Introduction
One of the best ways to communicate one's ideas is through some
form of picture or drawing. This is especially true for the engineer. The
purpose of this guide is to give you the basics of engineering sketching and
drawing.
This is just an introduction. Don't worry about understanding
every detail right now - just get a general feel for the language of graphics.
Because you'll be seeing a lot of it. Before we get
started on any technical drawings, let's get a good look at this strange block
from several angles.
Imagine that you have an object suspended by transparent threads
inside a glass box, as in figure
Then draw the object on each of three faces as seen from that
direction. Unfold the box and you have
the three views. We call this an "orthographic" or
"multitier" drawing.
Isometric Drawing
This is one of a family of three-dimensional views called
pictorial drawings. In an isometric drawing, the object's vertical lines are
drawn vertically, and the horizontal lines in the width and depth planes are
shown at 30 degrees to the horizontal. When drawn under these guidelines, the
lines parallel to these three axes are at their true (scale) lengths. Lines
that are not parallel to these axes will not be of their true length.
Any engineering drawing should show everything: a complete
understanding of the object should be possible from the drawing. If the
isometric drawing can show all details and all dimensions on one drawing, it is
ideal. One can pack a great deal of information into an isometric drawing.
However, if the object in figure 2 had a hole on the backside, it would not be
visible using a single isometric drawing. In order to get a more complete view
of the object, an orthographic projection may be used.
Dimensioning
We have "dimensioned" the object in the isometric
drawing in figure 7. As a general guideline to dimensioning, try to think that
you would make an object and dimension it in the most useful way. Put in
exactly as many dimensions as are necessary for the craftsperson to make it -no
more, no less. Do not put in redundant dimensions. Not only will this clutter the drawing, but if "tolerances" or accuracy levels have been
included, the redundant dimensions often lead to conflicts when the tolerance
allowances can be added in different ways.
Repeatedly measuring from one point to another will lead to
inaccuracies. It is often better to measure from one end to various points.
This gives the dimensions a reference standard. It is helpful to choose the
placement of the dimension in the order in which a machinist would create the
part. This convention may take some experience.
We can get around this by pretending to cut the object on a
plane and showing the "sectional view". The sectional the view is
applicable to objects like engine blocks, where the interior details are
intricate and would be very difficult to understand through the use of
"hidden" lines (hidden lines are, by convention, dotted) on an
orthographic or isometric drawing.
Drawing Tools
To prepare a drawing, one can use manual drafting instruments
(figure 12) or computer-aided drafting or design, or CAD. The basic drawing
standards and conventions are the same regardless of what design tool you use
to make the drawings. In learning to draft, we will approach it from the
perspective of manual drafting. If the drawing is made without either
instruments or CAD, it is called a freehand sketch.
Assembly" Drawings
An isometric view of an "assembled" the pillow-block the bearing system is shown in figure 13. It corresponds closely to what you
actually see when viewing the object from a particular angle. We cannot tell
what the inside of the part looks like from this view.
We can also show isometric views of the pillow-block being taken
apart or "disassembled" (figure 14). This allows you to see the inner
components of the bearing system. Isometric drawings can show overall
arrangement clearly, but not the details and the dimensions.
Cross-Sectional Views
A cross-sectional view portrays a cut-away a portion of the
object and is another way to show hidden components in a device.
Imagine a plane that cuts vertically through the center of the
pillow block as shown in figure 15. Then imagine removing the material from the
front of this plane, as shown in figure 16.
This is how the remaining rear section would
look. Diagonal lines (cross-hatches) show regions where materials have been cut
by the cutting plane.
This cross-sectional view (section A-A, figure 17), one that is
orthogonal to the viewing direction, shows the relationships of lengths and
diameters better. These drawings are easier to make than isometric drawings.
Seasoned engineers can interpret orthogonal drawings without needing an
isometric drawing, but this takes a bit of practice.
The top "outside" view of the bearing is shown in
figure 18. It is an orthogonal (perpendicular) projection. Notice the direction
of the arrows for the "A-A" cutting plane.
Half-Sections
The diagonal lines on
the section drawing are used to indicate the area that has been theoretically
cut. These lines are called section lining or cross-hatching. The lines are thin and are usually
drawn at a 45-degree angle to the major outline of the object. The spacing
between lines should be uniform.
A second, rarer, use of cross-hatching is to
indicate the material of the object. One form of cross-hatching may be used for
cast iron, another for bronze, and so forth. More usually, the type of material
is indicated elsewhere on the drawing, making the use of different types of
cross-hatching unnecessary.
Usually, hidden (dotted) lines are not used on
the cross-section unless they are needed for dimensioning purposes. Also, some
hidden lines on the non-sectioned part of the drawings is not needed (figure
12) since they become redundant information and may clutter the drawing.
Section is
also known as vertical section and sectional elevation or cross section. It is
imagined that a finished buildings is cut vertically along a line so that the
building is separated into two portions along the imagined vertical plane right
from top of the building to the lowest part of foundation. The view that can be
seen while travelling along this imaginary vertical plane when looking towards
left is drawn to the same scale as that adopted for the plan. The line, which
is drawn on the plan to indicate the section, is called sectional line and
represented by A-B or X-X. The arrow heads shall be marked to indicate the way
in which the sectional view is to be drawn. In some cases offset is given to
indicate the necessary details, but the offset is only to shift the vertical
plane from one position to another position
1. Residual
head or available head: It is the pressure head available at any particular
point in the distribution system.
2. Plumbing
System: It is the entire system of pipes fixtures, appliances etc for providing
water supply and drainage to building.
3. Water main or street main: This is the
water supply pipe for public or community use and maintained by local or
administrative authority.
4. Service pipe : Any pipe used for conveying
water from water main to any building or premises and it is subjected to water
pressure from the water main is called service pipe
LAYOUT OF
A SEPTIC TANK:
The layout
for a septic tank sewerage system should be simple and as direct as possible.
The pipes should be laid in straight lines in both vertical and Horizontal
planes as far as possible.
COMPONENTS
OF SEPTIC TANK:
The septic tank consists of a
rectangular or circular underground chamber built with brick masonary or stone
masonary. It should be plastered inside and outside with 1:4 c.m. The floor
should be constructed with of 1:10 towards the sludge outlet. The septic tank
should have a minimum liquid capacity of 1000litres with a minimum width of
750mm and depth 1000mm. A minimum freeboard of 300mm should be provided. The
following are the components of the septic tank
Inlet :
for tanks of width less than 1200mm,
the inlet is T-shaped dip pipe of the same diameter as the incoming drain. The pipe
should be fixed inside the tank with top-level extending above slum level and
bottom limb extending about 300mm below the top water level. For wider tanks, a
baffle wall should be provided 150mm from the inlet of the tank, extending
150mm below the invert of the inlet pipes and 150mm above the top water level.
Outlet :
For narrow
tanks, T-Pipe if 100mm dia is fixed inside the tank with the top limb rising
above the slum level and the bottom extending to about 1/3 of the liquid depth.
The invert of the pipe should be 50mm below the invert of the inlet pipe. For
wider tanks, a weir outlet is provided extending the full width of the tank, A
scum board is fixed 150mm from the weir and extending 150mm above and 1/3 of
liquid depth below the top of water level. A deflector is provided at the base
of the scrum board to prevent particles from reaching the outlet weir.
Partitions
:
Where the capacity of the septic tank exceeds
2000litres, the tank is divided into 2 chambers by partition. Suitable Civil
Engineering Drawing- openings are provided in the partition at 300mm below the
tank water level.
Openings and cover: Each compartment should be
provided with a rectangular or circular opening with a cover of R.C.C or C.I.
The cover should neatly fit the openings to prevent water from entering through it.
Ventilating
pipe:
Every septic tank should be provided
with a ventilating pipe of dia 50mm. The top of the pipe should be provided with
mosquito proof mesh.
