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TVET CURRICULUM DEVELOPMENT, ASSESSMENT AND CERTIFICATION COUNCIL (TVET CDACC)

FORMATIVE ASSESSMENT

Unit of competency: Perform lathe work Unit Code: ENG/OS/ME/CR/4/06

Qualification: Mechanical production technician level 6

Qualification Code:

ASSESSOR INSTRUCTIONS

This assessment requires the candidate to demonstrate competence against unit of competency:

Perform lathe work

In this assessment, the candidate will be required to answer oral, written questions and perform

lathe work.

a) Allocate 10 minutes to the candidate to answer oral questions

b) Allocate I hour and 20 minutes to the candidate to answer written questions

c) Allocate 10 minutes to the candidate to review the working drawing

d) Allocate 20 minutes to the candidate to prepare the work operation plan

e) Allocate 10 minutes to the candidate to collect the tools as per the work operation plan

f) Allocate 5 minutes to the candidate to prepare the blank material

g) Allocate 3 hours to the candidate to set up the machine and perform the machining

operation as per the working drawing, assess quality of machined parts, maintain

machine tools and perform housekeeping.

N/B: General tolerance

• Linear dimensions ±0.04

• Diameters ±0.02

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The following resources will be required during the assessment:

Knurling tools Threading tools Lathe cutting tool Boring tool Parting tool Drilling bits Centre drill Mild steel bar of diameter 60 mm by 110mm Measuring tools Lathe machine Lathe accessories Oil can Lubricating oil Cleaning brush Chips remover Waste bins Brooms Cotton waste

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OBSERVATION CHECKLIST

Candidate’s name & Registration No.

Assessor’s name & Reg. code

Unit(s) of Competency

Venue of Assessment

Date of assessment

Items to be evaluated: Tick as appropriate: YES, if the candidate performs the task correctly, NO, if the

candidate did not perform the task correctly. Give a brief comment where a NO is awarded).

Yes No Comments

1. Adhered to prescribed safety as per workplace procedures

Wore PPEs (clear goggles, overall, safety boots).

Observed machine safety (no speed change when machine is running, secured work and tool, removal of chuck key, machine guard in place)

Observed environmental safety (waste disposal, no spills on the floor, adequate ventilation and lighting

2. Prepared operation work Plan as per the working drawings

Serial No.

Description Tools and equipment required

Estimated duration

1.2.3.N/B: Operations to be listed in order of working procedure.

3. Calculated speeds and feeds to be used as per the operation plan (consider diameter, material, surface finish required and type of operation)

4. Selected machine tools as per operation plan

5. Mounted tool and work piece on the chuck as per the operation plan (tool height and true running of the work)

6. Machined work piece as per the specifications

7. Inspected dimensions of finished work piece as per specification

8. Inspected machine, reported faults as per the workplace procedure

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9. Oiled and lubricated machines and tools as per machine manual and workplace procedure

10. Carried out housekeeping as per work place requirement

11. Stored tools and equipment as per the workplace procedure and organization policy

12. Utilized resources effectively in accordance with workplace policy (no material wastage)

13. Demonstrated care and safe custody of tools and machines

PRODUCT CHECKLISTTick as appropriate: YES, if the candidate performs the task correctly, NO, if the candidate did not perform the task correctly. Give a brief comment where a NO is awarded).

Yes No Comments

14. Dimensions Linear (±0.02)

38 mm 62.5 mm 80 mm 85mm 100mm

Diameters (±0.01) Ø20 Ø 30 Ø 38 Ø 50 Ø 12.5

Thread pitch (1.5)15. Surface finish

quality of thread as per specification quality of turned and faced surfaces

(Roughness) quality of knurl (medium diamond

knurl) quality of the internal bored hole(H8) quality of the chamfers as per

specification (1x45⁰) burrs removed

16. Geometry Straightness of machined surfaces Squareness of cut edges Concentricity of the bored hole and

the turned diameters as per the specification

The candidate was found to be: Competent Not yet competent

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(Please tick as appropriate)

(The candidate is competent if s/he gets 10 of the 13 items on the observation checklist correct, with items (1-6)on the observation checklist being compulsory, and all the dimensions in item no 14, on the product checklist correct.)

Feedback from candidate:

Feedback to candidate:

Candidate’s signature:Date:

Assessor’s signature:Date:

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MODEL ANSWERS FOR THE ORAL TEST

Note to Assessor: These are suggested answers to act as guidelines

S/

No.

Question Model answers Marks

1 Name two personal protective

equipment required while

operating the lathe

Protective clear goggles

overall

safety boots

(Any two correct answers)

2

2 Mention three safety

precautions to be observed

while operating a lathe machine

-Always remove the chuck key

from the chuck

Secure the work firmly before

starting the machine

Do not change gears while the

machine is in motion

Do not remove chips using bare

hands

Ensure the cutting tool is firmly

held in position

3

3 Name any four major parts of a

lathe machine

Headstock

Bed

Tail stock

Carriage

Cross slide

Compound slide

Tool post

(Any four correct answers)

4

4 What is the difference between

ferrous material and non-ferrous

material

Ferrous metals contain Iron as

the main constituent while non-

ferrous contain no Iron.

2

5 How do you dispose the waste

products as a result of the lathe

machining operations

Disposal starts by sorting based

on material machined

Recycling and burying those

2

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that cannot be recycled.

6 Mention two ways of

maintaining the lathe machine

Clean machine after use

lubricate moving parts

Oiling the guide ways

(Any two correct answers)

2

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MODEL ANSWERS FOR THE WRITTEN TEST

Note to Assessor: These are suggested answers to act as guidelines

SECTION A: MULTIPLE CHOICE QUESTIONS [10 marks]

1.One of the following is not a hazard associated with the lathe machine?

a. Burns from chipsb. Unguarded rotating chuckc. Unsecured work

Fumes 2. One of the following materials does not produce continuous chips when machined on the

lathe machine?a. Mild steelb. Copper

Brassc. Aluminum

3. Which of the following material requires the use of coolant while being machined on the lathe machine?

a. Copper b. Mild steel

Cast iron c. Stainless steel

4. Functions of the cutting fluid used in lathe operations does not include?a. Washing away the swarf

Lubricating the machineb. Cooling the workc. Cooling the tool

5. Which one of the following is not a mechanical property of engineering material?a. Ductility

Thermal conductivityb. Hardness c. Brittleness

6. Daily routine maintenance practice on a lathe machine involves?a. Lubricating moving parts

Oiling of guideways b. Cleaning machine after usec. Spindle alignments

7. Identify which one of the following is not a lathe machine operation?a. Knurlingb. Boring

Slot cuttingc. Taper turning

8. The main reason why knurling is carried out is to:a. To increase the diameter of the workpieceb. To increase the length of the workc. To increase the roughness of the surface

To increase the grip and appearance of the product9. A clearance fit result when:

a. The shaft and hole are equalb. When the hole is slightly bigger or smaller than the shaftc. When the shaft is bigger than the hole

When the shaft is smaller than the hole10. A shaft has its diameter designated as 50± 0.02, its allowance is:

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a. + 0.02b. - 0.02

0.04c. 0.00

SECTION B (STRUCTURED QUESTIONS)

1. Differentiate between the two types of chucks used on the lathe machine [2 Marks]

Three jaw chuck is a self-centering chuck while the four-jaw chuck is an

independent chuck.

The three-jaw chuck is used for cylindrical work while the four jaw may be used for

square, hexagonal and irregular shaped work pieces.

2. List any four methods of work holding on the lathe machine [2 Marks]

Three jaw chuck

Four jaw chuck

Catch plate / Lathe dog

Collets

Between centers

Face plate

3. Explain the effect of setting the cutting tool below or above the center on the lathe

[4mks]

When the tool is set below the center the work rides over the tool and can cause tool damage

When the tool is set above the tool the rubs the work and poor surface finish results.

4. Outline factors that govern the selection of speeds and feeds while machining on the

lathe. [5mks]

Depth of cut: The higher the depth of cut the lower the cutting speed as well as the feed

rate.

Tool Material: Different tool materials have different specified/recommended cutting

speeds (HSS, Tungsten Carbides etc)

Work Material: High cutting speeds are recommended for ductile materials while brittle

materials are cut at moderately low speeds.

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Surface finish required: Roughing is usually done at low speed while finish cutting is done

at high speed.

Machine Condition: Machining on Robust and Computerized Numerically Controlled

machines is done at high speeds while light and conventional machines requires machining

at moderately low speeds because of minimal vibrations.

5. In a lathe machine turning operation, a free cutting mild steel bar of 25 mm diameter is to be turned down to 20 mm diameter to a length of 75m. allowing a cutting speed of 150m/min and a feed rate of 30 cuts per centimeter, calculate the spindle speed and the cutting time. [5marks]

N=1000 Sπd

Where, N =spindle speed,

S= cutting speed

D=diameter

N=1000 X 150π 25 = 1909 rev/min, select 1910 rev/min

cutting time= No . of revolutionsspeed∈revolutionsper minute

cutting time = (length in cm x feed rate)/(speed in revolutions per minute)

cutting time = (7.5 cm x 30) / (1910) =0.118 min

6. Describe three methods of taper turning (8 marks)

Tailstock set over ( 3 Marks

This method is recommended for long work pieces. The work is held between the chuck and the

tailstock. The tailstock lock nut is released and the tailstock is offset to the required angle of taper.

Compound slide method (2 Marks)

In this method the cutting tool is positioned at the tool post perpendicular to the work axis.

The compound slide is the swiveled to the required angle of taper.

Taper turning attachment. (3 Marks)

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Modern lathes have a taper bar fitted at the back of the bed which can be adjusted through a

range of angles to suit the angle of taper.

7. Briefly explain three types of chips produced while machining on the lathe

machine[9mks]

i. Continuous chip

Continuous chip is produced by the metal ahead of the tool becoming greatly

compressed and flowing across the rake face of the tool

This form of chip indicates good cutting conditions with low chip friction, long tool

life, good surface finish and power consumption. It usually occurs when cutting a

ductile material at a high speed and fine feed, with a large rake angle, polished tool

face, and good lubrication.

ii. Continuous chip with built up edge

Formed in a similar manner but due to intense pressure and high temperature small

pieces of work metal become welded to the tool tip. The built-up edge usually occurs

when a ductile material is being cut under conditions causing extreme heat and

pressure e.g. poor tool face finish, poor lubrication and too small rake angle

iii. Discontinuous chip

Occurs when the force involved in bending the chip cause complete breakdown of

the shear zone and individual segments of the metal come away separately. This is

due to cutting on brittle materials e.g. cast iron, brass etc. it also occurs when the

cutting speeds is too low and the rake angle to small.


ORAL TEST ASSESSMENT MARKS SHEET



Unit of Competency

Venue of Assessment

Date of assessment:

Question Marks Available

Marks Obtained

Question 1 2

Question 2 3

Question 3 4

Question 4 2

Question 5 2

Question 6 2

TOTAL: 15 `


(The candidate is competent if s/he gets 50% or higher)

Comments by Assessor:


WRITTEN TEST ASSESSMENT MARKS SHEET



Unit of Competency

Venue of Assessment

Date of assessment:

Question Marks Available

Marks Obtained

SECTION A (MULTIPLE CHOICE QUESTIONS)Question 1-10 10

SECTION B (STRUCTURED QUESTIONS)

Question 1 2

Question 2 2

Question 3 4

Question 4 5

Question 5 5

Question 6 8

Question 7 9

TOTAL: 45 `


(The candidate is competent if s/he gets 50% or higher)

Comments by Assessor:


ASSESSMENT RECORDS

Qualification & Level

Unit(s) of competency

Candidate details: Candidate Name:Candidate registration no.:Candidate Signature: Date (dd/mm/yyyy)Assessor details: Assessor Name:Assessor Reg. Code:Assessor Signature: Date (dd/mm/yyyy)Verifier details: Verifier name:Verifier Reg. Code:Verifier signature: Date (dd/mm/yyyy)

ASSESSMENT TASKSOUTCOME

(Please tick (√) as appropriate)Competent

Not yet competent

a) Oral Assesmentb) Written Assessmentc) Practical assessment

Assessment outcome(Tick as appropriate. Candidate is competent if found competent in each of the assessment tasks in this assessment)

(Please tick (√) as appropriate)

Competent

Not yet competent

Feedback from candidate:

Date: Candidate Signature:Feedback to candidate:

Date: Assessor Signature: Feedback from verifier

Date: Verifier Signature:


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