Coarse threads vs Fine threads

The threads are divided into two categories such as coarse and fine series. The thread profiles of both the thread are generally similar but there has some minor difference between them. Let us have a deep insight into the comparison between coarse and fine threads. 

Both the screw threads are designated by the letter M followed by the value of the nominal diameter in mm. Example: M 12 

Difference : 

• Course thread has higher peaks and valleys than fine thread making them harder to strip.
• Fine thread is harder to loosen by vibration to its tighter coiling and they also require less torque to achieve the same holding power as a coarse thread would.  
• The height of coarse thread is greater than the corresponding fine thread so there is more material between each thread-making flank engagement greater.
• Coarse threads are less susceptible to being nicked or damaged, so they do not have to be handled with care as much as fine threads. 
• Coarse threaded fasteners are much faster to install than fine threaded fasteners.
• Coarse threads are not affected as much as fine threads by plating buildup.
• Fine threaded bolts of the same hardness are stronger than the corresponding coarse threaded bolts.
• Due to their smaller helix angle than coarse threads, fine threads tend to loosen under vibration.
• To develop equivalent preloads to the corresponding coarse thread bolt sizes, fine threads require less tightening torque.

Comparison according to advantages : 

Advantages of coarse threads :

• Easier to cut as compared to fine threads.
• It has more even stress distribution.
• During tightening, coarse threads are less likely to seize.
• The capacity of coarse threads to carry static load is higher.
• The manufacturing error is lower in coarse threads.
• Wear has less effect than fine threads on the strength of coarse threads.

Advantages of fine threads :

• Greater strength when subjected to fluctuating loads.
• Because of the lower helix angle, greater resistance to unscrewing.
• More reliable in terms of self-unscrewing than coarse threads.

Summary : 

Coarse threads are used for general industrial applications that are vibrations free while fine threads are used in the parts that are subjected to dynamic loads and vibrations.

Difference between set screw and cap screw

What is set screw?

A type of screw that is normally used to secure an object within or against another object without using a nut is called a set screw. Example: Secure a pulley or gear to a shaft. 

What is cap screw?

A cap screw is a type of screw with a cylindrical head and hexagonal drive hole is also known as a socket head cap screw. 

Let us have a deep insight into the difference between set and cap screw. 

Difference :  

• Setscrews are subjected to compressive force only while cap screw is subjected to tensile and shear forces also.
• Setscrew transmits force from threaded components to the other mating component by means of screw point but in case of a cap screw, the force transmitted only by the head.
• Setscrews are short and threaded over the full length of the shank as compared to cap screw.

Disadvantages of threaded joints

Threaded joints are widely used in mechanical assemblies its been like 60% of the parts have made by threads. Some advantages are due to the popularity of threaded joints.

Let us have a deep insight into the disadvantages provided by a threaded joint below. 

Disadvantages of threaded joint : 

• Threaded joints require holes in machine parts for clamping because of that stress concentration near the threaded portion of the parts it causes fatigue failure too in some case.
• Threaded joints loosen when subjected to vibrations.

Advantages of threaded joints

Threaded joints are widely used in mechanical assemblies its been like 60% of the parts have made by threads. Some advantages are due to the popularity of threaded joints.

Let us have a deep insight into the advantages provided by threaded joint below. 

Advantages of threaded joints : 

• Threaded joints are reliable joints no loosening of the parts that are held together by means of large clamping force.
• The parts are assembled using a spanner and the spanner length is large compared to the thread radius, so the mechanical advantages are greater and the force required to tighten the joint is small.
• It has small overall dimensions resulting in a compact construction.
• The threads are self-locking in order to place them in any position (also vertical, horizontal or inclined).
• For the threaded components, high accuracy can be maintained.
• Manufacturing of thread is very simple.
• The thread can be easily detached when needed in threaded joints.

Advantages of friction clutch

A friction clutch transmits the power by means of friction developed between contacting surfaces. The friction surface is flat and perpendicular to the axis of rotation. Single plate and multi-plate, centrifugal clutches and cone clutches are an example of this type of clutch. Now, let us have a deep insight into the advantages provided by a friction clutch. 

Advantages of friction clutch :

• The engagement is smooth.
• Power loss and consequent heat generation do not create problems because of slip occur only during engaging operation.
• Once the clutch is engaged, there is no slip between the contacting surface.
• Friction clutch serves as a safety device.
• In friction clutch wear is low.
• Capable of transmitting partial power. 
• Minimum shock during the engagement. 
• Easy to operate. 

Difference between rigid and flexible coupling

What is Rigid coupling?

Rigid coupling some cases called sleeve or muff coupling are economical and mostly designed for the aligned shafts only. 

What us Flexible coupling?

A flexible coupling is used to transmit torque from one shaft to another which is slightly misaligned. 

Let us have a deep insight into the comparison between the rigid and flexible coupling. 

Difference between rigid and flexible coupling :

• Flexible coupling couple with rotating members such as motors and driveshafts, while allowing misalignment in either angular or parallel offset orientation while rigid coupling couple with rotating members such as shafts. 
• A rigid coupling is simple and inexpensive while the flexible coupling is comparatively costlier due to additional parts.
• A rigid coupling can not tolerate misalignment between the axis of shafts used only when there is precise alignment between two shafts while flexible elements like bush or disk can tolerate 0.5⁰ of angular misalignment and 5 mm of axial displacement between the shafts.
• The flexible elements in the flexible coupling absorb shocks and vibrations while the motion is free of shocks and vibrations in the rigid coupling.
• Rigid couplings have limited application compared to flexible couplings because rigid couplings do not have the ability to compensate for shaft misalignment and are therefore used where shafts are already positioned in accurate lateral and angular alignment.
• Rigid coupling does not allow for angular or parallel misalignment while flexible coupling does.
• Deflection is less in rigid coupling while flexible coupling has more.

Explore more information : 

• Why flexible coupling is preferred over rigid coupling?
• What is coupling?
• What are the disadvantages of muff coupling?

Hot working vs Cold working

What is hot working?

Metal deformation process that is carried out above the recrystallization temperature is called a hot working process.

What is cold working?

Metal deformation process that is carried out below the recrystallization temperature is called a cold working process.

Now one question arises in your mind that what is re-crystallization temperature?

The temperature at which the metal formed new stress-free grains is called the temperature of re-crystallisation.

Let us have a deep insight into the comparison between the hot and cold working process. 

Difference between hot and cold working : 

• Hot rolled components have higher toughness and ductility while cold rolled components have higher hardness and strength.
• The dimensions of cold-rolled parts are very accurate as compared to hot rolled.
• Hot-working requires expensive tools while tooling required for cold working is comparatively inexpensive.
• Hot-working reduces residual stresses in the component while cold working induces residual stresses in the component.
• Cold worked components have a better surface finish than hot rolled parts.
• In the hot working process risk of the crack is less while in the cold working risk of the crack is more.
• Internal and residual stresses are produced in the cold working process while not produced in hot working.
• Hot-working requires less energy for plastic deformation because at higher temperature metal become more ductile and soft while cold working requires more energy for plastic deformation.
• Heavy oxidation occurs during hot working so pickling is required to remove oxide while pickling is not required in cold working because no oxidation takes place in this process.
• Material is uniform after the hot working process while the material is not uniform after the cold working process.
• The cold working process can easily maintain better tolerance while hot working not. 
• Hot-working refines metal grains resulting in improved mechanical properties while most of the cold-working processes lead to distortion of grains. 
• Due to recrystallization, very negligible Harding of metal takes place in hot-working on the other hand, metal gets work hardened in cold-working. 
• The stress required for deformation is much less in case of hot-working due to higher deformation temperature and stress required is more in cold-working for deformation. 

Advantages and disadvantages of sand casting

Sand casting is the most popular casting process among all of the casting process. Typically relies on silica-based materials. Casting sand consists of finely ground, spherical grains that can be tightly packed together into a moulding surface. The casting designed to reduce tearing, cracking by allowing a moderate degree of flexibility and shrinkage during the cooling phase. Many automotive products, such as housings, engine blocks are manufactured by this process. Let us have a deep insight into the advantages and disadvantages of sand casting to know more about it. 

Advantages of sand casting:

• Almost all types of alloys can be cast by this process as they melt and are pourable. 
• Sand casting is the cheapest methods of manufacturing. As the cost of equipment is low because only sand and reusable patterns are involved. 
• The tooling required for the casting process is relatively simple and inexpensive.
• Any component with a complex shape can be cast easily even large components too.
• Creep-resistant metal-based alloys for gas turbines are not mechanically workable and can only be cast.
• Dimensional accuracy in the range of +-0.8 to 3.2 mm. 
• Sand casting can be used to produce virtually any size part from a piston trigger to an engine block.
• The process is highly adaptable and can be used for mass production. 
• The lead time to make the mould short, and making sand casting ideal for short production runs. Therefore, a high production rate. 
• This process creates an isotropic structure. 

Disadvantages of sand casting: 

• A lower degree of accuracy than an alternate method. 
• This process tends to yield products that have a comparatively rough surface finish.
• Low material strength due to porosity. 
• Surface finish dimensional accuracy is very poor. 
• Defects such as shrinkage, porosity, surface defect, pouring metal defects are unavoidable. 
• The secondary machining process is required if close tolerance is required. 
• Due to it is backing process, use the extra time, labour. 
• This process is now suitable for large with heavy size casting as they are hard to back.

Thus, sand casting process may be a cheaper alternative to investment casting and can provide much more complex shapes, get the same accuracy, finish, and overall part quality. 

Explore more information:

1. What is sand casting process?

Disadvantages of glass reinforced plastic

Reinforced plastic has more strength and high resistance against weather, thus finding its use in outdoor applications and other many applications so it allows many advantages. Let us have a deep insight into the disadvantages of glass-reinforced plastic.

Disadvantages of glass-reinforced plastic :

• Glass-reinforced plastic has poor rigidity and stiffness.
• Glass-reinforced plastic is limited up to a temperature of 300 ⁰C.
• Glass fibre being considered as cancer-causing, it is labelled a health concern.
• Glass fibre also irritates a person's skin as well as eyes and lungs. 

Advantages of ceramics engine components over conventional metal components

• Ability to withstand higher operating temperature.
• Excellent wear and corrosion resistance.
• Lower frictional loss.
• Ability to operate without cooling system.
• Light weight construction with low inertia force.

Advantages and disadvantages of ceramics

The advantages of modern engineering ceramics are following below :

• Most of the ceramics possess high hardness due to strong covalent bonds between atoms in their crystal structure.
• Ceramics have high melting points because of this advantages it used for the lining of the furnaces.
• Ceramics are good thermal insulators hence it possess excellent insulating property.
• Ceramics have extremely high electrical resistivity hence they are used for electrical insulators.

Note : Alumina is used for spark plug insulation.

• The densities of ceramics are low as compared to other engineering material. This results in lightweight components.
• Ceramics are chemically resistance to most of the acids, alkalis and organic substances this increases durability of the ceramics components.

Disadvantages of ceramics :

• Ceramics are brittle in nature hence brittle fracture in cast iron components.
• They are highly susceptible to stress concentration.
• In ceramics ductility is almost zero because of presence of small voids in the structure of ceramics parts.
• Ceramics have poor tensile strength.
• Ceramics are difficult to shape and machine.

We will see the advantages and disadvantages of ceramics but a number of parts of automotive engines are now a days made of ceramics include cylinder liners, pistons, valves and engine blocks. 

Therefore the principle advantages of ceramics engine components over conventional metal parts are also interesting that we have to discuss.

Ergonomic consideration in design

First of all, before we go to the point where the ergonomic used in the design of the machine. We should know first what is ergonomic?

Ergonomics :

Ergonomics is defined as the relationship between man and machine and the application of anatomical and physiological to solve the problems arising from the man-machine relationship.

The word ergonomics comes from the two Greek words :

Ergon means work and Nomos means Natural laws.

So we see above Ergonomics means the natural laws of work.

In the following design concentration ergonomics study are important :

• Design of hand levers and handwheels.
• The layout of instrument dials and displays panels for accurate perception by the operators.
• Anatomical factors in the design of a driver's seat.
• Energy expenditure in hand and foot operations.
• Lighting, noise and climatic conditions in the machine environment.
• The ergonomics applied during the design phase of this door assures the easy and correct use, without any harms to the driver.

We have seen above how ergonomics must be present at all stages of development of a project. 

In short, we must emphasize the understanding and the contribution of ergonomics to the management of the design. You have considered ergonomics as part of the whole design process.

Use of standards in machine design

The following standards are used to all mechanical engineer while design a machine components.

• Standards for materials, their chemical compositions, mechanical properties and heat treatment.
• Standards for shapes and dimensions of commonly used machine elements.
• Standards for fits, tolerance and surface finish of components.
• Standards for testing of products.
• Standards for engineering drawing of components.

Mainly there are three types of standards used in design.

• Company standards

They are used in particular company or group of company.

• National standards

National standards are :

IS ( Bureau of Indian Standards ) 

DIN ( German )

AISI or SAE ( USA )

BS ( UK )

• International standard

These are prepared by the International Standards Organization ( ISO )

What is hardness

What is hardness :

Answer 

• Hardness if defined as the resistance of the material to penetration or permanent deformation.

Hardness of the material depends upon the resistance of plastic deformation.

What is brittleness

What is brittleness :

Answer 

• Brittleness is the properties of a material which shows negligible plastic deformation before fracture takes place.

Brittleness is the opposite to ductility.

What is ductility

What is ductility?

Answer 

• Ductility is defined as the ability of a material to deform to a greater extent before the sign of a crack when it is subjected to a tensile force.

Ductility is a permanent strain that accompanies fracture in a tension test.

Ductility is characteristic of substances with metals.

You can also check it out: 

• Property of ductility. 

What is malleability

What is malleability?

Answer :

• Malleability is defined as the ability of a material to deform to a greater extent before the sign of a crack, when it is subjected to a compressive force.

Malleability comes from a word from a hammer.

What is toughness

What is toughness?

Answer :

• Toughness is defined as the ability of the material to absorb energy before fracture takes place.

Toughness is the energy for failure by fracture.

Toughness is important for machine components which are required to withstand impact loads.

Toughness is measured by a quantity called modulus of toughness.

What is resilience

What is resilience?

Answer :

• Resilience is defined as the ability of the material to absorb energy when deformed elastically and to release this energy when unloaded.

A resilient material absorbs energy within elastic range without any permanent deformation.

Resilience is measured by a quantity called modulus of resilience.

What is stiffness

What is stiffness :

Answer

• Stiffness is defined as the ability of the material to resist deformation under the action of eternal load.

All materials are deform when they are stressed, to a more or less extent.

Stiffness is also called like rigidity.