Download - Introduction to engineering graphics
INTRODUCTION TO ENGINEERING
GRAPHICS
Prepared By:-Sagar Patel
CONTENTS DRAWING INSTRUMENTS SHEET LAYOUT SCALES LINES
INTRODUCTION Engineering drawing is a technique of creating graphical
representation that contains all necessary information such as dimensions, specifications and notes, using which an abstract concept can be transformed into real world object. Application of engineering drawing are valid for e.g.: Shipping industry, manufacturing, construction and many more.
Some important concept of engineering drawing is like projection. The word projection means to throw forward. It is a process of plotting an object in an imaginary plane. Projection has two types:
1. Parallel projection2. Perspective projection Each of these has further subtypes.
DRAWING INSTRUMENTS1. Drawing paper: The size of drawing paper should be
less than drawing board and paper should be fixed properly.
2. Drawing board: It is a plane and smooth surface use for drawing purpose.
3. T-square: It is a T shape drawing tool whose edge slide along width of drawing board with the help of stop. It is useful in drawing straight line.
4. Compass: It is used for drawing circles and arcs. The divider is little different with both legs made of steel and use for transferring distance.
DRAWING INSTRUMENTS5. French Curves: They are used to draw irregular
curves such as ellipse, hyperbola and parabola.6. Drafter: It is useful tool for drawing parallel lines at
any inclination. It has scale as well as protractor inbuilt.7. Protractor: It is use to measure and layout angles.8. Set Square: It is also known as triangle. They comes
in flavors of 30, 60, 30 and 45, 90, 45.
DRAWING INSTRUMENTS
Typical Drawing Equipment
Objectives in Drawing
1. Accuracy
2. Speed
3. Legibility
4. Neatness
DRAFTER It is useful tool for drawing parallel lines at any
inclination. It has scale as well as protractor inbuilt.
FRENCH CURVES They are used to draw irregular curves such as
ellipse, parabola and hyperbola.
DRAWING BOARDDrawing Boards
The left edge and right edge of a drawing board has a true straight edge.
For right-handed people, the left-hand edge of the board is called the working edge because the T-square head slides against it.
For left-handed people, the right-hand edge of the board is called the working edge because the T-square head slides against it.
T-Squares
The T-square is made of a long strip called the blade, fastened at right angles to a shorter piece called the head.
T-SQUAREThe drawing paper should be placed close to the working edge of the board to reduce any error resulting from the bending of the blade of the T-square.
The paper should also be placed close enough to the upper edge of the board to permit space at the bottom of the sheet for using the T-square.
Drafting tape is used to fasten the drawing paper to the drawing board.
DRAWING PENCILSDrawing Pencils
High-quality drawing pencils should be used in technical drawing, never ordinary writing pencils.
Many makes of mechanical pencils are available together with refill leads in all grades. Choose a mechanical pencil that feels comfortable in your hand.
DRAWING LEADSDrawing Leads
The first consideration in the selection of a grade of lead is the type of line work required. For light construction lines and guide lines for lettering use a hard lead. For all other line work, the lines should be BLACK. The lead chosen should be soft enough to produce jet black lines but hard enough not to smudge.
HARD MEDIUM SOFT
9H 8H 7H 6H 5H 4H 3H 2H H F HB B 2B 3B 4B 5B 6B 7B
Hard leads are used where extreme accuracy is required. Generally these leads are used for construction lines.
Medium leads are used for general purpose line work in technical drawing.
Soft leads are used for various kinds of art work. These leads are too soft to be useful in mechanical drafting.
SET SQUARETrianglesMost inclined lines are drawn at standard angles using the 45º x 45º triangle and the 30º x 60º triangle.
In addition to drawing angles of 90º, 45º, 30º, and 60º, triangles can be combined to draw angles of 15º increments.
COMPASSGiant Bow Sets
Giant bow sets contain various combinations of instruments.
Giant Bow Compass
The giant (large) bow compass has a center wheel and can be adjusted simply by opening or closing the legs of the compass while turning the center wheel.
SCALEScalesScales are instruments used in making technical drawings full size or at a given reduction or enlargement.
Types of scales include metric scales, engineers’ scales, decimal scales, mechanical engineers’ scales, and architects’ scales.
Scales are usually made of plastic or boxwood and are either triangular of flat in shape.
SHEET LAYOUT Sheet size: The preferred
sizes of drawing sheet as recommended by the bureau of Indian standards are given below as per SP:46(2003).
Sheet Designation Trimmed size (mm)
Untrimmed size (mm)
A0 841*1189
880*1230
A1 594*841
625*880
A2 420*594
450*625
A3 297*420
330*450
A4 210*297
240*330
A5 148*210
165*240
SHEET LAYOUT Margin: Margin is provided in the drawing sheet by
drawing margin lines. Prints are trimmed along this lines. Border lines: Clear working space is obtained by
drawing border lines. More space is kept on the left-hand side for the purpose of filling or binding if necessary.
Borders and frames: SP:46(2003) recommends the borders of 20mm width for the sheet sizes A0 and A1, and 10mm for sizes A2, A3, A4 and A5.
SHEET LAYOUT Title Block: Space for title
block must be provided in the bottom right-hand corner of the drawing sheet. The size of the title block as recommended by the B.I.S is 185mm*65mm for all designations of the drawing sheet. All title blocks should contain at least the particulars as shown in the figure:
SCALES A scale is defined as the
ratio of the linear dimensions of element of the object as represented in a drawing to the actual dimensions of the same element of the object itself.
The scales generally used for general engineering drawings are:
1) Reducing scales
1:2 1:10 1:5
1:20 1:50 1:100
1:200 1:500 1:1000
1:2000
1:5000
1:10000
2) Enlarging scales
50:1 20:1 10:1
5:1 2:1
3) Full size scales
1:1
SCALES Representative fraction: The ratio of length
of the object represented on drawing to the actual length of the object represented is called RF.
If RF>1 then the drawing is enlarged. If RF<1 then the drawing is reduced view. The different types of scales are:1. Plain scale2. Diagonal scale3. Comparative scale4. Vernier scale5. Scale of chords
LINES Lines are predominant and fundamental drawing
element in every drawing. Various types of lines are used to represent different
objects like visible lines are used for drawing outlines of visible edges and surface line which represent the object. These are drawn in bold dark and continuous lines.
Hidden lines are shown with medium thick lines consisting of short dashes and use to represent invisible ages and surface boundary.
Centre lines are thin lines drawn with ultimate long dashes and dots and are used for representing symmetrical objects. Then there are dimension and cutting lines.
Main Line Types
Lines
Hidden Lines
Center Lines
Dimension Lines
Extension Lines
Leader LinesCutting Planes
Section Lines
Phantom Lines
Viewing Planes
Break Lines
Visible Lines
LINES
Cutting Plane Lines
• Thick broken line that is terminated with short 90 degree arrowheads.
• Shows where a part is mentally cut in half to better see the interior detail.
Extension Lines• Thin lines used to establish the extent of a dimension.• Can also be used to show extension of a surface to a
theoretical intersection as shown in (b).• Begin 1.5mm from the object and extend to 3mm
beyond the last dimension.• They should not cross dimension lines.
Dimension Lines• Thin lines capped on the ends with arrowheads and
broken along their length to provide a space for the dimension numeral.
• They indicate length.
Center Lines• Thin line consisting of alternating long and short
dashes.• Used to represent the center of round or cylindrical
features, or the symmetry of a feature.
Section Lines
• Thin line usually drawn at a 45 degree angle.• Indicates the material that has been cut through in a
sectional view.
Section Line
Hidden Lines• Light, narrow, short, dashed lines.• Shows the outline of a feature that can not be seen in
a particular view.• Used to help clarify a feature, but can be omitted if
they clutter a drawing.
Visible/Object Lines• Dark, heavy lines.• Used to represent the outline or contour of the object
being drawn.• Define features you can see in a particular view.