Second Year Metalwork.

1. Second Year Metalwork. Class Notes and Homework Workbook

2. Second Year Metalwork Topics to be covered Computer Numerical control in machining Mechanisms Engines Design Electronics Decorative metalwork Properties of materials.

3. The C.N.C. Lathe. • C.N.C. stands for computer numerical control. • This is a lathe that is controlled by the computer. • The operator programmes or draws the part on the computer. The computer then controls the machine. • This machine is used mainly for mass production. • The machine can make the same part over and over without error. • C.N.C. machines can work 24 hours a day without rest. • They can work in dangerous environments.

4. The C.N.C. Lathe.

5. The C.N.C. Lathe. The Chuck. • This is the same as in the normal lathe. The three jaws close at the same time centring the piece. The Stepper Motors. • These motors are used to move the cross slide and carriage. They are very accurate and can move very small amounts at a time.

6. The C.N.C. Lathe. Tool Post. • The c.n.c. lathe is fitted with a quick change tool post allowing the tools to be changed quickly. • Some lathes are fitted with a turret which allows them to hold more than one tool at a time. • The cutting tool is usually made from a carbide material which is very hard.

7. The C.N.C. Lathe. The Acrylic Guard. • This is similar to a chuck guard except that it covers the whole machine. As a safety feature the machine cannot be started unless it is closed. The Emergency stop button. • This turns off the power to the machine straight away. The machine and the programme have to be reset when it is pressed.

8. The C.N.C. Lathe. Manual buttons. • These are used by the operator to control the stepper motors which move the tools. • There are four buttons that move the tool along the Z axis (+Z and -Z) X axis (+X and -X). • The buttons are used to take trial cuts when setting up the programme.

9. The C.N.C. Lathe. Tool Movements and Axes. • These are the directions that the tool move. To move the tool left we use the -Z direction to the right we use +Z.. • To move the tool up we use the +X direction and to move it down we use the -X as seen in the diagram.

10. The C.N.C. Lathe. Dimensioning. Incremental. • Here each section of the piece is dimensioned. Absolute. • Here all the dimensions are given from a point or a line.

11. The C.N.C. Lathe. G. Codes. • These are the codes that are used to control the movement of the tool. A selection of codes are given below.

12. The C.N.C. Lathe. M. Codes. • These codes are used to carry out a range of different jobs like starting the spindle or for a tool change.

13. The C.N.C. Lathe. Canned Cycle. • These are used to complete the same task over and over for example facing off or parallel turning.

14. The C.N.C. Lathe. C.A.D. • This stands for Computer Aided Design. Here rather than drawing a part on paper it can be designed or drawn on the computer. This is usually quicker and mistakes can be changed rapidly without any problems. C.A.M. • This stands for computer aided machining. Here the C.A.D. drawing is taken by the computer and changed into code for the C.N.C. This is usually much quicker than manual programming.

15. Computers in Technology. Hardware. • These are the physical parts of the computer for example the keyboard the monitor the mouse the hard drive a printer and scanner. Software. • These are the programmes that run on the computer such as word, excel and PowerPoint. Computer games and C.d ROM's

16. Computers in Technology. Input devices. • These are devices used to put information into the computer. Examples include. • Keyboard. • Mouse. • Floppy disk • CD-ROM. • Scanner. • Digitiser. • Hard disk

17. Computers in Technology. Output devices. • These are devices used to display or give out information from the computer. The can devices controlled by the computer. • Examples include. • Monitor. • Printer. • Plotter. • C.N.C. machines. • Robots.

18. Computers in Technology. Computer terms. Memory. • This is the holding place for information needed by the computer. ROM. (Read only memory). • This is information that is stored on the computer but cannot be changed for example a computer game. RAM ( Random access memory). • This is memory used by the computer to store information as its being worked on for example a word document.

19. Computers in Technology. Computer terms. CD-ROM. (compact disc). • This is a disc used to hold software for the computer. D.O.S. (disk operating system) • this is the basic software needed to run the computer for example windows 98 or XP. Menu • a list of options displayed on the screen.

20. Computers in Technology. Computer terms. File • Information given a name and stored on the computer for example a project report. Virus • A computer programme can damage the computer. Floppy disk • These are used to store small amounts of information and can transfer information from one computer to another

21. Mechanisms Before we look at mechanisms we must first take a look at motion. There are four different types to look at. • Linear. Here the object is moving in one direction only a line almost for example a train on tracks a car on the road. • Rotary. This is a spinning or turning motion for example the wheel of a car or the chuck of the lathe. • Reciprocating. This is like a sawing motion similar to a hack saw or the piston in an engine. • Oscillating. This is the type of motion you get from the pendulum of a clock a swinging motion similar to a playground swing.

22. Mechanisms • Motion diagram

23. Mechanisms • The next thing we will look at are forces. They can be seen best in the diagram below.

24. Mechanisms • Levers.

25. Mechanisms • Linkages These are made up from levers. They can be used to change the direction of a force and also can cause something to have more than one out put such as a steering wheel.

26. Mechanisms • Toggle mechanism. These are clamping type mechanisms where levers are pushed together so that both levers are in a line and held by pressure. This can be seen in vice grips.

27. Mechanisms • Toggle mechanisms.

28. Mechanisms • Pulleys. These are used to transfer rotary motion from one shaft to another. By twisting the belt the turning direction can be changed. By using different size pulleys different speeds can be made. Pulley belts can slip however losing power and so in some cases toothed belts are used.

29. Mechanisms • Toothed pulley. • Changing speeds.

30. Mechanisms • Calculation of pulley speeds

31. Mechanisms • Chains and sprockets. This is similar to a belt and pulley except that there is no slippage. They cannot rotate at very high speeds like pulleys.

32. Mechanisms • C alculation of Chain Speed.

33. Mechanisms • Gears. These are another way of transferring motion from one shaft to another. The gear wheels are always in contact and this means they can transfer great loads without losing power through slip. Different speeds can be achieved by changing the size of the driven gear contacting the driver gear. By using a third gear called an idler the direction of the motion can be changed.

34. Mechanisms • Calculations on gears.

35. Mechanisms • Calculations on gears.

36. Mechanisms • Calculations on gears.

37. Mechanisms • Bevel gears. This type of gear is used to transfer motion through 90 degrees. They are used in the drive mechanisms to transfer power to the wheels and also in hand drills as shown.

38. Mechanisms • Worm and worm wheel. This is another way of transferring motion through 90 degrees. However there is a large reduction in speed which can also be used.

39. Mechanisms • Rack and Pinion. These gears are used to transfer rotary motion into linear motion. Examples are steering mechanisms or the feed mechanism on the drill.

40. Mechanisms • Cams. This mechanism is used to change rotary motion into reciprocating motion. The cam rotates moving the follower in the required direction. The shape of the cam controls the movement of the follower.

41. Mechanisms • Cams at work.

42. Mechanisms • Screw threads. These allow rotary motion to be turned into linear motion. They are generally used for clamping or lifting.

43. Mechanisms • Ratchets. Ratchets are used to allow rotation in one direction only for example the wire tensioner. The direction of the motion can be changed by rotating the pawl in a spanner or in the shaping machine shown.

44. Mechanisms • Clutches. This is a mechanism that allows shafts to be connected and disconnected easily. There are two main types. Positive clutches These are simple and easy to maintain they are used for example on the automatic feed on the lathe. Both shafts must be stopped before they are engaged or disengaged and this can be a disadvantage.

45. Mechanisms • Friction clutches. This type of clutch allows two shafts to be disengaged without the driver stopping for a change of gear for example. They then allow the driven shaft to be taken up to speed slowly as in the case of a car.

46. Mechanisms • Cranks. These are used to apply torque (turning force). This is best explained by a wheel brace. The greater the rotational distance between handle and the head the greater the torque. This makes it easier to loosen the nut or bolt or do the job needed.

47. Mechanisms • Crank and Slider. This is a mechanism that allows rotary motion to be turned into reciprocating motion. This is best seen in the power hacksaw.

48. Mechanisms • Bearings. • This is another way of allowing parts move freely. Here a shaft is inserted into the bearing and the bearing supports its weight and allows it to move freely. The result of this is that a motor turning this shaft can then be less powerful.

49. Mechanisms • Lubrication. When two surfaces move across each other they cause friction. This friction produces heat and causes wear. As it is difficult to move the surfaces across each other more power is needed. Lubrication makes it easier for the surfaces to move this helps: 1. Reduce wear. 2. Reduce the heat produced because of friction. 3. Reduce the power needed to move the surfaces. 4. Keep the surfaces cool. Lubricants: oil, grease, carbon powder.

50. Engines. • There have been many types of engines through the ages from steam at the start of the industrial revolution to the hybrid engines of today that can run on hydrogen. • However the engines we will look at are the internal combustion engines both petrol and diesel. • We will look at both the two and four stroke cycle and the people who invented them. We will look at both the advantages and disadvantages of these types of power.