Search in the document preview
Indian Institute of Technology Hyderabad ME 101: WORKSHOP PRACTICE I
April 2009 PREFACE
The engineers can create a new kind of civilization, based on technology, where art, beauty and
finer things of life are accepted as everyone’s due. Engineers, whatever be their line of activity, must be proficient with all aspects of manufacturing. However, it should not be forgotten that practice without theory is blind and the theory without practice is lame. A person involved in acquiring manufacturing skills must have balanced knowledge of theory as well as practice.
This book is written to meet the objectives of the training courses in workshop practice for all the first year engineering courses in Indian institute of technology Hyderabad. It imparts basic knowledge of various tools and their use in different sections of manufacture such as fitting, carpentry, welding, machine shop etc.
The study of workshop practice acts as the basis for further technical studies. This book gives the perception to build technical knowledge by acting as a guide for imparting fundamental knowledge. Numerous neatly drawn illustrations provided in the text will help the students in understanding the subject, and the concepts related it, better.
Sincere attempts have been made to present the contents in a simple language, supplemented with line diagrams, which are self explanatory and easy to reproduce.
We would like to express our sincere thanks to professors and colleagues for their consistent support. Suggestions for improvement in this book will be thankfully acknowledged and incorporated in the next edition.
K. Sathyanarayana N.A. Somasundaram
25 April 2009
Preface Table of Contents page 1. Fitting Shop 1.1 Introduction 1.2 Holding tools 1.3 Marking and measuring tools 1.4 Cutting tools 1.5 Finishing tools 1.6 Miscellaneous tools 1.7 Safe practice 1.8 Models for preparation Exercises
1 1 2 5 8 10 11 12 13
2. Carpentry 2.1 Introduction 2.2 Timber 2.3 Marking and measuring tools 2.4 Holding tools 2.5 Planing tools 2.6 Cutting tools 2.7 Drilling and boring tools 2.8 Miscellaneous tools 2.9 Wood joints 2.10 Safe practice Exercises
15 15 16 17 18 28 20 21 22 24 25
3. Welding 3.1 Introduction 3.2 Arc welding 3.3 Welding tools 3.4 Techniques of welding 3.5 Types of joints 3.6 Welding positions 3.7 Advantages & disadvantages of arc welding 3.8 Safe practice Exercises
28 28 30 31 32 33 33 34 35
4. Machine Shop 4.1 Introduction 4.2 Lathe 4.3 Work holding devices 4.4 Measuring tools 4.5 Cutting parameters 4.6 Tool materials 4.7 Tool geometry 4.8 Lathe operations 4.9 Safety precautions
39 39 40 40 41 41 42 42 44
Exercises 45 References 48
Chapter 1 FITTING SHOP
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 component which must be fit accurately with another component on reassembly. This involves a certain amount of hand fitting. The assembly of machine tools, jigs, gauges, etc, involves certain amount of bench work. 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, where as fitting deals which 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 efforts. The operations in the above works consist of filing, chipping, scraping, sawing drilling, and tapping. 1.2 HOLDING TOOLS 1.2.1 Bench vice
The bench vice is a work holding device. It is the most commonly used vice in a fitting shop. The bench vice is shown in Figure 1.1.
Figure 1.1: Bench Vice
It is fixed to the bench with bolts and nuts. The vice body consists of two main parts, fixed jaw
and movable jaw. When the vice handle is turned in a clockwise direction, the sliding jaw forces the work against the fixed jaw. Jaw plates are made of hardened steel. Serrations on the jaws ensure a good grip. Jaw caps made of soft material are used to protect finished surfaces, 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. 1.2.2 V‐block
V‐block is 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 measurement, for measuring operations or for drilling for this the bar is faced longitudinally in the V‐Groove and the screw of V‐clamp is tightened. This grip the rod is firm with its axis parallel to the axis of the v‐groove. 1.2.3 C‐Clamp This is used to hold work against an angle plate or v‐block or any other surface, when gripping is required.
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.
Figure 1.2: V‐block Figure 1.3: C‐clamp 1.3 MARKING AND MEASURING TOOLS 1.3.1 Surface plate The surface plate is machined to fine limits and is used for testing the flatness of the work piece. It is also used for marking out small box and is more precious than the marking table. The degree of the finished 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 and grade. Handles are provided on two opposite sides, to carry it while shifting from one place to another.
Figure 1.4: Surface plate Figure 1.5: Angle plate
1.3.2 Try square It is measuring and marking tool for 900 angle .In practice, it is used for checking the squareness
of many types of small works when extreme accuracy is not required .The blade of the Try square is made of hardened steel and the stock of cast Iron or steel. The size of the Try square is specified by the length of the blade. 1.3.3 Scriber A Scriber is a slender steel tool, used to scribe or mark lines on metal work pieces. It is made of hardened and tempered High Carbon Steel. The Tip of the scriber is generally ground at 12oto 15o . 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.
Figure 1.6: Try square Figure 1.7: Scriber
1.3.4 Odd leg Caliper
This is also called ‘Jenny Caliper’ or Hermaphrodite. This is used for marking parallel liners from a finished edge and also for locating the center of round bars; it has one leg pointed like a divider and the other leg bent like a caliper. It is specified by the length of the leg up to the hinge point.
1.3.5 Divider It is basically similar to the calipers except that its legs are kept straight and pointed at the measuring edge. This is used for marking circles, arcs laying out perpendicular lines, by setting lines. It is made of case hardened mild steel or hardened and tempered low carbon steel. Its size is specified by the length of the leg.
Figure 1.8: Odd leg caliper and divider
1.3.6 Trammel Trammel is used for drawing large circles or arcs.
1.3.7 Punches These are used for making indentations on the scribed lines, to make them visible clearly. These
are made of high carbon steel. A 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 30mm.
Dot punch is used to lightly indent along the layout lines, to locate center of holes and to provide a small center mark for divider point, etc. for this purpose, the punch is ground to a conical point having 60° included angle.
Center punch is similar to the dot punch, except that it is ground to a conical point having 90° included angle. It is used to mark the location of the holes to be drilled.
Figure 1.9: Punches
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 made of Case hardened mild steel or hardened and tempered low carbon steel. While using, but the legs of the caliper are set against the surface of the work, whether inside or outside and the distance between the legs is measured with the help of a scale and the same can be transferred to another desired place. These are specified by the length of the leg. In the case of outside caliper, the legs are bent inwards and in the case of inside caliper, the legs bent outwards.
Figure 1.10: Calipers
1.3.9 Vernier Calipers 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.
Figure 1.11: Vernier caliper
1.3.10 Vernier Height Gauge The Vernier Height gauge clamped with a scriber. It is used for Lay out work and offset scriber is
used when it is required to take measurement from the surface, on which the gauge is standing. The accuracy and working principle of this gauge are the same as those of the vernier calipers. Its size is specified by the maximum height that can be measured by it. It is made of Nickel‐Chromium Steel.
Figure 1.12: Vernier Height gauge
1.4 CUTTING TOOLS 1.4.1 Hack Saw The Hack Saw 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 for centimeter. Hacksaw blades have a number of teeth ranging from 5 to 15 per centimeter (cm). Blades having lesser number of teeth per cm are used for cutting soft materials like aluminum, brass and bronze. Blades having larger number of teeth per centimeter are used for cutting hard materials like steel and cast Iron.
Hacksaw blades are classified as (i) All hard and (ii) flexible type. 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.
Figure 1.13: Hacksaw frame with blade The teeth of the hacksaw blade are staggered, as shown in figure and known as a ‘set of teeth’.
These make slots wider than the blade thickness, preventing the blade from jamming.
Figure 1.14: Set of teeth
Chisels are used for removing surplus metal or for cutting thin sheets. 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 hard cutting edge. Annealing relieves the internal stresses in a metal. The cutting angle of the chisel for general purpose is about 60°.
Figure 1.15: Flat chisel 1.4.3 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. The parallel shank twist drill can be held in an ordinary self – centering drill check. The tapper shank twist drill fits into a corresponding tapered bore provided in the drilling machine spindle.
Figure 1.16: Twist drills 1.4.4 Taps and Tap wrenches
A tap is a hardened and steel tool, used for cutting internal thread in a drill hole. Hand Taps are usually supplied in sets of three in each diameter and thread size. Each set consists of a tapper tap, intermediate tap and plug or bottoming tap. Taps are made of high carbon steel or high speed steel.
Figure 1.17: Taps and tap wrench
1.4.5 Dies and die‐holders
Dies are the cutting tools used for making external thread. Dies are made either solid or split type. They are fixed in a die stock for holding and adjusting the die gap. They are made of Steel or High Carbon Steel.
Figure 1.18: Dies and die holder
1.4.6 Bench Drilling Machine Holes are drilled for fastening parts with rivets, bolts or for producing internal thread. Bench drilling machine is the most versatile machine used in a fitting shop for the purpose. Twist drills, made of tool steel or high speed steel are used with the drilling machine for drilling holes. Following are the stages in drilling work 1. Select the correct size drills, put it into the check and lock it firmly 2. Adjust the speed of the machine to suit the work by changing the belt on the pulleys. Use high speed
for small drills and soft materials and low speed for large diameter drills and hard materials. 3. Layout of the location of the pole and mark it with a center punch. 4. Hold the work firmly in the vice on the machine table and clamp it directly on to the machine table. 5. Put on the power, locate the punch mark and apply slight pressure with the Feed Handle.
6. Once Drilling is commenced at the correct location, apply enough pressure and continue drilling. When drilling steel apply cutting oil at the drilling point.
7. Release the pressure slightly, when the drill point pierces the lower surface of the metal. This prevents the drill catching and damaging the work or drill.
8. On completion of drilling retrace the drill out of the work and put‐off the power supply.
Figure 1.19: Bench drill
1.5 FINISHING TOOLS 1.5.1 Reamers
Reaming is an operation of sizing and finishing a drilled hole, with the help of a cutting tool called reamer having a number of cutting edges. For this, a hole is first drilled, the size of which is slightly smaller than the finished size and then a hand reamer or machine reamer is used for finishing the hole to the correct size.
Hand Reamer is made of High Carbon Steel and has left‐hand spiral flutes so that, it is prevented from screwing into the whole during operation. The Shank end of the reamer is made straight so that it can be held in a tap wrench. It is operated by hand, with a tap wrench fitted on the square end of the reamer and with the work piece held in the vice. The body of the reamer is given a slight tapper at its working end, for its easy entry into the whole during operation, it is rotated only in clock wise direction and also while removing it from the whole.
Figure 1.20: Reamers
Filing is one of the methods of removing small amounts of material from the surface of a metal part. A file is hardened steel too, having small 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. The figure shows various parts of a hand file. The hand file is parallel in width and tapering 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 a safe edge.
Figure 1.21: Parts of a hand file
Files are classified according to their shape, cutting teeth and pitch or grade of the teeth. The
figure shows the various types of files based on their shape.
Figure 1.22: Single and double cut files
Figure 1.23: Types of files
1.6 MISCELLANEOUS TOOLS 1.6.1 File card
It is a metal brush, used for cleaning the files, to free them from filings, clogged in‐between the teeth.
Figure 1.24: File card
1.6.2 Spirit level
It is used to check the leveling of machines.
1.6.3 Ball‐ Peen Hammer Ball‐ Peen 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.
Figure 1.25: Ball peen hammer
1.6.4 Cross‐Peen Hammer
It is similar to ball peen hammer, except the shape of the peen. This is used for chipping, riveting, bending and stretching metals and hammering inside the curves and shoulders. 1.6.5 Straight‐Peen Hammer
This is similar to cross peen hammer, but its peen is in‐line with the hammer handle. It is used for swaging, riveting in restricted places and stretching metals.
Figure 1.26: Cross peen hammer Figure 1.27: Straight peen hammer 1.6.6 Screw driver A screw driver is designed to turn screws. 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. A star screw driver is specially designed to fit the head of star screws. The end of the blade is fluted instead of flattened. The screw driver is specified by the length of the metal part from handle to the tip.
Figure 1.28: Screw drivers 1.6.7 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. They are named according to the application. The size of the spanner denotes the size of the bolt on which it can work.
Figure 1.28: Spanners 1.7 SAFE PRACTICE
The following are some of the safe and correct work practices in bench work and fitting shop, with respect to the tools used 1. Keep hands and tools wiped clean and free of dirt, oil and grease. Dry tools are safer to use than slippery tools. 2. Do not carry sharp tools on pockets. 3. Wear leather shoes and not sandals. 4. Don’t wear loose clothes. 5. Do no keep working tools at the edge of the table. 6. Position the work piece such that the cut to be made is close to the vice. This practice prevents springing, saw breakage and personal injury. 7. Apply force only on the forward (cutting) stroke and relieve the force on the return stroke while sawing and filing. 8. Do not hold the work piece in hand while cutting. 9. Use the file with a properly fitted tight handle. 10. After filing, remove the burrs from the edges of the work, to prevent cuts to the fingers. 11. Do not use vice as an anvil.
12. While sawing, keep the blade straight; otherwise it will break 13. Do not use a file without handle. 14. Clean the vice after use. 1.8 MODELS FOR PRACTICE
Prepare the models, as per the dimensions and fits shown in below.
Figure 1.30: Dovetail Fitting Figure 1.31: V‐fitting
Figure 1.32: Half‐round fitting Figure 1.33: Cross fitting
Figure 1.34: Drilling and Tapping
ME101 Workshop Practice I Fitting
Exercise 1 Square Filing
Aim To file the given two Mild Steel pieces in to a square shape of 48 mm side as shown in Figure F‐E1 Tools required Bench vice, set of Files, Steel rule, Try‐square, Vernier caliper, Vernier height gauge, Ball‐peen hammer, Scriber, Dot punch, Surface plate, Angle plate and Anvil. Sequence of operations 1. The dimensions of the given piece are checked with the steel rule. 2. The job is fixed rigidly in a bench vice and the two adjacent sides are filed, using the rough flat file
first and then the smooth flat file such that, the two sides are at right angle. 3. The right angle of the two adjacent sides is checked with the try‐square. 4. Chalk is then applied on the surface of the work piece. 5. The given dimensions are marked by scribing two lines, with reference to the above two datum sides
by using Vernier height gauge, Angle plate and Surface plate. 6. Using the dot punch, dots are punched along the above scribed lines. 7. The two sides are then filed, by fitting the job in the bench vice; followed by checking the flatness of
the surfaces. As the material removal through filing is relatively less, filing is done instead of sawing. Result The square pieces of 48 mm side is thus obtained by filing, as discussed above.
a. Raw material b. Finished job
Figure F‐ E1: Square filing
ME101 Workshop Practice I Fitting
Exercise 2 V‐Fitting
Aim To make V‐ fit from the given two MS plates and drilling and Tapping as shown in Figure F‐E2 Tools required Bench vice, set of Files, Try‐square, Scriber, Steel rule, Ball‐peen hammer, Dot punch, Hacksaw, Vernier caliper, Surface plate, Angle plate, Vernier height gauge, 5mm drill bit, 3mm drill bit, M6 tap set with wrench, Anvil and Drilling machine. Sequence of operations 1. The burrs in the pieces are removed and the dimensions are checked with steel rule. 2. Make both pieces surface levels and right angles by fixing in the Vice, use Files for removing material
to get level. 3. With the help of Try square check the right angles and surface levels. 4. Using Surface plate and Angle plate mark the given two metal pieces as per drawing with Vernier
height gauge. 5. Punch the scribed lines with dot punch and hammer keeping on the Anvil. Punch to punch give 5
mm gap. 6. Cut excess material wherever necessary with Hacksaw frame with blade, Drill bits and Taps. 7. The corners and flat surfaces are filed by using square/flat and triangular file to get the sharp
corners. 8. Dimensions are checked by vernier caliper and match the two pieces. Any defect noticed, are
rectified by filing with a smooth file. 9. Care is taken to see that the punched dots are not crossed, which is indicated by the half of the
punch dots left on the pieces. Result The required V‐ fitting is thus obtained, by following the stages, as described above.
Figure F‐ E2: V‐Fitting
Chapter 2 CARPENTRY
2.1 INTRODUCTION Carpentry may be defined as the process of making wooden components. It starts from a
marketable form of wood and ends with finished products. It6 deals with the building work, furniture, cabinet making. Etc. joinery, i.e., preparation of joints is one of the important operations in all wood‐ works. It deals with the specific work of carpenter like making different types of joints to form a finished product. 2.2 TIMBER
Timber is the name given to the wood obtained from well grown trees. The trees are cut, sawn into various sizes to suit building purposes.
The word, ‘grain’, as applied to wood, refers to the appearance or pattern of the wood on the cut surfaces. The grain of the wood is a fibrous structure and to make it strong, the timber must be so cut, that the grains run parallel to the length. 2.2.1 Timber sizes
Timber sold in the market is in various sizes and shapes. The following are the common shapes and sizes. a. Log ‐ The trunk of the tree which is free from branches. b. Balk ‐ The log, sawn to have roughly square cross section. c. Post ‐ A timber piece, round or square in cross section, having its diameter or side
from 175 to 300mm. d. Plank ‐ A sawn timber piece, with more than 275 mm in width, 50 to 150 mm in
thickness and 2.5 to 6.5 meters in length. e. Board ‐ A sawn timber piece, below 175 mm in width and 30 to 50 mm in thickness. f. Reapers ‐ Sawn timber pieces of assorted and non‐standard sizes, which do not confirm
to the above shapes and sizes.
2.2.2 Classification of Timber Wood suitable for construction and other engineering purposes is called timber. Woods in
general are divided into two broad categories: Soft woods and Hard woods. Soft woods are obtained from conifers, kair, deodar, chir, walnut and seemal. Woods obtained
from teak, sal, oak, shisham, beach, ash mango, neem and babul are known as hard wood, but it is highly durable.
Another classification of woods is based on the name of the trees like teak, babul, shisham, neem, kair, chir, etc.
2.2.3 Seasoning of Wood
A newly felled tree contains considerable moisture content. If this is not removed, the timber is likely to wrap, shrink, crack or decay. Seasoning is the art of extracting the moisture content under controlled conditions, at a uniform rate, from all the parts of the timber. Only seasoned wood should be used for all carpentry works. Seasoning makes the wood resilient and lighter. Further, it ensures that the wood will not distort after it is made into an object.
2.2.4 Characteristics of Good Timber The good timber must possess the following characteristics a. It should have minimum moisture content, i.e., the timber should be well seasoned. b. The grains of wood should be straight and long. c. It must retain its straightness after seasoning. d. It should produce near metallic sound on hammering. e. It should be free from knots or cracks. f. It should be of uniform color, throughout the part of the wood. g. It should respond well to the finishing and polishing operations. h. During driving the nails and screw, it should not split easily.
2.3 MARKING AND MEASURING TOOLS Accurate marking and measurement is very essential in carpentry work, to produce parts to
exact size. To transfer dimensions onto the work; the following are the marking and measuring tools that are required in a carpentry shop.
2.3.1 Steel rule and Steel tape
Steel rule is a simple measuring instrument consisting of a long, thin metal strip with a marked scale of unit divisions. It is an important tool for linear measurement. Steel tape is used for large measurements, such as marking on boards and checking the overall dimensions of the work.
Figure 2.1: Steel rule and Steel tape
2.3.2 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 stock (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 3 mm and the end are 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.
a. Marking gauge b. Mortise gauge Figure 2.2: Marking gauges 2.3.3 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. Its size varies from 150 to 300 mm, according to the length of the blade. It is less accurate when compared to the try‐square used in the fitting shop.
Figure 2.3: Try square
2.3.4 Compass and divider
Compass and divider, are used for marking arcs and circles on the planed surfaces of the wood.
2.3.5 Scriber or marking knife It is used for marking on timber. It is made of steel having one end pointed and the other end
formed into a sharp cutting edge. 2.3.6 Bevel
It is used for laying‐out and checking angles. The blade of the bevel is adjustable and may be held in place by a thumb screw. After it is set to the desired angle, it can be used in much the same way as a try‐square. A good way to set it to the required angle is to mark the angle on a surface and then adjust the blade to fit the angle.
Figure 2.4: Compass and Divider Figure 2.5: Scriber and Bevel 2.4 HOLDING TOOLS 2.4.1 Carpenter's vice
Figure 2.6 shows the carpenter's 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 is movable by means of a screw and a handle. The Carpenter's vice jaws are lined with hard wooden' faces.
Figure 2.6: Carpenters vice Figure 2.7: C‐clamp 2.4.2 C‐clamp
Figure 2.7 shows a C‐clamp, which is used for holding small works. 2.4.3 Bar cramp
Figure 2.8 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.
Figure 2.8: bar cramp
2.5 PLANING TOOLS Planing is the operation used to produce flat surfaces on wood. A plane is a hand tool used for
this purpose. The cutting blade used in a plane is very similar to a chisel. The blade of a plane is fitted in a wooden or metallic block, at an angle.
2.5.1 Jack plane
It is the most commonly used general purpose plane. It is about 35 cm 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.
2.5.2 Smoothing plane
It is used for finishing work and hence, the blade should have a straight cutting edge. It is about 20 to 25 cm long. Being short, it can follow even the slight depressions in the stock, better than the jack plane. It is used after using the jack plane.
2.5.3 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.
2.5.4 Plough plane
It is used to cut grooves, which are used to fix panels in a door. Figure 2.9 shows the various types of planes mentioned above.
Figure 2.9: Types of planes 2.6 CUTTING TOOLS 2.6.1 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. 184.108.40.206 Cross‐cut or hand saw
It is used to cut across the grains of the stock. The teeth are so set that the saw kerf will be wider than the blade thickness. This allows the blade to move freely in the cut, without sticking.
220.127.116.11 Rip saw It is used for cutting the stock along the grains. The cutting edge of this saw makes a steeper
angle, i.e., about 60° whereas that of crosscut saw makes an angle of 45° with the surface of the stock.
18.104.22.168 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 this saw is very thin and so it is stiffened with a thick back steel strip. Hence, this is sometimes called as back‐saw. In this, the teeth are shaped like those of cross‐cut saw.
22.214.171.124 Compass saw
It has a narrow, longer and stronger tapering blade, which is used for heavy works (Fig. 1.13). It is mostly used in radius cutting. The blade of this saw is fitted with an open type wooden handle.
Figure 2.10: Types of saws 2.6.2 Chisels
Chisels are used for cutting and shaping wood accurately. Wood chisels are made in various blade widths, ranging from 3 to 50 mm. They are also made in different blade lengths. Most of the wood chisels are made into tang type, having a steel shank which fits inside the handle. These are made of forged steel or tool steel blades.
Figure 2.11: Parts of chisel
126.96.36.199 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 Figure 2.12 a. 188.8.131.52 Dovetail chisel It has a blade with a beveled back, as shown in Figure, due to which it can enter sharp comers for finishing, as in dovetail joints. 184.108.40.206 Mortise chisel It is used for cutting mortises and chipping inside holes, etc. The cross‐section of the mortise chisel is proportioned to withstand heavy blows during mortising. Further, the cross‐section is made stronger near the shank.
a. Firmer b. Dovetail c. Mortise
Figure 2.12: Types of chisels
2.7 DRILLING AND BORING TOOLS 2.7.1 Carpenter’s brace
It is used for rotating auger bits, twist drills, etc., to produce holes in wood. In some designs, braces are made with ratchet device. With this, holes may be made in a corner where complete revolution of the handle cannot be made. The size of a brace is determined by its sweep.
2.7.2 Auger bit
It is the most common tool used for making holes in wood. During drilling, the lead screw of the bit guides into the wood, necessitating only moderate pressure on the brace. The helical flutes on the surface carry the chips to the outer surface.
2.7.3 Hand drill
Carpenter's brace is used to make relatively large size holes; whereas 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.
2.7.4 Gimlet It has cutting edges like a twist drill. It is used for drilling large diameter holes with the hand
Figure 2.13: Drilling tools
2.8 MISCELLANEOUS TOOLS 2.8.1 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. 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.
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.
2.8.3 Claw hammer
It has a striking flat face at one end and the claw at the other, as shown in figure. 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 0.75 kg.
2.8.4 Screw driver
It is used for driving screws into wood or unscrewing them. The screw driver of a carpenter is different from the other common types, as shown in figure. 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. 2.8.5 Wood rasp file
It is a finishing tool used to make the wood surface smooth, remove sharp edges, finish fillets and other interior surfaces. Sharp cutting teeth are provided on its surface for the purpose. This file is exclusively used in wood work. 2.8.6 Bradawl
It is a hand operated tool, used to bore small holes for starting a screw or large nail.
a. Mallet b. Pincer c. Claw hammer d. Bradawl
e. Wood rasp file f. Screw driver
Figure 2.14: Miscellaneous tools
2.9 WOOD JOINTS There are many kinds of joints used to connect wood stock. Each joint has a definite use and
requires lay in‐out, cutting them together. The strength of the joint depends upon amount of contact area. If a particular joint does not have much contact area, then it must be reinforced with nails, screws or dowels. The figure 2.15 shows some commonly used wood joints.
a. Butt b. Dowell c. Dado d. Rabbet
e. Lap f. Mortise and tenon g. Miter
Figure 2.15: Common wood joints
2.9.1 Lap joints In lap joints, an equal amount of wood is removed from each piece, as shown in figure 2.16. Lap
joints are easy to layout, using a try‐square and a marking gauge. Follow the procedure suggested for sawing and removing the waste stock. If the joint is found to be too tight, it is better to reduce the width of the mating piece, instead of trimming the shoulder of the joint. This type of joint is used for small boxes to large pieces of furniture.