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Bow instruments: Bow pencil and bow pen compass are used for drawing circles of approximately 25 mm radius. Bow divider is used for marking or dividing smaller spaces. There are two types (i) Integral legs with spring action (4e) (ii) two legs held with a curved spring on top with handle on it.

Bow instruments may have adjusting wheel and nut. To draw circles, it is better to mark the required distance separately and set the instruments and check. Then only the circles or arcs should be drawn on the drawing.

Main Types of Engineering Drawing

Engineering drawing is used in all branches of engineering. However, based on major engineering fields, it can be classified into the following types:

1. Mechanical Engineering Drawings:

These drawings are related to machine parts and assemblies used in mechanical engineering.

It serves the functions of a Tee square, set square, protractor and scale. They come in different sizes and a pattern called ‘Pantagraph’ type. It is fitted on the top left side, edge of the drafting board, mounted on an adjustable frame or table. It requires large area of working place. The angle of the drafting board can be adjusted by pedal operating system. There are two counter weights to balance the angular position of the board and the drafting head. It is more suitable for production drawing office.

When, on a drawing, if a part of a line or some lines among many other lines need to be erased or modified, in normal way of erasing will damage the other nearby lines. In such a situation an erasing shield is effectively useful. It is a thin metallic sheet having small openings of different sizes and shapes. A suitable opening is aligned to the line to be erased and the line is removed by the eraser.

It has a knee joint in one leg that permits the insertion of pen or pencil point or attaching lengthening bar with pen or pencil point attached to it. It is used for drawing large circles/arcs also for taking large measurements. The pin on the other leg can be swivelled to vertical position when drawing large circles, while drawing the circles of arcs it should be held in such a way that the needle point leg and pencil point leg should be bent so as to make perpendicular to the paper.

बड़ा डिवाइडर एक महत्वपूर्ण ड्रॉइंग उपकरण है जिसका उपयोग माप (dimensions) को स्थानांतरित (transfer) करने तथा रेखाओं को समान भागों में विभाजित करने के लिए किया जाता है।

Scales: Scales are used to transfer and or to measure the dimensions. They are made of wood, steel, ivory, celluloid or plastic, stainless steel scales are more durable. different types of scales used are shown in Figs 1,2 & 3. They are either flat, bevel edged or triangular cross-section. Scales of 15 cm long, 2 cm wide or 30 cm long 3.5 cm wide flat scales are in general use. Thin section or bevel edged scales are preferred over thick flat scales. Parallax error will be nil or least while using thin / tapered edge scales

Drawing Paper

Drawing Paper is an essential material used in engineering drawing. It is mainly classified into two types:

• Hand-made Paper
• Mill-made Paper

Hand-made papers have rough surfaces and are pale in color. They are generally not used for regular drawing work but are suitable for charts. Mill-made papers are widely used for regular work and are available in different sizes and rolls. These papers are specified by their weight (kg per ream) or density (grams per square meter).

Technical drawings allows efficient communication among engineers and can be kept as a record of the planning process. Since a picture is worth a thousand words, a technical drawing is a much more effective tool for engineers than a written plan.

The economical success of any country is mainly depended on its industrial development. Due to the globalization any industry of our country expected to be of global market standard. Due to the above said reason our Indian product required to be of very high quality with respect to size of dimension, fit, tolerance and finish etc.