Introduction to Engineering Drawing

Lecture-1

Drawing

A drawing is a graphical representation of an object, or a part of it, and is the result of creative thought by an artist, engineer or technician. Drawing is the process of representing objects, concepts, or ideas visually on a surface using lines, shapes, and symbols. It is an essential form of communication in art, design, and engineering. Drawings can be freehand, detailed, or technical, depending on their purpose.

Types of Drawings

Artistic Drawing:

Artistic drawings can vary widely, ranging from simple line sketches to world-renowned paintings. This type of drawing serves as a medium for artists to convey emotions, beliefs, philosophies, and creative ideas.

Engineering / Technical Drawing

An engineering drawing is a type of technical drawing that is used to convey information about an object.

An engineering drawing is a technical document that communicates specific information about objects, or structures. It uses standardized symbols, notations, and scales to represent details precisely.

Engineering drawing is a graphical language used by engineers and technical personnel to accurately represent three-dimensional objects. It is a two-dimensional representation of a real or imaginary object using graphics, symbols, letters, and numbers, using engineering drawing instruments.

 

•      Drawing is the language of engineers. An engineer must be well conversant with drawings.

•      Drawing represents the reduce shape of the structures and owner visualizes what is going to be happen.

•      Drawing provides instructions and guidance to architects, engineers and workmen at field to construct the structure according to the dimension shown in the drawings.

Engineering Drawing

§  Freehand Sketch

§  Instrumental Drawing

§  Computer aided drawing

 

Key elements of an engineering drawing include

1.     Geometry: The shape and size of the object or system.

2.     Dimensions: Exact measurements of the components and overall structure.

3.     Annotations: Notes and labels providing additional information.

4.     Views: Different perspectives (e.g., top, side, front) to give a complete understanding of the object.

5.     Scale: The ratio of the drawing's size to the actual size of the object.

6.     Tolerance: Allowable variations in dimensions.

7.     Material Specifications: Information on the materials to be used.

8.     Standards: Adherence to industry standards for symbols, notations, and drawing conventions

 

Requirements of Good Drawings

•      It should be simple, clear and clean.

•      It should give exact information so that work can be carried out at site without scaling for missing measurement.

•      Notes on the drawing should be held in the minimum to support the drawing.

•      Ample space should be provided between views to permit placing of dimensions without crowding.

•      All secondary lines should be light & all the primary line should be dark.

 

Significance of Engineering Drawing

Engineering drawing is crucial because:

·         It serves as a universal language in engineering and design.

·         It ensures accuracy and reduces errors in manufacturing and construction.

·         It aids in visualization and facilitates quality control.

·         Clear and precise drawings reduce misunderstandings, revisions, and delays, thereby saving time and money.

 

Drawing Instruments

Developing proficiency in engineering drawing requires familiarity with drawing tools and their usage approaches. Selecting the right drawing instruments is crucial to easily acquiring the required accuracy. The following is a list of typical drawing tools and accessories:

1. Drawing board
2. Mini drafter (A small drafter facilitates the drawing of horizontal, vertical, or inclined parallel lines of specified lengths on the drawing sheet with significant absence of difficulty or effort)

3. Drawing sheet
4. Drawing Pencil
5. Compass
6. Divider

7. Protractor (A protractor is utilized to construct and define angles, as well as to divide circles or sectors into a specified number of equal segments. They are available in semi-circular and circular shapes)
8. Ruler (scale)
9. French curves (French curves are used to draw smooth curves of almost any desired curvature in mechanical drawings)
10. Set squares
11. Eraser or rubber
12. Sheet fasteners ·        Drawing pins ·        Drawing clips ·        Adhesive tape
13. Template
14. Pencil cutter
15. Sand paper pad	A sand paper pad or block is used to sharpen the pencil lead.
16. Brush or towel cloth	The brush, duster or towel cloth is used to keep the drawing surface clean
17. T-Square
18. Anti-Cutter

Keeping the Drawing Sheet

Drawing sheet sizes

Drawing Scale

It is not always realistic to draw the actual object at its true scale on a drawing sheet. For instance, when illustrating a building on a sheet, one must proportionately reduce its actual dimensions by an appropriate factor to ensure it fits inside the confines of the sheet. But if we have to draw a part of a clock into a sheet, we need to increase its real size by a reasonable factor. The ratio by which we decrease or enlarge the actual dimensions of the object in the drawing is referred to as scale.

Scale is a ratio between the linear dimension of an element of an object shown in the drawing to the real linear dimension of the same element of the object.

The following are the scales used in engineering drawings:

Full-Size Scale:

When a drawing is prepared to the actual size of the object, the scale is said to be full size scale and the drawing is said to be full size drawing. It is specified by 1:1. It means 1 unit of the drawing is equal to 1 unit of the real size.

Reduction scale:

When a drawing is prepared smaller than the actual size of the object, the scale is said to be reduction scale and the drawing is said to be reduce sized drawing. The commonly used reducing scales are 1:2, 1:5, 1:10, 1:20, 1:50, 1:100, etc. The scale specified by 1:2 means 1 unit of drawing is equal to 2 units of the real size.

Enlargement scale:

When the drawing is prepared larger than the actual size, the scale is said to be an enlargement scale and the drawing is said to be enlarge sized drawing. The commonly used enlarging scales are 2:1, 5:1, 10:1 etc. The scale specified by 2:1 means 2 units of drawing is equal to 1 unit of the real size.