a trimetric. When two of the 3 angles are equal the drawing is classified equally a dimetric. When all three angles are equal the drawing is classified as a isometric.
Although there are an infinite number of positions that can be used to create such a drawing only few of them are used.
Enlarged detail
To eliminate the crowding of details or dimensions, an enlarged removed view may be used.
- The enlarged view should exist oriented in the same manner as the main view,
- the scale of enlargement must exist shown, and
- both views should be identified by one of the methods shown in the illustrations – with the leader line or with the circle line. The circumvolve enclosing the area on the main view should be fatigued with a thin line.
Source: https://www.mcgill.ca/engineeringdesign/engineering-design-process/basics-graphics-communication/projections-and-views
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