Mechanical Technology Grade 12 NSC November 2020 Memo (Eng)

Downloaded from hlayiso.com SENIOR CERTIFICATE/ NATIONAL SENIOR CERTIFICATE GRADE 12 MECHANICAL TECHNOLOGY: FITTING AND MACHINING NOVEMBER 2020 MARKING GUIDELINES MARKS: 200 This marking guideline consist of 23 pages. Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology (Fitting and Machining) 2 DBE/November 2020 SC/NSC – Marking Guideline QUESTION 1: MULTIPLE-CHOICE QUESTIONS (GENERIC) 1.1 A (1) 1.2 D (1) 1.3 A (1) 1.4 C (1) 1.5 B (1) 1.6 B (1) [6] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology (Fitting and Machining) 3 DBE/November 2020 SC/NSC – Marking Guideline QUESTION 2: SAFETY (GENERIC) 2.1 Work procedures on machine: Switch off machine.  (1) 2.2 The horizontal band saw:  No adjustments to machine or work piece.   Ensure sufficient coolant on work piece and blade.   Do not leave machine unattended while in operation.   Do not lean on machine.   Keep hands clear from blade.  (Any 2 x 1) (2) 2.3 Surgical gloves:  Prevent contamination of wound   To prevent transmission of HIV/AIDS or any blood related diseases to the first aid helper.  (2) 2.4 Personal protective equipment (PPE) during arc welding:  Welding helmet / Helmet   Safety goggles / Face shield   Leather apron / Apron   Leather gloves / Gloves   Leather spat / Spats   Safety boots / Safety shoes   Over-all   Skull cap   Neck protection   Ear plugs / Ear muffs.   Respirator  (Any 2 x 1) (2) 2.5 Responsibility of the employer regarding the health and safety:  Sufficient lighting   Sufficient ventilation   Provide first-aid equipment   Provide a safe / clean working environment   Provide personal protective equipment (PPE)   Provide safety training to employees  (Any 1 x 2) (2) 2.6 Responsible for administering first aid: A qualified / trained first aid person  (1) [10] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology (Fitting and Machining) 4 DBE/November 2020 SC/NSC – Marking Guideline QUESTION 3: MATERIALS (GENERIC) 3.1 Tests to identify various metals: 3.1.1 Sound test:  Tapping the metal with a hammer (any metal object)  and identify the sound.   Dropping the metal on the floor  and identify the sound.  (Any 1 x 2) (2) 3.1.2 File test: File the metal and pay attention to the bite of the file into the metal.  The bigger the bite the softer the metal. OR The smaller the bite the harder the metal.  (2) 3.2 Purpose of heat treatment of steel:  To change  the properties  of steel.  To change  the grain structure  of steel. (Any 1 x 2) (2) 3.3 Purpose of case hardening on steel: To create a hard / wear resistance surface / case  with a tough core.  (2) 3.4 The tempering process for steel:  Heat the steel to a temperature (temper colour) below the critical temperature.   Soak it at that temperature for a period.   Quench / cool in an appropriate quenching agent.  (water, brine, or oil) (3) 3.5 THREE factors for heat treatment of steel:  Heating temperature / Carbon content   Soaking (Time period at temperature) / Work piece size   Cooling rate / Quenching rate (Quenching medium)  (3) [14] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology (Fitting and Machining) 5 DBE/November 2020 SC/NSC – Marking Guideline QUESTION 4: MULTIPLE-CHOICE QUESTIONS (SPECIFIC) 4.1 C (1) 4.2 B (1) 4.3 A (1) 4.4 A/B (1) 4.5 C (1) 4.6 B (1) 4.7 C (1) 4.8 C (1) 4.9 D (1) 4.10 A (1) 4.11 C (1) 4.12 B (1) 4.13 B (1) 4.14 C (1) [14] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology (Fitting and Machining) 6 DBE/November 2020 SC/NSC – Marking Guideline QUESTION 5: TERMINOLOGY (LATHE AND MILLING MACHINE) (SPECIFIC) 5.1 Taper turning: 5.1.1 Taper: Drawing =  Any 2 labels / dimensions =  31,6 40 Ɵ Ɵ 2 60 (3) 5.1.2 Included angle: θ Dd Tan  2 2L θ 40 - 31,6  Tan  2 2  60  θ  4,004  2 θ  8  (4) 5.1.3 Angle of compound slide: Half the included angle: θ  4  2 (1) 5.2 Parallel key: Width: diameter Width W  4 30   4  7,5 mm  Length: Length L  1,5  diameter  1,5  30   45 mm  (4) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology (Fitting and Machining) 7 DBE/November 2020 SC/NSC – Marking Guideline 5.3 Centring a milling cutter: diameter of workpiece - thickness of cutter X  2 60  15  2 45   2  22,5 mm  (3) 5.4 Straddle milling: Drawing =  Milling cutters Any 2 labels =  Arbour Work piece (3) [18] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology (Fitting and Machining) 8 DBE/November 2020 SC/NSC – Marking Guideline QUESTION 6: TERMINOLOGY (INDEXING) (SPECIFIC) 6.1 Spur gear terminology: 6.1.1 Outside diameter: Outside diameter  PCD  2m  mT  2m  (3  51)  (2  3)   153  6  159 mm  OR Outside diameter  m(T  2)  3(51 2)   3(53)  159 mm  (Any 1 x 2) (2) 6.1.2 Cutting depth: Cutting depth  2,157m  2,157  3   6,471 mm  OR Cutting depth  2,25m  2,25  3   6,75 mm  (Any 1 x 2) (2) 6.1.3 Simple indexing: 40 Simple Indexing  N 40   51   0 full turns and 40 holes on the 51-hole circle (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology (Fitting and Machining) 9 DBE/November 2020 SC/NSC – Marking Guideline 6.2 Differential indexing: 6.2.1 Differential indexing: (Choose 80 divisions) 40 Simple indexing  n 40 SI  indexing not possible, choose 80 83 40 DI   80 1 12   2 12 12   24   No full turns and 12 holes on the 24 hole circle No full turns and 14 holes on the 28 hole circle No full turns and 15 holes on the 30 hole circle No full turns and 17 holes on the 34 hole circle No full turns and 19 holes on the 38 hole circle No full turns and 21 holes on the 42 hole circle No full turns and 23 holes on the 46 hole circle No full turns and 27 holes on the 54 hole circle No full turns and 29 holes on the 58 hole circle No full turns and 31 holes on the 62 hole circle No full turns and 33 holes on the 66 hole circle (Any 1 x 4) (4) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology (Fitting and Machining) 10 DBE/November 2020 SC/NSC – Marking Guideline 6.2.2 Change-gears: Driver A  N 40 Driver A  N 40     Driven A 1 Driven A 1 80  83 40  80  83 40      80 1 80 1   - 3 40 - 3 40   OR   80 1 80 1 - 120 - 120   80 80 - 12 6 - 12 4       8 6 8 4 - 72  - 48    48  32  ALTERNATIVE FORMULA Change-gears: Driver 40 Driver 40  A  N  A  N Driven A Driven A 40 40  80  83    80  83   80 80   1 OR 1  -3   -3  2 2 3  24 3  16     2  24 2  16 72  48    48  32  (Any 1 x 5) (5) 6.2.3 The rotation of the index plate relative to the index crank: Index plate rotates in the opposite  direction to the index crank. (1) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology (Fitting and Machining) 11 DBE/November 2020 SC/NSC – Marking Guideline 6.3 Dove tail: 'X' 160 D E 32 B 30° Ø25 Y A C Calculate X: X  Y  2AC  r  B 12,5 30° A C Calculate AC: OR Calculate AC: BC BC Tan θ  Sin 30° = AC AB BC BC AC   AB = Tan θ OR Sin 30° 12.5 12,5  = Tan 30 Sin30°  21,65 mm  = 25mm  AC2 = AB2 - BC2 AC = 252 -12,52 = 21,65mm  Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology (Fitting and Machining) 12 DBE/November 2020 SC/NSC – Marking Guideline Calculate DE: Calculate DE: D E D E 60° 32 32 30° OR A A AD DE Tan 60° = Tan 30  DE AD AD DE  Tan30  AD  DE =  OR Tan 60°  Tan30  32 32 =  18,48 mm  Tan 60° = 18,48mm  Calculate Y: Y  160  2DE   160  218,48  160  36,96 Y  123,04 mm  Calculate X: X  Y  2AC  r    123,04  221,65  12,5   123,04  68,3 X  191,34mm  (9) 6.4 Reasons for balancing a work piece on a lathe:  Prevent unnecessary bearing loads   Prevent excessive vibration   To obtain a good finish   To prevent clatter on the gear teeth   To prevent the spindle from bending   To ensure accuracy   Ensure the safety of the worker   Prevent damage to the cutting tool / equipment   Ensure that the work piece is perfectly round   Prevent work piece from slipping from the chuck  (Any 2 x 1) (2) [28] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology (Fitting and Machining) 13 DBE/November 2020 SC/NSC – Marking Guideline QUESTION 7: TOOLS AND EQUIPMENT (SPECIFIC) 7.1 Brinell hardness tester: LOAD STEEL BALL   INDENTATION WORK PIECE Rockwell hardness tester: INDENTATION LOAD DIAMOND CONE   WORK PIECE (4) 7.2 Function of tensile tester: To demonstrate the fundamentals / tensile properties  of different materials.  (2) 7.3 Precision measuring instruments:  Outside micrometer   Inside micrometer   Depth micrometer  (3) 7.4 Properties determined by a tensile test:  Tensile strength   Elasticity   Ductility   Plasticity   Strain  (Any 3 x 1) (3) 7.5 Measuring instrument for root diameter on a screw thread:  Screw thread micro meter   Vernier calliper  (Any 1 x 1) (1) [13] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology (Fitting and Machining) 14 DBE/November 2020 SC/NSC – Marking Guideline QUESTION 8: FORCES (SPECIFIC) 8.1 Resultant: 120 N 90cos45° 90 N 90sin45° ° 45° 30° 110sin30° 110cos30° 110 N  HC  90cos45  110cos30  VC  120  90sin45  110sin30       63,64  95,26  120  63,64  55  158,90 N   128,64N  OR Horizontal Vertical Magnitudes Magnitudes components components 120 120 N  90Cos45° 63,64 N  90Sin45° 63,64 N  110Cos30° 95,26 N  -110Sin30° -55 N  TOTAL 158,90 N  TOTAL 128,64 N  HC  R 2  HC2  VC 2 VC R  158,902  128,642  R R  204,44N  α Ɵ VC HC Tanθ  Tanα  HC VC 128,64 158,90   OR   158,90 128,64 θ  38,99 or 3859'24"  α  51,01 or 5000'36"  R  204,44 N at 38,99 north of east  OR R  204,44 N at 51,01 east of north  Can also state cos 330° instead of cos 30°/ and sin 330° instead of sin 30° (13) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology (Fitting and Machining) 15 DBE/November 2020 SC/NSC – Marking Guideline 8.2 Moments: Take moments about “O”.  RHM  LHM  500  " X"  3000  1,5  500  " X"  4500 4500  " X"  500 " X"  9 m  (4) 8.3 Stress and Strain: 8.3.1 Type of stress: Compressive stress  (1) 8.3.2 Stress: A  L B   0,03  0,016   0,48  10 m -3 2  F σ A 50  103   0,48  10-3 σ  104,17  106 Pa  σ  104,17 MPa  (6) 8.3.3 Change in length: σ E  ε σ ε  E 104,17  106   90  109  1,16  10 3  ΔL ε L ΔL  ε  L     1,16  10 3  80   0,09 mm  (6) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology (Fitting and Machining) 16 DBE/November 2020 SC/NSC – Marking Guideline 8.3.4 Safe working stress: Break stress Safety factor  Safe working stress Break stress Safe working stress  Safety factor  600   4  150 MPa  (3) [33] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology (Fitting and Machining) 17 DBE/November 2020 SC/NSC – Marking Guideline QUESTION 9: MAINTENANCE (SPECIFIC) 9.1 Preventative maintenance of a belt drive system:  Checking for wear and tear on belt.   Checking belt alignment.   Checking the tension setting.   Checking the tensioning device, e.g. jockeys.   Checking for wear on the pulleys.   Checking for wear on pulley bushes.   Check for dirt on the system.  (Any 3 x 1) (3) 9.2 Results of a lack of preventative maintenance on a gear drive system:  A loss / lack of lubrication.   Loose components.   Misalignment of gear components.   Contamination of lubricants.   Noisy operation.   Excessive wear on components.   Excessive vibration in the system.   Excessive heat generated.   Malfunctioning of gear system   Loss of production   Risk of injuries / death   Financial loss  (Any 3 x 1) (3) 9.3 Procedures to reduce wear on a chain drive system:  Adjust the chain alignment.   Adjust the chain tension / mechanism.   Prevent overloading of the system.   Keep the sprockets and chain clean.   Repair or replace worn sprockets and chains.   Ensure adequate lubrication.  (Any 2 x 1) (2) 9.4 Replace the belt on a flat belt drive system:  Switch off the machine   Release the tension on the belt.   Remove the belt from the pulleys.   Fit the correct size replacement belt onto the pulleys.   Check the pulley's condition and alignment.   Apply adequate tension to the belt and lock the system.   Check for proper functioning.  (Any 5 x 1) (5) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology (Fitting and Machining) 18 DBE/November 2020 SC/NSC – Marking Guideline 9.5 Properties of Bakelite:  Non-conductive (Heat and Electricity)   Heat-resistant   Brittle   Hard   Can’t be deformed by heat (Thermo-hardened / Thermosetting)   Cast easily   Resistance to chemicals  (Any 2 x 1) (2) 9.6 Properties that make Vesconite an outstanding bearing material:  Wear resistance / Longer lifespan   Very versatile   High load bearing strength / strong   High temperature limits   Little to no water absorption   High chemical resistance   Very low co-efficient of friction   Resistance to fuels, oils and hydrocarbons   Very good machinability   Tough  (Any 3 x 1) (3) [18] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology (Fitting and Machining) 19 DBE/November 2020 SC/NSC – Marking Guideline QUESTION 10: JOINING METHODS (SPECIFIC) 10.1 Square thread: 10.1.1 The lead of the thread: Lead  pitch  no of starts  63   18 mm  (2) 10.1.2 The helix angle of the screw thread: P Pitch diameter  OD    2 6  58   2  55 mm  Pitch circumference  π  Pitch diameter  π  55  172,79 mm  Lead Helix angle tanθ  Pitch circumference 18   172,79 θ  5,95 or 557'  OR Lead Helix angle tanθ    P π   OD    2 18    6 π   58 -    2 18   172,79 θ  5,95 or 557'  (5) 10.1.3 Leading angle: Leading angle  90  helix angle  clearanceangle  90  5,95  3   81,05  (2) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology (Fitting and Machining) 20 DBE/November 2020 SC/NSC – Marking Guideline 10.1.4 Following angle: Following angle  90  helix angle  clearanceangle  90  5,95  3   92,95  (2) 10.2 M20 x 2,5. Drill size: Drill diameter  OD  P   20  2,5   17,5 mm  (3) 10.3 Pitch of a screw thread: The pitch is the axial distance  measured from any given point  on the screw thread to a corresponding point  on an adjacent thread.  (4) [18] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology (Fitting and Machining) 21 DBE/November 2020 SC/NSC – Marking Guideline QUESTION 11: SYSTEMS AND CONTROL (DRIVE SYSTEMS) (SPECIFIC) 11.1 Advantages of a belt drive system compared to a gear drive system:  Silent operation   Cheaper parts   Transmit power over a longer distance   Can change direction without additional parts   Easy to replace parts   No lubrication needed   Belt drive slip may prevent system damages or injuries  (Any 2 x 1) (2) 11.2 Belt drive system: 11.2.1 Rotation frequency of driven pulley in r/sec: NDN  DDN  NDR  DDR NDR  DDR NDN   DDN 1100  0,24   0,36  733,33 r/min   12,22 r/sec  (4) 11.2.2 The power transmitted in kW: P T1  T2 πDN 60  P 200  90π  0,24  1100  60 1520,53 Watt  1,52 kW  OR P T1  T2 πDN 60  P 200  90π  0,36  733,33  60  1520,53 Watt   1,52 kW  (4) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology (Fitting and Machining) 22 DBE/November 2020 SC/NSC – Marking Guideline 11.2.3 The belt speed in m.s-1: πDN πDN V V 60 60  OR  π  0,24  1100  π  0,36  733,33    60 60  13,82 m.s1   13,82 m.s1  (3) 11.3 Hydraulics: 11.3.1 Fluid pressure: 2 πD A AA  4 π0,04 2 AA   4 A A  1,26  10-3 m 2  FA P AA 80 P  0,00126 P  63,49  10 3 Pa OR 63,66  10 3 Pa  P  63,49 kPa OR 63,66 kPa (4) 11.3.2 Diameter of piston B in millimetres: FA F  B AA AB FB  A A AB  FA  320  0,00126   80  5,04  10-3 m2  Calculation without rounding off: π  DB 2 π  DB 2 AB  AB  4 4 AB  4 AB  4 DB   DB   π π  5,04  10  4  OR 3  5,026548246  10  4 3  π π  0,0801 m   0,08 m  1000   80,11 mm   80 mm  (7) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology (Fitting and Machining) 23 DBE/November 2020 SC/NSC – Marking Guidelines 11.4 Gear drive system: Rotition frequency of driven gear: NF TA  TC  TE  NA TB  TD  TF TA  TC  TE NF   NA  TB  TD  TF 20  18  42 NF   1440  36  46  80 164,35 r/min   60  2,74 r/sec  OR NB  TB  NA  TA NB  36  1440  20 1440  20 NB  36 NB  800 r/min  NB  NC ND  TD  NC  TC ND  46  800  18 800  18 ND  46 ND  313,04 r/min  ND  NE NF  80  313,04  42 313,04  42 NF  80 164,35 r/min NF   60 NF  2,74 r/sec  (4) [28] TOTAL: 200 Copyright reserved