MARKING GUIDELINES

QUESTION 1: MULTIPLE-CHOICE QUESTIONS (GENERIC)
1.1 B (1)
1.2 A (1)
1.3 D (1)
1.4 A / C (1)
1.5 A (1)
1.6 C (1)
[6]

QUESTION 2: SAFETY (GENERIC)
2.1 First-aid applications to an open wound:

• Use surgical gloves.
• Do not remove anything that is stuck to the wound.
• Never use sticky plaster on the wound.
• Cover the wound with a clean, lint-free cloth.
• Avoid using any oily substances or lotions on wounds.
• If necessary, cool wounds with cold water.
• Apply pressure to prevent blood loss if necessary.
• Avoid contact with blood from patient.
• If the wound is on your arm, raise the arm above your head to stop the bleeding.
  (Any 2 x 1) (2)

2.2 Surface grinder: (Already switched on)

• Never leave the grinder unattended.
• Switch off the machine when leaving.
• Don’t try to stop revolving emery wheel with your hand.
• Don’t adjust the machine while working.
• Don’t open any guard while the machine is on.
• Do not force the grinding wheel on to the work piece.
• Approach the work piece slowly and evenly.
• Don’t clean the machine while working.
• Do not put hands near the work piece when grinder is in motion.
• Don’t clean or adjust the machine while working.
• Check for oil on the floor while working (spilling of cutting fluid on floor while working)
• Check that he grinding wheel is running evenly.
  (Any 2 x 1) (2)

2.3 Gauges calibrated:

• To ensure accurate readings.
• To prevent overloading.
  (Any 1 x 1) (1)

2.4 Finger protectors’ hazards on power driven guillotines:

• The finger protector prevents the hazards of getting the fingers cut by the blades.
• To be crushed by the hold-downs. (2)

2.5 Welding or flame cutting operation safety:

• An operator has been instructed on how to use the equipment safely.
• A workplace is effectively partitioned off.
• An operator uses protective equipment.
• Ensure that all equipment is in safe working condition.
• Ensure that here are no flammable materials around the welding area.
• Weld area must be well ventilated.
• Fire extinguisher must be in close proximity.
  (Any 2 x 1) (2)

2.6 Workshop layout:

• Product layout. (1)

[10]

QUESTION 3: MATERIALS (GENERIC)
3.1 File test:
3.1.1 Difficult (1)
3.1.2 Easy (1)
3.1.3 Difficult (1)
3.2 Heat treatment:

• A. – Grain growth.
• B. – Recrystallisation.
• C. – Recovery. (3)

3.3 Bending test:

• Bend the test piece through a specific angle or around a mandrel or bar, having a defined radius, until a rupture in the metal occurs.
• Place the material in a vice and bend it then observe the ductility of the material.
  (Any 1 x 3) (3)

3.4 Purpose of case hardening:

• Creates a hard surface with a tough core. (2)

3.5 Quenching media:

• Water
• Brine (saltwater)
• Oil
• Soluble oil and water
• Nitrogen air-infused air
  (Any 3 x 1) (3)

[14]

QUESTION 4: MULTIPLE-CHOICE QUESTIONS (SPECIFIC)
4.1 C (1)
4.2 B (1)
4.3 A (1)
4.4 A (1)
4.5 D (1)
4.6 D (1)
4.7 C (1)
4.8 C (1)
4.9 B / D (1)
4.10 D (1)
4.11 A (1)
4.12 A (1)
4.13 B (1)
4.14 D (1)
[14]

QUESTION 5: TERMINOLOGY (LATHE AND MILLING MACHINE) (SPECIFIC)
5.1 Advantages of compound slide method:

• Tapers with large angles can be cut.
• External and internal tapers can be cut.
• The set-up is simple.
  (Any 2 x 1) (2)

5.2 Taper cutting:
5.2.1 Length of taper:

(5)
5.2.2 Tailstock set-over:

(3)
5.3 Key ways:
5.3.1 Width:
Width = D/4
Width = 75 ?
= 18,75 mm ? (2)

5.3.2 Thickness:
Thickness = D/6
Thickness = 75/6
= 12,50 mm ?  (2)

5.3.3 Length:
Length= 1,5 x diameterof shaft
= 1,5 x 75 
= 112,50 mm ? (2)

5.4 Disadvantages of down-cut milling:

• Vibration in the arbor is unavoidable.
• A fine feed must be used.
• When milling material with hard scale, the cutter teeth come directly in contact with the scale, which can damage the cutter.
• The process is time consuming.
  (Any 2 x 1) (2)

[18]

QUESTION 6: TERMINOLOGY (INDEXING) (SPECIFIC)
6.1 Gear terminology:
6.1.1 Pitch-circle diameter:

• PCD = m x T
  = 1,5 x 200 ?    OR       CP = m x π
  = 300 mm?                   = 1,5 x π
  
  = 4,71mm ?
  PCD = CP x T
                  π
  = 4,71 x 200
           π
  = 299,85mm ? (2)

6.1.2 Dedendum:

• Dedendum= 1,157 x m               Dedendum= 1,25 x m
  = 1,157 x 1,5 ?               OR      = 1,25 x 1,5 
  = 1,74 mm ?                              = 1,88 mm ? (2)

6.1.3 Outside diameter:

• OD = PCD + 2 x m                          OD = m(T + 2)
  = 300 + 2(1,5) ?             OR           = 1,5(200 + 2) ?
  = 303 mm ?                                    = 303 mm ?    (2)

6.1.4 Working depth:

• WD = 2 x m                    WD = 2 x a
  = 2 x 1,5 ?         OR      = 2 x 1,5 
  = 3 mm ?                      = 3 mm ?  (2) 

6.2 Dovetails:

• W = 210 + 2(DE)
  m = W – 2(AC) – 2(R)

6.2.1 Maximum width distance of dove tail: (W)
Calculate DE or y:

• tanθ = DE
             AD
  DE = tanθ x AD ?
  = tan30°x 45 
  = 25,98 mm ?
  W = 210 + 2(DE) ?
  = 210 + 2(25,98) ?
  = 210 + 51,96
  = 261,96 mm ? (6)

6.2.2 Distance between the rollers: (m)
Calculate AC or x:

• Tanθ = BC 
              AC
  AC = BC ?
         Tanθ
  AC = 17 ?
         Tan30º
  = 29,44mm ?
  
  m = W - 2(AC) - 2(R) ?
  = 261,96 - 2(29,44) - 2(17) ?
  = 261,96 - 58,88 - 34
  = 169,08 mm ?  (6)

6.3 Milling of spur gear:
6.3.1 Indexing:

• Indexing = 40 = 40 
                    N    137
  = 40 = 40  
      A    140
  = 4 x 2 
    14   2
  = 8 ?
    28
• Indexing: 8 holeson a 28 - hole circle ?

OR

• 12 holeson a 42 - hole circle ?

OR

• 14 holes on a 49-hole circle. ? (3) 

6.3.2 Change gears: (Markers to note alternative answers and calculations to award full marks if the answer is correct)

• Dr=( A - n) x  40
  Dn                  A
  Dr =(140 - 137) x  40 ?
  Dn                        140
  =  3 x 40
          140
  = 120/140 
  = 12/14 x 2/2
  Dr = 24   OR 48 ?
  Dn   28 ?      56 ?(5)

[28]

QUESTION 7: TOOLS AND EQUIPMENT (SPECIFIC)
7.1 Functions of a moment and force tester:

• To determine the reaction on either side of a simple loaded beam.
• To illustrate the concept of the triangle of force. (2)

7.2 TWO hardness testers:

• Brinell
• Rockwell
• Vickers
  (Any 2 x 1) (2)

7.3 Precision measuring instrument:

• Depth micrometer
• Vernier caliper
  (Any 1 x 1) (1)

7.4 Identify tester:

• Tensile tester (1)

7.5 There are THREE ways that hardness is measured:

• Resistance to penetration.
• Elastic hardness.
• Resistance to abrasion / scratching / file test.
• Sound test (dropping it on the floor and listen to the sound).
  (Any 3 x 1) (3)

7.6 Screw thread height:

• H = 0,866 x P
  = 0,866 x 2
  = 1,73 mm     (2)

7.7 Measuring instrument:

• Vernier caliper (1)

7.8 Interchangeable extension:

• To measure depths greater than 25 mm. (1)

[13]

QUESTION 8: FORCES (SPECIFIC)
8.1 Calculate resultant:

(15)
8.2 Moments:

8.2.1 Point load for UDL:

• 16kN/m x 5m
  80 kN   (2)

8.2.2 Take moments about B:

• A x 10,25) = (4,5 x 5,25) + (80 x 7,75) + (9,5 x 10,25)
  10,25A = 23,625 + 620 + 97,375
  A = 741/10,25
  A = 72,29 kN  (3)

8.2.3 Take moments about A:

• B x 10,25) = (9,5 x 0) + (80 x 2,5) + (4,5 x 5)
  10,25B = 0 + 200 + 22,5
  B = 222,5/10,25
  B = 21,71kN  (3) 

8.3.1 The stress in the material in MPa:

• σ = F/A
  σ = 90 x 10³
       6,17 x 10^-3
  σ = 14586709,89 Pa
  σ = 14,59 MPa    (2)

8.3.2 The diameter of the mild steel shaft:

(5)
8.3.3 Original length:

(3)
[33]

QUESTION 9: MAINTENANCE (SPECIFIC)
9.1 Preventative maintenance:

• Planned or scheduled maintenance.
• Condition-based maintenance. (2)

9.2 Preventative maintenance of gear drive systems:

• Checking and replenishment of lubrication levels.
• Ensuring that gears are properly secured to shafts.
• Cleaning and replacement oil filters.
• Reporting excessive noise, wear, vibration and overheating for expert attention.
  (Any 3 x 1) (3)

9.3 Purpose of jockey pulley:

• The jockey pulley helps setting the tension on the system.
• To increase the angle of contact in an open belt drive.
  (Any 1 x 1) (1)

9.4 Properties of materials:
9.4.1 Teflon:

• Water resistant.
• Resistant to grease.
• Resistant to heat.
• Resistant to corrosion.
• Can withstand high temperatures.
• Need no lubricants.
• Electrical insulator
• Thermoplastic /Easy to be reshaped / recycled.
  (Any 2 x 1) (2)

9.4.2 Nylon:

• Tough.
• Hard-wearing.
• Cheap.
• Needs no or little maintenance.
• Can withstand high temperatures.
• Need no or little lubricants.
• Is light.
• Can absorb shock.
• Resistant to chemicals.
• Non-toxic.
• Thermoplastic /Easy to be reshaped.
• Has high load-bearing strength
  (Any 2 x 1) (2)

9.4.3 Vesconite:

• Wear resistant.
• Low friction.
• Operate with little or no lubrication.
• Easy to machine.
• Load carry higher than white metal.
• Cost effective material.
• Gives long life span.
• Performs well, in unhygienic, dirty and un-lubricated environments.
• Low maintenance.
• Low or no water absorption
• High chemical resistance
• Versatile
• Can handle high temperatures
• Thermoplastic /Easy to be reshaped
  (Any 2 x 1) (2)

9.5 Use of material:
9.5.1 Polyvinyl chloride (PVC): (Due to the large number of alternatives, marker discretion must be used - discuss with IM).

• Electrical cable isolation.
• Electrical pipes.
• Water pipes.
• Artificial leather.
• Cling wrap.
• Credit / bank / phone cards.
• Window frames.
• Fences.
• Furniture.
  (Any 1 x 1) (1)

9.5.2 Glass fibre: (Due to the large number of alternatives, marker discretion must be used - discuss with IM).

• Boats.
• Motor vehicles bodies.
• Transparent roof sheeting.
• Petrol tanks.
• Swimming pools.
• Furniture.
• Fruit and salad bowls.
• Ornaments.
• Fishing equipment.
  (Any 1 x 1) (1)

9.6 Difference between thermoplastic and thermo-hardened composites:

• Thermoplastic can be re-heated and reshaped again where a thermo- hardened plastic cannot be re-heated, to be softened, shaped and moulded again. (4)

[18]

QUESTION 10: JOINING METHODS (SPECIFIC)
10.1 Screw thread:

• Square thread
• Acme thread
• V-screw thread
• Trapezium thread / Buttress thread
  (Any 3 x 1 ) (3)

10.2 Square Thread:
10.2.1 Pitch diameter:

• Pitch = Lead /Numberof starts
  = 36/2
  =18 mm ?
  
  PD = OD - P/2
  = 80 - 18/2
  = 71 mm ? (4)

10.2.2 Helix angle of the thread:

• Tanθ =    Lead   
              π x PD
  Tanθ =       36     
             π x 71 ?
  θ = tan^-1(0,161396562)
  = 9,17º   (4)

10.2.3 Leading angle:

• Leading angle = 90° - (helix angle + clearance angle)
  = 90° - (9,17° + 3°)
  = 77,83° (2)

10.2.4 Following angle:

• Following angle = 90° + (helix angle - clearance)
  = 90° + (9,17° - 3°)
  = 96,17° (2) 

10.3 Multiple screw threads:

• They provide more bearing surface than single start screw thread / does not strip easily.
• To provide faster linear movement.
• They are more efficient as they lose less power to friction compared to single start screw threads. (3)

[18]

QUESTION 11: SYSTEMS AND CONTROL (DRIVE SYSTEMS) (SPECIFIC)
11.1 Hydraulics:
11.1.1 The fluid pressure:

(4)
11.1.2 Force at ram:

(5)
11.2 Functions hydraulic reservoir:

• A fluid storage tank.
• Promotes air separation from the fluid.
• Support for the pump and electric motor.
• Promotes heat dispersion.
• Acts as a base plate for mounting control equipment.
• Permits contaminants to settle at the bottom in order to be drained.
  (Any 1 x 1) (1)

11.3 Efficiency of pneumatic systems:

• Pneumatic tools are environmentally friendly.
• Last long.
• It is robust (powerful / less force required)
• Easy to use.
• It is compact.
• Easy to maintain as there are so few working parts.
  (Any 2 x 1) (2)

11.4 Applications for pneumatic systems: (Due to the large number of alternatives, marker discretion must be used - discuss with IM).

• Drills.
• Brake systems.
• Jackhammers
• Nail guns
• Missiles
• Doors
• Spray guns
• Air blow guns
• Air socket wrench
• Grinders
  (Any 2 x 1) (2)

11.5 Belt drives:
11.5.1 Rotation frequency:

(3)
11.5.2 Power transmitted:

(4)

11.6 Gear drives:
11.6.1 Rotation frequency:

(4)

11.6.2 Gear ratio:

• Gear ratio = Product of teeth on driven gears/Product of teeth on driver gears
  Gear ratio = 40 x 60
                      30 x 20
  Gear ratio = 4 : 1

OR

• Speed ratio = N_A
                        N_D
  = 2300
      575
  = 4:1 (3)

[28]
TOTAL: 200