RRB ALP Engineering Drawing Study Plan 2018 - Part I

By Rahul Chadha|Updated : November 27th, 2018

Engineering Drawings help us in developing our thoughts and ideas into a final product. Engineering Drawings are also necessary for engineering industries since they are required and are being used at various stages of development of an engineering product.  Engineering drawing is completely different from artistic drawing, which are used to express aesthetic, philosophical, and abstract ideas. In an industry, these drawings help both the technical as well as commercial staffs at various stages like:

  • conceptual stage
  • design stage
  • modification stage
  • prototype development stage
  • process and production planning
  • production
  • inspection
  • marketing
  • Servicing and maintenance,  etc.

What information should be available in an engineering drawing?
A  perfect engineering drawing should have the following information:

  • Shape of an object
  • Exact Sizes and tolerances of various parts of the object
  • The finish of the product
  • The details of materials
  • The company’s name
  • Catalogue no of the product
  • Date on which the drawing was made
  • The person who made the drawing

Drawings are the road maps which show how to manufacture products and structures. No industrial level construction/manufacturing of any (man-made) engineering objects is possible without engineering drawing.

There is an international standard on the code of practice for drawing which is followed and adopted by Bureau of Indian Standard (BIS).

Note: The ISO ‘A’ series of sheet is based on a constant width to length ratio of 1:2

SCALES

The word ‘scale’ is usually employed for an instrument used for drawing or measuring the length of a straight line. It is also used to represent the proportion in which the drawing is made with respect to the object. It is used to make full size, reduced size or enlarged size drawing conveniently depending upon the size of the object and that of the drawing sheet. Usually, the engineer's scale is made up of cardboard and as recommended by the Bureau of Indian Standards (BIS) there are eight set of scales.
These are designated from M1 to M8

DRAWING PENCIL

Various grades of pencils are available according to the proportion of graphite to clay mixture in the pencil lead.
HB – (soft grade) - Used for drawing border lines, lettering and freehand sketching.
H – (medium grade) - Used for drawing visible outlines, visible edges, and boundary lines.
2H – (hard grade) - Used for construction lines, dimension lines, leader lines, extension lines, centre lines, hatching lines and hidden lines.

LAYOUT OF A DRAWING SHEET

  • It lies within the drawing space of bottom right hand corner of the sheet. It has maximum length 170mm.
    Centring Marks
  • Four centring marks are provided on all drawing to meet the requirement of the positioning of the drawing for microfilmed reproduction.
    Orientation Marks
  • Two orientation mark is provided in layout to indicate the orientation of drawing.
    Border of Layout
  • It is enclosed by the edges of the trimmed sheet and frame limiting the drawing space.
    Grid Reference System
  • It is practiced for all sizes in order to find easy location on the drawing of details and also to find the object location for additions and modification work etc.
  • A typical layout of a drawing sheet does not contain identification mark.
  • Grid references on a drawing sheet provide the following information: Location of details, additions, modifications, revisions, etc. of drawing.
    Lettering should be done freehand using HB grade pencil (conical end).
    1. Type B is preferred over type A because of the division of height.
    2. Vertical letters are preferred over slopped letters because of easy execution.
    3. The line width of type A lettering is always less than that of type B lettering.
  • First we have to draw border lines and title box and then we have to start drawing.

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  • We have many types and sizes of drawing sheets..  like A4,A3,A2,A1,A0 etc.

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DRAWING INSTRUMENTS AND ACCESSORIES

The following set of instruments are required for ensuring perfection in the manual drawing:

1. Drawing board

Drawing board is made of soft wooden platens.  Almost perfect planning of the working surface of the drawing board is to be ensured. A  strip of hard ebony edge is fitted up in a groove on the shorter edge of the board and perfectly lined to provide the guide for the T-square.  The standard sizes of the drawing board is shown in Table 1.1 below. D2 size of drawing board is normally recommended for the First year Engineering students.byjusexamprep2. Drawing Sheet

Drawing sheet is the medium on which drawings are prepared by means of pencils or pen.  Drawing sheets are available in standard sizes as shown in Table 1.2. A standard A0 size sheet is the one with an area of 1 m-2 and having dimensions of 1189 x 841. Each higher number sheet (A1, A2, A3, etc. in order) is half the size of the immediately lower  numbered sheet.  For drawing practice for first year engineering students, A2 size is the preferred drawing sheet. The recommended  sizes obtained for various drawing sheets are shown in the below given figure -byjusexamprep

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3. Mini-drafter

This is a device used to draw parallel or inclined lines very effectively with ease. This is mounted on the top left corner of the drawing board by means of a clamping mechanism which is an integral part of the device. Below given Figure shows the photograph of a typical college level mini drafter. An L-shaped scale which is graduated in millimeters acts as the working edge of the mini-drafter. The L-Shaped scale also has a degree scale for angle measurement. The working edge can be moved to any desired location on the drawing board. 

Procedure for clamping the mini-drafter
Set the protractor head with reference mark indexing zero degrees, then fix the clamp of the mini-drafter at the top left corner either along the top horizontal edge of the board or along the left vertical edge of the board. With the drawing sheet placed underneath the scales of the mini-drafter, fix the drawing sheet to the drawing board with the scales of the mini- drafter aligned either with the vertical or the horizontal borderlines of the drawing sheet.

byjusexamprep4. Set squares

Set squares are a set of 45° set square and 30°-60° set-square, as shown in the below-given figure. They are used in conjunction with each other and with T-square to draw parallel, inclined and perpendicular lines. They are made of transparent acrylic. Each is having beveled edges with engraved mm or inch marking. The 45° set square generally has a protractor where as the 30°-60° set-square includes French curves.

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5. Compasses

These are used to draw arcs or circles. Generally, two sizes of compasses: one large compass and the other a small spring bow compass are commonly found. Each compass consist of a needle point and a pencil point. For drawing very large radius arcs, the pencil point leg can be removed from the knee joint and a lengthening bar can be inserted to increase the radius of the arc. The below given figure shows the photograph of a compass. The below given shows the photograph of a compass.

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6. Divider

Dividers are used to transfer lengths to the drawings either from scales or from the drawing itself. Similar to the compasses, two sizes of dividers are used in technical drawings. One large divider and the other small spring bow divider.

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7. Pencils / lead sticks/ pencil sharpener / eraser/etc:

The primary tool used in technical drawings is the pencil or lead sticks. Generally, for technical drawings, the three grades of pencil used is HB, H and 2H . For different purposes, different grades of pencils are used. Pencil sharpener is is used to mend the pencils. Eraser  is used to erase the unnecessary part of the pencil drawing.

8. French curve/Flexible curve

French curve is free form template made of acrylic and is used to draw a smooth curve passing through a  number of points. The outer profile of the French curve is adjusted such the smooth curve passes through more than three points and a curve passing through these lines are drawn. The next part of the curve is then drawn by using the next three points in addition to the last two points of the previous curve. A typical French curve is shown in the below given figure. 
A flexible curve is consists of a flexible, generally made of metallic wire coated with a thick rubber material. This can be bend into any shape so that its working edge can be matched with a number of points and a smooth curve can be.

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Layout of drawing sheets

Any engineering drawing has to follow a standard format. The drawing sheet consist of drawing space, title block and sufficient margins. After fixing the drawing sheet on the drawing board, margins should be drawn.   The layout should facilitate quick reading of important particulars. Drawings are prepared at various locations and shared and quick references should be located easily. 
A typical drawing sheet consist of the following:

  1. Borders – space left all around in between the trimmed edges of the sheet. A minimum of 10 mm
  2. Filling margin – 20 mm minimum on left hand side with border included. This is provided for taking perforations. 
  3. Grid reference system – For all sizes of drawing sheets for easy location of drawing within the frame. The length and the width of the frames are divided into even number of divisions. Number of divisions for a particular sheet depends on the complexity of the drawing. The length of the grids lies between 25 mm to 75mm depending on the Drawing sheet size. The grids along vertical edges are named by capital letters whereas grids along the horizontal edges are by numerals. Numbering and lettering start from the corner of the sheet opposite to the title box and are repeated on the opposite sides. The numbers and letters are written upright. Repetition of letters or numbers like AA, BB, etc. are practiced in case they exceed that of the alphabets.
  4. Title box – An important feature which is a must in every drawing sheet. The title box is drawn at the bottom right hand corner of every drawing sheet and provides technical and administrative details regarding the drawing/component. Though there are various dimensions for the title box, for Engineering students it is advisable to use a title box of size 170 mm x 65 mm.

    The title box is divided in to two zones: (a) part identification zone and (b) additional information zone. In the part identification zone, information like  the component identification number , name of the part, the legal owner of the drawing (i.e. the name of firm/component/etc will be highlighted where as in the additional information zone, technical information like symbols indicating the system of projection, scale of drawing,  method of indicating surface texture, geometric tolerances, etc. will be highlighted.

DIMENSIONING [IS 11669: 1986]

BIS (Board of Indian Standards SP 46: 2003) defines a dimension as a numerical value expressed in appropriate units of measurement and indicated graphically on technical drawings with lines, symbols, and notes.

  • Centre lines are drawn as, long-dashed dotted narrow lines.
  • A long-dashed dotted narrow line is used to represent, line of symmetry, centre line, pitch circle of gears and holes.
  • The inclination of letters as recommended by BIS is 75°
  • The two recommended systems of placing the dimensions are unidirectional and aligned systems.
  • A rounded interior corner is called a Fillet.
  • Centreline is used to indicate the axis of the cylinder, centreline of the hole, axis of symmetry.
  • A short break line is used to indicate a long part of a uniform cross-section.
  • The type of line used to indicate a cutting plane is long dashed dotted.
  • In parallel or progressive dimensioning, placement of a number of single dimension lines parallel to one another starting from a common extension line situated at one end is done. Smaller dimensions are always placed nearer to the view.

GEOMETRICAL CONSTRUCTIONS

  • When two graphic entities are at a constant distance apart along the length, it is commonly referred as Parallelism.
  • If a line intersects a circle at two points and does not pass through the centre, the line segment inside the circle is referred as Chord.
  • When a circle passes through three given points, its centre lies at the intersection of the perpendicular bisectors of the lines that connect the points.
  • In a big circle, three small circles of equal size are drawn. Each of the small circles is tangent to the big circle and the other two circles. The centres of the small circles lie at the corner of an equilateral triangle.
  • Knowledge of geometrical constructions is essential in designing the specific profiles on the object. For a regular polygon, each interior angle is given as (N-2)x180 /(N), where n is the total number of sides of the regular polygon. Here n = 5 (for Pentagon) 80, each interior angle is 108° Hence statement II is wrong.
  • Each exterior angle = 360°/N
  • Sum of exterior angle = 360°.
  • Sum of interior angle = 180°×(N–2)
  • The perpendicular bisector of the chord of an arc/circle always passes through the centre of the arc/circle. A regular pentagon can be inscribed exactly in a given circle.

SCALES

REPRESENTATIVE FRACTION (R.F.): Ratio of the drawing size of an object to its actual size is called as a representative fraction.
Plain Scale: A plain scale is used to represent two consecutive units i.e. a unit and its sub-division.
Diagonal Scale: A diagonal scale is used to represent three units. i.e. main unit, its sub unit and subdivision of sub unit. A diagonal scale is constructed on the principle of similarity of triangles.
Scale of Chords: It is used to measure or construct angles when a protractor is not available.

  • A plain scale is used to indicate the distances in a unit and its immediate subdivision, whereas a vernier scale and diagonal scale indicate the distances in a unit and its immediate two subdivision.
  • A diagonal scale is based on the similarity of triangles. Hence statement I is true. A vernier scale is a backward vernier scales if VSD > MSD and its least count is given by LC = VSD – MSD.
  • All the divisions on the base of a scale of chords are not equal but decrease gradually from one end to other.
  • Measurement of the distances is simpler in a diagonal scale than in a vernier scale.
  • If in the diagonal scale, horizontal subdivision represents y cm. Then to get LC of the scale, it is divided into n equal parts so that LC = y/ n cm.

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