CONTENTS

CERTIFICATE

ACKNOWLEDGEMENT

CHAPTER TITLE

1. INTRODUCTION

2. BLOCK DIAGRAM

3. MATRIAL DESCRIPTION

4. MATRIAL LIST

5. MATRIAL DESCRIPTION

6. REFERENCES

1

INTRODUCTION

INTRODUCTION

The power hand hacksaw is common types of sawing machines used to

cut metal or wood in the machine shop. The power hand hacksaw uses a

reciprocating (back and forth) cutting action similar to the one used in a hand

hacksaw. The power hacksaw is used for square or angle cutting of stock.

OBJECTIVE:-

All power hand hacksaw machines are basically similar in design. Shows

a typical power hacksaw and identifies its main parts, which are discussed below.

Application

Metal or wood cutting.

2

BLOCK

DIAGRAM

BLOCK DIAGRAM

3

MATERIAL

DESCRIPTION

MATERIAL DESCRIPTION

1) DC Motor

DC motor is an electric motor that runs on direct current (DC) electricity.  DC

motors were used to run machinery, often eliminating the need for a local steam

engine or internal combustion engine. DC motors can operate directly from

rechargeable batteries, providing the motive power. Modern DC motors are

nearly always operated in conjunction with power electronic devices.

2) Aluminum Strip with holes

Sheet metal is simply metal formed into thin and flat pieces. It is one of the

fundamental forms used in metalworking, and can be cut and bent into a variety

of different shapes. Countless everyday objects are constructed of the material.

Thicknesses can vary significantly, although extremely thin thicknesses are

considered foil or leaf, and pieces thicker than 6 mm (0.25 in) are

considered plate. And holes were cut by blanking process in an organized

manner

3) Power supply

This consist a 12V power supply source through DC adopter.

4) Square tube

Hollow square tube, which have a uniform cross-section with only one

enclosed void along their whole length in the shape of rectangles (including

squares), and which have a uniform wall thickness.

5) Hack saw

A hacksaw is a fine-tooth hand saw with a blade held under tension in a

frame, used for cutting materials such as metal or plastics. Hand-held

hacksaws consist of a metal arch with a handle, usually a pistol grip, with

pins for attaching a narrow disposable blade. A screw or other mechanism is

used to put the thin blade under tension. The blade can be mounted with the

teeth facing toward or away from the handle, resulting in cutting action on

either the push or pull stroke. On the push stroke, the arch will flex slightly,

decreasing the tension on the blade, often resulting in an increased tendency

of the blade to buckle and crack. Control of the cut and longer blade life.

6) Nut bolt

In normal use, a nut-and-bolt joint

holds together because the bolt is

under a constant tensile

stress called the preload. The preload pulls the nut threads against the bolt

threads, and the nut face against the bearing surface, with a constant force,

so that the nut cannot rotate without overcoming the friction between these

surfaces. If the joint is subjected tovibration, however, the preload increases

and decreases with each cycle of movement. If the minimum preload during

the vibration cycle is not enough to hold the nut firmly in contact with the bolt

and the bearing surface, then the nut is likely to become loose.

7) Switches

DPDT (double pole, double throw): A DPDT switch routes two separate

circuits, connecting each of two inputs to one of two outputs. A DPDT switch

has six terminals: two for the inputs, two for the A out puts, and two for the B

outputs.

8) Plywood

Plywood layers (called veneers) are glued together, with adjacent plies

having their wood grain at right angles to each other, to form acomposite

material. This alternation of the grain is called cross-graining and has several

important benefits: it reduces the tendency of wood to split when nailed at the

edges; it reduces expansion and shrinkage, providing improved dimensional

stability; and it makes the strength of the panel consistent across both

directions. There is usually an odd number of plies, so that the sheet is

balanced—this reduces warping. Because plywood is bonded with grains

running against one another and with an odd number of composite parts, it is

very hard to bend it perpendicular to the grain direction.

4

MATERIAL

LIST

MATERIAL LIST:-

1) DC Motor

2) Aluminum Strip with holes

3) Square tube

4) Hack saw

5) Nut bolt

6) Switches

7) Plywood

8) Power supply block

5

MATERIAL

DESCRIPTION

MATERIAL DESCRIPTION

DC MOTORS:

Basically, the motors can be categorized into two parts, AC and

DC. The basic principle of operation is almost same. In any electric

motor, the operation is based on simple electromagnetism. A current

carrying conductor generates a magnetic field; when this is placed in

an external magnetic field, it will experience a force proportional to

the current in the conductor, and the strength of the external

magnetic field. The internal configuration of a DC motor is designed

to harness the magnetic interaction between a current carrying

conductor and an external magnetic field to generate rotational

motion.

DC Motors can be classified as:

1. Externally Excited DC Motor:

This type of DC motor is constructed such that the field is not

connected to the armature. This type of DC motor is not normally

used

2. Shunt DC Motor:

The motor is called a "shunt" motor

because the field is in parallel, or "shunts" the armature. This type of

motor runs practically constant speed, regardless of the load. It is the

type generally used in commercial practice and is usually

recommended where starting conditions are not usually severs.

Speed of the shunt-wound motors may be regulated in two ways:

first, by inserting resistance in series with the armature, thus

decreasing speed: and second, by inserting resistance in the field

circuit, the speed will vary with each change in load: in the latter, the

speed is practically constant for any setting of the controller. A shunt

wound motor has a high-resistance field winding connected in parallel

with the armature. It responds to increased load by trying to maintain

its speed and this leads to an increase in armature current. This

makes it unsuitable for widely-varying loads, which may lead to

overheating.

3. Series DC Motor:

The motor field windings for a series motor are in series with the

armature.

This type of motor speed varies automatically with the load,

increasing as the load decreases. Use of series motor is generally

limited to case where a heavy power demand is necessary to bring

the machine up to speed, as in the case of certain elevator and hoist

installations, for steel cars, etc. Series-wound motors should never be

used where the motor can be started without load, since they will race

to a dangerous degree. A series wound motor has a low-resistance

field winding connected in series with the armature. It responds to

increased load by slowing down and this reduces the armature

current and minimizes the risk of overheating.

4. Compound DC Motor:

A compounded DC motor is constructed so that it contains both a

shunt and a series field. This particular schematic shows a

cumulatively-compounded" DC motor because the shunt and series

fields are aiding one another combination of the shunt wound and

series wound types combines the characteristics of both.

Characteristics may be varied by varying the combination of the two

windings. These motors are generally used where severe starting

conditions are met and constant speed is required at the same time.

Speed control:

Generally, the rotational speed of a DC motor is proportional to the

voltage applied to it, and the torque is proportional to the current.

Speed control can be achieved by variable battery tapings, variable

supply voltage, resistors or electronic controls.

In a circuit known as a chopper, the average voltage applied to the

motor is varied by switching the supply voltage very rapidly. As the

"on" to "off" ratio is varied to alter the average applied voltage, the

speed of the motor varies. The percentage "on" time multiplied by the

supply voltage gives the average voltage applied to the motor.

Therefore, with a 100 V supply and a 25% "on" time, the average

voltage at the motor will be 25 V. During the "off" time, the armature's

inductance causes the current to continue through a diode called a

"fly back diode", in parallel with the motor. At this point in the cycle,

the supply current will be zero, and therefore the average motor

current will always be higher than the supply current unless the

percentage "on" time is 100%. At 100% "on" time, the supply and

motor current are equal. The rapid switching wastes less energy than

series resistors. This method is also called pulse-width modulation

(PWM) and is often controlled by a microprocessor. An output filter is

sometimes installed to smooth the average voltage applied to the

motor and reduce motor noise.

DC MOTOR DRIVER:

As the most of the PORT of MCU or

any other controlling ICs are not powerful enough to drive DC motors

directly so we need some kind of drivers. A very easy and safe is to

use popular L293D chips. It is a 16 PIN chip. The pin configuration is

shown in the diagram.

This chip is

designed to control 2 DC motors.

There are 2 INPUT and 2 OUTPUT pins for each motor. The

diagram with proper connection is shown in the next diagram. The

‘RA3’ and ‘RA2’ pins are used to control the motor one and ‘RA0’ and

‘RA1’ pins are used to control motor B. Pin1 and Pin9 are enable

pins. If these pins are not connected to +5V, then both the drivers will

remain deactivated until they are enabled. Whatever power supply we

provide at pin 8 and pin 16, this supply will go to both motors. Hence

we have to be careful about the rating of

motors while connecting the power

supply to this IC using this IC.

The behavior of both motors are

similar are exactly similar. Here the

table describes the controlling method

of one motor; same is applicable for

other motor.

Signal at

RA3

Signal at

RA2

Rotation of Motor A

LOW LOW Stop

LOW HIGH clockwise

HIGH LOW Anticlockwise

High High Stop

From the above discussion it is clear that the motor can be stopped in

two ways, either by sending ground signal to both controlling lines, or

by sending high on both signal pins. If we have to stop the motor

immediately, then we should send high on both signal pins. This is

known as active braking, by which the motor is stopped instantly.

The basic idea behind controlling any DC motor is explained below;

this circuit arrangement is known as H Bridge because it looks like an

‘H’. The circuit diagram for H Bridge is shown. In general an H bridge

is a rather simple circuit, containing four switching elements with the

load at the center, in an H like configuration. The switching elements

(Q1….Q4), are usually bi-polar or FET transistors, in some high-

voltage applications IGBTs. In fact the similar arrangement is present

in our L293D IC. The operation of the circuit is very easily understood

by the following diagram.

The basic operating mode

of an H-bridge is fairly simple: if

Q2 and Q3 are turned on, the

left lead of the motor will be

connected to ground, while the

right lead is connected to the

power supply. Current starts

flowing through the motor which

energizes the motor in (let's say) the forward direction and the motor

shaft starts spinning. If Q1 and Q4 are turned on, the converse will

happen, the motor gets energized in the reverse direction, and the

shaft will start spinning in that way.

The role of cathode diodes is explained below:

The basic principle is very simple: while the bridge is on, two of the

four switching elements will carry the current, the diodes have no

role. However once the bridge is turned off the switches will not

conduct current any more. As discussed earlier, by far the most

common load for an H-bridge is an electric DC motor, which is an

inductive load. What this means is that during the on-time the motor

will build an electromagnetic field inside it. When the switch is turned

off, that field has to collapse, and until that happens, current must still

flow through the windings. That current cannot flow through the

switches since they are off, but it will find a way. The catch diodes are

in the design to provide a low-resistance path for that collapse current

and thus keep the voltage on the motor terminals within a reasonable

range.

Aluminum Strip with holes

Marsden Matting is standardized, perforated steel matting material

originally developed by the United States at the Waterways Experiment Station

shortly before World War II, primarily for the rapid construction of temporary

runways and landing strips. The material is also commonly known as Marston

mats (or Marston Plate) for a town in North Carolina adjacent to Camp Mackall

airfield where the material was first manufactured[1] and used in November 1941.[2] The material was also used in the Korean and Vietnam Wars where its

common name, from its NATO Stock Number nomenclature, is pierced (or

perforated) steel planking (PSP). Marsden matting consisted of steel strips

with holes punched through it in rows and a formation of U-shaped channels

between the holes. Hooks were formed along one long edge and slots along the

other long edge so that they could be connected to each other. The short edges

were straight cut with no holes or hooks. To achieve lengthwise interlocking, the

mats were laid in a staggered pattern. The hooks were usually held in the slots

by a steel clip that filled the part of the slot that is empty when the adjacent

sheets are properly engaged together. The holes were bent up at their edges so

that the beveled edge stiffened the area around the hole. In some mats a T-

shaped stake could be driven, at intervals, through the holes to keep the

assembly in place on the ground. Sometimes the sheets were welded together.

The typical Marsden matting was the M8 landing mat. A single piece weighed

about 66 pounds and was 10 ft (3.0 m) long by 15 in (0.38 m) wide. The hole

pattern for the sheet was three holes wide by 29 holes long resulting in 87 holes

per mat. A variation made from aluminum was produced to allow easier

transportation by aircraft, since it weighed about 2/3 as much. It was referred to

as PAP for perforated aluminum planking,[3] but was not as common as

aluminum was a controlled strategic material during World War II. PSP was

later, after the war, used by many early southeastern U.S. auto racing teams as

it was manufactured in the area, and used in many abandoned military airfields.

It was also used during a similar period when NASCAR teams used car trailers.

DPDT Switch

In electrical engineering, a switch is an electrical component that can

break an electrical circuit, interrupting the current or diverting it from one

conductor to another. The most familiar form of switch is a manually operated

electromechanical device with one or more sets of electrical contacts, which are

connected to external circuits. Each set of contacts can be in one of two states:

either "closed" meaning the contacts are touching and electricity can flow

between them, or "open", meaning the contacts are separated and the switch is

nonconducting. The mechanism actuating the transition between these two

states (open or closed) can be either a "toggle" (flip switch for continuous "on" or

"off") or "momentary" (push-for "on" or push-for "off") type. A switch may be

directly manipulated by a human as a control signal to a system, such as a

computer keyboard button, or to control power flow in a circuit, such as a light

switch. Automatically operated switches can be used to control the motions of

machines, for example, to indicate that a garage door has reached its full open

position or that a machine tool is in a position to accept another workpiece.

Switches may be operated by process variables such as pressure, temperature,

flow, current, voltage, and force, acting as sensors in a process and used to

automatically control a system. For example, a thermostat is a temperature-

operated switch used to control a heating process. A switch that is operated by

another electrical circuit is called a relay. Large switches may be remotely

operated by a motor drive mechanism. Some switches are used to isolate electric

power from a system, providing a visible point of isolation that can be padlocked

if necessary to prevent accidental operation of a machine during maintenance, or

to prevent electric shock.

Contact terminology

In electronics, switches are classified according to the arrangement of

their contacts. A pair of contacts is said to be "closed" when current can flow

from one to the other. When the contacts are separated by an insulating air gap,

they are said to be "open", and no current can flow between them at normal

voltages. The terms "make" for closure of contacts and "break" for opening of

contacts are also widely used. In a switch where the contacts remain in one state

unless actuated, such as a push-button switch, the contacts can either be

normally open (abbreviated "n.o." or "no") until closed by operation of the

switch, or normally closed ("n.c." or "nc") and opened by the switch action. A

switch with both types of contact is called a changeover switch. These may be

"make-before-break" ("MBB" or shorting) which momentarily connects both

circuits, or may be "break-before-make" ("BBM" or non-shorting) which

interrupts one circuit before closing the other. The terms pole and throw are also

used to describe switch contact variations. The number of "poles" is the number

of separate circuits which are controlled by a switch. For example, a "2-pole"

switch has two separate identical sets of contacts controlled by the same knob.

The number of "throws" is the number of separate positions that the switch can

adopt. A single-throw switch has one pair of contacts that can either be closed or

open. A double-throw switch has a contact that can be connected to either of two

other contacts, a triple-throw has a contact which can be connected to one of

three other contacts, etc. These terms have given rise to abbreviations for the

types of switch which are used in the electronics industry such as "single-pole,

single-throw" (SPST) (the simplest type, "on or off") or "single-pole, double-

throw" (SPDT), connecting either of two terminals to the common terminal.

Electronics

specification

and

abbreviation

Expansion

of

abbreviation

British

mains

wiring

name

American

electrical

wiring

name

Description Symbol

DPDTDouble pole,

double throw

Equivalent to

two SPDT

switches

controlled by a

single

mechanism.

Contact bounce

Contact bounce (also called chatter) is a common problem with

mechanical switches and relays. Switch and relay contacts are usually made of

springy metals. When the contacts strike together, their momentum and elasticity

act together to cause them to bounce apart one or more times before making

steady contact. The result is a rapidly pulsed electric current instead of a clean

transition from zero to full current. The effect is usually unimportant in power

circuits, but causes problems in some analogue and logic circuits that respond

fast enough to misinterpret the on-off pulses as a data stream. The effects of

contact bounce can be eliminated by use of mercury-wetted contacts, but these

are now infrequently used because of the hazard of mercury release.

Alternatively, contact circuits can be low-pass filtered to reduce or eliminate

multiple pulses. In digital systems, multiple samples of the contact state can be

taken or a time delay can be implemented in order for the contact bounce to

settle before the contact input is used to control anything. One way to implement

this with an SPDT Switch is by using an SR Latch.[7] These are referred to as

"debouncing" circuits.By analogy, the term "debounce" has arisen in the software

development industry to describe rate-limiting or throttling the frequency of a

method's execution.

Arcs and quenching

When the power being switched is sufficiently large, the electron flow

across opening switch contacts is sufficient to ionize the air molecules across the

tiny gap between the contacts as the switch is opened, forming a gas plasma,

also known as an electric arc. The plasma is of low resistance and is able to

sustain power flow, even with the separation distance between the switch

contacts steadily increasing. The plasma is also very hot and is capable of

eroding the metal surfaces of the switch contacts. Electric current arcing causes

significant degradation of the contacts and also significant electromagnetic

interference (EMI), requiring the use of arc suppression methods. Where the

voltage is sufficiently high, an arc can also form as the switch is closed and the

contacts approach. If the voltage potential is sufficient to exceed the breakdown

voltage of the air separating the contacts, an arc forms which is sustained until

the switch closes completely and the switch surfaces make contact. In either

case, the standard method for minimizing arc formation and preventing contact

damage is to use a fast-moving switch mechanism, typically using a spring-

operated tipping-point mechanism to assure quick motion of switch contacts,

regardless of the speed at which the switch control is operated by the user.

Movement of the switch control lever applies tension to a spring until a tipping

point is reached, and the contacts suddenly snap open or closed as the spring

tension is released. As the power being switched increases, other methods are

used to minimize or prevent arc formation. A plasma is hot and will rise due to

convection air currents. The arc can be quenched with a series of nonconductive

blades spanning the distance between switch contacts, and as the arc rises its

length increases as it forms ridges rising into the spaces between the blades,

until the arc is too long to stay sustained and is extinguished. A puffer may be

used to blow a sudden high velocity burst of gas across the switch contacts,

which rapidly extends the length of the arc to extinguish it quickly. Extremely

large switches in excess of 100,000-watt capacity often have switch contacts

surrounded by something other than air to more rapidly extinguish the arc. For

example, the switch contacts may operate in a vacuum, immersed in mineral oil,

or in sulfur hexafluoride. In AC power service, the current periodically passes

through zero; this effect makes it harder to sustain an arc on opening.

Manufacturers may rate switches with lower voltage or current rating when used

in DC circuits.

Power switching

When a switch is designed to switch significant power, the transitional

state of the switch as well as the ability to withstand continuous operating

currents must be considered. When a switch is in the on state, its resistance is

near zero and very little power is dropped in the contacts; when a switch is in the

off state, its resistance is extremely high and even less power is dropped in the

contacts. However, when the switch is flicked, the resistance must pass through

a state where a quarter of the load's rated power (or worse if the load is not

purely resistive) is briefly dropped in the switch. For this reason, power switches

intended to interrupt a load current have spring mechanisms to make sure the

transition between on and off is as short as possible regardless of the speed at

which the user moves the rocker. Power switches usually come in two types. A

momentary on-off switch (such as on a laser pointer) usually takes the form of a

button and only closes the circuit when the button is depressed. A regular on-off

switch (such as on a flashlight) has a constant on-off feature. Dual-action

switches incorporate both of these features.

Inductive loads

When a strongly inductive load such as an electric motor is switched off,

the current cannot drop instantaneously to zero; a spark will jump across the

opening contacts. Switches for inductive loads must be rated to handle these

cases. The spark will cause electromagnetic interference if not suppressed; a

snubber network of a resistor and capacitor in series will quell the spark.

Incandescent loads

When turned on, an incandescent lamp draws a large inrush current of

about ten times the steady-state current; as the filament heats up, its resistance

rises and the current decreases to a steady-state value. A switch designed for an

incandescent lamp load can withstand this inrush current.

Wetting current

Wetting current is the minimum current needing to flow through a

mechanical switch while it is operated to break through any film of oxidation that

may have been deposited on the switch contacts.[12] The film of oxidation occurs

often in areas with high humidity. Providing a sufficient amount of wetting

current is a crucial step in designing systems that use delicate switches with

small contact pressure as sensor inputs. Failing to do this might result in

switches remaining electrically "open" due to contact oxidation.

Actuator

The moving part that applies the operating force to the contacts is called

the actuator, and may be a toggle or dolly, a rocker, a push-button or any type

of mechanical linkage (see photo).

Biased switches

The momentary push-button switch is a type of biased switch. The most

common type is a "push-to-make" (or normally-open or NO) switch, which makes

contact when the button is pressed and breaks when the button is released.

Each key of a computer keyboard, for example, is a normally-open "push-to-

make" switch. A "push-to-break" (or normally-closed or NC) switch, on the other

hand, breaks contact when the button is pressed and makes contact when it is

released. An example of a push-to-break switch is a button used to release a

door held closed by an electromagnet. The interior lamp of a household

refrigerator is controlled by a switch that is held open when the door is closed.

Toggle switch

A toggle switch is a class of electrical switches that are manually actuated

by a mechanical lever, handle, or rocking mechanism. Toggle switches are

available in many different styles and sizes, and are used in countless

applications. Many are designed to provide the simultaneous actuation of

multiple sets of electrical contacts, or the control of large amounts of electric

current or mains voltages. The word "toggle" is a reference to a kind of

mechanism or joint consisting of two arms, which are almost in line with each

other, connected with an elbow-like pivot. However, the phrase "toggle switch" is

applied to a switch with a short handle and a positive snap-action, whether it

actually contains a toggle mechanism or not. Similarly, a switch where a

definitive click is heard, is called a "positive on-off switch". Multiple toggle

switches may be mechanically interlocked to prevent forbidden combinations.

Special types

Switches can be designed to respond to any type of mechanical stimulus:

for example, vibration (the trembler switch), tilt, air pressure, fluid level (a float

switch), the turning of a key (key switch), linear or rotary movement (a limit switch

or microswitch), or presence of a magnetic field (the reed switch). Many switches

are operated automatically by changes in some environmental condition or by

motion of machinery. A limit switch is used, for example, in machine tools to

interlock operation with the proper position of tools. In heating or cooling systems

a sail switch ensures that air flow is adequate in a duct. Pressure switches

respond to fluid pressure.

Mercury tilt switch

The mercury switch consists of a drop of mercury inside a glass bulb with

2 or more contacts. The two contacts pass through the glass, and are connected

by the mercury when the bulb is tilted to make the mercury roll on to them. This

type of switch performs much better than the ball tilt switch, as the liquid metal

connection is unaffected by dirt, debris and oxidation, it wets the contacts

ensuring a very low resistance bounce-free connection, and movement and

vibration do not produce a poor contact. These types can be used for precision

works. It can also be used where arcing is dangerous (such as in the presence of

explosive vapour) as the entire unit is sealed.

Knife switch

Knife switches consist of a flat metal blade, hinged at one end, with an

insulating handle for operation, and a fixed contact. When the switch is closed,

current flows through the hinged pivot and blade and through the fixed contact.

Such switches are usually not enclosed. The knife and contacts are typically

formed of copper, steel, or brass, depending on the application. Fixed contacts

may be backed up with a spring. Several parallel blades can be operated at the

same time by one handle. The parts may be mounted on an insulating base with

terminals for wiring, or may be directly bolted to an insulated switch board in a

large assembly. Since the electrical contacts are exposed, the switch is used

only where people cannot accidentally come in contact with the switch or where

the voltage is so low as to not present a hazard. Knife switches are made in

many sizes from miniature switches to large devices used to carry thousands of

amperes. In electrical transmission and distribution, gang-operated switches are

used in circuits up to the highest voltages. The disadvantages of the knife switch

are the slow opening speed and the proximity of the operator to exposed live

parts. Metal-enclosed safety disconnect switches are used for isolation of circuits

in industrial power distribution. Sometimes spring-loaded auxiliary blades are

fitted which momentarily carry the full current during opening, then quickly part to

rapidly extinguish the arc.

Footswitch

A footswitch is a rugged switch which is operated by foot pressure. An

example of use is in the control of a machine tool, allowing the operator to have

both hands free to manipulate the workpiece. The foot control of an electric guitar

is also a footswitch.

Reversing switch

A DPDT switch has six connections, but since polarity reversal is a very

common usage of DPDT switches, some variations of the DPDT switch are

internally wired specifically for polarity reversal. These crossover switches only

have four terminals rather than six. Two of the terminals are inputs and two are

outputs. When connected to a battery or other DC source, the 4-way switch

selects from either normal or reversed polarity. Such switches can also be used

as intermediate switches in a multiway switching system for control of lamps by

more than two switches.

Light switches

In building wiring, light switches are installed at convenient locations to

control lighting and occasionally other circuits. By use of multiple-pole switches,

multiway switching control of a lamp can be obtained from two or more places,

such as the ends of a corridor or stairwell. A wireless light switch allows remote

control of lamps for convenience; some lamps include a touch switch which

electronically controls the lamp if touched anywhere. In public buildings several

types of vandal resistant switches are used to prevent unauthorized use.

Electronic switches

A relay is an electrically operated switch. Many relays use an

electromagnet to operate a switching mechanism mechanically, but other

operating principles are also used. Solid-state relays control power circuits with

no moving parts, instead using a semiconductor device to perform switching—

often a silicon-controlled rectifier or triac. The analogue switch uses two

MOSFET transistors in a transmission gate arrangement as a switch that works

much like a relay, with some advantages and several limitations compared to an

electromechanical relay. The power transistor(s) in a switching voltage regulator,

such as a power supply unit, are used like a switch to alternately let power flow

and block power from flowing. Many people use metonymy to call a variety of

devices "switches" that conceptually connect or disconnect signals and

communication paths between electrical devices, analogous to the way

mechanical switches connect and disconnect paths for electrons to flow between

two conductors. Early telephone systems used an automatically operated

Strowger switch to connect telephone callers; telephone exchanges contain one

or more crossbar switches today. Since the advent of digital logic in the 1950s,

the term switch has spread to a variety of digital active devices such as

transistors and logic gates whose function is to change their output state

between two logic levels or connect different signal lines, and even computers,

network switches, whose function is to provide connections between different

ports in a computer network.[14] The term 'switched' is also applied to

telecommunications networks, and signifies a network that is circuit switched,

providing dedicated circuits for communication between end nodes, such as the

public switched telephone network. The common feature of all these usages is

they refer to devices that control a binary state: they are either on or off, closed

or open, connected or not connected.

Power supply

A regulated power supply is an embedded circuit; it converts

unregulated AC into a constant DC. With the help of a rectifier it converts AC

supply into DC. Its function is to supply a stable voltage (or less often current),

to a circuit or device that must be operated within certain power supply limits.

The output from the regulated power supply may be alternating or unidirectional,

but is nearly always DC (Direct Current).

The type of stabilization used may be restricted to ensuring that the output

remains within certain limits under various load conditions, or it may also include

compensation for variations in its own supply source. The latter is much more

common today.

D.C. variable bench supply (a bench power supply usually refers to a

power supply capable of supplying a variety of output voltages useful for

bench testing electronic circuits, possibly with continuous variation of the

output voltage, or just some preset voltages; a laboratory (lab) power

supply normally implies an accurate bench power supply, while a

balanced or tracking power supply refers to twin supplies for use when a

circuit requires both positive and negative supply rails).

Mobile Phone power adaptors

Regulated power supplies in appliances

Various amplifiers and oscillators

Many topologies have been used since the regulated supply was invented.

Early technologies included iron-hydrogen resistors, resonant

transformers, nonlinear resistors, loading resistors, neon stabiliser tubes,

vibrating contact regulators etc.

Modern regulated supplies mostly use a transformer, silicon diode bridge

recitifer, reservoir capacitor and voltage regulator IC. There are variations

on this theme, such as supplies with multiple voltage lines, variable

regulators, power control lines, discrete circuits and so on. Switched mode

regulator supplies also include an inductor.

At times regulated supplies can be much more complex. An example

supply from a 1980s TV used bidirectional interaction between the main

supply and the line output stage to operate, generating a range of output

voltages with varying amounts of stabilisation. Since neither stage could

start without the other running, the supply also included a kickstart system

to pulse the system into operation. The supply also monitored voltages in

the TV power circuitry, shutting down if these voltages went out of spec.

For special applications, supplies can become even more complex.

PLYWOOD

Foam board is a very strong, lightweight, and easily cut material used for

the mounting of photographic prints, as backing in picture framing, in 3D design,

and in painting. It is also in a material category referred to as "Paper-faced

Foam Board". It consists of three layers — an inner layer of polystyrene foam

clad with outer facing of either a white claycoated paper or brown kraft paper.

The surface of the regular board, like many other types of paper, is slightly

acidic. However for modern archival picture framing and art mounting purposes

it can be produced in a neutral, acid-free version with a buffered surface paper,

in a wide range of sizes and thicknesses. Foam-cored materials are also now

available with a cladding of solid (non-foamed) polystyrene and other rigid

plastic sheeting, some with a textured finish. Foamcore does not adhere well to

some glues, such as superglue, and certain types of paint. The foam tends to

melt away and dissolve. Some glue works well in casual settings, however, the

water in the glue can warp the fibers in the outer layers. Best results are

typically obtained from higher-end spray adhesives. A hot glue gun can be used

as a substitute, although the high viscosity of hot glues can affect finished

projects in the form of board warping, bubbles, or other unsightly blemishes.

Self-adhesive foam boards, intended for art and document mounting are also

available, though these can be very tricky to use properly; this is because the

glue sets very fast. It is considered cheaper to buy plain foam board and then

re-positionable spray mount adhesive. Foamcore is commonly used to produce

architectural models, prototype small objects and to produce patterns for

casting. Scenery for scale model displays, dioramas, and computer games are

often produced by hobbyists from foamcore. It's also often used by

photographers as a reflector, in the design industry to mount presentations of

new products, and in picture framing as a backing material; the latter use

includes some archival picture framing methods, which utilize the acid-free

versions of the material. Another use is with aero-modellers for building radio-

controlled aircraft.

Square tube

Hollow square tube, which have a uniform cross-section with only one

enclosed void along their whole length in the shape of rectangles (including

squares), and which have a uniform wall thickness.

Hack saw

A hacksaw is a fine-tooth hand saw with a blade held under tension in a

frame, used for cutting materials such as metal or plastics. Hand-held hacksaws

consist of a metal arch with a handle, usually a pistol grip, with pins for attaching

a narrow disposable blade. A screw or other mechanism is used to put the thin

blade under tension. The blade can be mounted with the teeth facing toward or

away from the handle, resulting in cutting action on either the push or pull stroke.

On the push stroke, the arch will flex slightly, decreasing the tension on the

blade, often resulting in an increased tendency of the blade to buckle and crack.

Cutting on the pull stroke increases the blade tension and will result in greater

control of the cut and longer blade life.

Blades are available in standardized lengths, usually 10 or 12 inches for a

standard hand hacksaw. "Junior" hacksaws are half this size. Powered hacksaws

may use large blades in a range of sizes, or small machines may use the same

hand blades.

The pitch of the teeth can be anywhere from fourteen to thirty-two teeth

per inch (tpi) for a hand blade, with as few as three tpi for a large power hacksaw

blade. The blade chosen is based on the thickness of the material being cut, with

a minimum of three teeth in the material. As hacksaw teeth are so small, they are

set in a "wave" set. As for other saws they are set from side to side to provide a

kerf or clearance when sawing, but the set of a hacksaw changes gradually from

tooth to tooth in a smooth curve, rather than alternate teeth set left and right.

Hacksaw blades are normally quite brittle, so care needs to be taken to

prevent brittle fracture of the blade. Early blades were of carbon steel, now

termed 'low alloy' blades, and were relatively soft and flexible. They avoided

breakage, but also wore out rapidly. Except where cost is a particular concern,

this type is now obsolete. 'Low alloy' blades are still the only type available for the

Junior hacksaw, which limits the usefulness of this otherwise popular saw.

For several decades now, hacksaw blades have used high speed steel for

their teeth, giving greatly improved cutting and tooth life. These blades were first

available in the 'All-hard' form which cut accurately but were extremely brittle.

This limited their practical use to benchwork on a workpiece that was firmly

clamped in a vice. A softer form of high speed steel blade was also available,

which wore well and resisted breakage, but was less stiff and so less accurate for

precise sawing. Since the 1980s, bi-metal blades have been used to give the

advantages of both forms, without risk of breakage. A strip of high speed steel

along the tooth edge is electron beam welded to a softer spine. As the price of

these has dropped to be comparable with the older blades, their use is now

almost universal.

Hacksaw blade specifications: The most common blade is the 12 inch

or 300 mm length. Hacksaw blades have two holes near the ends for mounting

them in the saw frame and the 12 inch / 300 mm dimension refers to the center

to center distance between these mounting holes.[1]

12 Inch Blade:

Hole to Hole: 11 7/8 inches / 300 mm

Overall blade length: 12 3/8 inches / 315 mm (not tightly controlled)

Mounting Hole diameter: 9/64 to 5/32 inch / 3.5 to 4 mm (not tightly controlled)

Blade Width: 7/16 to 33/64 inch / 11 to 13 mm (not tightly controlled)

Blade Thickness: 0.020 to 0.027 inches / 0.5 to 0.70 mm (varies with tooth pitch

and other factors)

The kerf produced by the blades is somewhat wider than the blade

thickness due to the set of the teeth. It commonly varies between 0.030 and

0.063 inches / 0.75 and 1.6 mm depending on the pitch and set of the teeth.

The 10 inch blade is also fairly common and all the above dimensions

apply except for the following:

Hole to Hole: 9 7/8 inches / 250 mm

Overall blade length: 10 3/8 inches / 265 mm (not tightly controlled)

A panel hacksaw eliminates the frame, so that the saw can cut into panels of

sheet metal without the length of cut being restricted by the frame.

Junior hacksaws are the small variant, while larger mechanical hacksaws are

used to cut working pieces from bulk metal.

A power hacksaw (or electric hacksaw) is a type of hacksaw that is

powered either by its own electric motor or connected to a stationary engine.

Most power hacksaws are stationary machines but some portable models do

exist. Stationary models usually have a mechanism to lift up the saw blade on the

return stroke and some have a coolant pump to prevent the saw blade from

overheating.

While stationary electric hacksaws are reasonably uncommon they are still

produced but saws powered by a stationary engines have gone out of fashion.

The reason for using one is that they provide a cleaner cut than an angle grinder

or other types of saw. Large, power hacksaws are sometimes used in place of a

bandsaw for cutting metal stock to length.

Nut

A nut is a type of fastener with a threaded hole. Nuts are almost always

used opposite a mating bolt to fasten a stack of parts together. The two partners

are kept together by a combination of their threads' friction, a slight stretch of the

bolt, and compression of the parts. In applications where vibration or rotation

may work a nut loose, various locking mechanisms may be employed:

Adhesives, safety pins or lockwire, nylon inserts, or slightly oval-shaped threads.

The most common shape is hexagonal, for similar reasons as the bolt head - 6

sides give a good granularity of angles for a tool to approach from (good in tight

spots), but more (and smaller) corners would be vulnerable to being rounded off.

Other specialized shapes exist for certain needs, such as wing nuts for finger

adjustment and captive nuts for inaccessible areas.

Nuts are graded with strength ratings compatible with their respective

bolts; for example, an ISO property class 10 nut will be able to support the bolt

proof strength load of an ISO property class 10.9 bolt without stripping. Likewise,

an SAE class 5 nut can support the proof load of an SAE class 5 bolt, and so on.

A wide variety of nuts exists, from household hardware versions to specialized

industry-specific designs that are engineered to meet various technical

standards.

Types

Acorn nut (cap nut)

Barrel nut

Cage nut

Clip-on nut (J-nut or U-nut)

Coupling nut

Cross dowel

Flange nut (collar nut)

Insert nut

Sex bolt

Slotted nut

Split nut

Sleeve nut

Square nut

Staked/welded nut (for plastic)

Swage nut

T-nut

T-slot nut (T-groove) nut

Weld nut

Well nut

Wing nut

Locknuts

Castellated nut

Distorted thread locknut

o Centerlock nut

o Elliptical offset locknut

o Toplock nut

Interfering thread nut

o Tapered thread nut

Jam nut

Jet nut (K-nut)

Keps nut (K-nut or washer nut) with a star-type lock washer

Nyloc plate nut

Polymer insert nut (Nyloc)

Serrated face nut

Serrated flange nut

Speed nut (Sheet metal nut or Tinnerman nut)

Split beam nut

Standard metric hex nuts sizes

flat (wrench) sizes differ from industry standards. For example, wrench

sizes of fastener used in Japanese built cars comply with JIS automotive

standard.

Use of two nuts to prevent self-loosening

In normal use, a nut-and-bolt joint holds together because the bolt is under

a constant tensile stress called the preload. The preload pulls the nut threads

against the bolt threads, and the nut face against the bearing surface, with a

constant force, so that the nut cannot rotate without overcoming the friction

between these surfaces. If the joint is subjected to vibration, however, the

preload increases and decreases with each cycle of movement. If the minimum

preload during the vibration cycle is not enough to hold the nut firmly in contact

with the bolt and the bearing surface, then the nut is likely to become loose.

Specialized locking nuts exist to prevent this problem, but sometimes it is

sufficient to add a second nut. For this technique to be reliable, each nut must be

tightened to the correct torque. The inner nut is tightened to about a quarter to a

half of the torque of the outer nut. It is then held in place by a wrench while the

outer nut is tightened on top using the full torque. This arrangement causes the

two nuts to push on each other, creating a tensile stress in the short section of

the bolt that lies between them. Even when the main joint is vibrated, the stress

between the two nuts remains constant, thus holding the nut threads in constant

contact with the bolt threads and preventing self-loosening. When the joint is

assembled correctly, the outer nut bears the full tension of the joint. The inner nut

functions merely to add a small additional force to the outer nut and does not

need to be as strong, so a thin nut (also called a jam nut) can be used.

Bolt

A screw, or bolt, is a type of fastener characterized by a helical ridge,

known as an external thread or just thread, wrapped around a cylinder. Some

screw threads are designed to mate with a complementary thread, known as an

internal thread, often in the form of a nut or an object that has the internal thread

formed into it. Other screw threads are designed to cut a helical groove in a

softer material as the screw is inserted. The most common uses of screws are to

hold objects together and to position objects.

A screw will always have a head, which is a specially formed section on

one end of the screw that allows it to be turned, or driven. Common tools for

driving screws include screwdrivers and wrenches. The head is usually larger

than the body of the screw, which keeps the screw from being driven deeper than

the length of the screw and to provide a bearing surface. There are exceptions;

for instance, carriage bolts have a domed head that is not designed to be driven;

set screws often have a head smaller than the outer diameter of the screw; J-

bolts have a J-shaped head which is not designed to be driven, but rather is

usually sunk into concrete allowing it to be used as an anchor bolt. The

cylindrical portion of the screw from the underside of the head to the tip is known

as the shank; it may be fully threaded or partially threaded. [1] The distance

between each thread is called the "pitch". The majority of screws are tightened

by clockwise rotation, which is termed a right-hand thread; a common mnemonic

device for remembering this when working with screws or bolts is "righty-tighty,

lefty-loosey." Screws with left-hand threads are used in exceptional cases. For

example, when the screw will be subject to counterclockwise torque (which would

work to undo a right-hand thread), a left-hand-threaded screw would be an

appropriate choice. The left side pedal of a bicycle has a left-hand thread. More

generally, screw may mean any helical device, such as a clamp, a micrometer, a

ship's propeller or an Archimedes' screw water pump.

7

REFERENCES

REFERENCES

Website:

Google.com

Philips Semiconductor