Table of Contents General Metal Work...1

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1 General Metal Work

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3 Table of Contents General Metal Work...1 GENERAL SURVEY METALS AND THEIR PROPERTIES Classification of Metals Identification of Metals (Examples) Properties of Metals Shapes and Sizes of Metal TECHNICAL DRAWING Introduction into Technical Drawing Types of Lines Drawing Paper with title block Basic Rules Drawing in three Elevations METROLOGY Metric System Inch System Metrology Introduction Common Measuring Tasks Measuring Equipment FITS AND ISO TOLERANCES LAYING OUT Layout Tools and Accessories Layout Procedure BENCH WORK TOOLS Work Bench Bench Vise Hand Hacksaw Chisel Tools Files Hammer...46 Bench Work Exercise...47 Bench Work Exercise New PRINCIPLES OF MECHANICAL METAL CUTTING Classification of Metal Cutting Processes Angles of tools Cutting Tool Guideline DRILLING Drill Press Twist drill Different Drill Press Operations Facts and Problems Drill Press Safety CUTTING THREADS WITH TAP & DIES Main Parts of a Screw Thread Hand Tapping Threading Dies SHARPENING TOOLS Bench Grinder or Pedestal Grinder Sharpening Tools Safety Precautions:...78 LIST OF NEEDED RESSOURCES FOR GENERAL METAL COURSE APPENDIX...79 APPENDIX NO APPENDIX NO GENERAL METAL WORK FINAL TEST...81 i

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5 General Metal Work With technical assistance from: GERMAN DEVELOPMENT SERVICE August 2000 Dear Reader, I would like to comment this handout, because otherwise you might get a little confused while studying it. The most important thing to know is, that this handout is developed for a non formal Training Center. The participating government officials and the involved companies were not interested in long term courses. So, I had to respect the wish of my project partners for a course with this length and was limited on the most important subjects. One or two of the modules are still under construction. Sorry for this. DED Development Worker GENERAL SURVEY TARGET PARTICIPANTS min 18 years old, High school graduates, no experience needed LENGTH OF COURSE 120 hours / 15 days OBJECTIVES At the end of the course, the participants should be able to: Distinguish different metals and their properties and know the most common shapes of metals Read and draft simple blue prints in order to fabricate workpieces to the required specification Know how to measure, use the most important measuring tools and prevent the most common mistakes while measuring Understand the importance of limits and fits in fabrication and know how to use them Lay out some workpieces with the necessary tools Understand the basics of angles of cutting tools Properly use hand hacksaw, file, chisel, hammer and other hand tools Know the process of drilling with a drill press and the needed tools and equipment Know how to sharpen tools using the bench grinder Cut internal and external threads with taps and dies and know how to prepare the workpiece 1

6 Make use of different power tools typically used in a metal workshop Know how to use SMAW welding machine while welding mild steel Cut metals with Oxy Acetylene cutting outfit Know and use the proper safety procedures and equipment COURSE OUTLINE THEORY (30%) HANDS ON TRAINING (70%) METHOD Metals and their properties Various types of drawings, scales, views, lines, symbols of blue prints Measuring tools and measuring errors. Metric and inch system Procedure of laying out Limits and fits Principles of metal cutting and cutting angles of tools Bench and hand tools Drilling operation, threading and reaming Sharpening tools using bench grinder Cutting and grinding with power tools SMAW welding process Oxy Acetylene cutting Safety procedures and equipment Draw and read some simple drawings Use measuring tools like steel rule, vernier calibers, micrometer, protractor Use laying out tools like scriber, divider, center punch, try square Make use of hand hacksaw and files while preparing workpieces following the specifications of blue prints Make use of a drill press and the necessary equipment. Know how to calculate the RPM for drilling Sharpen tools like scriber, center punch, chisel, drill bits Experience the different power tools like bench grinder, power hacksaw, chop saw, angle and die grinder, drill SMAW welding exercises (mild steel with different joints and various positions) Correct welding defects Oxy Acetylene cutting exercises Time Frame Plan of General METAL Work Course (Zero skills level Course Duration 120 hours) Lectures/Discussion Practical Sessions Case studies Teaching Videos Topic Theory? Methodology Resources Needed Hours Hands On Training (Practical Sessions) Hours Total Hours Orientation Training Overview? Lecture/Discussion Manuals General, Policy and Procedure 1.0 Familiarization tour to the workplace (2.0) Work Attitude Work Attitude and Time is Money? Lecture/Discussion (4.0) Metals and their Properties Property definition Ferrous metals Nonferrous metals and nonferrous alloys Identification of metals Shapes and sizes of metals? Lecture/Discussion? Demonstration Training Handout Assorted Samples of metals (6.0)

7 Technical Drawing Tools needed for drawing Types of drawings and views Types of lines Dimensioning Limits Scaling Basic Drafting symbols? Lecture/Discussion? Demonstration Training Handout Samples of blue prints Self practice exercises in reading and drafting blue prints and preparing different workpieces 12.0 (18.0) Measurement Metric and Inch System Measuring tools and care (Steel rules, Vernier calipers, Micrometers, compass, Height Gauges) Inspection of measuring tools? Lecture/Discussion? Demonstration Training Handout Samples of Measuring tools 4.0 Self practice exercises in measuring different samples (28.0) Limits and Fits Interchangeability, types of fits, limits of tolerance on technical drawings? Lecture/Discussion? Training Handout (30.0) Laying Out Types of laying out Layout Equipment and tools (Surface plate, Combination square, Scriber, Center punch, Divider, Steel rule, Protractor, surface gauge) Layout Accessories (Angle Plate, V Blocks, Vernier height gauge, machine lay out)? Lecture/Discussion? Demonstration Training Handout Samples of Laying tools 2.0 Self practice exercises in laying out different workpieces (35.0) Bench Work Explain the use of bench vise, hammer, hand hacksaw, file, chisel, letter stamp, anvil? Lecture/Discussion? Demonstration Training Handout Samples of handtools 1.0 Bench work exercise (MS plate 180mm 100mm 10mm) (56.0) Principles of Metal Cutting Machineability of metals Cutting tool design? Lecture/Discussion? Demonstration Training Handout (59.0) Drill Press, drilling tools, drilling operation Types of drill press and the important parts Tool holding device and taper shank tools Twist drills (materials, sizes, cutting speeds and? Lecture/Discussion? Demonstration Training Handout Assorted Samples of drill bits 3.0 Drilling exercise (MS plate 180mm 100mm 10mm) (67.0) 3

8 feeds) Machine vise, drill press operation, Cutting fluid, countersinking, counterboring Threading Hand taps and tap wrenches Tap drill size and taping a hole Treading dies and holder Treading lubricants? Lecture/Discussion? Demonstration Training Handout 1.0 Exercise for tap and die (71.0) Resharpening tools Explain bench grinder Sharpen tools like chisel, center punch, scriber, drill bit Safety, care and maintenance of bench grinder? Lecture/Discussion? Demonstration Training Handout 1.0 Self practice exercises in resharpening different tools (75.0) Cutting with Power Tools Explain power hacksaw and chop saw Process on cutting with power hacksaw and chop saw Safety, care and maintenance of power hacksaw and chop saw? Lecture/Discussion? Demonstration Training Handout 1.0 Self practice exercises in cutting different shapes of metals Hands on training in maintain the machines and in mount and dismount hacksaw blade and cutting disc (79.0) SMAW Welding Fundamentals and its Processes Definition of the various types of the most common welding technologies Power Sources SMAW Processes Tools and equipment? Lecture/Discussion Training Handout Teaching Video (81.0) SMAW Welding Electrodes Types of electrodes (mild steel, low hydrogen electrode)? Lecture/Discussion Training Handout Teaching Video (83.0) Welding Processes in Various Positions Striking the arc The most common types of joints (Butt, T, lap, corner, edge) The most common types of grooves (Square, beveled, V, double V) Welding positions (flat, horizontal, vertical, overhead)? Demonstration? Lecture/Discussion Training Handout Teaching Video 3.0 Setting up the equipment Weld with different types of mild steel electrodes Prepare metal plates and grooves for welding Weld (108.0) 4

9 Manipulation of electrode standardized workpieces Identification of Welding Defects E.g. Incomplete penetration, slag inclusion, undercut, spatters? Lecture/Discussion Training Handout Sample of workpiece 1.0 Analyze welding defects and correct them during the practical work (112.0) Oxy Acetylene Cutting Types of gas for cutting metals Gas cylinder, gas flow meter and pressure regulator Cutting tools Cutting process? Lecture/Discussion? Demonstration Training Handout 1.0 Cutting Exercises (116.0) Safety (included in the previous topics) Safety in the workshop? Lecture/Discussion? Demonstration Training Handout (120.0) Total METALS AND THEIR PROPERTIES 1.1 Classification of Metals Steels are the most important ferrous metals used in machine shop work. They are generally classified by their carbon content. It can be custom made to fit a wide range of requirements. By using various chemical and alloying elements, steels with many different properties can be produced. 1.2 Identification of Metals (Examples) Metal Carbon Content % Appearance Uses Cast Iron (C.I.) 2.5 to 3.5 Grey, rough sandy surface Parts of machines, such as lathe beds, water pump pitcher type, etc. 5

10 Machine Steel (M.S.) Cold Rolled (C.R.S.) 0.10 to 0.30 Black, scaly surface Bolts, rivets, nuts, machine parts 0.10 to 0.30 Dull silver, smooth surface Shafting, bolts, screws, nuts Tool steel (T.S.) 0.60 to 1.5 Black, glossy Drills, taps, dies, tools High Speed Steel (H.S.S.) Alloy Steel Black, glossy Dies, taps, tools, drills, toolbits Brass / Yellow (various shades), rough if cast, smooth if rolled Bushings pump parts, ornamental work Copper / Red brown, rough if cast, smooth if rolled Metals are usually identified by one of the following four methods: By their appearance By spark testing By manufacturer s stamp By a code color painted on the bar. Exercise Sheet Classify the materials. Please mark your answer by a X. Soldering irons, electric wire, water pipes Metals Non Metals Ferrous Metal Nonferrous Metal Natural Material Artificial Material Wood Aluminum Leather Glass Copper Mild Steel Cast Iron Rubber Ore Brass Ceramics Tool Steel Bronze Lead PVC Teflon Tin Stainless Steel 6

11 Materials used in Car Production Use one of these expressions to complete the statements below: covered with or made of or contain(s) The pipes of the radiator. copper. The bumper chromium. The door handles zinc. The cables... plastic. The windscreen.. glass. The battery. lead. The pistons. aluminum. The cylinder block. cast iron. 1.3 Properties of Metals To better understand the use of the various metals, you should be familiar with the following metallic properties: Physical Properties: Melting Point: The melting point is the temperature at which a material starts to melt. Ferrous Copper Lead Aluminum Tin 1,536 degree Celsius 1,083 degree Celsius 327 degree Celsius 658 degree Celsius 232 degree Celsius Tungsten 3,387 degree Celsius Electrical Conductivity: The electrical conductivity describes the ability of a material to conduct electricity. Copper 100% Silver 106% Lead 8% Aluminum 62% Ferrous 17% Zinc 29% 7

12 Density: The density (kg/dm 3 ) of a material gives the quotient of mass and volume of a body. Water 1.00 Copper 8.90 Lead Aluminum 2.70 Steel 7.85 Tungsten Thermal longitudinal expansion: To express the thermal longitudinal expansion, there is a coefficient that gives for each material the expansion of a body with the length of 1 Meter at a change of temperature of 1 degree Celsius Mechanical Technological Properties: Elasticity: Is the ability of a metal to return to its original shape after being distorted. Properly heat treated springs are good examples of elastic materials. Ductility: Is the ability of a metal to be permanently deformed without breaking. Metals such as copper and machine steel, which may be drawn into wire, are ductile materials 8

13 Tensile Strength: The ability of material to resist fracture under tensile load. Compressive Strength: The ability of a material to withstand heavy compressive load. Brittleness: Is the property of a metal that allows no permanent distortion before breaking. Cast iron is a brittle metal; it will break rather than bend under shock or impact. Toughness: Is the ability of metals to withstand shock or impact. Toughness is the opposite of brittleness. Shear Strength: The ability of a material to resist fracture under shear load. Flexural Strength: The ability of a metal to resist under flexural force. Torsional Strength: The ability of a metal to resist torsional force. 9

14 Collapsing Stress: The ability of a metal with a slim form to resist axial directed force. Hardness: The ability of metal to withstand abrasion or penetration Manufacturing Technological Properties: Weldability: Means the ability to weld two metals together. The grade of weldability depends on the content of carbon. Steels with a content of max. 0.22% are more or less good weldable. Machinability: Indicates how easy or difficult materials can be machined. Malleability: Is the property of metals that allows it to be hammered or rolled into other sides and shapes. Castability: Is the property of metals that allows it to be molten and after it to be casted without any pores. Hardenability: Is the property of iron metals that allows it to increase the hardening through structural transformations Chemical Properties: 10

15 Corrosion Resistance: Is the ability of a material to resist the attack of water, gases, acids or other chemicals. 1.4 Shapes and Sizes of Metal Due to the wide variety of work performed in a metal shop and the necessity of conserving time, as well as reducing the amount of metal cut into steel chips, metals are manufactured in a wide variety of shapes and sizes. There is a proper method for specifying the sizes and dimensions of metal when ordering: Flat bar: Thickness Width Length Round bar: Diameter Length Square bar: Width Length Angle bar: Thickness Width Length Hexagon bar: Diameter Length (or Distance Across Flats Length) Pipe: Diameter Schedule Length # 20 is thinner than # 40 Square tubing: Thickness Width Length Channel Bar: Width Height Length 11

16 I Beam: Length Thickness pounds Z Bar: Width Length T Bar: Width Length Metal Sheet: Gauge Width Length 2. TECHNICAL DRAWING A technical drawing, sometimes referred to us as a drawing or print, is the language used for technical communication. It depends on the job how exactly the drawing should be made. Sometimes it is enough to sketch with freehand lines, but when it comes to more important parts the draft should be made very exactly. 2.1 Introduction into Technical Drawing Drawing Equipment The basic equipment is: Drawing board T Square Drawing paper Compass Protractor Pencils Eraser Drawing Paper sizes ISO A 0 A 1 A 2 A 3 A 4 A 5 A 6 mm Scale Size 12

17 Scale is used to indicate the ratio of the drawing size to the actual size of the part. Scaling is often necessary to enlarge small parts for clarity and to have room for dimensions and other details. Large objects are often drawn at a reduced scale in order to get the necessary information to fit a convenient size sheet of paper. The scale is generally found in the title block of a drawing. The dimensions shown on the drawing give the correct size of the part required. The actual drawing should never be measured to determine that size to be machined. 2.2 Types of Lines Various standard line styles and widths are used on technical drawings by the designer to precisely specify what is required. The examples below is the so called alphabet of lines : Standard lines used for technical drawings: Type Description Thickness mm Use Free hand line Thin black lines 0,25 to 0,35 Sketches; break line Object line Thick black lines 0,5 to 0,7 Indicate the visible form or edges of an object Thin unbroken line Thin black line 0,25 to 0,35 Shading line, Thread line, Diagonal line Hidden line Center line Medium weight black lines (dash: approx. 4 mm, gap: 1 mm) Thin lines with alternating long lines and short dashes (dash: approx. 10 mm, gap: 1 mm) 0,35 to 0,5 Indicate hidden contours of an object 0,5 to 0,7 Indicate centers of holes, cylindrical objects, and other sections Dimension line Thin black lines with arrowhead at each end. 0,25 to 0,35 Indicate dimensions of an object 13

18 Cutting plane line Thick black line (dash: approx. 7 mm, gap: 1 mm) 0,5 to 0,7 Show imagined section Cross section line Exercise Sheet Fine evenly spaced parallel lines at 45. Line spacing is in proportion to the part size Fill up the boxes with the given line type 0,25 to 0,35 Show surfaces exposed when a section is cut 2.3 Drawing Paper with title block 14

19 Exercise Sheet 1. Draw and dimension the object below using the given measurements. Use a piece of paper with a title block. 2. Draw and dimension the object below using the given measurements. Use a piece of paper with a title block. 15

20 2.4 Basic Rules Dimensions are entered in millimeters without measures. Dimension lines must have a distance of about 10 mm from the object edge and 7 mm from parallel dimension lines. The dimensions should be placed above the dimension lines and should be staggered. Dimensions must be either read from below or from the right. For small dimensions the arrows are placed outside. Symmetrical workpieces are dimensioned symmetrical to the center line which extends 2 3 mm beyond the object edge. 16

21 Simple workpieces are mostly drawn in front elevation only. If an elevation in which the area of a circle appears as a straight line is to be dimensioned, the diameter symbol is to be placed in front of the dimension figure. If the circle is shown in the elevation, then it is not necessary to draw the diameter symbol. The diameter is shown by two dimension arrows on the circumference or drawn on the extension lines of the circle. In this cases no diameter symbol will be used. A radius is symbolized by R and has only one dimension arrow at the circumference. The center point is fixed by the crossing of center lines. Concealed edges are drawn as dash lines. The length of each dash depends on the size of the drawing. Dash lines start and end with a dash at the object edges. If visible and concealed edges coincide, the visible edges are drawn. 17

22 Section views are used to show the interior form of an object that could not be shown clearly by conventional methods. The section areas are shaded, not the hollow spaces. The smaller the section area the closer the shading lines. In order to insert dimension figures the shading has to be broken. The shading lines are thin unbroken lines, which are angled at 45 degree to the center line or angled to the base edge. Assembled workpieces are identified by opposite or varied shading. Section areas of one object are always shaded in the same direction. The outer diameter of a bolt thread is drawn as an object line, the core diameter as a thin unbroken line. The distance between the thick and thin lines represents the thread diameter. Looking in direction of the shaft end the core diameter appears as a three quarter circle in any position. 18

23 The ends of screws are normally 45 degree chamfered. The core diameter of the internal thread is drawn as an object line, the outer diameter as a thin unbroken line. All lines of concealed thread are drawn as invisible edges. The thin three quarter circle becomes a full circle shown in broken line. To be dimensioned are: Outer diameter (e.g. M 10 or UNC ¾) Useful length of thread Length of shaft with end, or respectively depth of core hole without drill cone. 2.5 Drawing in three Elevations Sometimes it is necessary to draft workpieces in three elevations to show all important parts of it. 19

24 3. METROLOGY Over 90% of all countries in the world are presently using the Metric System. But there are still some countries using the Inch System (e.g. United States, Canada, and England). With the reality of global manufacturing continually expanding, the need for metal workers in both systems of measurement will continue to grow. 3.1 Metric System The metric system uses the meter and linear units based on the meter as its standards of measure. At the General Conference on Weights and Measures in October, 1983, the meter, defined as the distance traveled by light in a vacuum during 1/299,792,458 of a second, was approved as a world standard. 20

25 All multiplies and subdivisions of the meter are directly related to the meter by a factor of ten. This makes it easy to use the decimal system for calculations involving metric units. Kilometer = km 1 km = 1,000 m Meter = m 1 m = 10 dm = 100 cm = 1,000 mm Decimeter = dm 1 dm = 10 cm = 100 mm Centimeter = cm 1 cm = 10 mm Millimeter = mm 1 mm = 1,000 mm Micrometer = mm Exercises Metric System Change into smaller units 1 m = 10 dm = 100 cm = 1,000 mm 2.5 m dm = cm = mm 0.9 m = dm = cm = mm 1.2 m = dm = cm = mm 0.1 m = dm = cm = mm Change into larger units 100 mm = 10 cm = 1 dm = 0.1 m 25 mm = cm = dm = m 120 mm = cm = dm = m 19 mm = cm = dm = m 386 mm = cm = dm = m Summing Up 20 cm + 10 dm + 30 mm + 25 cm = 1,48 m 10 cm + 5 dm + 28 mm cm = mm 38 mm + 42 cm dm m = cm 5.5 dm mm + 44 cm m = dm 2.2 m + 86 cm + 77 cm mm = m 0.1 mm cm cm mm = mm Mixed Operations 1 m + 37 mm 5 dm + 40 cm = 937 cm 1.47 m 37 mm 1.8 dm cm = cm 96 mm 3.8 cm m + 98 dm = dm 0.4 cm 12 mm m 8.4 dm = m 11 cm + 11 mm dm m = m 21

26 19.4 dm 87.5 cm m 94 mm = dm Conversion from Metric to Inch or opposite 1 millimeter = inch 1 inch = 25.4 millimeters 1 centimeter = inch 1 inch = 2.54 centimeters 1 meter = inches 1 foot = meter 3.2 Inch System Unlike the Metric System, within the Inch System there is no relationship of other linear units to the base inch unit. The values of yard, rod, mile, etc. have to be studied and kept in memory in order to use them. The inch can be dived in halves (1/2), quarters (1/4), eighths (1/8), sixteenth (1/16), thirty seconds (1/32), sixty fourth (1/64), tenth, hundreds, thousandth, ten thousands etc. 3.3 Metrology Introduction Engineering metrology is defined as the measurement of dimensions: length, thickness, diameter, taper, angle, flatness, profiles and others. An important aspect of metrology in manufacturing processes is dimensional tolerances. That is, the permissible variation in the dimensions of a part. Tolerances are important not only for proper functionings of products, they also have a major economic impact on manufacturing costs. The smaller we make the tolerances, the higher the production costs. These and related aspects of tolerances and tolerancing are described later on in this course. 3.4 Common Measuring Tasks Inside Outside Height Depth Diameter 22

27 Distance Angle Taper Gear Surface Geometrical Form and Position 3.5 Measuring Equipment A modern industrial fabrication could not function without precise measuring equipment. The parts produced are useless if they are not made to the exact sizes specified by the customer. 23

28 3.5.1 Care of Measurement Tools Proper care of measuring tools and instruments is very important to maintain the accuracy and quality of these tools. Precision measuring tools and instruments are expensive and should be treated with care, otherwise their accuracy can be destroyed. Never drop a measuring tool. Keep measuring tools away from chips, welding and grinding sparks. Never place measuring tools on oily or dirty surfaces. Store measuring tools in separate boxes to avoid scratches, nicks, or dents. Clean the tools and apply a light film of oil on the handling surfaces before putting them away Sample of Gauges Outside Radius Gauge Inside Radius Gauge Angle Form Gauge Limit Snap Gauge 24

29 Thread Gauge Angle Form Gauge Limit Plug Gauge Outside Thread Ring Gauge Inside Thread Plug Gauge Indirect Reading Instruments Inside and Outside Calipers are comparison tools used to make approximate measurements of the outside diameter of round workpieces. The caliper cannot be read directly and its setting must be checked with a rule or a vernier caliper. 25

30 Inside caliper with curved legs, a spring, and an adjusting nut Outside caliper with curved legs, a spring, and an adjusting nut Angle Measuring Instruments With a simple Protractor the measuring arm can be set against a circular degree scale from 0 degree to 180 degree. The measuring error is around 1 degree. With a more precise Universal Bevel Protractor angular measurements can be carried out with an accuracy of 5 minutes. Simple Protractor Universal Bevel Protractor 26

31 3.5.5 Comparative Length Measuring Instruments These instruments compare dimensions, hence the word comparative. Dial Caliper Digital Caliper Digital Micrometer 27

32 Dial Gauge Direct Reading Instruments Steel Rules Steel rules are the most common linear measuring tools and are available in the metric or inch system. Metric rules are graduated in both millimeters and half millimeters. Some rules are available with both inch and millimeter graduation. 28

33 Measure all given shapes in metric and inch Vernier Calipers Exercise Sheet Measuring with the Steel Rule Vernier calipers are precision measuring instruments used to make internal, external and depth measurements. Both systems metric and inch are available, and some styles of vernier caliper provide metric readings on one side and inch readings on the other side. The common size of verniers for machine shops are 200 mm, 250 mm and 300 mm. The precision depends on the vernier scale. Common types provide an accuracy of either 0.05 mm or 0.02 mm. The example below shows an accuracy of 0.05 mm. How to read a Metric Vernier Caliper (accuracy 0.05 mm): 29

34 1. The last numbered division on the bar to the left of the zero on the vernier scale represents the number of millimeters. In the example above the #2 (20 mm) is the last number left of the zero on the vernier scale. 2. Count the graduations between the last number (#2) and the zero on the vernier scale. In the example above there are 8 (8 mm) graduations between the #2 and the zero on the vernier scale. 3. Locate the line on the vernier scale that aligns with a bar line. Divide the number below the line by 10. In the example above it is the line with #7 (7/10=0.7 mm). 4. The measurement in the example above is 20 mm + 8 mm mm = 28.7 mm Exercise Sheet Read a Vernier Caliper with an accuracy 0.05 mm 30

35 Exercise Sheet Read a Vernier Caliper with an accuracy 0.02 mm Hands On Measurement Exercise Steel Ruler Vernier Caliper No. mm inch No. mm inch

36 Hands On Measurement Exercise Steel Ruler Vernier Caliper No. mm inch No. mm inch

37 4. FITS AND ISO TOLERANCES Limits and Fits In the world of manufacturing it is almost impossible to reach exactly the given dimension for a workpiece. Therefore the off sizes must be tolerated. To make sure, that all mating parts will fit each other they should be fabricated within certain limits of nominal dimension. Common Expressions in the world of manufacturing: Nominal The given size in the technical drawing N Upper Limit The maximum allowed size. UL Lower Limit The minimum allowed size. LL Upper Tolerance Is the difference between Nominal and Upper Limit UT Lower Tolerance Is the difference between Nominal and the Lower Limit LT Tolerance Is the difference between the Limits T Shaft with a nominal dimension of 20 mm 33

38 Shaft with toleranced dimension, 2 mm plus and 2 mm minus is allowed. UL = N + UT LL = N LT T = LT + UT Limits Exercise Sheet Nominal Dimension Upper Limit (max. Æ) Lower Limit (min. Æ) Upper Tolerance Lower Tolerance Tolerance mm mm mm 0.00 mm 0.00 mm 0.00 mm mm mm mm 0.50 mm 0.00 mm 0.50 mm mm mm mm 0.25 mm 0.25 mm 0.50 mm mm mm mm 0.00 mm 0.20 mm 0.20 mm mm mm mm 0.15 mm 0.05 mm 0.20 mm mm mm mm 0.00 mm 0.05 mm 0.05 mm mm mm mm 0.02 mm 0.01 mm 0.03 mm mm mm mm 0.01 mm 0.01 mm 0.02 mm 34

39 20.00 mm mm mm mm 0.00 mm mm mm mm mm mm mm mm Classes of Fits Force Fit (Interference Fit) Transition Fit 35

40 Loose Fit (Clearance Fit) 5. LAYING OUT Laying out is the operation of scribing center locations, straight lines, arcs, circles, or contour lines on the surface of a piece of metal to show the machinist the finished size and shape of the part to be manufactured. The information regarding the size and shape of part is taken from a technical drawing. The care and accuracy of the layout plays an important role in determining the accuracy of finished parts, since the machinist uses these layout lines as a guide for machining. 5.1 Layout Tools and Accessories Tools & Accessories Surface Plate or Marking Table Steel Rule Scriber Center Punch Solid Square or Try Square Divider Protractor Surface Gauge or Vernier Height Gauge Details Is a plate or a table made of cast iron or of granite. It must be adjusted absolute horizontally. Its surface must be perfect plane to ensure accurate scribing. To bring workpieces to the correct position on the marking table there are some other devices like prism, angle plate, V Blocks and Parallels. Steel rules are the most common linear measuring tools and are available in the metric or inch system. Metric rules are graduated in both millimeters and half millimeters. Some rules are available with both inch and millimeter graduation. A scriber is a layout tool used for drawing layout lines on a workpiece. They are made of tool steel with hardened and tempered points. It is important that the point of the scriber be as sharp as possible to produce clear, thin, layout lines. Normally ground to an angle of 90 degree. Before drilling a hole the center must be punched. To make a line more visible for cutting or oxy acetylene cutting it is helpful to punch the line. Is used for laying out workpiece in combination with steel rule and scriber. It is also used to check the angles and the surfaces for flatness. The divider is used to transfer length or circles to the workpiece. Dividers are available with and without fixing devices. A simple protractor has a measuring range from 0 to 180 degree. The measuring error is around 1 degree. Is normally used in combination with a surface plate and an angle plate to mark parallel lines. Using the simple type, the height can be adjusted with a steel rule. 36

41 Angle Plate V Blocks or Prism An angle plate is a precision L shaped tool usually made of hardened steel. All its surfaces are ground to an accurate 90 degree angle and are square and parallel. It is used to support workpieces on a 90 degree angle during the layout process. It is an accurate fabricated layout device to hold cylindrical workpieces during the layout process. They have one or more accurate 90 degree V slots. 5.2 Layout Procedure Laying out with Try Square and Steel Rule 1. Remove all burrs from the workpiece and clean it properly. 2. Start the layout from a square machined (or filed) surface. 3. Use a try square and a steel rule. 4. Place the point of the sriber on the workpiece against the try Square edge. Hold the scriber 15 degree inclined away from the workpiece and in the direction in which it is to be drawn. 37

42 5.2.2 Laying Out Circles with the Divider 1. Lay out the center of the circle 2. Punch the center of the circle 3. Adjust the divider to the proper radius while using a steel rule or a vernier caliber 4. Place one point of the divider in the center punch hole and give some force to this leg. 5. Move around the fixed leg and scratch the surface. Laying out circles Laying out parallel lines Laying Out with Surface Gauge 38

43 5.2.4 Laying Out with Protractor Center Punch Procedure 1. Make sure that the point of the punch is sharp before starting. 2. Hold the punch at a 45 degree angle and place the point carefully on the layout line. 3. Tilt the punch to a vertical position and strike it gently with a light hammer. 4. If the punch mark is not in the proper position, correct it as necessary. 6. BENCH WORK TOOLS Even in the time of CNC technology it is important to know how to do bench work using different hand tools, because still today bench work plays a big rule in machine maintenance or in metal fabrication. 39

44 This chapter will provide the trainee with the necessary knowledge about bench work. This includes the basic tools as well as their proper use. 6.1 Work Bench The workbench should be sturdy and when possible fixed with the shop floor. It is advisable to use wood for the bench board. The height of the workbench should depend on the height of the craftsman. Keep the workbench clean. Put only the tools necessary for the work on it. Measuring tools should be all the time separated from the other tools. Place them accurately on the wooden tray board. 6.2 Bench Vise The base of a bench vise is normally made of cast iron. The jaws are hardened. Clamping soft workpieces requires covering the jaws with an aluminum sheet cover. The size of the bench vise is measured by the width of the jaws and the maximum opening between the jaws. There are different types of bench vises available: With or without an anvil plate, with a pipe clamping device, machine vise for drill press, and adjustable in any position within 360 degree. 40

45 6.3 Hand Hacksaw A hand hacksaw mainly serves to separate materials and also to produce grooves and slits. By moving the saw in the direction of cut (cutting motion) with simultaneous pressure on the saw (cutting pressure), the teeth penetrate into the material and remove chips. There are different hacksaw blades, depending on the metal to be cut, available: Coarse: Medium: Fine: for soft materials appr. 14 teeth per inch. for normal material appr. 22 teeth per inch. for hard material appr. 32 teeth per inch. In order to achieve a perfect cut, file with a triangular file a small notch beside the marking line to get a good start, then place the saw with an angle of tilt (as shown in the picture below) and start with sawing. 41

46 Forward stroke with pressure. Return stroke without pressure. Use the full length of the saw blade. Saw in a straight line along the marking line. Work safety: When sawing through reduce pressure on hand hacksaw just before the workpiece separate. 6.4 Chisel Tools In chiseling the cutting edge of a chisel is driven into a workpiece by impact. A chisel must be harder than the piece being worked. Most chisels are made of alloyed tool steels. Flat Chisel Wedge angle for soft materials 30 to 50 degree; for mild steel 60 to 70 degree; for alloyed steels 70 to 80 degree Work Process: The workpiece must be properly clamped when chiseling. The chisel must be struck on the center of the head, in the direction of the axis of the chisel. The correct wedge angle must be maintained when grinding the chisel (measure with an angle gauge). The tool must be cooled frequently when sharpening, so that it does not lose its temper. 42

47 Shearing with a shearing chisel The head of the chisel must be free of burrs and grease 6.5 Files The file is a cutting tool to work materials. It has many cutting edges which are like small chisels (file teeth) and are harder than the material being worked upon. For cutting metals normally Cross Cut files are used. These files have an overcut, and an upcut. When using a file, several cutting wedges always act at the same time. To file different materials there are various coarses available, such as smooth cut, second cut, and bastard cut. 43

48 Types of Files The length of the file body normally used is between 100 mm and 350 mm. The file handle is either from wood or from plastic. 1. Square File large 2. Flat File 3. Square File small 4. Triangle File 5. Round File 44

49 6. Half Round File 7. Knife File 8. Flat Triangle File 45

50 File Handling Clamp the workpiece as close as possible to the jaws of the vise. Use protective jaws (Aluminum) to protect the workpiece. Start with a rough file for removing more material then take a smooth file to reach a good surface. Forward stroke with pressure; Return stroke without pressure. Move with the file crosswise to control the area of filing. Clean the file from time to time (especially smooth files) with a wire brush to prevent messy finishes. Never work with a file without a file grip. Make sure that the file grip is properly attached, that it has the right dimension and that it is not splitted. 6.6 Hammer A hammer is used nearly in every operation related to metal works. They are made of cast steel or carbon steel. It mainly consists of a face, peen and body. The face and the peen are hardened and tempered but the rest of the body is kept soft. A wooden handle is fitted in the eyehole of the hammer with the help of a wedge. The wedge spreads the handle and fixes it inside the hole. Hammers are made in the size range of 25 Gram to 10 Kg. There are different types of hammer available: Fitters hammer, Ball pane hammer, Rubber mallet, Plastic hammer, Wood hammer, Sledge hammer, Claw hammer, Aluminum hammer, copper etc., 46

51 Safety: The handle of a hammer should be dry and not greasy The surface of a handle should be smooth The face of a hammer should not be spotted, if it so then make it smooth by grinding Hold the hammer handle always nearer to its tail end. Bench Work Exercise Necessary material and tools for this exercise: 1 piece flatbar 200 mm 102 mm 10 mm steel rule 400 mm scriber center punch hammer 200 g protractor 47

52 try square combination square vernier caliber 250 mm depth vernier caliber hand hacksaw flat file 250 mm rough and bastard triangular file 250 mm rough and bastard different twist drills different screw taps different countersink letter stamps chisel Metal Plate Working Step No Take a piece of flat bar with a measurement of 200 mm lengths and 105 mm width and 10 mm thickness. 2. Take the letter A stamp and stamp it as shown in the above drawing. 3. File surface of edge A even and remove all rust and forging scale. First use a rough file, then for finishing the surface a bastard file. Control the evenness with the try square. 4. Layout lines from the left side as well as on the right side. Use edge A as a reference to put the try square and scribe the lines. 5. Center punch the lines with at least 5 mm distance between the marking points. 6. Cut on the outer part of the lines using the hand hacksaw and leave at least 1mm allowance for filing. 7. File the surfaces of edges B and D in a right angle to surface A. File the 1mm excess to the size required. 8. File surface of edge C even and parallel to edge A to the size required. First use a rough file, then for finishing the surface a bastard file. Metal Plate Working Step No. 2 48

53 1. Take a combination square and set 135 degrees angle using a protractor. 2. Put the combination square at edge A. 3. Scribe a line with the scriber. 4. Center punch the line with at least 5 mm distance between the marking points. 5. Cut on the outer part of the line using the hand hacksaw and leave at least 1mm allowance for filing. 6. File the surface of edge B in an angle of 135 to surface A. File the 1mm excess to the size required. Metal Plate Working Step No Take divider and steel rule for laying out the central point of radius = 40 mm. 49

54 2. For laying out, use surfaces A and B as basis. 3. Set the divider on 40 mm radius. 4. Scribe a circle on the left lower corner of the work piece. 5. Center punch with at least 5 mm distance between the marking points along the line. 6. Cut on the outer part of the layout line leaving 2 mm allowance for filing. Metal Plate Working Step No Lay out using surface A and B as a basis, scribe and punch following the illustration given below on the right lower corner of the work piece. 2. Cut on the outer part of the layout line leaving 1 mm allowance for filing. 3. File the work piece and check if it is in the right measurement. Metal Plate Working Step No. 5 50

55 1. Lay out the two squares which are 30 mm 30 mm and 20 mm 20 mm as shown in the drawing above using surface A and B as a basis. 2. Mark the squares exactly as shown in the drawing above. 3. Centerpunch the lines as shown in the drawing above. 4. Drill the punch mark of the inner square with a 8.5 mm twist drill. Metal Plate Working Step No Cut the bridge between the wholes using chisel and hammer. 2. File the outer square 30 mm 30 mm using the necessary files. 3. Check if the filed square is parallel to surfaces A, B, C and D. Metal Plate Working Step No. 7 51

56 1. Mark a border line for the height of the letters and vertical line for each letter. For the width let approximately 1 mm clearance both sides. 2. Adjust the letter stamp on the surface of the work piece. 3. Strike the letter stamp using a 200 g hammer. Metal Plate Working Step No Lay out the lines for drilling using the measurement given. 2. Punch all the mark for drilling. Metal Plate Working Step No. 9 52

57 1. Drill the holes with required twist drills. 2. Countersink both sides of holes with countersink tool. 3. Tap the threads with required screw taps. 4. Check the specifications for holes 1 and 2 in the complete technical drawing of the workpiece. Bench Work Exercise New 53

58 Necessary material and tools for this exercise: 1 piece flatbar 100 mm 100 mm 10 mm steel rule 400 mm scriber center punch hammer 200 g protractor try square combination square vernier caliber 250 mm depth vernier caliber hand hacksaw flat file 250 mm smooth and rough triangular file 250 mm smooth and rough square file 250 mm smooth and rough different twist drills different screw taps different countersink letter stamps chisel Metal Plate Working Step No. 1 54

59 1. Take a piece of flat bar with a measurement of 100 mm lengths and 100 mm width and 10 mm thickness. 2. The fianl dimension of the workpiece should be 95 mm 90 mm 10 mm with a tolerance of plus 0.2 mm and minus 0.2 mm. 3. Take the letter A stamp and stamp it as shown in the above drawing. 4. File surface of side A even and remove all rust and forging scale. First use a rough file, then for finishing the surface a smooth file. Control the evenness with the try square. 5. Layout lines from the left side as well as on the right side. Use side A as a reference to put the try square and scribe the lines. 6. Center punch the lines with at least 5 mm distance between the marking points. 7. Cut on the outer part of the lines using the hand hacksaw and leave at least 1mm allowance for filing. 8. File the surfaces of sides B and D in a 90 degree angle to surface A. File the 1mm excess to the size required. 9. File surface of edge C even and parallel to side A to the size required. First use a rough file, then for finishing the surface a smooth file. Metal Plate Working Step No. 2 55

60 1. Take a combination square and set 135 degrees angle using a protractor. 2. Put the combination square at side A. 3. Scribe a line with the scriber. 4. Center punch the line with at least 5 mm distance between the marking points. 5. Cut on the outer part of the line using the hand hacksaw and leave at least 1mm allowance for filing. 6. File the surface in an angle of 135 to surface A. File the 1mm excess to the size required. Metal Plate Working Step No. 3 56

61 1. Take divider and steel rule for laying out the central point of radius = 40 mm. 2. To layout, use surfaces A and D as basis. 3. Set the divider on 40 mm radius. 4. Scribe a circle on the left lower corner of the work piece. 5. Center punch with at least 5 mm distance between the marking points along the line. 6. Cut on the outer part of the layout line leaving 2 mm allowance for filing. 7. File the surface exactly following the marks. Metal Plate Working Step No Lay out the two squares which are 30 mm 30 mm and 20 mm 20 mm as shown in the drawing above using surface A and B as your basis. 2. Mark the squares exactly as shown in the drawing above. 3. Centerpunch the lines as shown in the drawing above. 4. Drill the punch mark of the inner square with 8.5 mm twist drill. Metal Plate Working Step No. 5 57

62 1. Cut the bridge between the wholes using chisel and hammer. 2. File the outer square 30 mm 30 mm using the necessary files. 3. Check if the filed square is parallel to surfaces A, B, C and D. Metal Plate Working Step No Mark two lines for the height of the letters and vertical lines for each letter. For the width let approximately 1 mm clearance both sides. 2. Adjust the letter stamp on the surface of the work piece. 3. Strike the letter stamp using a 200 g hammer. Metal Plate Working Step No. 7 58

63 1. Lay out the lines for drilling using the measurement given. 2. Punch all the marks for drilling. Metal Plate Working Step No Drill the holes with required twist drills. 2. Countersink both sides of holes with countersink tool. 3. Tap the threads with required screw taps. 4. Check the specifications for holes 1 and 2 in the complete technical drawing of the workpiece. 59

64 7. PRINCIPLES OF MECHANICAL METAL CUTTING A large portion of manufacturing operations in the world consists of machining metal to size and shape. To be competitive, it is important that machining operations be as cost efficient as possible. This requires a good knowledge of metals, cutting tools, and machining conditions and processes. 7.1 Classification of Metal Cutting Processes Hand Cutting Processes Filing Chiseling Hand Hacksawing Shearing Hand Tapping Die Tapping Hand Reaming Machine Cutting Processes Drilling Hacksawing Turning Milling Grinding Shaping Machine Threading Machine Reaming Chiseling Sawing Turning Grinding 7.2 Angles of tools What is common to all cutting tools is the wedge shape BETA (?). To cut metals, the tool must be wedge shaped, be resistant to abrasion and tenacious. 60

65 For different cutting operations there is a need for different tool angles. Cutting tools with small wedge angles penetrate the material more easily but also tend to break off more easily if the material is hard Wedge Angle Beta (?): The wedge angle must suit to the material being worked. The smaller the wedge angle is, the lower the expenditure of force. The harder the material, the larger the wedge angle should be chosen. Clearance Angle Alpha (?): The clearance angle is the angle between the flank of the tool and the surface being cut. Friction and heating depend upon this angle. The angle should be chosen as such that the tool could cut freely. Soft materials require a larger clearance angle because they generate more heat and friction. Rake Angle Gamma (?): The rake angle is the angle between the cutting face and the plane of reference of the tool, an imaginary surface perpendicular to the cut surface. The rake angle influences the chip formation. Large angle: good chip flow, low cutting force Small to negative angle: great cutting force, highly robust cutters 61

66 7.3 Cutting Tool Guideline Cutting tools are expensive therefore take care of them. Always use sharp cutting tools to ensure an efficient cutting action and accurate work. Use the largest nose radius possible (Cold chisel, lathe tool.) Clamp the workpiece as short as possible and securely. Always use the speeds, feeds, and depth of cuts recommended by the manufacturer for the material being cut and the cutting tool used. Use enough of the proper coolant for the material being cut and the cutting tool used. 8. DRILLING 8.1 Drill Press A drill press is a machine used for drilling operations available in a wide variety of types and sizes to suit different types and sizes of workpieces. The most common machine type found in a metal shop is the floor type drill press Drill Press Parts Although drill presses are manufactured in a wide variety of sizes, all drilling machines contain certain basic parts. Base: The base, usually made of cast iron, provides stability for the machine and rigid mounting for the column. The base is usually provided with holes so that it may be bolted to a table or bench to keep it rigid. The slots or ribs in the base allow the work holding device for the workpiece to be clamped to the base. Column: The column is an accurate, vertical, cylindrical post that fits into the base. The table, which is fitted on the column, may be adjusted to any point between the base and head. The head of the drill press is mounted near the top of the column. Table: The table, either round or rectangular in shape, is used to support the workpiece to be machined. The table, whose surface is at 90 degree to the column, may be raised, lowered, and swiveled around the column. On some models it is possible to tilt and lock the table in either direction for drilling holes on an angle. Slots are provided in most tables to allow jigs, fixtures, or large workpieces to be clamped directly to the table. Drilling Head: The head, mounted close to the top of the column, contains the mechanism to revolve the cutting tool and advance into the workpiece. The spindle, which is a round shaft that holds and drives the cutting tool, is housed in the spindle sleeve. The spindle sleeve does not resolve, but is moved up and down by the hand feed lever that is connected to the pinion on the rack of the spindle sleeve. The end of the spindle may have a tapered hole to hold taper shank tools, or it may be threaded or tapered for attaching a drill chuck. The hand feed lever is used to control the vertical movement of the spindle sleeve and the cutting tool. A depth stop, attached to the spindle sleeve, can be set to control the depth that a cutting tool enters the workpiece. 62