What is Engineering Drawing?
In engineering drawing, engineering related objects like buildings, walls, electrical fittings, pipes, machines etc. are represented with specifications like size, shape, materials etc.
Several engineering drawing software with more accuracy are available. But, drawing on paper is still being used in some areas and for small constructions.
Importance of Engineering Drawing
Drawing plays vital role in the engineering and construction works. The drawing requires no language any one can read it. So, drawings of other countries structures can also be studied easily.
The drawing improves the imagination and new inventions can be developed. The estimate for the project can be done using the details provided in the drawing.
The structure can be analyzed completely before construction by using drawing. So, every engineering construction department especially civil engineering requires drawing to start a project.
Instruments Used in Engineering Drawing
The instruments used in engineering drawing are:
- Drawing sheet
- Drawing board
- Mini drafter
- T square
- Set squares
- French curves
Drawing sheet is a white paper on which an object is drawn which is available in various sizes. The sheet used for engineering should be of good quality. It should be white in color with uniform thickness with must resist the easy torn of paper. The surface of sheet must be smooth.
Various sizes of drawing sheets recommended by Indian standards are listed below.
|Drawing Sheet Type||Dimensions (Length X Width) (mm)|
|A0||841 X 1189|
|A1||594 X 841|
|A2||420 X 594|
|A3||297 X 420|
|A4||210 X 297|
|A5||148 X 210|
Drawing board is generally made of soft wood and it is in rectangular shape. It is used to support drawing sheet, so, the size of board is made according the size of the drawing sheet.
The wood portions are joined by tongue and grove type joint to prevent cracks. At the edge of board, straight ebony edge is provided for the T-square usage.
Different types of drawing boards and their sizes according to IS classification are listed below.
|Type of Drawing Board||Length X Width X Thickness (mm)|
|D0||1500 X 1000 X 25|
|D1||1000 X 700 X 25|
|D2||700 X 500 X 15|
|D3||500 X 350 X 15|
Mini drafter is an instrument which can be used for multiple functions in drawing. It contains two arms which is adjustable to required angle and at the end of the lower arm a scale set is attached.
The scale set contains two scales connected perpendicular to each which cannot be separated. This instrument is fixed to the drawing board at one edge with the help of screw provided for the drafter.
Mini drafter is used for drawing horizontal lines, vertical lines, inclined lines, angles, parallel lines, perpendicular lines etc.
T square is used to draw horizontal and vertical lines on drawing sheet. It made of wood or plastic and in T shape. The vertical part of T is called as blade and horizontal part of T is called as head.
The edge of head is uniform level and attached to the edge of the board. The working edge is used to draw lines anywhere on the sheet by moving the instrument top to bottom.
Compass is used to draw an arc or circle with known dimensions on engineering drawing. It is generally made of steel and consists two legs. One leg contains needle at the bottom and other leg contains a ring in which a pencil is placed.
The needle tip is placed at the respected point and pencil tip is adjusted to the height at least 1mm just above the tip of the needle. The gap is nothing but the paper thickness.
The divider looks like a compass, but the difference is the two legs of divider are provided with needles. This is used to divide a line or curve into equal parts. It is also used to check the measurements.
Set squares are used to draw lines with an angle between them. In most of the structures, 30, 45, 60 and 90-degree lines are most common. So, set squares make the work easier for this type of drawings.
Generally, set squares are of two types. One is 45 degree set square and another one is called as 30 – 60 degree set square. Both are required in the drawing. 45 set square has a side of 25 cm while 30-60 set square has 25 cm length on one side.
Clinograph is an instrument used to draw parallel lines to the inclined lines. It contains one adjustable wing or strip which can be adjusted to required angle. So, it can be termed as adjustable set square.
Protractor is used to draw and measure the angles of lines in the drawing. It is transparent and made of plastic. It is in the shape of semi-circle, and the edge of semi-circle part consists reading with one-degree accuracy.
The bottom line joins the 0o to the 180o. The center of this bottom line is marked as “O” or “C” from which the angles are measured.
French curves are made of plastic and they are in irregular shapes. Sometimes the drawing requires irregular curves or shapes or arcs which cannot be drawn using compass. In that case French curves are suitable.
Generally French curves are more suitable for small curves and for long curves splines are used.
Templates are nothing but plastic or wooden boards which contains spaces of several shapes or letters. Non-dimensional shapes or variety font letters are drawn by using templates which makes drawing easier and perfect.
Pencil is used to draw on the paper. Any type of pencil is not suitable for drawing. There are some limitations, the drawing appearance should be very neat and understandable.
Every line of the drawing should indicate its importance. It depends upon the hardness of pencil.
Based on the hardness quality pencils are classified into 18 grades and they are
|Grade of Pencil||Hardness of Pencil|
|6H, 5H, 4H||Extremely Hard|
|B||Moderately soft and black|
|2B||Soft and black|
|3B||Very soft and black|
|4B, 5B, 6B||Very soft and very black|
Out of the above 18 grades of pencils, following grades are used in engineering drawings.
|Grade of Pencil||Used to Draw|
|2H||Dimension lines, center lines, sectional lines, hidden lines|
|H||Object lines, lettering|
|HB||Dimensioning, boundary lines|
Eraser is used to remove the lines or spots which drawn by mistake or with wrong measurements. The eraser used should be of good quality and soft. It should not damage the paper while erasing.
When the drawing sheet is placed on the board it may not be in fixed position. To fix the drawing sheet to the board paper holders are used.
Generally used paper holders are thumb pins, spring clips, stick tapes etc. Care should be taken while removing the clips or tapes otherwise the sheet may tore.