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PRAGATI ENGINEERING COLLEGE (Approved by AICTE, Permanently Affiliated to JNTUK Kakinada & Accredited by NBA)

1-378, ADB Road, Surampalem – 533 437, Near Peddapuram, E.G.Dist., A.P.

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DEPARTMENT OF MECHANICAL ENGINEERING

ENGINEERING WORKSHOP

Certificate

This is to certify that this is the bonafide observation of the work done in

the Engineering Workshop laboratory by Mr. /Ms.

B.tech year semester. H.T.No of

branch during the academic year 20 to 20 .

Faculty in charge Head of the Department



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INDEX

S.NO. NAME OF THE JOB SHEET

NOS DATE MARKS

FACULTY SIGN

BLACK SMITHY

1 Conversion of round rod to square bar

08-10

2 S-Hook 11-13

CARPENTRY

3 Cross lap joint 25-27

4 T-lap joint 28-30

FITTING

5 Square fit 48-50

6 Vee fit 51-53

HOUSE WIRING

7 Series/ Parallel connection 66-68

8 Staircase wiring 69-71

TIN SMITHY

9 Square box without lid 79-81

10 Open scoop 82-84



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BLACK SMITHY

INTRODUCTION

Black smithy or hand forging is an ancient trade. It consists of heating metal stock till it

acquires sufficient plasticity, followed by hand forging, involving hammering; bending etc., till

desired shape is attained.

Hand forging is the term used when the process is carried out by hand tools. The hand

forging process is generally employed for relatively small components. However, it calls for a

remarkably high degree of skill and judgment.

If power operated machines are used for the process, it is known as machine forging.

Hooks, links, lifting tackles and agricultural implements are some of the items that are

produced by machine forging.

The following are the advantages of forging:

1. Strength and toughness is high.

2. Strength to weight ratio is high.

3. Internal defects are eliminated.

4. Forged parts need less or no machining.

TOOLS AND EQUIPMENT

FORGE OR HEARTH

A smith’s forge or hearth is used to heat the metal to be shaped. Hearths are used

for heating small jobs to be forged by hand. Gas, oil or coal firing may be used for the purpose.

The required air for the fire, is supplied under pressure, by a blower through the tuyere in the

hearth, the blowers may either be hand operated or power driven. In the latter case, the amount

of air supply is controlled by values near the forge. Figure 9.1 illustrates the forge. The hood,

shown in figure, collects gases of combustion and sends through a chimney. The following are

the forging temperatures of various metals (Table 9.1):



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Fig. 9.1. Smith’s forge

Table 9.1 Forging temperature of metals

Metal Forging temperature, 0c

Mild steel 750-1300

Wrought iron 900-1300

Medium carbon steel 750-1250

High carbon and alloy steel 800-1150

Heating of a metal to proper temperature is essential as excessive temperature

may result in burning of the metal that destroys cohesion between atoms. Insufficient

temperature will not induce sufficient plasticity to the metal, to shape it properly by

hammering. Insufficient temperature also results in cold working defects like strain hardening

and cracking.

ANVIL

It provides the necessary support during forging by resisting the heavy blows rendered

to the job. It is also useful for operations such as bending, swaging, etc. Its body is generally



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made of cast steel, wrought iron or mild steel, with a hardened top layer of about 20 to 25 mm

thick. Figure 9.2 shows an anvil with various parts marked on it.

Fig. 9.2 Anvil

The beak or horn is used for bending metal to round shape of different radii. The portion

between the beak and face is called ledge, which is used as a base for cutting operations, using

hot chisels.

The square hard i.e., hole is used to hold square shank tools like swages and fullers. A

round hole is also provided near the hard i.e., hole, which is used for bending round rods and

as a die for hot punching operation.

Anvils are made in sizes weighing from 25 kg to 250 kg. An anvil weighing about 75 kg

is suitable for general purpose.

SWAGE BLOCK

It is also a supporting tool used in a forge shop. It has a number of slots of different

shapes and sizes along its four side faces and through holes of different shapes and sizes,

running from its top to bottom faces (Fig 9.3). this is used as a support while forming

(swaging) different shapes, bending and in punching holes. It is generally made of cast iron and

cast steel.

Fig. 9.3 Swage block



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LEG VICE

It is a heavy duty vice, fixed to the work bench at one end of a leg or set in a concrete

base. It is mainly used for light forging and bending work (Fig 9.4).

Fig. 9.4 Leg vice

HAMMERS

Hammers of different types and weights are used in smithy. The ball-peen hammer used

for forging, weighs 0.5 kg to 1 kg. The sledge hammer (Fig 9.5) which is used for heavy work,

has flat ends on either side and weighs 3 kg to 8 kg. The length of the handle of a hammer

increases with its weight.

Fig. 9.5 Sledge hammer

TONGS

The metal to be forged must be held securely, while it is being shaped. A pair of tongs of

suitable size and shape must be used for the purpose. Figure 9.6 shows the most commonly

used shapes in a smithy shop. They are made of mild steel and the sizes vary from 40 cm to 60

cm in length and 0.6 cm to 5.5 cm opening.



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Fig. 9.6 Tongs

A flat bit tongs can hold along the entire length of its jaws. It is used for holding work of

rectangular section. Round bit tongs is used for holding a round rod. Square bit tongs is used

for holding a square rod. Pick –up tongs is used for pick-up the heated rods from the hearth.



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Experiment No: Date:

CONVERSION OF ROUND ROD TO SQUARE BAR

AIM:

To prepare the square cross-section from the given circular cross sectional bar.

MATERIAL REQUIRED:

M.S bar of dimensions .Length=150 mm, Diameter=12mm

TOOLS AND EQUIPMENT REQUIRED:

1. Open Hearth (Forge fire)

2. Round Tong

3. Flat Tong

4. Hand Hammer

5. Sledge Hammer

6. Anvil

7. Flatter

8. Steel rule

PROCEDURE:

1. Take the work piece of required dimensions i.e., Length (L) =150 mm, Diameter (D)=12 mm dia.

2. Hold the work piece with the help of tongs and place it in the hearth (forge fire). 3. Heat the work piece until it get red hot condition i.e., at which it possess high plastic

properties. 4. Hold work piece on one end with the help of round tongs and place it on the anvil. 5. Hammering is done with help of hand hammer due to this top and bottom faces are

flattered. 6. Rotate the work piece 900 and the other two faces are hammered to get the required

square shape. 7. If the temperature falls, repeat the steps 2, 3,4,5,6 until the required shape is obtained.



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Diagrams:



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PRECAUTIONS:

1. Hold the work piece tightly with the help of suitable tongs when it is in red-hot condition.

2. The work piece is observed for proper heating. 3. Hammering of the raw material is done in red heat condition only. 4. Watch properly while hammering. 5. Beware of your clothes. Do not expose them to heat. 6. Use gloves and gum boots

RESULT:



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S-HOOK

AIM: To prepare the S-HOOK from the given mild steel round rod.

MATERIAL REQUIRED:

M.S round rod of length 182 mm and 6 mm diameter.

TOOLS AND EQUIPMENT REQUIRED:

1. Open Hearth (Forge fire)

2. Flat Tong

3. Swage block

4. Hand Hammer

5. Sledge Hammer

6. Cold Chisel

7. Anvil

8. Flatter

9. Steel rule

PROCEDURE:

1. Take the work piece of required dimensions i.e., MS round bar of cross section 6×6 mm, Length (L) =182 mm.

2. Hold the work piece with the help of tongs and place it in the hearth (forge fire). 3. Heat the work piece until it get red hot condition i.e., at which it possess high plastic

properties. 4. Hold work piece on one end with the help of round tongs and place it on the anvil. 5. Bend the work piece by hammering with the help of hand hammer. 6. Repeat the same procedure for the other end to get the required S-shape.



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Diagram:



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PRECAUTIONS: 1. Hold the work piece tightly with the help of suitable tongs when it is in red-hot

condition. 2. The work piece is observed for proper heating. 3. Hammering of the raw material is done in red heat condition only. 4. Watch properly while hammering. 5. Beware of your clothes .Do not exposes them to heat. 6. Use gloves and gum boots

RESULT:



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CARPENTRY

INTRODUCTION:

Carpentry may be defined as the process of making wooden components. It starts from a

marketable form of wood and ends with a finished product. It deals with the building work,

furniture; cabinet marking, etc., joinery, i.e., preparation of joints are one of the important

operations in all wood-works. It deals with the specific work of a carpenter like making

different types of joints to form a finished product.

CARPENTRY TOOLS:

The following are the tools that are made use of in all the wood working operations.

MARKING AND MEASURING TOOLS

Accurate marking and measurement is very essential in carpentry work, to produce

parts to exact size. To transfer dimensions on to the work; the following are the marking

and measurement tools that are required in carpentry shop.

STEEL RULE

It is an important tool for linear measurement .it can also be used as a marking tool

(Fig.1.1).

Fig.1.1 Steel rule



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MARKING GAUGE

It is a tool used to mark lines parallel to the edge of a wooden piece. It consists of a

square wooden stem with a sliding wooden stop (head) on it. On the stem is fitted a

marking pin, made of steel. The stock is set at any desired distance from the marking point

and fixed in position by a screw. It must be ensured that the marking pin projects through

the stem, about 3mm and the end is sharp enough to make a very fine line (Fig.1.3a).A

mortise Gauge (Fig.1.3b) consist of two pins. In this it is possible to adjust the distance

between the pins, to draw two parallel lines on the stock.

Fig.1.3 Gauges

TRY SQUARE

It is used for marking and testing the squareness and straightness of planed

surfaces. It consists of a steel blade, fitted in a cast iron stock. It is also used for checking

the planed surfaces for flatness (Fig.1.4). Its size varies from 150 to 300mm, according to

the length of the blade. It is less accurate when compared to the try square used in the

fitting shop.



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Fig. 1.4 Try square

Fig1.5. Compass and divider, as shown in Fig.1.5, are used for marking arcs and circles on

the planed surfaces of the wood.

SCRIBER OR MARKING KNIFE: It is used for marking on timber (Fig.1.6).it is made of

steel, having one end pointed and the other end formatted into a sharp cutting edge.

Fig.1.6 Scriber or Marking Knife



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HOLDING TOOLS

These are the tools used to hold the work piece on operations to be done.

CARPENTER VICE

Figure 1.7 shows the carpenters Bench Vice, used as a work holding device in a

carpenter shop. Its one jaw is fixed to the side of the table while the other jaw is movable

by means of a screw and a handle. The jaws are lined with hard wooden faces.

Fig.1.7 Carpenter Vice Fig.1.8 C-clamp Fig.1.9 Bar cramp

C-CLAMP

Figure 1.8 shows C-clamp. It is used for holding small works.

BAR CRAMP

Figure 1.9 shows a Bar cramp. It is made of steel bar of T-section, with malleable

iron fittings and a steel screw. It is used for holding wide works such as frames or tops.



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PLANNING TOOLS

Planning is the operation used to produce flat surfaces on wood. A plane is a hand

tool used for the purpose. The cutting blade used in a plane is very similar to chisel. The

blade of a plane is fitted in wooden or metallic block, at an angle.

JACK PLANE

It is the most commonly used general purpose plane. It is above 35cm long. The

cutting iron (blade) should have a cutting edge of slight curvature. It is used for quick

removal of material on rough work and is also used in oblique planning.

SMOOTHING PLANE

It is used for finishing work and hence, the blade should have a straight cutting

edge. It is about 20 to 25cm long. Being short, it can follow even though slight depression

in the stock, better than the jack plane. it is used after using the jack plane.

REBATE PLANE

It is used for making a rebate. A rebate is a recess along the edge of a piece of wood,

which is generally used for positioning glass in frames and doors.

PLOUGH PLANE

It is used to cut grooves, which are used to fix panels in a door. Figure 1.10 shows

the various types of planes mentioned above.



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Fig 1.10 Types of Planes

CUTTING TOOLS

SAWS

A saw is used to cut wood into pieces .there are different types of saws, designed to

suit different purposes .a saw is specified by the length of its toothed edge.

CROSS- CUT / HAND SAW

It is used to cut across the grains of the stock. The teeth are so set that the saw kerfs

will be wider than the blade thickness (Figs.1.11a and b). This allows the blade to move

freely in the cut without sticking.

RIP SAW

It is used for cutting the stock along the grains. The cutting edge of the saw makes a

steeper angle, i.e., about 600 (Fig.1.11c), where as that of cross cut saw makes an angle of



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450 with the surface of stock.

TENON SAW

It is used for cutting the stock either along or across the grains. It is used for cutting

tenons and in fine cabinet work. However it is used for small and thin cuts. The blade of

the saw is very thin and so it is stiffen with a thick back steel strick hence, this is sometimes

called as back- saw (Fig.1.12). In this, the teeth are shaped like those of cross- cut saw.

COMPASS SAW

It has a narrow, longer and stronger tapering blade, which is used for heavy work

(Fig.1.13). It is mostly used in radius cutting. The blade of the saw is fitted with an open

type wooden handle.

Figs.1.11

CHISELS

Chisels are used for cutting and shaping wood accurately. Wood chisels are made in

various blade widths, ranging from 3 to 50mm.They are also made into tang type, having a

steel shank which fits inside the handle (fig.1.14).These are made of forged steel or tool

steel blades.



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Fig.1.14 Parts of Chisel

FIRMER CHISEL

The word ‘firmer’ means ‘stronger’ and hence firmer chisel is stronger than other

chisels. It is a general purpose chisel and is used either by hand pressure or by a mallet.

The blade of a firmer chisel is flat, as shown in fig.1.15a.

Fig.1.15 chisels

DOVETAIL CHISEL

It has a blade with a beveled back, as shown in fig.1.15b, due to which it can enter

sharp corners for finishing, as in dovetail joints.



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MORTISEL CHISEL

It is used for cutting mortises and chipping inside holes, etc. This cross-section of

the mortise chisel is proportioned to withstand heavy blows during mortising

(fig.1.15c).Further; the cross-section is made stronger near the shank.

MISCELLANEOUS TOOLS:

MALLET

It is used to drive the chisel, when considerable force is to be applied, which may be

the case in making deep rough cuts (Fig.1.20).Steel hammer should not be used for the

purpose, as it may damage the chisel handle. Further, for better control, it is better to apply

a series of light taps with the mallet rather than a heavy single blow.

Fig.1.20

PINCER

Figure 1.21 shows the shape of a pincer. It is made of two forged steel arms with a

hinged joint and is used for pulling-out small nails from wood. The inner faces of the

pincer jaws are beveled and the outer faces are plain. The end of one arm has a ball and the

other has a claw. The beveled jaws and the claw are used for pulling out small nails, pins

and screws from the wood.

CLAW HAMMER

It has a striking flat face at one end and the claw at the other, as shown in

Fig.1.22.The face is used to drive nails into wood and for other striking purposes and the

claw for extracting relatively large nails out of wood. It is made of cast steel and weighs

from 0.25 kg to 0.75kg.



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SCREW DRIVER

It is used for driving wood screws into wood or unscrewing them. The screw driver

of a carpenter is different from the other common types, as shown in Fig.1.23.The length of

a screw driver is determined by the length of the blade. As the length of the blade

increases, the width and thickness of the tip also increase.

Fig.1.21 Fig.1.22 Fig.1.23

WOOD RASP FILE

It is a finishing tool used to make the wood surface smooth; remove sharp edges,

finish fillets and other interior surfaces (Fig.1.24).Sharp cutting teeth are provided on its

surface for the purpose. This file is exclusively used in wood work.

Fig.1.24 Fig.1.25



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SAFE PRACTICES:

GENERAL

1. Tools that are not being used should always be kept at their proper places.

2. Make sure that your hands are not in front of sharp edged tools while you are using

them.

3. Use only sharp tools. A dull tool requires excessive pressure, causing the tool to slip.

4. Wooden pieces with nails should never be allowed to remain on the floor.

Saws

Be Careful when you using your thumb as a guide in cross cutting and ripping.

Chisels

1. Test the sharpness of the cutting edge on wood or paper, but not on your hand.

2. Never chisel towards any part of the body.

Screw Driver

1. Select the longest screw driver i.e. appropriate for the job intended.

2. The Longer the tool, the greater the effort applied.

3. The tip of the screw driver must fit the slot without wobbling.

4. The width of the tip should be equal to the length of the screw slot.

5. Keep the screw driver properly pointed to prevent injury to hands.



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CROSS LAP JOINT

AIM: To prepare a Cross lap joint of required dimensions

MATERIAL REQUIRED:

Teakwood piece of dimensions 48*32*300 mm3

TOOLS REQUIRED:

Handsaw, jackplane, steel rule, hammer, marking gauge, firmer chisel, try square.

SEQUENCES OF OPERATIONS:

1. Planning

2. Cutting

3. Marking

4. Sawing

5. Chiseling

6. Joining

PROCEDURE:

1. The given piece of wood is fitted to the carpentry vice; planning is done on all the four sides to required dimensions (35*20*300 mm3) with help of the jack plane, steel rule and try square.

2. The planed wooden piece is cut into two halves by handsaw. 3. Then the two pieces are marked as per the drawing of T lap joint with the help of try square,

marking gauge and steel rule. 4. Unwanted material of the two wooden pieces is removed by sawing and chiseling. 5. The above two finished pieces are joined to form the T lap joint.



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Diagrams:



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PRECAUTIONS:

1. The wooden pieces should be fitted between jaws of carpentry vice tightly. 2. While planning, uniform pressure should be applied. 3. Chiseling must be done layer by layer so that we get a fine finish.

RESULT:



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T-LAP JOINT

AIM: To prepare a T joint of required dimensions

MATERIAL REQUIRED:

Teakwood piece of dimensions 48*32*300 mm3

TOOLS REQUIRED:

Handsaw, jackplane, steel rule, Hammer, Marking gauge, Firmer chisel, Try square.

SEQUENCES OF OPERATIONS:

1. Planning

2. Cutting

3. Marking

4. Sawing

5. Chiseling

6. Joining

PROCEDURE:

1. The given piece of wood is fitted to the carpentry vice, planning is done on all the four sides to required dimensions (35*20*300 mm3) with help of the jack plane, steel rule and try square.

2. The planed wooden piece is cut into two halves by handsaw. 3. Then the two pieces are marked as per the drawing of T joint with the help of try square,

marking gauge and steel rule. 4. Unwanted material of the two wooden pieces is removed by sawing and chiseling. 5. The above two finished pieces are joined to form the T joint.



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Diagrams:



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PRECAUTIONS:

1. The wooden pieces should be fitted between jaws of carpentry vice tightly. 2. While planning, uniform pressure should be applied. 3. Chiseling must be done layer by layer so that we get a fine finish.

RESULT:



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FITTING

INTRODUCTION

Machine tools are capable of producing work at a faster rate, but, there are occasions when components are processed at the bench. Sometimes, it becomes necessary to replace or repair a component which must fit accurately with another component on re-assembly. This involves certain amount of hand fitting. The accuracy of work done depends upon the experience and skill of the fitter.

The term,” Bench work” refers to the production of components by hand on the bench, whereas fitting deals with the assembly of mating parts, through removal of metal, to obtain the required fit.

Both the bench work and fitting requires the use of number of simple hand tools and considerable manual effort. The operations in the above works consist of filing, chipping, scrapping, sawing, drilling, tapping, etc.

FITTING TOOLS

HOLDING TOOLS

Bench vice

Fig.2. 1 Bench vice

The bench vice is a work-holding device (Fig.2.1).It is the most commonly used vice



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in a fitting shop. It is fixed to the bench with bolts and nuts. The vice body consists of two main parts, fixed jaw and a movable jaw. When the vice handle is turned in a clockwise direction, the sliding jaw forces the work against the fixed jaw. The greater the pressure applied to the handle, the tighter is work held. Jaws caps made of soft material are used to protect finished surface, gripped in the vice. The size of the vice is specified by the length of the jaws. The vice body is made of cast iron which is strong in compression, weak in tension and so fractures under shocks and therefore should never be hammered.

V -block with clamp

The v-block is a rectangular or square block with V-groove on one or both sides,

opposite to each other. The angle of the ‘V’ is usually 900.V-block with a clamp is used to

hold cylindrical work securely, during layout of measurements, for measuring operation

or for drilling (Fig.2.2.).For this the bar is placed longitudinally in the V-groove and the

screw of V-clamp is tightened. This grips the rod firmly, with its axis parallel to the axis of

the V-groove.

Fig.2. 2 V-Block with clamp Fig. 2. 3 C-Clamp C-clamp

This is used to hold work against an angle plate or V-block or any other surface, when gripping is required(Fig.2.3).Its fixed jaw is shaped like English alphabet, ”C” and the movable jaw is round in shape and directly fitted to the threaded screw at the end. The working principle of this clamp is the same as that of the bench vice.

MARKING AND MEASURING TOOLS



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Surface plate

The surface plate (Fig.2.4) is machined to fine limits and is used for testing the flatness of the work piece .It is also used for marking out small works and is more precise than the marking table. The degree of fineness of the finish depends upon whether it is designed for bench work in a fitting shop or for using in an inspection room. The surface plate is made of cast iron, hardened steel or granite stone. It is specified by length’ width’ height’ grade. Handles are provided on two opposite sides, to carry it while shifting from one place to another.

Fig.2. 4 Surface plate Fig.2. 5. Angle plate Angle plate

The angle plate is made of cast iron. It has two surfaces, machined at right angle to each other (Fig.2.5).Plates and components, which are to be marked out, may be held against the upright face of the angle plate, to facilitate the marking. Slots are provided on the angle plate to clamp the work in position.



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Universal scribing block

Fig.2. 6.Universal scribing block Fig.2. 7 Try-square

This is used for scribing lines for layout work and checking parallel surfaces

(Fig.2.6).Referring the figure, it may be noted that its spindle can be quickly adjusted to any angle, by an adjusting screw. In some designs, the base of the block will have a “V” shaped groove, to enable the block to rest on round bars if require, to set-off the dimensions from the bar to the surface of the components. Try-square

It is a measuring and marking tool for 90 degrees angle. In practice, it is used for checking the squareness of many types of small works, when extreme accuracy is not required (Fig.2.7).The blade of the try-square is made of hardened steel and the beam, of cast iron or steel. The size of the try-square is specified by the length of the blade. Combination set

It is a combination of measuring tools used for measuring linear dimensions, angular dimensions and for checking flatness of surfaces. It consists of a rule, square head, centre head, protractor and spirit level (Fig.2.8).This may be used as a rule, a square, a depth gauge, for marking meters (450), for locating the centre on the end of a round bar and for measuring and marking angles. The rule is made of tempered steel with grooves. The combination set is specified by the length of its rule.



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Fig.2. 8 Combination Set Scriber

A scriber is a slender steel tool, used to scribe or mark lines on metalwork pieces (Fig.2.9).It is made of hardened and tempered high carbon steel. The tip of the scriber is generally ground at 120 to 150. It is generally available in lengths, ranging from 125mm to 250mm.It has two pointed ends. The bent end is used for marking lines where the straight end cannot reach.

Fig.2. 9 Scriber

Odd-leg calliper

This is also called ‘Jenny Calliper’ or Hermaphrodite’. This is used for marking parallel lines from a edge and also for locating the centre of round bars (Fig.2.10.).As shown in figure, it has one leg pointed like a divider and the other leg bent like a calliper. It is specified by the length of the leg up to the hinge point.



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Fig.2. 10 Odd-leg calliper Fig.2.11 Divider Divider

It is basically similar to the callipers except that its legs are kept straight and pointed at the measuring edge. This is used for marking circles, arcs, laying out perpendicular lines, bisecting lines, etc.(Fig.2.11).It is made of case hardened mild steel or hardened and tempered low carbon steel. Its size is specified by the length of the legs. Punches

These are used for making indentations on the scribed lines, to make them visible clearly. These are made of high carbon steel’s punch is specified by its length and diameter, say as 150,12.5mm.It consists of a cylindrical knurled body, which is plain for some length at the top of it. At the other end, it is ground to a point the tapered point of the punch is hardened over a length of 20 to 30 mm.

Fig.2. 12 Punches



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Dot punch This is used to lightly indent along the layout lines, to locate centre of hole sand to

provide a small centre mark for divider point, etc. For this purpose, the punch is ground to a conical point having 60 degrees included angle (Fig.2.12a.). Centre punch

This is similar to the dot punch, except that it is ground to a conical point having 90 degrees included angle (Fig.2.12b).It is used to mark the location of the holes to be drilled.

CUTTING TOOLS: Hacksaw

The hacksaw is used for cutting metal by hand. it consists of a frame ,which holds a thin blade, firmly in position .Hacksaw blade is specified by the number of teeth per centimetre. Hack saw blades have a number of teeth ranging from 5 to 15 per centimetre .blades having lesser number of teeth per cm are used for cutting soft materials like aluminium, brass and bronze. Blades having large no of teeth per centimetre are used for cutting hard materials like steel and cast iron.

Hacksaw blades are classified as: (i) all hard and (ii) Flexible types. The all hard

blades are made of H.S.S, hardened and tempered throughout to retain their cutting edges longer .these are used to cut hard metals .these blades are hard and brittle and can break easily by twisting and forcing them into the work while sawing .flexible blades are made of H.S.S or low alloy steel but only the teeth are hardened and the rest of the blade is soft and flexible. These are suitable for use by un-skilled or semi–skilled persons.

Fig.2. 13 hacksaw frames with blades

The teeth of the hacksaw blade are staggered , as shown in fig.2.14 and are known as

a ‘set of teeth ‘.these are slots wider than the blade thickness ,preventing the blade from jamming.



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Chisels Chisels are used for removing surplus metal or for cutting thin sheets(fig.2.15). These

tools are made from 0.9% to 1.0% carbon steel of octagonal or hexagonal section. Chisels are annealed, hardened and tempered to produce a tough shank and a hard cutting edge. Annealing relieves the internal stresses in the metal .the cutting angle of the chisel for general purpose is about 600.

Fig.2. 14 set of teeth Fig.2. 15 flat chisel Combination pliers

This is made of high carbon steel by proper hardened and tempering and is used for cutting as well as for gripping the work (Fig.2.16).It has small cutting edges in both the jaws, which make it able to cut small diameter wires. The serrations in the jaws offer the facility for gripping, it is named as combination plier. Its handles are well insulated, which makes it suitable for electrical working.

Fig.2. 16 Combination plier Nose plier

It is similar to combination plier but its gripping jaws have extra length in tapered form which makes it suitable for gripping small objects and also gripping in narrow spaces (Fig.2.17).

Fig.2. 17 Nose plier



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Bench drilling machine Holes are drilled for fastening parts with rivets, bolts or for producing internal

threads. Bench drilling machine is the most versatile machine used in a fitting shop for the purpose (fig.2.18).twist drills, made of tool or high speed steel are used with the drilling machine for drilling holes.

Fig.2. 18 Bench Drilling machine Fig.2. 19 Portable drill Portable electric drill

It is the most useful of all pieces of drilling equipment .it is readily portable and convenient for use. Generally, it is used for drilling holes in small pieces held in a vice (fig. 2.19).the capacity of the portable drill is designated by the maximum diameter of the hole it can drill in steel.

FINISHING TOOLS Files

Filing is one of the methods of removing small amounts of material from the surface of a metal part. A file is a hardened steel tool, having slant parallel rows of cutting edges or teeth on its surfaces. On the faces, the teeth are usually diagonal to the edge. On end of the file is shaped to fit into a wooden handle. Fig 2.20 shows the parts of a hand file. The hand file is parallel in width and tampering slightly in thickness, towards the tip. It is provided with double cut teeth on the faces, single cut on one edge and no teeth on the other edge, which is known as the safe edge.



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Fig.2. 20 Hand file Types of files

Files are classified according to their shape, cutting teeth and pitch or grade of the teeth. Figure 2.21 shows the various types of files based on their shape. Types of files and their description and uses are given below.

Fig.2. 21 Types of files

Further, single cut and double cut files are shown in fig.2.22.single cut files are rows of teeth running in one direction, across their faces and double cut files have a second row of teeth, cut diagonally to the first row.



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Fig.2. 22 Single and double cut files Hand file

Rectangular in section, tapered in thickness but parallel in width. The faces have double cut teeth and one of the edges, single cut. The other edge does not have any teeth and hence called as safe edge file. It is used for filing a surface, at right angle to an already finished surface. Flat file

Rectangular in section and tapered for 1/3rd length in width and thickness. The faces have double cut teeth and the edges, single cut. Used for general purpose filing. Square file

Square in section and tapered for 1/3rd length on all faces. All the faces have double cut teeth. Used for filing corners and slots and also o cut keyways. Triangular file

Equilateral triangular in section and tapered for 1/3rd length on all faces .All the faces have double cut teeth. Used for filing internal corners. Half round file

It has one flat face, connected by a curved face and tapered for 1/3rd length. The curved face is not exactly semi-circular but only a part of circle. The flat face has double cut teeth and the curved face, single cut. Used for filing concave surfaces and internal corners. Round file

Circular cross-section and tapered for 1/3rd length. It has double cut teeth.Used for filing concave surfaces and circular openings.



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Swiss or needle file It is normally 150mm long, with cut teeth. Used for filing corners, grooves,narrow

slots, etc., in intricate work. File card

It is a metal brush, used for cleaning the files, to free them from filings, clogged in-between the teeth (Fig.2.23).

MISCELLANEOUS TOOLS Ball-peen hammer

Hammers are named, depending upon their shape and material and specified by their weight. A ball-peen hammer has a flat face, which is used for general work and a ball end, particularly used for riveting (Fig.2.24).

Fig.2. 23 File card Fig.2. 24 Ball-peen hammer Cross-peen hammer

It is similar to ball-peen hammer, except the shape of the peen(Fig.2.25).This is used for chipping, riveting, bending and stretching metals and hammering inside the curves and shoulders. Straight-peen hammer

This is similar to cross-peen hammer, but its peen is in –line with the hammer handle (Fig.2.26).It is used for swaging, riveting in restricted places and stretching metals.



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Fig.2. 25 Cross-peen hammer Fig.2. 26 Straight –peen hammer Screw driver

A screw driver is designed to turn screws (Fig.2.27a).The blade is bade of steel and is available in different lengths and diameters. The grinding of the tip to the correct shape is important .A Phillips (star) screw driver is specially designed to fit the head of Phillips screws. The end of the blade is fluted instead of flattened (Fig.2.27b).The size of a screw driver is specified by the length of the metal part from handle to the tip.

Fig.2. 27 Screw Drivers

FITTING OPERATIONS: CHIPPING

Riveting the metal with a chisel is called and is normally used where machining is not possible (Fig.2.28).While chipping, safety goggles must be put on, to protect eyes from the flying chips. To ensure safety of others, a chip guard is placed in position. Care should be taken to see that the chisel is free from mushroom head. NOTE: For better results, the angle of chipping must be the same throughout the operation.



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Fig.2. 28 Chipping FILLING

There are several methods of filing, each with a specific purpose (Fig.2.29).With reference to the figure, the following may be noted: 1. Holding the file For heavy work and to remove more metal, a higher pressure is used.

For light and fine work, a light pressure is applied. 2. Filing internal curves A part of half round file only makes contact as shown, during

filing operation. Movement of the file is indicated by arrows. 3. Cross filing is carried out across two diagonals, to produce medium surface finish. NOTE: The possibility of the surface becoming curved is drastically reduced due to

continuous changing of directions. 4. Draw filing A smooth file with a flat face is used for this purpose and to produce fine

grained structure. NOTE: Draw filing is preferred for the edges of long and narrow work pieces. For this, the file is placed at right angle to the work and held in both the hands across its body, as close as possible. During work, the file is pushed backward and forward, along the edge being filed. Pinning of files This is caused by soft metals, clogging the file teeth and scratching the surface of the work. The pins are removed with a file card. Pinning may be prevented by rubbing chalk into the teeth before filing. Checking flatness and squareness To check flatness, try-square is used .No light should be seen between the bottom edge of the square and the top surface of the work piece, when both are held against light. Similarly, the flatness across thickness of plate is tested as shown.



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Fig.2. 29 Filling SCRAPING:

It is an operation by which high spots left on the surface of a job after filing or other

machining operations, are removed by using a tool known as scraper. Scraping is aimed at removing only a little amount of metal, to get perfect flat surface. Scraping operation is carried out by holding the scraper in the both hands and then removing it too and fro (fig.2.30).

Fig.2. 30 Scraping



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Fig.2. 31 Methods of measuring and marking MARKING AND MEASURING

Accurate marking is the first step and the methods and instruments used are common in all fitting works. Measurements are taken either from a finished edge or from the centre line. Scriber lines on non ferrous materials and oxide coated steels are readily visible but bright steel needs coating with copper sulphate solution or engineers glue (Prussian blue), for the visibility of the line. Measuring and testing are continuous processes throughout the manufacturing, drawings.



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The following are the measuring methods in the order of increasing accuracy. a. Direct measurement from a rule b. Calipers set to a rule c. Calipers set to a plug gauge d. Vernier calipers e. Micrometer f. Dial indicator PRINCIPLES OF SAWING

Hack saw blades are specified by length and number of teeth in a standard length along the cutting edge. The correct choice of pitch should ensure that at least 3 teeth are in contact with the section to be sawn (fig.2.32).

Hacksaw blade should be inserted in the frame, with the teeth pointing forward, as the saw cuts on forward stroke only. The blade should be tightening such that the blade produces a musical twang when struck lightly with the finger. Only little downward pressure is needed in sawing, as teeth are designed to pull themselves into the work. About 40 strokes per minute is the correct sawing speed.

Fig. 2.32 Selection of blade pitch



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SQUARE – FIT

AIM: To prepare a square- fit of required dimensions using two mild steel flat pieces.

MATERIALS REQUIRED:

Two Mild steel flat pieces of dimensions 50x50x4mm2

TOOLS REQUIRED:

Steel rule, try square, bench vice, flat file, scriber, Dot punch, hammer, hacksaw, Chisel,

anvil, square file, finishing file.

SEQUENCE OF OPERATIONS:

1. Filing,

2. Marking,

3. Punching,

4. Sawing,

5. Finishing.

PROCEDURE:

1. The given two mild steel flat pieces are filed to required dimensions by using bench vice, flat

file, steel rule and try square.

2. Apply chalk on one of the faces of both the pieces and mark the required dimensions as per the

drawing steel rule, scriber and try square.

3. Punching should be done along the marked lines using dot punch and hammers.

4. Remove the unwanted material as per the drawing of square fit by sawing and chiseling.

5. The cut edges are evenly filed to get the required finish and fit.



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Diagrams:



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PRECAUTIONS:

1. Filing should be done parallel to bench vice.

2. Marking should be done carefully.

3. Punching should be done adjacent to the marked line towards the unwanted material.

4. Chiseling should be done carefully.

RESULT:



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VEE – FIT

AIM: To prepare a Vee-fit of required dimensions using two mild steel flat pieces.

MATERIAL REQUIRED:

Two mild steel flat pieces of dimensions 50x50x4mm2

TOOLS REQUIRED:

Steel rule, try square, bench vice, flat file, scriber, dot punch, hammer, hacksaw, triangular

file, finishing file.


1. Filing,

2. Marking,

3. Punching,

4. Sawing,

5. Finishing.

PROCEDURE:

1. The given two mild steel flat pieces are filed to required dimensions (48mmx48mmx4mm) by

using bench vice, flat file, steel rule and try square.

2. Apply chalk on one of the faces of both the pieces and mark the required dimensions as per the

drawing using steel rule, scriber and try square.

3. Punching should be done along the marked lines using dot punch and hammer.

4. Remove the unwanted material as per the drawing of v-fit by cutting the hacksaw.

5. The cutting edges are evenly filed to get the required finish and fit.



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Diagrams:



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PRECAUTIONS:

1. Filing should be done parallel to bench vice.

2. Marking should be done carefully.

3. Punching material should be done adjacent to the marked line towards the unwanted material.

RESULT:



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HOUSE WIRING

INTRODUCTION:

Power is supplied to domestic installations through a phase and a neutral, forming a

single phase A.C.230V, two-wire system. For industrial establishments, power is supplied

through three-phase four wire system, to give 440V. Figure 3.1 shows the power tapping

for domestic and industrial purposes. The neutral is earthed at the distribution sub-station

of the supply.

When supplied to domestic utilities, power is fed to a kilowatt meter and then to a

distribution panel. The panel distributes power along several circuits. It also protects these

circuits from overload by safety devices like fuses or circuit breakers. The panel also

serves as a main switch.

As a safety practice, all single-phase devices such as switches, fuses, etc., are

connected to the live conductor. All electrical conductors and cables are colour coded and

must be correctly connected-up. Electrical wiring is defined as a system of electric

conductors, components and apparatus for conveying electric power from the source to

the point of use. The wiring system must be designed to provide a constant voltage to the

load.

Fig.3.1 3 phase- 4 wire supply



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ELEMENTS OF HOUSE WIRING:

FUSES AND CIRCUIT BREAKERS:

These are the devices designed to provide protection to a circuit against excess

current. In old type of distribution panels, open link fuses, plug or cartridge fuses were

used. In newer panels, circuit breakers are used. If something goes wrong with an

appliance or supply, the line becomes over loaded or short-circuited. Then, either the fuse

blows-out or circuit breaker trips open, isolating that circuit or appliance. In such cases,

the appliance must be checked for defects or it must be ensured that there are not too

many appliances in that particular circuit.

Fig. 3.2 shows several forms of fuses that are in use. Open link fuses are not safe in

operation, even though they are cheaper and reliable. It consists of a thin strip of metal or

wire. Here, when the fuse blows-off due to heavy current in the circuit, the metal is spilled

around. A modified version of it consists of a porcelain fuse link, backing the wire safely.

Fig.3.2 Forms of fuses

Through the plug fuse confines the molten metal thrown out while blowing, it is not

very accurate in operation. The length of the element also is very short. The cartridge fuse

of non-renewable type, enclose the fuse element in a fibre tube with a non-inflammable



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material. During the blowing-off, the arc produced is chilled by the non-inflammable

material. In case of a renewable type, a cheap renewable fuse material is used in the

cartridge.

The trouble with fuses is that they must be replaced once they burn away, whereas

the circuit breaker can be reset after the original condition is established. An

electromagnetic circuit breaker is shown in Fig.3.3.A set of switch contacts inside the

circuit breaker is normally kept closed by an armature. When too much current flows

through the coil, the armature is attracted breaking the circuit. The circuit breaker may be

reset by a toggle lever.

Fig.3.3 Circuit breaker

ELECTRIC SWITCH:

This is a device that makes and breaks or changes the course of electric circuit. It

consists of two or more contacts mounted on an insulating structure and arranged such

that, they may be moved into and out of contact with each other by a suitable operating

mechanism.Fig.3.4.shows one way and two way switches used in domestic wiring

practice.



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Fig.3.4 Electric switches

PLUG:

It is a device, carrying two or three metallic contacts in the form of pins, intended for

engaging with corresponding socket contacts and arranged for attachment to appliances

such as radio, T.V., table fan, etc. Figure 3.5a shows both two pin and three pin plugs.

SOCKET OUTLET:

It is a device, carrying two or three contacts, designed for engagement with the

corresponding plug pins and arranged for connection to fixed wiring.Fig.3.5b shows

socket outlet for both two and three pin plugs.



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Fig.3.5 Plug and socket out lets.

LAMP HOLDER:

Lamp holders are designed to hold lamps and connect them in the circuit. Both

bayonet cap and screw lamp holders are available up to 200 W lamps. Figure 3.6 shows a

lamp holder (pendant type).

Fig.3.6 Pendant lamp holder

CEILING ROSE:

A ceiling rose consists of a circular base and a cover made of Bakelite as shown in

Fig.3.7. The base has two or three terminal plates. One end of the plates is connected to

supply and the other end, to flexible wire connected to pendant lamp, ceiling fan, exhaust

fan, etc.



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Fig.3.7 ceiling rose

MAIN SWITCH:

This is a switch intended to connect or cut-off the supply of electricity to the whole of

an installation. It is generally of metal clad type (Fig.3.8).The metal clad type gives greater

strength and safety. The main switch contains one or more fuses. Iron clad double pole

switches are used for single phase A.C.circuits.

Fig.3.8 Main (iron clad) switch Fig.3.9 parts of a Bulb



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INCANDESCENT LIGHT:

Incandescent means ‘glowing at white hot’ .A lamp actually works like a heating

element, except that it gives off light by becoming white hot. Figure 3.9.shows the parts of

a bulb. The amount of power it consumes is stamped on the bulb. Higher the voltage,

brighter the light. The bulbs have filaments made of tungsten. However, special bulbs are

available with inside coating and filled with gas.

WIRES AND WIRE SIZES:

A wire is defined as a bare or an insulated conductor consisting of one or several

strands. An insulated wire consists of a conductor with insulating material made of

vulcanized India rubber (VIR) or poly vinyl chloride (PVC). The wire may consist of one

or several twisted strands. A multi core conductor consists of several cores insulated from

one another and enclosed in a common sheathing (fig.3.10).

Wire sizes are specified by diameter of the wire, using a standard wire gauge (SWG),

which also gives an idea of the current carrying capacity. The specification consists of both

the no. of strands and the diameter of each wire in it. For example, the specification, (i) silk

wire 14/36 indicates 14 strands of 36 SWG each and (ii) 3/18 PVC indicates 3 strands of 18

gauge each.

Fig.3.10 wires

WIRING METHODS



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A circuit is a path along which the electric current flows from the negative side of the

power source to the positive side. There are three types of electrical circuits that are used

for connecting devices or controls to the power source, viz., series circuit, parallel circuit

and combination of the two.

LAMP WITH INDEPENDENT CONTROL FROM TWO PLACES

The series circuit provides a single, continuous path through which current flows in

this, the devices are connected one after another and the current flows through them until

it returns to the power source (fig.3.11a). Hence, even when one device breaks down, the

remaining devices will not operate, because the circuit is broken.

In parallel circuit, the devices are connected side by side so that, current flows in a

no. of parallel paths. In this type of circuit, each device is connected across the power

source so that even if one device breaks down the other devices continue to operate

(fig.3.11b). Hence, this type of circuit is used in house wiring. The wires used in house

wiring contain multi strand copper wire, covered with fabric rubber or plastic insulation.

Fig.3.11 wiring methods



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COMMON HOUSE WIRING CONNECTIONS

ONE LAMP CONTROLLED BY A ONE WAY SWITCH

Figure 3.12a shows the wiring diagram for a lamp controlled by a one way switch.

This is the normal connection one comes across in house wiring. However, more than one

lamp may be connected either in series or parallel and controlled by a one way switch as

shown in figure3.12b and figure3.12c respectively.

It is sometimes desirable to control from two different places. One may come across

this situation with stair case, bed room, long corridors or hall containing two entrances,

etc. This is achieved by two way switches as shown in fig.3.12d.

TWO LAMPS CONNECTED IN SERIES OR PARALLEL BY A ONE WAY SWITCH

Two lamps may be connected by a one way switch in parallel for bright glow or in

series for dull glow. This is recommended when the intensity in the room as to be

controlled (fig.3.12e).

TUBE LIGHT CONNECTION

Figure 3.12f shows a typical tube light connection. Tube lights are the commonly

used light sources for illumination in the houses, industries, commercial organizations,

etc. A tube light is a low power mercury discharge lamp with internal surface coated with

suitable fluorescent material.



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Fig.3.12 types of connections

This lamp consists of a glass tube, provided at both ends with caps having two pins

and oxide coated tungsten filament. The tube contains argon or krypton gas to facilitate

starting with small quantity of mercury at low pressure.

Fluorescent material, when subjected to electromagnetic radiations of a particular

wave length produced by the discharge through mercury vapour gets excited and in turn

gives out radiations at some other wave length, which falls under visible spectrum. These

secondary radiations from fluorescent powder increase the efficiency of the lamp. Tube

lights are generally made of 20watt or 40watt rating. In order to make a tube light self

starting, a starter and a choke are connected in the circuit as shown in figure.

When switch S1 is closed, full supply voltage induces across the starter electrode P

and Q which are enclosed in a glass bulb, filled with organ gas. This voltage causes

discharge in the organ gas, resulting in the heating of the electrodes. Due to this heating,



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the electrode P which is made of bimetallic strip, bends closes the contact of the starter. At

this stage the choke, the filaments M1 and M2 of the tube T and the starter become

connected in series across the supply causing current flow through the filaments M1 and

M2 and heating them. Mean while, the argon gas discharges in the starter tube disappears

causing sudden break between electrodes P and Q. This causes a high value of induced

e.m.f in the choke.

The induced e.m.f in the choke is applied across the tube light electrodes M1 and M2

and is responsible for initiating a gaseous discharge. Thus, the tube light starts giving light

output. Once the discharge through the tube is established, a much lower voltage than the

supply voltage is required to maintain it. A reduction in voltage available at the tube

during running condition is achieved by having a voltage drop across the choke. The

capacitor connected across the starter terminals P and Q is used to suppress the

electromagnetic waves generated at the gap due to sparking.

Note: The wattage of the tube, choke and starter should be the same.

EARTHING

The definition of the term, ‘earthling’ or ‘grounding’ as it is otherwise called, refers to

the connection of the electrically equipment, to the mass of the earth by a wire of

negligible resistance ,for the safety of the human body from shocks. The metallic covers of

the machines, the frames of the machines, sheathing of wiring etc are generally dead.

Failure of insulation or workmanship may make these alive. When this happens, a person

touching the parts receives an electric shock. To avoid this, the relevant parts are earthed.

A good earthling system should have a very low resistance and should be in a position to

allow the leakage current through it.

The following are the methods of earthling.

(i) Earthling through a water main,

(ii) Plate earthling, and

(iii) Pipe earthling.



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The following are the some of the items that need earthling:

Metallic coverings, contain electric supply wire, switches, distribution fuse boards,

ceiling fans, generator frames, stationary and portable motors, metallic parts of

transformer, refrigerators, energy meters, cooking oven, a electric heaters, etc.

SAFE PRACTICES:

1. When closing the electric switch, always grasp the switch by the insulated handle

2. Do not run too many electrical items from one point.

3. Use fuses in the circuit breakers of proper capacity, so as to interrupt the current before

it becomes dangerous.

4. Disconnect the units to be repaired, free from power supply and make sure that they

might not be energized while the repair work continues.

5. Do not pour water to put off fires in electric wires and electric equipment. You will be

subjected to electric shock or you will be electrocuted, use sand to put off fires in

electric items.

6. Whenever there is power failure, put-off the power supply to all equipment, in order to

prevent spontaneous recovery.

7. Never remove a plug from an outlet by pulling the cord. Always pull by the plug.

8. Never work on electric wires when the power is on.

9. Never work with bare feet.

10. While testing, always keep one hand in your pocket. If the hands are in contact with

a circuit, a current will flow across your body and is more dangerous.

11. Electricity has no respect for ignorance. Do not apply voltage or turn-on any device

until, it has been properly checked.

12. Check the earth connection before switching-on portable equipment.

13. Before replacing the blown fuse, always switch-off the main switch.



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PARALLEL / SERIES CONNECTION OF THREE BULBS

AIM: Check the dim and bright connections with two-way control switch.

TOOLS REQUIRED:

1. Tester

2. Screw driver

3. Cutting pliers

4. Ball peen hammer

MATERIAL REQUIRED:

1. Two way switch-1 no

2. Lamp holder-2 nos

3. Lamp (40 watts)-2nos

4. 1/18 Electrical cables of different colors

5. Link clips

6. Nails

PROCEDURE:

1. Draw the circuit diagram on the wooden board with the help of chalk.Fix the link clips on

the board along the circuit diagram with the help of nail and ball peen hammer.

2. Give the connections as per the circuit diagram by taking two different colored electric

cables (1/18) generally red color is for phase (P) and the other is for neutral (N).

3. Link clips are locked so that electrical cables will not move from the positions.

4. Keep the first two-way control switch in position 1 and the second is in the position 2.

5. Give the 230 volts supply to the circuit.

6. Operate the first two-way control switch by keeping position 2, immediately the bulb

glows. Next operate the second two-way control switch by keeping position1,

immediately the bulb is off.

7. This type of wiring is called dim and bright connections with a two way control switch.



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DIAGRAMS:



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PRECAUTIONS:

1. Use different color wires to distinguish phase and neutral wires.

2. Care should be taken while connecting the wires so that there is no short circuit.

3. Connections should be connected properly without loose contact.

4. Don’t touch the connections when the main is in ON position.

RESULT:



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Experiment No: Date: STAIR CASE WIRING

AIM: Controlling of one lamp by using two-way control switch

TOOLS REQUIRED:

1. Tester

2. Screw driver

3. Cutting pliers

4. Ball peen hammer

MATERIAL REQUIRED:

1. Two way switch-2nos

2. Lamp holder-1

3. Lamp (40 watts)-1

4. 1/18 Electrical cables of different colors

5. Link clips

6. Nails

PROCEDURE:

1. Draw the circuit diagram on the wooden board with the help of chalk

2. Fix the link clips on the board along the circuit diagram with the help of nail and ball

peen hammer.

3. Give the connections as per the circuit diagram by taking two different colored electric

cables (1/18) generally red color is for phase (P) and the other is for neutral (N).

4. Link clips are locked so that electrical cables will not move from the positions.

5. Keep the first two-way control switch in position 1 and the second is in the position 2.

6. Give the 230 volts supply to the circuit.

7. Operate the first two-way control switch by keeping position 2, immediately the bulb

glows. Next operate the second two-way control switch by keeping position1,

immediately the bulb is off.

8. This type of wiring is called controlling of one lamp by using two way control switches.



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DIAGRAMS:



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PRECAUTIONS:

1. Use different color wires to distinguishing phase and neutral wires.

2. Care should be taken while connecting the wires so that there is no short circuit.

3. Connections should be connected properly without loose contact.

4. Don’t touch the connections when the main is in ON position.

RESULT:



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TIN SMITHY

INTRODUCTION:

Many engineering and house hold articles such as hoppers, guards, covers, boxes,

cans, funnels, ducts, etc., are made from a flat sheet of metal; the process being known as

tin smithy. For this, the development of the article is first drawn on the sheet metal, then

cut and folded, to form the required shape of the article. The edges of the article are then

secured through welding, brazing, soldering, riveting, etc. For successful working in the

trade, one should have a thorough knowledge of projective geometry and development of

surfaces.

Allowance should be given in the drawing stage for folding and bending. This

allowance depends upon the radius of the bend and thickness of the sheet metal.

SHEET METAL MATERIALS

A variety of metals are used in a used in a sheet metal shop such as black iron,

galvanized iron, copper, tin aluminum and stainless steel.

Black iron is the cheapest metal. The name black iron is because of its black color. It is

rolled to the desired thickness and then annealed. It corrodes rapidly, because it is not

coated. The application of this metal is limited to articles that are to be painted.

A sheet of soft steel, which is coated with molten zinc is known as galvanized iron.

The zinc forms a coating that resists rust, improves the appearance of the metal and

permits it to be soldered with greater ease.

Copper sheets are available as cold or hot rolled sheets. Copper is highly resistant to

corrosion. As it is a ductile material, copper sheets can be formed into complex shapes and

the joints can be brazed easily.

Iron sheets, coated with tin are known as tin sheets. Tin sheets are used for dairy

equipment, cans, pans, food containers, etc. The thickness of tin sheets is denoted by

special marks and not by gauge numbers.

Aluminum in the form of sheets can be used with the addition of small quantities of

metals like copper, silicon, manganese and iron. It is widely used for processing vessels

and tanks, house-hold appliances, refrigerator trays, kettles, etc. Aircraft structures are

mainly made from aluminum and its alloys.



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Stainless steel is an alloy of steel with 8-10% nickel, 18% chromium and traces of

other metals. It has got greater resistance to corrosion and can be welded. It is used for

making kitchen-ware, dairy and food processing plants, chemical plants, etc.

HAND TOOLS

The common hand tools used in sheet metal work are, steel rule, usually of 60 cm

length, wire gauge, dot punch, trammel, scriber, ball-peen hammer, straight-peen

hammer, cross-peen hammer, mallet, snips and soldering iron.

TRAMMEL

Sheet metal layout requires marking of arcs and circles. This may be done by using

the trammel, as shown in Fig. 10.1. The length of the beam decides the maximum size of

the arc that can be scribed.

Fig. 10.1 Trammel

WIRE GUAGE

The thickness of sheet metal is referred in numbers known as standard wire gauge

(SWG). The gaps on the circumference of the gauge are used to check the gauge number as

shown in Fig. 10.2. Some of the standard wire gauge numbers with corresponding

thicknesses are as follows (Table.10.1):

SWG No Thickness, mm

10 3.20

12 2.60

14 2.30

16 1.60

20 1.00



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22 0.70

24 0.65

26 0.45

30 0.30

Fig. 10.2 Standard wire gauge

BENCH SHEAR

Sheet metal may be cut by shearing action. Figure 10.3 shows a bench shear. In this,

the force is applied through a compound lever, making it possible to cut sheet metal upto

4 mm thick. The chopping hole can shear a mild steel rod upto 10 mm diameter.

Fig. 10.3 Bench shear Fig. 10.4 Snips



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SNIPS

Snips are hand shears, varying in length from 200 mm to 600 mm,200 mm and 250

mm being the lengths commonly used. Figure 10.4 shows straight and curved snips. The

straight snip is used for cutting along outside curves and straight lines and curved snip or

bent snip is for trimming along inside curves.

HAMMERS

Light weight hammers and mallets are used in sheet metal work (Fig.10.5).

Fig. 10.5 Hammers

Ball-peen hammer has a cylindrical, slightly curved face and a ball head. It is a

general purpose hammer, used mostly for riveting in sheet metal work. Cross-peen

hammer shown has a tapered peen end and is perpendicular to the table. Because of this it

can reach awkward corners as shown.

Straight-peen hammer has the peen end similar to the cross-peen, but it is positioned

parallel to the handle which can be used conveniently for certain operations of folding,

Mallet is used for bending and folding work. It is called as soft hammer. Generally, it is

made of wood. It is light in weight, covers more area and does not dent the work.

STAKES



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Stakes are nothing but anvils, which are used as supporting tools and to form, seam,

bend or rivet sheet metal objects. These are available in different shapes and sizes as

shown in Fig. 10.6, to suit the requirements of the work. They are made from wrought

iron, faced with steel.

Fig. 10.6 Stakes

SHEET METAL JOINTS



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Various types of joints are used in sheet metal work, to suit the varying

requirements. Some commonly used sheet metal joints and folded edges are shown in Fig.

10.7. These are self secured joints, formed by joining together two pieces of sheet metal

and using the metal itself to form the joint. These joints are to be used on sheets of less

than 1.6 mm thickness.

Fig. 10.7

Various forms of seams and hems are associated with sheet metal works; as described

below:

A seam is a joint made by fastening two edges together .The following are the types

of seams (refer Fig. 10.7):

Single seam: It is used to join a bottom to a vertical body.

Double Seam: It is similar to single seam, with the main difference that is formed edge is

bent upwards against the body. The layout process for this seam is similar to that used for

a single seam.

Grooved seam: It is made by hooking two folded edges together and then off-setting the

seam. A hem is an edge made by folding. The following are the types of hems (refer fig.

10.7):

Single hem: It is made by folding the edge of the sheet metal, to make it smooth and stiff.

Double hem: It is a single hem, with its end bend.

Wired edge: It consists of an edge which has been wrapped around a piece of wire. This

edge is used where more strength is needed.



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SHEET METAL LAYOUT:

In sheet metal work, it is required to lay the full size pattern on the metal sheet, so

that when it is cut along the pattern and folded or bent, it will result in the required object.

This laying-out of the complete surface on the metal sheet is known as the development of

the surface of the object. However, while laying-out it is necessary to provide excess

material for the joints known as allowance. Figure 10.8 shows the layouts of certain and

the shapes obtained when formed.



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SQUARE BOX WITHOUT LID

AIM:

To prepare a square box without lid of given dimensions (l=80mm, b=80mm, h=50mm)

using a galvanized iron sheet.

MATERIAL REQUIRED:

Galvanized iron sheet of 180mm x 140mm.

TOOLS REQUIRED:

Steel rule, scriber, stake, straight snip, mallet, nose pliers.


1. Cleaning and marking,

2. Cutting

3. Edge folding

4. Bending

5. Joining

6. Finishing

PROCEDURE:

1. Prepare the development of the rectangular tray as per the dimensions given

(l=80,b=80mm,h=25mm)

2. Choose a G.I sheet size to accommodate the development.

3. Clean the sheet and mark the development using steel rule, scriber and divider.

4. Remove the unwanted material by using a straight snip.

5. Fold the edges on the required sides by using a suitable stake.

6. Bend the sheet at required markings to get the shape using suitable stake and mallet.

7. The rectangular tray of required dimensions is obtained.



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DIAGRAMS:



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PRECAUTIONS:

1. Cutting should be done along the marked lines carefully.

2. Selection of stake is important for the required shape.

3. Excessive hammering of mallet during edge folding and finishing should be avoided.

4. Since the sheet metal has sharp edges it should be handled carefully to avoid injuries.

RESULT:



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OPEN SCOOP

AIM: To prepare an Open scoop of given dimensions using a galvanized iron sheet.

MATERIAL REQUIRED: Galvanized iron sheet of 110mmx 140 mm.

TOOLS REQUIRED: Steel rule, scriber, stake, straight snip, mallet, nose pliers.


1. Cleaning and marking,

2. Cutting

3. Edge-folding

4. Bending

5. Joining

6. Finishing

PROCEDURE:

1. Prepare the development of the Open scoop as per the dimensions given. ( l= 104mm, b1=50mm, b2=70mm ,h1=14mm, h2=24mm.

2. Choose a G.I sheet size to accommodate the development. 3. Clean the sheet and mark the development using steel rule, scriber and divider. 4. Remove the unwanted material by using a curved snip. 5. Fold the edges on the required sides by using a suitable stake. 6. Bend the sheet at required markings to get the shape using suitable stake and mallet. 7. The Open scoop of required dimensions is obtained.



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DIAGRAMS:



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PRECAUTIONS:

1. Cutting should be done along the marked lines carefully. 2. Selection of stake is important for the required shape. 3. Excessive hammering of mallet during edge folding and finishing should be avoided. 4. Since the sheet metal has sharp edges it should be handled carefully to avoid injuries.

RESULT:

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