JSS 2.After Mid Term.TOPIC 7: UNDERSTANDING BUILDING TERMINOLOGIES.

Most terminologies used in building construction vary with different meaning and application. Below are some of these terminologies.

(i).Foundation: This is the lower part of the building that transfers the load of the building to the soil below without cracking.
(ii).Architect: This is the professional that draws the building plan(blueprint).
(iii). Quantity surveyor: This is a professional that quantifies the amount of money, material, labour and workmanship that could finish a particular project or building.
(iv). Builder: This is the engineer that erects the building according to   plan of the building.
(v). Statutory personnel: This is a government official who makes sure that any building meets local, state or national standard. If it does not meet the standard, such buildings are usually demolished.
(vi). Structural engineers: This is a professional that determines and specifies the strength and types of building materials like cement ratio, number of steel, etc, for any construction.  
(vii). Landscaping: This is the process of making the surrounding of a building more beautiful by planting trees and flowers and the general topography of the land.
(viii). Timbering: This is the practice of using timber to support the vertical  sides of a trench,  so as to avoid collapse.
(ix). Foundation footing: This is the wide base that carries the walls, pillars or columns of any building.

(xi).Excavation: This is the digging up of earth to a required dept, width and length. This can be done both manually and mechanically. 
(xii). Soil: Soil can be defined as any loose material deposit, such as gravel, sand, clay or the mixture of all these other materials listed. There are two types of soil namely, cohesive and non-cohesive.
(a). Cohesive soil: This is the type of soil that is sticky and closely bonded together. Example of such soil is mud and clay soil.
(b).Non-cohesive soil: This type of soil is loose in nature. It includes sharp sand or loamy soil.
(xiii).DPC: The acronym DPC means damp proof course. This is the layer that prevents the penetration of moisture or water into the building from underground. Materials that can be used for DPC include waterproof, polythene and mackintosh.
 (xiv).Lintel: This is the material put over an opening in a wall to enable the wall to continue above  the opening.
(xv).Rendering: This is the method of spraying mortar or concrete on the surface of wall, such that the wall then looks coarse (rough).
 (xvi).Bonding: This is the  type of arrangement used when laying blocks to ensure that no vertical joints occurs.
(xvii).Slab: This is a horizontal part of a building, made from concrete and supported by columns or walls.
(xviii).Batching: This is the process of measuring concrete either by volume or mass.
(xix). Curing: This is the process of maintaining a satisfactory moisture condition for a freshly placed concrete.

Class Work

State the difference between the following professionals:
1.architect
2.quantity surveyor
3.statutory personnel and
4.structural engineer.

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JSS 1..After Mid Term:TOPIC 7: WOOD DEFECTS AND PRESERVATION

DEFINITION

Wood preservation is the process of adding chemical to wood so as to prevent termites, insects, weevils and fungi from attacking the wood. These chemicals are called preservatives. It can be applied to wood through spraying or brushing.

Examples of wood preservatives are creosote, coal- tar,  solignum, chlorinatephenol, paints, etc.

                                                Defects in Wood

Defects are faults or irregularities in wood caused either naturally or during processing of the wood which reduces the value or quality of the timber.
(1). Natural defects: These are defects which occur during the growth of a tree.
They include the following:

(a).Knots: A knot is a defect that occurs at the branch of a tree. If a branch falls from a tree it may leave a knot hole on the tree eg

(b).Cross grain: This is the condition which occurs when the wood fibre is not aligned parallel t o the axis of the piece of wood. it is caused by the manner the tree grew. It gives plants low strength.

(c).Shakes: This is the complete separation of parts of a stem in a living tree. it occurs because of stress variation in the stem. There is the ring shake and the heart shake. Eg

(2) Artificial defects: This is also referred to as processing defects. It includes checks and warps.

(a) Checks: This is a defect which creates a separation of wood grain along the grain board. Eg

(b) Warps: Twists in timber are called warps.  They may be caused by improper seasoning procedure.

Examples on Images:

Class Work

What is wood preservation?

Explain 4 types of wood defects.



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JSS 3.TOPIC 6: ISOMETRIC DRAWING

Definition: Isometric drawing is defined as a 3-dimensional drawing of an object. It is a pictorial method of drawing. What you see is what you draw to the given scale. The three dimensions are the length, width and height.

Isometric Axis: The term isometric axis means the lines formed by the 30⁰ set square and the vertical line of any given plane or block to be drawn. The lines that slant at 30⁰ are called the receeding lines. The vertical line is also drawn using the side of the 30⁰/60⁰ set square.(your teacher will show you how).
The lines drawn are often referred to as projection lines. Apart from the vertical lines, all other lines are inclined at 30⁰ slant. It is always better to complete the drawing in construction line (faint lines) first, check that everything is correct before outlining the block given.

Steps Involved in Isometric Drawing: Drawing isometric views goes through four main stages. They are:
(i). Drawing of the isometric axis
(ii).Drawing of the given isometric box
(iii).Shaping of the box through outlining of the edges (i.e. making the box drawn thicker).
(iv).Dimensioning.

1. Drawing the Isometric Axis: After setting your paper on your board and drawing border lines and title block, follow the steps below:
i.   On the lower section of your drawing paper mark a small cross(+).
ii.  Using the 30⁰-60⁰ set-square, supported by the T-square, draw the first vertical axis from the intersection of the +.
iii.  Turn the set square to the 30⁰ slant with the edge intersecting at the + either to the right or left and draw the first receeding axis.
iv.  Rotate the set-square until another edge rest as base on the T-square on the same intersection and draw the second receeding axis.(your teacher will demonstrate).

                                                         Drawing Isometric Boxes

To draw the block given in isometric drawing, you can follow the steps below:
i.   Starting on the marked point(+), locate the length, breadth and height with the aid of a pair of compasses and mark these on the already drawn axis.
ii.   With the aid of the 30⁰ slant, starting from the marks made on the axis, draw parallel lines to the previous ones including the vertical axis.
iii.  Draw all parallels to complete any given block. (teacher will demonstrates)
NOTE: Please, note that all the steps explained above must be done in construction (faint) lines using the 2H pencil.

2. Outlining the Edges: Finally, using the HB pencil with moderate pressure, thicken the outline of the given block. You may erase the extra projected lines on your work since they may not be required as part of the given block.

3. Dimensioning: This is the technique of adding the actual size (length, breadth and height) of any block given. The following steps explains how:
(i). With the aid of the set-square and a little distance from the block drawn, draw faint projections (the projection lines should not touch the block) as the block.
(ii). Rotating the set square appropriately, draw arrowhead lines to indicate demarcations on the given block.

Practice Exercises:
1. Using the block sown on page 157 (fig. 7), draw the block in Isometric projection as shown.
2. Draw the block shown on page 158 (fig.11) in isometric projection.
(The teacher demonstrates)

                                                                   ASSIGNMENT

Draw the Isometric blocks shown on pages 156 – 165 of your J.N. Green Technical Drawing Text Book.
(i).Figure 10
(ii).Figure 9
(iii).Figure 8.

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JSS 1. TOPIC 5: DRAWING PRACTICE: Drawing Instruments and Materials

Drawing practice is simply technical drawing. Technical drawing is the language used by engineers and architects to interpret objects, symbols, lines, curves and conventional representations on paper.

Drawing Instruments:
 Drawing instruments are tools used in technical drawing that do not get consumed while using them. They include the following:

(i). Drawing Board: This is a flat wooden board with a smooth, rigid surface. It is suitable for  A3 paper.

(ii). Tee-square: This is a T-shape instrument containing a head and a stock. It is used for drawing all horizontal lines and for setting the paper on the board. 

(iii). Set-square: We have the 45⁰ and 30⁰/60⁰ set-squares. They are used for drawing vertical and angled lines.

 (iv). Rules: This is a 30cm wooden or plastic instrument, used for measuring lengths and for dimensioning scaled drawings.

(v). Protractor: The protractor is used for measuring angles in degrees.

(vi). French curves: This instrument is used to draw different shapes of curves. 

(vii). Drawing set: This is a pack containing different drawing items like pair of compasses, divider, etc.

Drawing Materials:
Drawing materials on the other hand, are items that get consumed with use. They include the following:

(i). Drawing paper: The paper commonly used for technical drawing is the A3 paper. Other drawing papers are the A1, A2, A4, etc, depending on the work to be done.
(ii). Pencil: The 2H pencil is used for construction lines, ‘H’ is for lettering and thickening of visible lines. The HB pencil is good for free-hand sketching.
(iii). Pencil sharpeners: This is a material used to sharpen all pencils to a conical point shape.
(iv).Emery cloth:  Instead of re-sharpening the pencil, this material is used to restore sharpness to the pencil.
(v). Brush:  The brush is used to remove dirt from the paper after erasing.
(vi). Eraser: This material is used to remove mistakes. It is made of soft quality rubber.

                               Care and Storage of Drawing Instruments and Materials.

To care for their drawing instruments, students should do the following:

(i). Do not use any sharp objects on the edges of the drawing board.
(ii). When not in use, cover the face of the board to avoid dust.
(iii).The Tee-square should not be used as a sword or staff to play with.
(iv). Never use any sharp object on the edges of your set-squares.
(v). When you are not working with your instruments, keep them on their sheaths and packs.
(vi). Drawing paper should be kept in a flat file or jacket.

REVIEW QUESTIONS

(i). Define drawing practice.
(ii). What is the difference between drawing instrument and drawing material?

ASSIGNMENT
State the uses of the following drawing instruments and drawing materials:
i. Tee square
ii. Sketch pad
iii. Set square
iv. Eraser
v. HB pencil

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JSS1, TOPIC 4: FIRST C.A TEST QUESTIONS.

 Instruction: Attempt ALL questions.
1.An accident could be caused by any of the following EXCEPT…
a. horse play
b. wrong use of tools
c. poor lighting
d. over carefulness

2. To prevent suffocation in a technology workshop, the workshop must be well:
a. designed
b. lighted
c. ventilated
d. located

3. Which of the following  safety habits concerns all technical workers?
a. wearing overall occasionally
b. wearing eye goggle and necktie
c. keeping long hair
d. lifting heavy loads manually

 4. Workshops are always located away from residential houses because of…
a. distractions from people
b. unavailable space
c. air pollution in the neighborhood
d. Noise

5. Which of these is NOT a safety habit to practice in the workshop?
a. switch off power supply before wiring installation
b. always keep a water tank full of water in the workshop
c. keep working environment clean
d. always switch off all machines after use.

6. Technology is basically a subject for…

a. girls only

b. boys only

c. anybody
d. adults.

7. Technology should be studied for the following reasons EXCEPT…

a. pleasure and recreation
b. empowerment
c. money making
d. safety reasons

8. Technology has affected us in all of the following areas EXCEPT.
a. industrialization
b. improved health care delivery
c. high standard of living
d. highly developed technology

9. Technology can be defined as…………
a. a technologist
b. using scientific process to solve physical problems
c. using electronic gadgets
d. using fishing net when fishing.

10. There are two types of Technology that we have learnt. They are:
a. western/modern technology
b. derived/African technology
c. developed/under-developed technology
d. none of the above

11. The use of one of the following is related to a high-developed technology.
a.  knife and hoes
b.  hooks and nets
c.  horse drawn carts
d.  air-crafts and cars.

12. Safety in the workshop does not involve the following EXCEPT….
a. lean on running machine
b. obeying all workshop rules and regulations
c. using loose chisel.
d. stopping a running machine with bare hand.

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JSS1,TOPIC 3: WORKSHOP SAFETY RULES & REGULATIONS/ACCIDENT.

Definition: A workshop is a building or area where engineering work is carried out. An industrial workshop must meet certain standard for approval before they can function as an engineering workshop.

 Workshop Layout (What is needed in a Workshop).
In a workshop, the following layout should be strictly maintained:
(i). Uncongested working area.
(ii). Adequate ventilation and lighting.
(iii). Safe storage for tools and stacking of materials.
(iv). A clear gang way.
(v). Provision of toilets, dressing room and bathroom.

Accident:  Accident can be defined as an unexpected occurrence that may lead to either injury or death or damage to a machine.

Causes of Accident in the Workshop
1. Lack of provision of safety devices.
2. Failure to use safety devices.
3. Use of damaged tools and machines.
4. Carelessness in the workshop by students.
5. Loss of concentration due to tiredness.
6. Over congestion of working area.
7. Inadequate lighting and congestion.

Types of Accident
 1.Gas Leakage: Inhaling of leaking gas like carbon monoxide fumes and any carbon compound can kill.
2. Injury from cuts: This happens when sharp edged tools are badly applied when working.
3. Fire:  There are two types of fire to be considered. Electrical fire and Chemical fire.
(a). Electrical Fire: This occurs as a result of electrical sparks and overloading of a circuit leading to heat.
(b). Chemical Fire: When there is an oil spillage, the risk of fire is high.

Accident Preventive Techniques
(a). Always work under the supervision of an instructor.
(b). Observe all safety rules.
(c). Always use safety devices.
(d). Sand buckets and fire extinguishers must be placed in position to arrest any fire outbreak.

Safety
Safety can be defined as the method of working without harm, danger or injury. It is the removal of hazards to both man and machines.
Safety Devices
All safety devices are generally referred to as ‘ Personal Protective Equipment’ (PPE). These PPEs include the following:
1. Goggle and Eyelids: These equipment protect the eyes during welding  and grinding operations.
2. Lab coats and Boots: Students and teacher are expected to change into these attires before starting work at the workshop. The boot protects against any sharp object on the floor.
3. Helmet: This device is needed where heavy machines  are suspended. This is a must in all construction companies.
4. Sand bucket: This is used to handle fire outbreak in the absence of fire extinguisher.
5.  Nose cap: This is the device that protects against dust  and fumes in the workshop.
 6. First Aid Box: In the workshop, a first aid box must be present in an event that  an  accident  does occur, for minor injuries.

                                                 Safety Rules and Regulations

Safety Rules for Machine Users.
1. Do not play with the switches of a machine.
2. Ensure that the working environment is well lighted and ventilated.
3. Do not operate any machine you don’t have knowledge about.
4. Do not be allowed to be distracted while operating a machine.
5. Always switch off machines after use and remove them from the socket after use.
6. The workshop floor should not be littered with dangerous objects.

Safety Rules for Bench Users.

1.Do not use files or chisels without handles.
2. Learn to use tools in the proper way and keep them in a safe place.
3. When using the bench vice there should be no horseplay.
4. Wear protective shoes with toe cover.
5. Wear goggle or eyelids while filing, cutting and welding.
6. Do not carry any sharp object in your pockets.
7. Do not wear overflowing garments, bangles and chains in the workshop.
8. Do not wear neck ties while working on the bench or any machine.

REVIEW QUESTIONS

(i). How would you define a workshop?
(ii). In your opinion, what makes a workshop a standard workshop?
(iii). Define accident.
(iv). State four rules that bench users must strictly follow in the workshop.
(v). State three rules you will take to avoid accident when working with a machine.

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JSS1, TOPIC1. CONCEPT OF TECHNOLOGY

Definition of Technology: Technology can be defined as the method or process of using scientific  knowledge to solve physical problems in a simplified and fast manner through the use of machines..

Technology and Economic Development

Technology results in economic development. However, in Nigeria, our indigenous technology is still developing. Technology can improve a country from mainly extraction from nature to helping us provide raw materials, and manufacturing products from these raw materials to improve our living conditions.

 As such, any nation that sells her raw material is under- developed while a nation that processes its raw materials into finished products is regarded as highly developed.

Technology leads to economic development when a country converts its raw material into manufactured finished products which are exported to international market for foreign exchange. This exchange coupled with good governance results in economic development.

                                                Who Should Study Technology?

To answer the question raised above, one will think that technology can only be studied by men  or boys. But they are wrong. The truth is that everybody (boys, girls, men and women) can study technology.

                                                    Reasons for Studying Technology.

1. Empowerment: The knowledge of technology can empower one to use tools, machines and the computer effectively.
 2. Self Reliance:  Knowledge derived from technological subjects can equip us to be able to maintain and repair appliances on our own
3. Safety: Technology teaches us how to be safety conscious in all areas of life, thereby reducing the risk of accident.
4. Comfort and Pleasure:  The knowledge acquired from technology can make it possible for us to operate some equipment, machines and appliances that make work easy, faster and safer, thereby giving us comfort and pleasure while working.
5. Dream Realization:  Through technology, most students are able to realize their rewarding careers and other fields of interests.

REVIEW QUESTIONS 

(a).How would you define technology?
(b).Explain in your own words, how technology has improved our lives in the following areas:
(i). sports  (ii).transportation  (iii).fishing  (iv).farming  (v).music.

ASSIGNMENT
Using a table, describe the method applied in the following activities as developed or under developed technology.
Activities                           Under developed Tech.       Developed Tech.

(i).Fishing
(ii).Communication
(iii).Transportation
(iv). Farming
(v). Education.

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JSS3, TOPIC 3: Career Prospects and Opportunities in Technology

What is a Career?
 A career can be defined as a profession or job one is trained to do for the rest of his/her life time. Doing this career brings monetary benefits and fulfillment.

Technology Related Careers

Careers related to technology includes the following in Nigeria:
1. Mechanical Engineering
2. Electrical/Electronic Engineering
3. Civil Engineering
4. Building Engineering
5. Production Engineering
6. Chemical Engineering
7. Computer Engineering
8. Automobile Engineering
9. Metallurgical Engineering
10. Mining Engineering
11. Petroleum Engineering
12. Aeronautical Engineering.

                                    Importance of Technology Related careers

1.Mechanical Engineering: The skill and training in this profession has led to the invention of machines used in transportation, manufacturing, plumbing installations, pipe-network construction for gas, water and petroleum products.

2. Building: This is a professional who interprets the plan documents drawn by an architect, into a physical reality.
3. Automobile Engineering: This is a field of engineering that deals with the design, construction and maintenance of automobiles.
4. Aeronautical Engineering: The study that deals with the design, construction and maintenance of aeroplanes is called aeronautical engineering.
5. Production Engineering: This is the field of engineering that deals with how to put different machines together (called assembly lines) used for manufacturing goods like brewing.
6. Metallurgical Engineering: These are professionals that that focus on improving the strength, performance and durability of metals.

                        EMPLOYMENT PROSPECTS FOR TECHNOLOGY STUDENTS

The different areas where students of technology can be gainfully employed in Nigeria include the following:

Private Companies: In Nigeria, there are employment opportunities in most private industries that render services related to engineering. Manufacturing companies, banks and other industries also employ technicians and engineers.

Educational Sector: To train future engineers, secondary schools, polytechnics and universities employ engineers as tutors and lecturers to impart knowledge to younger ones.

Public Sector: In most government ministries like transportation, science and technology, power and mining, etc, it is engineers that the government  sort after for gainful employment to man these parastatals.

Consultancy: This is a partnership between different fields of engineers providing services of their choice. These consultancies can employ graduates from diverse engineering disciplines also.

Independent Practice: Engineering graduates can also set-up personal enterprise of their choice to employ other graduates so as to earn a living.

To succeed as an engineering student, you must be interested and take the following subjects seriously:
Mathematics, Basic Technology, Physics, Chemistry and Technical drawing.

REVIEW QUESTIONS

1. List five areas where engineers can work both in Nigeria and overseas.

2. In your own words, what do you think could delay becoming a successful engineer in Nigeria

3. State FIVE steps you will take to prepare yourself for an Engineering career.

4.Define career.
5.List 7 technology related careers.
6. Explain the functions of 5 of the technology related careers listed above.

ASSIGNMENT
What are the functions of the following professionals:
i. Computer Engineer
ii. Mining Engineer
iii. Petroleum Engineer
iv. Chemical Engineer
v. Civil Engineer.

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JSS 3, TOPIC 4: ORTHOGRAPHIC PROJECTION

Definition:
The word orthographic is coined from the word orthogonal (or perpendicular) and  graphic (or view). Orthographic projection can be defined as a two-dimensional drawing that shows different views of a structure. It contains the vertical and the horizontal planes as shown below. 

                                                           Angles of Projection.

i.First angle projection: Where the plan of a structure is positioned below the quadrant. E.g.
                                    1^st angle:   F.E.
                                                   PLAN

ii.Third angle projection: This is a condition where the plan of a structure is positioned above the quadrant. E.g. 
                                  3^RD angle: PLAN  
                                                     F.E. 

                       
                                                                   Elevations(views) .

In orthographic projection, there three basic views reffered to as elevations. These elevations are as follows:
(i).Plan: This is the view of an object as seen or projected from the top.
(ii).Front elevation: This is the view of an object as seen or projected from the front side of the object or block.
(iii).End(side) Elevation: This view is sometimes reffered to as the auxiliary vertical plane in some text books. It is the view showing the right or left side of any block when viewed from the front.

                          Steps in Orthographic Projection and Worked Illustrations.   

(i).Make a sketch of the required views.
(ii).Draw both the vertical and the horizontal axis to intersect midway.
(iii).Determine the placing of the views.
(iv).Begin drawing with either the plan or front views.
(v).From either of the views drawn above, project lines for the other view.
(vi).Draw the reflector line at 45⁰ .
(vii).Project the horizontal lines from the front elevation.
(viii).Project the plan to meet the reflector line of the 45⁰.
(ix).Take note of hidden details and outline the elevations to complete the job.

                                                 Worked Examples.

Draw the block shown on page 168 of the J.N. Green in orthographic projection in both 1^st and 3^rd angle projections, using arrow x as the front elevation.
( the teacher sketches the block on the board  and demonstrates different examples on the board for students to follow practical procedure involved in orthographic projection).

    
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JSS 3, TOPIC 2: TRANSMISSION OF ELECTRICITY AT HIGH FREQUENCY.

The transmission of electricity at high frequency takes place at low voltage. Instead of using high tension transmission power, it uses low tension transmission power. The frequency cuts across a broad band so that many networks can operate at the same time.

Appliances like radio, television and telecommunication gadgets operate on these frequencies. The frequencies or bands include AM, MW,SW and FM bands(this is for the radio frequencies). For the television band, we have the UHF, VHF and SHF channels.

                      Principles of Operation in High Frequency Transmissions.

The basic principle in the transmission of electricity at high frequency lies in the principle of the tank circuit. It is the conversion of audio or visual signals into electromagnetic waves, which is radiated from a sending aerial into space, where the receiving aerial cuts across it, to be transmitted to the final consumers.

                       Equipment Used in Radio Transmission.

 (i).Microphone/Camera: This equipment is used to convert sound and light energy into electrical signals which are used to modulate the carrier waves.
(ii).Transmitter: The transmitter oscillates the carrier waves between the transmitting aerial and the microphone. It contains a tank circuit which transmits the carrier waves at appropriate frequency.
(iii).Transmitting Aerial: This aerial radiates out the electromagnetic waves received from the transmitter.
(iv).Receiving Aerial: It used to trap the electromagnetic waves from space radiated by the transmitting aerial.
(v).Receiver: The receiver de-modulates (separates) the carrier waves and amplifies the message signals to the loudspeaker.
(vi).Loudspeaker/TV screen: This equipment converts the message signals into sound and electrical energy as images in television signals.eg (Radio Transmission system diagram).

Radio Transmission System.

REVIEW QUESTIONS

(i).list the components used for effective radio communication system.
(ii). explain the functions of the components listed above.(iii). State one difference between the transmission of electricity at high frequency and the transmission of electricity at low frequency.

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JSS 3, TOPIC 1: TRANSMISSION OF ELECTRICITY AT LOW FREQUENCY

Definition: Transmission of electricity deals with the production (generation), distribution and utilization of electricity in a particular region of a country.

Production of Electricity: This is the act of generating electricity from a particular location by the use of generators, turbines, gas and water (hydro).
Distribution of Electricity: This refers to the injection of electrical power into villages, towns and cities through sub-stations.

Utilization of Electricity: This is the process of putting electricity to optimum  use in households, commercial centers and industries.

Transmission of electricity at low Frequency.

In Nigeria, electricity is transmitted at low frequency but at high voltage. This is measured at 50Hertz(Hz) per second. Transmission is usually in alternating current principle. PHCN generates power at 11KVA and it is steeped up to 132KVA so that each station is connected to a common grid called the National grid.

                    Equipment Used in the Transmission of Electricity at Low Frequency.

(i). Generation Control Panels: This is the location where power is generated at power stations by many generators connected to a common 3-phase panel to obtain a common frequency.
(ii). Sub-Station: This is a place outside the power station for the conversion, transformation and control of electric power.
(iii). Circuit breaker: This equipment is used to make and break the flow of current to protect against earth leakages and overload current (especially during maintenance).
(iv). Transformer: They are used for stepping-up and stepping-down of electrical voltages.
(v). Transmission lines: These are aluminum cables used in power transmission.
(vi). Line support: These are the poles that carry the overhead lines.
(vii). Insulators: Insulators bond the overhead lines from the poles to avoid electrocution by anyone who may touch the poles. There are different types namely the pin, strain and the suspension types.
(viii). Lightning arrestor: This equipment arrests lightning surges that creates over voltage to the lines so as to protect the lines.
(ix).Fuses: Fuses are used to protect the lines in the event of over- voltage or current. In the event of spark, the fuse melts and drops.
(x). R.M.U. This simply means Ring Main Unit. It is the equipment used in separating feeders to an area.

                                             Power Transmission system diagram 

REVIEW QUESTIONS

1. List 5 equipment used during electricity transmission in Nigeria.
2. State one advantage of the lightning arrestor in electricity transmission.3. Define the following terms:
(a).transmission of electricity
(b).production of electricity

JSS 2. TOPIC 2: DRILLS AND DRILLING MACHINES

Drills are cutting tools used in the production of cylindrical holes in the machine shop. They include the following types:
(i).Twist drill: The twist drill has two, three or four lip types. While the two-lip drill is mainly used for drilling holes from origin, the three and four-lip drills are used for finishing or enlarging already-drilled holes. Eg. (to be drawn on the board).

Twist drills

Drilling Machines
 In drilling larger holes and at faster speed, drilling machines are used. Drilling machines make drilling job easier and faster. They include the following:

(i).Sensitive drilling machine:  It is a machine used for lighter jobs, with drill ranging from 1mm to 6mm diameter. It is electrically powered. Eg.

(ii). Bench drilling machine: This drilling machine is used where a hole of up to 15mm diameter is required on a large structure.eg.

(iii).Pillar drilling machine: This drilling machine is used for heavy-duty work, with drills of up to 20mm and above.eg.

(iv).Radial-arm drilling machine: This is a drilling machine used where a large work has to be maneuvered to bring each drilling point in position under the drill. It is usually larger than the first three mentioned. .eg.Bench, Sensitive, Radial and Pillar  drilling machines.

                                          Screw Thread-Forming

A thread is a line forming a groove round the outside of a bolt and screw or the inside of a nut or a hole. It is used to assemble parts of a machines in metal work.
When a thread is made on the outside of a metal, such as on a bolt or screw, it is called an external thread. However, when the thread is made on the inside of the object, it is called an internal thread.

                       Methods/Tools Used for Thread-Forming

(i).Internal Thread: The tool used for forming internal(female) thread is called the tap. There are three types of taps called taper tap, second tap and plug tap. It is necessary to drill a hole equal to the core-diameter of the thread, before taps could be used. Eg.

Tap              

Taps.

The handles for taps are called wrenches. This enables someone to use the manual method to form an internal thread. There is the adjustable wrench and the fixed-size wrench. Eg.

(ii).External thread: The tool used for forming external thread is called the Die. The handle used on the die is called the stock. There are different types of dies called the split die and solid or rectangular die.

                                                   Types of Dies 
(i). Circular split die: This die contains three screws provided for limited adjustment.eg.
(ii). Rectangular split die: This die has two piece screws marked 1 and 2. This die provides for a wide range of adjustment in size.eg.

                                                    Types of Threads
(i). Vee Thread: This is the most common type of thread used for screws and nuts of lighter jobs. Eg.                            

(ii). Whitworth thread: This thread is slightly different from the vee thread. It is also applied on lighter jobs.eg. 
(iii). Acme thread: The acme thread is used by heavy-duty machines and plants. Eg.                                                                                
(iv). Buttress thread: This thread has a little variation from the acme thread. It is also used for heavy-duty jobs. Eg
(v). Iso thread: This thread is used for gears and chains in most machines, especially for loads not too heavy. Eg. 
(vi). Square thread: The square thread is used for wrenches and adjustable devices or in cranes.eg.           

REVIEW QUESTIONS

(i). Explain internal and external threading.
(ii). List and explain four types of threads.
(iii). How is internal thread formed?


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JSS 2. TOPIC 1: METAL WORK HOLDING DEVICES

Metal work-holding devices are used for holding objects in position during cutting operations. They include vices and clamps.

1.Vices: Vices are used for holding heavy jobs. The different types of vices are as follows:

(i). Bench vice: This is a device fastened to the workbench near its edge, used for all types of heavy work, like filing, chipping, sawing, etc. eg

(ii).Hand vice: The hand vice is used where the work piece to be held by the bench vice seems to be too small to be held conveniently .eg.

(iii). Machine vice: The machine vice is used for holding work down on the table for the purpose of milling, shaping, drilling, etc. eg.

2. Clamps: Clamps are handy tools of various used for smaller articles. They include the following:
(i). Pliers: These are very handy tools of various sizes and shapes used for the general purposes of holding small articles and for cutting small wires. They can also be used for pulling, pushing, turning and twisting.eg.

(ii). Toolmaker’s clamp: This is a clamp used for holding parts together during assembling (coupling parts together), riveting, clamping work piece during drilling. Eg.

REVIEW QUESTIONS

(i). name two types of vices used in a metal workshop.
(ii). explain the uses of the vices listed above.