Creating engineering drawings is a whole subject area of its own; there
are whole degrees given in Drafting Technology. It is also a timehonored art form. Drawings are used all fields of Engineering
(Mechanical, Civil, Architectural, Electrical, Aerospace, etc.) The type of
drawings we will be creating in this class are Mechanical, but the
concepts are all transferable to the other Engineering fields.
The main purpose of engineering drawings is to communicate to other
engineers, machinists, etc. Drawings do the communication best merely
because a picture is worth a thousand words. Giving all of the
information needed to make the product and being accurate in that
information is the main goal. Engineers are very picky about their
drawings and must pay attention to detail.
Below are the basics concepts of Engineering Drawings. The attempt
here is to take volumes of drafting text material and boil it down to just
what you need for this class.
They include:
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Orthographic Views
Half Views and Partial Views
Linetypes
Dimensions and Notes
Half Views and Partial Views
Auxiliary Views
Section Views
Full Section
Half Section
Offset (Sketched) Section
Revolved Section
Broken Out (Local) Section
Detailed Views
Conventional Breaks
Scaling
ORTHOGRAPHIC VIEWS
Orthographic Views are two-dimensional views of objects where the
viewpoint of the object is at right angles to (or looking directly at)
surfaces. They are used in technical and engineering drawings for
accuracy. If one's viewpoint is not at right angles, it is considered a
"Foreshortened" view.
You can also think of these views as an object inside a box with its
surfaces "projecting" on to the sides of the box. You can then unfold the
box to project the views on a flat surface.
Because the views are only two dimensional, more than one view is
needed to completely describe the object. Usually two or three views is
enough (Front, Top and Side), but often more are required.
Traditionally, the views contain dimensions as follows:
VIEW DIMENSIONS
Front
Width and
Height
Top
Width and
Depth
Side
Width and
Height
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LINETYPES
OBJECT LINES
Object lines depict the visible edges of an object. The edges you would see
looking at the object with your naked eyes. They shown as dark, solid lines.
HIDDEN LINES
Hidden lines depict invisible edges inside an object. The edges you would not
see looking at the object with your naked eyes. They are shown as dashed
lines.
CENTER LINES
Center lines depict the center of any cylindrical-shaped object whether it be a
cylinder or hole. They are shown as a long line followed by a short line,
followed by a long line.
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DIMENSIONS, THEIR COMPONENTS AND NOTES
Dimensions tell how far it is from one point on an object to another
point. The most basic type is called a Linear Dimension because it
gives the straight-line distance from one point to another. There are
also Radial, Diameter and Angular Dimensions.
Dimensions have four basic components:
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Dimension Text
Dimension Line andArrows
Extension Lines
Gap
Note that the extension lines can cross over Object Lines (Visible Edges
of the Object) to reach their destination, but still leave a gap.
Notes are added text to describe things on the drawing. The simplest type is
just text, as in the title of the drawing. The other type of note contains a leader,
which is an arrow that points to the subject of the note.
The box around the drawing is called the Title Block or the Format.
BASIC DIMENSIONING TIPS:
ARROW AND TEXT PLACEMENT
The Placement of your dimension lines (arrows) and dimension text depends on
the amount of space there is between the extension lines.
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HALF VIEWS AND PARTIAL VIEWS
Half Views and Partial veiws are used to simply save space when half of, or
portion of a view is not needed or is redundant.
AUXILIARY VIEWS
Auxiliary Views are used to accurately depict features on Inclined Surfaces. If
there is no feature on the inclined surface, there is no need to create an
auxilliary view.
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SECTION VIEWS
Section views are used to get rid of the confusing hidden lines:
They are a way to, in our imagination, cut through an object and create an
orthographic view inside the object. It is as if the object were cut in two.
Where the object is cut is called the cutting plane and the direction of view is
depicted by arrows. The SECTION A-A note is for use if the view is on a
different page from the main views.
The material that is supposedly cut is "Hatched" with patterns. The patterns
often depict the actual material of the object.
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FULL SECTIONS
Full section views cut all the way across the object.
Full Section Views can be placed on the same page or on another page.
The Cutting Plane and Arrows always are displayed.
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HALF SECTIONS
Half Section Views are used primarily on symmetrically shaped objects (where
both halves are the same). They are a great shortcut because you can depict the
inside and outside of the object all in one view.
Half Section Views can be placed on the same page or on another page.
If the view is displayed on another page, the Cutting Plane and
Arrows always are displayed.
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OFFSET (SKETCHED) SECTIONS
Offset Section Views (Called Sketched Sections in Pro/E) are like full section
views except that the Cutting Plane bends to follow certain features inside the
object.
Offset Section Views can be placed on the same page or on another page.
The Cutting Plane and Arrows always are displayed.
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REVOLVED VIEWS
Revolved Views are a shortcut way to show a section view that shows
the internal shape of an object without creating a completely separate section
view. The cutting plane passes through the object at the desired location and
is revolved, in place, to show the section view. Revolved Section Views are
placed on the same page.
Revolved Views can be inside the regular view:
Or removed.
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BROKEN OUT (LOCAL) SECTIONS
Broken Out Sections (Called Local Sections in Pro/E) are another sectioning
shortcut. It is a way to make a section veiw of only a specific and usually small
area.
Broken Out Section Views are placed on the same page.
The Cutting Plane and Arrows are not displayed.
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DETAILED VIEWS
Detailed views are created to show small, detailed areas of a view in a
special scaled-up view. The scale is usually twice that of the normal
view.
Detailed Views can be placed on the same page or another page.
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CONVENTIONAL BREAKS
Conventional Breaks are a way of depicting a very long object without showing
the entire length. It is often used for objects like rods, tubing/piping or wooden
objects
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SCALING
Scaling is used to depict objects on paper that are either larger or smaller than
the paper.
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If the object is larger than the paper, then the views of the object are
scaled Down
If the object is smaller than the paper, then the views of the object are
scaled Up
If the object fits on the paper, then the views are depicted at Full scale
(1:1)
In Mechanical Drawings, we generally use Decimal Inch or Metric scaling
The number on the left of the colon indicates the units on the Page.
The number on the right of the colon indicates the Units on the Object or
PAGE:OBJECT
You want to think of it like this when you see a Decimal Inch scale of 1:2
ONE UNIT ON THE PAGE = TWO UNITS ON THE OBJECT, or 1/2
Scale.
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