CLASSIFICATION OF DRAWING

1.MACHINE DRAWING

 It is pertaining to machine parts or components. It is presented through a number of

orthographic views, so that the size and shape of the component is fully understood. Part

drawings and assembly drawings belong to this classification. An example of a machine drawing

is given in Fig.

2. PRODUCTION DRAWING

A production drawing, also referred to as working drawing, should furnish all the dimensions,

limits and special finishing processes such as heat treatment, honing, lapping, surface finish,

etc., to guide the craftsman on the shop floor in producing the component. The title should also

mention the material used for the product, number of parts required for the assembled unit,

etc.

Since a craftsman will ordinarily make one component at a time, it is advisable to prepare

the production drawing of each component on a separate sheet. However, in some cases the

drawings of related components may be given on the same sheet. Figure 1.2 represents an

example of a production drawing.

3.PART DRAWING

Component or part drawing is a detailed drawing of a component to facilitate its manufacture.

All the principles of orthographic projection and the technique of graphic representation must

be followed to communicate the details in a part drawing. A part drawing with production

details is rightly called as a production drawing or working drawing.

4.ASSEMBLY DRAWING

A drawing that shows the various parts of a machine in their correct working locations is an

assembly drawing . There are several types of such drawings.

4.1 DESIGN ASSEMBLY DRAWING

When a machine is designed, an assembly drawing or a design layout is first drawn to clearly

visualize the performance, shape and clearances of various parts comprising the machine.

4.2 DETAILE ASSEMBLY DRAWING

It is usually made for simple machines, comprising of a relatively smaller number of simple

parts. All the dimensions and information necessary for the construction of such parts and for

the assembly of the parts are given directly on the assembly drawing. Separate views of specific

parts in enlargements, showing the fitting of parts together, may also be drawn in addition to

the regular assembly drawing.

4.3 SUB ASSEMBLY DRAWING

Many assemblies such as an automobile, lathe, etc., are assembled with many pre-assembled

components as well as individual parts. These pre-assembled units are known as sub-assemblies.

A sub-assembly drawing is an assembly drawing of a group of related parts, that form a

part in a more complicated machine. Examples of such drawings are: lathe tail-stock, diesel

engine fuel pump, carburettor, etc.

4.4 INSTALLATION ASSEMBLY DRAWING

On this drawing, the location and dimensions of few important parts and overall dimensions of

the assembled unit are indicated. This drawing provides useful information for assembling the

machine, as this drawing reveals all parts of a machine in their correct working position.

4.5 ASSEMBLY DRAWING FOR CATALOGUES

Special assembly drawings are prepared for company catalogues. These drawings show only

the pertinent details and dimensions that would interest the potential buyer. Figure  shows

a typical catalogue drawing, showing the overall and principal dimensions.

Speed change lever (1)

Depth adjusting knob (2)

Mech. feed engagement lever (3)

Hand feed lever (4)

Feed change knob (5)

Switch for tapping (6)

Gear shifting lever (7)

Main switch (8)

Lamp switch (9)

Selector switch (10)

Forward/reverse switch (11)

Pilot lamp (12)

Feed disengagement push button (13)

Start push button (14)

Emergency stop (15)

Elevating handle (16)

Clamping handle (17)

Supply inlet (18)

4.6 ASSEMBLY DRAWING FOR INSTRUCTION MANUAL

These drawings in the form of assembly drawings, are to be used when a machine, shipped

away in assembled condition, is knocked down in order to check all the parts before reassembly

and installation elsewhere. These drawings have each component numbered on the job. Figure

 shows a typical example of such a drawing.

4.7 EXPLODED ASSEMBLY DRAWING

In some cases, exploded pictorial views are supplied to meet instruction manual requirements.

These drawings generally find a place in the parts list section of a company instruction manual.

Figure 1.6 shows drawings of this type which may be easily understood even by those with less

experience in the reading of drawings; because in these exploded views, the parts are positioned

in the sequence of assembly, but separated from each other.

 4.8 SCHEMETIC ASSEMBLY DRAWING

It is very difficult to understand the operating principles of complicated machinery, merely

from the assembly drawings. Schematic representation of the unit facilitates easy understanding

of its operating principle. It is a simplified illustration of the machine or of a system, replacing

all the elements, by their respective conventional representations. Figure shows the

schematic representation of a gearing diagram.

4.9 MACHINE SHOP DRAWING

Rough castings and forgings are sent to the machine shop for finishing operation (Fig).

Since the machinist is not interested in the dimensions and information of the previous stages,

a machine shop drawing frequently gives only the information necessary for machining. Based

on the same principle, one may have forge shop drawing, pattern shop drawing, sheet metal

drawing, etc.

4.10 PATENT DRAWING

When new machines or devices are invented, patent drawings come into existence, to illustrate

and explain the invention. These are pictorial drawings and must be self-explanatory. It is

essential that the patent drawings are mechanically correct and include complete illustrations

of every detail of the invention. However, they are not useful for production purposes. The

salient features on the drawing are numbered for identification and complete description.

GRAPHIC LANGUAGE

 

A technical person can use the graphic language as powerful means of communication with

others for conveying ideas on technical matters. However, for effective exchange of ideas with

others, the engineer must have proficiency in (i) language, both written and oral, (ii) symbols

associated with basic sciences and (iii) the graphic language. Engineering drawing is a suitable

graphic language from which any trained person can visualise the required object. As an

engineering drawing displays the exact picture of an object, it obviously conveys the same

ideas to every trained eye.

Irrespective of language barriers, the drawings can be effectively used in other countries,

in addition to the country where they are prepared. Thus, the engineering drawing is the

universal language of all engineers.

Engineering drawing has its origin sometime in 500 BC in the regime of King Pharos of

Egypt when symbols were used to convey the ideas among people.

IMPORTANCE OF GRAPHIC LANGUAGE

The graphic language had its existence when it became necessary to build new structures and

create new machines or the like, in addition to representing the existing ones. In the absence

of graphic language, the ideas on technical matters have to be conveyed by speech or writing,

both are unreliable and difficult to understand by the shop floor people for manufacturing.

This method involves not only lot of time and labour, but also manufacturing errors. Without

engineering drawing, it would have been impossible to produce objects such as aircrafts,

automobiles, locomotives, etc., each requiring thousands of different components.

NEED FOR CORRECT DRAWING

The drawings prepared by any technical person must be clear, unmistakable in meaning and

there should not be any scope for more than one interpretation, or else litigation may arise. In

a number of dealings with contracts, the drawing is an official document and the success or

failure of a structure depends on the clarity of details provided on the drawing. Thus, the

drawings should not give any scope for mis-interpretation even by accident.

It would not have been possible to produce the machines/automobiles on a mass scale

where a number of assemblies and sub-assemblies are involved, without clear, correct and

accurate drawings. To achieve this, the technical person must gain a thorough knowledge of

both the principles and conventional practice of draughting. If these are not achieved and or

practiced, the drawings prepared by one may convey different meaning to others, causing

unnecessary delays and expenses in production shops.

Hence, an engineer should posses good knowledge, not only in preparing a correct drawing

but also to read the drawing correctly. The course content of this book is expected to meet

these requirements.

The study of machine drawing mainly involves learning to sketch machine parts and to

make working and assembly drawings. This involves a study of those conventions in drawings

that are widely adopted in engineering practice.

CLASSIFICATION OF DRAWING