MEMORANDUM

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

QUESTION 2: SAFETY (GENERIC)
2.1 Safety Precautions

• Pressure gauges must be checked and tested regularly and adjusted or replaced if any malfunctioning occurs.
• Supporting pins that keep the platform at a desired height on the frame must be inspected for damage.
• Check the floor for oil and apparatus for leaks.
• The platform on which the workpiece rests must be rigid and square with the press cylinder. (Any 2 x 1)  (2)

2.2 Product layout
(2)
2.3 Perspex shield

• is installed to shield flying objects from harming the operator’s eye.   (1)

2.4
2.4.1 Machine Identification

• Surface grinder  (1)

2.4.2 Surface grinder parts label

1. Workpiece
2. Machine spindle
3. Magnetic table
4. Grinding wheel  (4)

[10]

QUESTION 3: MATERIALS (GENERIC)
3.1 Heat treatment refers to heating and cooling of metals under controlled conditions in their solid state so as to change their properties.(2)
3.2 Heat treatment properties

(4)
3.3 Purpose of case-hardening

• It hardens the surface.
• It provides a wear resistant surface.
• Strengthens core to withstand applied loads. (Any 2 x 1)  (2)

3.4 Carbon effect

• Steel with low carbon content will not respond very much to the hardening process.(2)

3.5 Workshop tests on materials

• Sound test
• Bend test
• Filing test
• Machining test (Any 2 x 1)  (2)

3.6 Reasons for annealing

• To relieve internal stresses that may have been set up during other processes.
• To soften them in order to facilitate the machining processes.
• To make material ductile.
• Refine their grain structures.
• Reduce brittleness (Any 2 x 1)  (2)

[14]

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

QUESTION 5: TERMINOLOGY (LATHE AND MILLING MACHINE) (SPECIFIC)
5.1 Lathe Taper turning
5.1.1

• Set-over = 𝐷−𝑑 × 𝐿𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑤𝑜𝑟𝑘𝑝𝑖𝑒𝑐𝑒
                      2          𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑡𝑎𝑝𝑒𝑟
  = (75-50)/2 x 400 / 250
  = 12.5 x 1.6
  = 20 mm (2)

5.1.2

• tan 𝜃 = 𝑋.
        2    𝐿
  = 12.5 / 250
  = 0.05
  = tan⁻¹ 0.05 𝑥 2
  Θ = 5.724° (3)

5.2 Milling Cutters.
5.2.1

1. – Helical milling cutter
2. – Side and face Cutter/ also Accept Staggered tooth cutter
3. – Dovetail
4. – T–Slot
5. – End mill (5)

5.3 Cutting Square Threads
5.3.1 Lead = Pitch x Number of Starts

• = 2 x 12 = 24 mm (1)

5.3.2 Mean Diameter = OD – 0,5 Pitch

• = 85 – 0,5 x 12
  = 91 mm (2)

5.3.3 Tan θ = Lead / π x Dm

• Tan θ = 24 / 91
  Θ = 14,77 ° (2)

5.4 Dividing Head components

• A – Index plate: the aim of the index plate is to enable one revolution of the crank to be further subdivided into fractions of a revolution, especially where the fraction is not a factor of 40.
• D – Worm-shaft with a Single – start worm engages with a worm gear with 40 teeth.
• E – Worm wheel/gear obtain a rotary movement of the spindle. (3)

[18]

QUESTION 6: TERMINOLOGY (INDEXING) (SPECIFIC)
6.1 GEAR CALCULATIONS:
6.1.1 Gang Milling: Simultaneously using several cutters of different diameters and forms on the arbor, workpiece can be machined to size in one movement of the milling machine table. (1)
6.1.2 Straddle Milling: consists of two side and face cutters, separated by spacing collars of required dimensions to produce parallel work in one cut. (1)
6.2 Procedure to cut external metric V-screw thread using compound slide method

• Set up the workpiece in the centre lathe and turn the part to be threaded to the required diameter of the thread.
• Set the compound slide to 30º to the left of the centre line of that cross- slide and set the cutting tool up accurately in the tool post.
• Consult the index plate of the quick-change gear box and shift the levers accordingly for the necessary pitch of the screw thread.
• Start the centre lathe and set the cutting tool at touching point on the workpiece.
• Move the cutting tool a short distance off, to clear the end of the workpiece and feed the compound slide 0.05 mm inwards.
• With the centre lathe revolving, engage the half nuts at the correct line on the threading dial, putting the first cut of the screw thread in progress.
• Stop the centre lathe and check the screw thread pitch with a screw thread pitch gauge. (Any 5 x 1) (5)

6.3 Definition of Indexing is the process of evenly dividing the circumference of a circular work piece into equally spaced divisions, such as in cutting gear teeth, cutting splines, milling grooves in the reamers and taps. (1)
6.4 Milling methods

• Up-cut milling
• Down-cut milling (2)

6.5 Differential indexing

6.5.1 Indexing Required

• Indexing = 40
                    𝐴
  = 40/120
  = 1 x 22
     3   22
  = 22/66
  Indexing is 22 holes in a 66-hole circle (3)

6.5.2 Change of gears

• Gear ratio: 𝐷𝑟𝑖𝑣𝑒𝑟 = 𝐴−𝑁 𝑥 40
                   𝐷𝑟𝑖𝑣𝑒𝑛       𝐴       1
  = 120 −113 𝑥 40
          120
  = + 7 𝑥 8
        3    8
  = 56/24
• The driver gear has 56 teeth
• The driven gear has 24 teeth (5)

6.5.3

• The direction of motion is clockwise
• The crank handle will turn the same direction as index plate (2)

6.6 Dove tail Calculations

• Θ = 40°
  α = 20°
• x = r /(tan α)
  = 10 /(tan 20)
  = 27,47 mm
• X = 80 + 2 R + 2 x
  = 80 + 20 + (2 x 27,47)
  = 154,949 mm (6)

6.7 Types of Milling machines

• Vertical milling machine
• Horizontal milling machine (2)

Related Items

[28]

QUESTION 7: TOOLS AND EQUIPMENT (SPECIFIC)
7.1 Hardness Testers
7.1.1 Brinell Hardness tester

• The Brinell Hardness Test involves indenting the test material with a piece hardened steel or carbide ball of 10 mm. The diameter of the indentation left in the test material is measured with a low-powered microscope.(3)
  

7.1.2 Rockwell Hardness tester

• Rockwell Hardness Test method involves indenting the test material with a diamond cone or hardened steel-ball indenter.(3)
  

7.2 Hardness measure of a metal.

• Resistance to penetration
• Elastic hardness
• Resistance to abrasion (Any 2 x 1) (2)

7.3 Screw thread micrometre
(5)
[13]

QUESTION 8: FORCES (SPECIFIC)
8.1 Resultant Force Calculations:

• Xcom = 100 cos 50 + 80 cos 40 - 60
  = 65,56 N        (2)
• Ycom = 100sin 50 – 80 sin 40 - 70
  = 95,18 N    (2)
• R = √(𝑋2 + 𝑌²)
  R = 115.576 N
  Tan θ = y/x
  Tan Θ = 95.18/65.56
  Θ = 55.44
  = 55.44 °

Equilibrant = Resultant BUT IN THE OPPOSITE DIRECTION
Equilibrant = 115.567 N at 235.44 º (5)
8.2 Moments

• Converting the UDL to Point Load
  4 x 10 = 40 kN @ 3 m from the left hand end 

Calculation the Reactions by taking moments:

• CLOCKWISE MOMENTS = ANTICLOCK-WISE MOMENTS
  (RC x 4) + (5 x 1) = (5 x 6) + (40 x 2) + (8 x 5)
  Rc = 36,25 kN
  (RB x 4) + (5 x 2) + (8 x 1) = (40 x 2) + (5 x 5)
  RB = 21,75 kN (5)

8.3 Stress Calculations
8.3.1 Tensile Stress Calculations
F = 40 kN; D = 98, d = 67mm: L = 80 mm: E = 90 PGa
(5)
8.3.2 The Strain calculations
(3)
8.3.3 Change in length
(3)
8.4 Stress/Strain diagram
 

1. – Limit of Proportionality
2. – Elastic limit
3. – Yield point
4. – Maximum Force/Point
5. – Point of Fracture   (6)

8.5 FOS stands for Factor Of Safety or Safety Factor. (2)
[33]

QUESTION 9: MAINTENANCE
9.1 Material Classifications
9.1.1 PVC – Thermoplastic (1)
9.1.2 Glass fibre – Thermo-setting plastic (1)
9.1.3 Nylon – Thermoplastic (1)
9.2 Reasons for using cutting fluid when working on the centre lathe.

• It prolongs the life of a cutting tool.
• It prevents the shavings or metal chips from sticking and fusing to the cutting tool.
• It will carry away the heat generated by the turning process.
• It flushes away shavings/metal chips.
• It improves the quality of the finish of the turned surface. (Any 2 x 1)  (2)

9.3 Gear Drives Maintenance.

• Checking and replenishment of lubrication levels
• Ensuring that gears are properly secured to shafts
• Cleaning and replacement of oil filters
• Reporting excessive noise and wear, vibrations and overheating for expect attention. (Any 2 x 1) (2)

9.4 Reasons for the use of carbon fibre

• It is light in weight.
• It is tougher and stronger.
• It can be bent to any shape when heated above 150 ºC. (Any 2 x 1) (2)

9.5 ONE property and ONE use of each composite

(6)
9.6

• Contact pressure
• Temperature
• Sliding velocity
• Type of a lubricant
• Surface roughness (Any 3 x 1) (3)

[18]

QUESTION 10: JOINING METHODS (SPECIFIC)
10.1 Square Thread Calculations: T = 48 mm ; m = 3
10.1.1

• PCD = T x m
  = 48 x 3 = 144 mm  (2)

10.1.2 Add = Module = 3 mm (1)
10.1.3

• Clearance = 0,157 x 3
  = 0,471 mm  (2)

10.1.4

• Ded = 1,157 x 3
  = 3,471 mm  (2)

10.1.5

• OD = PCD + 2 x 3
  = 150 mm   (2)

10.1.6

• Circular Pitch
  = π x m
  = π x 3 = 9,424 mm  (1)

10.2 Left-hand square screw thread
 

1. – Leading Angle (1)
2. – Following or Trailing Angle (1)
3. – Clearance (1)
4. – Helix angle (1)

10.3 A multi-start thread allows for a faster travel or movement and is more efficient as it loses less power through friction compared to single start thread. (2)
10.4 Screw Thread fit is a combination of allowances and tolerances and a measure of tightness or looseness between the bolt and nut. (2)
[18]

QUESTION 11: SYSTEMS AND CONTROL (DRIVE SYSTEMS) (SPECIFIC)
11.1 Rotational velocity is where a body rotates (spin) around its axis. It is the rotation rate or how fast a body revolves or turns. It is measured in radians
per second. (2)
11.2 Hydraulic system calculations
11.2.1 Calculate the Fluid pressure 
(4)
11.2.2 Load on the piston B
 (4)
11.2.3 Hydraulic System Applications

• Machine tools, motor vehicle, hydraulic jacks (Any 2 x 1) (2)

11.3 Hydraulics refers to the transmission and control of forces and movement by means of fluid. Fluid (generally oil) is used to transmit energy. (2)
11.4 Belt Drive Calculations

• Nmotor x Dmotor = Nblade x Dblade
  130 x 1205 = 385 x Dblade
  Dblade = 406,883 pm (2)

11.5 Pneumatic symbols

11.6
11.6 Gear-Drive system calculations:
Data: (6)
11.6.1 Rotation speed of Electric motor
(3)
11.6.2 Velocity ratio  

• VR = N_INPUT
           N_OUTPUT
  = 1380
      160
  = 8,625:1
  - 863:1     (2)

11.6.3 Driven will rotate Clockwise (1)

[28]
TOTAL: 200