SAFETY PRECAUTIONS WITH CUTTING TOOLS-5

 Abrasives

• If the lathe is used for polishing, make sure that the machine is protected from the abrasive grains that fall from the polishing wheels during polishing. They can cause rapid wear of the precision parts.
• Do not rub fingers or hand across a piece that has just been polished by abrasive.
• Cuts and burns should always be treated immediately by using first aid facility.
• Always remove all the abrasive particles by washing them thoroughly after the polishing operation.

SAFETY PRECAUTIONS WITH CUTTING TOOLS-4

 Reamers

• One should remove all bars from the reamed holes.
• Never use your hands to remove chips and cutting fluids from the reamer and work. Use a piece of cotton to remove waste. 

SAFETY PRECAUTIONS WITH CUTTING TOOLS-3

 Saws

• Never test the sharpness of the blade by a running a finger across the teeth.
• Do not brush the chips away with your hand.
• All hard blades can shatter and produce flying chips. Wear your toggles & goggles.
• One should make sure that the blade is properly tensioned.
• Store the saw so that you will not accidentally reach into the teeth when you pick it up.
• If the blade breaks while you are on cutting stroke, your hand may strike the works and cause an injury. Therefore saw operator should work carefully. 

SAFETY PRECAUTIONS WITH CUTTING TOOLS-2

 Chisels

• Always hold the chisel in a way that the hammer blow may not miss the chisel to injure your hand.
• Edges of metal cut with the chisel are often sharp and cause bad cuts.
• Flying chips are dangerous. Wear transparent plastic safety goggles and use a shield when using a chisel to protect yourself and those working near you.
• Sharp edges of chisels are removed by grinding or filing.
• Mushroomed head of the chisel should be removed by grinding. 

SAFETY PRECAUTIONS WITH CUTTING TOOLS-1

 Files

• Always use a file card to clean the file. Never use your hand. The chips may penetrate in hand and cause a painful infection.
• Never use a file without a handle.
• Short burns formed in filling may cause serious cuts. Always use a piece of cloth to wipe the surface being field.
• Files are highly brittle and should never be used as a hammer otherwise the file will break.
• Never hammer on a file. It may shatter and chips may fly in all directions.

SAFETY PRECAUTIONS WITH HAND TOOLS-3

 Hammers

1. One should not operate the hammer unless its head is tightly fixed to the handle.
2. Place the hammer on the bench carefully. A falling hammer can cause serious foot injuries.
3. Never strike two hammers together. The faces are very hard and the blow might cause a chip to break off.
4. Never hold the hammer too far on the handle when striking a blow.
5. Unless the blow is struck squarely, the hammer may glance at the work.

SAFETY PRECAUTIONS WITH HAND TOOLS-2

 Wrenches

1. One should not hammer a wrench to loosen a stubborn fastener, unless the tool has been specially designed for such treatment.
2. Always pull on a wrench. One can have more control over the tool if pulling instead of pushing is done, and there is less chance of injury.
3. It is dangerous practice to lengthen the wrench handle for additional leverage. Use a larger wrench.
4. Choose a wrench that fit properly. A loose fitting wrench may slip and round off the corners of the bolt head and nut.
5. When using wrenches, clean grease or oil from the floor in the work area. This will reduce the possibility of slipping and losing balance. 

SAFETY PRECAUTIONS WITH HAND TOOLS-1

 Screw Drivers

1. When working on electrical equipment use only a screw driver with an approved handle.
2. One should wear goggles when re-sharpening screw-driver tips.
3. Screws with burred heads are dangerous and must be replaced or the burrs should be removed with file or an abrasive cloth.
4. One should use the correct tip of screw drivers while screwing. Too narrow or too wide tip will damage the work. 

SAFETY PRECAUTIONS IN WORKSHOP

 General Safety Precautions while Working in a Workshop: 

• One should not leave the machine ON even after the power is OFF and until it has stopped running completely.
• Operator should not talk to other industrial persons when he is operating a machine. 
• One should not oil, clean, adjust or repair any machine while it is running. Stop the machine and lock the power switch in the OFF position. 
• One should not operate any machine unless asked to do so by the authorized person in the shop.
• Always check whether work and cutting tools on any machine are clamped securely before starting. 
• The floor should be kept clean and clear of metal chips or curls and waste pieces.
• Defective guards must be replaced or repaired immediately.
• One should not operate any machine in absence of supervisor or instructor.
• All set screws should be of flush or recessed type. Projecting set screws are very dangerous because they catch on sleeves or clothing.
• One should not try to stop the machine with hands or body.
• Only trained operator should operate machine or switches as far as possible.
• Always take help for handling long or heavy pieces of materials.
• Always follow safe lifting practices.
• No one should run in the shop at work time.
• Always keep your body and clothes away from moving machine parts. Get first aid immediately for any injury.
• Stop the machine before making measurements or adjustments.
• Never wear necktie, loose sweater, wristwatch, bangles, rings, and loose fitting clothing while working in workshop.
• Always wear overcoat or apron.
• Stop machines before attempting to clean it.
• Make sure that all guards are in their place before starting to operate a machine. 
• Be thoroughly familiar with the ‘stop’ button and any emergency stop buttons provided on the machines.
• Remove burrs, chips and other unwanted materials as soon as possible.
• Do not leave loose rags on machines.
• Wash your hands thoroughly after working to remove oils, abrasive particles, cutting fluid, etc.
• Report all injuries to the foreman, howsoever small. Cuts and burns should be treated immediately.
• Keep your mind on the job, be alert, and be ready for any emergency.
• Always work in proper lighting.
• One should not lean against the machines.

CAUSES OF ACCIDENTS-4

The other general causes of accidents in workshops are listed below:

1. Ignorance in working with equipments, i.e., hand tools, cutting tools and machine tools.
2. Operating machine and equipments without knowledge.
3. Extra curiosity to work without knowing.
4. Due to poor working conditions.
5. Due to speedy work.
6. Improper method of work.
7. Due to use of improper tools.
8. Due to lack of discipline.
9. Due to carelessness.
10. Due to over confidence.
11. Because of excessive over times duty by industrial workers.
12. Lack of cleanliness.
13. Due to poor planning. 

CAUSES OF ACCIDENTS-3

Mechanical Causes 

• Continued use of old, poorly maintained or unsafe equipment may result in accidents.
• Accidents commonly occur due to use of unguarded or improperly guarded machines or equipments.
• Unsafe processes, unsafe design and unsafe construction of building structure may lead to accidents in the plant.
• Accidents occur due to improper material handling system and improper plant layout. 
• Accidents may occur due to non use of safety devices such as helmets, goggles, gloves, masks etc.

CAUSES OF ACCIDENTS-2

Environmental Causes 

• Accidents may occur during working at improper temperature and humidity, as it causes fatigue to the workers.
• The presence of dust fumes and smoke in the working area may cause accidents. 
• Poor housekeeping, congestion, blocked exits, bad plant layout etc. may cause accidents. 
• Accidents occur due to inadequate illumination. 
• Improper ventilation in the plant may lead to industrial accidents.

CAUSES OF ACCIDENTS-1

The accidents may take place due to human causes, environmental causes and mechanical causes. These causes are discussed as under.

Human Causes 

• Accidents may occur while working on unsafe or dangerous equipments or machineries possessing rotating, reciprocating and moving parts. 
• Accidents occur while operating machines without knowledge, without safety precautions, without authority, without safety devices. 
• Accidents generally occur while operating or working at unsafe speed. 
• Accidents may occur while working for long duration of work, shift duty etc. 
• Accidents commonly occur during use of improper tools. 
• Accidents may occur while working with mental worries, ignorance, carelessness, nervousness, dreaming etc. 
• Accidents occur because of not using personal protective devices.

EFFECT OF ACCIDENTS

The adverse effects of the accident are given as under— 
(A) Effect on the owner of factory 

• Direct cost of an accident 
• Compensation paid to the workers. 
• Money paid for treatment. 
• Monetary value of damaged tools, equipments and materials. 
• Indirect cost of an accident 
• Lost time of the injured worker. 
• Time lost by other employees. 
• Delays in production. 
• Time lost by supervisors, safety engineers etc. 
• Lowered production due to substitute workers. 

(B) Effect on worker 

• The industrial workers may get temporary or permanent disability. 
• If the industrial worker dies, his family loses the earner and the compensation never equals to his earnings. 
• Accident also affects the morale of the employees working in the manufacturing environment. 

(C) Effect on society 
Work connected with injuries put a considerable burden on society. It is given as under:

• Cost of accidents is included in the products, so the society has to pay more prices for the industrial products. 
• If some industrial workers do not come under compensation act, the need for help from society is much greater. 
• Loss of production hours may causes fewer products in market. So more prices if demand is more than production.

ACCIDENTS

The accidents are the mishaps leading injury to man, machines or tools and equipment and may cause injury and result either death or temporary disablement or permanent disablement of the industrial employees.

There are various types of common accidents  as follows: 

• Near Accident: An accident with no damage or injury is called near accident. 
• Trivial: An accident with very less damage is called trivial. 
• Minor Accident: It is an accident with damage and injury more than trivial. 
• Serious Accident: An accident with heavy damage and lot of injury is called serious accident. 
• Fatal: It is an accident with very heavy damage. There may be loss of lives also.

INVERSIONS OF DOUBLE SLIDER

Elliptical trammel
It is a device used to trace ellipses. Here frame is fixed and the sliders translates inside it making every points on the connecting rod to trace an ellipse.






Oldham Coupling
It is a device used to connect two parallel offset beams. Here sliders are perpendicular to each other connected by a disc. Their translation results in the rotation of frame.

Watch mechanism of Elliptical Trammel

Watch mechanism of Oldham Coupling

INVERSIONS OF SINGLE SLIDER

First inversion
frame is fixed and slider reciprocates.
Example:
Reciprocating engine



Second inversion
Crank is fixed hence cylinder acts as crank (i.e.,it rotates).
Example:
- Witworth quick return motion mechanism
- Rotary engine


Third inversion
Connecting rod is fixed hence cylinder acts as connecting rod (i.e., it oscillates).
Example:
- Oscillating cylinder engine
- Crank and slotted lever mechanism



Fourth inversion
Slider is fixed
Example:
Handpump

Watch mechanism of Reciprocating Engine

Watch mechanism of Rotary Engine (Gnome)

Watch mechanism of Osillating Engine

Watch mechanism of Hand Pump

SLIDER CRANK CHAIN

When one of the turning pair of a four bar chain is replaced by a sliding pair then it is called as single slider crank chain.

It is also possible two replace two sliding pairs of a four bar chain to get double slider crank chain.

Different mechanisms obtained by fixing different links of a kinematic chain are termed as inversions.

KINEMATIC CHAIN

A kinematic chain is a assembly of links in which relative motion of links is possible and the motion of each relative to other is definite.

Degree of freedom of a plane mechanism can be calculated using GRUEBLER'S CRITERION, i.e., F=3(N-1)-2P-Q where each movable link possess 3 degree of freedom.

For linkages with single degree of freedom KUTZBACK'S CRITERION is followed, i.e., 2P=3N-4 

In the above equations-
N = total number of links in a mechanism
:. N-1 = number of movable links
F = degree of freedom
P = number of pairs having one degree of freedom
Q = number of pairs having two degree of freedom

DEGREE OF FREEDOM

An unconstrained rigid body in space can describe the following independent motions:

1. Translational motion along any three mutually perpendicular axes (x, y, or z)
2. Rotational motion about these axes

• A rigid body possess 6 degree of freedom
• for a body, number of restraints can never be-
• six (joint becomes solid)
• zero (joint is disconnected)

Degree of freedom of a pair is defined as the number of independent relative motion, both translational and rotational.

Degree of freedom of a pair = 6 - number of restraints

KINEMATIC PAIR- RELATIVE MOTION

On the basis of nature of relative motion kinematic pairs can be classified as:
* Sliding Pair
* Turning Pair
* Rolling Pair
* Helical Pair
* Spherical Pair

Sliding Pair
If two links have sliding motion relative to each other.
Example:
A rectangular rod in a rectangular hole

Turning Pair
When one link has a revolving motion relative to other.
Example:
Circular shaft revolving inside a bearing

Rolling Pair
If links of pair have rolling motion relative to each other.
Example:
Ball and roller bearings

Helical Pair (Screw Pair)
When the links of a pair have turning as well as sliding motion.
Example:
nut-bolt

Spherical Pair
If one of the two links is spherical and it turns inside the other.
Example:
Ball and socket joint

KINEMATIC PAIR- MECHANICAL CONSTRAINT

According to nature of mechanical constraint kinematic pairs can be classified as:
* Closed pair
* Unclosed pair

Closed Pair
- When the elements of the pair are held together mechanically
- Elements are geometrically identical
- Contact can be broken only by destruction of atleast one member
Example:
Screw pair



Unclosed Pair
- When elements are connected either by force of gravity or by spring action
- Links are not held together mechanically
Example:
Cam and follower pair

KINEMATIC PAIR- NATURE OF CONTACT

According to nature of contact kinematic pairs can be classified as:

* Higher Pair
* Lower Pair

HIGHER PAIR

When the pairs has point or line contact. Or the contact surface is dissimilar.

Example:

- Ball and roller bearings

- Cam and follower pair, etc...

 

LOWER PAIR

When the pairs has surface or area contact. Or the contact surface is similar.

Example:

- Nut turning on a screw

- Universal joint, etc...

KINEMATIC PAIR

When two links combine to form a pair such that the motion between them is completely or successfully constrained, then they are termed as kinematic pair.

They can be classified according to:

- Nature of contact
- Nature of mechanical constraint
- Nature of relative motion

CONSTRAINT MOTION

There are 3 types of constraint motion:


Completely constraint motion:-

when the motion between 2 elements of a pair is in definite direction irrespective of the direction of the force applied.

Example:

sliding pair

turning pair

Incompletely constraint motion:-

when the motion between 2 elements of a pair is possible in more than one direction depending on the fore applied.

Example:

a circular shaft without collar

Successfully constraint motion:-

when motion between 2 elements of a pair is possible in more than one direction but is constrained to remain in one direction by application of external forces.

Example:

Foot step bearing

MOTION

Motion is a change in position of an object with respect to time. 

Motion is typically described in terms of displacement, distance (scalar), velocity, acceleration, time and speed.

Machines

When mechanisms combine to produce work they are termed as machines.

Example:
- Engine is a machine and reciprocation of piston inside cylinder due to rotation of crank is a mechanism

- Lathe machine
- Shaper machine
- Slotter machine
- Drilling machine
- Sewing machine
- Washing machine which works on electrical mechanism
- Grinder, etc....

Mechanism

if a number of bodies are connected in such a way that the motion of one constrains the motion of other, or gives a predictable motion then it is called as mechanism.

Examples:

motion of hands of clock

internal combustion engine

rope drives

chain drives

gears, etc...

watch mechanism of a watch