ME6601 DESIGN OF TRANSMISSION SYSTEMS TWO MARK QUESTION & ANSWERS

R.M.K COLLEGE OF ENGINEERING
AND TECHNOLOGY
RSM NAGAR, PUDUVOYAL-601206
DEPARTMENT OF MECHANICAL ENGINEERING
ME6601 – DESIGN OF TRANSMISSION SYSTEM
VI SEM MECHANICAL ENGINEERING
Regulation 2013
TWO MARKS QUESTION AND ANSWERS
PREPARED BY
R.ASHOK KUMAR M.E, (Ph.D.)
S.ARUNKUMAR M.E, (Ph.D.)

R.M.K COLLEGE OF ENGG AND TECH / AQ / R2013/ ME6601 / VI / MECH / DEC 2017 – MAY 2018
ME6601 – DESIGN OF TRANSMISSION SYSTEM TWO MARKS QUESTION AND ANSWERS by
ASHOK KUMAR.R & ARUNKUMAR.S 2
ME6601 – DESIGN OF TRANSMISSION SYSTEMS
UNIT – I DESIGN OF FLEXIBLE ELEMENTS 9
Design of Flat belts and pulleys - Selection of V belts and pulleys – Selection of hoisting wire
ropes and pulleys – Design of Transmission chains and Sprockets.
UNIT – II SPUR GEARS AND PARALLEL AXIS HELICAL GEARS 9
Speed ratios and number of teeth-Force analysis -Tooth stresses - Dynamic effects – Fatigue
strength - Factor of safety - Gear materials – Design of straight tooth spur & helical gears based
on strength and wear considerations – Pressure angle in the normal and transverse plane-
Equivalent number of teeth-forces for helical gears.
UNIT – III BEVEL, WORM AND CROSS HELICAL GEARS 9
Straight bevel gear: Tooth terminology, tooth forces and stresses, equivalent number of teeth.
Estimating the dimensions of pair of straight bevel gears. Worm Gear: Merits and demerits-
terminology. Thermal capacity, materials-forces and stresses, efficiency, estimating the size of
the worm gear pair. Cross helical: Terminology-helix angles-Estimating the size of the pair of
cross helical gears.
UNIT – IV GEAR BOXES 9
Geometric progression - Standard step ratio - Ray diagram, kinematics layout -Design of sliding
mesh gear box - Design of multi speed gear box for machine tool applications - Constant mesh
gear box - Speed reducer unit. – Variable speed gear box, Fluid Couplings, Torque Converters
for automotive applications.
UNIT – V CAMS, CLUTCHES AND BRAKES 9
Cam Design: Types-pressure angle and under cutting base circle determination-forces and
surface stresses. Design of plate clutches –axial clutches-cone clutches-internal expanding rim
clutches- Electromagnetic clutches. Band and Block brakes - external shoe brakes – Internal
expanding shoe brake. TOTAL: 45 PERIODS
TEXT BOOKS:
 Bhandari V, “Design of Machine Elements”, 3rd Edition, Tata McGraw-Hill Book Co, 2010.
 Joseph Shigley, Charles Mischke, Richard Budynas and Keith Nisbett “Mechanical
Engineering Design”, 8th Edition, Tata McGraw-Hill, 2008.
REFERENCES:
 Sundararajamoorthy T. V, Shanmugam .N, “Machine Design”, Anuradha Publications,
Chennai, 2003.
 Prabhu. T.J., “Design of Transmission Elements”, Mani Offset, Chennai, 2000.

PROGRAM OUTCOMES (POs)
 PO1: Engineering Knowledge: Apply the knowledge of mathematics, science,
engineering fundamentals, and an engineering specialization to the solution of complex
engineering problems.
 PO2: Problem Analysis: Identify, formulate, review research literature, and analyze
complex engineering problems reaching substantiated conclusions using first principles of
mathematics, natural sciences, and engineering sciences.
 PO3: Design/Development of Solutions: Design solutions for complex engineering
problems and design system components or processes that meet the specified needs with
appropriate consideration for the public health and safety, and the cultural, societal, and
environmental considerations.
 PO4: Conduct Investigations of Complex Problems: Use research-based knowledge
and research methods including design of experiments, analysis and interpretation of data,
and synthesis of the information to provide valid conclusions.
 PO5: Modern Tool Usage: Create, select, and apply appropriate techniques, resources, and
modern engineering and IT tools including prediction and modeling to complex engineering
activities with an understanding of the limitations.
 PO6: The Engineer and Society: Apply reasoning informed by the contextual knowledge
to assess societal, health, safety, legal and cultural issues and the consequent responsibilities
relevant to the professional engineering practice.
 PO7: Environment and Sustainability: Understand the impact of the professional
engineering solutions in societal and environmental contexts, and demonstrate the knowledge
of, and need for sustainable development.
 PO8: Ethics: Apply ethical principles and commit to professional ethics and responsibilities
and norms of the engineering practice.

 PO9: Individual and Team Work: Function effectively as an individual, and as a member
or leader in diverse teams, and in multidisciplinary settings.
 PO10: Communication: Communicate effectively on complex engineering activities with
the engineering community and with society at large, such as, being able to comprehend and
write effective reports and design documentation, make effective presentations, and give and
receive clear instructions.
 PO11: Project Management and Finance: Demonstrate knowledge and understanding of
the engineering and management principles and apply these to one's own work, as a member
and leader in a team, to manage projects and in multidisciplinary environments.
 PO12: Life-long learning: Recognize the need for, and have the preparation and ability to
engage in independent and life-long learning in the broadest context of technological change.
Program
Outcomes
PO
1
PO
2
PO
3
PO
4
PO
5
PO
6
PO
7
PO
8
PO
9
PO
10
PO
11
PO
12
Level of PO K3 K4 K4 K5
K3,
K5,
K6
A3 A2 A3 A3 A3 A3 A2
Program Specific Outcome (PSO)
 PSO1: Develop the process for extraction of oil from seeds, plastics and analyse their
properties based on the concepts of thermal science.
 PSO2: Design and implement product life cycle management for digital manufacturing
process.
 PSO3: Utilize composite materials to develop quality consumer goods at affordable price
Program Specific
Outcomes
PSO1 PSO2 PSO-3
Level of PSO K4 K4 K4

COURSE OUTCOMES:
After successful completion of the course, the students should be able to
MAPPING OF COURSE OUTCOMES WITH PROGRAM OUTCOMES:
Course
Out
Comes
Level
of CO
Program Outcomes
Program Specific
Outcomes
K3 K4 K4 K5
K3,K5
,K6
A3 A2 A3 A3 A3 A3 A2 K4 K4 K4
PO-
1
PO-
2
PO-
3
PO-
4
PO-5
PO-
6
PO-
7
PO-
8
PO-
9
PO-
10
PO-
11
PO-
12
PSO-
1
PSO-
2
PSO-
3
C311.1 K3 3 2 2 2
C311.2 K3 3 2 2 2
C311.3 K3 3 2 2 2
C311.4 K3 3 2 2 2
C311.5 K3 3 2 2 2
C311.6
K3
&
A2
3 2 2 2 2 2 3 2
C311 3 2 2 2 2 2 3 2
CO No. Course Outcomes Highest Level
C311.1
Compute the design parameters of flexible transmission elements like
belts, chains and wire ropes for given condition
K3
C311.2
Compute the spur and helical gear terminology considering strength
and wear
K3
C311.3
Compute the required parameters in designing worm, bevel and double
helical gear power transmission
K3
C311.4
Calculate the speed ratio and gear box parameters for the given
application
K3
C311.5
Compute the parameters require to design cam, clutches and brakes for
varied applications
K3
C311.6
Calculate the parameters to design power transmission elements using
standard catalogue
K3 & A2

UNIT – I – DESIGN OF FLEXIBLE ELEMENTS
PART - A
1.1) What is a power drive? Mention their types.
The power drive us a set of machine members employed to transmit power
or energy produced in one machine to another machine. The main type of power
drive are
 Mechanical drive
 Hydraulic drive
 Pneumatic drive
 Electrical drive
1.2) What is meant by mechanical drives?
The drives which transmits power by means of contact forces are called as
mechanical drives
1.3) Define Co-efficient of friction. [AU, Apr / May – 2018]
Coefficient of Friction (μ) is the ratio of the limiting force of friction (F)
and the normal Reaction (RN) between two surfaces.
𝜇 =
𝐹
𝑅 𝑁
1.4) What do you mean by angle of friction?
Angle of friction, ‘ϕ’ is the angle made by the resultant (R) of the normal
reaction (~) and the limiting force of friction (F) with the normal reaction (RN).
𝑡𝑎𝑛𝜙 = 𝜇 =
𝐹
𝑅 𝑁
1.5) State the law of belting.
Law of belting states that the centre line of the belt, as if approaches the
pulley lie in a plane perpendicular to the axis of that pulley or must lie in the plane
of the pulley otherwise the belt will run off the pulley.
1.6) Why are belt drives called as flexible drives?
A belt is a loop of flexible material used to link two or more rotating shafts
mechanically, most often parallel. Belts may be used as a source of motion, to
transmit power efficiently or to track relative movement.
1.7) What are the types of belts?

 Flat belt
 V – belt
 Circular belt or Rope
 Multi groove belt
 Timing belt
 Ribbed belt
1.8) Name different types of belts. [AU, Nov / Dec – 2017]
 Flat belt
 V – belt
 Timing belt
 Ribbed belt
1.9) Name the four types of belts used for transmission of power.
[AU, Nov / Dec – 2018]
 Flat belt
 V – belt
 Timing belt
 Ribbed belt
1.10) What is meant by the ply of belt? [AU, Nov / Dec –2013]
The layer of belts is called as ply. The total number of belt layers used in
a belt is called number of plies. A number of layers of belt material is cemented
together to achieve the desired thickness of belt.
1.11) What is meant by ply in a flat belt? [AU, Apr / May – 2016]
The layer of belts is called as ply. The total number of belt layers used in
a belt is called number of plies. A number of layers of belt material is cemented
together to achieve the desired thickness of belt.
1.12) Mention the different types of joints employed for joining flat - belts.
 Cemented Joint
 Laced Joint

 Crest Joint
 Hinged Joint
1.13) How the ends of flat are – belt joined? [AU, Apr / May – 2010]
 Cemented Joint
 Laced Joint
 Crest Joint
 Hinged Joint
Cemented joint: The cemented joint uses any cementing adhesive to form an endless belt.
Hinged joint: Metal hinges may be fastened to the belt ends and connected by a steel or fibre
pin.
Laced joint: In the laced joint, holes are punched across the belt, leaving a margin between
the edge and the holes.
 A raw hide strip is used for lacing the two ends together to form a joint, this
form joint known as straight-stitch raw hide laced joint
 Metal laced joint is made like a staple connection.
1.14) Mention the materials used for making belts. [AU, Nov / Dec – 2011]
 Cotton or Fabric and Canvas
 Leather
 Rubber
 Balata
 Nylon core
1.15) Name the few materials for belt drives. [AU, Apr / May – 2016]
 Leather

 Rubber
 Balata
 Nylon core
1.16) What are the materials used for belt – drive? [AU, May / Jun – 2013]
 Leather
 Rubber
 Balata
 Nylon core
1.17) Why should the tight - side of the belt be at the bottom side of the pulley?
[AU, Apr / May – 2005]
If the tight side of the belt is at the bottom side of the pulley, and the slack
side is at the top side, then the sag caused by the self-weight of belt, for long centre
distance drive will increases the arc od contact of belt with the pulley and hence the
effect of power transmission is increased. +
1.18) Differentiate open - belt drive and cross - belt drive.
Open Belt Drive Cross Belt Drive
 Driving Shaft and drive shaft
rotate in same direction
 Power transmission is low
compare to cross belt drive
 Wear and tear is low
 The angle of contact is less
 Power transmission is high
compare to open belt drive
 Wear and tear is high
 The angle of contact is high
1.19) Distinguish between open drive and cross drive of a belt drive. Which is
better? [AU, Apr / May – 2011]
Open Belt Drive Cross Belt Drive
 Power transmission is low
 Power transmission is high

 Wear and tear is low
 The angle of contact is less
 Wear and tear is high
 The angle of contact is high
Except wear and tear crossed belt drive is better.
1.20) What is belt rating?
Flat belts are made of different sizes such as 3 ply, 4 ply and V belts are
made up of different grades such as A, B, C, D and E grade belts. Belt rating is
defined as the power transmitting capacity of unit size of flat belt or a particular
grade of V belt.
1.21) Why are thin wide flat belts preferred over thick narrow belts?
The thin wide belt possess more surface contact are with pulley that thick
narrow belt, thin belt can transmit more power than thick belt for a constant weight.
Hence thin wide belts are preferred.
1.22) A longer belt will last more than a shorter belt, why?[AU, Apr / May – 2017]
Longer belts reduces the bending radius of belt to a greater extent. This
reduces the fatigue and creep stress. Hence the belt life increases and will last more
than a shorter belt.
1.23) Briefly explain initial tension in belts.
The motion of belt and pulleys are governed by a firm grip between the
belt and pulley. In order to increase the grip for power transmission, the belt is
tightened up. Due to tightening the belt is subjected to tension is called as initial
tension
1.24) Give the expression for tension ratio in a belt drive.[AU, May / Jun – 2007]
𝑇1
𝑇2
= 𝑒 𝜇𝜃
T1 – Tension in tight side of the belt (N)
T2 – Tension in slack side of the belt (N)
 – Angle of belt (radians)
 – Coefficient of friction

1.25) Give an expression for ratio of tensions in a flat belt drive.
[AU, Nov / Dec –2012]
𝑇1
𝑇2
= 𝑒 𝜇𝜃
1.26) What is the condition to transmit maximum power in a flat belt drive?
[AU, Nov / Dec – 2016, 2018]
The condition to transmit maximum power in flat belt drive is
𝐵𝑒𝑙𝑡 𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦 = 𝑣 = √
𝑇 𝑚𝑎𝑥
3𝑚
𝑇 𝑚𝑎𝑥 = 3𝑇𝐶
Tmax – Maximum permissible tension (N)
TC – Centrifugal tension of the belt (N)
m – Mass of belt per unit length (kg/m)
1.27) Why tight – side of the belt should be at the bottom side of the pulley?
[AU, Nov / Dec –2004, May / Jun – 2006]
If the tight side is at bottom so the slack side will increase the arc of
contact at the pulley at top. The increase in arc of contact will increase in power
transmitting capacity.
1.28) What will be the effect on the limiting ratio of tensions of a belt if the co-
efficient of friction between the belt and rim of pulley is doubled while angle of
lap remains the same? [AU, Nov / Dec –2007]
The tension ratio
𝑇1
𝑇2
= 𝑒 𝜇𝜃

If coefficient of friction () is doubled. Then tension ratio will be
𝑇1
𝑇2
= 𝑒2𝜇𝜃
= [𝑒 𝜇𝜃
]
2
The new ratio of tensions will be square of the original ratio.
1.29) What are the various losses in the power transmission by belts?
[AU, Nov / Dec –2005, 2008]
 Speed losses due to the slip and creep that occur in belt when
running over pulleys.
 Friction losses in the interface of belt and pulley
 Windage losses as the belt moves through the air
 Power loss in the form of heat generated due to the combined losses
1.30) Mention the losses in belt drives. [AU, Nov / Dec –2014]
 Speed losses due to the slip and creep that occur in belt when
running over pulleys.
 Friction losses in the interface of belt and pulley
 Windage losses as the belt moves through the air
 Power loss in the form of heat generated due to the combined losses
1.31) Why is the face of a pulley crowned? [AU, Nov / Dec –2009]
The crowning tends to keep the belt in centre on a pulley rim while in
motion. The height of the crown depends upon the width, speed and length of belt.
1.32) Define the term "crowning of pulley". [AU, Nov / Dec – 2016]
Crowning in pulley is the process of providing slight downward taper from
the centre towards the ends in the pulley top surface. This increases the frictional
resistance and prevents the slip of the belt from the pulley. The crowning tends to
keep the belt in centre on a pulley rim while in motion. The height of the crown
depends upon the width, speed and length of belt.

1.33) Explain the term crowning of pulley.
[AU, Apr / May – 2005, May / Jun – 2011]
1.34) Brief the term "Crowning of Pulley [AU, May / Jun – 2014]

1.35) What is crowning of pulley? Specify the purpose of crowning of pulley.
[AU, May / Jun – 2006]
1.36) What is the effect of centre distance and diameter of pulley on the life of a
belt? [AU, Nov / Dec –2005]
The increased centre distance and higher pulley diameters reduce the
bending radii of belts to a greater extent. This results in reduced fatigue and creep.
Hence, the belt life increases.
1.37) Define creep in belt. What is its effect on the speed?
The slow movement of the belt; moving back slightly relative to the
driving pulley and forward slightly relative to the driven pulley due to unequal
stretching of the belt in the tight side and slack side of the belt drive in operation is
known as creep.

The effect of creep back on the driving pulley is to slow down the speed of
the belt with respect to driving pulley. The effect of creep forward on the driven
pulley is to slow down the speed of driven pulley as a result, the speed ratio is
reduced
1.38) State the reasons for V – belt drive being preferred to flat belt drive?
[AU, Nov / Dec –2010]
 Replacement of V – belt is easy, because V belts are available
according to standards.
 Power transmitted by the V – belts is more.
 For smaller centre distances V – belts are more suitable
 Efficiency is high compared to flat belt.
1.39) Write the disadvantages of flat belt drive. [AU, Nov / Dec –2015]
 It is a non-positive drive and hence, slip and creep occur.
 Requires more space.
 Angular velocity ratio is not necessarily constant or equal to the ratio of
pulley diameters, because of slipping and stretching.
 Heat build-up occurs.
 Speed is limited.
 Power transmission is limited.
1.40) What is a slack adjuster? [AU, Nov / Dec –2004]
Slack adjuster is a movable device used for adjusting the slack/ tension in a
belt drive. By this, the tension is adjusted so that the required initial tension T0 is
maintained in the belt drive.
This is usually done in two ways:
 By adjusting the centre distance between the pulleys
 By introducing an idler pulley that presses against the belt to adjust the
tension
1.41) Write the different types of pulleys used in belt drives.
 Solid Pulley
 Split pulley
 Stepped or cone pulley

1.42) When is a split pulley used? How is it tightened on a shaft?
Split pulley are used in flat belt, line shaft applications. The split pulley is
tightened to shaft with bolt and nut.
1.43) When do you use stepped pulley drive?
[AU, Apr / May – 2016, Nov / Dec – 2018]
Stepped pulley drive is used when the speed of the driven shaft is to be
changed very frequently as in case of machine tools such as lathe, drilling machine
etc. A stepped pulley is an integral casting having three or more number of pulleys
of different diameter
1.44) What are the factors upon which the coefficient of friction between the belt
and pulley depends? [AU, May / Jun – 2014]
 Material of the belt
 Material of the pulley
 Speed of the belt
 Nature of contact surfaces between the belt and the pulleys.
1.45) Sketch the cross - section of a V- belt and label its important parts.
[AU, Nov / Dec –2009]

1.46) How is a V - belt specified? [AU, May / Jun – 2012, Nov / Dec –2012]
V-belts are designated by their cross section symbol (A, B, C, D or E)
followed by its nominal inside length in mm.
Example: C 3048/120- The belt cross section is 'C, and nominal inside length is
3048 mm (120 inches).
1.47) What are the advantages of V belt drive? [AU, Nov / Dec –2012]
 High power transmission capacity because V-grooves provide excellent
grip.
 The functioning of the belt and the pulley is smooth and quiet.
 The V-belt drive provides compactness due to the small distance
between the centers of the pulleys.
 Slip between the belt and the pulley is negligible.
 The axis can be horizontal, vertical or inclined.
 They can dampen vibration.
1.48) What are the advantages and disadvantages of V - belt drive over flat belt
drive? [AU, May / Jun – 2011]
Advantages:
 Negligible slip due to wedging action between the belt and V-groove
pulley
 Require little pretension
 Compact design and smooth operation
 High velocity ratio.
 Can transmit more power for the same coefficient of friction.
 V-belt can run even the belt is vertical.
Disadvantages:
 The V-belt drive cannot be used for long distances due to greater
weight per unit of length.
 They are not applicable to the synchronous machines because they are
not free from creep.
 The centrifugal tension prevents the use of belts at speeds below 5 m/s
and above 50 m/s.

 The construction of pulleys for V-belts is more complicated than flat
belt.
1.49) Write the advantages of V - belt over flat belt. [AU, Nov / Dec – 2017]
 Negligible slip due to wedging action between the belt and V-groove
pulley
 Require little pretension
 Compact design and smooth operation
 High velocity ratio.
 Can transmit more power for the same coefficient of friction.
 V-belt can run even the belt is vertical.
1.50) Mention the disadvantages of V belts over flat belts. [AU, May / Jun – 2012]
 The V-belt drive cannot be used for long distances due to greater
weight per unit of length.
 They are not applicable to the synchronous machines because they are
not free from creep.
 The centrifugal tension prevents the use of belts at speeds below 5 m/s
and above 50 m/s.
 The construction of pulleys for V-belts is more complicated than flat
belt.
1.51) In what ways are the timing belts superior to ordinary V belts?
[AU, May / Jun – 2006, 2007, Apr / May – 2015]
 The timing belt has cogs and hence, there will not be any slip.
 In the absence of slip, timing belt maintains exact speed ratio.
 Less maintenance.
 No initial tension required.
1.52) Give the relationship of ratio of tensions in a V-belt drive.
[AU, Apr / May – 2008]
𝑇1
𝑇2
= 𝑒
(
𝜇𝜃
𝑠𝑖𝑛𝛽
)
Where T1 & T2 – Tensions on the tight side and slack side
μ - Coefficient of friction
θ - Angle of contact (lap)

β - Groove angle
1.53) Why slip is less in the case of V – belts when compared with flat belts?
[AU, May / Jun – 2013]
 The wedging action between the V-belt and V-pulleys permits small arc
of contact.
 This wedging action reduces belt slip when compared to flat belt.
 As a result, the power transmission capacity is increased
1.54) Define maximum tension in a belt. [AU, Apr / May – 2008]
The maximum tension in the belt is the tension on the tight side. That is,
TMax = T1
If centrifugal tension, Tc is not significant and hence not considered
TMax = T1 + Tc
If centrifugal tension is considered
1.55) What is centrifugal effect on belts? [AU, Nov / Dec –2015]
When the belt with a significant mass runs at reasonably higher speed (>10
m/s) over a pulley, it experiences a centrifugal force acting radially outwards. This
tension caused in the running belt by the centrifugal force is known as the
centrifugal tension.
Tc = m * v2
; where,
m - mass of the belt per metre length,
m = (Density of Belt Material * Belt Width * Belt Thickness)
v - linear velocity of the belt, m/s.
Centrifugal tension increases both the tensions at the tight side and slack
side. However, the centrifugal tension has no impact on the power transmission
1.56) Give the condition for maximum power transmission in terms of
centrifugal tension in case of belt drive. [AU, May / Jun – 2009, 2011]
The condition to transmit maximum power in a flat belt drive is:
Belt Velocity,𝑣 = √
𝑇 𝑚𝑎𝑥
3𝑚
m - mass of belt per unit length, kg/m.
Maximum Permissible Tension, Tmax = 3Tc
Tension on Tight Side, T1 = 2Tc

1.57) What are the five parts of roller chain? [AU, Apr / May – 2010]
The important elements in a roller chain are:
 Pin
 Bushing
 Roller
 Inner link plate
 Outer link plate.
1.58) Specify the five parts of roller chain. [AU, Nov / Dec –2011]
The important elements in a roller chain are:
 Pin
 Bushing
 Roller
 Inner link plate
 Outer link plate.
1.59) What do you mean by galling of roller chains? [AU, Nov / Dec –2010]
 Galling is a stick-slip phenomenon between the pin and bushing.
 When the chain tension is high due to heavy loads and high chain speeds,
micro welds are formed at the high spots of the contact area.
 Such microscopic welds are immediately broken due to the relative
motion between the contact surfaces.
 This results in excessive wear even in the presence of lubrication.
 This abnormal wear is known as Galling.
1.60) Mention the materials used for making link plates in chain drives.
[AU, May / Jun – 2012]
The materials used for link plates are
 Alloy steels C45, C50 and 40Crl.
 Medium carbon steel
1.61) What is chordal action in chain drives? [AU, Nov / Dec –2015]
When chain passes over a sprocket, it moves as a series of chords instead
of a continuous arc as in the case of a belt drive. This results in varying speed of
the chain drive. This phenomenon is known as Polygonal Effect (or) Chordal

Action. In order to reduce the chordal effect, the number of teeth on the sprocket
should be increased.
1.62) What is meant by chordal action in chain drives?
[AU, Apr / May – 2004, 2010]
1.63) What is meant by chordal action of chain? Also name a company that
produces driving chains. [AU, Apr / May – 2015, May / Jun – 2006]
Companies that manufacture driving chains:
 Renold India, Gudalur, Tamilnadu.
 TIDC India Ltd., Ambattur, Tamilnadu.
 Galaxy Chains Pvt. Ltd., Rajkot, Gujarat.
1.64) What is done to accommodate initial sag in chain drive?
[AU, May / Jun – 2007]
In order to accommodate initial sag in the chain, the value of the centre
distance, 'a' should be decreased by [0.01 * a] (or) 2 to 5 mm.
1.65) What factors will affect the working conditions of the chain drive?
[AU, Nov / Dec – 2016]
The factors affecting the working conditions of the chain drive are:
 Type of loading: constant (or) variable.
 Centre distance between the shafts
 Position of driving shaft: horizontal (or) inclined.
 Nature of lubrication: continuous, drop (or) periodic.
 Service: continuous (or) fixed no. of hours per day.

 Operating environment: corrosive (or) dirty.
1.66) List the chain drive failures. [AU, Nov / Dec – 2017]
 Overload- chain subjected to excessive one-off load which causes
permanent deformation of material and leads to very short chain life.
 Fatigue- chain subjected to repetitive high load beyond the endurance
limit, causing it to eventually fracture.
 Wear- Load normally between pin and bush eventually wears away
material such that the chain stretches beyond its usable limit. Most chain
are designed to fail due to wear.
 Galling - Lack of lubrication or excessively high running loads. Metal to
metal welding. Smeared and grooved surface. This pin is also corroded.
1.67) In chain drives, the sprocket has odd number of teeth and the chain has
even number of links. Why? [AU, Nov / Dec –2012]
In order to have uniform wear on all the links, it is preferable to have odd
number of teeth on the smaller sprocket and an even number of pitches in the
chain.

1.68) What are the advantages of chain drives? [AU, Apr / May – 2018]
 Chain drives has more power transmitting capacity
 Higher efficiency and compact size
 Except less load on shaft since no initial tension is applied on the
sprocket
1.69) Give any three applications of chain drives. What are their limitations?
[AU, Apr / May – 2011]
Applications:
Chain drives are used in many types of industrial applications, such
as:
 Rigging and moving heavy materials
 Hydraulic lift truck fork operation
 Overhead hoists
 Operating conveyer belts.
Limitations:
 The production cost of chains is relatively high.
 The chain drive needs accurate mounting and careful
maintenance, particularly lubrication and slack adjustment.
 The chain drive has velocity fluctuations especially when
unduly stretched
 Cannot be used in applications where the drive must slip
 Are noisy and can cause vibrations
 Do not have the load capacity or service life of gear drives
1.70) Give the advantages of chain drives over belt drives. [AU, May / Jun – 2012]
 For the transmission of more power over a longer as well as shorter
distances.
 Compact than belt drives.
 Slip is less compared to belt drive.
1.71) Under what circumstances chain drives are preferred over V belt drives?
[AU, Apr / May – 2016]
Chain drives are preferred over V-belt drives under the following
conditions:

 For the transmission of more power over a longer as well as shorter
distances.
 Where higher speeds and more accurate speed ratio are required.
 They can be operated under adverse temperature and atmospheric
conditions.
 They can transmit power to several shafts by one chain.
1.72) What do you understand by simplex, duplex and triplex chains?
[AU, May / Jun – 2007]
Simplex chain consists of length of single links (single strand), duplex is
length of double links (double strands) and triplex is length of triple links (triple
strands). From PSGDDB @ 7.71 Chain numbers with prefix R & B denote
simplex, DR & DB denote duplex and TR & TB denote triplex chains.
1.73) In what way is a silent chain better than an ordinary driving chain?
[AU, Apr / May – 2005, Nov / Dec –2008, May / Jun – 2011]
Silent (or) inverted tooth chain is a type of chain with teeth formed on its
links to engage with the teeth in the sprockets.
Advantages:
 Operate with less vibrations and noise.
 They can be installed without dismantling drive components.
 They can be used in varying temperature ranges.
 Higher speed and power transmitting capacity
 Greater efficiency.

1.74) What is a silent chain? In what situations, silent chains are preferred?
[AU, Nov / Dec –2007]
Silent (or) inverted tooth chain is a type of chain with teeth formed on its
links to engage with the teeth in the sprockets.
Advantages:
 Operate with less vibrations and noise.
 They can be installed without dismantling drive components.
 They can be used in varying temperature ranges.
 Higher speed and power transmitting capacity
 Greater efficiency.
1.75) Sketch and name the different types of compound wire ropes.
[AU, Apr / May – 2004, 2010]
Regular lay ropes - Strands rotate around the rope in the opposite
direction to the wires of the strand.
Lang lay ropes - The Strands rotate around the rope in the same direction
to the wires of the strand.
Alternate lay ropes - Here, the rope is constructed using alternate strands
of right regular lay and right lang lay.

1.76) How the wire ropes are designated? [AU, Nov / Dec – 2016, 2018]
Wire ropes are designated by the no. of strands & the no. of wires in each
strand. Example: Wire rope, 7 x 19 means: The wire rope has 7 Strands and each
Strand has 19 wires each.
1.77) How is a wire - rope designated? [AU, May / Jun – 2007]
1.78) How is a wire rope specified? [AU, May / Jun – 2009]
1.79) What kind of stresses should be considered during the selection of wire -
ropes?
The stresses that act on a rope are:
 Direct tensile stress due to load and self weight

 Bending stress due to the bending of rope round the drum and,
 Stresses due to speed changes, starting and stopping.
1.80) What do you understand by 6 x 19 construction in wire ropes?
[AU, Nov / Dec –2014]
Wire rope, 6 x 19 means: The wire rope has 6 Strands and each Strand has
19 wires each.
1.81) Write any four wire rope applications. [AU, Nov / Dec –2013]
 Used in mines, tram ways and power transmission
 Used in hoisting equipment like cranes, elevators
 Used in hand operated hoisting machinery and as ropes for fitting
tackles hooks etc.
1.82) List the advantages of wire ropes compared to chains.
[AU, Apr / May – 2017]
The metal chains can handle a large load, if one link in that chain breaks or
suffers a defect, then the whole length of the chain is rendered useless. If wires or a
strand within a rope break or snap, the load can still be supported by the rest of the
strands, especially the strong core.
1.83) What are the advantages of belt drives in compare with that of the chain
and rope drives? [AU, Nov / Dec – 2017]
The metal chains can handle a large load, if one link in that chain breaks or
suffers a defect, then the whole length of the chain is rendered useless. If wires or a
strand within a rope break or snap, the load can still be supported by the rest of the
strands, especially the strong core.

UNIT – II – SPUR GEARS AND PARALLEL AXIS HELICAL GEARS
Part – A
2.1) What is a gear drive?
Gear drive is a mechanism consisting of toothed wheels that engage and
transmit rotary motion, usually transforming angular velocity and torques.
2.2) Enumerate the advantages and disadvantages of gear - drives over flexible
drives.
Advantages:
 By using gear trains, large velocity ratio can be obtained with
minimum space.
 Gears are mechanically strong, so higher loads can be lifted.
 They are used for transmitting motion over small centre distance of
shafts
 They are used for large reduction in speed and for transmission of
torque.
 Gears require only lubrication, hence less maintenance is required.
 Using gear systems, we can transmit motion between non-parallel
intersecting shafts.
 They have long life, so the gear system is very compact.
Disadvantages:
 They are not suitable for large velocities.
 They are not suitable for transmitting motion over a large distance.
 Due to the engagement of toothed wheel of gears, some part of
machine may get permanently damaged in case of excessive
loading.
 They have no flexibility.
 Gear operation is noisy.
2.3) State the advantages of toothed gears over the other types of transmission
systems. [AU, Nov / Dec – 2018]
 By using gear trains, large velocity ratio can be obtained with
minimum space.
 Gears are mechanically strong, so higher loads can be lifted.

 They are used for transmitting motion over small centre distance of
shafts
 They are used for large reduction in speed and for transmission of
torque.
 Gears require only lubrication, hence less maintenance is required.
 Using gear systems, we can transmit motion between non-parallel
intersecting shafts.
 They have long life, so the gear system is very compact.
2.4) How are gears classified?
 Parallel Axes Gears
 Spur Gear
 Spur rack
 Internal gear
 Helical gear
 Helical rack
 Double helical gear
 Intersecting Axes Gears
 Straight bevel gear
 Spiral bevel gear
 Zerol bevel gear
 Nonparallel and Nonintersecting
 Screw gear
 Worm gear
2.5) Label a) addendum b) flank in a simple sketch of a gear tooth.
[AU, May / Jun – 2007]

2.6) Specify the types of gear - failures. [AU, Apr / May – 2018]
2.7) What are the main types of gear tooth failure? [AU, May / Jun – 2013, 2016]

2.8) Mention the advantages of non – metallic gears? [AU, Nov / Dec –2012]
 Require minimum (or) no lubrication
 Less noise, less wear, reduced vibrations and shocks during operation.
 Light weight and minimum maintenance
 Can operate at high speeds.
 Longer life
 Resistant to corrosion. Not affected by water and oil.
2.9) Mention the disadvantages of non-metallic gears. [AU, Nov / Dec –2011]
 Less load-carrying capacity compared to similarly sized metal gears.
 Molded gears cannot hold the same high tolerances that metal gears can.
 Plastic is less dimensionally stable when compared to metal and this
results in dimensional variations due to temperature and humidity
conditions.
 Material cost is significantly higher than that of base metals and can vary
widely due to fluctuations in the cost of base chemicals.
 Difficulty in attaching plastic gears to metal shafts.
2.10) Specify the significance of minimum number of teeth in pinions.
[AU, May / Jun – 2012]
The minimum number of teeth in pinion is important to avoid interference
and undercutting.
2.11) What condition must be satisfied in order that a pair of spur gears may
have a constant velocity ratio? [AU, Nov / Dec –2009, May / Jun – 2014]
 It should satisfy the law of gearing.
 Law of gearing states that, in order to maintain a constant angular
velocity ratio between two meshing gears, the common normal of the
tooth profiles, at all contact points within mesh, should always pass
through a fixed point on the line of centers, called the pitch point.
2.12) What is meant by pressure angle? [AU, May / Jun – 2006]
The Pressure Angle is the acute angle between the line of action and a
normal to the line connecting the gear centers.

2.13) What is pressure angle? What is the effect of increase in pressure angle?
[AU, May / Jun – 2006, 2014, Apr / May – 2015]
The Pressure Angle is the acute angle between the line of action and a
normal to the line connecting the gear centers.
The effects of increasing the pressure angle are:
 Higher pressure angle improves the tooth strength.
 Increasing pressure angle results in smaller base circle so more
portion of tooth becomes involute thus can eliminate interference.
 Increasing pressure angle will improve power transmission but, at
the same time will increase gear wear and meshing noise.
2.14) What is the effect of increase in pressure angle? [AU, Apr / May – 2005]
 Increasing pressure angle results in smaller base circle so more portion
of tooth becomes involute thus can eliminate interference.
 Increasing pressure angle will improve power transmission but, at the
same time will increase gear wear and meshing noise.
2.15) What is the effect of increasing the pressure angle in gears?
[AU, Nov / Dec –2011]
2.16) Specify the effects of increasing the pressure angle in gear design.
[AU, Nov / Dec –2014]

2.17) What are the effects of increasing or increasing the pressure angle in gear
design? [AU, Apr / May – 2017]
 Decreasing the pressure angle will increase the minimum number of
teeth required on the pinion to avoid interference / undercutting.
2.18) Why pinion is made harder than gear? [AU, Nov / Dec – 2018]
The pinion is made harder than gear because the teeth of pinion undergoes
more number of cycle than the teeth of gear and hence it will get wear easily than
gear.
2.19) Why is tangential component of gear tooth force called useful component?
[AU, Apr / May – 2010]
The tangential component of the gear tooth force, Ft is only responsible for
the transmission of power. Hence, it is called the useful component of gear tooth
force.
2.20) What does the load correction factor account for in gear design?
[AU, May / Jun – 2012]
Load distribution factor which accounts for non-uniform spread of the load
across the face width. It depends on the accuracy of mounting, bearings, shaft
deflection and accuracy of gears.
2.21) Define module. [AU, Apr / May – 2011, May / Jun – 2013, Nov / Dec –2015]
Module, m is the ratio of Pitch Circle Diameter in millimeters to the
Number of Teeth.
𝑚 =
Pitch Circle Diameter
Number of Teeth
2.22) Differentiate between circular pitch and diametral pitch.
[AU, Nov / Dec –2013]
Circular pitch, pc is the space in pitch circle used by each tooth.

Diametral pitch, pd is the ratio of number of teeth to the pitch circle
diameter.
𝒑 𝒅 =
𝝅
𝒑 𝒄
=
𝟏
𝑴𝒐𝒅𝒖𝒍𝒆
2.23) Define the following terms (a) backlash (b) gear ratio
[AU, Apr / May – 2008]
Backlash is the tangential space between teeth of mating gears at pitch
circles. In other words, it is the difference between the tooth thickness of one gear
and the tooth space of the mating gear.
The Gear Ratio is the ratio of number of teeth of larger gear to that of
smaller gear. It is also defined as the ratio of high speed to the low speed in gear
drive.
2.24) Define Backlash. What factors influence backlash? [AU, Nov / Dec – 2016]
Backlash is the tangential space between teeth of mating gears at pitch
circles. In other words, it is the difference between the tooth thickness of one gear
and the tooth space of the mating gear.
Factors influence backlash:
 Errors in profile, pitch, tooth thickness, helix angle and center
distance, and run-out.
 The greater the accuracy, the smaller the backlash needed
2.25) Backlash of Spur gear depends on which of two factors?
[AU, Nov / Dec – 2016, 2018]
Errors in profile, pitch, tooth thickness, helix angle and center distance, and
run-out.
2.26) Why is dedendum value more than addendum value?[AU, Nov / Dec –2004]
In order to get clearance between the tooth of one gear and bottom surface
of mating gear so as to avoid interference, dedendum is having more value than the
addendum.
2.27) What is working depth of a gear - tooth?
[AU, Apr / May – 2005, May / Jun – 2011]
 Working depth is the depth of engagement of two mating gears
 It numerically equals to the sum of their operating addendums.

2.28) What are the profiles of a spur gear? [AU, Apr / May – 2016]
The common standard profiles are:
 Cycloidal profile
 Involute profile
 Circular arc (or) Nivikov profile.
2.29) What are the common profiles used for gear tooth?
[AU, May / Jun – 2007, Nov / Dec – 2016, 2018, Apr / May – 2011]
2.30) What are the generally used gear profiles? [AU, May / Jun – 2012]
2.31) Sketch the profile of spur gear and mark terminology used to specify the
gear. [AU, Apr / May – 2010]
2.32) What is beam strength of spur gear? What is the effect of module on beam
strength of a tooth in a spur gear? [AU, Apr / May – 2010]
When stresses reaches the permissible magnitude of bending stresses, the
corresponding force (Ft) is called the beam strength. Therefore the beam strength is
maximum value of the tangential force that the tooth can transmit without bending
failure. If the module is increased the beam strength of tooth also increases.

2.33) State any two important applications where the spur gear is used.
[AU, Nov / Dec – 2017]
 Spur gears are commonly used in gear pumps and gear motors.
 They are widely used in steel sectors for rolling mills, power units and
cement units.
 Nautical industries, especially in marine engines.
 Gate controlling mechanisms, commonly in port sectors.
 Rack and pinion drive mechanisms.
 Film industry, film winding equipment, film cutting equipment and
more.
2.34) Why is a gear tooth subjected to dynamic loading?
[AU, Nov / Dec –2007, 2014, May / Jun – 2011]
 Inaccuracies of tooth spacing
 Irregularities in tooth profiles
 Misalignment of bearings
 Deflection of teeth under load
 Dynamic unbalance of rotating masses. 000
2.35) How does the number of teeth affect the design of gears
[AU, Nov / Dec –2005]
The major dimensions of the gears depends upon the number of teeth. The
module of the gear is mostly depends upon the number of teeth.
2.36) State the law of gearing.
[AU, May / Jun – 2005, 2006, 2007, Nov / Dec –2012, Apr / May – 2015]
In order to maintain a constant angular velocity ratio between two meshing
gears, the common normal of the tooth profiles, at all contact points within mesh,
should always pass through a fixed point on the line of centers, and called the pitch
point.
2.37) Specify the conditions based on which gear cutters are selected.
[AU, Nov / Dec –2004]
Gear cutters are selected based on
 Properties of materials for workpiece and tools
 Production rate

 Cost of production
 Structure of gears
 Module of gear
2.38) How do spur - gears fail?
Gears may fail due to
 Tooth breakage by overload and misalignment of shafts
 Corrosion of teeth by improper lubrication
 Tooth wear because of insufficient lubrication
 Interference because of no under cut
2.39) How does failure by pitting happen in gears? [AU, Nov / Dec –2011]
 Pitting is a surface fatigue failure of the gear tooth.
 It occurs due to repeated loading of tooth surface and the contact
stress exceeding the surface fatigue strength of the material.
 Material in the fatigue region gets removed and a pit is formed.
 The pit causes stress concentration and soon the pitting spreads to
adjacent region till the whole surface is covered.
2.40) What factors influence that backlash in gear drives?
[AU, Apr / May – 2005, Nov / Dec –2008, May / Jun – 2011]
2.41) What factors influence backlash in gear drives? [AU, Apr / May – 2005]
2.42) What is stub tooth? Why it is preferred? [AU, May / Jun – 2012]
The thickness of the tooth at top surface and its root is more compared to
full depth tooth. The tooth which has less working depth compared with full depth
tooth is known as stub tooth. It is usually 20% less than full depth tooth.
It is preferred mostly in the gears with a small number of teeth to take
heavy loads.

2.43) What is meant by stub tooth in gear drives? [AU, Nov / Dec – 2017]
The thickness of the tooth at top surface and its root is more compared to
full depth tooth. The tooth which has less working depth compared with full depth
tooth is known as stub tooth. It is usually 20% less than full depth tooth.
2.44) In a pair of spur gears, the module is 6mm. Determine the circular pitch
and diametral pitch. [AU, Nov / Dec –2010]
Circular pitch (pc) = π * m
= π * 6
= 18.849 mm
Diametral pitch (pd)=
𝜋
𝑝 𝑐
=
𝜋
𝜋∗ 𝑚
=
1
𝑚
=
1
6
= 0.1667 /mm
2.45) Where do we use spiral gears? [AU, Nov / Dec –2013]
Spiral gears are used to transmit power and motion between
nonintersecting and non-parallel axes. They are also called as crossed helical gear
(or) screw (or) skew gears.
2.46) What is helical gear?
A helical gear is a cylindrical gear similar to spur gear except that the teeth
are cut at an angle, known as helix angle, to the axis of the gear shaft. In spur gear
the teeth are cut parallel to the axis.
2.47) Compare the contact between mating teeth of spur and helical gears.
[AU, Apr / May – 2010]
In spur gears the line of contact is parallel to the axis of rotation. In spur
gear the total length of contact line is equal to the face width.
In helical gears the line of contact is diagonal across the face of the tooth,
the total length of contact line is greater than the face width. This lowers the unit
loading and increases load carrying capacity.

2.48) Differentiate double helical and herringbone gears.
[AU, Nov / Dec –2015, Apr / May – 2017]
Both types of gears are constructed by joining two identical helical gears of
the same module, number of teeth and pitch circle diameter, but with teeth opposite
hand of helix. There will be a groove between two gears in a double helical gear,
whereas; herringbone has no such groove.
2.49) Where do we use helical gears? [AU, Apr / May – 2016]
It is used in Automobiles, turbines and high speed applications
2.50) Mention a few gear materials. [AU, May / Jun – 2009, 2011]
 Both metals and non-metals are used for manufacturing gears.
 Cast Iron, Steel, Brass, Bronze and Aluminium alloys are a few
popular metals used in gear manufacturing.
 Wood, compressed paper and synthetic plastics like nylon are used
for gears, especially for reducing noise.

2.51) In what ways are helical gears different from spur gears?
[AU, Apr / May – 2018]
SPUR GEAR HELICAL GEAR
 Teeth are cut parallel to the axis
 Rough and noisy operation
 Less power transmission
 Entire width of tooth is
simultaneously engaged with full
width of the mating gear
 Teeth are cut inclined to the axis
 Smooth and silent operation
 More power transmission
 Gradual engagement is obtained
since their teeth are inclined to
axis
2.52) What are the advantages of the helical gear over spur gear?
[AU, Nov / Dec –2005, Apr / May – 2008]
 Due to the gradual engagement of helical teeth, the operation is silent and
smooth.
 Helical gears are preferred for heavy load applications.
 Helical gears could be used to transmit the motion and power between
two parallel shafts and also between two non-parallel shafts.
 The load will be distributed between several teeth at any time and hence,
there will be less wear and tear in operation of helical gears.
2.53) State an advantage and a disadvantage of helical gear.
[AU, May / Jun – 2009, Nov / Dec –2012]
Advantages of helical gear:
 Due to the gradual engagement of helical teeth, the operation is silent and
smooth.
 Helical gears are preferred for heavy load applications.
 Helical gears could be used to transmit the motion and power between
two parallel shafts and also between two non-parallel shafts.
 The load will be distributed between several teeth at any time and hence,
there will be less wear and tear in operation of helical gears.
Disadvantages of helical gear:
 When a pair of helical gear meshes with each other, there will be creation
of axial thrust load on gear due to helix angle of gear teeth.

 There will be sliding movement between mating gear teeth in case of
helical gear and heat generation will be more as compared to spur gear
application.
 One pair of mating helical gear will have less efficiency as compared to
efficiency of mating spur gears of similar size.
 Manufacturing and designing cost of helical gears will be more as
compared to spur gear designing and manufacturing cost.
2.54) Differentiate the following terms with respect to helical gears:(a) transverse
circular pitch, (b) normal circular pitch and (c) axial pitch
[AU, Nov / Dec –2007]
Transverse circular pitch (pc): It is the distance between the c
corresponding points of two successive teeth, measured along the plane
perpendicular to the gear axis.
Normal circular pitch: It is the distance between the corresponding points
of two successive teeth, measured along the plane perpendicular to the helix
Axial pitch (pa): It is the distance between the corresponding points of two
successive teeth, measured along the plane parallel to the gear axis.
2.55) A helical gear has a normal pressure angle of 20°, a helix angle of 45°,
normal module of 4 mm and has 20 teeth. Find the Pitch Diameter.
[AU, Nov / Dec – 2016]
𝑑 =
𝑚 𝑛
𝑐𝑜𝑠 𝛽
∗ 𝑧
𝑑 =
4
𝑐𝑜𝑠 45
∗ 20
𝒅 = 𝟏𝟏𝟑. 𝟏𝟑𝟕 𝒎𝒎
2.56) Where do we use skew gears?
[AU, Nov / Dec –2004, 2008, Apr / May – 2005]
Skew gears are used to connect two non-parallel and non-intersecting shaft.
It is commonly used in fuel pumps, washing machines, gear motors etc.
2.57) What are the applications of skew helical gears? [AU, May / Jun – 2011]
Skew gears are used to connect two non-parallel and non-intersecting shaft.
It is commonly used in fuel pumps, washing machines, gear motors etc.

2.58) Define virtual number of teeth in helical gears. [AU, Nov / Dec – 2017]
It is also called as Formative (or) Equivalent number of teeth. The number
of teeth in an equivalent spur gear in its normal plane is known as virtual number
of teeth.
𝑉𝑖𝑟𝑡𝑢𝑎𝑙 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑇𝑒𝑒𝑡ℎ 𝑍 𝑣 =
Circumference of the equivalent spur gear
Circular pitch
𝑍 𝑣 =
𝑍
𝑐𝑜𝑠3 𝛽
Z = Actual number of teeth in the helical· gear
β = Helix angle of the helical gear.
2.59) What is virtual number of teeth in helical gears? [AU, Nov / Dec –2012]
of teeth in an equivalent spur gear in its normal plane is known as virtual number
of teeth.
𝑉𝑖𝑟𝑡𝑢𝑎𝑙 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑇𝑒𝑒𝑡ℎ 𝑍 𝑣 =
Circumference of the equivalent spur gear
Circular pitch
𝑍 𝑣 =
𝑍
𝑐𝑜𝑠3 𝛽
Z = Actual number of teeth in the helical· gear
β = Helix angle of the helical gear.
2.60) What is the interference in involute profile? [AU, Nov / Dec –2005, 2008]
Interference is the phenomenon when the tip of one tooth pinion undercuts
the root of its mating gear (wheel). As a result, some part of the involute profile of
the tooth of the wheel is removed.
2.61) State the advantages of herring bone gear.
[AU, May / Jun – 2006, 2007, Apr / May – 2015, Nov / Dec – 2018]
 Herringbone gear is a side by side combination of two helical gears of
opposite hands, without any groove in between.
 When a pair of helical gears meshes with each other, there will be
creation of axial thrust load on gear due to helix angle of gear teeth.
 The opposite hands of helix angles in the Herringbone gear will balance
each other, the axial thrust forces induced.

2.62) What is herringbone gear? [AU, Apr / May – 2016]
A herringbone gear is a specific type of double helical gear. It is a side by
side combination of two helical gears of opposite hands, without any groove in
between. This balances the induced axial thrust.
2.63) What is herringbone gear? Where are they used? [AU, Nov / Dec –2009]
They are used in heavy machinery and gear boxes
2.64) What is herringbone gear? State its application.
[AU, Nov / Dec –2005, Apr / May – 2008]

They are used in heavy machinery and gear boxes

UNIT – III – BEVEL, WORM AND CROSS HELICAL GEARS
PART – A
3.1) What is bevel gear?
Bevel gear is the type of gear for which the teeth are cut on conical surface
in contrast with spur and helical gears for which the teeth are cut on cylindrical
surfaces. The structure of bevel gear is similar to an uniformly serrated frustum of a
cone.
3.2) How bevel gears are manufactured? [AU, Apr / May – 2016]
In manufacture of bevel gears, first the blanks are performed by casting or
forging followed by machining to desired dimensions in lathes or special purpose
machine. Then the teeth are produced in the blank by machining.
Straight toothed bevel gear:
 By forming using milling cutter -low productivity and quality.
 By generation- high accuracy and finish.
Spiral and hypoid bevel gears:
 By generation-the cutter resembles face milling cutter.
3.3) When do we use bevel gears?
[AU, May / Jun – 2007, Apr / May – 2008, 2009, 2018]
If power and motion are to be transmitted between two intersecting shafts
then, bevel gears are used. Bevel gears are used in differential drives. Bevel gears
are used as the main mechanism for a hand drill. Spiral bevel gears are important
components on rotorcraft drive systems.

3.4) When bevel gears are used? [AU, May / Jun – 2007]
3.5) When bevel gear is preferred? [AU, May / Jun – 2009, Nov / Dec –2012]
3.6) Under what situation, bevel gears are used? [AU, Apr / May – 2011]
3.7) Define back cone radius for a bevel gear. [AU, Nov / Dec – 2016]
Cone distance (or) Back cone radius (or) pitch cone radius (R) in a bevel
gear is the distance along an element of the back cone from its apex to the pitch
cone.
3.8) What is a crown gear? [AU, May / Jun – 2011, Nov / Dec – 2016]
A crown gear is type of bevel gear whose shaft are right angle to each other
and the pitch angle of pinion is not equal to pitch angle of gear. The pitch cone
angle is 90 degrees.
𝜙 = 𝛿1 + 𝛿2 = 90°
𝛿1 ≠ 𝛿2
3.9) What is the specific feature of a miter gear? [AU, Nov / Dec –2004]
Miter gear is the special type of crown gear in which the shaft angle is 90
degree and the pitch angle of pinion and gear are equal. The pitch angle is 45
degree.
𝜙 = 𝛿1 + 𝛿2 = 90°
𝛿1 = 𝛿2 = 45°

3.10) State whether true or false and justify. Mitre gears are used for connecting
non - intersecting shafts. [AU, Nov / Dec –2005]
False. Mitre gears are used for connecting intersecting shafts.
3.11) What is meant by Mitre gears? [AU, Nov / Dec – 2017]
degree.
𝜙 = 𝛿1 + 𝛿2 = 90°
𝛿1 = 𝛿2 = 45°
3.12) What is virtual number of teeth in bevel gears?
[AU, Apr / May – 2004, May / Jun – 2014, Nov / Dec –2014]
of teeth in an equivalent spur gear in a plane normal to the tooth of bevel gear at
the larger end is known as virtual number of teeth.
𝑉𝑖𝑟𝑡𝑢𝑎𝑙 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑡𝑒𝑒𝑡ℎ 𝑍 𝑣 =
𝑍
𝑐𝑜𝑠𝛿
Z = Actual number of teeth in the bevel gear
δ = Reference angle of the bevel gear.
3.13) Define the following terms.(a) pitch angle (b) shaft angle (c) cone distance
(d) face angle [AU, Apr / May – 2005, May / Jun – 2014]
Pitch Angle is the half of the cone angle subtended by a bevel gear at its
apex.
Shaft angle is the sum of the pitch angles of pinion and gear of a bevel
gear pair.
𝜙 = 𝛿1 + 𝛿2 = 90°
𝜙 = 𝑆ℎ𝑎𝑓𝑡 𝐴𝑛𝑔𝑙𝑒
𝛿1 = 𝑃𝑖𝑡𝑐ℎ 𝐴𝑛𝑔𝑙𝑒 𝑜𝑓 𝑃𝑖𝑛𝑖𝑜𝑛
𝛿2 = 𝑃𝑖𝑡𝑐ℎ 𝐴𝑛𝑔𝑙𝑒 𝑜𝑓 𝐺𝑒𝑎𝑟
Cone Distance (or) Back cone radius (or) pitch cone radius (R) in a bevel
gear is the distance along an element of the back cone from its apex to the pitch
cone.
Face angle is the angle subtended by the face of a tooth at the cone centre.

Face angle= Pitch angle + Addendum angle
3.14) What is known as formative number of teeth on bevel gears?
[AU, Apr / May – 2017]
of teeth in an equivalent spur gear in a plane normal to the tooth of bevel gear at
the larger end is known as virtual number of teeth.
𝑉𝑖𝑟𝑡𝑢𝑎𝑙 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑡𝑒𝑒𝑡ℎ 𝑍 𝑣 =
𝑍
𝑐𝑜𝑠𝛿
Z = Actual number of teeth in the bevel gear
δ = Reference angle of the bevel gear.
3.15) What are the various forces acting on a bevel gear?
[AU, Nov / Dec –2009, May / Jun – 2013]
The force components acting on a bevel gear are:
 Tangential force, Ft
 Radial force, Fr
 Axial force, Fa
3.16) List the forces acting on bevel gears. [AU, Nov / Dec – 2018]
The force components acting on a bevel gear are:
 Tangential force, Ft
 Radial force, Fr
 Axial force, Fa
3.17) What is a Zerol bevel gears? [AU, Apr / May – 2015, Nov / Dec – 2018]
Zerol bevel gear is also a spiral bevel gear in which, the spiral angle is zero
at the middle of the face width.
3.18) What is the difference between an angular gear and a miter gear?
[AU, Nov / Dec –2012, 2013, 2015]
degree.
𝜙 = 𝛿1 + 𝛿2 = 90°
𝛿1 = 𝛿2 = 45°

In some bevel-gear drives, the angles between the shafts may not be 90°,
but either more or less than 90°. These gears are called ‘Angular bevel gears’.
3.19) Specify the features of skew bevel gears. [AU, May / Jun – 2012]
Spiral gears are used to transmit power and motion between
nonintersecting and non-parallel axes. They are also called as crossed helical gear
(or) screw (or) skew gears.
3.20) Differentiate a straight bevel gear and a spiral bevel gear.
[AU, Apr / May – 2016]
STRAIGHT TEETH BEVEL GEAR SPIRAL TEETH BEVEL GEAR
 In case of straight teeth bevel gear,
elements of the teeth are in the
form of a straight line, which
converges on a common apex.
 Here contact between teeth of two
meshing gears occurs suddenly.
 Due to sudden engagement, teeth
are subjected to impact loading.
 Sudden engagement of teeth also
causes vibration and noise.
 Load carrying capacity of straight
teeth bevel gear is comparatively
low
 These are suitable for low to
moderate speed applications.
 Life of the straight teeth bevel gear
is shorter as it is subjected to
impact loading and vibration.
 In case of spiral teeth bevel gear,
elements of the teeth are in the form
of a spiral curve, which also
converges on a common apex.
 Here contact between teeth of two
meshing gears occurs gradually.
 Due to gradual engagement, teeth
are subjected to gradual loading.
 Operation of spiral teeth bevel gear
is smooth and quite.
 Load carrying capacity of spiral
teeth bevel gear is high
 These can be utilized at high speed
applications also.
 Spiral teeth bevel gears have longer
life.
3.21) Mention two characteristics of hypoid gear. [AU, Apr / May – 2010]
 These gears are similar to spiral bevel but the pitch surfaces are
hyperbolic and not conical.

 Pinion can be offset above, or below the gear centre, thus allowing
larger pinion diameter.
 The operation is quiet and smoother.
 They have high reduction ratio and longer life.
3.22) Write down the relation between the axial force and tangential force
component. [AU, Nov / Dec –2010]
𝐹𝑎 = 𝐹𝑡 ∗ 𝑡𝑎𝑛𝛼 + 𝑠𝑖𝑛𝛿1
Fa = Axial Force
Ft = Tangential Force
α = Pressure Angle
δ1 = Reference angle of pinion
3.23) What is Lewis (tooth) form factor? [AU, Apr / May – 2010]
The form factor, Y, is a function of the number of teeth, pressure angle,
and involute depth of the gear. It accounts for the geometry of the tooth, but does
not include stress concentration.
3.24) What is reference angle? How is it related to speed ratio of bevel gear ratio?
[AU, May / Jun – 2012]
Pitch cone angle or Reference angle (δ2) is the angle that the pitch line
makes with the gear axis.
𝑖 = 𝑡𝑎𝑛 𝛿2
𝛿2 = 𝑃𝑖𝑡𝑐ℎ 𝐴𝑛𝑔𝑙𝑒 (𝑜𝑟) 𝑅𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒 𝐴𝑛𝑔𝑙𝑒 𝑜𝑓 𝐺𝑒𝑎𝑟
3.25) What kind of contact occurs between worm and wheel? How does it differ
from other gears? [AU, Nov / Dec –2015]
In worm gear drive, sliding contact is occurred between the worm and
wheel whereas other gears such as spur, helical and bevel gears transmit power by
rolling contact.
3.26) What are the commonly used materials for worm and wheel?
[AU, May / Jun – 2007]
Worm materials: Carbon steels and alloy steels
Worm wheel materials: Cast iron and phosphor bronze.

3.27) Why phosphor bronze is widely used for worm gears?
[AU, Nov / Dec –2013]
The phosphor bronze is widely used for worm gears in order to resist and
reduce wear of the worms. The wear will be excessive with cast iron or steel.
3.28) When do we use worm gears? [AU, May / Jun – 2013]
Worm gears are constructed of a worm and a gear (sometimes referred to
as a worm wheel), with non-parallel, non-intersecting shafts oriented 90 degrees to
each other.
Worm drives are used in presses, rolling mills, conveying engineering,
mining industry machines, on rudders, and worm drive saws. In addition, milling
heads and rotary tables are positioned using high-precision duplex worm drives
with adjustable backlash. Worm gears are used on many lift/elevator and escalator-
drive applications due to their compact size and the non-reversibility of the gear.
3.29) Under what circumstances, the worm gears are used for power
transmission? [AU, Nov / Dec – 2017]
They are used in most of the stringed instruments.
 In conventional steering mechanisms, worm and worm wheels are
used.
 Used in lifts/ elevators because of their compactness and self-locking
characteristic.
 Chain pulley block.
3.30) Give some applications of worm - gear drive. [AU, May / Jun – 2007]
used.
characteristic.
3.31) Write some applications of worm-gear drive.
[AU, May / Jun – 2011, Nov / Dec – 2016]

used.
characteristic.
3.32) In worm gear drive, only the wheel is designed. Why?
[AU, Apr / May – 2011]
 In a worm gear drive, the worm is stronger than the wheel.
 Hence, only the wheel has to be designed which is the weaker part.
3.33) Mention the reason for irreversibility in worm gears. [AU, Nov / Dec –2010]
A worm and worm wheel drive is said to be self-locking or irreversibility
if the coefficient of friction is greater than the tangent of the lead angle.
𝝁 > 𝒕𝒂𝒏 𝜸
3.34) What is irreversibility in worm gear? [AU, Nov / Dec – 2018]
A worm and worm wheel drive is said to be self-locking or irreversibility
if the coefficient of friction is greater than the tangent of the lead angle.
3.35) Write the conditions of self-locking of worm gears in terms of lead and
Pressure angles. [AU, Apr / May – 2017]
A worm and worm wheel drive is said to be self-locking if the coefficient
of friction is greater than the product of cosine of pressure angle and tangent of the
lead angle.
𝜇 ≥ 𝑐𝑜𝑠𝛼 ∗ 𝑡𝑎𝑛𝛾
3.36) What are the various forces acting on worm and worm gears?
 Tangential force
 Axial or thrust force
 Radial or separating force
3.37) What is helical angle of worm? [AU, Apr / May – 2016]
Helix angle, β in a worm is the angle between a tangent to the thread at the
pitch diameter and the axis of the worm. The helix angle is preferably 6°
maximum.

3.38) Give the speed ratio range of worm – wheel drive. [AU, May / Jun – 2012]
The speed ratio that can be obtained in a worm wheel drive can be up to
300:1.
3.39) Usually worm is made of hard materials and worm gear is made of softer
material – Justify. [AU, Nov / Dec –2009]
In general, worm is made of hard metal while the worm gear is made from
relatively soft metal.
The reasons are:
 Worm is subjected to more number of stress cycles than the worm
wheel
 The number of teeth on the worm gear is relatively high compared to
worm with its number of starts being usually 1 to 4.
 By reducing the worm gear hardness, the friction, contact stress and
hence the wear on the worm teeth is reduced.
 Also, the plastic flow and cold working of the soft material will tend
to correct the errors in the tooth action that arise due to the
misalignment.
3.40) Why is dynamic loading rarely considered in worm gear drives?
[AU, Nov / Dec –2011]
The dynamic load in a worm gear drive is not so severe because of its
sliding action between the worm and worm wheel. Hence, the dynamic loading is
usually not considered in worm gear drives.
3.41) In which gear – drive is self – locking available?
[AU, Nov / Dec –2008, Apr / May – 2015, 2018]
Self-locking mechanism is available in a worm and worm gear drive.
3.42) What is a 'Self-locking condition' in worm and worm wheel?
In general;
 The worm is the driver and worm wheel is the driven members.
 The power and motion can be transmitted only from the worm to the
worm wheel.
 The reverse motion is not possible.
 This condition is known as self-locking of worm and worm wheel.

 A worm and worm wheel drive is said to be self-locking if the
coefficient of friction is greater than the tangent of the lead angle.
3.43) Why is a multistart worm more efficient than a single start one?
[AU, Nov / Dec – 2005]
If the coefficient of friction and diameter factor, ‘q’ are constant. The
efficiency of a worm drive is inversely proportional to the speed ratio. The
efficiency is directly proportional to the lead angle ‘γ’.
𝐺𝑒𝑎𝑟 𝑅𝑎𝑡𝑖𝑜 (𝑜𝑟) 𝑆𝑝𝑒𝑒𝑑 𝑅𝑎𝑡𝑖𝑜 𝑖 =
𝑁𝑜 𝑜𝑓 𝑡𝑒𝑒𝑡ℎ 𝑜𝑛 𝑡ℎ𝑒 𝑤ℎ𝑒𝑒𝑙
𝑁𝑜 𝑜𝑓 𝑠𝑡𝑎𝑟𝑡𝑠
𝐿𝑒𝑎𝑑 𝐴𝑛𝑔𝑙𝑒 𝛾 = 𝑡𝑎𝑛−1
[
𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟 𝑓𝑎𝑐𝑡𝑜𝑟
]
Multi start worm has less speed ratio and high lead angle. Hence, they have
high efficiency.
3.44) When the number of start of a worm is increased in a worm gear drive, how
it affects the other parameters and action of the drive? [AU, Apr / May – 2004]
𝐺𝑒𝑎𝑟 𝑅𝑎𝑡𝑖𝑜 (𝑜𝑟) 𝑆𝑝𝑒𝑒𝑑 𝑅𝑎𝑡𝑖𝑜 𝑖 =
𝑁𝑜 𝑜𝑓 𝑡𝑒𝑒𝑡ℎ 𝑜𝑛 𝑡ℎ𝑒 𝑤ℎ𝑒𝑒𝑙
𝐿𝑒𝑎𝑑 𝐴𝑛𝑔𝑙𝑒 𝛾 = 𝑡𝑎𝑛−1
[
𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟 𝑓𝑎𝑐𝑡𝑜𝑟
]
The increasing the number of starts reduces the speed ratio and increases
the lead angle. If the coefficient of friction and diameter factor, ‘q’ are constant.
The efficiency of a worm drive is inversely proportional to the speed ratio. The
efficiency is directly proportional to the lead angle ‘γ’. Hence, the efficiency
increases.
3.45) Write the advantages of worm gear drive. [AU, May / Jun – 2008]
The advantages of a worm gear drive are:
 Worm gear drives operate silently and smoothly.
 They are self-locking. Reverse movement will be restricted.
 They occupy less space.
 They have good meshing effectiveness.
 They can be used for reducing speed and increasing torque.

High velocity ratio of the order of 300 can be obtained in a single
step.
3.46) Mention the advantages of worm gear drive. [AU, Nov / Dec –2014]
The advantages of a worm gear drive are:
 Worm gear drives operate silently and smoothly.
 They are self-locking. Reverse movement will be restricted.
 They occupy less space.
 They have good meshing effectiveness.
 They can be used for reducing speed and increasing torque.
 High velocity ratio of the order of 300 can be obtained in a single
step.
3.47) What are the disadvantages of worm gear drive? [AU, Nov / Dec – 2017]
The disadvantages of a worm gear drive are:
 Low efficiency
 Low power transmission
 More heat will be produced and hence this drive can be operated
inside an oil reservoir or extra cooling fan is required in order to
dissipate the heat from the drive
3.48) State the advantage of worm gear drive in weight lifting machines.
[AU, Apr / May – 2008]
 The self-locking feature acts as a secondary brake and prevents
damage to the load and the system.
 The lowering speed can be regulated easily and the load will not be
allowed to free fall.
 The drive does not require complicated controls (or) high
maintenance mechanism to ensure safe lifts.
3.49) What are the main types of failure in worm gear drives?
[AU, May / Jun – 2012, Nov / Dec –2012]
Pitting:
Pitting is a form of surface fatigue and may be of three types:
 Initial (corrective)
 Destructive

 Normal
Tooth fracture:
 Such failures are rare and are indicative of overloading.
 Tooth breakage may be the result of high overloads of either
impact or static in nature.
Ridging:
 Ridging is caused by wear or plastic flow of surface and
subsurface material due to high contact compressive stresses
and low sliding velocities.
3.50) What are the two types of failure in worm gear drives?
[AU, Nov / Dec – 2016]
Pitting:
Pitting is a form of surface fatigue and may be of three types:
 Initial (corrective)
 Destructive
 Normal
Tooth fracture:
 Such failures are rare and are indicative of overloading.
 Tooth breakage may be the result of high overloads of either
impact or static in nature.
Ridging:
 Ridging is caused by wear or plastic flow of surface and
subsurface material due to high contact compressive stresses
and low sliding velocities.
3.51) Define normal pitch of a worm gear. [AU, Apr / May – 2016]
Normal pitch, pn in a worm is the distance measured from a point in one
thread to the corresponding point on the adjacent thread, along a normal to the
thread of the worm.
3.52) A pair of worm gears is designated as 2 / 54 / 10 / 5. Find the gear ratio.
[AU, Nov / Dec –2010]
A standard worm gear pair is designated as zw / zg / q / m / a.
zw = number of starts on worm,

zg = number of teeth on worm gear,
q = diametral quotient,
m = module
a = centre distance.
A pair of worm gears is designated as 2 / 54 / 10 / 5
zw = number of starts on worm = 2
zg = number of teeth on worm gear = 54
q = diametral quotient = 10
m = module = 5
𝑖 =
𝑧2
𝑧1
=
𝑧 𝑔
𝑧 𝑤
=
54
2
= 27
3.53) Why is the efficiency of a worm gear drive comparatively low?
[AU, Apr / May – 2004, Nov / Dec –2007]
 They have a smaller gear-tooth lead (helix) angle, which causes more
surface contact between the teeth.
 This sliding action causes higher friction which results in heat
generation and power loss.
 The "churning" of lubricating oil also reduces the efficiency.
("Churning" is the undesirable friction that occurs between fluids due
to continued agitation of the lubricant. Over lubrication is the main
cause for this.)
3.54) How do you specify a worm gear pair?
A standard worm gear pair is designated as zw / zg / q / m / a.
zw = number of starts on worm,
zg = number of teeth on worm gear,
q = diametral quotient,
m = module
a = centre distance.
3.55) When do we employ crossed helical gear? [AU, Apr / May – 2010]
A pair of crossed helical gears, also known as spiral gears, are used to
connect and transmit motion between two non-parallel and non-interesting shafts.

The contact between the mating teeth is always a point, these gears are suitable for
low power transmission applications only.
3.56) Why is the crossed helical gear drive not used for power transmission?
[AU, Nov / Dec –2007]
While meshing, the teeth have only point contact. Hence, the contact stress
is very high which results in rapid wear. Therefore, they have a very low load
carrying capacity and not recommended for high power transmission.
3.57) Calculate the angle between the shafts of a crossed helical gears made of two
right handed helical gears of 15º helix angle each. [AU, May / Jun – 2009]
𝑆ℎ𝑎𝑓𝑡 𝐴𝑛𝑔𝑙𝑒 𝛾 = 𝛽1 + 𝛽2
(“+” is used since both gears are of the same hand)
𝐻𝑒𝑙𝑖𝑥 𝐴𝑛𝑔𝑙𝑒 = 𝛽1 = 𝛽2 = 15°
𝑆ℎ𝑎𝑓𝑡 𝐴𝑛𝑔𝑙𝑒 𝛾 = 𝛽1 + 𝛽2 = 15 + 15 = 30°
3.58) Calculate the angle between the shafts of a crossed helical gears made of two
left handed helical gears of 10º helix angle each. [AU, Nov / Dec –2012]
𝑆ℎ𝑎𝑓𝑡 𝐴𝑛𝑔𝑙𝑒 𝛾 = 𝛽1 + 𝛽2
(“+” is used since both gears are of the same hand)
𝐻𝑒𝑙𝑖𝑥 𝐴𝑛𝑔𝑙𝑒 = 𝛽1 = 𝛽2 = 10°
𝑆ℎ𝑎𝑓𝑡 𝐴𝑛𝑔𝑙𝑒 𝛾 = 𝛽1 + 𝛽2 = 15 + 15 = 20°

UNIT – IV – GEAR BOXES
PART – A
4.1) What is a gear box?
The gearbox that uses gears and gear trains to provide speed and torque
conversions from a rotating power source to another device.
4.2) What purpose does the housing of a gear - box serve?
Gear box housing or casing is use as container inside which, the gears,
shafts, bearings and other components are mounted. It also prevents the entry of
dust inside the housing and reduce noise of operation. The housing safe guard the
inner components
4.3) What is the function of spacers in a gear - box?
[AU, Nov / Dec –2004, 2008, Apr / May – 2005, May / Jun – 2011]
Spacers are sleeve like components which are mounted on shafts between
gears and bearings or one gear to another gear in order to maintain the distance
between them and avoid interruption between them.
4.4) For what purpose are gear - box used? [AU, Apr / May – 2018]
Gearboxes are used to increase torque while reducing the speed of a prime
mover output shaft (e.g. a motor crankshaft). This means that the output shaft of a
gearbox rotates at a slower rate than the input shaft, and this reduction in speed
produces a mechanical advantage, increasing torque.
4.5) Specify four types of gearboxes. [AU, Nov / Dec –2014]
 Constant Mesh Gearbox
 Sliding Mesh Gearbox
 Synchromesh Gearbox
 Epicyclic Gearbox.
4.6) What is a speed diagram? [AU, Apr / May – 2018]
Speed diagram or structural diagram is the graphical representation of
different speed of output shaft, motor shaft and intermediate shafts.
4.7) What is multispeed gear box? [AU, Apr / May – 2016]
A gearbox that gives multi output speeds is called a multispeed gearbox. A
multispeed gearbox converts a single high speed input into a number of speed

outputs in many stages. It has more than two gears and equivalent number of
shafts.
4.8) Name the series in which speeds of multi - speed gear box are arranged.
[AU, May / Jun – 2007, 2011]
The series, R5, R10, R20, R40 & R80; R20 and R40 are widely used in
multispeed gearboxes. These series follow geometric progression.
4.9) What is R20 series? [AU, Apr / May – 2016]
R20 refers to Renard preferred numbers series 20. It has a total of 20
members in the series. Leaving 1.00; First number is equal to the step ratio 𝜙 =
( √10
20
)
1
= 10(1
20⁄ )
= 1.16. Each member will be multiplied by the step ratio to
get the next number in the geometric series. The last number will be 10.00
4.10) What are preferred numbers?
[AU, Apr / May – 2011, 2016, Nov / Dec –2012, 2014, May / Jun – 2013]
Preferred numbers are the conveniently rounded off values derived from
geometric series, including the integral powers of 10 and having as common ratios
the following factors: √10
5
; √10
10
; √10
20
; √10
40
𝑎𝑛𝑑 √10
80
These ratios are called
as the Step Ratios, ϕ and approximately equal to 1.58, 1.26, 1.12, 1.06 and 1.03
respectively.
4.11) What are the main components of a gear - box?
 Gears for getting different speeds
 Shafts for mounting gears
 Bearings for supporting shafts
 Spacers to maintain the distance between gears.
 Levers for changing the position of gear engagement
 Gear box housing for covering all the inner components
 Oil seals for lubrication
4.12) What is a speed reducers?
A speed reducer (or) transmission box (or) commonly known as gearbox is
a gear mechanism used to reduce the angular speed of the output shaft when
compared with that of the input shaft. They are used to obtain different speeds with
varying torques. If the speed is low, the torque will be high and vice versa.

4.13) Name the types of speed reducers
 Single reduction speed reducers
 Multi reduction speed reducers
The single reduction speed reducer is one set of gear drive such as pinion
and one gear (wheel) can be operated. In multi reduction speed reducers two or
more set of gears are employed.
4.14) Classify speed reducers. [AU, Nov / Dec –2012]
 Single reduction speed reducers
 Multi reduction speed reducers
4.15) What are the methods of lubrication in speed reducers?
[AU, Nov / Dec –2004, 2011]
The methods of lubrication in speed reducers (gearboxes) are:
 Splash (spray) lubrication
 Force-feed (pressure) lubrication.
4.16) What does the ray - diagram of a gear - box indicate?[AU, May / Jun – 2012]
Ray diagram (or) speed diagram is a graphical representation of the
structural formula used in the gear box design. It provides the number of stages
(shafts) in the system, the transmission ratio at each stage and the different speeds
at each stage. The last stage gives the total number of final speeds with their
corresponding values.
4.17) What is meant by ray diagrams? [AU, Apr / May – 2010, May / Jun – 2012]
4.18) Write the significance of structural formula. [AU, Nov / Dec –2015]
Structural formula is the formula that gives the method of obtaining the
required number of output speeds in a gearbox. It is used to obtain the number of
stages (shafts) and required number of gears to obtain the desired range and steps
of output speeds in a gear box design.

4.19) Differentiate ray diagram and structural diagram.
[AU, Nov / Dec –2007, 2016]
Structural diagram (or) Kinematic layout is a pictorial representation of
the gearbox describing the arrangement of gears. It also provides the number of
stages (shafts), the pair of gears that will mesh and their arrangement.
4.20) Distinguish between structural diagram and speed diagram.
[AU, Nov / Dec –2011]
Structural diagram (or) Kinematic layout is a pictorial representation of
the gearbox describing the arrangement of gears. It also provides the number of
stages (shafts), the pair of gears that will mesh and their arrangement.
4.21) What is step ratio? [AU, May / Jun – 2007, Nov / Dec –2013, 2016]
Step ratio (or) Progression ratio, ϕ is the ratio between the maximum
speed to the minimum speed among the two adjacent speeds in a transmission. In
other words, it is the ratio between one speed to the previous lower speed.
𝜙 𝑛−1
=
𝑁 𝑚𝑎𝑥
𝑁 𝑚𝑖𝑛
4.22) What is step ratio in gear box? [AU, May / Jun – 2012]
Step ratio (or) Progression ratio, ϕ is the ratio between the maximum
speed to the minimum speed among the two adjacent speeds in a transmission. In
other words, it is the ratio between one speed to the previous lower speed.
𝜙 𝑛−1
=
𝑁 𝑚𝑎𝑥
𝑁 𝑚𝑖𝑛

ME6601 DESIGN OF TRANSMISSION SYSTEMS TWO MARK QUESTION & ANSWERS

ME6601 DESIGN OF TRANSMISSION SYSTEMS TWO MARK QUESTION & ANSWERS

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ME6601 DESIGN OF TRANSMISSION SYSTEMS TWO MARK QUESTION & ANSWERS