Download Workshop Practice-Mechanical Workshop-Instruction Mannual and more Exercises Mechanical Engineering in PDF only on Docsity! Indian Institute of Technology Hyderabad ME 101: WORKSHOP PRACTICE I Pushing frontiers… Docsity.com 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 P. Raju 25 April 2009 Docsity.com 2 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. Docsity.com 3 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. Docsity.com 4 Figure 1.9: Punches 1.3.8 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 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 Docsity.com 7 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. Docsity.com 8 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 1.5.2 Files 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. Docsity.com Face
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\e Hard temper
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.
Double cut tite
Half-round tile
OE SS
Square file
Qe
Round file
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Triangular file
61 Ca =>
Needle file
Figure 1.23: Types of files
9 Docsity.com
12 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 Docsity.com 13 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 Docsity.com 14 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 Docsity.com 17 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 Docsity.com 18 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. 2.6.1.1 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. Docsity.com 19 2.6.1.2 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. 2.6.1.3 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. 2.6.1.4 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 Docsity.com 22 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. Docsity.com 23 Figure 2.16: Lap joints 2.9.2 Mortise and Tenon Joints It is used in the construction of quality furniture. It results in a strong joint and requires considerable skill to make it. The following are the stages involved in the work. a. Mark the mortise and tenon layouts. b. Cut the mortise first by drilling series of holes within the layout line, chiseling out the waste stock and trimming the corners and sides. c. Prepare the tenon by cutting and chiseling. d. Check the tenon size against the mortise that has been prepared and adjust it if necessary. Figure 2.17: Mortise and Tenon joints 2.9.3 Bridle joint This is the reverse of mortise and tenon joint in form. The marking‐out of the joint is the same as for mortise and tenon joint. This joint is used where the members are of square or near square section and unsuitable for mortise and tenon joint. Figure 2.18: Bridle joint Docsity.com 24 2.10 SAFE PRACTICE The following are some of the safe and correct work practices in carpentry shop, with respect to the tools used 1. Tools that are not being used should always be kept at their proper places. 2. Make sure that your hands are not in front of sharp edged tools while you are using them. 3. Use only sharp tools. A dull tool requires excessive pressure, causing the tool to slip. 4. Wooden pieces with nails, should never be allowed to remain on the floor. 5. Be careful when you are using your thumb as a guide in cross‐cutting and ripping. 6. Test the sharpness of the cutting edge of chisel on wood or paper, but not on your hand. 7. Never chisel towards any part of the body. 8. Do not use chisels where nails are present. Do not use chisel as a screw driver. 9. Do not use a saw with a loose handle. 10. Always use triangular file for sharpening the teeth. 11. Do not use a saw on metallic substances. 12. Do not use mallet to strike nails. 13. Do not use plane at the places, where a nail is driven in the wood. Docsity.com 27 ME101 Workshop Practice I Carpentry Exercise 3 Mortise and Tenon joint Aim To make a mortise and tenon joint as shown in Fig. 1.34b, from the given reaper of size 50 x 35 x 250 mm. Tools required Carpenter's vice, steel rule, jack plane, try‐square, marking gauge, 25 111m firmer chisel, 6 mm mortise chisel, cross‐cut saw, tenon saw, scriber and mallet. Sequence of operations 1. The given reaper is checked to ensure its correct size. 2. The reaper is firmly clamped in the carpenter's vice and one of its faces are planed by the jack plane and checked for straightness. 3. The adjacent face is then planed and the faces are checked for squareness with the try‐square. 4. Marking gauge is set and lines are drawn at 30 and 45 mm, to mark the thickness and width of the model respectively. 5. The excess material is first chiseled out with the firmer chisel and then planed to correct size. 6. The mating dimensions of the parts X and Yare then marked using the scale and marking gauge. 7. Using the cross‐cut saw, the portions to be removed in part Y (tenon) is cut, followed by chiseling. 8. The material to be removed in part X (mortise) is carried out by using the mortise and firmer chisels. 9. The parts X and Yare separated by cross‐cutting with the tenon saw 10. The ends of both the parts are chiseled to exact lengths. 11. Finish chiseling is done wherever 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 sequence of operations. Figure C‐E 3: Mortise and Tenon joint Docsity.com 28 Chapter 3 WELDING 3.1 INTRODUCTION Welding is the process of joining similar metals by the application of heat, with or without application of pressure or filler metal, in such a way that the joint is equivalent in composition and characteristics of the metals joined. In the beginning, welding was mainly used for repairing all kinds of worn or damaged parts. Now, it is extensively used in manufacturing industry, construction industry (construction of ships, tanks, locomotives and automobiles) and maintenance work, replacing riveting and bolting, to a greater extent. The various welding processes are: 1. Electric arc welding, 2. Gas welding 3. Thermal welding 4. Electrical Resistance welding and 5. Friction welding However, only electric arc welding process is discussed in the subject point of view. 3.2 ELECTRIC ARC WELDING Arc welding is the welding process, in which heat is generated by an electric arc struck between an electrode and the work piece. Electric arc is luminous electrical discharge between two electrodes through ionized gas. Figure 3.1: Arc welding set up. Any arc welding method is based on an electric circuit consisting of the following parts: a. Power supply (AC or DC); b. Welding electrode; c. Work piece; d. Welding leads (electric cables) connecting the electrode and work piece to the power supply. Electric arc between the electrode and work piece closes the electric circuit. The arc temperature may reach 10000°F (5500°C), which is sufficient for fusion the work piece edges and joining them. When a long joint is required the arc is moved along the joint line. The front edge of the weld pool melts the welded surfaces when the rear edge of the weld pool solidifies forming the joint. Transformers, motor generators and rectifiers’ sets are used as arc welding machines. These machines supply high electric currents at low voltage and an electrode is used to produce the necessary arc. The electrode serves as the filler rod and the arc melts the surface so that, the metals to be joined are actually fixed together. Sizes of welding machines are rated according to their approximate amperage capacity at 60% duty cycle, such as 150,200,250,300,400,500 and 600 amperes. This amperage is the rated current output at the working terminal. Docsity.com 29 3.2.1 Transformers The transformers type of welding machine produces A.C current and is considered to be the least expensive. It takes power directly from power supply line and transforms it to the voltage required for welding. Transformers are available in single phase and three phases in the market. 3.2.2 Motor generators These are D.C generators sets, in which electric motor and alternator are mounted on the same shaft to produce D.C power as pert the requirement for welding. These are designed to produce D.C current in either straight or reversed polarity. The polarity selected for welding depends upon the kind of electrode used and the material to be welded. 3.2.3 Rectifiers These are essentially transformers, containing an electrical device which changes A.C into D.C by virtue of which the operator can use both types of power (A.C or D.C, but only one at a time).In addition to the welding machine, certain accessories are needed for carrying out the welding work. 3.2.4 Welding cables Two welding cables are required, one from machine to the electrode holder and the other, from the machine to the ground clamp. Flexible cables are usually preferred because of the case of using and coiling the cables. Cables are specified by their current carrying capacity, say 300 A, 400 A, etc. 3.2.5 Electrodes Filler rods are used in arc welding are called electrodes. These are made of metallic wire called core wire, having approximately the same composition as the metal to be welded. These are coated uniformly with a protective coating called flux. While fluxing an electrode; about 20mm of length is left at one end for holding it with the electrode holder. It helps in transmitting full current from electrode holder to the front end of the electrode coating. Flux acts as an insulator of electricity. Figure.4 shows the various parts of an electrode. Figure 3.2: Parts of an electrode In general, electrodes are classified into five main groups; mild steel, carbon steel, special alloy steel, cast iron and non‐ferrous. The greatest range of arc welding is done with electrodes in the mild steel group. Various constituents like titanium oxide, potassium oxide, cellulose, iron or manganese, Ferro‐ silicates, carbonates, gums, clays, asbestos, etc., are used as coatings on electrodes. While welding, the coating or flux vaporizes and provides a gaseous shield to prevent atmospheric attack. The size of electrode is measured and designated by the diameter of the core wire in SWG and length, apart from the brand and code names; indicating the purpose for which there are most suitable. Electrodes may be classified on the basis of thickness of the coated flux. As 1. Dust coated or light coated 2. Semi or medium coated and 3. Heavily coated or shielded Electrodes are also classified on the basis of materials, as 1. Metallic and 2. Non‐metallic or carbon Metallic arc electrodes are further sub‐divided into 1. Ferrous metal arc electrode (mild steel, low/medium/high carbon steel, cast iron, stainless steel, etc ) 2. Non‐ferrous metal arc electrodes (copper, brass, bronze, aluminum, etc). In case of non‐metallic arc electrodes, mainly carbon and graphite are used to make the electrodes. Docsity.com 32 momentarily broken arc quickly. If the electrode sticks to the work, quickly bend it back and forth, pulling at the same time. Make sure to keep the shield in front of the face, when the electrode is freed from sticking. d) As soon as the arc is struck, move the electrode along, slowly from left to right, keeping at 15º to 25º from vertical and in the direction of welding. Strike and withdraw Touch and withdraw Figure 3.9: striking an arc 3.4.3 Weaving A steady, uniform motion of the electrode produces a satisfactory bead. However, a slight weaving or oscillating motion is preferred, as this keeps the metal molten a little longer and allows the gas to escape, bringing the slag to the surface. Weaving also produces a wider bead with better penetration. 3.5 TYPES OF JOINTS Welds are made at the junction of the various pieces that make up the weldment. The junctions of parts, or joints, are defined as the location where two or more numbers are to be joined. Parts being joined to produce the weldment may be in the form of rolled plate, sheet, pipes, castings, forgings, or billets. The five basic types of joints are listed below. Figure 3.10: Types of welding joints. A butt joint is used to join two members aligned in the same plane (fig. 3.10, view A). This joint is frequently used in plate, sheet metal, and pipe work. A joint of this type may be either square or grooved. Docsity.com 33 Corner and tee joints are used to join two members located at right angles to each other (fig. 3.10, views B and C). In cross section, the corner joint forms an L‐shape, and the tee joint has the shape of the letter T. Various joint designs of both types have uses in many types of metal structures. A lap joint, as the name implies, is made by lapping one piece of metal over another (fig. 3.10, view D). This is one of the strongest types of joints available; however, for maximum joint efficiency, you should overlap the metals a minimum of three times the thickness of the thinnest member you are joining. Lap joints are commonly used with torch brazing and spot welding applications. An edge joint is used to join the edges of two or more members lying in the same plane. In most cases, one of the members is flanged, as shown in figure 3.10, view E. While this type of joint has some applications in plate work, it is more frequently used in sheet metal work. An edge joint should only be used for joining metals 1/4 inch or less in thickness that are not subjected to heavy loads. 3.6 WELDING POSITIONS Depending upon the location of the welding joints, appropriate position of the electrode and hand movement is selected. The figure shows different welding positions. Figure 3.11: Welding positions 3.6.1 Flat position welding In this position, the welding is performed from the upper side of the joint, and the face of the weld is approximately horizontal. Flat welding is the preferred term; however, the same position is sometimes called down hand. 3.6.2 Horizontal position welding In this position, welding is performed on the upper side of an approximately horizontal surface and against an approximately vertical surface. 3.6.3 Vertical position welding In this position, the axis of the weld is approximately vertical as shown in figure. 3.6.4 Overhead position welding In this welding position, the welding is performed from the underside of a joint. 3.7 ADVANTAGES & DISADVANTAGES OF ARC WELDING Advantages 1. Welding process is simple. 2. Equipment is portable and the cost is fairly low. 3. All the engineering metals can be welded because of the availability of a wide variety of electrodes. Disadvantages 1. Mechanized welding is not possible because of limited length of the electrode. 2. Number of electrodes may have to be used while welding long joints. 3. A defect (slag inclusion or insufficient penetration) may occur at the place where welding is restarted with a fresh electrode. Docsity.com 34 3.8 SAFE PRACTICE Always weld in a well ventilated place. Fumes given off from welding are unpleasant and in some cases may be injurious, particularly from galvanized or zinc coated parts. 1. Do not weld around combustible or inflammable materials, where sparks may cause a fire. 2. Never weld containers, which have been used for storing gasoline, oil or similar materials, without first having them thoroughly cleaned. 3. Check the welding machine to make sure that it is properly grounded and that all leads properly insulated. 4. Never look at the arc with the naked eye. The arc can burn your eyes severely. Always use a face shield while welding. 5. Prevent welding cables from coming in contact with hot metal, water, oil, or grease. Avoid dragging the cables around sharp corners. 6. Ensure proper insulation of the cables and check for openings. 7. Always wear the safety hand gloves, apron and leather shoes. 8. Always turn off the machine when leaving the work. 9. Apply eye drops after welding is over for the day, to relieve the strain on the eyes. 10. While welding, stand on dry footing and keep the body insulated from the electrode, any other parts of the electrode holder and the work. Docsity.com 37 ME101 Workshop Practice I Carpentry Exercise 3 Corner joint Aim To make a corner joint, using the given mild steel pieces and by arc welding. Material used Two mild steel pieces of 100X40X6 mm. Tools and equipment used Arc welding machine, Mild steel electrodes, Electrode holder, Ground clamp, flat nose Tong, Face shield, Apron, Hand gloves, Metallic work Table, Bench vice, Rough flat file, Try square, Steel rule, Wire brush, Ball peen hammer, Chipping hammer, Chisel and Grinding machine. Sketch Figure 3.14: Corner joint Operations to be carried out 1. Cleaning the work pieces 2. tack welding 3. full welding 4. cooling 5. chipping 6. finishing Procedure 1. Take the two mild steel pieces of given dimensions and clean the surfaces thoroughly from rust, dust particles, oil and grease. 2. Remove the sharp corners and burrs by filing or grinding and prepare the work pieces. 3. The work pieces are positioned on the welding table such that, the L shape is formed. 4. The electrode is fitted in to the electrode holder and the welding current is set to a proper value. 5. The ground clamp is fastened to the welding table. 6. Wearing the apron, hand gloves, using the face shield and holding the pieces the arc is struck and the work pieces are tack‐welded at both the ends. 7. The alignment of the corner joint is checked and the tack‐welded pieces are reset, if required. 8. Welding is then carried out throughout the length. 9. Remove the slag, spatters and clean the joint. Result The Corner joint is thus made, using the tools and equipment as mentioned above. Docsity.com 38 ME101 Workshop Practice I Carpentry Exercise 4 T‐ joint Aim To make a T‐ joint, using the given mild steel pieces and by arc welding. Material used Two mild steel pieces of 100X40X6 mm. Tools and equipment used Arc welding machine, Mild steel electrodes, Electrode holder, Ground clamp, flat nose Tong, Face shield, Apron, Hand gloves, Metallic work Table, Bench vice, Rough flat file, Try square, Steel rule, Wire brush, Ball peen hammer, Chipping hammer, Chisel and Grinding machine. Sketch Figure 3.15: T‐joint Operations to be carried out 1. Cleaning the work pieces 2. tack welding 3. full welding 4. cooling 5. chipping 6. finishing Procedure 1. Take the two mild steel pieces of given dimensions and clean the surfaces thoroughly from rust, dust particles, oil and grease. 2. Remove the sharp corners and burrs by filing or grinding and prepare the work pieces. 3. The work pieces are positioned on the welding table such that, the T shape is formed. 4. The electrode is fitted in to the electrode holder and the welding current is set to a proper value. 5. The ground clamp is fastened to the welding table. 6. Wearing the apron, hand gloves, using the face shield and holding the pieces the arc is struck and the work pieces are tack‐welded at both the ends. 7. The alignment of the T joint is checked and the tack‐welded pieces are reset, if required. 8. Welding is then carried out throughout the length of the T joint as shown in the figure. 9. Remove the slag, spatters and clean the joint. Result The Tee joint is thus made, using the tools and equipment as mentioned above. Docsity.com 39 Chapter 4 MACHINE SHOP 4.1 INTRODUCTION In a machine shop, metals are cut to shape on different machine tools. A lathe is used to cut and shape the metal by revolving the work against a cutting tool. The work is clamped either in a chuck, fitted on to the lathe spindle or in‐between the centers. The cutting tool is fixed in a tool post, mounted on a movable carriage that is positioned on the lathe bed. The cutting tool can be fed on to the work, either lengthwise or cross‐wise. While turning, the chuck rotates in counter‐clockwise direction, when viewed from the tail stock end. 4.2 PRINCIPAL PARTS OF A LATHE Figure 4.1 shows a center lathe, indicating the main parts. The name is due to the fact that work pieces are held by the centers. Figure 4.1: Parts of a center lathe 4.2.1 Bed It is an essential part of a lathe, which must be strong and rigid. It carries all parts of the machine and resists the cutting forces. The carriage and the tail stock move along the guide ways provided on the bed. It is usually made of cast iron. 4.2.2 Head stock It contains either a cone pulley or gearings to provide the necessary range of speeds and feeds. It contains the main spindle, to which the work is held and rotated. 4.2.3 Tail stock It is used to support the right hand end of a long work piece. It may be clamped in any position along the lathe bed. The tail stock spindle has an internal Morse taper to receive the dead center that supports the work. Drills, reamers, taps may also be fitted into the spindle, for performing operations such as drilling, reaming and tapping. 4.2.4 Carriage or Saddle It is used to control the movement of the cutting tool. The carriage assembly consists of the longitudinal slide, cross slide and the compound slide and apron. The cross slide moves across the length of the bed and perpendicular to the axis of the spindle. This movement is used for facing and to provide the necessary depth of cut while turning. The apron, which is bolted to the saddle, is on the front of the lathe and contains the longitudinal and cross slide controls. 4.2.5 Compound Rest It supports the tool post. By swiveling the compound rest on the cross slide, short tapers may be turned to any desired angles. Docsity.com 42 tools are 18 percent tungsten, 4 percent chromium and 1 percent vanadium.5 to 10 percent cobalt is also added to improve the heat resisting properties of the tool. Carbide tipped tools fixed in tool holders, are mostly used in production shops. 4.7 TOOL GEOMETRY A single point cutting tool used on lathe may be considered as a simple wedge. Figure 4.8 shows the common turning tools used for different operations. Figure 6.9 shows the basic angles of a simple turning tool. Figure 4.8: Common turning tools Figure 4.9: Tool geometry 4.8 LATHE OPERATIONS 4.8.1 Turning Cylindrical shapes, both external and internal, are produced by turning operation. Turning is the process in which the material is removed by a traversing cutting tool, from the surface of a rotating work piece. The operation used for machining internal surfaces is often called the boring operation in which a hole previously drilled is enlarged. For turning long work, first it should be faced and center drilled at one end and then supported by means of the tail‐stock centre. 4.8.2 Boring Boring is enlarging a hole and is used when correct size drill is not available. However, it should be noted that boring cannot make a hole. 4.8.3 Facing Facing is a machining operation, performed to make the end surface of the work piece, flat and perpendicular to the axis of rotation. For this, the work piece may be held in a chuck and rotated about the lathe axis. A facing tool is fed perpendicular to the axis of the lathe. The tool is slightly inclined towards the end of the work piece. 4.8.4 Taper Turning A taper is defined as the uniform change in the diameter of a work piece, measured along its length. It is expressed as a ratio of the difference in diameters to the length. It is also expressed in degrees of half the included (taper) angle. Taper turning refers to the production of a conical surface, on the work piece on a lathe. Short steep tapers may be cut on a lathe by swiveling the compound rest to the required angle. Here, the cutting tool is fed by means of the compound slide feed handle. The work piece is rotated in a chuck or face plate or between centers. Docsity.com 43 4.8.5 Drilling Holes that are axially located in cylindrical parts are produced by drilling operation, using a twist drill. For this, the work piece is rotated in a chuck or face plate. The tail stock spindle has a standard taper. The drill bit is fitted into the tail stock spindle directly or through drill chuck. The tail stock is then moved over the bed and clamped on it near the work. When the job rotates, the drill bit is fed into the work by turning the tail stock hand wheel. 4.8.6 Knurling It is the process of embossing a diamond shaped regular pattern on the surface of a work piece using a special knurling tool. This tool consists of a set of hardened steel rollers in a holder with the teeth cut on their surface in a definite pattern. The tool is held rigidly on the tool post and the rollers are pressed against the revolving work piece to squeeze the metal against the multiple cutting edges. The purpose of knurling is to provide an effective gripping surface on a work piece to prevent it from slipping when operated by hand. 4.8.7 Chamfering It is the operation of beveling the extreme end of a work piece. Chamfer is provided for better look, to enable nut to pass freely on threaded work piece, to remove burrs and protect the end of the work piece from being damaged. 4.8.8 Threading Threading is nothing but cutting helical groove on a work piece. Threads may be cut either on the internal or external cylindrical surfaces. A specially shaped cutting tool, known as thread cutting tool, is used for this purpose. Thread cutting in a lathe is performed by traversing the cutting tool at a definite rate, in proportion to the rate at which the work revolves. Figure 4.10: Operations of Lathe Docsity.com 44 4.9 SAFETY PRECAUTIONS 1. Always wear eye protection ‐ preferably industrial quality safety glasses with side‐shields. The lathe can throw off sharp, hot metal chips at considerable speed as well as spin off spirals of metal that can be quite hazardous. Don't take chances with your eyes. 2. Wear short sleeve shirts, loose sleeves can catch on rotating work and quickly pull your hand or arm into harm's way. 3. Wear shoes ‐ preferably leather work shoes ‐ to protect your feet from sharp metal chips on the shop floor and from tools and chunks of metal that may get dropped. 4. Remove wrist watches, necklaces, chains and other jewelry. Tie back long hair so it can't get caught in the rotating work. Think about what happens to your face if your hair gets entangled. 5. Always double check to make sure your work is securely clamped in the chuck or between centers before starting the lathe. Start the lathe at low speed and increase the speed gradually. 6. Get in the habit of removing the chuck key immediately after use. Some users recommend never removing your hand from the chuck key when it is in the chuck. The chuck key can be a lethal projectile if the lathe is started with the chuck key in the chuck. 7. Keep your fingers clear of the rotating work and cutting tools. This sounds obvious, but I am often tempted to break away metal spirals as they form at the cutting tool. 8. Avoid reaching over the spinning chuck. For filing operations, hold the tang end of the file in your left hand so that your hand and arm are not above the spinning chuck. 9. Never use a file with a bare tang ‐ the tang could be forced back into your wrist or palm. Docsity.com 47 ME101 Workshop Practice I Machine shop Exercise 3 Shoulder turning Aim To obtain required diameters on a cylindrical work piece with the given dimensions. Tools & Equipment Lathe machine, Mild steel bar, right hand cutting tool, box key or tool post key, chuck key, steel rule, outside calipers or vernier calipers. Sketch Figure 4.13: Shoulder Turning Procedure 1. The given work piece is held in the 3‐jawchuck of the lathe machine and tightened firmly with chuck key. 2. Right hand single point cutting tool is taken tightened firmly with the help of box key in the tool post. 3. Machine is switched on and the tool post is swiveled and the cutting point is adjusted such that it positioned approximately for facing operation then the tool is fed into the work piece and the tool post is given the transverse movement by rotating the hand wheel of the cross slide. 4. With this facing is completed and the tool post is swiveled and cutting point is made parallel to the axis of work piece. 5. Depth of cut is given by cross slide to the tool post and the side hand wheel is rotated to give the longitudinal movement for the tool post and job is turned to the required length and diameters. 6. After completion of the job it is inspected for the dimensions obtained with the help of steel rule and outside caliper or vernier caliper. Precautions 1. Work piece should be held firmly. 2. In rough turning operation do not over feed the tool, as it may damage the cutting point of the tool. 3. Exercise over hung of tool should be avoided as it results in chatter and causes rough machined surface. 4. It is important to ensure that during facing operation the cutting is performed from center point to the outer diameter of the work piece. Result The job is thus made according to the given dimensions. Docsity.com References
Workshop manual by P. Kannaiah & K. L. Narayana
www.technologystudent.com
www.wikipedia.org
www.mewelding.com
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