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PEC University of Technology, Chandigarh

Production Engineering Department

CAPSTONE PROJECT (8th Semester)

DESIGN & FABRICATION OF

MOTORIZED SCREW JACK

Submitted by:-

10109001 - Abhishek Garg

10109002 - Akhil Chowdhary

10109012 - Lacshay Shekhar

10109036 - Anshit Malik

10109038 - Chinmay Pandit

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DECLARATION

We hereby declare that the project work entitled “Design & Fabrication of

Motorized Screw Jack” is an authentic record of our own work carried out at PEC

University of Technology, Chandigarh as part of our 4-year B.E. degree in Production

Engineering at PEC University of Technology, Chandigarh, under the guidance of our

professors and workshop heads from the department.

Date: ___________________

Signature of the Students involved in the Project Work –

Abhishek Garg :

Akhil Chowdhary :

Lacshay Shekhar :

Anshit Malik :

Chinmay Pandit :

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ACKNOWLEDGEMENT

We would like to express our sincere regards to all our professors in the Production

Department at PEC University of Technology, Chandigarh who took us under their

wing and flooded us with information to succeed in this project. We are very

thankful to them for giving us the charge and backing us up at every turn of this

project with their abundant experience in the field of Production Technology.

Our special thanks goes to Mr. Jasbir Singh for teaching us the practical methods for

machining and fabrication of different components required in this project. He has

been an inspiration to us all and this project would not have completed without his

innovative ideas to help us along the way.

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NOMENCLATURE p - Pitch of screw thread (mm) l - Lead of screw thread (mm) d - Nominal diameter of screw (mm) dc - Core diameter of screw (mm) dm - Mean diameter of screw α - Helix angle of screw (degree) W - Load (kg) N - Normal reaction μ - Coefficient of friction P - Effort (N) θ - Friction angle (degree) T - Torque (N.m) η - Efficiency (%) Fc - Direct compressive stress (N/mm2) Ft - Torsional shear stress (N/mm2) Fs - Principal shear stress (N/mm2) Ts - Transverse shear stress (N/mm2) t - Thread thickness at the core diameter (mm) n - Number of threads in engagement with the nut. Tn - Transverse shear stress at the root of the nut (N/mm²) Pb - Unit bearing pressure (N/mm²) k - Least radius of gyration of the cross-section about its axis (mm) I - Least moment of inertia of the cross-section (mm4) A - Area of the cross-section (mm2) Pcr - critical load (N). E - Modulus of elasticity (N/mm²) Syt - Yield strength of the material (N/mm2) M - Maximum bending moment at the critical section WT - Tangential load acting at the tooth (N) h - Length of the tooth (mm) y - Half of the thickness of the tooth (t) at critical section (mm) b - Width of gear face (mm) Fw - Permissible working stress y - Lewis form factor Fo - allowable static stress (N/mm2) Cv - velocity factor. v - Pitch line velocity (m/s.) WD - Total dynamic load (N) WT - Steady transmitted load (N), WI - Incremental load due to dynamic action (N) C - A deformation or dynamic factor (N/mm) K - A factor depending upon the form of the teeth of a gear EP - Young‟s modulus for the material of the pinion in N/mm2

EG - Young‟s modulus for the material of the gear in N/mm2

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e - Tooth error action in mm WS - Static tooth load (N) Wd - Dynamic tooth load Ww - Maximum or limiting load for wear (N) Dp - Pitch circle diameter of the pinion in mm Q - Ratio factor K - Load stress factor (N/mm2) - Surface endurance limit (N/mm²) - Pressure angle N1 - Motor speed (RPM) N2 - Output speed (RPM) D2 - Diameter of the roller gear wheel (mm) D1 - Diameter of the motor gear wheel (mm)

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ABSTRACT

With the increasing levels of technology, the efforts being put to produce any kind

of work has been continuously decreasing. The efforts required in achieving the

desired output can be effectively and economically be decreased by the

implementation of better designs.

Power screws are used to convert rotary motion into translatory motion. A screw

jack is an example of a power screw in which a small force applied in a horizontal

plane is used to raise or lower a large load. The principle on which it works is similar

to that of an inclined plane. The mechanical advantage of a screw jack is the ratio

of the load applied to the effort applied. The screw jack is operated by turning a

lead screw. The height of the jack is adjusted by turning a lead screw and this

adjustment can be done either manually or by integrating an electric motor.

In this project, an electric motor will be integrated with the screw jack and the

electricity needed for the operation will be taken from the battery of the vehicle

and thereby the mechanical advantage will be increased.

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CONTENTS

DECLARATION ........................................................................................................ 2

ACKNOWLEDGEMENT ............................................................................................ 3

NOMENCLATURE .................................................................................................... 4

ABSTRACT .............................................................................................................. 6

Chapter I. LITERATURE SURVEY ....................................................................... 10

Chapter II. POWER SCREWS ............................................................................. 14

Section 2.01 Applications ............................................................................... 14

Section 2.02 Advantages ................................................................................ 14

Section 2.03 Disadvantages ........................................................................... 15

Section 2.04 Forms of Threads ....................................................................... 16

(a) Advantages of square threads .............................................................. 16

(b) Disadvantages of square threads .......................................................... 16

(c) Advantages of Trapezoidal Threads ....................................................... 17

(d) Disadvantages of Trapezoidal Threads .................................................. 17

(e) Advantages of Buttress Threads ............................................................ 18

Section 2.05 Designation of Threads .............................................................. 19

(a) Multiple Threaded Power Screws ......................................................... 19

Section 2.06 Terminology of Power Screw ..................................................... 20

Section 2.07 Torque Requirement- Lifting Load .............................................. 22

Section 2.08 Torque Requirement- Lowering Load ......................................... 24

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Section 2.09 Self-Locking Screw ..................................................................... 25

Section 2.10 Efficiency of Square Threaded Screw ......................................... 26

Section 2.11 Coefficient of Friction ................................................................ 27

Section 2.12 Buckling of Columns .................................................................. 27

Chapter III. SCREW JACK ................................................................................... 30

Section 3.01 The Screw .................................................................................. 31

Section 3.02 Operation .................................................................................. 31

Section 3.03 Construction of a Screw Jack ..................................................... 32

Section 3.04 Function .................................................................................... 32

Section 3.05 Features ..................................................................................... 32

Section 3.06 Benefits ..................................................................................... 33

Section 3.07 Types ......................................................................................... 33

(a) Mechanical Jacks .................................................................................. 33

(b) Hydraulic Jacks ...................................................................................... 36

Section 3.08 Design of Screw Jack .................................................................. 37

(a) Loads & Stresses in a Screw .................................................................. 37

(b) Thrust Bearings ..................................................................................... 39

(c) Operational Considerations of a Screw Jack .......................................... 40

Chapter IV. MOTORIZED SCREW JACK ............................................................... 42

Section 4.01 Introduction .............................................................................. 42

Section 4.02 Need for Automation ................................................................. 42

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Section 4.03 Parts of Motorized Screw Jack ................................................... 43

(a) Power Source ........................................................................................ 44

(b) Toggle Switch ........................................................................................ 45

(c) Control Cables ...................................................................................... 46

(d) 12V DC Motor ....................................................................................... 46

(e) Connecting Shaft .................................................................................. 47

(f) Screw Jack ............................................................................................ 48

Section 4.04 Advantages ................................................................................ 49

Chapter V. DESIGN CALCULATIONS .................................................................. 50

Section 5.01 To Check the Safety of Lead Screw ............................................. 50

Section 5.02 To Check Buckling of Screw ........................................................ 51

Chapter VI. conclusion ...................................................................................... 52

Chapter VII. Bibliography ................................................................................ 53

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CHAPTER I. LITERATURE SURVEY

Screw type mechanical jacks were very common for jeeps and trucks of World War

II vintage. For example, the World War II jeeps (Willys MB and Ford GPW) were

issued the "Jack, Automobile, Screw type, Capacity 1 1/2 ton", Ordnance part

number 41-J-66. This jacks, and similar jacks for trucks, were activated by using the

lug wrench as a handle for the jack's ratchet action to of the jack. The 41-J-66 jack

was carried in the jeep's tool compartment. Screw type jack's continued in use for

small capacity requirements due to low cost of production raise or lower it. A

control tab is marked up/down and its position determines the direction of

movement and almost no maintenance.

The virtues of using a screw as a machine, essentially an inclined plane wound

round a cylinder, was first demonstrated by Archimedes in 200BC with his device

used for pumping water.

There is evidence of the use of screws in the Ancient Roman world but it was the

great Leonardo da Vinci, in the late 1400s, who first demonstrated the use of a

screw jack for lifting loads. Leonardo’s design used a threaded worm gear,

supported on bearings, that rotated by the turning of a worm shaft to drive a lifting

screw to move the load - instantly recognizable as the principle we use today.

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We can’t be sure of the intended application of his invention, but it seems to have

been relegated to the history books, along with the helicopter and tank, for almost

four centuries. It is not until the late 1800s that we have evidence of the product

being developed further.

With the industrial revolution of the late 18th and 19th centuries came the first use

of screws in machine tools, via English inventors such as John Wilkinson and Henry

Maudsley The most notable inventor in mechanical engineering from the early

1800s was undoubtedly the mechanical genius Joseph Whitworth, who recognized

the need for precision had become as important in industry as the provision of

power.

While he would eventually have over 50 British patents with titles ranging from

knitting machines to rifles, it was Whitworth’s work on screw cutting machines,

accurate measuring instruments and standards covering the angle and pitch of

screw threads that would most influence our industry today.

Whitworth’s tools had become internationally famous for their precision and

quality and dominated the market from the 1850s. Inspired young engineers began

to put Whitworth’s machine tools to new uses. During the early 1880s in Coaticook,

a small town near Quebec, a 24-year-old inventor named Frank Henry Sleeper

designed a lifting jack. Like da Vinci’s jack, it was a technological innovation because

it was based on the principle of the ball bearing for supporting a load and

transferred rotary motion, through gearing and a screw, into linear motion for

moving the load. The device was efficient, reliable and easy to operate. It was used

in the construction of bridges, but mostly by the railroad industry, where it was able

to lift locomotives and railway cars.

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Local Coaticook industrialist, Arthur Osmore Norton, spotted the potential for

Sleeper’s design and in 1886 hired the young man and purchased the patent. The

“Norton” jack was born. Over the coming years the famous “Norton” jacks were

manufactured at plants in Boston, Coaticook and Moline, Illinois.

Meanwhile, in Alleghany County near Pittsburgh in 1883, an enterprising

Mississippi river boat captain named Josiah Barrett had an idea for a ratchet jack

that would pull barges together to form a „tow‟. The idea was based on the familiar

lever and fulcrum principle and he needed someone to manufacture it. That person

was Samuel Duff, proprietor of a local machine shop.

Together, they created the Duff Manufacturing Company, which by 1890 had

developed new applications for the original „Barrett Jack‟ and extended the

product line to seven models in varying capacities.

Over the next 30 years the Duff Manufacturing Company became the largest

manufacturer of lifting jacks in the world, developing many new types of jack for

various applications including its own version of the ball bearing screw jack. It was

only natural that in 1928, The Duff Manufacturing Company Inc. merged with A.O.

Norton to create the Duff-Norton Manufacturing Company.

Both companies had offered manually operated screw jacks but the first new

product manufactured under the joint venture was the air motor-operated power

jack that appeared in 1929. With the aid of the relatively new portable compressor

technology, users now could move and position loads without manual effort. The

jack, used predominantly in the railway industry, incorporated an air motor

manufactured by The Chicago Pneumatic Tool Company.

Air Motor Power Jack

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There was clearly potential for using this technology for other applications and only

10 years later, in 1940, the first worm gear screw jack, that is instantly recognizable

today, was offered by Duff-Norton, for adjusting the heights of truck loading

platforms and mill tables. With the ability to be used individually or linked

mechanically and driven by either air or electric motors or even manually, the first

model had a lifting capacity of 10 tons with raises of 2” or 4”.

Since then the product has evolved to push, pull, lift, lower and position loads of

anything from a few kilos to hundreds of tonnes. One of the biggest single screw

jacks made to date is a special Power Jacks E-Series unit that is rated for 350 tonnes

–even in earthquake conditions for the nuclear industry.

More recent developments have concentrated on improved efficiency and

durability, resulting in changes in both lead screw and gearbox design options for

screw jacks.

A screw jack that has a built-in motor is now referred to as a linear actuator but is

essentially still a screw jack. Today, screw jacks can be linked mechanically or

electronically and with the advances in motion-control, loads can be positioned to

within microns. Improvements in gear technology together with the addition of

precision ball screws and roller screws mean the applications for screw jacks today

are endless and a real alternative to hydraulics in terms of duty cycles and speed at

a time when industry demands cleaner, quieter and more reliable solutions.

Worm Gear Jack

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CHAPTER II. POWER SCREWS

A power screw is a mechanical device used for converting rotary motion into linear

motion and transmitting power. A power screw is also called translation screw. It

uses helical translatory motion of the screw thread in transmitting power rather

than clamping the machine components.

Section 2.01 Applications

The main applications of power screws are as follows:

(i) To raise the load, e.g. screw-jack,

(ii) To obtain accurate motion in machining operations, e.g. lead-screw of lathe,

(iii) To clamp a work-piece, e.g. vice, and

(iv) To load a specimen, e.g. universal testing machine.

There are three essential parts of a power screw, viz. screw, nut and a part to hold

either the screw or the nut in its place. Depending upon the holding arrangement,

power screws operate in two different ways. In some cases, the screw rotates in its

bearing, while the nut has axial motion. The lead screw of the lathe is an example

of this category. In other applications, the nut is kept stationary and the screw

moves in axial direction. Screw-jack and machine vice are the examples of this

category.

Section 2.02 Advantages

Power screws offer the following advantages:

(i) Power screw has large load carrying capacity.

(ii) The overall dimensions of the power screw are small, resulting in compact

construction.

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(iii) Power screw is simple to design

(iv) The manufacturing of power screw is easy without requiring specialized

machinery. Square threads are turned on lathe. Trapezoidal threads are

manufactured on thread milling machine.

(v) Power screw provides large mechanical advantage. A load of 15 kN can be raised

by applying an effort as small as 400 N. Therefore, most of the power screws used

in various applications like screw-jacks, clamps, valves and vices are usually

manually operated.

(vi) Power screws provide precisely controlled and highly accurate linear motion

required in machine tool applications.

(vii) Power screws give smooth and noiseless service without any maintenance.

(viii) There are only a few parts in power screw. This reduces cost and increases

reliability.

(ix) Power screw can be designed with self-locking property. In screw-jack

application, self-locking characteristic is required to prevent the load from

descending on its own.

Section 2.03 Disadvantages

The disadvantages of power screws are as follows:

(i) Power screws have very poor efficiency; as low as 40%.Therefore, it is not used

in continuous power transmission in machine tools, with the exception of the lead

screw. Power screws are mainly used for intermittent motion that is occasionally

required for lifting the load or actuating the mechanism.

(ii) High friction in threads causes rapid wear of the screw or the nut. In case of

square threads, the nut is usually made of soft material and replaced when worn

out. In trapezoidal threads, a split- type of nut is used to compensate for the wear.

Therefore, wear is a serious problem in power screws.

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Section 2.04 Forms of Threads

There are two popular types of threads used for power screws viz. square and I.S.O

metric trapezoidal.

(a) Advantages of square threads

The advantages of square threads over trapezoidal threads are as follows:

(i) The efficiency of square threads is more than that of trapezoidal threads.

(ii) There is no radial pressure on the nut.

Since there is no side thrust, the motion of the nut is uniform. The life of the nut is

also increased.

(b) Disadvantages of square threads

The disadvantages of square threads are as follows:

(i) Square threads are difficult to manufacture. They are usually turned on lathe

with single-point cutting tool. Machining with single-point cutting tool is an

expensive operation compared to machining with multi-point cutting tool.

(ii) The strength of a screw depends upon the thread thickness at the core diameter.

Square threads have less thickness at core diameter than trapezoidal threads. This

reduces the load carrying capacity of the screw.

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(iii) The wear of the thread surface becomes a serious problem in the service life of

the power screw. It is not possible to compensate for wear in square threads.

Therefore, when worn out, the nut or the screw requires replacement.

(c) Advantages of Trapezoidal Threads

The advantages of trapezoidal threads over square threads are as follows:

(i) Trapezoidal threads are manufactured on thread milling machine. It employs

multi-point cutting tool. Machining with multi-point cutting tool is an economic

operation compared to machining with single point-cutting tool. Therefore,

trapezoidal threads are economical to manufacture.

(ii) Trapezoidal thread has more thickness at core diameter than that of square

thread. Therefore, a screw with trapezoidal threads is stronger than equivalent

screw with square threads. Such a screw has large load carrying capacity.

(iii) The axial wear on the surface of the trapezoidal threads can be compensated

by means of a split-type of nut. The nut is cut into two parts along the diameter. As

wear progresses, the looseness is prevented by tightening the two halves of the nut

together, the split-type nut can be used only for trapezoidal threads. It is used in

lead-screw of lathe to compensate wear at periodic intervals by tightening the two

halves.

(d) Disadvantages of Trapezoidal Threads

The disadvantages of trapezoidal threads are as follows:

(i) The efficiency of trapezoidal threads is less than that of square threads.

(ii) Trapezoidal threads result in side thrust or radial pressure on the nut. The radial

pressure or bursting pressure on nut affects its performance.

There is a special type of thread called acme thread. Trapezoidal and acme threads

are identical in all respects except the thread angle. In acme thread, the thread

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angle is 29° instead of 30°.The relative advantages and disadvantages of acme

threads are same as those of trapezoidal threads.

There is another type of thread called buttress thread. It combines the advantages

of square and trapezoidal threads. Buttress threads are used where heavy axial

force acts along the screw axis in one direction only.

(e) Advantages of Buttress Threads

The advantages of buttress threads are as follows:

(i) It has higher efficiency compared to trapezoidal threads.

(ii) It can be economically manufactured on thread milling machine.

(iii) The axial wear at the thread surface can be compared by means of spit-type

nut.

(iv) A screw with buttress threads is stronger than equivalent screw with either

square threads or trapezoidal threads. This is because of greater thickness at the

base of the thread.

The buttress threads have one disadvantage. It can transmit power and motion only

in one direction. On the other hand, square and trapezoidal threads can transmit

force and motion in both directions.

Square threads are used for screw-jacks, presses and clamping devices. Trapezoidal

and acme threads are used for lead-screw and other power transmission devices in

machine tools. Buttress threads are used in vices, where force is applied only in one

direction. Buttress threads are ideally suited for connecting tubular components

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that must carry large forces such as connecting the barrel to the housing in anti-

aircraft guns.

Section 2.05 Designation of Threads

There is a particular method of designation for square and trapezoidal threads. A

power screw with single-start square threads is designated by the letters “Sq”

followed by the nominal diameter and the pitch expressed in millimeters and

separated by the sign “x”. For example,

Sq 30 x 6

It indicates single-start square threads with 30mm nominal diameter and 6mm

pitch.

Similarly single-start I.S.O metric trapezoidal threads are designated by letters „Tr‟

followed by the nominal diameter and the pitch expressed in millimeters and

separated by the sign “x”. For example,

Tr 40x7

It indicates single-start trapezoidal threads with 40mm nominal diameter and 7mm

pitch.

(a) Multiple Threaded Power Screws

Multiple threaded power screws are used in certain applications where higher

travelling speed is required. They are also called multiple start screws such as

double-start or triple-start screws. These screws have two or more threads cut side

by side, around the rod.

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Multiple-start trapezoidal threads are designated by letters “Tr” followed by the

nominal diameter and the lead, separated by sign “x” and in brackets the letter “P”

followed by the pitch expressed in millimetres. For example,

Tr 40 x 14 (P7)

In above designation,

Lead=14mm pitch=7mm

Therefore, No. of starts =14/7=2

It indicates two-start trapezoidal thread with 40mm nominal diameter and 7mm

pitch. In case of left handed threads. The letters „LH‟ are added to thread

designation. For example,

Tr 40 x 14 (P7) LH

Section 2.06 Terminology of Power Screw

The terminology of the screw thread is as follows:

(i) Pitch: The pitch is defined as the distance, measured parallel to the axis of the

screw, from a point on one thread to the corresponding point on the adjacent

thread. It is denoted by the letter “p”.

(ii) Lead: The lead is defined as the distance, measured parallel to the axis of the

screw, that the nut will advance in one revolution of the screw. It is denoted by the

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letter „l‟. For a single-threaded screw, the lead is same as the pitch, for a double-

threaded screw, the lead is twice that of the pitch, and so on.

(iii) Nominal diameter: It is the largest diameter of the screw. It is also called major

diameter. It is denoted by the letter “d”.

(iv) Core diameter: It is the smallest diameter of the screw thread. It is also called

minor diameter. It is denoted by the letters “dc”.

(v) Helix angle: It is defined as the angle made by the helix of the thread with a

plane perpendicular to the axis of the screw. Helix angle is related to the lead and

the mean diameter of the screw. It is also called lead angle. It is denoted by α.

From the figure, dc = d – [p/2 + p/2]

or, d = d – (p)

The mean diameter of the screw is denoted by dm and it is given by, dm = 0.5[d + dc]

= [d + (d-p)]

or, dm= (d-0.5p)

Imagine that one thread of the screw is unwound and developed for one complete

turn. The thread will become the hypotenuse of a right-angled triangle, whose base

is (πdm) and whose height is the lead (l).Considering this right-angle triangle, the

relationship between helix angle, mean diameter and lead can be expressed in the

following form,

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Tan α = 𝑙

𝜋𝑑𝑚

Where, α is the helix angle of the thread.

The following conclusions can be drawn on the basis of the development of thread:

(i) The screw can be considered as an inclined plane with α as inclination.

(ii) The load W always acts in vertically downward direction. When the load W is

raised, it moves up the inclined plane. When the load W is lowered, it moves down

the inclined plane.

(iii) The load W is raised or lowered by means of an imaginary force P acting at the

mean radius of the screw. The force P multiplied by the mean radius (dm/2) gives

the torque required to raise or lower the load. Force P is perpendicular to load W.

Section 2.07 Torque Requirement- Lifting Load

The screw is considered as an inclined plane with inclination α.When the load is

being raised, following forces act at a point on this inclined plane:

(i) Load W: It always acts in vertically downward direction.

(ii) Normal reaction N: It acts perpendicular (normal) to the inclined plane.

(iii) Frictional force μN: Frictional force acts opposite to the motion. Since the load

is moving up the inclined plane, frictional force acts along the inclined plane in

downward direction.

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(iv) Effort P: The effort P acts in a direction perpendicular to the load W. It may act

towards right to overcome the friction and raise the load.

For an equilibrium of horizontal forces,

P = μ N cos α + N sin α (a)

For an equilibrium of vertical forces,

W = N cos α – μ N sin α (b)

Dividing expression (a) by (b),

𝑝 = 𝑊(𝜇.𝑐𝑜𝑠𝛼+𝑠𝑖𝑛𝛼)

(𝑐𝑜𝑠𝛼−𝜇.𝑠𝑖𝑛𝛼) (c)

Dividing the numerator and denominator of the right hand side by cos α,

𝑝 = 𝑊(𝜇 + 𝑡𝑎𝑛𝛼)

(1 − 𝜇. 𝑡𝑎𝑛𝛼)

The coefficient of friction μ is expressed as,

μ = tan θ (d)

where, θ is the friction angle.

Substituting μ = tan θ in Eq. (c),

𝑝 = 𝑊(𝑡𝑎𝑛𝜃 + 𝑡𝑎𝑛𝛼)

(1 − 𝑡𝑎𝑛𝜃. 𝑡𝑎𝑛𝛼)

or, P = W tan (θ + α) (e)

The torque “T” required to raise the load is given by,

T = P . dm/2 = W . dm/2 . tan(θ + α)

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Section 2.08 Torque Requirement- Lowering Load

When the load is being lowered, the following forces act at a point on the inclined

plane:

(i) Load W: It always acts in vertically downward direction.

(ii) Normal reaction N: It acts perpendicular (normal) to the inclined plane.

(iii) Frictional force μN: Frictional force acts opposite to the motion. Since the load

is moving down the inclined plane, frictional force acts along the inclined plane in

upward direction.

(iv) Effort P: The effort P acts in a direction perpendicular to the load W.It should

act towards left to overcome the friction and lower the load.

For an equilibrium of horizontal forces,

P = μ N cos α - N sin α (a)

For an equilibrium of vertical forces,

W = N cos α + μ N sin α (b)

Therefore, P = W tan (θ - α)

The torque “T” required to lower the load is given by,

T = W . dm/2 . tan(θ - α)

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Section 2.09 Self-Locking Screw

The torque required to lower the load can be given by,

T = W . dm/2 . tan(θ - α)

It can be seen that when, θ < α; the torque required to lower the load is negative.

It indicates a condition that no force is required to lower the load. The load itself

will begin to turn the screw and descend down, unless a restraining torque is

applied. This condition is called “overhauling” of screw.

When, θ > α; a positive torque is required to lower the load. Under this condition,

the load will not turn the screw and will not descend on its own unless effort P is

applied. In this case, the screw is said to be “self-locking”. The rule for self-locking

screw is as follows:

A screw will be self-locking if the coefficient of friction ids equal to or greater than

the tangent of the helix angle.

Therefore, the following conclusions can be made:

(i) Self-locking of screw is not possible when the coefficient of friction (μ) is low. The

coefficient of friction between the surfaces of the screw and the nut is reduced by

lubrication. Excessive lubrication may cause the load to descend on its own.

(ii) Self-locking property of the screw is lost when the lead is large. The lead

increases with number of starts. For double-start thread, lead is twice of the pitch

and for triple threaded screw, three times of pitch. Therefore, single threaded is

better than multiple threaded screw from self-locking considerations.

Self-locking condition is essential in applications like screw-jack.

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Section 2.10 Efficiency of Square Threaded Screw

Refer to the force diagram for lifting the load, illustrated in Fig. Suppose the load W

moves from the lower end to the upper end of the inclined plane. The output

consists of raising the load.

𝜂 = 𝑡𝑎𝑛𝛼

tan (𝜃 + 𝛼)

From the above equation, it is evident that the efficiency of the square threaded

screw depends upon the helix angle α and the friction angle θ. The following figure

shows the variation of the efficiency of square threaded screw against the helix

angle for various values of coefficient of friction. The graph is applicable when the

load is lifted.

Following conclusions can be derived from the observation of these graphs,

(i) The efficiency of square threaded screw increase rapidly up to helix angle of 20°.

(ii) The efficiency is maximum when the helix angle between 40 to 45°.

(iii) The efficiency decreases after the maximum value is reached.

(iv) The efficiency decreases rapidly when the helix angle exceeds 60°

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(v) The efficiency decreases as the coefficient of friction increases.

There are two ways to increase the efficiency of square threaded screws. They are

as follows:

(i) Reduce the coefficient of friction between the screw and the nut by proper

lubrication, and

(ii) Increase the helix angle up to 40 to 45° by using multiple start threads.

However, a screw with such helix angle has other disadvantages like loss of self-

locking property.

Section 2.11 Coefficient of Friction

It has been found that the coefficient of friction (μ) at the thread surface depends

upon the workmanship in cutting the threads and on the type of the lubricant. It is

practically independent of the load, rubbing velocity or materials. An average of

0.15 can be taken for the coefficient of friction, when the screw is lubricated with

mineral oil.

Section 2.12 Buckling of Columns

When a short member is subjected to axial compressive force, it shortens according

to the Hooke‟s law. As the load is gradually increased, the compression of the

member increases.

When the compressive stress reaches the elastic limit of the material, the failure

occurs in the form of bulging. However, when the length of the component is large

compared to the cross-sectional dimensions, the component may fail by lateral

buckling. Buckling indicates elastic instability. The load at which the buckling starts

is called critical load, which is denoted by Pcr. When the axial load on the column

reaches Pcr, there is sudden buckling and a relatively large lateral deflection occurs.

28

An important parameter affecting the critical load is the slenderness ratio. It is

defined as,

Slenderness ratio = 𝑙

𝑘

where, l = length of column (mm)

k = least radius of gyration of the cross-section about its axis (mm)

The radius of gyration is given by,

𝑘 = √𝐼

𝐴

where, I = least moment of inertia of the cross-section (mm4)

A = area of the cross-section (mm2)

When the slenderness ratio is less than 30, there is no effect of buckling and such

components are designed on the basis of compressive stresses. Columns, with

slenderness ratio greater than 30 are designed on the basis of critical load. There

are two methods to calculate the critical load- Euler’s equation and Johnson’s

equation.

According to the Euler’s equation,

𝑃𝑐𝑟 =𝑛𝜋2𝐸𝐴

(𝑙𝑘

)2

where, Pcr = critical load (N); n = end fixity coefficient

E = modulus of elasticity (N/mm²); A = area of cross-section (mm²)

The load carrying capacity of the column depends upon the condition of restraints

at the two ends of the column. It is accounted by means of a dimensionless quantity

called end fixity coefficient (n).

According to Johnson’s equation,

29

𝑃𝑐𝑟 = 𝑆𝑦𝑡𝐴[1 −𝑠𝑦𝑡

4𝜋𝑛2𝐸𝑥 (

𝑙

𝑘)

2

]

Where, Syt is the yield strength of the material.

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CHAPTER III. SCREW JACK

A screw jack is a portable device consisting of a screw mechanism used to raise or

lower the load. The principle on which the screw jack works is similar to that of an

inclined plane. There are mainly two types of jacks-hydraulic and mechanical. A

hydraulic jack consists of a cylinder and piston mechanism. The movement of the

piston rod is used to raise or lower the load. Mechanical jacks can be either hand

operated or power driven.

Jacks are used frequently in raising cars so that a tire can be changed. A screw jack

is commonly used with cars but is also used in many other ways, including industrial

machinery and even airplanes. They can be short, tall, fat, or thin depending on the

amount of pressure they will be under and the space that they need to fit into. The

jack is made out of various types of metal, but the screw itself is generally made

out of lead.

While screw jacks are designed purposely for raising and lowering loads, they are

not ideal for side loads, although some can withstand side loads depending on the

diameter and size of the lifting screw. Shock loads should also be avoided or

minimized. Some screw jacks are built with anti-backlash. The anti-backlash device

moderates the axial backlash in the lifting screw and nut assembly to a regulated

minimum.

A large amount of heat is generated in the screw jack and long lifts can cause serious

overheating. To retain the efficiency of the screw jack, it must be used under

ambient temperatures, otherwise lubricants must be applied. There are oil

lubricants intended to enhance the equipment’s capabilities. Apart from proper

maintenance, to optimize the capability and usefulness of a screw jack it is

imperative to employ it according to its design and manufacturer’s instruction.

Ensure that you follow the speed, load capacity, temperature recommendation and

other relevant factors for application.

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Section 3.01 The Screw

The screw has a thread designed to withstand an enormous amount of pressure.

This is due to the fact that it is generally holding up heavy objects for an extended

amount of time. Once up, they normally self-lock so that they won't fall if the

operator lets go, and they hold up well to the wear of repeated use. If they are made

with a ball nut, they will last longer because there is less friction created with this

type of jack. However, they will not self-lock. This can be dangerous and handled

carefully.

Section 3.02 Operation

The jack can be raised and lowered with a metal bar that is inserted into the jack.

The operator turns the bar with his hands in a clockwise direction. This turns the

screw inside the jack and makes it go up. The screw lifts the small metal cylinder

and platform that are above it. As the jack goes up, whatever is placed above it will

raise as well, once the jack makes contact. The bar is turned until the jack is raised

to the level needed. To lower the jack the bar is turned in the opposite direction.

An automatic screw jack has gears inside the jack that are connected to the screw.

Theses gears are connected by other gears and bars that are turned by a power

source to raise and lower the jack.

Although a jack is a simple and widely used device, the use of any lifting device is

subject to certain hazards. In screw-jack applications, the hazards are dropping,

tipping or slipping of machines or their parts during the operation. These hazards

may result in serious accidents. The main reasons of such accidents are as follows:

(i) The load is improperly secured on the jack

(ii) The screw-jack is over loaded

(iii) The centre of gravity of the load is off centre with respect to the axis of the jack

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(iv) The screw-jack is not placed on hard and level surface.

(v) The screw-jack is used for a purpose, for which it is not designed.

Proper size, strength and stability are the essential requirements for the design of

the screw-jack from safety considerations.

Section 3.03 Construction of a Screw Jack

Screw jack consists of a screw and a nut. The nut is fixed in a cast iron frame and

remains stationary. The rotation of the nut inside the frame is prevented by pressing

a set screw against it. The screw is rotated in the nut by means of a handle, which

passes through a hole in the head of the screw. The head carries a platform, which

supports the load and remains stationary while the screw is being rotated. A washer

is fixed to the other end of the screw inside the frame, which prevents the screw to

be completely turned out of the nut.

Section 3.04 Function

The basic function of a screw jack is to lift a portion of a vehicle. Typically this is

used to change a tire although other maintenance is sometimes performed.

Section 3.05 Features

All jacks have safety features to protect the user from accidental injury. Wide bases

help to stabilize a jack and prevent tilting or sinking into soft soil. Most car jacks also

come equipped with their own handle or cranking mechanism, but alternately

many of these also will accept the flat end of a tire tool to jack up a vehicle. When

in the extended position, jacks will have a stop point that prevents the user from

overextending the jack beyond its rated capabilities. When in the contracted

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position, jacks that are provided by the manufacturer will have a storage area

specially formed or designed for the jack to rest in when not in use.

Section 3.06 Benefits

Equipping motorists with car jacks has provided many benefits to those who are on

the road. Most importantly, jacks have equipped drivers with the ability to change

a tire in an emergency situation without having to call for assistance, which can save

service fees and potential towing fees as well. Car jacks also provide the home auto

enthusiast with a tool to use in maintenance of their own vehicle with the simpler

tasks such as changing brake pads, oil and belts. When used appropriately with

safety in mind, car jacks are an essential resource for anyone owning or operating

a motorized vehicle.

Section 3.07 Types

Screw Jacks are of mainly two types- mechanical and hydraulic. They vary in size

depending on the load that they are used to lift:

(a) Mechanical Jacks

A mechanical jack is a device which lifts heavy equipment. The most common form

is a car jack, floor jack or garage jack which lifts vehicles so that maintenance can

be performed. Car jacks usually use mechanical advantage to allow a human to lift

a vehicle by manual force alone. More powerful jacks use hydraulic power to

provide more lift over greater distances. Mechanical jacks are usually rated for

maximum lifting capacity. There are two types of mechanical jacks.

(i) Scissor Jacks

Scissors jacks are also mechanical and have been in use at least since the 1930s.

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A scissor jack is a device constructed with a cross-hatch mechanism, much like a

scissor, to lift up a vehicle for repair or storage. It typically works in just a vertical

manner. The jack opens and folds closed, applying pressure to the bottom supports

along the crossed pattern to move the lift. When closed, they have a diamond

shape.

Scissor jacks are simple mechanisms used to drive large loads short distances. The

power screw design of a common scissor jack reduces the amount of force required

by the user to drive the mechanism. Most scissor jacks are similar in design,

consisting of four main members driven by a power screw.

A scissor jack is operated simply by turning a small crank that is inserted into one

end of the scissor jack. This crank is usually "Z" shaped. The end fits into a ring hole

mounted on the end of the screw, which is the object of force on the scissor jack.

When this crank is turned, the screw turns, and this raises the jack. The screw acts

like a gear mechanism. It has teeth (the screw thread), which turn and move the

two arms, producing work. Just by turning this screw thread, the scissor jack can lift

a vehicle that is several thousand pounds.

1) Construction

A scissor jack has four main pieces of metal and two base ends. The four metal

pieces are all connected at the corners with a bolt that allows the corners to swivel.

A screw thread runs across this assembly and through the corners. As the screw

thread is turned, the jack arms travel across it and collapse or come together,

forming a straight line when closed. Then, moving back the other way, they raise

and come together. When opened, the four metal arms contract together, coming

together at the middle, raising the jack. When closed, the arms spread back apart

and the jack closes or flattens out again.

2) Design & Lift

A scissor jack uses a simple theory of gears to get its power. As the screw section is

turned, two ends of the jack move closer together. Because the gears of the screw

are pushing up the arms, the amount of force being applied is multiplied. It takes a

35 | P a g e

very small amount of force to turn the crank handle, yet that action causes the

brace arms to slide across and together. As this happens the arms extend upward.

The car's gravitational weight is not enough to prevent the jack from opening or to

stop the screw from turning, since it is not applying force directly to it. If you were

to put pressure directly on the crank, or lean your weight against the crank, the

person would not be able to turn it, even though your weight is a small percentage

of the cars.

(ii) Bottle (or cylindrical) jacks

Bottle screws may operate by either,

(i) Rotating the screw when the nut is fixed; or

(ii) Rotating the nut and preventing rotation of the screw.

Bottle jacks mainly consist of a screw, a nut, thrust bearings, and a body. A

stationary platform is attached to the top of the screw. This platform acts as a

support for the load and also assists it in lifting or lowering of the load. These jacks

are sturdier than the scissor jacks and can lift heavier loads.

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(b) Hydraulic Jacks

Hydraulic jacks are typically used for shop work, rather than as an emergency jack

to be carried with the vehicle. Use of jacks not designed for a specific vehicle

requires more than the usual care in selecting ground conditions, the jacking point

on the vehicle, and to ensure stability when the jack is extended. Hydraulic jacks

are often used to lift elevators in low and medium rise buildings.

A hydraulic jack uses a fluid, which is incompressible, that is forced into a cylinder

by a pump plunger. Oil is used since it is self-lubricating and stable. When the

plunger pulls back, it draws oil out of the reservoir through a suction check valve

into the pump chamber. When the plunger moves forward, it pushes the oil through

a discharge check valve into the cylinder. The suction valve ball is within the

chamber and opens with each draw of the plunger. The discharge valve ball is

outside the chamber and opens when the oil is pushed into the cylinder. At this

point the suction ball within the chamber is forced shut and oil pressure builds in

the cylinder.

37 | P a g e

In a bottle jack the piston is vertical and directly supports a bearing pad that

contacts the object being lifted. With a single action piston the lift is somewhat less

than twice the collapsed height of the jack, making it suitable only for vehicles with

a relatively high clearance. For lifting structures such as houses the hydraulic

interconnection of multiple vertical jacks through valves enables the even

distribution of forces while enabling close control of the lift.

In a floor jack a horizontal piston pushes on the short end of a bell-crank, with the

long arm providing the vertical motion to a lifting pad, kept horizontal with a

horizontal linkage. Floor jacks usually include castors and wheels, allowing

compensation for the arc taken by the lifting pad. This mechanism provide a low

profile when collapsed, for easy maneuvering underneath the vehicle, while

allowing considerable extension.

Section 3.08 Design of Screw Jack

(a) Loads & Stresses in a Screw

The load on the screw is the load which is to be lifted W, twisting moment M,

between the screw threads and force F at the handle to rotate the screw.

The load W is compressive in nature and induces the compressive stress in the

screw. It may also lead the screw to buckle.

The load F produces bending and it is maximum, when the screw is at its maximum

lift. The screw also experiences twisting moment due to F. the shear stress is also

induced in the screw due to the twisting moment between the threads of screw

and nut.

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Step I Problem Specification

It is required to design a screw jack for supporting the machine parts during their

repair and maintenance. It should be a general purpose jack with a load carrying

capacity of 50KN and a maximum lifting height of 0.3m. The jack is to be operated

by means of a D.C motor.

Step II Selection of Materials

(i) The frame of the screw jack has complex shape. It is subjected to compressive

stress. Grey cast iron is selected as the material for the frame. Cast iron is cheap

and it can be given any complex shape without involving costly machining

operations. Cast iron has higher compressive strength compared with steel.

Therefore, it is technically and economically advantageous to use cast iron for the

frame.

(ii) The screw is subjected to torsional moment, compressive force and bending

moment. From strength consideration, EN8 is selected as material for screw.

39 | P a g e

Screw

(iii) There is a relative motion between the screw and the nut, which results in

friction. The friction causes wear at the contacting surfaces. When the same

material is used for these two components, the surfaces of both components get

worn out, requiring replacement. This is undesirable. The size and shape of the

screw make it costly compared with the nut. The material used for the nut is

stainless steel.

Nut

Step III Design of Screw

(i) The screw jack is an intermittently used device and wear of threads is not an

important consideration. Therefore, instead of trapezoidal threads, the screw is

provided with square threads. Square threads have higher efficiency and provision

can be made for self-locking arrangement. When the condition of self-locking is

fulfilled, the load itself will not turn the screw and descend down, unless an effort

in the reverse direction is applied

(b) Thrust Bearings

Thrust ball bearings are used to replace the sliding force with rolling friction. The

friction torque is so small, that it can be neglected.

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Thrust ball bearing is suitable for a purely axial load. It is a single-direction thrust

ball bearing, because it can support axial load in one direction only, i.e., vertically

downward. This ball bearing should not be subjected to radial load.

Single-direction thrust ball bearings are separable and the mounting is simple as

the components can be mounted individually. There are three separable parts of

this bearing known as shaft washer, a housing washer and the ball and cage

assembly. The mounting of thrust bearing I shown in the figure below.

Thrust Bearing

The inner diameter of the shaft washer is press fitted in the screw body. The outer

diameter of the housing washer is press fitted in the cup. These two components

are separately mounted before final assembly. The life of thrust bearing is assumed

to be 3000 hours.

(c) Operational Considerations of a Screw Jack

Maintain low surface contact pressure:

Increasing the screw size and nut size will reduce thread contact pressure for the

same working load. The higher the unit pressure and the higher the surface speed,

the more rapid the wear will be.

Maintain low surface speed:

Increasing the screw head will reduce the surface speed for the same linear speed.

41 | P a g e

Keep the mating surfaces well lubricated:

The better the lubrication, the longer is the service life. Grease fittings or other

lubrication means must be provided for the power screw and nut.

Keep the mating surfaces clean:

Dirt can easily embed itself in the soft nut material. It will act as a file and abrade

the mating screw surface. The soft nut material backs away during contact leaving

the hard dirt particles to scrap away the mating screw material.

Keep heat away:

When the mating surfaces heat up, they become much softer and are more easily

worn away. Means to remove the heat such as limited duty cycles or heat sinks must

be provided so that rapid wear of over-heated materials can be avoided.

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CHAPTER IV. MOTORIZED SCREW JACK

Section 4.01 Introduction

With the increasing levels of technology, the efforts being put to produce any kind

of work has been continuously decreasing. The efforts required in achieving the

desired output can be effectively and economically be decreased by the

implementation of better designs.

A screw jack is an important tool in any car as it lifts the car for any kind of service

or for a quick tyre change. In this project, a DC motor has been integrated with this

screw jack to make the process of lifting the car for any work a lot easier, just by

switching ‘on’ a push button. All the heavy lifting would be done by the motor.

This project concentrates on people who are not able to rotate the screw jack

properly (especially elderly people or women) or find it difficult to do so, and it also

caters to the needs of small and medium automobile garages in which loads of cars

have to be lifted in a day, which could drain a lot of stamina and cause fatigue. This

is a simple automation project in which the process to lift the car in an emergency

is semi-automated, i.e. it also requires a little manual or human effort.

The project along with achieving its main objectives, and strives to stay compact so

that it is also easily transported from one place to another without any hassle.

Section 4.02 Need for Automation

The manufacturing operation is being atomized for the following reasons:

To achieve mass production

To reduce man power

To increase the efficiency of the plant

To reduce the work load

To reduce the production cost

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To reduce the production time

To reduce the material handling

To reduce the fatigue of workers

To achieve good product quality

Less Maintenance

Section 4.03 Parts of Motorized Screw Jack

Fig. Block diagram showing the different parts in the motorized screw jack and their connections

– by Anshit Malik

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(a) Power Source

For a motor to rotate and properly carry out it’s operations, it needs certain amount

of power. This project is not just about integrating a motor into the screw jack, but

to do it efficiently such that the whole motorized screw jack stays compact, easy to

handle, use and effectively utilizes resources available easily when on the road and

in an emergency.

Therefore, the power source for the project is the 12 volt socket which is present in

almost every car these days.

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(b) Toggle Switch

The current through this power source flows into the motor, through a toggle

switch, which controls the flow of current to the motor. This toggle switch controls

the

A switch is used in order to start or stop the entire operation of the screw jack. The

type of switch that is used is known as a toggle switch. A toggle switch is a class of

electrical switches that are manually actuated by a mechanical lever, handle, or

rocking mechanism.

Toggle switches are available in many different styles and sizes, and are used in

countless applications. Many are designed to provide, e.g., the simultaneous

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

electric current or mains voltages.

The word "toggle" is a reference to a kind of mechanism or joint consisting of two

arms, which are almost in line with each other, connected with an elbow-like pivot.

However, the phrase "toggle switch" is applied to a switch with a short handle and

a positive snap-action, whether it actually contains a toggle mechanism or not.

Similarly, a switch where a definitive click is heard, is called a "positive on-off

switch".

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(c) Control Cables

These control cables are used to connect different electrical components and

transfer electrical signals. The connections are made as shown in the block diagram

above.

(d) 12V DC Motor

A 12V DC motor derives power from car’s 12V socket through a toggle switch which

is controlling the direction of flow of current in the motor. The direction of flow of

current controls the horse shoe electromagnet inside the motor which determines

the direction in which the motor will rotate the drive shaft.

This control over the rotation is very important as the screw jack has to go both

ways, upwards and downwards.

This is actuated using proper connections in a 6 pin toggle switch which is used in

the project.

As clearly visible in the photograph above, toggle switch has three positions, one

off and two on, one for clockwise rotation and other for anti-clockwise.

The motor is further connected to connecting shaft.

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(e) Connecting Shaft

The connecting shaft is 16mm thick and made of Mild Steel to take the stresses

induced during the process. On one end, motor is attached by drilling a blind hole

and locking the rotation of both together through a perpendicular drilled hole and

key inserted.

On the other end, it is attached to the screw jack, using nut-bolt-washer assembly.

When the motor rotates, the connecting shafts rotates with the same direction &

rpm and it then transfers the momentum to the screw jack.

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(f) Screw Jack

The screw jack used in the project is a mostly used & easily available mechanical

scissor screw jack. The connections that lead to the rotation of screw jack are visible

in the picture below.

The toggle switch controls the rotation of motor and then it rotates the screw jack

in either direction which controls the upward and downward motion in turn

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Section 4.04 Advantages

1. The loaded light vehicles can be easily lifted.

2. Checking and cleaning are easy, because the main parts are screwed.

3. Handling is easy

4. No Manual power required.

5. Easy to Repair.

6. Replacement of parts are easy

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CHAPTER V. DESIGN CALCULATIONS

Section 5.01 To Check the Safety of Lead Screw

Maximum Load to be lifted = 5 Ton

= 50 x 103 N

= 50KN

For a 5 Ton capacity screw jack, the suitable screw is the one whose nominal (major)

diameter is 36mm.

Corresponding to the nominal diameter 36mm, the pitch (p) selected is 6mm.

The core diameter (dc) = 30mm

The mean diameter (dm) = 33mm

EN8 material is used for lead screw. The ultimate and yield stresses are 450N/mm2

and 230N/mm2 respectively.

The compressive stresses induced in lead screw due to load of 50KN is given by:

𝐹𝐶 = 𝑊

𝜋

4𝑑𝐶

2 = 70.73 N/mm2

Safety Factor = 230/70.73 = 3.25

Hence lead screw will bear 50KN easily

The helix angle of screw = tanα = P/ 𝜋. dm = 0.057

Therefore, α = 3.31o

Assuming coefficient of friction between screw and nut,

µ = tanθ = 0.14 ; θ = tan-1(0.14) = 7.96°

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Since, α < θ, hence it is a self-locking screw.

The turning moment required to rotate screw under design load is given by,

T = W (dm/2) tan (α+θ)

T = (50x103) (33/2) tan (3.31°+7.96°) =164.40KN.mm

The shear stress due to torque, Ft = 16T/ (πdc3)

= (16x164.40x103)/π(30)3

= 31.01N/mm2

Direct stress is given by

Fs = ½√ (Fc2 + 4Ft

2)

= ½√(70.73)2 + 4(31.01)2 = 47.03N/mm2

The lead screw material has 115N/mm2 shear strength.

Safety factor = 115/47.03 = 2.44

Section 5.02 To Check Buckling of Screw

The maximum length of the screw above the nut when lifting the load is 100mm.

Radius of gyration (K) = ¼ dс = ¼ x 30 = 7.5mm

Area = 𝜋

4𝑑𝑐

2 = 706.85 mm2

L/K slenderness ratio = 100/7.5 = 13.33

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CHAPTER VI. CONCLUSION

Screw Jacks are the ideal product to push, pull, lift, lower and position loads of

anything from a couple of kilograms to hundreds of tons. The need has long existed

for an improved portable jack for automotive vehicles. It is highly desirable that a

jack become available that can be operated alternatively from inside the vehicle or

from a location of safety off the road on which the vehicle is located. Such a jack

should desirably be light enough and be compact enough so that it can be stored in

an automobile trunk, can be lifted up and carried by most adults to its position of

use, and yet be capable of lifting a wheel of a 4,000-5,000 pound vehicle off the

ground. Further, it should be stable and easily controllable by a switch so that

jacking can be done from a position of safety. It should be easily movable either to

a position underneath the axle of the vehicle or some other reinforced support

surface designed to be engaged by a jack.

Thus, the product has been developed considering all the above requirements. This

particular design of the motorized screw jack will prove to be beneficial in lifting

and lowering of loads.

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CHAPTER VII. BIBLIOGRAPHY

Design of machine elements by V.B.Bhandari

A text book of machine design by Rajendra Karwa

Analysis and Design of Machine Elements by V K Jadon, Suresh Verma

Tribology in Machine Design by T. A. Stolarski

A text book of Machine Design by R.S.Khurmi,J.K.Gupta

Design of Machine Elements by Farazdak Haideri

Machine Design by S.G.Kulkarni

Design of machine elements by K.Rao

http://en.wikipedia.org/wiki/Jack_(device)

http://hubpages.com/hub/Automobile-Jacks

http://www.powerjacks-de.com/Screw-Jacks-FAQ.html

http://www.radicon.com/screw-jacks.php

http://www.powerjacks.com/PowerJacks-History-The-Screw-Jack-Story.php

http://www.scribd.com/doc/38577261/Screw-Jack-Design