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Faculty of Technology and Education ‫برنامج الميكاترونيكس‬ Metal Processing and Manufacturing 3rd Year 2024/2025 Lecture notes prepared by; Production Technology Department Staff Members...

Faculty of Technology and Education ‫برنامج الميكاترونيكس‬ Metal Processing and Manufacturing 3rd Year 2024/2025 Lecture notes prepared by; Production Technology Department Staff Members 1 Index Title Page Industrial Safety 1 Hand Tools, Layout and Hand operations 10 Machinability and principles of metal cutting 31 Speeds and Feeds for Machine Tools 37 Lathe Machining Operations 41 Milling Machine 73 Shaper 96 Drilling Operations 105 Grinding and Abrasive Machining Processes 115 Sheet Metal Work 127 2  Industrial Safety Objectives of industrial safety Industrial safety is needed to check all the possible chances of accidents for preventing loss of life and permanent disability of any industrial employee, any damage to machine and material as it leads to the loss to the whole establishment: 1. It is needed to eliminate accidents causing work stoppage and production loss. 2. It is needed to prevent accidents in industry by reducing any hazard to minimum. 3. It is needed to reduce workman’s compensation, insurance rate and all the cost of accidents. 4. It is required to educate all members regarding the safety principles to avoid accidents in industry. 5. It is needed to achieve better morale of the industrial employees. 6. It is required to have better human relations within the industry. 7. It is needed to increase production means to a higher standard of living. 3  There are various Types of common accidents needing due attention to prevent them which are as follows: 1. Near Accident, An accident with no damage or injury is called near accident. 2. Trivial Accident, An accident with very less damage is called trivial. 3. Minor Accident, It is an accident with damage and injury more than trivial. 4. Serious Accident, An accident with heavy damage and lot of injury is called serious accident. 5. Fatal Accident, It is an accident with very heavy damage. There may be loss of lives also. General health and safety precautions Horseplay i) work is not the place for horseplay, practical jokes, or silly tricks. Hygiene i) always wash your hands, before meals, before and after going to the toilet, and at the end of each shift; ii) dry your hands carefully on the clean towels or driers provided – don’t wipe them on old rags; iii) paraffin, petrol or similar solvents should never be used for skin-cleaning purposes; 4  Housekeeping i) never throw rubbish on the floor; ii) keep gangways and work area free of metal bars, components, etc.; iii) if oil, or grease is spilled, wipe it up immediately or someone might slip and fall. Moving about i) always walk – never run; ii) keep to gangways – never take shortcuts; iii) look out for and obey warning notices and safety signs; iv) never ride on a vehicle not made to carry passengers, e.g. fork-lift trucks. Personal protective equipment i) use all personal protective clothing and equipment, such as ear and eye protectors, dust masks, overalls, gloves, safety shoes and safety helmets; ii) get replacements if damaged or worn. 5  Ladders i) do not use ladders with damaged, missing or loose steps; ii) always position ladders on a firm base and at the correct angle Machinery i) ensure you know how to stop a machine before you set it in motion; ii) keep your concentration while the machine is in motion; iii) never leave your machine unattended while it is in motion; iv) take care not to disturb other machine operators; v) never clean a machine while it is in motion ; vi) never clean swarf away with your bare hands; vii) keep your hair short or under a cap or hairnet; viii) avoid loose clothing –ensure that any neckwear is placed in and secure; ix) do not wear rings, chains or watches at work ; x) do not allow unguarded bar to extend beyond the end of a machine, e.g. in a centre lathe; xi) always ensure that all guards are correctly fitted and in position – remember, guards are fitted on machines to protect you and others from accidentally coming in contact with dangerous moving parts. 6  Harmful substances i) learn to recognize hazard warning signs and labels; ii) follow all instructions; iii) before you use a substance find out what to do if it spills onto your hand or clothes; iv) never eat or drink in the near area; v) do not take home any clothes which have become soaked or damaged with harmful substances; vi) do not put liquids or substances into unlabelled or wrongly labelled bottles or containers. Electricity i) make sure you understand all instructions before using electrical equipment; ii) do not use electrical equipment for any purpose other than, nor in the area other than the intended one; iii) always switch off or isolate before connecting or disconnecting any electrical equipment. brown wire live conductor blue wire neutral conductor green/yellow wire earth conductor. Compressed air i) only use compressed air if allowed to do so; ii) never use compressed air to clean a machine – it may blow in your face or someone else’s and cause an injury. 7  Fire i) take care when using flammable substances:- cloth, wood, paper and fabric / metals:- (Magnesium, Lithium or Aluminum powders or swarf) ii) never smoke in ‘no smoking’ areas; iii) do not throw rubbish, cigarette ends and matches in corners or under benches; iv) always make sure that matches and cigarettes are put out before throwing them away; v) know the correct fire drill. First aid i) have first aid treatment for every injury however trivial; ii) know the first aid arrangements for your workplace. 8 9 Understand Safety signs 10 Workshop Practice using Hand Tools 11 Arbor Press and Shop Presses Two basic types of hand-powered arbor presses are manufactured and used: the hydraulic and the mechanical. The major uses of the arbor press are installing and removing bushings, installing and removing ball and roller bearings, pressing shafts into hubs, pressing mandrels into work-pieces, straightening and bending, and broaching key-seats. 12 Work-Holding and Hand Tools The bench vise is a basic but very necessary tool in the shop. With proper care and use, this work-holding tool will give many years of truthful service. Vises are used to hold work for filing, hacksawing, chiseling, and bending light metal. They are also used for holding work when assembling and disassembling parts. Bench vises should occasionally be taken apart so that the screw, nut, and thrust collars can be cleaned and lubricated. The screw and nut should be cleaned in solvent. A heavy grease should be packed on the screw and thrust collars before reassembly. 13 CLAMPS C-clamp and Parallel clamp are used to hold parts together while they are worked on by machines. The size of the clamp is determined by the largest opening of its jaws. A parallel clamp is ideal for holding small work. For maximum clamping action, the jaw faces must be parallel. PLIERS Pliers hold parts together while they are worked on by hand. Pliers come in several shapes and with several types of jaw action. Simple combination or slip joint pliers will do most jobs for which you need pliers. The slip joint allows the jaws to expand to grasp a larger size workpiece. 14 HAMMERS Hammers are classified as either hard or soft. Hard hammers have steel heads, It has a hardened striking face and is used for all general purpose work that requires a hammer. Soft hammers are made of plastic, brass, copper, lead and useful for setting work tightly on parallels (steel bars) when mounting material in a vise and used to position workpieces, that have finishes that would be damaged by a hard hammer. PUNCHES the top of the illustration is a pin punch, used to drive out straight, taper, and roll pins. The second tool in the figure, the drift punch it is used as a starting punch for driving out pins. In the middle is a center punch that makes a starting point for drilling. Chisels are considered cutting tools. The two bottom tools are cold chisels. Cold chisels are made in many shapes and are useful for chip metal from castings, cutting off rivet heads and welds. 15 16 The hacksaw Making the Cut: Grasp the hacksaw firmly by the handle and front of the frame. Apply enough pressure on the forward stroke to make the teeth cut. Insufficient pressure will permit the teeth to slide over the material, dulling the teeth. Also, lift the saw slightly on the return stroke. Cut the full length of the blade and make about 40 to 50 strokes per minute. More strokes per minute may generate enough heat to draw the blade sharpness and dull the teeth. Keep the blade moving in a straight line. Avoid any twisting or binding, which can bend or break the blade. Hand Saw use, The hardness and thickness of a workpiece determine to a great extent which pitch blade to use. As a rule, you should use a coarse-tooth blade on soft materials, to have sufficient clearance for the chips, and a fine-tooth blade on harder materials. But you should also have at least three teeth cutting at any time, which may require a fine-tooth blade on soft 17 materials with thin cross sections. Saw Blades: All hacksaw blades are heat-treated to provide the hardness and toughness needed to cut metal. The shape and kind of material to be cut has an important bearing on blade choice, in terms of the number of teeth per inch. Typical blade sizes; 8, 14, 18, 24, or 32 TPI (tooth- per-inch). The set of side teeth , causes the blade to cut wider than itself to prevent rubbing or jamming, break up the chips and help the teeth clear themselves. Wavy set for fine-toothed blades for thin metal to minimize undressing of the teeth from blade and reduce vibration. 18 FILES Files are made in many different lengths ranging from 4 to 18 in. Files are manufactured in many different shapes. They are manufactured in four different file cuts: single, double, curved tooth, and rasp. The single cut, double cut, and curved tooth are commonly encountered in machine shops. Rasps are generally used with wood. Curved tooth files will give excellent results with soft materials such as aluminum, brass, plastic, or lead. Files are manufactured in different coarseness: rough, coarse, bastard, second cut, smooth, and dead smooth. The longer the file, the coarser the teeth. For maximum metal removal a double- cut file is used. If the emphasis is on a smooth finish, a single-cut file is recommended. The face of most files is slightly convex because they are made thicker in the middle than on the ends. Because of this curvature only some of the teeth are cutting at any one time, which makes them penetrate better. Files were originally designed to sharpen large saws in lumber mills, but now they are used for draw filing, filing on a lathe, or filing a finish on a workpiece. 19 Of the many file shapes available, the most commonly used are flat, pillar, square, 3-square, knife, half-round, crossing, and round. Each shape is available in many sizes and degrees of coarseness: rough, coarse, bastard, second-cut, smooth, and dead smooth. In selecting the file, many factors must be considered if maximum cutting efficiency is to be attained: The nature of the work (flat, concave, convex, notched, etc.}. Kind of material. Amount of material to be removed. Surface finish and accuracy demanded. 20 Rifflers, also known as die sinkers, are double-ended files with a 6-inch overall length. Both of their ends have teeth with a handle between them. Their long, thin shape allows rifflers access to very tight spaces such as the inside or bottom of cavities, of molds. 21 When a file breaks, particles will fly quite a distance at high speed and may cause an injury. Files should be stored so that they are not in contact with any other file. The same applies to files on a workbench. Do not let files lie on top of one another because one file will break teeth on the other. Teeth on files will also break if too much pressure is put on them while filing. On the other hand, if not enough pressure is applied while filing, the file only rubs the workpiece and dulls the teeth. A dull file can be identified by its shiny, smooth teeth and by the way it slides over the work without cutting. Dulling of teeth is also caused by filing hard materials or by filing too fast. A good filing speed is 40 to 50 strokes per minute, but remember that the harder the material, the slower the strokes should be; the softer the material, the coarser the file should be. 22 Too much pressure on a new file may cause pinning, that is, filings wedged in the teeth; the result is deep scratches on the work surface. If the pins cannot be removed with a file card, try a piece of brass, copper, or mild steel, and push it through the teeth. Do not use a scriber or other hard object for this operation. A file will not pin as much if some blackboard chalk is applied to the face. Never use a file without steel rule to test for flatness, you can easily determine where the high spots are that have to be filed away. It is best to make flatness checks often, because if any part is filed below a given layout line, the rest of the workpiece may have to be brought down just as far. A smooth finish is usually obtained by draw filing, whereby a single-cut file is held with both hands and drawn back and forth on a workpiece. The file should not be pushed over the ends of the workpiece, as this would leave rounded edges. When a round file or half-round file is used, the forward stroke should also include a clockwise rotation for deeper cuts and a smoother finish. Thread files are used to clean up and reshape damaged threads. 23 Hand Reamers Holes produced by drilling are seldom accurate in size and often have rough surfaces. A reamer is used to finish a hole to an exact dimension with a smooth finish. Hand reamers are often used to finish a previously drilled hole to an exact dimension and a smooth surface. Hand reamers are designed to remove only a small amount of material from a hole, usually from 0.025 to 0.12mm. Hand reamers have a long starting taper that is usually as long as the diameter of the reamer, but may be as long as one-third of the fluted body. This starting taper is usually slight and may not be apparent at a casual glance. Hand reamers do their cutting on this tapered portion. The gentle taper and length of the taper help to start the reamer straight and keep it aligned in the hole. 24 The use of a cutting fluid also improves the cutting action and the surface finish when reaming most metals. Exceptions are cast iron and brass, which should be reamed dry. When a hand reamer is started it should be checked for squareness on two sides of the reamer, 90 degrees apart. Another way to ensure alignment of the reamer with the drilled holes is to use the drill press as a reaming fixture. Hand reamers for cylindrical holes are made as solid or expansion types. Expansion reamers are designed for use where it is necessary to enlarge a hole slightly for proper fit, such as in maintenance applications. These reamers have an adjusting screw that allows limited expansion to an exact size. The maximum expansion of these reamers is approximately 0.15 mm. Straight flute cut tools are best suited for softer materials and less finish and less demanding applications, while helical flute cut tools are better suited for harder materials and higher-speed machining and better surface finish. Spiral flute to cut blind holes as the flutes will draw the swarf out of the pre- drilled hole, this prevents the swarf from being packed into the bottom of the blind hole 25 In all hand reaming with solid, expansion, or adjustable reamers, never rotate the reamer backward to remove it from the hole, as this will dull it rapidly. If possible, pass the reamer through the hole and remove it from the far side without stopping the forward rotation. If this is not possible, it should be withdrawn while maintaining the forward rotation. On deep holes, or especially on holes reamed with taper reamers, it becomes necessary to remove the chips frequently from the reamer flutes to prevent blockage. Remove these chips with a brush to avoid cutting your hands. Taps Most internal threads produced today are made with taps. These taps are available in a variety of styles, each one designed to perform a specific type of tapping operation efficiently. The size of the hole to be drilled is usually obtained from tap drill charts, which usually show a 75 percent thread depth. The 25% is for clearance between bolt and threads in 26 hole and for lubrication. Full engagement (M5×0.8) 75% engagement (M5×0.8) Drill size 4 or less Drill size 4.2 50% engagement (M5×0.8) Drill size 4.5 27 Thread-Cutting Dies A die is used to cut external threads on the surface of a bolt or rod. The solid Die nut is not usually employed for cutting threads from the solid, but for repairing damage and knocks to existing screws. The split Die springs in small amount open or closed for a certain amount of adjustment by screw bolt. This permits the dies to be set a small amount open whilst the first cut is taken down and closed in to the correct size for the final finishing cut. 28 Basic Precision Layout Practice Layout is the process of placing reference marks on the workpiece. These marks may indicate the shape and size of a part or its features. Layout marks often indicate where machining will take place. Machinists may use layout marks as a guide for machining while checking their work by actual measurement. This kind of layout may be a simple pencil or chalk mark and is one of the basic tasks of semi-precision layout. Precision layout can be a complex and involved operation making use of sophisticated tools. In the aircraft and shipbuilding industries, reference points, lines, and planes may be laid out using optical and laser instruments. In the machine shop, you will be concerned with layout for stock cutoff, filing and off-hand grinding, drilling, milling, and occasionally in connection with lathe work. 29 TOOLS OF LAYOUT Surface Plates The surface plate is an essential tool for many layout applications. A surface plate provides an accurate reference plane from which measurements for both layout and inspection may be made. It should be covered when not in use and kept clean when being used. No surface plate should be hammered on. The cast iron and semi-steel surface plate has all but given way to the granite plate. Granite is superior to metal because it is harder, denser, and water-resistant. Layout Dyes To make layout marks visible on the surface of the workpiece, a layout dye is used. Layout dyes are available in several colors. Among these are red, blue, and white. The blue dyes are common. Scribers and Dividers Several types of scribers are in common use. The pocket scriber has a removable tip that can be stored in the handle. This permits the scriber to be safely in the pocket. The engineer’s scriber has one straight and one hooked end. The hook permits easier access to the line to be scribed. 30 The layout/prick punch has an included point angle of 30 degrees. This is the only punch that should be used in layout. The center punch has an included point angle of 90 degrees and is used to mark the workpiece prior to such machining operations as drilling. A center punch should not be used in place of a layout punch. Similarly, a layout punch should not be used in place of a center punch. The center punch is used only to deepen the prick punch mark. prick punch 31 32 SIMPLE LAYOUT EXERCISE STEPS Each layout hand operation job requires planning before the operation can be started. Figure shows a typical job. Use the following planning procedure: 1. Carefully study the drawings.(All dimensions in inches) 2. Cut stock to size and remove all burrs and sharp edges. 3. Clean all dirt, grease and oil from the work surface. Apply layout dye. 4. Locate and scribe a reference line (base line).You will make all measurements from this line. If the material has one true edge, it can be used in place of the base line. 5. Locate and center points of all circles and arcs. 6. Use a prick punch to mark the point where centerlines intersect. The sharp point (30°) of this punch makes it easy to locate the position. After the prick punch mark has been checked, it is enlarged slightly with a center punch,. Use hand tools (Bench vice, steel rule, scriber, cener punch, surface plate, Hachsaw, rough and smooth Files, Drilling, …..) to cut and finish to size as in drawing. 33 34  Machinability and principles of metal cutting Machinability, is the ease with which a metal can be cut (machined) permitting the removal of the material with a satisfactory finish at low cost, with regard to tool life, surface finish, and power consumption. In general, softer materials are easier to machine than harder ones. In machining operations, either the tool rotates or moves in a linear motion or the workpiece rotates or moves. The moving or rotating tool must be made to move into the work material to cut a chip. This procedure is called feed. The amount of machine feed controls the thickness of the chip. The depth of cut is often called infeed. In addition to single-point tools with one cutting edge, as they are called in lathe, shaper, and planer operations, there are multiple- point tools such as milling machine cutters, drills, and reamers. In one sense, grinding wheels could be considered to be multiple-point cutters, because small chips are removed by many tiny cutting points on grinding wheels. 35 Check machinability of metals: 1- Files can be used to establish the relative hardness between samples 36 Spark Testing Spark testing is a useful way to test for carbon content in many steels. When held against a grinding wheel. 37 Cutting Tool Geometry (rake angle) When metals are cut dry, pressure welding is a definite problem, especially in the softer metals such as 1100 aluminum and low- carbon steels. Pressure welding produces a built-up edge (BUE) that causes a rough finish and a tearing of the surface of the workpiece. A built-up edge is also caused by speeds that are too slow; this often results in broken tools from excess pressure on the cutting edge. Chips formed at low surface speeds are thicker than they would have been at higher speeds. A thin chip indicates a clean cutting action with a better finish. Saw-tooth-like chips for difficult to cut, low thermal conductivity metals and at high cutting speed. Discontinuous chips, a non-uniform thickness, broken into smaller parts, and easier chip removal. Caused primarily in brittle materials, larger chip thickness, at low speeds. At higher speed, better finish and smaller chip 38 thickness. Zero- and negative-rake tools are stronger and have a longer working life than positive- rake tools. Negative-rake tools produce poor finishes at low cutting speeds but give a good finish at high speeds. Positive-rake tools are allowed cutting at low speeds and can produce good finishes when they are properly sharpened. A chip breaker is designed to curl the chip against the work and then to break it off to produce the proper type of chip. Soft metals such as copper, 1100 series aluminum, and low-carbon hot-rolled steel tend to have poor finishes when cut with ordinary tooling. Cutting tools tend to tear the metal away rather than cut these soft metals; however, sharp tools and larger rake angles plus the use of cutting fluids can help produce better finishes. Harder, tougher alloys almost always produce better finishes even with negative-rake carbide tools. Chip Breakers 39  Speeds and Feeds for Machine Tools Modern machine tools are powerful, and with modern tooling they are designed for a high rate of production. However, the operator who uses the incorrect feeds and speeds for the machine operation will have a much lower production rate and an inferior product. 1000 × 𝑉 𝝿𝐷 40 41 42 43 Turning Machine Lathe Operations 44  LATHE MACHINE Lathe is one of the most versatile and widely used machine tools all over the world. It is commonly known as the mother of all other machine tool. The main function of a lathe is to remove metal from a job to give it the required shape and size. The job is securely and rigid1y held in the chuck or in between centers on the lathe machine and then turn it against a single point cutting tool which wi1l remove meta1 from the job in the form of chips. Fig. shows the working principle of lathe. An engine lathe is the most basic and simplest form of the lathe. It derives its name from the early lathes, which obtained their power from engines. Besides the simple turning operation as described above, lathe can be used to carry out other operations also, such as drilling, reaming, boring, taper turning, knurling, screw thread cutting, grinding etc. 45  SPECIFICATION OF LATHE (i) Maximum swing over bed LATHE OPERATIONS (ii) Maximum swing over carriage (iii) Height of centers over bed (a) Operations, which can be performed in a lathe either (iv)Maximum distance between centers by holding the workpiece between centers or by a chuck (v) Length of bed are: (vi) Width of bed (vii) Morse taper of center (viii) Diameter of hole through spindle (ix)Face plate diameter (x) Size of tool post (xi)Number of spindle speeds (xii) Lead screw diameter and number of threads per cm. (xiii) Size of electrical motor (xiv) Pitch range of metric and inch threads etc. (b) Operations which are performed by holding the work by a chuck or a faceplate or an angle plate are: 46 CONSTRUCTION OF LATHE MACHINE 47 Tailstock: The function of the tailstock is to hold a centre when turning between centres. It is used to hold drills and reamers when producing holes. It is graduated on its outer top surface for use when drilling to depth. It can be fed in or out by means of the handwheel at the rear. Saddle ‫الكرسى‬: rests on top of the bed and is guided by two guideways which, for stability, are the two furthest apart. Accurate movement is thus maintained relative to the centre line of the spindle and tailstock for the complete length of the bed. The top surface contains the dovetail slideway into which the cross-slide is located and the cross-slide leadscrew, complete with handwheel and graduated dial. Top slide: often referred to as the compound slide, fits on its slideway and can be adjusted for wear by means of a gib strip and adjusting screws. Movement is transmitted by the leadscrew. A tool post, usually four-way hand-indexing, is located on the top surface and can be locked in the desired position by the locking handle. Movement of this slide is usually quite short, 92 mm on the machine illustrated, and only hand feed is available. Used in conjunction with the swivel base, it is used to turn short tapers. 48 Bed: It is made from cast iron, designed with thick sections to ensure complete rigidity and freedom from vibration. On the top surface, two sets of guideways are provided, each set consisting of an inverted vee and a flat, Fig. The outer guideways guide the saddle, and the inner guideways guide the tailstock and keep it in line with the machine spindle. The guideways are hardened and accurately ground. A gap bed, where a section of the guideways under the spindle nose can be removed. Removal of this section increases the swing of the lathe, Headstock: The complete headstock consists of a box-shaped casting rigidly clamped to the guideways of the bed and contains the spindle, gears to provide a range of 12 spindle speeds, and levers,.. The speed range is from 40 to 2500 rev/min. The spindle is supported at each end by precision taper-roller bearings and is bored through to accept bar material. The inside of the spindle nose has a Morse taper to accept centres. The outside of the spindle nose is equipped with means of locating and securing the chuck, faceplate or other work- holding device fig. The gearbox, fitted on the lower side of the headstock, provides the range of feeds to the saddle and cross- slide through the feed shaft, and the screw-cutting range through the leadscrew. By selecting the appropriate combination of lever positions in accordance with a table on the machine, a wide range of feed rates and thread pitches can be obtained. 49 50  Apron mechanism : The inner details of apron mechanism is shown in figure. When the spindle gear rotates, the lead screw and feed rod will rotate through tumbler gears. Splined shaft K will be rotating from lead screw and gears F and G will be always rotating. There is a feed check knob E, which has three positions, neutral, push-in and pull-out. For hand feeds, the knob E is put in neutral position. Now, gears F and G have no connection with H and R. Now, hand wheel C is rotated. Pinion I rotates through J and H. Pinion I will move on the rack and so, longitudinal hand feed takes place. For hand cross feed, handwheel D is rotated. Now cross slide screws S rotates and hand cross feed takes place. For automatic longitudinal feed, the knob E is pushed in. Now, rotating gear G will be engaged to H and H to I. I will rotate on rack and so automatic longitudinal feed takes place. For automatic cross feed, the knob E is pulled out. Now, the rotating gear F is connected to R and R to Q. For thread cutting, half nut is engaged by lever B after putting E in neutral position. Now, lead screw will move the carriage for thread cutting. Both longitudinal and cross feed can be reversed by operating the tumbler gear handle. 51 TYPES OF LATHE 1- Speed Lathe Speed lathe is simplest of all types of lathes in construction and operation. The important parts of speed lathe are following- (1) Bed (2) Headstock (3) Tailstock, and (4) Tool post mounted on an adjustable slide. It has no feed box, 1eadscrew or conventional type of carriage. The tool is mounted on the adjustable slide and is fed into the work by hand contro1. The speed lathe finds applications where cutting force is least such as in wood working, spinning, centering, polishing, wire winding, buffing etc. This lathe has been so named because of the very high speed of the headstock spindle. 52 2- Centre Lathe or Engine Lathe The term “engine” is associated with this lathe due to the fact that in the very early days of its development it was driven by steam engine. This lathe is the important member of the lathe family and is the most widely used. Similar to the speed lathe, the engine lathe has all the basic parts, e.g., bed, headstock, and tailstock. But its headstock is much more robust in construction and contains additional mechanism for driving the lathe spindle at multiple speeds. An engine lathe is shown in Fig. Unlike the speed lathe, the engine lathe can feed the cutting tool both in cross and longitudinal direction with reference to the lathe axis with the help of a carriage, feed rod and lead screw. 53 Bench Lathe This is a small lathe usually mounted on a bench. It has practically all the parts of an engine lathe or speed lathe and it performs almost all the operations. This is used for small and precision work. Tool Room Lathe This lathe has features similar to an engine lathe but it is much more accurately built. Vibration free and extremely quiet. With fewer mechanical parts and exceptional built quality, It has a wide range of spindle speeds ranging from a very low to a quite high speed up to 2500 rpm. This lathe is mainly used for precision work on tools, dies, gauges and in machining work where accuracy is needed. Turret Lathe It is vastly used for mass production work. The distinguishing feature of this type of lathe is that the tailstock of an engine lathe is replaced by a hexagonal turret, on the face of which multiple tools may be fitted and fed into the work in proper sequence. These tools are capable in performing multiple tasks like turning, boring, thread cutting, drilling and facing without re- setting of work or tools, and a number of identical parts can be produced in the minimum54time.  Automatic Lathe Turret Lathe Bench Lathe Special Purpose Lathe 55 Special Purpose Lathes These lathes are constructed for special purposes and for jobs, which cannot be accommodated or conveniently machined on a standard lathe. The wheel lathe is made for finishing the journals and turning the tread on railroad car and locomotive wheels. The gap bed lathe, in which a section of the bed adjacent to the headstock is removable, is used to swing extra-large-diameter pieces. The T-lathe is used for machining of rotors for jet engines. The bed of this lathe has T-shape. Duplicating lathe is one for duplicating the shape of a flat or round template on to the job. Automatic Lathes These lathes are so designed that all the working and job handling movements of the complete manufacturing process for a job are done automatically. These are high speed, heavy duty, mass production lathes with complete automatic control. 56  Accessories and Attachments of Lathe There are many lathe accessories provided by the lathe manufacturer along with the lathe, which support the lathe operations. Lathe centers The most common method of holding the job in a lathe is between the two centers generally known as live centre (head stock centre) and dead centre (tailstock centre). They are made of very hard materials to resist deflection and wear and they are used to hold and support the cylindrical jobs. Driving dog and Driving plate These are used to drive a job when it is held between two centers. Carriers or Driving dogs are attached to the end of the job by a setscrew. A use of lathe dog for holding and supporting the job. Driving plate is either screwed or bolted to the nose of the headstock spindle. A projecting pin from the catch plate or carrier fits into the slot provided in either of them. This imparts a positive drive between the lathe spindle and job. 57 Driving dog and driving plate Lathe centers 58 Chucks Chuck is one of the most important devices for holding and rotating a job in a lathe. It is basically attached to the headstock spindle of the lathe. The internal threads in the chuck fit on to the external threads on the spindle nose. Jobs of short length and large diameter or of irregular shape, which cannot be conveniently mounted between centers, are held quickly and rigidly in a chuck. There are a number of types of lathe chucks, e.g. (1) Three jaws or universal (2) Four jaw independent chuck (3) Magnetic chuck (4) Collet chuck (5) Air or hydraulic chuck, (6) Combination chuck (7) Drill chuck. 59 Face plates Face plates are employed for holding jobs, which cannot be conveniently held between centers or by chucks. A face plate possesses the radial, Plain and T slots for holding jobs or work-pieces by bolts and clamps. Face plates consist of a circular disc bored out and threaded to fit the nose of the lathe spindle. They are heavily constructed and have strong thick ribs on the back. They have slots cut into them, therefore nuts, bolts, clamps and angles are used to hold the jobs on the face plate. They are accurately machined and ground. Angle plates Angle plate is a cast iron plate having two faces machined to make them absolutely at right angles to each other. Holes and slots are provided on both faces so that it may be clamped on a faceplate and can hold the job or workpiece on the other face by bolts and clamps. The plates are used in combining with a face plate when the holding surface of the job should be kept horizontal. 60 Mandrels A mandrel is a device used for holding and rotating a hollow job. The job revolves with the mandrel, which is mounted between two centers. It is rotated by the driving dog and the driving plate and it drives the work by friction. Rests A rest is a lathe device, which supports a long slender job, when it is turned between centers or by a chuck, at some intermediate point to prevent bending of the job due to its own weight and vibration set up due to the cutting force that acts on it. The two types of rests commonly used for supporting a long job in an engine lathe are the steady/ centre rest and the follower rest. 61  Toper turning by offset tailstock, Jobs that can be turned between centers may be taper turned by this technique. Only external tapers can be machined in this way, however. Calculating offset when, TPI or TPF is known (standard taper as morse taper) TPI = Taper per inch, TPF = Taper per foot The same procedure would be followed ·when using metric units. However, all 𝐿 × 𝑇𝑃𝐼 dimensions ‘ “would be in millimeters. Offset = 2.54 × 2 when taper per foot (TPF) is known, it must be converted to taper per inch (TPI). The following formula takes this into account: 𝐿 × 𝑇𝑃𝐹 Offset = 12 × 2 62 63 Calculating offset when dimensions of tapered sections are known but TPI or TPF is not given: All dimensions must either be in inches or in millimeters. 64 Plain or Telescopic taper attachment The plain taper attachment requires disengaging the cross-slide screw from the cross-slide feed nut. The cutting tool is advanced by using the compound rest feed screw. If the machine is fitted with a plain taper attachment, tighten the binding screw that engages the cross-slide feed to the attachment. make a trial cut. If necessary, readjust until the taper is being cut to specifications. Complete the cutting operation. The telescopic taper attachment is made in such a way that it is not necessary to disconnect the cross-slide feed nut. The tool can be advanced into the work with the cross-slide screw in the usual manner. Both internal and external tapers can be cut. 65 center hole drilled with a bell-type center drill 66  metric thread form, ISO (International Organization for Standardization) adopted in 1898, is similar to the American National Standard. Sixty-Degree Thread Unified American National and sharp “V” Forms 67 A sharp 60 degree tool will make a thread, but it will not be exactly to spec. A true thread has a root radius or flat, and a crest radius. One tool can't make those flats and radii to specification. The full form insert is the only way to get them. Sharp V thread insert ANU, rounded root and flat crest Partial Acme thread insert Full Acme thread insert carbide square thread insert 68 CUTTING THE THREAD Set the pitch to the value, 0.200 in., or 5 threads per inch (tpi). Set the quick-change gearbox at 5 tpi. Step 1: Move the tool off the work and turn the crossfeed micrometer dial back to zero. Step 2: Feed it in.002 in. on the compound dial. Step 3: Turn on the lathe and engage the half-nut lever Step 4: Take a scratch cut without using cutting fluid Disengage the half-nut at the end of the cut. Stop the lathe and back out the tool using the crossfeed. Return the carriage to the starting position. Step 5: Check the thread pitch with a screw pitch gage or a rule. If the pitch is wrong, it can still be corrected. Step 6: Apply appropriate cutting fluid to the work Step 7: Feed the compound in.005 to.020 in. for the first pass, depending on the pitch of the thread. For a coarse thread, heavy cuts can be taken on the first few cuts. Reduce the depth of cut for each pass until it is about.002 in. at the final passes. Bring the crossfeed dial to zero. 69 70 Step 8: Make the second cut. Step 9: Continue this process until the tool is within.010 in. of the finished depth. Step 10: Brush the threads to remove the chips. Check the thread fit with a ring gage, standard nut or mating part, or screw thread micrometer. You may remove the work from between centers and return without disturbing the threading setup, provided that the tail of the dog is returned to the same slot. Step 11: Continue to take cuts of.001 or.002 in., and check the fit between each cut. Thread the nut with your fingers; it should go on easily but without end play. A class 2 fit is desirable for most purposes. Step 12: Chamfer the end of the thread to protect it from damage. 71 72 CUTTING MULTIPLE-LEAD THREADS Several methods are used for indexing or dividing multiple-lead threads. One method is to use an accurately slotted face plate. The lathe dog is moved 180 degrees for two leads, 120 degrees for three leads, and 90 degrees for four leads. This method will work only on external threading. Another method is to mark the stud gear at 180 degrees for two leads, disengage the gear, rotate it 180 degrees, and reset it. This procedure will work only if the spindle and stud gear have a 1:1. 73 Tool-holding for the Lathe For lathe work, cutting tools must be supported and fastened securely in the proper position to machine the workpiece. There are many different types of toolholders available to satisfy this need. 74 Example: A 150-mm-long, 12.5-mm-diameter 304 stainless-steel rod is being reduced in diameter to 12.0 mm by turning on a lathe. The spindle rotates at N = 400 rpm, the tool is traveling at an axial speed of 200 mm/min and the torque required for cut is 3.1 N.m. Calculate the cutting speed, material- removal rate, cutting time, power dissipated, and cutting force. Solution: The cutting speed is the tangential speed of the work-piece. The maximum cutting 75 speed is at the outer diameter; Do, and is obtained from the equation 76  Machine Tools Milling Machines 77 The Milling Machine A milling machine rotates a multi-toothed cutter into the workpiece to remove material. Each tooth of the cutter removes a small individual chip of material. A wide variety of cutting operations can be performed on a milling machine. The milling machine is capable of machining flat or contoured surfaces, slots, grooves, threads, gears, spirals, and other configurations. Machined surface is formed in one or more passes of the work. The work to be machined is held in a vice, a rotary table, a three jaw chuck, an index head, between centers, in a special fixture or bolted to machine table. The rotatory speed of the cutting tool and the feed rate of the workpiece depend upon the type of material being machined. 78 Milling machine rotates the cutter mounted on the arbor of the machine and at the same time automatically feed the work in the required direction. The milling machine may be classified in several forms, but the choice of any particular machine is determined primarily by the size of the workpiece to be undertaken and operations to be performed. With the above function or requirement in mind, milling machines are made in a variety of types and sizes. According to general design, the distinctive types of milling machines are shown in figure: Base It is a foundation member for all the other parts, which rest upon it. It carries the column at its one end. In some machines, the base is hollow and serves as a reservoir for cutting fluid. Column The column is the main supporting member mounted vertically on the base. It is box shaped, heavily ribbed inside and houses all the driving mechanism for the spindle and table feed. The front vertical face of the column is accurately machined and is provided with dovetail guideway for supporting the knee. Knee The knee is a rigid grey iron casting which slides up and down on the vertical ways of the column face. An elevating screw mounted on the base is used to adjust the height of the knee and it also supports the knee. The knee houses the feed mechanism of the table, and different controls to operate it. Saddle The saddle is placed on the top of the knee and it slides on guideways set exactly at 90° to the column face. The top of the 79 saddle provides guide-ways for the table. Table The table rests on ways on the saddle and travels longitudinally. A lead screw under the table engages a nut on the saddle to move the table horizontally by hand or power. In universal machines, the table may also be swiveled horizontally. For this purpose the table is mounted on a circular base. The top of the table is accurately finished and T -slots are provided for clamping the work and other fixtures on it Overhanging arm It is mounted on the top of the column, which extends beyond the column face and serves as a bearing support for the other end of the arbor Front bracket It is an extra support, which is fitted between the knee and the over-arm to ensure further rigidity to the arbor and the knee. Spindle It is situated in the upper part of the column and receives power from the motor through belts, gears. and clutches and transmit it to the arbor. Arbor It is like an extension of the machine spindle on which milling cutters are securely mounted and rotated. The arbors are made with taper shanks for proper alignment with the machine spindles having taper holes at their nose. The draw bolt is used for managing for locking the arbor with the spindle and the whole assembly 80 Horizontal Milling Machine 81 82 Vertical Milling Machine 83 Universal Milling Machine 84 Milling operations Form (contour) contour ( profile)milling forming 85 End mill, applications cut spiral cut thread cut circular slot (groove) 86 OFFSET BORING HEAD Most holes in workpieces are machined by drilling. When a better surface finish and better diameter accuracy are required, reaming may follow drilling. However, drilling and reaming are limited to standard sizes in which these tools are available. In addition, drilled holes may drift off position during a machining operation. To machine holes of any size and at exact locations, the offset boring head may be used. A boring head can be used only to enlarge existing holes in the workpiece. The workpiece must be predrilled on the mill or drill press. If you are boring holes considerably larger than the largest diameter drill available, you may save time by using a high-speed hole saw to cut out most of the unwanted material. This will save many additional boring steps required to enlarge a hole to its finished size. 87 88 89 90 1. Direct Indexing: The dividing head has an index plate, fitted directly on the spindle. The intermediate use of worm and worm-wheel is avoided. The index plate has 24 holes and the periphery of job can be divided into 2, 3, 4, 6, 8 and 12 equal parts directly. 2. Simple Indexing: In this case, different index plates with varying number of holes are used to increase the range of indexing. The index is fixed in position by a pin called lock pin. The spindle is then rotated by rotating the handle which is keyed to the worm-shaft as shown in Fig. The following types of index-plates having the holes given against them are available. Plate 1 : 15, 16, 17, 18, 19 and 20. Plate 2 : 21, 23, 27, 29, 31 and 33. Plate 3 : 35, 37, 39, 41, 43, 47 and 49. 91 The following relation is used for simple indexing: T = 40/N, where T gives the number of turns or parts of a turn through which the index crank must be rotated to obtain the required number of divisions (N) on the job periphery. Let us take an example of a gear blank on which 28 teeth are to be cut. 40 12 6 3 15 T= =1 =1 =1 =1 28 28 14 7 35 I.e., the worm is to be rotated by the handle one compete turn and 15 holes from 35 holes circle. Example. Indexing 62, 41, 76 divisions 92 3. Compound Indexing: The principle of operation of compound indexing is the same as that of simple indexing, but the only difference is that compound indexing uses two different circles of one plate. The principle of compound indexing is to obtain the required division in two stages: (i) By rotating the handle in usual way keeping the index plate fixed. (ii) By releasing the back pin and then rotating the index plate with the handle. For example, if a 77 teeth gear is to be cut, then T = 40/77 77 = 11 × 7 So for each tooth, the worm will be rotated by 9 holes of 21 hole circle with the help of the crank and then the index plate is rotated by 3 holes of the 33 hole circle in the same direction. 93 94 95 96 97 98 99  Machine Tools Shaper & Planer 100  The Shaper Shaper is a reciprocating type of machine tool in which the ram moves the cutting tool backwards and forwards in a straight line. The basic components of shaper are shown. 101 A single point cutting tool is held in the tool holder, which is mounted on the ram. The workpiece is rigidly held in a vice or clamped directly on the table. The ram reciprocates and thus cutting tool held in tool holder moves forward and backward over the workpiece. In a standard shaper, cutting of material takes place during the forward stroke of the ram. The backward stroke remains idle and no cutting takes place during this stroke. The feed is given to the workpiece and depth of cut is adjusted by moving the tool downward towards the workpiece. The time taken during the idle stroke is less as compared to forward cutting stroke and this is obtained by quick return mechanism. Standard Shaper In standard shaper, the table has only two movements, horizontal and vertical, to give the feed. Universal Shaper A universal shaper is mostly used in tool room work. In this type of shaper, in addition to the horizontal and vertical movements, the table can be swiveled about an axis parallel to the ram ways, and the upper portion of the table can be tilted about a second horizontal axis perpendicular to the first axis. 102 The automatic feed mechanism of the table is done by rotating a ratchet wheel, mounted at the cross-feed screw. This enables a corresponding equal rotation of the cross-feed screw after each stroke. 103  List of most shaping operations: Making a Chuck Key V Block External Key way Dovetail Rack Gear 104 Marking after machining Dividing Head (splines) 105 PLANER Like a shaper, planer is used primarily to produce horizontal, vertical or inclined flat surfaces by a single point cutting tool. But it is used for machining large and heavy workpieces that cannot be accommodated on the table of a shaper. In addition to machining large work, the planer is frequently used to machine multiple small parts held in line on the platen. Tool heads are mounted on a horizontal cross rail that can be moved up and down. Cutting is achieved by applying the linear primary motion to the workpiece (motion X) and feeding the tool at right angles to this motion (motion Y and Z). The primary motion of the worktable is normally accomplished by a rack and pinion drive using a variable speed motor. In a planer, the work which is supported on the table reciprocates past the stationary cutting tool and the feed is imparted by the lateral movement of the tool. Double Housing Planer 106 107 108  Machine Tools Drilling Operations 109 Drilling is an operation of making a circular hole by removing a volume of metal from the job by cutting tool called drill. In drilling machine the drill is rotated and drill fed along its axis of rotation in the stationary workpiece. A drill is a rotary end-cutting tool with one or more cutting lips and usually one or more flutes for the passage of chips and the charge of cutting fluid. A drilling machine is a machine tool designed for drilling holes in metals. It is one of the most important and versatile machine tools in a workshop. Besides drilling round holes, many other operations can also be performed on the drilling machine such as counter-boring (‫)التخويش االسطوانى‬, countersinking (‫( )التخويش المائل‬machining between centers parts), honing, reaming, lapping, sanding etc. Chips are produced in great quantities and must be safely handled. The operator must also be protected from these chips as they fly from the machine as well as from the rotating parts of the machine. 110  Sanding a- reaming b- counterboring c- countersinking d- spot-facing 111 Types of Drilling Machines 1- The upright drill press )‫ (المثقاب القائم‬is used for heavy-duty drilling. 2- The radial drill press )‫ (مثقاب الدف‬is used for drilling large, heavy workpieces that are difficult to move. In a plain radial drilling machine, provisions are made for following three movements - 1. Vertical movement of the arm on the column, 2. Horizontal movement of the drill head along the arm, and 3. Circular movement of the arm in horizontal plane about the vertical column. 3- Special-purpose drilling machines range from the microscopic drilling machine, which can drill a hole smaller than a human hair, to deep-hole drilling machines and turret head drills, which are often computer controlled for automatic operation. 4- The gang drilling machine )‫ (مثقاب جماعى‬is used when several successive operations are needed by shifting the work from one position to the other on the worktable. It has several drilling heads mounted over a single table, with each spindle tooled for drilling, reaming, or counterboring. Hard tooling, such as jigs and fixtures, is typically used on gang drilling machines. Tool guidance is provided by the jigs while the workpiece is clamped in the fixture. 5- Multiple-Spindle Drilling Machine (‫)مثقاب متعدد أعمدة الدوران‬ The multiple-spindle drilling machine is used to drill a number of holes in a job simultaneously and to reproduce the same pattern of holes in a number of identical pieces in a mass production work. This machine has several spindles and all the spindles holding drills are fed into the work simultaneously. Feeding motion is usually obtained by raising the worktable. 112 113 WORK-HOLDING DEVICES Work must be mounted solidly on the drilling machine. If work is mounted improperly, it may spring or move, causing drill damage or breakage. Serious injury can result from work that becomes loose and spins on a drill press. 114 The helix angle in drill has a big difference on the cutting efficiency. The higher the drill helix angle, the greater the force pushing chips axially out of the hole. However, the higher the drill helix angle, the smaller the cross sectional area of the drill and the weaker it is. High-helix drills, Used for high feed rate, low cutting speed and designed to remove chips from deep holes. Straight fluted drills are used for drilling on sheet metal from brass and other soft materials because the zero rake angle. Low-helix drills, are more rigid cross section than standard helix drills and can stand more torque. Used with high spindle speeds on hard to drill material (steels) and small rake angle. 30˚ The higher the cutting forces (harder, stronger material), the 40˚ lower the helix angle must be. 12˚ 115 Conventional Point (118º) Most commonly used drill point Gives satisfactory results for most general- purpose drilling Long Angle Point 60º - 90º Used on low helix drills for drilling of nonferrous metals, soft cast irons, plastics, fibers, and wood Flat Angle Point 135º -150º Used to drill hard and tough materials Shorter cutting edge tends to reduce friction and heat during drilling Shop Tools and Techniques The large rake angle makes these drills suitable for soft non- ferrous metals such as aluminum and brass. 116 Factors Causing Early Dulling (‫ )التثليم‬of Drill Drill speed may be too high for hardness of material being cut Feed may be too heavy and overload cutting lips Feed may be too light and cause lips to scrape rather than cut May be hard spots on work surface Shop Tools and Techniques More Factors Work or drill may not be supported properly, resulting in springing and chatter Drill point may be incorrect for material being drilled Finish on lips may be poor because of poor Shop Tools and Techniques Check angle of drill point and length of lips with drill point gage Wire gauge drill bits are used in wood, metal and plastic applications where more precisely sized holes are required. The bits drill an exact hole size, making them ideal for tapping. Diameters fall between standard fractional sizes 117 Drill Size Drill sizes are expressed by the following series: Numbers-#80 to #1 Letters-A to Z (0.234'' to 0.413" diameters). Inches and fractions- 1/64" to 3 1/2" diameters. 118 Metric-0.15 mm to 76.0 mm diameters. Wire gauge drill bits decimal equivalent Without the tap and drill information 60 holes from no. 1 to 60 Marked with number sizes and decimal equivalents 119 120 Tap and Die Thread Set Decimal Drill Set 121  Machine Tools Grinding and Abrasive Machining Processes 122 Grinding and Abrasive Machining Processes 123  Grinding and Abrasive Machining Processes Grinding, like milling, drilling, sawing, planning, and turning, is a cutting operation. However, instead of using one, two, or several cutting edges, grinding makes use of an abrasive tool composed of thousands of cutting edges. Since each of the abrasive particles is actually a separate cutting edge, the grinding wheel might be compared to a many-toothed milling cutter. The practice of precision grinding can result in precise and accurate work with tolerances becoming ever smaller. Types of surface grinders include; Type I: Horizontal spindle with reciprocating table Type II: Horizontal spindle with rotary table Type III: Vertical spindle with either reciprocating or rotary table Types of Cylindrical Grinders Cylindrical grinders are used to grind the diameters of cylindrical workpieces; 1. Center-type 2. Roll-type 3. Centerless 4. Internal cylindrical 5. Tool and cutter 124 Accessory spindles and special wheel shaping (dressing) add to the versatility of this (reciprocating table version) grinding machine. 125  Center-Type Grinder, grinds the outside diameter of a cylindrical workpiece mounted between centers. Swiveling the table allows conical shapes can be ground. The Centerless Grinding Rotating cylindrical work is supported by a work rest while being fed between the grinding wheel and a regulating wheel. The grinding wheel runs at normal speed and the regulating wheel runs slower and controls the spin of the workpiece 126  Internal grinding, which requires a special attachment mounted on the Roll-Type Grinder Roll grinders are used wheel head. It also requires either a to grind and resurface large steel rolling chuck or a faceplate on the headstock. mill rolls. Because these rolls are usually heavy, they are supported in bearings (rather than on centers) while in the grinding machine. In most of the The wheel is positioned relative larger roll grinding machines, the wheel to the face of the tooth in the head is traversed along the rotating cutter grinding machine. workpiece to accomplish the grinding. 127  Wheel balancing The appearance of the grinding wheel surface Machining Fundamentals indicates the amount of glaze. A wheel dresser should be used to remove the glaze. Grinding wheels can be a source of danger and Grinding Rules : should be examined frequently for concentricity Grind using the face of a wheel, not the sides. (running true), roundness, and cracks. Move the work back and forth across the wheel face. This will A new wheel can be tested by suspending it on a wear the wheel evenly and prevent grooves from forming. string or wire, or holding it lightly with one finger, Keep the wheel dressed and the tool rests properly adjusted. and drumming the side lightly with a metal rod or Soft metals (aluminum, brass, and copper) tend to load (clog) screwdriver handle. A solid wheel will give off a clear grinding wheels. When possible, these metals should be ringing sound. A wheel that does not give off a clear sound should be assumed to have a fault. ground on an abrasive belt grinder. 128 129  The Grinding Wheel A grinding wheel consists of abrasive particles and bonding material. The bonding material holds the particles in place and establishes the shape and structure of the wheel. Wheel Structure and Wheel Grade; Where Pg = proportion of abrasive grains in the total wheel volume, Pb = proportion of bond material, and Pp = proportion of pores (air gaps). Typical structure of a grinding wheel Diamond abrasive is especially useful in the grinding of ceramics and tungsten carbide. Diamond abrasives are not effective on steels or superalloys containing cobalt or nickel. At the elevated operating temperature of grinding these materials, they readily pick up carbon from diamond. Cubic Boron Nitride (cBN) works best on hardened ferrous alloys, especially the difficult to- machine cobalt and nickel superalloys used widely in jet engine applications. 130  Selection and Identification of Grinding Wheels First Symbol: Type of Abrasive (A 60-J8V) Six major abrasives are in common use: A - Aluminum oxide B - Cubic boron nitride C - Silicon carbide D - Diamond Second Symbol: Grit Size (A 60-J8V) Grit refers to the size of the abrasive grains Fourth Symbol: Structure (A 60-J8V) Structure, or the spacing of the abrasive grains in the wheel is indicated by the numbers; 1 (dense) to 15 (very open). Structure provides chip clearance so that chips may be thrown from the wheel by centrifugal force or washed out by the griding fluid. If this does not happen, the wheel becomes loaded with workpiece particles 131 and must be dressed. Third Symbol: Grade of Hardness (A 60-J8V) Fifth Symbol: Bond (A 60-J8V) Bond is identified by letter according to the following: Grade of hardness is a measure of the bond strength of V Vitrified the grinding wheel. The bond material holds the B Resinoid abrasive grains together in the wheel. The stronger the R Rubber E Shellac bond, the harder the wheel. Precision grinding wheels M Metal tend to be softer grades, because it is necessary to Shellac belted superfinishing have dull abrasive grains pulled from the wheel as soon In the machine shop, vitrified bonds are the most common. Vitrified (glass bond) wheels are used mostly for precision as they become dulled, to expose new sharp grains to grinding. Resinoid bond wheels are typically used in rough- the workpiece. If this does not happen, the wheel will grinding operations where some flexibility is needed, such as become glazed with dull abrasive. Cutting efficiency ripping of castings in a foundry, with high wheel speeds and heavy stock removal. Rubber-bonded grinding wheels are and surface finish will be poor. Later alphabet letters used in the finish grinding of bearing surfaces. Shellac indicate harder grades. For example, (organic material) belted superfinishing methods like rolls,... A: are soft, M: medium whereas R to Z are hard. Metal-bonded diamond wheels are also used for grinding hard non-metallics such as ceramics and stone, for diamond abrasive, electrically conductive bond in electrolytic grinding. 132 133 Grinding Wheel Safety Rules 1. Handle and store grinding wheels carefully 2. Never use wheels that have been dropped. 3. Inspect all wheels for cracks or chips before mounting. Ring test them. 4. Do not alter a wheel to fit the grinding machine, and do not force it onto the machine spindle. 5. Make sure that the operating speed never exceeds the maximum allowable operating speed of the wheel. 6. Ensure that mounting flanges have equal and correct diameters. The bearing surfaces must be clean for using mounting flanges. 7. Use mounting blotters unless the wheel is designed for some other mounting method. 8. Do not overtighten the mounting nut. 9. If the machine is a pedestal or bench grinder, adjust the work rest properly, just clear but not to exceed -in. clearance. 10. Do not grind on the side of a straight wheel). There are certain detailed exceptions to this rule. In applications such as shoulder and form grinding, some amount of side grinding takes place. 11. Use a safety guard that covers at least half of the grinding wheel, and do not start the machine until the guard is in place. 12. Allow the grinding wheel to run at least one minute before using it to grind (with the guards in place, of course), and do not stand directly in line with the rotating grinding wheel. 13. Always wear approved (ANSI Z-87.1) safety glasses or other approved eye protection. 134 135  Sheet Metal Cutting Operations A piece of metal whose thickness is between 0.15 mm and 6.35 mm. -Anything thinner is referred to as a foil and thicker is considered as a plate. -Sheet metal can be cut, bent and stretched into nearly any shape. BLANKING & PIERCING BLANKING Sheet metal cutting to separate piece from surrounding stock. It is the cutting operation of a flat metal sheet & the part punched out is known as Blank. PIERCING Similar to Blanking, except cut piece is scrap, called a slug. It is the cutting operation with the help of which holes of various shapes are produced in the sheet. 136  Metal pieces are punched from the edges of a sheet 137 Trimming: is the removal of excess metal from a stamped part to allow the part to reach the finished stage or to prepare it for subsequent operations. Perforating Shaving 138 139 140 141 142 143 144 Exercise : Choose the correct answer 1- A piece of metal whose thickness is between ………………… is considered as sheet metal. a. 0.15 mm and 2 mm b) 0.15 mm and 3 mm c) 0.15 mm and 5 mm d) 0.15 mm and 6 mm 2- At the end of sheet metal working operation, when the pressure released the spring back occurs, because of …………………….. a-elastic recovery b- plastic deformation c- over bending d- under bending 3- ………………………. is used for making axi-symmetrical cup shaped parts. a. Ironing b- Stretch forming c- Spinning d- notching 4- …………………….. is the cutting operation where holes of square shapes are produced in the sheet. a. Piercing b- Perforating c- Lancing d- Slitting 5- In …………………………. metal pieces are cut from the edges of a sheet a. Piercing b- notching c- Lancing d- Slitting 6. A built-up edge mainly is caused by ………. of soft material. a. high cutting speed b- use negative rake angle c. using chip breaker d- cut dry 145 7. Which rake angle produces a stronger tool? a. a positive rake b- a negative rake c- a zero rake d- both b and c are correct 8. Which rake angle produces a good surface finish at low cutting speeds? a. a positive rake b- a negative rake c- a zero rake d- both b and c are correct 9. A thin chip indicates a clean cutting action with a ………… a. rough finish b- built-up edge c- better finish d- negative rake angle 10. ………………. produce short carrier lines with many red carbon bursts when held against the grinding wheel. a. cast iron b- low carbon steel c. high carbon steel d- high speed steel 11. ………………. produce straight and yellow carrier lines with small carbon bursts when held against the grinding wheel. a. low carbon steel b- cast iron c. high carbon steel d- high speed steel 12. File bites easily into ……………….. when checking its machinability. a. mild steel b- medium carbon steel c. high carbon steel d- tool steel 146 13. File bites only with extreme pressure into ……………….. when checking its machinability. a. low carbon steel b- medium carbon steel c-high carbon steel d- tool steel 14. Effect of Accidents on workers, …………………… a. delays in production b- temporary or permanent disability c- work stoppage d- damaged tools 15. Which is not one of the causes of accidents? a. Human Causes b- Society Causes c. Environmental Causes d- Mechanical Causes 16. An accident with heavy damage and lot of injury is called ………….. accident. a. Near b- Serious c- Trivial d- Minor 17. An accident with no damage or injury is called ………….. accident. a. Near b- Serious c- Trivial d- Minor 18. Which is not one of the objectives of industrial safety? a. increase production b- educate all members regarding the safety principles c. long duration of work d- reduce workman’s compensation 147 19. Which is not a direct accident cost of the owner of the factory? a. substitute worker b- compensation c- damaged tools d- treatment 20. Shop press is used for … a. installing and removing bushings b- removing ball and roller bearings c- straightening and bending d- all the above are correct 21. The bench vice is used ……. a. to hold work b- for filing, c- for chiseling, d- all are correct 22. Clamps are used for ……. a. Filling b- Chiseling c- Holding work d- Hacksawing 23. Hard hammers have ………. Heads a. Steel b- Plastic c- Brass d- Lead 24. Punches are useful for drive out ……. a. straight pins b- bearings c- rivet heads d- clean welds 25. Chisels are useful for ….. a. finishing a hole to an exact dimension b- cutting off rivet heads c-cutting internal thread d- cutting external thread 148 26. For maximum metal removal a ……………. file is used a. Single-cut b- double-cut c- rasp d- rough 27. Half round files are used for …… a. Internal curves b- External curves c- Small curves d- Enlarge holes 28. Too much pressure on a new file may cause ….. a. Pinning b- Fracture c- Slipping d- Friction 29. The cutting-die is used to cut ……….. threads on the surface of a bolt or rod a. Internal b- External c- Both internal and external d- None of the above 30. In turning operation, the job is secure1y and rigid1y held in the chuck or ………… a. between centers b- with the vice c-with C clamp d- with Holder 31. Cutting a work by a Lathe is done by turning it against …….. a. Multi edge cutting tool b- Tool post c- Drill d- Single point cutting tool 32. Speed Lathe is used for ……….. a. wood working b- threading c- knurling d- taper turning 33. Which is not a part of Speed Lathe? a. Gear box b- Bed c- Tailstock d- Tool post 149 34. Which is not a part of Engine Lathe? a. Hexagonal Turret b- carriage, c- lead screw d- feed rod 35- Tool Room Lathe built to operate with …… …. a. Precision workpieces b-small range of spindle speeds c-medium range of spindle speeds d- mass production 36- Driving dog and catch plates are used to drive a job when it is held ….. a. in a chuck b- between centers c- in a face plate d- collet chuck 37- Mandrel is a device used for holding and rotating a ………… job. a. Solid b- square c- cylindrical d- hollow 38- Rest is a lathe device, which …. a. mounts work between two centers b- supports a long slender work c-clamps work on the chuck d- none of the above 39- Angle plates clamped on …… a. Face plate -- b- Tree jaw Chuck c- Four jaw chuck d- Magnetic chuck 40- A milling machine rotates a ……………………………… into the workpiece. a. single point cutting tool b- thousand cutting edges tool 150 c- multi-toothed cutter d- chuck 41- The milling machine is capable of machining a. flat surfaces, b- slots, c- gears, d- all are correct 42- The work to be machined in milling operation is held in a a. vice b- rotary table c- an index head d- all the above 43- Which of the following is not a milling process? a. Face b- thread c- profile d- gang 44- The index crank turns to machine a gear with 28 teeth, when using an indexing head with a 40:1 gear ratio and the available index plate has circles of 25, 28, 30, 34, 37, and 38 holes is.. a. one turn plus 10 holes in the 25 hole circle b- one turn plus 12 holes in the 28 hole circle c-one turn plus 10 holes in the 30 hole circle d- one turn plus 12 holes in the 38 hole circle 45- For milling a circular slot ……………. is used. a. gang mill b- form mill c- face mill d- rotary table 46- To machine a pocket on milling machine ……………. is used. a. cutter b- end mill c- face mill d- side mill 47- A radius is machined on a work using milling machine with ……………….. a. profile mill b- rotary table c- offset boring head d- side mill 151 48- In shaper machine tool the ram ……………… a. moves backwards and forwards in a straight line b- reciprocates c- rotates d- both a and b are correct 49- Which is not a shaping operation? a. V block b- Rack c- Reaming d- Key way 50- In the Shaper, feed motion takes place during the ………. a. forward stroke b- backward stroke c- reciprocating motion d- rotary motion 51- In standard shaper, the table has only ………………… , to give the feed. a. horizontal movement b- vertical movement c- both horizontal and vertical movements d- rotary motion 52- In Universal Shaper the table can be ……….. a. rotated b- swiveled c- reciprocated d- moved 53- Planer is used for machining …………. a. Heavy workpieces b- large workpieces c- small workpieces d- both a and b are correct 54- The shaper is driven using the …… …….. a. quick return mechanism b- rack and pinion gear 152 c- hydraulic means d- motor 55- several tools can cut simultaneously on the ……… …. a. Planner b- milling machine c- shaper d- both a and b are correct 56- Which of the following is not a typical drilling operation? a. countersinking b- counterboring c- V groove d- sanding 57- Which of the following is used for drilling large, heavy workpieces that are difficult to move? a. Radial drill b- upright drill c- gang drill d- center drill 58- Which of the following is not correct for the higher drill helix angle? a. the smaller the cross-sectional area of the drillb- the weaker the drill c- the higher the cutting speed d- the higher the feed rate 59- Straight fluted drills is used when cutting, ………. a. ferrous metals b- aluminum c- hard materials d- soft sheet metals 60- normal fluted drills has …………. rake angle. a. zero b- 12 c- 30 d- 40 61- When cutting stronger material (alloy steel), the ………… helix angle must be. a. Zero b-low c- normal d- high 153 62- Flat angle drill point 135º -150º , used to drill …………. Materials. a. ferrous metals b- hard and tough c- plastics d- soft cast iron 63- Which of the following is not a Factor causing early dulling of Drill? a. feed may be too heavy b- feed may be too light c- drill supported properly d- drill speed too high 64- In roll-type grinder the workpieces are supported ………………….. a. between centers b- in bearings c- in chuck d- on table 65- In Centerless Grinding the ……………….. controls the spin of the workpiece. a. work rest b- grinding wheel c- regulating wheel d- special attachment 66- ……………… is especially useful in the grinding of ceramics and tungsten carbide. a. Aluminum Oxide b- Silicon Carbide c- Cubic Boron Nitride d- Diamond 67- ……………… is especially useful in the grinding of steels. a. Aluminum Oxide b- Silicon Carbide c- Cubic Boron Nitride d- Diamond 154 68- In hand Hacksaw………………………. a. at least two teeth cutting at any time b- fine-tooth blade on soft materials c- course-tooth blade on harder materials d- set of side teeth to cut wider 69- In wavy set of Hacksaw blade ……………………….. a. fine-toothed blades is used b- to cut a thin metal c-to reduce vibration d- all are correct 70- Which of the following is a file cut type? a. Rough b- coarse c- rasp d- bastard 155  Assembly diagram for milling fixture (10 parts) A fixture is also a device, which is fastened to the table of a machine tool, such as milling machine. The device enables loading and unloading of components with ease give unique location of workpiece in relation to the fixture and also holds (clamps) good the work. with the direction of gravity, and hence needs to be analyzed more closely. The final aspect, which distinguishes a fixture from a jig, is the absence of bushes to guide the tools. However, the requirement of setting blocks may not be always necessary as in the case of turning or welding fixtures. The requirement is more pronounced in the case of milling fixtures while cutting slots, keyways, side milling of fastener heads. 1-milling fixture base, 2-support bracket, 3-cross cylinder head screw, 4-eccentric arm, 5-grooved bolt, 6-activity V block, 7-Cutter set block, 8-fixed V block, 9-bolts, 10-cylinder pin shaft 11- Feeler gauge  Assembly diagram for drilling Jig A device that does both functions (holding the work and guiding a tool) is called a jig. A jig is a device, in which the component is clamped in a specific location so that cutting tools are guided to perform one or more operations. Jigs, which are independent devices, are fastened to the table of a machine tool. They are so designed to facilitate loading and unloading of components with ease. The third feature of a jig is that it has locating devices to position a component in a unique way. The fourth aspect of a jig specification is the gripping of the workpiece through a clamping device. To necessitate the need of jigs, fixtures and special tools, The four main engineering classes of production are as follows: 1. Job Production: This involves the manufacture of specialized components or systems to meet the specific needs of the customers. Examples of job production are the manufacture of jigs, fixtures and press tools. 2. Batch Production: Some of the examples of batch production are the manufacture of aeroplanes, aero- engines, tanks, etc., that use the concept of intermittent manufacture of large range of products, produced in batches. 3. Mass Production: In this type of plants, the products are produced in mass quantities by specialized and repetitive methods, without requiring specialised layouts as in the case of flow production. Examples are mass production of screws, pins, hand tools, like chisels, spanners, hammers, etc. 4. Flow Production: In flow production, the standardised finished products are produced in plants, specifically laid out for this purpose. Examples of flow production are water desalination plants. The present day trend is to produce components and systems to meet the basic specifications of: (i) Accuracy (ii)Interchangeability (iii)Economic production rate. In order to achieve the above objectives the following tooling equipment are deployed: (i) Jigs (ii)Fixtures (iii)Special tools like broaching tool, gear shaping tools, special class of taps and reamers (iv)Gauges to verify if dimensions are within the limits. Some degrees of freedom is restricted by locators/supports and the rest degrees of freedom Locators and supports are arrested by external forces usually provided directly by clamping. The terms “locator” and “support” both describe locating devices. The term “support” refers to locators that bear the weight of the workpiece. Supports are generally placed under a part. The term “locator” refers to the elements that position the part on the axes not bearing the weight of the part. When there is considerable variation in part dimensions from batch to batch, an eccentric locator can be sued.  Location from cylinder Direct pressure Cam Clamp Fixed V Clamp TYPE OF CLAMPS Strap/Plat clamps Third-class lever action The spacing of the three elements is important. The distance between the fastener (effort) and the workpiece should always be less than that between the fastener and the heel pin (fulcrum). This increases the mechanical advantage of the clamp and increases the holding force on the workpiece. Screw Clamps Screw clamps are widely used for jigs and fixtures. They offer the tool designer almost unlimited application potential, lower costs, and, in many cases, less complex designs. The only disadvantage in using screw clamps is their relatively slow operating speeds. For faster clamping indirect screw clamping can be used. Direct pressure Cam Clamp Fixed V Clamp Locating the Cutters When the cut plate requires parallel shoulders, The size of the set block used to locate the cutters is calculated by first determining the maximum and minimum allowable sizes on the butt plate. Once this is done, the size of the feeler gauge must be determined. In this case, a.125-inch feeler gauge is selected. Finally, the feeler gauge size is subtracted from the minimum butt plate size to determine the size of the set block. Exercise Construct a Clamp fixture for milling; Clamping is performed by four cam-action strap clamps positioned two on each side (Figure). Cam clamps were again selected for their fast action and easy removal from the part.  Channel Jig This jig features a channel-like cross-section. Operators mount the workpiece within the channel and secure it by turning a knurled knob. The drill bush then guides the tool during operation. 170 Template Jig These are the simplest types of jigs. The plate serves as a template with holes. The jig is fitted onto the workpiece. The operator directs the drill through these holes towards the workpiece, and drilling occurs. Then, the operator makes the holes at the same location as those on the template, with the same size and shape. Template jigs improve drilling process efficiency by lowering the possibility of errors and rework through accurate guidance. 171 Angle- Plate jig Just as the name suggests, it is ideal for supporting up the workpiece at an angle. 172 Diameter Jig It enables drilling of rounded workpieces that are hard to secure using other jigs. For instance, making radial holes in a cylindrical or spherical workpiece 173 Ring Jig The workpiece is stationary and clamped onto the drill body while the drill bushes guide the holes made. It is suitable for drilling holes on circular flanged parts 174 Box Jig Box jig has a box-shaped component where the work is tightly enclosed in it. Operators can drill or machine the work from numerous angles at a single setting, depending on which face of the jig faces the tool. 175 specific example of a drilling jig BOX JIG References: -Machine tool practices / Richard R. Kibbe... [et al.]. — 9th ed. p. cm. Includes index. PEARSON, ISBN-13: 978-0-13-501508-7 (casebound), 2010 -Machine-shop practice. I. Kibbe, Richard R.- PEARSON, ISBN-10: 0-13-501508-1, 2010 - Machining Fundamentals From Basic to Advanced Techniques / by John R. Walker, by THE GOODHEART-WII.lCOX COMPANY, INC. 2000. Richard R. K.(2010). Machine tool practices, 9th ed. PEARSON, ISBN-13: 978-0-13-501508-7. Kibbe I. , Richard R. (2010). Machine-shop practice. PEARSON, ISBN-10: 0-13-501508-1. John R. Walker (2000). Machining Fundamentals From Basic to Advanced Techniques. The Goodheart-wii.Lcox COMPANY, INC. 178 179