WORKSHOP PRACTICE MANUAL

CARPENTRY

1.1 INTRODUCTION

Carpentry may be defined as the process of making wooden components. Wood obtained from tree is the chief product of forest. It has been universally acceptable as raw material for manufacturing wooden products or appliances. Preparation of joints is 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.

1.2 TYPES OF COMMON TIMBERS, THEIR QUALITIES AND USES

The common types of well recognized timbers available in India are Shisham, Sal, Teak, Deodar, Mango, Mahogany, Kail, Chid, Babul, Fir wood, Walnut and Haldu,. Out of these, Deodar, Chid, Kail, Fir wood and Haldu fall in the categories of softwoods and Shisham, Sal, Teak, Kiker, Mango, Walnut fall in the categories of hardwoods. ome of the other foreign timbers commonly used in India are Ash, Burma, Hickory, Oak and Pine.

Shisham: It is dark brown in color and it possesses golden and dark brow stripes. Itis very hard to work and generally wears or blunts the sharp edge of cutting tool very soon. It is available in India in Himalayan range at heights from 1000-1500 meters and in deep forests. It is recognized as highly strong and durable wood and it is mainly used for making good variety of furniture, tool handles, beds, cabinets, bridge piles, plywood etc.

Sal: This exists in rose brown color which slowly turns into dark brown. This wood is commonly available in India in Himalayas, M.P and U.P. It is free from attack of white ants insects and it is very difficult to work. It has poor finish and therefore is not used for decorative furniture. It finds tremendous applications in making doors, windows, cots, wooden handles, furniture and railway sleepers etc.

Teak wood: It is hard, very costly and it possesses wide applications. It is availablein golden yellow or dark brown color. Special stripes on it add to its beauty. In India,it is found in M.P. It is very strong, durable and it maintains good polish. It is mainly used for making good quality furniture, plywood, ships etc.

Deodar: It is white in color when soft. But when it is hard, its color turns toward lightYellow. It is strong and durable. It provides fragrance when smelled. It is not easily attacked by insects as it has some quantity of oil in it. It is commonly available in Himalayas at a height from 1500 to 3000 meters. It is used for manufacturing of doors, furniture, patterns, railway sleepers etc.

Mango: It is brown in color and it can be easily shaped in various products. It is widely used in India as a cheap wood for making doors, packing cases, toys and inferior furniture.

Mahogany: It is reddish brown in color which is highly durable when dry. It also contains some oil in it that prevents it from the attack of insects. It is commonly utilized for manufacturing cabinet, fine furniture, pattern making work etc.

Kail: This wood possesses too many knots in it. This wood is commonly found in Himalayas of India. It yields a close grained, moderately hard and durable wood which can be easily painted. It is commonly utilized for making cheap furniture, wooden doors, packing case etc.

Chid: It is also known as Chir. Its color is dark brown when is soft, but it is reddishbrown when hard. It has stripes of dark brown color. It has oily smell and is used for interior work in the house.

Babul: It is close grained tough and pale red colored wood and is used for making tool handles etc.

Fir wood: It is light brown in color when soft but harder variety is found in dark brown color. It can be easily attacked by insects. It is commonly utilized for makingDrawers, packing cases, doors etc.

Walnut: It is a good variety of wood which resists the attack of white ants. It can bePolished easily in a better way. This wood is generally used for making musical instruments, furniture, cabinet work, decoration work etc.

Haldu: It is white in color at the time of cutting, but once cut, its color becomes yellow. It can be dried and polished satisfactorily. It is widely used for making smallobjects such as stool, picture frames, trays, cabinet etc.

1.2.1 Classification of Timber

Wood suitable for construction and other engineering purpose is called timber. Woods in general are divided into two broad categories: 1).Soft woods: It obtains from conifers, kair, deodar, chir, walnut and seemal etc…2).Hard woods: It obtains from teak, sal, oak, shisham, beach, mango, neem etc…

1.2.2 Characteristics of Good Timber

Timber is free from knots, insects attack, excessive moisture, discoloration, twisted fibers, cup and ring shake, sound, bright and free from any discoloration. It is solid with annual rings but not hallow in the center. Timber should be well seasoned for easily workable specific use. It should possess straight fibers and high fire resistance. It should not split when nails are driven in it. It should not clog with the saw teeth during the sawing operation. Timber should be highly suitable for polishing and painting.

1.2.3 Factors Influencing the Timber selection

The factors influencing the selection of timber involve the quality of timber in terms of its durability, workability, weight, hardness, cohesiveness, elasticity, type of texture, type of grains, resistance to fire, resistance to various stresses, ability to retain shape, suitability for polishing and painting.

1.3 COMMON TOOLS USED IN CARPENTARY SHOP

A broad classification of tools used in the wood working or carpentry shop are measuring and marking tools, supporting and holding tools, cutting tools, striking tools and miscellaneous tools. Most of commonly used tool and measuring devices as mentioned below are in this chapter used in fitting and sheet metal work also.

1.3.1 MARKING AND MEASURING TOOLS

Marking in order to make wooden components of the required size or the marking of exact dimensions on the wooden piece is essential to produce quality jobs. A number of marking and measuring instruments that are required in a carpentry shop are…

1.3.1.1 Steel Rule: It is an important tool for linear measurement. It can also be used as a marking tool. As shown in Fig.1.1.

1.3.1.2 Steel Tape: It is used for large measurements, such as marking on boards and checking the overall dimensions of the work. As shown in Fig.1.2. 1.3.1.3 Marking gauge: It is used to mark lines, As shown in Fig.1.3. parallel to the edge of a wooden piece. It consists of a square wooden stem with a sliding wooden stock (head) on it. On the stem is fitted a marking pin, made of steel. The stock is set at any desired from the marking point and fixed in position by a screw. It must be ensured that the marking pin projects through the stem, about 3 mm and the end is sharp enough to make a very fine line. A mortise gauge. Consists of two pins. In this, it is possible to adjust the distance between the pins, to draw two parallel lines on the stock.

1.3.1.4 Mortise gauge: This is an improved form of marking gauge,As shown in Fig.1.4. which consists of main components as fixed pin, sliding pin, brass strip, stem, rose wood stock and thumb screw. The fixed pin of the gauge is attached to a short brass strip which is screwed to the stem. The sliding pin is fixed to a long brass strip or slider is adjusted by means of a thumbscrew. The threaded portion of which engages in a cylindrical nut which is embedded in the stem. The stock is locked in position by a metal set screw. This gauge is used for marking out of the parallel sides of mortises or tenons and other similar joints.

1.3.1.5 Try-Square: Try square, As shown in Fig.1.5. is generally utilized for measuring and checking of squareness, perpendicularity, dimensions, testing of finish of planned surfaces and drawing parallel and perpendicular lines. The steel blade and metallic or wooden handle of try square are at right angles to each other. Try squares are used for testing the level, edge and squareness of the wooden surfaces. It is also used for marking lines across the face or edge of wooden block.

1.3.1.6 Compass and Divider: Compass and divider are used for marking arcs and circles on the planed surfaces of the wood. As shown in Fig.1.6.

1.3.1.7 Scriber or marking knife: It is used for marking on timber. It is made of steel having one end point and the other end formed into a sharp cutting edge. As shown in Fig.1.7.

1.3.1.8 Bevel Gauge: Bevel gauge is also known as an adjustable bevel which is mainly used for marking, measuring and inspecting angles from 0 to 180 degree. its blade can be adjusted and set to any desired angle. As shown in Fig.1.8.

1.3.2 HOLDING TOOLS

1.3.2.1 Carpenter’s vice: Carpenter vice is very important tool in wood working shops for holding wooden jobs. It’s one jaw is fixed to the side of the table while the other is movable by means of a screw and a handle. The jaws are lined with hard wooden faces. As shown in Fig.1.9.

1.3.2.2 C-clamp: It is used for holding small works. Shown in Fig.1.10.

1.3.2.3 Bar clamp: It is made of steel bar of T-section. As shown in Fig.1.11. With malleable iron fittings and a steel screw. It is used for holding wide works such as frames or tops.

1.3.3 PLANING TOOLS

A plane is a special tool with a cutting blade for smoothing and removing wood as shavings. It is just like a chisel fixed in a wooden or steel body. The modern plane has been developed from the chisel. They can also be classified as jack plane, smooth plane, jointer plane, trying plane, rabbet plane, and circular plane and fore plane.

1.3.3.1 Jack plane: It is most commonly used general purpose plane. As shown in Fig.1.12 (a).Metal Jack plane as shown in Fig.1.12 (b). It is about 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. 1.3.3.2 Smoothing Plane: Smoothing plane is shown in Fig.1.13. Which is somewhat smaller than the jack plane, measuring between 6 and 10 inches in length? It is a fine utility tool, especially useful for planning end grain, chamfering, and other edge shaping of wooden part. This plane is also used for cleaning up after gluing and assembly, but owing to its short length should not be used for producing very true surfaces.

1.3.4 CHISELS

A Chisel Fig. is a strong sharp edge cutting tool with a sharp bevel edge at one end. Its construction is composed of handle, tang, ferrule, shoulder, and blade. Chisels are generally made up of high carbon steel. They are used to shape and fit parts as required in joint making.

1.3.4.1 Firmer Chisel: Firmer chisel is shown in Fig.1.14. Which possesses a blade of rectangular section. It consists of the following parts blade made of cast tool steel and it is used for general bench work.

1.3.4.2 Mortise Chisel: Mortise chisel as shown in Fig.1.15. is designed for heavy work. A mortise chisel has a blade which is very nearly square in section and so may be used as a lever for removing chips and will withstand heavy blows from a mallet.

1.3.4.3 Dovetail Chisel: It has a blade with a beveled back, as shown in Fig.1.16. Due to which it can enter sharp corners for finishing, as in dovetail joints.

1.3.5 DRILLING AND BORING TOOLS

1.3.5.1 Carpenter’s brace: It is used for rotating auger bits, twist drills, etc…to produce holes in wood as shown in Fig.1.17. The size of a brace is determined by its sweep.

1.3.5.2 Auger bit: It is the most common tool used for making holes in wood. The helical flutes on the surface carry the chips to the outer surface. As shown in Fig.1.18.

1.3.5.3 Hand drill: Hand drill is used for drilling small holes. A straight shank drill is used with this tool. It is small, light in weight and may be conveniently used than the brace. The drill bit is clamped in the chuck at its end. And is rotated by a handle attached to gear and pinion arrangement. As shown in Fig.1.19.

1.3.5.4 Gimlet: It has cutting edges like a twist drill. It is used for drilling large diameter holes with the hand pressure. As shown in Fig.1.20.

1.3.6 CUTTING TOOLS

Various kinds of cutting tools namely various kinds of saws, planes, chisels, scraper, files, and rasp adze and axe and boring tools such as brace and bits, bradawl, auger, gimlet are used in the carpentry shop.

1.3.6.1 SAWS

Saws are wood cutting tools having handle and a thin steel blade with small sharp teeth along the edge. They are utilized to cut wood to different sizes and shapes used for making the wooden joints that hold parts together. They can be further classified into three major types namely hand Saws (Rip, Cross-cut, Panel, Keyhole and, Pad saw), Snuff Saws (Tenon and Dovetail) and Frame Saws (Coping, Bow and Fret). Few important types of saws are shown in figures.1.21 to 1.24.

1.3.6.2 Crosscut saw: Cross cut saw is shown in Fig. which is similar to rip saw in shape. It is primarily designed for cutting across the grains of wood. The teeth are knife shaped and bent alternately to the right and left for making the saw to cut wider than the blade. The saw cut is called the kerf. Since the kerf is wider than the blade, the blade will not stick as the sawing is done. As shown in Fig.1.21.

1.3.6.3 Rip saw: The rip saw is shown in Fig.1.22. It is used for cutting timber along the grains. The teeth of rip saw are chisel-shaped and are set alternately to the right and left. A 24" long point saw is a good for sawing work. Depending upon whether the saw is designed to rip or cross-cut, the shape of the teeth will also vary. In the case of a ripsaw, the teeth are shaped like chisels.

1.3.6.4 Compass saw: Compass saw carries a tapered blade which is long as shown in Fig.1.23. Which is one of the special saw having thin, narrow and flexible blade? This type of saw is commonly used for making cutouts on the inside surface of a piece of work. A hole is first bored inside the portion which is to be cut out and the pointed compass saw is pushed into the hole to start the sawing operation.

1.3.6.5 Tenon saw: It is used for cutting the stock either along or across the grains. It is used for cutting tenons and in finite cabinet work. However it is used for small and thin cuts. The blade of this saw is very thin and so it is stiffened with a thick back steel strip. Hence, this is sometimes called as back saw as shown in Fig.1.24. In this, Teeth are shaped like those of cross-cut saw.

1.3.7 MISCELLANEOUS TOOLS

1.3.7.1 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. As shown in Fig.1.25.

1.3.7.2 Pincer: as shown in Fig.1.26. 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 end of one arm has a ball and the other has a claw. The jaws and the claw are used for pulling out small nails, pins and screws from the wood.

1.3.7.3 Claw hammer: It has a striking flat face at one end and the claw at the other, as shown in Fig.1.27. 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.

1.3.7.4 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.1.28. 1.3.7.5 Wood rasp file: It is a finishing tool used to make the wood surface smooth, remove sharp edges, and finish fillets and other interior surfaces. Sharp cutting teeth are provided on its surface for the purpose. As shown in Fig.1.29.

1.3.7.6 Bradawl: It is a hand operated tool, used to bore small holes for starting a screw or large nail as shown in Fig.1.30.

1.4 CARPENTRY MACHINES

1.4.1 WOOD WORKING LATHE:

A general wood working lathe is shown in Fig.1.31. Which resembles roughly

to an engine lathe? It consists of a cast iron bed, a headstock, tailstock, tool rest, live

and dead centers and drawing mechanisms. The long wooden cylindrical jobs are held

and rotated between the two centers. The tool is then fed against the job and the round

symmetrical shape on the jobs is produced. Scrapping tool and turning gauge are

generally used as a turning tool on a woodworking lathe.

1.4.2 CIRCULAR SAW:

A circular saw is shown in Fig.1.32. It is also called as table or bench saw

which is used to perform various operations such as grooving, rebating, chamfering

etc. It consists of a cast iron table, a circular cutting blade, cut off guides, main motor,

saw guide, elevating hand wheel, tilting hand wheel etc. The work is held on the table

and moved against the circular saw to perform the quick and automatic sawing

operation and other operation on wood as said above. The principal parts include the

frame, arbor, table, blade, guides for taking cuts, guards and fencing.

1.4.3 BAND SAW:

Band saw is shown in Fig.1.33. Which generally used to cut the heavy logs to

required lengths, cutting fine straight line and curved work. It consists of a heavy cast

bed, which acts as a support for the whole machine, a column, two wheel pulleys, one

at the top and other at the bottom, an endless saw blade band, a smooth steel table and

guide assembly. It is manufactured in many sizes ranging from little bench saw to a

larger band saw mill.

1.5 COMMON WOOD JOINTS

All wooden objects whether doors, windows, furniture, pattern, core boxes, handicrafts, toys, cots, etc., are all assembled with joints. The various common as shown in Figures 1.34.(a) and 1.34.(b). Used wood working joints are given below…

1.6 COMMON SAFETY IN CARPENTRY SHOP

There are some general safety precautions to be taken care of while working in carpentry shop. Some of which are discussed as under.

1. Before starting any wood working machine, it should be ensured that all the safety guards are in proper places and secured well.

2. While working on a circular saw, one should not stand in a line with the plane of the rotating blade and always keep your fingers always away from the reach of blade.

3. The wooden pieces should not be fed to the sawing machines faster than the cutting speed of the machine.

4. While working on wood lathes, the job should be properly held.5. One should not use defective or damaged carpentry tools while carrying out

carpentry work.6. Nails, screws should be properly kept in a box for proper housekeeping.7. Sufficient safety precautions are to be taken for preventing fire in the carpentry

shop.8. No carpentry tools should be thrown for saving time in handling.

1.7 VIVA VOICE MODEL QUESTIONS

1. Name the commonly available shapes of timber in the market?2. Classify wood used for construction purposes?3. What is the difference between marking gauge and marking knife?4. What is the difference between C-clamp and bar clamp?5. What for a plane is used in a carpentry shop?6. Classify the planning tools?7. Classify the chisels and their applications?8. Name the tools used for pulling nails?9. On what parameters, the strength of the joint depends?10. Name the various joinery materials used in carpentry?11. What is the difference between hard wood and soft wood?12. Why preservation of timber is necessary?13. What do you understand by “grains in wood”?14. What are the commercial sizes of timber?15. What is ‘setting’ of saw teeth?16. What do you understand by term ’joinery’?17. What are the common types of mortising machine used in wood working?18. What is the specific use of wood turning lathe?19. What are machine sanders?20. How does a belt sander differ from a disc sander?

1.9 CARPENTRY PRACTICES

EXPERIMENT - 1

T – Lap Joint

Aim: To make a T-lap joint from the given wood size of 50 X 35 X 250 mm.

Tools required:

Carpenter’s vice, steel rule, jack plane, try-square, marking gauge, firmer

chisel, cross-cut saw, tenon saw, scriber and mallet.

Procedure:

The given wood piece is checked to ensure its correct size. The wood piece is

firmly clamped in the carpenter’s vice and any two adjacent faces are planed by the

jack plane and the two faces are checked for squareness with the try-square. Marking

gauge is set and lines are drawn at 30 and 45 mm, to mark the thickness and width of

the model respectively. The excess material is first chiseled out with firmer chisel and

then planed to correct size. The mating dimensions of the parts X and Y are the

marked using scale and marking gauge. Using the cross-cut saw, the portions to be

removed are cut in both the pieces, followed by chiseling and also the parts X and Y

are separated by cross-cutting, using the tenon saw. The ends of both the parts are

chiseled to the exact lengths. A fine finishing is given to the parts, if required so that,

proper fitting is obtained. The parts are fitted to obtain a slightly tight joint.

Result:

The T-lap joint is thus made by following the above procedure. As shown in

Fig.1.35.

EXPERIMENT - 2

Dovetail lap joint

Aim: To make a dovetail lap joint from the given wood of size 50 X 35 X 250 mm.

Tools required:

Carpenters vice, steel rule, jack plane, try-square, marking gauge, firmer chisel,

cross-cut saw, tenon saw, scriber and mallet.

Procedure:

The given wood piece is checked to ensure its correct size. The wood piece is

firmly clamped in the carpenter’s vice and any two adjacent faces are planed by the

jack plane and the two faces are checked for squareness with the try-square. Marking

gauge is set and lines are drawn at 30 and 45 mm, to mark the thickness and width of

the model respectively. The excess material is first chiseled out with firmer chisel and

then planed to correct size. The mating dimensions of the parts X and Y are the

marked using scale and marking gauge. Using the cross-cut saw, the portions to be

removed are cut in both the pieces, followed by chiseling and also the parts X and Y

are separated by cross-cutting, using the tenon saw. The ends of both the parts are

chiseled to the exact lengths. A fine finishing is given to the parts, if required so that,

proper fitting is obtained. The parts are fitted to obtain a slightly tight joint

Result:

The dovetail lap joint is thus made by following the above procedure. As

shown in Fig. 1.36.

EXPERIMENT - 3

Mortise and tenon joint

Aim: To make a mortise and tenon joint from the given wood of size 50 X 35 X

250mm.

Tools required:

Carpenters vice, steel rule, jack plane, try-square, marking gauge, firmer chisel,

mortise chisel, cross-cut saw, tenon saw, scriber and mallet.

Procedure:

The given wood piece is checked to ensure its correct size. The wood piece is

firmly clamped in the carpenter’s vice and any two adjacent faces are planed by the

jack plane and checked for straightness. The adjacent face is then planed and the faces

are checked for squareness with the try-square. Marking gauge is set and lines are

drawn at 30 and 45 mm, to mark the thickness and width of the model respectively.

The excess material is first chiseled out with firmer chisel and then planed to correct

size. The mating dimensions of the parts X and Y are the marked using scale and

marking gauge. Using the cross-cut saw, the portions to be removed in part Y (tenon)

is cut, followed by chiseling. The material to be removed in part X (mortise) is carried

out by using the mortise and firmer chisels. The parts X and Y are separated by cross-

cutting, using the tenon saw. The ends of both the parts are chiseled to the exact

lengths. Finish chiseling is done whenever needed so that, the parts can be fitted to

obtain a near tight joint.

Result:

The mortise and tenon joint is thus made by following the above procedure. As

shown in Fig. 1.37.

FITTING

2.1 INTRODUCTION

These days small, medium and heavy industries are using automatic machines. But bench and fitting work also plays a significant role for completing and finishing a job to the desired accuracy. Most of semi-finished works can be accomplished with fairly good degree of accuracy in a reasonable time through various kinds of quick machining operations. They still require some minor operations to be performed to finish the job by hand. The term bench work denotes the production of an article by hand on the bench. Whereas fitting is the assembling of parts together and removing metals to secure the necessary fit, and may or may not be carried out at the bench. These two types of work require the use of a large number of hand tools and other devices or equipments that involve a number of operations for accomplishing the work to the desired shape and size.

2.2 HOLDING TOOLS 2.2.1 Bench vice: (Fig 2.1) shows a bench vice commonly used in fitting shop for holding a variety of jobs. It is fixed to the bench with bolts and nuts. The vice body consists of two main parts, fixed jaw and a movable jaw. Jaws are made of hardened steel. Jaw caps are made of soft material are used to protect finished surfaces. Vice body made of cast iron which is strong in compression, weak in tension.

2.2.2 V-block with clamp: The V-block is a rectangular or square block with a 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).

2.2.3 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 ‘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.

2.3 MARKING AND MEASURING TOOLS

2.3.1 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. It 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 other.

2.3.2 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.

Fig.2.1. Bench vice Fig.2.2. V-block with clamp

Fig.2.3. C-clamp Fig.2.4. Surface plate

Fig.2.5. Angle plate

2.3.3 Universal scribing block: This is (Fig 2.6). used for scribing lines for layout

work and checking parallel surfaces. It can 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 required.

2.3.4 Try-square: It is measuring and marking tool for 900angle. In practice it is used for checking the squareness of many types of small works, when extreme accuracy is not required. (Fig 2.7).

2.3.5 Combination set: It is a combination of measuring tools used for measuring linear dimensions, angular dimensions and for checking flatness of surfaces. It (Fig 2.8). consists of a rule, square head, centre head, protractor and spirit level. This may be used as a rule, a square, a depth gauge, for locating the centre on the end of the round bar and for measuring and marking angles.

2.3.6 Scriber: Scriber sometimes called the metal worker’s pencil. These are made up of high carbon steel and are hardened from the front edge. Scriber (Fig 2.9). is used for scratching lines on the sheet metal during the process of laying out a job.

2.3.7 Odd-leg caliper: This is also called ‘Jenny Caliper’ or ‘Hermaphrodite’ (Fig 2.10). This is used for marking parallel lines from a finished edge and also for locating the centre of round bars. It has one leg pointed like a divider and the other leg bent like a caliper.

2.3.8 Divider: It is basically similar to the calipers except that its legs are kept straight and pointed at the measuring edge. This is (Fig 2.11). used for making circles, arcs, laying out perpendicular lines, bisecting lines etc…

2.3.9 Punches: These are used for making indentations on the scribed lines, to make them visible clearly. These are made of high carbon steel.

2.3.10 Dot punch: This is used to lightly indent along the layout lines, to locate centre of holes and to provide a small centre mark for divider point, etc…for this purpose, the punch is ground to a conical point having 600 included angles. (Fig 2.12).

2.3.11 Centre punch: This is similar to the dot punch, except that it is ground to a conical point having 900 included angles. It is used to mark the location of the holes to be drilled. (Fig 2.13).

2.3.12 Calipers: They are indirect measuring tools used to measure or transfer linear dimensions. These are used with the help of a steel rule to check inside and outside measurements. These are specified by the length of the legs. (Fig 2.14(a) and 2.14(b)).

2.3.13 Vernier caliper: These are used for measuring outside as well as inside dimensions accurately. It may also be used as a depth gauge. It has two jaws. One jaw is formed at one end of its main scale and the other jaw is made part of a vernier scale. (Fig 2.15). Least count of the vernier = 1 main scale division – 1 vernier scale division.

Fig.2.6. Universal scribing block Fig.2.7. Try-square

Fig.2.8. Combination set Fig.2.9. Scriber

Fig.2.10. Odd-leg caliper Fig.2.11. Divider Fig.2.12. Dot punch

Fig.2.13. Centre punch Fig.2.14(a).Outside Caliper Fig.2.14(b).Inside Caliper

Fig.2.15. Vernier caliper 2.3.14 Vernier height gauge: The vernier height gauge, clamped with a scriber. It is used for layout work. An off-set scriber is used when it is required to take measurements from the surface, on which the gauge is standing. the working principal of this instrument is same as that of the vernier caliper. As shown in (Fig 2.16).

2.3.15 Vernier depth gauge: It is used for precision measurement of blind holes, slots, grooves, etc… the working principal of this instrument is same as that of the vernier caliper. As shown in (Fig 2.17).

2.3.16 Outside micrometer: This is used for measuring external dimensions accurately. Its accuracy range is 0.01 mm, These are available in different ranges with interchangeable anvils. It works on the principle of screw thread’s pitch and lead. As shown in (Fig 2.18).

2.3.17 Inside micrometer: This is used to measure inside dimension accurately. The construction of inside micrometer is the same as outside micrometer except that it has no frame. So its spindle can be used to take measurements from inside of blind holes. As shown in (Fig 2.19).

2.4 CUTTING TOOLS 2.4.1 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 centimeter. Blades having lesser number of teeth per centimeter are used

for cutting soft materials like aluminium, brass and bronze. Blades having larger number of teeth per centimeter are used for cutting hard materials like steel and cast iron. As shown in (Fig 2.20).

2.4.2 Chisels: These are used for removing surplus metal or for cutting thin sheets. These tools are made from carbon steel. Chisels are annealed, hardened and tempered to produce a tough shank and a hard cutting edge. The cutting angle of the chisel for general purpose is about 600. As shown in (Fig 2.21).

2.4.3 Combination plier: This is made of high carbon steel by proper hardening and tempering and is used for cutting as well as for gripping the work. 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. As shown in (Fig 2.22).

2.4.4 Nose plier: It is similar to combination plier but its gripping jaws have extra length in tapered from which makes it suitable for gripping small objects and also gripping in narrow spaces. As shown in (Fig 2.23).

2.4.5 Twist drill: Twist drills are used for making holes. These are made of high speed steel. Both straight and taper shank twist drills are used. As shown in (Fig 2.24).

The parallel shank twist drill can be held in an ordinary self-centering drill chuck, say that of a portable drilling machine, which has parallel jaws.

The taper shank twist drill has two helical flutes, with a taper shank for handling and driving the drill. The tapered shank fits into a corresponding tapered bore provided in the drilling machine spindle.

Fig 2.16.Vernier height gauge Fig 2.17. Vernier depth gauge

Fig 2.18. Outside micrometer Fig 2.19. Inside micrometer

Fig 2.20. Hacksaw frame with blade

Fig 2.21. Chisels Fig 2.22. Combination plier

Fig 2.23. Nose plier Fig 2.24. Twist drill

2.4.6 Taps and tap wrenches: A tap is a hardened steel tool, used for cutting internal threads in a drilled hole. Hand taps are usually supplied in sets of three for each diameter and thread size. Each set consists of a taper tap, intermediate tap and plug or bottoming tap. Taps are made of high carbon steel or high speed steel. (Fig 2.25).

2.4.7 Dies and die holders: Dies are the cutting tools used for making external threads. Dies are made either solid or split type. They are fixed in a die-holder for holding and adjusting the die gap. They are made of tool steel or high carbon steel. (Fig 2.26). 2.4.8 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. Twist drills, made of tool or high speed steel are used with the drilling machine for drilling holes. (Fig 2.27).

2.4.9 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 2.28).

2.4.10 Reamer: The drill does not always produce the correct hole some time with good finish. Thus a correct hole is produced with good finish of a pre drilled hole using a reamer. During reaming operations, the job should be properly supported and rigidly held. A stock wrench of appropriate size for holding the reamer is used. The reamer must be kept in its correct position relative to the job. It should be always being turned in the cutting direction. (Fig 2.29).

2.5 FINISHING TOOLS

2.5.1 File: 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. One end of the file is shaped to fit into a wooden handle. (Fig 2.30).

2.5.2 Types of files: Files are classified according to their shape, cutting teeth and pitch or grade of the teeth. (Fig 2.31).

2.5.3 File card: It is a metal brush, used for cleaning the files, to free them from filing, clogged in between the teeth. (Fig 2.32).

Fig 2.25.Taps and tap wrenches Fig 2.26.Dies and die holders

Fig 2.27. Bench drilling machine Fig 2.28.Portable electric drill

Fig 2.29.Reamer Fig 2.30.File

Fig 2.32.File card Fig 2.31.Types of files

2.6 MISCELLANEOUS TOOLS

2.6.1 Ball peen hammer: These 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 2.33).

2.6.2 Cross –peen hammer: It is similar to bal peen hammer, except the shape of the peen (Fig.2.34). This is used for chipping, riveting, bending and stretching metals and hammering inside the curves and shoulders.

2.6.3 Straight-peen hammer: This is similar to cross-peen hammer, but its peen is in-line with the hammer handle (Fig.2.35). It is used for swaging, riveting in restricted places and stretching metals.

2.6.4 Screw driver: A screw driver is designed to turn screws (Fig.2.36). The blade is made of steel and is available in different lengths and diameters. The grinding of the tip to the correct shape is very important.

2.6.5 Spanners: A spanner or wrench is a tool for turning nuts and bolts. It is usually made of forged steel. There are many kinds of spanners as shown in (Fig.2.37). They are named according to the application.

Fig 2.33. Ball peen hammer Fig 2.34. Cross –peen hammer

Fig 2.35. Straight-peen hammer

Fig 2.36. Screw driver

Fig 2.37. Spanners

2.7 FITTING OPERATIONS

2.7.1 Chipping: Removing the metal with a chisel is called chipping and is normally used where machining is not possible (Fig.2.37). While chipping, safety goggles must be put on, to protect eyes from the flying chips.

2.7.2 Filing: There are several methods of filing, each with a specific purpose (Fig.2.37 (a) to Fig.2.38 (d)). 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. Fig.2.38 (a).

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. Fig.2.38(b).

3. Cross filing Cross filing is carried out across two diagonals, to produce medium surface finish. Fig.2.38(c).

4. Draw filing A smooth file with a flat face is used for this purpose and to produce fine grained structure. Fig.2.38(d).

2.7.3 Scraping: It is an operation by which high spots left on the surface of a job after filing or other machining operation, are removed by using a tool known as a scraper. Scraping is aimed at removing only a little amount of metal, to get perfect flat surface. As shown in (Fig.2.39).

2.7.4 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 a centre line. Scriber lines on non-ferrous materials are readily visible but bright steel needs coating for the visibility of the line. (Fig.2.40(a) to Fig.2.40(f)). The following are the measuring methods in the order of increasing accuracy.

1. Direct measurement from a rule.2. Caliper set to a rule.3. Calipers set to a plug gauge.4. Vernier calipers.5. Micrometer.6. Dial indicator.7. Protractor is used to measure an angle.

Fig.2.37. Chipping Fig.2.38(a).Holding a file Fig.2.38(b).Filing internal curves

Fig.2.38(c).Cross filing Fig.2.38 (d).Draw filingss

Fig.2.39.Scraping Fig.2.40(a).Use of scribing Block

Fig.2.40(b).Use of odd-leg caliper Fig.2.40(c).Use of divider

Fig.2.40(d).Measuring with Calipers Fig.2.40(e).Reading the measurement

Fig.2.40 (f).Measuring with Protractor

Fig.2.40. Various Marking and Measuring operations

2.8 COMMON SAFETY IN FITTING SHOP

1. Dry tools are safer to use than slippery tools.2. Do not carry sharp tools in pockets.3. Wear leather shoes and not cheppals.4. Don’t wear loose clothes.5. Do not keep working tools at the edge of the table.6. Never work in a place where there is no sufficient light.7. When sawing in a vice, make sure that the work is held tight. A loose vice is

dangerous.8. For cutting thin metal strips, clamp them between two pieces of wood.9. Apply force only on the forward (Cutting) stroke and relieve the force on the

return stroke in sawing.10. Do not hold the work piece in hand while cutting.11. Do not strike hammer with more force than necessary

2.9 VIVA VOICE MODEL QUESTIONS

1. Define the terms ‘Bench work’ and ‘fitting’?2. What are the operations that are normally performed under ‘bench work’ and

‘fitting’?3. With which material is vice-body made. What is the characteristic of that

material?4. What for a C-clamp is used?5. Classify hacksaw blades?6. Classify the twist drills, based on the shape of the shank?7. Differentiate between ‘Single cut’ and ‘Double cut’ files?8. What are the applications of ‘Single cut’ and ‘Double cut’ files?9. Differentiate between ‘Cross filing’ and ‘Draw filing’?10. With what the size of a spanner is denoted?11. What is meant by pinning of files?12. Name the different types of hammers used in fitting work?13. Define ‘least count’ of a Vernier?14. Define ‘Least count’ of a Vernier?

15. Differentiate between ‘All hard’ and ‘Flexible’ hacksaw blades?16. What are the different processes done in fitting?17. What are different parts of a hard hammer?18. What are the different types of chisels used in a fitting work?19. What are the various types of files?20. What is the difference between a file and a scrapper in regard to their use?21.

2.10 FITTING PRACTICES

EXPERIMENT - 1

Dovetail Fitting

Aim: To make a dovetail fitting from the given two M.S. pieces.

Tools required: Bench vice, steel rule, try-square, ball-peen hammer, scriber, dot punch, set of files, surface plate, jenny caliper, and hacksaw with blade and flat chisel.

Procedure: The burrs in the pieces are removed and the dimensions are checked with the steel rule. The pieces are clamped on after other and the outer mating edges are filed and checked for their flatness, with the help of the try-square. The side edges of the two pieces are filed such that, they are at right angle to each other and widths are exactly 48mm. chalk is then applied on the surfaces of the two pieces. The given dimensions of the dovetail fitting are marked, by using the jenny caliper, steel rule and surface plate. Using the dot punch, dots are punched along the above scribed lines. Using the hack saw, the unwanted portions are removed. Using the flat chisel, the unwanted material in the piece Y is removed. The cut edges are filed by the half round file. The corners of the stepped surfaces are filed by using or triangular file to get the sharp corners. The pieces (X and Y) are fitted together and the mating is checked for the correctness of the fit. Any defects noticed, are rectified by filing with a smooth file. Result: The required dovetail fitting is thus obtained, by following the stages, as shown in (Fig 2.41).

Fig.2.41. Dovetail Fitting

EXPERIMENT - 2

Half round fitting

Aim: To make a half round fitting from the given two M.S. pieces.

Tools required: Bench vice, steel rule, try-square, ball-peen hammer, spring divider, dot and centre punch, set of files, surface plate, jenny caliper, and hacksaw with blade.

Procedure: The burrs in the pieces are removed and the dimensions are checked with the steel rule. The outer mating edges are filed, by rigidly fixing in the bench vice. The flatness of the edges is also checked by the try-square. The side edges of the two pieces are filed such that, they are at right angle to each other and widths are exactly 48mm. chalk is then applied on the surfaces of the two pieces. The given half rounds (semi-circles) are marked on the two pieces, by using the jenny caliper and spring divider. Using the dot punch, dots are punched along the above scribed lines. Using the hack saw the unwanted portions are removed to the extent possible. The cut edges are filed by using square and half round files. The pieces (X and Y) are fitted together and the mating is checked for the correctness of the fit. Any defects noticed, are rectified by filing with a smooth file.

Result: The required half round fitting is thus obtained as shown in (Fig 2.42).

Fig 2.42. Half round fitting

EXPERIMENT - 3

Drilling and tapping

Aim: To prepare a square flat with a drilled hole and four tapped holes.

Tools required: Bench vice, steel rule, try-square, ball-peen hammer, jenny caliper, scriber, hacksaw, dot and centre punches, set of files, surface plate, drill bits and tap set.

Procedure: The burrs in the pieces are removed and the dimensions are checked with the steel rule. Any two adjacent sides of the flat are filed, by using rough and smooth files such that, they are perpendicular to each other. Wet chalk is applied on one side of the flat and dried for marking. Lines are marked at 48 mm from the two edges, using the jenny caliper and steel rule. Using the dot punch, dots are made along the marking lines. The excess material is either filed or cut with the hacksaw and then filed to correct size. By using jenny caliper and steel rule, lines are marked to locate the centres of the holes. Using the centre punch, dots are made at the centres of the holes. Choosing appropriate sizes of drill bits, holes are made; using a bench drill. The corner holes are tapped by using the hand tap set. All the sharp edges around the holes are deburred.

Result: the square flat with a drilled hole and four tapped holes are thus made, by

following the stages as shown in (Fig. 2.43).

Fig. 2.43. Drilling and tapping

SHEET METALWORK(TIN SMITHY)

3.1 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.

3.2 METALS USED IN SHEET METAL WORK

The following metals are generally used in sheet metal work:

3.2.1 Black Iron Sheet: It is probably the cheapest of all the metal used for sheet metal work. It is bluish black in appearance and is used generally in form of uncoated sheet. It can be easily rolled into the desired thickness. Since it is uncoated it corrodes rapidly. Hence to increase its life it can be painted or enameled. This metal is generally used in the making or roofs, food containers, stove pipes, furnace fittings, dairy equipments, tanks, cans and pans, etc.

3.2.2 Galvanized Iron (G.I.): It is popularly known as G.I. sheets. It is soft steel coated with molten zinc. This coating resists rust formation on surface and improves appearance and water resistance. Articles such as pans, furnaces, buckets, cabinets etc. are made from GI sheets.

3.2.3 Stainless Steel: It is an alloy of steel with nickel, chromium and small percentages of other metals. It has good corrosion resistance. It is costlier but tougher than GI sheets. 1t is used in kitchenware, food processing equipments, food handling articles, tools and instruments for surgery work in hospitals and components of

chemical plants etc. Other metal sheets used for sheet metal work are made up of copper, aluminum, tin, and lead.

3.3 SHEET METAL TOOLS

The following tools are commonly used for sheet-metal work(i) Hand shears or snips(ii) Hammers(iii) Stakes and stake holder(iv) Cutting tools(v) Measuring tools(vi) Miscellaneous hand tools

3.3.1 HAND SHEARS OR SNIPS

Fig 3.1 shows the types of hand shears or snips. They resemble with pair of scissors and are used like them to cut thin soft metal sheets of 20 gauge or thinner. They are required to size and shape the sheets. They can make straight or circular cuts. Different types of hand shears are…..

3.3.1.1 Straight hand shear: It is used for general purpose cutting, making straight cuts and trimming away extra metal.

3.3.1.2 Universal shear: Its blades are designed for universal cutting straight line or internal and external cutting of contours. It may be of right hand or left hand type,easily identifiable, as the top blade is either on the right of on the left.

3.3.1.3 Curved hand shear: It is used for cutting circular or irregular curved shapes ranging from 20 to 35 cm.

Fig.3.1 Various types of Hand shears or Snips

3.3.2 HAMMERS

Fig 3.2 shows the various types of hammers used in sheet metal work for forming shapes. The uses of different kind of hammers are given in Fig.3.2

3.3.2.1 Smoothing hammer: Smoothing hammer (Fig. 3.2(a)) is used for leveling and smoothing a sheet metal joint.

3.3.2.2 Stretching hammer: Stretching hammer (Fig. 3.2(b)) is used for stretching sheet.

3.3.2.3 Creasing hammer: Creasing hammer (Fig. 3.2(c)) is used to close down joint edges of sheets metal part.

3.3.2.4 Hollowing hammer: Hollowing hammer (Fig. 3.2(d)) is used for hollowing sheet metal part. It is used for generating sharp radii also.

3.3.2.5 Riveting hammer: Riveting hammer (Fig. 3.2(e)) is used for forming riveted heads.

3.3.2.6 Planishing hammer: Planishing hammer (Fig. 3.2(f)) is used for removing

small marks or indentations from the sheet metal job surface and to true the shape of

the work. It smoothens off the finished sheet metal work.

3.3.2.7 Soft hammer or Mallets: Mallets (Fig. 3.2(g)) used during working with soft

metal sheets. They may be of wood, rubber or raw hide. A mallet strikes a blow with

the minimum damage to the surface. In sheet metal work, the commonly used mallets

are bossing mallet, tinman’s mallet (Fig. 3.2(h)) and rawhide mallet (Fig. 3.2(i)).

Fig.3.2 Various types of Hammers

3.3.3 STAKES

Stakes are used to form the metal sheets into various shapes. It is a sort of anvil, which supports the sheet for sheet metal work. It consists of a shank and a head or horn. The head or horn of stake is available in a number of varieties of sizes and shapes. Their working faces of stakes are machined or ground to needed shape. Some stakes are made of forged mild steel faced with cast steel. Whereas the better class stakes are made either of cast iron or cast steel. Fig 3.3 shows the various types of stakes.

3.3.3.1 Beak horn stake. Beak horn (Fig. 3.3(a)) is basically used for forming, riveting and seaming articles made of sheet metal part. It has a thick tapered horn at one end and a rectangular shaped horn at the other.

3.3.3.2 Funnel stake. Funnel stake (Fig. 3.3(b)) is commonly used for planishing tapered work and hand forming of funnels and similar conical shapes of sheet metal.

3.3.3.3 Half moon stake. Half moon stake (Fig. 3.3(c) is basically used for throwing up edges of curved sheet metal work and for preliminary stages of wiring curved edges.3.3.3.4 Round bottom stake. Round bottom stake (Fig. 3.3(d)) is commonly used for squaring up edges and setting up the bottom of cylindrical jobs made up of sheets.

3.3.3.5 Bick iron. Bick iron stake (Fig. 3.3(e)) is mainly used for forming taper handles, spouts and tubular work in general.

3.3.3.6 Hatchet stake. Hatchet stake (Fig. 3.3(f)) is generally used for making sharp bends, bending edges and forming boxes and pans of sheet metal by hand.

3.3.3.7 Creasing with horn stake. Creasing horn stake (Fig. 3.3(g)) has a round horn used for forming conical shaped pieces in sheets.

3.3.3.8 Needle case stake. Needle case stake (Fig. 3.3(h)) is generally used for bending of sheets. It has a round slender horn for forming wire rings and tubes.

3.3.3.9 Candle mold stake. Candle mold stake (Fig. 3.3(i)) has two horns for different tapers when forming, seaming and riveting long flaring articles made up of sheet metal.

3.3.3.10 Blow horn stake. Blow horn stake (Fig. 3.3(j)) is generally used in forming, riveting and seaming tapered articles such as funnels.

3.3.3.11 Conductor stake. Conductor stake (Fig. 3.3(k)) has two cylindrical horns of different diameters. It is used for forming, riveting, and seaming small sized pipes and tubes.

3.3.3.12 Double seaming stake. Double seaming stake (Fig. 3.3(l)) consists of two cylindrical horns of different diameters and it is commonly used for riveting forming, and seaming tubes and small pipes.

3.3.3.13 Stake Holder

Fig 3.4 shows the stake holder, which is a rectangular cast iron plate that has conveniently arranged tapered holes so that the various stakes may fit in and may be used in different positions for tackling the sheet metal job for a particular work.

Fig.3.3 Various types of Stakes

Fig.3.4 Stake Holder

3.3.4 CUTTING TOOLS

3.3.4.1 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. One end of the file is shaped to fit into a wooden handle. These are flat, square, round, triangular, knife, pillar, needle and mill types. As shown in Fig.3.5.

3.3.4.2 Chisels. The flat chisel and round nose chisel are most widely used in sheet metal work. These are used for removing surplus metal or for cutting thin sheets. These tools are made from carbon steel. The cutting angle of the chisel for general purpose is about 600. As shown in Fig.3.6.

3.3.4.3 Scrapers. (Fig 3.7) These are flat, hook, triangular, half round types. It is an operation by which high spots left on the surface of a job after filing or other machining operation, are removed by using a tool known as a scraper. Scraping is aimed at removing only a little amount of metal, to get perfect flat surface.

3.3.4.4 Hacksaws. Hacksaw used in sheet metal shop may be hand hacksaw or powerHacksaw. 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 centimeter. As shown in Fig.3.8 (a & b).

3.3.5 MEASURING TOOLS

3.3.5.1 Folding rule. It is used in measuring and laying out on sheets larger work with accuracy of 0.5 mm. (Fig.3.9).3.3.5.2 Steel rule. It is useful in measuring and laying out small work on sheets. It can also measure up to accuracy of 0.5 mm. (Fig.3.10).3.3.5.3 Outside micrometer: This is used for measuring external dimensions accurately. Its accuracy range is 0.01 mm. (Fig 3.11).3.3.5.4 Inside micrometer: This is used to measure inside dimension accurately. The construction of inside micrometer is the same as outside micrometer except that it has no frame. So its spindle can be used to take measurements from inside of blind holes. (Fig 3.12).3.3.5.5 Vernier caliper: These are used for measuring outside as well as inside dimensions accurately. It may also be used as a depth gauge. It has two jaws. One jaw is formed at one end of its main scale and the other jaw is made part of a vernier scale. (Fig 3.13).

Least count of the vernier = 1 main scale division – 1 vernier scale division.

3.3.5.6 Thickness gauge (Fillet and Radius Gauge): This instrument is highly useful for measuring and checking the inside and outside radii of fillets and other round surfaces. The fillet and radius gauges are made in thin strong strips curved to different radii at end. (Fig 3.14).

Fig.3.5 File Fig.3.6 Chisels

Fig.3.7 Flat, Hook, Triangular, Half round Scrapers

Fig.3.8(a) Hand hacksaw Fig.3.8(b) Power hacksaw

Fig.3.9 Folding rule Fig.3.10 Steel rule

Fig.3.11 Outside micrometer Fig.3.12 Inside micrometer

Fig.3.13 Vernier caliper Fig.3.14 Fillet and Radius Gauge

3.3.6 MISCELLANEOUS HAND TOOLS

3.3.6.1 Trammel: Fig. 3.15 shows a typical trammel and its operations. It is long rod

called a beam on which are mounted two sliding heads used to hold scribing points for

scribing work on sheets. The points are adjustable in nature and can be replaced by

pencils, caliper legs or ballpoints. It is a layout generally required to measure between

two points or to scribe large circles or arc too long for divider.

3.3.6.2 Semi-circular protector: Fig. 3.16 shows the semicircular protractor whose

head is circular and back is flat. It is generally used to for setting bevels, transferring

angles and other classes of work on metal sheets.

3.3.6.3 Pliers: Flat nose and round nose type pliers are commonly used for holding

the sheet work and forming different shapes respectively. As shown in Fig. 3.17.

3.3.6.4 Scribers: Fig. 3.18 shows the different kinds of scribers, which are made of

hardened steel. Its one end is pointed as sharp as possible for making scribing lines on

metal sheets.

3.3.6.5 Hand seamer: Fig. 3.19 shows a hand seamer, which is used for bending

narrow portions, which are difficult to fold, by other means. It has two adjustable

screws, which can be regulated for width of bend. The metal sheet is placed between

the jaws and the jaws are clamped together by squeezing the handles to grip the sheet

for further bending.

3.3.6.6 Groover: Fig. 3.20 shows a typical groover and its operation, which consists

of two folded edges called locks. The two edges are hooked together and locked with

a grooving tool called hand groover. These tools come with grooves of various width

and vary in size. The groover is used for offsetting an outside grooved seam. Initially,

the folding edges to 180° are made first. Then the folded edges are hooked together.

Finally grooving tool is then used to make strong joint of metal sheets as shown in

figure.

Fig. 3.15 Trammel Fig. 3.16 Semi-circular protector

Fig. 3.17 Flat nose Plier Fig. 3.18 Round nose Plier

Fig. 3.19 Scribers Fig. 3.20 Hand seamer

Fig. 3.21 Groover

3.4 FOLDING TERMINOLOGY OF SHEET METAL JOINT

3.4.1 SEAM: A seam is the section where pieces of sheet metal are joined together. Most common types of seams are: (a) Single seam, (b) Double seam, (c) Grooved seam. As shown in Fig. 3.22.

3.4.1.1 Single seam: It is used to join a bottom to a vertical body. Fig.3.22 (a).

3.4.1.2 Double seam: It is similar to single seam, with the main difference that its formed edge is bent upward against the body. The layout process for this seam is similar to that used for a single seam. Fig.3.22 (b).

3.4.1.3 Grooved seam: It is made by hooking two folded edges together and then off-setting the seam. Fig.3.22 (c).

3.4.2 HEM: A hem is an edge made by folding. The following are the types of hems.As shown in Fig. 3.23.

3.4.2.1 Single hem: It is made by folding the edge of the sheet metal, to make it smooth and stiff. Fig.3.23 (a).

3.4.2.2 Double hem: It is a single hem, with its end bent. Fig.3.23 (b).

3.4.2.3 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. Fig.3.23 (c).

3.5 FOLDED SHEET METAL JOINTS

3.5.1 Lap joint. It is very frequently used in sheet metal work and can be prepared by means of soldering or riveting. Fig.3.24(a).

3.5.2 Seam joint. This joint is a very generally used in sheet metal work. It is locked, as shown in the diagram, so as to ensure a positive grip and also to make the joint flush with the surface. Fig.3.24(b).

3.5.3 Locked seam joint. This joint is used for locking seam joints in sheet metal work Hem (single and double), wired edge, cup and angular joints. These enable the edges sheet metal part to join the pieces along them. Fig.3.24(c).

3.5.4 Flanged joint. It is commonly used in sheet metal work frequently in making pipe connections. Fig.3.24(d).

3.5.5 Cap joint. It provides another useful form of locked seam joint on sheet metalComponent with good appearance and strength. It is generally used for assemblingCross seam of ducts made up of in sheet metal part. Fig.3.24(e).

Fig. 3.22 Types of Seam

Fig.3.23 Types of Hem

Fig.3.24 (a). Lap joint.

Fig.3.24 (b). Seam joint

Fig.3.24 (c). Locked seam joint

Fig.3.24 (d). Flanged joint

Fig.3.24 (e). Cap joint

Fig.3.24 Types of Folded sheet metal joints

3.6 COMMON SAFETY IN TIN SMITHY SHOP

1. Use hand leather gloves while handling heavy sheets.

2. Avoid feeling the cut portion by hand while cutting with snip.

3. Do not let sheet metal slip through your hands. Most cuts from sheet metal

result from allowing it to slide through the hands.

4. Use snips only for metal that can be cut by force applied by hand.

5. Hand snips should never be used to cut wire. Such practice ruins the cutting

edges of the blades.

3.7 VIVA VOICE MODEL QUESTIONS

1. Name the metals commonly used in sheet metal work?

2. What are the types of hand tools used in sheet metal work?

3. What do you mean by stakes? Name the different types of stakes?

4. Why snips are used?

5. What are punches and shears used for?

6. Name the common sheet metal working machines?

7. What are the common sheet metal operations or processes?

8. Why are joints used in sheet metal work?

9. What are hems and seams?

10. What do you mean by “layout a pattern”? What are the various methods used in

laying out a pattern?

11. What is the thickness of a sheet metal? Why so?

3.8 SHEET METAL (TIN SMITHY) PRACTICES

EXPERIMENT - 1

RECTANGULAR TRAY

Aim: To make a rectangular tray, using the given sheet metal.As shown in Fig.3.25(a)

Tools required: 300 mm steel rule, try square, divider, scriber, straight snip, mallet, ball-peen hammer and hatchet stake.

Procedure: The size of the given sheet is checked with the steel rule. The layout of the tray is marked on the given sheet. The layout of the tray is cut by using the straight snip. Single hemming is made on the four sides of the tray. The four sides of the tray are bent to 900, as shown in Fig.3.25 (b).

Result: The rectangular tray is thus made, from the given sheet metal. as shown in Fig. Fig.3.25 (a).

Fig. 3.25 Rectangular tray

EXPERIMENT - 2

CONE

Aim: To make a cone, using the given sheet metal. As shown in Fig.3.26 (a).

Tools required: 300 mm steel rule, divider, protractor, scriber, straight and bent snips, mallet and funnel stake.

Operations: The size of the given sheet is checked with a steel rule. The development of the cone is marked on the given sheet. The angle subtended by the arc of the sector is calculated from the relation…..

The allowance for holding and bending is added to the development. The waste metal is cut-away by using the straight and bent snips. The development of the cone is folded by using the funnel stake, after forming the single hemmed joint shown in Fig. 3.26 (b). The joint is then soldered.

Result: The cone is thus made, from the given sheet metal. As shown in Fig. 3.26 (a).

Fig.3.26 ConeEXPERIMENT - 3

SQUARE TIN

Aim: To make a square tin, using the given sheet metal. As shown in Fig 3.27(h).

Tools required: 300 mm steel rule, try square, divider, scriber, straight edge, mallet, cross-peen hammer and hatchet stake.

Procedure: The size of the given sheet is checked with the steel rule. The layouts of the body and bottom are drawn on the tin sheet and cut as shown in Fig3.27 (e). The body is folded as shown in Fig 3.27 (b) (c). The flanges are bent to receive the bottom as shown in Fig 3.27(d). The bottom is bent as shown in Fig3.27(f). The bottom and body are placed in position and folded as shown in Fig 3.27(g). The bottom flange portion is again folded-up to complete the joint as shown in Fig 3.27(h).

Result: The square tin. Closed at one end is thus made, from the given sheet metal. As shown in Fig 3.27(h).

Fig. 3.27 Square tin

HOUSE WIRING

4.1 INTRODUCTION

Power is supplied to domestic installations through a phase and a neutral, forming a single phase A.C.230 V, two – wire system. For industrial establishments, power is supplied through three-phase four wire system, to give 440 V. The neutral is earthed at the distribution sub-station of the supply.

As a safe practice, all single-phase devices such as switches, fuses, etc… are connected to the live conductor. Al electrical conductors and cables are color 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.

4.2 SAFETY PRECAUTIONS

1. Always be careful.2. You should not energize any conductor unless you are sure that all is clear and

them is none working on it.3. You should not temper unnecessarily any alive electrical gear.4. You should not disconnect any plug by pulling the flexible cable.5. Before replacing a blown fuse, always, remember to put of the switch OFF.6. Safety demands good earthing, hence always keep earth connection in good

condition.7. Before using portable electrical things, see that those are well earthed.8. While handling an electrical appliance like table fan, iron, heaters etc…. be

sure that they are disconnected from the supply. Switching off is not enough. Leaky insulation may give serious shock.

9. Live wires should always be connected through the switch.10. Do not put a sharp edged tool in your pocket.11. Do not use a plier as a hammer.12. If you want to hand over any sharp tools, like knife, screw driver, file, hand

saw, etc… to someone else, give it from handle side otherwise it can injure the hand of other person.

13. Do not use tool like file, knife, scre driver, etc… without handle otherwise it can injure your hand.

14. In rainy season apply grease on tools on which rust can effect.15. In case of electric fire, do not throw water on live conductor and equipment as

it is dangerous. The best remedy is to disconnect the electric supply immediately and then throw sand or dust on the fire.

16. Every fire extinguisher cannot be used for electric fire but only CO2

extinguisher is used for this purpose.17. Before starting the work above ground on a pole or tower, you must use safety

belt and ladder. The ladder must be held by another person so that it may not slip away.

18. Do not tie with the pole the wire on which clothes are to be dryed.

4.3 HAND TOOLS

4.3.1 Screw driver: It is most important tool and is used more often than any other tool. These are available in different blade sizes, but 25cm driver with 15cm blade is a standard one which can be used to meet different types of jobs. They are used for taking out or driving in slotted head screw by turning them. (Fig.4.1).Precautions: 1). The edge should not be to sharp.

2). It must fit in the slot of screw head. 3). Do not use it as a hammer chisel.

4.3.2 Combination pliers: This type of pliers is commonly used by an electrician. It is used for cutting and twisting the wires. Only insulated pliers are used for electric work. These are available in 15, 20 and 25cm length size. (Fig4.2 (a) to 4.2(c)).Precautions: 1). Do not cut steel wire with pliers.

2). Do not use it as a hammer. 3). Do not hold hot substance with it.

4.3.3 Pocket knife: It is also one of the most important tools. It is generally used for removing insulation from the wires. It should be of high grade cutter steel. Do not use it for cutting wires. In open shape, it should not be kept in the pocket. (Fig.4.3).

4.3.4 Poker: It is generally difficult to insert a wooden screw into job, unless there is a small guide hole with the poker, an impression is made into the wood. It is a pointed tool and made from forged tool steel. Much care should be taken to handle such tool; it should be never being taken into pocket. (Fig.4.4).

4.3.5 Hammer: There are many types of hammers but an electrician uses mostly following types.

1. Ball peen hammer: It is used for riveting purposes. (Fig.4.5).2. Cross peen hammer: It is used for riveting purposes in awkward places.

(Fig.4.6).

4.3.6 Firmer chisel: It is used for chipping, scrapping and grooving in the wood. The size varies and is taken from the width of the blade; generally 4mm to 40mm size is available. (Fig.4.7).

4.3.7 Cold chisel: It is used for plaster cutting or brick cutting. It is made from forged alloy steel. Before use, these chisels are tempered. The cold chisels are generally available from 6mm to 25mm and 25cm long. For hammer job, 25mm wide and 20cm long chisel should be used. (Fig.4.8).

Fig4.1 Screw driver Fig4.2 (a) Combination pliers

Fig4.2 (b) Round Nose pliers Fig4.2(c) Nippers

Fig4.3 Pocket knife Fig4.4 Poker

Fig4.5 Ball peen hammer Fig4.6 Cross peen hammer

Fig4.7 Firmer chisel Fig4.8 Cold chisel

4.3.8 Hand drill: This is used for drilling holes in wooden blocks and wooden boards

to facilitate the passage of insulated wires while doing wiring. (Fig.4.9).

4.3.9 Wooden saw: Most wiring is done with wooden casing or batten. Therefore, it is

necessary to make use of carpenter’s saw for making joints or for cutting the casing

capping and batten. ( Fig.4.10).

4.3.10 Hack saw: It is used for cutting metals such as conduits, cables, etc… the hack

saw frame is adjustable and a blade of tool steel is used. The blade is usually 30cm

long with 24 or 38 teeth in 25cm. The less numbered ones are used for cores jobs

while more numbered ones are used for fine cuts. ( Fig.4.11).

4.3.11 Blow lamp: It is used for soldering a cable jointing purposes. It is capable of

producing very high temperatures. It works on the stove principle. It directs the flame

directly on to the job and increases its temperature to a high degree. ( Fig.4.12).

4.3.12 File: In conduct wiring purposes often in electric work require a file for

removing burs, etc…15cm size half-round file is used. ( Fig.4.13).

4.3.13 Wrenches: It is used for connecting or disconnecting the rigid conduit pipes.

For electrician a pipe wrench, which can handle a conduit up to diameter of 38cm, is

sufficient. ( Fig.4.14).

4.3.14 Raw plug tool: The tool has bits of tool steel suitable for the job. The tool bits

are numbered according to the size of plugs used. It is usually used to make holes in

concrete and stonewalls. ( Fig.4.15).

Fig.4.9 Hand drill Fig.4.10 Wooden saw

Fig.4.11 Hack saw Fig.4.12 Blow lamp

Fig.4.13 File

Fig.4.14 Wrenches

Fig.4.15 Raw plug tool

4.4 CONDUCTOR AND INSULATOR 4.4.1 What is a Conductor: Through which electricity can flow easily or those metals which offer a small resistance to the flow of electricity. Generally, copper and aluminum are the materials used as a conductor for wires.

4.4.2 What is an Insulator: Insulators are those substances, which offer a very high resistance to the flow of electricity. The type of the wire depends upon the type of the

insulation used. Generally rubber and polyvinyl chloride are used as insulation on wires.

4.5 VARIOUS TYPES OF WIRES AND CABLES

4.5.1 Cable means:

(1). A standard conductor (Single conductor cable).(2). A combination of conductors insulated from one another (multiple conductors).

The component conductors of the second kind of cable may be either solid or standard, and this kind of cable may or may not have a common insulating covering. The first kind of cable is a single conductor, while the second kind is a group of several conductors. The term cable is applied by some manufacturer to a solid wire heavily insulated and covered. This usage arises from the manner of the insulations, but such a conductor is not included under this definition of cable. The term cable is a general one and in practice, it is usually applied only a larger sizes. A small cable is called a ‘standard wire’ or a ‘cord’. Cables may be bare or insulated, and the latter may armored with lead, or with steel wires or bands.

4.5.2 Wire Means:

A slender rod or filament of drawn metal. The definition restricts the term to what would ordinarily be understand by the term ‘Solid wire’. In the definition, the word ‘slender’ is diameter. If a wire be covered with insulation, it is properly called the insulated wire, while primarily the term ‘wire’ refers to the metal nevertheless when the context shows that the wire is insulated, the term ‘wire’ will be understood to include the insulation.

1. P.V.C. Wire ( Polyvinyl chloride ) 2. V.I.R.(Vulcanized Indian Rubber) or V.R.I Wire 3. C.T.S (Cab Tyre Sheathed) or T.R.S ( Tough Rubber Sheathed)

4.6 INTRODUCTION TO VARIOUS TYPES OF WIRES

1. V.I.R. (Vulcanized India Rubber) Wires: These wires are used for general electrical wiring in casing, capping and conduit wiring. These wires absorb moisture quickly. (Fig 4.16)

2. C.T.S/T.R.S (Cab Tyre Sheathed/tough Rubber Sheathed) Wires: These wires are somewhat moisture-proof. These are available in single core, twin core and three cores. (Fig 4.17)

3. P.V.C. (polyvinyl-Chloride) Wires: In these types of wire conductors are insulated with P.V.C. insulations. Nowadays mostly these wires are used for better wiring.e.g; cleat wiring, casing, capping wiring and conduit wiring. P.V.C. insulation is harder than rubber, so cotton taping and braiding is not required for mechanical and moisture protection. These wires should not be used for giving connection to the heating appliances and pendant lighting, etc….. (Fig 4.18)

4. Lead Sheathed Wires: Such types are similar in construction with T.R.S as far as core section is connected but having outer sheath of lead alloy. These wires are used for the moisture full weather and for the snowfall area. (Fig 4.19)

5. Water Proof Wires: These wires are used for outdoor work as service lines. The conductors are insulated first with rubber then braiding of cotton thread. This braiding material is dipped in waterproof compound. (Fig 4.20)

6. Flexible wires: These wires are used for giving connection to heating appliances, pendant lights, portable appliances, etc…. the insulation used is pure rubber or vulcanized rubber on which single or double cotton or artificial silk braiding is provided or only P.V.C. is used. (Fig 4.21)

4.6.1 Flexible wires available in the market:

1. T.R.S. Flexible wires.2. Workshop flexible available in 3 core and 4 core.3. P.V.C. insulated flexible wires: These wires are made in the following voltage

grading, 250V, and 550V. By grading means the insulation of given wire can withstand safely the mentioned voltage.

4. Other wires(a).Nichrome wire: It is used as a heat producing resistance in heating appliances.(b). Hard down bare copper conductor: It is used in overhead lines and earth connection.(c). Aluminium conductor: It is used in overhead lines and nowadays it is used well in V.I.R. wires and C.T.S. wires and P.V.C. wires.(d). Enameled wire: It is used for winding all types of electric motors and generators. It is also used for making electromagnets.(e). Eureka wire: It is used in rheostats which are used variable resistance in the circuit.

Fig.4.16 V.I.R. (Vulcanized India Rubber) Wire

Fig.4.17 C.T.S/T.R.S (Cab Tyre Sheathed/tough Rubber Sheathed) Wire

Fig.4.18 P.V.C. (polyvinyl-Chloride) Wires

Fig.4.19 Lead Sheathed Wire Fig.4.20 Water Proof Wire

Fig.4.21 Types of Flexible wires 4.7 GRAPHICAL SYMBOLS USED IN MAKING CONNECTION DIAGRAMS

Below are the few commonly used Graphical symbols used in House wiring as shown in Tables 4.1 and 4.2.

Table 4.1

Table 4.2

4.8 THE VARIOUS TYPES OF WIRING SYSTEMS

1. Cleat wiring: This type of wiring is not used practically for permanent wiring and is only suitable for temporary wiring purpose. The porcelain or wooden cleats are very easy to erect and fixed at a distance of 4.5cm to 15cm apart. V.I.R. wires are normally used in this system through T.R.S. wires can also be insulated in special cleats for certain types of installations.

2. Batten wiring: The wires used are sheathed in tough rubber or P.V.C. and they are carried on wooden batten. This wiring is suitable for damp climate, but cannot withstand much heat and so is not suitable for outdoor use. Therefore, they should not be exposed to direct sunlight and where there are corrosive acid fumes.

3. Wooden casing and capping wiring: This is the most common type of wiring used for indoor and domestic installations. This system was introduced 50years ago. V.I.R. wires are carried in two or ripple channel of wooden casing and closed by wooden capping. The obvious objection to the wooden casing and capping system are that, wood is very inflammable even though coating of paints or shellac varnish, it is not damp proof. This type of wiring should not be used where there is a damage of mechanical damage or fire hazard. Positive and negative wires should be taken in different channels.

4. Lead sheathed wiring: In this system the conductor either of twin core or three core, each being separately insulated and covers with the common lead sheath is used. The lead sheathed wires are easily fixed by means of metal clips on wooden batten and forms a good surface system. Whenever the wires must be broken for connections to switch or light point, a junction box must be used. The junction boxes are usually of metal and provided with some means of earthing so that continuity of the sheath is obtained.

5. Conduit wiring: In this system P.V.C. wires are carried through steel or iron pipes giving good protection from mechanical injury or fire risks.

4.9 COMPARISION OF THE WIRING IN DOMESTIC USE

Below Table 4.3 will compare the different wirings in domestic use.

S.No DESCRIPTION CLEAT WIRING

WOOD CASING

CAPPING

C.T.S. WIRING

METAL SHEATED

CONDUIT WIRING

1 LIFE SHORT FAIR LONG LONG VERY LONG

2 MECHANICAL PROTECTION

NIL FAIR FAIR GOOD VERY GOOD

3 COST LOW MEDIUM MEDIUM MEDIUM HIGH4 FIRE POSSIBILITY NIL GOOD POOR POOR NIL5 PROTECTION

FROM DAMPNESSNIL SLIGHT GOOD GOOD POOR

6 TYPE OF LABOUR SEMI- SKILLED

HIGHLY SKILLED

SKILLED SKILLED HIGHLY SKILLED

Table 4.3

4.10 VIVA VOICE MODEL QUESTIONS

1. Define electric wiring?2. What are the safety devices used to protect the electric circuits from overload?3. What are the various types of fuses?4. Differentiate between a fuse and a circuit breaker?5. What for a lamp holder is used in an electric circuit?6. What are the types of lamp holders available in the market?7. What for a ceiling rose is used?8. Name the three types of electrical circuits?9. Name the different types of interior wiring?10. What is meant by an electric circuit?11. What are the places where “one lamp with independent control from two

places”. Is used?12. Name the motor driven household appliances?13. What for a circuit breaker is used?14. What are the precautions to be taken, while connecting the wires with electrical

accessories?15. Define the term”Earthing” or “Grounding”?16. What are the different methods of Earthing?17. What is the economy used types of fans that are working on A.C. power

supply?18. What is the principle of operation of an automatic electric iron?19. What is the difference between emergency lamp and indicator lamp?20. What is the principle of operation of a sodium vapour lamp?

4.11 FITTING PRACTICES

EXPERIMENT – 1

CLEAT WIRING SYSTEM

Aim: Wiring of one light point controlled by 230V AC supply. One single pole

tumbler switches SA in cleat wiring system.

Tools Required: Large Screw driver, Medium screw driver, Screw driver connector

type, Bradawl, Cutting pliers, try square, and Hand drilling machine.

Accessories:

1. Batten holder,

2. SPT switch 5A,

3. Porcelain two way cleats (4-pairs),

4. Round blocks (2-Nos),

5. Wood screws for porcelain cleats (4-Nos),

6. Wood screws for round blocks (2-Nos),

7. Wood screws for SPT switch (2-Nos),

8. Wood screws for batten holder (3-Nos),

9. PVC wires (1/18)″ - (2 ½)″ moles.

Procedure: At first fix three porcelain two way cleats in a raw. Then fix the fourth

one in between first and second in a perpendicular direction at equal distances. Fix the

phase wire and neutral wire to the terminal box. Pass the phase wire and neutral wire

through the first cleat and fix it tightly. Pass the neutral and half wires through 2nd and

3rd two way cleats. Through the 4th porcelain cleat pass half wire and phase wire and

then connect them to the 4X4 SPT switch. Connect the neutral and half wires to

rectangular 7X4 battery holder. Place the bulb in the holder and switch on the current

the bulb glows.

Result: Finally the bulb will glows with this Cleat wiring system connection. As

shown in Fig.

Fig. Cleat wiring system

EXPERIMENT – 2

TAP CASING WIRING SYSTEM

Aim: Wiring of one light point controlled by two single phase (Flush) type switches

with 5A (3/2) pin socket is to be fitted in a block.

Tools Required: Large Screw driver, Medium screw driver, Screw driver connector

type, Bradawl, Cutting pliers, try square, and Hand drilling machine.

Accessories:

1. Batten holder (1-Nos),

2. One way switches flush type (2-Nos),

3. 5A (3/2) pin socket (1-Nos),

4. 7/4 D/C Block (1-Nos), tap casing -3M,

5. Wooden screw for (2 ½)″ (4-Nos),

6. Sheet metal screw for ½ ″-6,

7. PVC (1/18) wire.

Procedure: First fix the three Tap cases continuous as shown in Fig. connect the

phase wire and neutral to the terminal block. Then pass the two wires through the first

and second Tap cases. Connect neutral wire and off wire to the holder provided with

battery. Then pass the three wires through the third Tap case. Connect the phase and

off wire to the switch in the switch board which is fixed. Connect the off wire and

neutral wire to the socket. Then fix the 7X4 D/C block with the help of the screw.

Then fix the bulb in the holder. When the current is switched on, then the current

flows through the circuit, and so the bulb glows.

Result: Finally the bulb will glows with this Tap casing wiring system connection. As

shown in Fig.

Fig. Tap casing wiring system