CONTENTS1. Introduction 1.1 Abstracts 1.2. Scissor jack basics 1.3. History 1.4. Applications 1.5. Advantages 1.6. Disadvantages 2. Literature Review 2.1. Description of Mechanical Components 2.2. Description of Special Mechanism Implemented 2.3. Study of Scissor Jack and its Working 3. Design and Fabrication 3.1. Load criteria and assumptions 3.2. Material selection 3.3. 3D model in CAD 4. Problems Faced 5. Solutions Adapted 6. Conclusion 7. Bibliography 3 4 5-7 8 9 10 12-15 15-20 20-23 25 26 27-34 35 36 37 38 GOVT. POLYTECHNIC COLLEGE, RAHOGARH Page 1 Chapter 1: Introduction 1.1. Abstract 1.2. Scissor Jack Basics 1.3. History 1.4. Applications 1.5. Advantages 1.6. Disadvantages 2|Page 1.1 Abstracts: 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. A jack is mechanical device used to lift heavy loads or apply great forces. Jacks employ a screw thread or hydraulic cylinder to apply very high linear forces. 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 a maximum lifting capacity. As our area of concern is a screw jack used for lifting the car that is scissor jack, so only the scissor jack and its background is discussed below. 3|Page 1.2 Scissor Jack Basics: 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. Power screw in a scissor jack is the foundation of whole mechanism of scissor jack. Fig 1.2.1 Conventional Scissor Jack 4|Page A control tab is marked up/down and its position determines the direction of movement and almost no maintenance. Ordnance part number 41-J-66. was first demonstrated by Archimedes in 200BC with his device used for pumping water. that rotated by the turning of a worm shaft to drive a lifting screw to move the load . and similar jacks for trucks.3 History: Screw type mechanical jacks were very common for jeeps and trucks of World War II vintage. Capacity 1 1/2 ton". the World War II jeeps (Willys MB and Ford GPW) were issued the "Jack. The 41-J-66 jack was carried in the jeep's tool compartment. 5|Page . Automobile.instantly recognisable as the principle we use today. Screw type. For example. supported on bearings. who first demonstrated the use of a screw jack for lifting loads. Leonardo‟s design used a threaded worm gear. in the late 1400s. This jacks. There is evidence of the use of screws in the Ancient Roman world but it was the great Leonardo da Vinci. essentially an inclined plane wound round a cylinder. The virtues of using a screw as a machine.1. were activated by using the lug wrench as a handle for the jack's ratchet action to of the jack. Screw type jack's continued in use for small capacity requirements due to low cost of production raise or lower it. it was Whitworth‟s work on screw cutting machines. who recognised the need for precision had become as important in industry as the provision of power.We can‟t be sure of the intended application of his invention. for almost four centuries. That person was Samuel Duff. in Alleghany County near Pittsburgh in 1883. but it seems to have been relegated to the history books. 6|Page . 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. Meanwhile. along with the helicopter and tank. 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‟. While he would eventually have over 50 British patents with titles ranging from knitting machines to rifles. It is not until the late 1800s that we have evidence of the product being developed further. The idea was based on the familiar lever and fulcrum principle and he needed someone to manufacture it. proprietor of a local machine shop. With the industrial revolution of the late 18th and 19th centuries came the first use of screws in machine tools. accurate measuring instruments and standards covering the angle and pitch of screw threads that would most influence our industry today. Together. that is instantly recognizable today. the first worm gear screw jack. The jack. for adjusting the heights of truck loading platforms and mill tables. developing many new types of jack for various applications including its own version of the ball bearing screw jack. Norton to create the Duff-Norton Manufacturing Company.O. used predominantly in the railway industry. incorporated an air motor manufactured by The Chicago Pneumatic Tool Company. they created the Duff Manufacturing Company. Air Motor Power Jack There was clearly potential for using this technology for other applications and only 10 years later. With the aid of the relatively new portable compressor technology. 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. merged with A. With the ability to be used individually or linked mechanically and driven by either air or electric motors or even manually. users now could move and position loads without manual effort. The Duff Manufacturing Company Inc. Worm Gear Jack 4 7|Page . which by 1890 had developed new applications for the original „Barrett Jack‟ and extended the product line to seven models in varying capacities. the first model had a lifting capacity of 10 tons with raises of 2” or 4”. was offered by Duff-Norton. It was only natural that in 1928. Over the next 30 years the Duff Manufacturing Company became the largest manufacturer of lifting jacks in the world. in 1940. In other applications. e. screw-jack. e. 8|Page .g.screw. (ii) To obtain accurate motion in machining operations. Screw-jack and machine vice are the examples of this category. e. (iv) To load a specimen. (iii) To clamp a workpiece. the nut is kept stationary and the screw moves in axial direction. the screw rotates in its bearing.g.g. while the nut has axial motion. power screws operate in two different ways. viz. lead-screw of lathe. nut and a part to hold either the screw or the nut in its place. universal testing machine.1.g. There are three essential parts of a power screw. e. Depending upon the holding arrangement. The lead screw of the lathe is an example of this category. In some cases.4 Applications: The main applications of power screws are as follows: (i) To raise the load. vice. 5 Advantages: Power screws offer the following advantages: (i) Power screw has large load carrying capacity. (vi) Power screws provide precisely controlled and highly accurate linear motion required in machine tool applications. Trapezoidal threads are manufactured on thread milling machine. This reduces cost and increases reliability. clamps. (ii) The overall dimensions of the power screw are small.1. In screw-jack application. valves and vices are usually manually operated. resulting in compact construction.Therefore. (vii) Power screws give smooth and noiseless service without any maintenance. (iii) Power screw is simple to design (iv) The manufacturing of power screw is easy without requiring specialized machinery. most of the power screws used in various applications like screw-jacks. Square threads are turned on lathe. 9|Page . (ix) Power screw can be designed with self-locking property. A load of 15 kN can be raised by applying an effort as small as 400 N. (v) Power screw provides large mechanical advantage. self locking characteristic is required to prevent the load from descending on its own. (viii) There are only a few parts in power screw. type of nut is used to compensate for the wear.1.Therefore. (iii) The most common problem encountered while using scissor jack is the instability of jack while giving jerks to loosen the wheel nut. wear is a serious problem in power screws. Power screws are mainly used for intermittent motion that is occasionally required for lifting the load or actuating the mechanism. In case of square threads. Also the common jack having small base is unable to provide proper support on uneven surface esp.6 Disadvantages: The disadvantages of power screws are as follows: (i) Power screws have very poor efficiency. 10 | P a g e . In trapezoidal threads. (ii) High friction in threads causes rapid wear of the screw or the nut. with the exception of the lead screw. as low as 40%. Therefore. it is not used in continuous power transmission in machine tools. a split. the nut is usually made of soft material and replaced when worn out. off-road and no inclination in that jack is tolerable. 1 Description of Mechanical Components 2.2 Description of Special Mechanism Implemented 2.Chapter 2: Literature Review 2.3 Study of Scissor Jack and its Working 11 | P a g e . which is termed a right-hand thread. It is also called translational screw. base frame. machine tools. aircraft flap extenders.2. vises. Screws with left-hand threads are used in exceptional cases. support frame. adjustable floor posts. Power screw: Power screws are used to convert rotary motion in to translational motion. For example. The frame is manufactured by sheet metal processes and forming by low-medium carbon steel.1 Description of Mechanical Components Various Mechanical parts used in Scissor Jack are: Frame Power screw Rivets Coupling nut Crank Frame: The entire frame of the scissor jack consists of links(top and bottom). The majority of screws are tightened by clockwise rotation. They find use in machines such as universal tensile testing machines. trench braces. 12 | P a g e . linear actuators. micrometers. automotive jacks. These grooves are cut either left hand or right hand. A screw thread is formed by cutting a continuous helical groove around the cylinder. and C-clamps. or steel mating nuts.1 Power screw 13 | P a g e .1. Pitch: is the distance from a point on one thread to the corresponding thread on the next adjacent thread. 3. or stainless steel and they are usually used with bronze. There are important terms and figures that need to be understood before designing power screws: 1. Fig 2. alloy steel.anticlockwise forces are applied to the screw (which would work to undo a right-hand thread). 2. lead is equal to pitch. Bronze and plastic nuts are popular for higher duty applications and they provide low coefficients of friction for minimizing drive torques. For single thread screw. Lead: is the distance the screw would advance relative to the nut in one rotation. Helix Angle: is related to the lead and the mean radius by the equation below. Power screws are typically made from carbon steel. measured parallel to the axial plane. a left-hand-threaded screw would be an appropriate choice. plastic. pumps or exhaust valves. Also. the nut undergoes a linear force (thrust) and the screw rotates or the screw undergoes a linear force (thrust) and the nut rotates. These two motions are commonly referred to as "back driving". pumps. filters. "reversing". They are ideal for replacing hydraulic and pneumatic drive systems as they require no compressors. And. "overhauling". or. valves or any other support items required by these systems. screw systems are quiet running . Power screw motions There are four distinct motion converting actions that can be produced by power screws and nuts. The two most common involve torque conversion to thrust. reliable and easy to utilize. In Figure 2. screws don't leak so there are no problems with seals which are so common to hydraulic and pneumatic systems. Fig2. improperly. Types of power screws There are 3 types of screw threads used in power screws: 14 | P a g e . The two less common motions involve thrust conversion to torque. tanks.no noisy compressors. the screw is rotated (torqued) and the nut moves linearly producing thrust or the nut is rotated (torqued) and the screw moves linearly. Screw systems are simple. piping. In Figure 1.Basics of power screws Power screws provide a compact means for transmitting motion and power. Fig1. 1. On installation the rivet is placed in a punched or pre-drilled hole. 2. Coupling nut: A coupling nut is a threaded fastener for joining two male threads. and coupling nuts with left-handed threads. Square threads: Is used for power transmission in either direction Results in maximum efficiency and minimum It is employed in screw jacks and clamps Acme threads: It is a modification of square thread Efficiency is lower than square threads The slope increases the area for shear It is easily manufactured Buttress Thread: It is used when large forces act along the screw axis in one direction only.e. which have a sight hole for observing the amount of engagement.5 times the original shaft diameter. Before being installed a rivet consists of a smooth cylindrical shaft with a head on one end. The outside of the fastener is usually a hex so a wrench can hold it. so that it expands to about 1. Variations include reducing coupling nuts. for joining two different size threads. holding the rivet in place. It is the strongest thread of all It has limited use of power transmission Rivets: A rivet is a permanent mechanical fastener. the original head is called the factory head and the deformed end is called the shop head or buck-tail. It has higher efficiency like square threads and ease of cutting like acme threads. 3. deformed). sight hole coupling nuts. and the tail is upset. The end opposite the head is called the buck-tail. or bucked (i. most commonly threaded rod. 15 | P a g e . To distinguish between the two ends of the rivet. Ultimately we come up with a design with of scissor jack with side supports.Crank: It is an arm keyed at right angles to the end of a shaft. by which motion is imparted to the power screw .2 Description of Special Mechanism Implemented It can be seen that the overall concept of the scissor jack is constant and that any new product will be based on that concept. The products above lack support from the sides.It mainly suffers from torsional stresses so medium carbon steel is used as it combines merits of malleability and sufficient torsional strength. 16 | P a g e . 2. so there is the possibility of the jack tipping (especially on an uneven surface. enhancing product life and functionality. the basic design and mechanics of the scissor jack are simplistic and lend little room for drastic change. Preliminary Designs As stated before. Below are three preliminary design concepts sketched : 17 | P a g e .1 Mechanically Advanced Scissor Jack We would like to incorporate some type of side support in my jack because it enhances safety and redistributes stress. In my design I would like the make it possible for the user to operate the jack with tools other than the crank provided. The designs above also lacked interchangeability.2. so any change will be a modification on this base model.Fig 2. 18 | P a g e .(a) Design #1 represents the base model of the scissor jack. it is the most simple. (b) Design #2 has an extended base to prevent tipping when the jack is under load. (c) 19 | P a g e . when the jack is lowered. The stabilizing arms on design #3 raise and lower with the jack. rotate to compact its shape and make storage easier. Simple design 2 No added stability between the top and bottom risks a collapse Shape is not compact. Added material. makes storage difficult.Design #3 Also aims to prevent tipping. lock into place while rising. cost weight 20 | P a g e . No added stability between the top risks a collapse Extended base makes tipping less likely. and. Design Pros Light weight Simple design (less places for failure) Cheap Uses little material Easy to store 1 Cons Small base makes tipping a risk. but also adds stability between the top and bottom of the jack. weight and storage (functionality has been omitted from this table because all three designs operate in the same basic manner and are capable of being used with a ratchet). the best performance receives a 3 and the worst a 1. 15because of its importance as a design goal. 3 Adds stability to jack. The designs will be assigned values based on their cost. Extended base makes tipping less likely. The values for safety will be rated by 5. the table below weighs the attributes of each design. The designs are ranked on their performance for each category. 10. the values are then totaled to determine the overall best design. Attribute Cost Safety Weight Storage Total Design #1 3 5 3 3 14 Design #2 2 10 1 1 14 Design #3 1 15 2 2 20 21 | P a g e . Prevents collapse Reduces to a compact shape that is easy to store Stability added with moderate weight increase Added complexity creates more areas for problems Added components add cost Comparing the best out of the three designs: To help make a decision for the final design. safety. 2.Design #1 uses the least amount of material. Design #2 adds safety but also weight. cost and poor storage. the lift on the right side lifts the object from its left side and vice versa. This allows the user to store the jack when it is not in use (with the diagonal beams flat) and to expand it when it is needed. because of the small amount of material. but.3 Study of Scissor Jack and its Working • The term "scissor jack" describes a wide variety of tools that all follow the same principle: using crossed beams to lift something. They do this by acting on the object they are lifting in a diagonal manner. weight and storage. Design #3 adds safety without compromising on weight and storage. 22 | P a g e . so it scored high in cost. but adds cost because it has the most parts. it is not as safe as the other designs. This allows the scissor lift to rise higher. • Scissor lifts basically fall into two categories: single scissor lifts and multiple scissor lifts. This ensures that weight is distributed equally throughout the scissor lift beams. 23 | P a g e .Fig 2. they also have a wide variety of power sources. multiple lifts have beams crossing each other.3. although electrical options do exist. and then attaching to more beams that go the opposite direction. • Since scissor lifts have such a wide variety of use. On the other end of the spectrum. On the other hand. hydraulically and of course mechanically. Scissor lifts for lifting cars can be powered electrically. In order to work. the distance from the loaded point to the cross point must be the same as the distance from the cross point to the ground." This means it can only go so high because the length of the crossbeams restricts the height of the lift. and making them too long would make it unstable. A single scissor lift has just two crossbeams and one "x. industrial scissor lifts that people stand on are often powered by diesel.1 Scissor jack • The major specification of scissor lifts is that they are all symmetrical. Then. coming together at the middle. the person would not be able to turn it. the jack arms travel across it and collapse or come together. yet that action causes the brace arms to slide across and together. Because the gears of the screw are pushing up the arms. Working A scissor jack uses a simple theory of gears to get its power. the arms spread back apart and the jack closes or flattens out again. raising the jack. they raise and come together. forming a straight line when closed. The car's gravitational weight is not enough to prevent the jack from opening or to stop the screw from turning. or lean your weight against the crank. As the screw section is turned. moving back the other way. As this happens the arms extend upward. A screw thread runs across this assembly and through the corners. The four metal pieces are all connected at the corners with a bolt that allows the corners to swivel. since it is not applying force directly to it. It takes a very small amount of force to turn the crank handle. If you were to put pressure directly on the crank. When closed. the four metal arms contract together. When opened. even though your weight is a small percentage of cars. As the screw thread is turned. two ends of the jack move closer together. the amount of force being applied is multiplied. Product Comparison Picture Features Pros Cons 24 | P a g e .Assembly A scissor jack has four main pieces of metal and two base ends. Tools to raise the jack are not interchangeable. 7’ power cord. size and weight. there is no stability provided from the sides.000kg object to operate.75”15. Extends 13”. Does not rely on electricity. so it can be stored easily. Extends from 3. Weighs 9kgs. Need of an electrical power source could be a hindrance when battery power is not adequate. compacts to less than 5”. Lifts 1133 kg. car. Figure 1 Can lift up to 990kg Electric motor powered by a 12V DC power source. the jack The motor adds simple and cost and the easy. increased Can complexity of the operate system creates jack away more opportunity from the for failure.4”. Required to be near (practically underneath a 2. Operating the crank can be difficult. The electric The added weight motor of the electric makes motor hurts fuel operating economy. The jack’s simple design minimizes cost . figure 2 25 | P a g e . Mechanical input required. Like the product above. Chapter3: Design and Fabrication 3. Material selection 3. Load criteria and assumptions 3. 3D drawing of various parts and assembly in CAD 26 | P a g e .3.2.1. Estimated vehicle weight: 1105kg/2440 kgs(weight of swift in unloaded condition. Factor of safety: 4 Weight for which is designed: 2440kgs. Weight on one side: 2440/4: 610kgs.1 Load criteria and assumptions: The load for which the jack is to be employed has to be considered first.3. Also the jack is handy enough to carry in the vehicle. scissor jack works efficiently and smoothly without much effort. For very heavy loads we have to deal with heavy duty jacks and in those situations scissor jacks do not work efficiently and most probably fail. So considering the above situation. While in case of low and medium intensity loads. 27 | P a g e . making a scissor jack for low and moderate dead loads will be a good idea. KHANNA) The material will be designed completely using plain carbon steel. the problem of material selection is solved by selecting some materials on the basis of their strength and modulus of elasticity. The four metal pieces are all connected at the corners with a bolt that allows the corners to swivel.P. 28 | P a g e . To overestimate the safety we will use calculations of strength using the plain carbon steel in its undisturbed. 3. the four metal arms contract together.2 Material selection: Secondly. plain carbon steels and alloy steel. As the screw thread is turned.Assembly A scissor jack has four main pieces of metal and two base ends. forming a straight line when closed. moving back the other way. raising the jack. When opened. the arms spread back apart and the jack closes or flattens out again. coming together at the middle. stainless steel and got an overall result for the best fit material to be low-medium carbon steel . When closed. A screw thread runs across this assembly and through the corners. aluminum . Designing a scissor jack using plain carbon steel is a work of sheet metal shop. solid form.(comparison on basis of data given in MATERIALS AND HEAT TREATMENT PROCESSES by O. they raise and come together. the jack arms travel across it and collapse or come together. Then. We here compared mild steel . 4 MPa 29 | P a g e . forgings and machined components. 66% of the UTS(87000 PSI=518.3 Ultimate shear strength= 57420 PSI=342. AISI 1040 steel Medium carbon steels can be heat treated to have a good balance of ductility and strength. MATERIAL PROPERTIES at 25c : low-medium carbon steel Density = 7845kg/m3 Young’s modulus (E)=200 GPa Poisson’s Ratio(v)-0. These steels are typically used in large parts.LOW-MEDIUM CARBON STEEL will be used 0.8 Mpa) Yield strength= 52500 PSI =353.4 MPa approx.54% carbon –e.29% to 0.g. Parts Base frame Bottom link 30 | P a g e . Bottom packing Bottom rivet 31 | P a g e . Link rivet Screw shaft 32 | P a g e . Coupling nut Top link 33 | P a g e . Support frame 34 | P a g e . Assembly Closed assembly 35 | P a g e . Open Assembly 36 | P a g e . Assembly with stability arrangement Assembly of mechanically advanced Scissor Jack Chapter 4:Problems Faced To fabricate the conventional jack. Using permanent joint with pantograph arrangement makes the problem in working of the pantograph. 37 | P a g e . heavy thickened steel sheet and heavy press is required which was not available in the nearby market. The locking system mechanism is difficult to fabricate. Arc welding in thin metal sheet completely melts the sheet and makes the joint weak. As arc welding melts the thin sheet. As permanent joint in pantograph arrangement makes the link rigid hence we used pivoted joints for implementing the mechanism.Chapter 5:Solution Adopted As the press working on heavy metal sheet is difficult as there is no press machine available in nearby market hence the conventional mechanical jack is not fabricated and readymade jack is taken for further mechanically advanced attachment. then the thickness of the sheet is increases. the Amperage rating of the arc welding is set to minimum position but the problem still persists. 38 | P a g e . lower and position loads of anything from a couple of kilograms to hundreds of tonnes.000-5. pull. Chapter 6:Conclusion Scissor jacks are the ideal product to push.000 pound vehicle off the 39 | P a g e . 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. Locking system mechanism was difficult to fabricate but with better design and better mechanism using the threaded shaft the problem of slipping is eliminated. lift. 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. The need has long existed for an improved portable jack for automotive vehicles. Such a jack should desirably be light enough and be compact enough so that it can be stored in an automobile trunk. Websites www. The experience gained has provided us confidence in dealing with practical aspects of engineering and will prove to be invaluable for future mechanical advancement.scribd.S. We faced new challenges while designing and analyzing scissor jack. A text book of Machine Design by R.K.com www. Chapter 6:Bibliography 1. Engineering Kinematics by William Griswold Smith 3. J.Khurmi. Also we explored new territories in technical creation. 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 mechanically advanced scissor jack.com 40 | P a g e .google.Gupta 2. This project proved to be most valuable in terms of teamwork and management to us.ground. Further. it should be stable and easily controllable by a switch so that jacking can be done from a position of safety. seminarprojects. en.org/wiki www.com 41 | P a g e .wikipedia.