TRIANGLE MULTI DRILL HOLDER
1.SYNOPSIS
Triangle drill heads are designed for use with most drilling machinery. They can, almost immediately, triple the drilling operations by simultaneously drilling in one operation. It has proved to be the most versatile method to drill close trianglular space holes.
This machine includes a first functional portion known as the bar support which assures the feeding, holding and driving of the bars. This part is provided with a set of spindles in which are respectively introduced the bars of material in question, which bars project from said spindles towards the cutting tools mounted on a supporting structure.
2. METHODOLOGY This project is designed with Drilling head Motor Drill bit Shaft
3. WORKING PRINCIPLE
This machine will drill three holes in triangular shape simultaneously in a work piece. Triangular drilling machines are employed for work of light character, especially repetition work, such as drilling small components for the automobile and Aircraft industries. A triangle multi drill holder has a three drill spindles driven by a single motor. All the spindles holding the drills are fed into the work piece at the same time. For this purpose, either the drill heads can be lowered onto the work piece using with the handle operated moves in the direction of up and down movement. Here the work piece is clamped in the vice on the lower table. the gear train mechanism is used.
Here
The rotary motion of the centre gear is
transferred to the three gears to which the drill heads are connected.
4. LINE DIAGRAM
5. ELECTRIC MOTOR An electric motor converts electrical energy into mechanical energy. Most electric motors operate through interacting magnetic fields and current-carrying conductors to generate force, although a few use electrostatic forces. The reverse process, producing electrical energy from mechanical energy, is accomplished by some type of generator such as an alternator or a dynamo. Many types of electric motors can be run as generators, and vice versa. For example a starter/generator for a gas turbine, or traction motors used on vehicles, often perform both tasks.
Electric motors are found in applications as diverse as industrial fans, blowers and pumps, machine tools, household appliances, power tools, and disk drives. They may be powered by direct current (e.g., a battery powered portable device or motor vehicle), or by alternating current from a central electrical distribution grid. The smallest motors may be found in electric wristwatches. Medium-size motors of highly standardized dimensions and characteristics provide convenient mechanical power for industrial uses. The very largest electric motors are used for propulsion of large ships, and for such purposes as pipeline compressors, with ratings in the millions of watts. Electric motors may be classified by the source of electric power, by their internal construction, by their application, or by the type of motion they give.
5.1. SYNCHRONOUS ELECTRIC MOTOR A synchronous electric motor is an AC motor distinguished by a rotor spinning with coils passing magnets at the same rate as the alternating current and resulting magnetic field which drives it. Another way of saying this is that it has zero slip under usual operating conditions. Contrast this with an induction motor, which must slip to produce torque. A synchronous motor is like an induction motor except the rotor is excited by a DC field. Slip rings and brushes are used to conduct current to rotor. The rotor poles connect to each other and move at the same speed hence the name synchronous motor.
5.2. INDUCTION MOTOR
An induction motor is an asynchronous AC motor where power is transferred to the rotor by electromagnetic induction. An induction motor resembles a rotating transformer, because the stator (stationary part) is essentially the primary side of the transformer and the rotor (rotating part) is the secondary side. Polyphase induction motors are widely used in industry.
Induction motors may be further divided into squirrel-cage motors and wound-rotor motors. Squirrel-cage motors have a heavy winding made up of solid bars, usually aluminum or copper, joined by rings at the ends of the rotor. Currents induced into this winding provide the rotor magnetic field. The shape of the rotor bars determines the speed-torque characteristics. At low speeds, the current induced in the squirrel cage is nearly at line frequency and tends to flow in the outer parts of the rotor cage. As the motor accelerates, the slip frequency becomes lower, and more current flows in the interior of the winding. By shaping the bars to change the resistance of the windings portions in the interior and outer parts of the cage, effectively a variable resistance is inserted in the rotor circuit.
In a wound-rotor motor, the rotor winding is made of many turns of insulated wire and is connected to slip rings on the motor shaft. An external resistor or other control devices can be connected in the rotor circuit. Resistors allow control of the
motor speed, although significant power is dissipated in the external resistance. A converter can be fed from the rotor circuit and return the slip-frequency power that would otherwise be wasted back into the power system.
The wound-rotor induction motor is used primarily to start a high inertia load or a load that requires a very high starting torque across the full speed range. By correctly selecting the resistors used in the secondary resistance or slip ring starter, the motor is able to produce maximum torque at a relatively low supply current from zero speed to full speed. This type of motor also offers controllable speed.
Motor speed can be changed because the torque curve of the motor is effectively modified by the amount of resistance connected to the rotor circuit. Increasing the value of resistance will move the speed of maximum torque down. If the resistance connected to the rotor is increased beyond the point where the maximum torque occurs at zero speed, the torque will be further reduced.
When used with a load that has a torque curve that increases with speed, the motor will operate at the speed where the torque developed by the motor is equal to the load torque. Reducing the load will cause the motor to speed up, and increasing the
load will cause the motor to slow down until the load and motor torque are equal. Operated in this manner, the slip losses are dissipated in the secondary resistors and can be very significant. The speed regulation and net efficiency is also very poor.
Early motors
Faraday's electromagnetic experiment, 182
Perhaps the first electric motors were simple electrostatic devices created by the Scottish monk Andrew Gordon in the 1740s.[2] The theoretical principle behind production of mechanical force by the interactions of an electric current and a magnetic field, Ampère's force law, was discovered later by AndréMarie Ampère in 1820. The conversion of electrical energy into mechanical energy by electromagnetic means was demonstrated by the British scientist Michael Faraday in 1821. A free-hanging wire was dipped into a pool of mercury, on which a permanent magnet (PM) was placed.
When a current was passed through the wire, the wire rotated around the magnet, showing that the current gave rise to a close circular magnetic field around the wire.[3] This motor is often demonstrated in physics experiments, brine substituting for toxic mercury. Though Barlow's wheel was an early refinement to this Faraday demonstration, these and similar homopolar motors were to remain unsuited to practical application until late in the century.
Jedlik's "electromagnetic self-rotor", 1827 (Museum of Applied Arts, Budapest). The historic motor still works perfectly today.
In 1827, Hungarian physicist Ányos Jedlik started experimenting with electromagnetic coils. After Jedlik solved the technical problems of the continuous rotation with the invention of commutator, he called his early devices "electromagnetic self-rotors". Although they were used only for instructional purposes, in 1828 Jedlik demonstrated the first device to contain the three main components of practical DC motors: the stator, rotor and commutator. The device employed no permanent magnets, as the magnetic fields of both the stationary and revolving components were produced solely by the currents flowing through their windings. Success with DC motors
After many other more or less successful attempts with relatively weak rotating and reciprocating apparatus the German-speaking Prussian Moritz von Jacobicreated the first real rotating electric motor in May 1834 that actually developed a remarkable mechanical output power. His motor set a world record which was improved only four years later in September 1838 by Jacobi himself. His second motor was powerful enough to drive a boat with 14 people across a wide river. It was not until 1839/40 that other developers worldwide managed to build motors of similar and later also of higher performance.
The first commutator DC electric motor capable of turning machinery was invented by the British scientist William Sturgeon in 1832.[12] Following Sturgeon's work, a commutator-type direct-current electric motor made with the intention of commercial use was built by the American inventor Thomas Davenport, which he patented in 1837. The motors ran at up to 600 revolutions per minute, and powered machine tools and a printing press. [13] Due to the high cost of primary battery power, the motors were commercially unsuccessful and Davenport went bankrupt. Several inventors followed Sturgeon in the development of DC motors but all encountered the same battery power cost issues. No electricity distribution had been developed at the time. Like Sturgeon's motor, there was no practical commercial market for these motors.
In 1855, Jedlik built a device using similar principles to those used in his electromagnetic self-rotors that was capable of useful work. [5][11] He built a model electric vehicle that same year
The first commercially successful DC motors followed the invention by Zénobe Gramme who had in 1871 developed the anchor ring dynamo which solved the double-T armature pulsating DC problem. In 1873, Gramme found that this dynamo could be used as a motor, which he demonstrated to great effect at exhibitions in Vienna and Philadelphia by connecting two such DC motors at a distance of up to 2 km away from each other, one as a generator.[16] (See also 1873 : l'expérience décisive [Decisive Workaround] .
In 1886, Frank Julian Sprague invented the first practical DC motor, a non-sparking motor that maintained relatively constant speed under variable loads. Other Sprague electric inventions about this time greatly improved grid electric distribution (prior work done while employed by Thomas Edison), allowed power from electric motors to be returned to the electric grid, provided for electric distribution to trolleys via overhead wires and the trolley pole, and provided controls systems for electric operations.
This allowed Sprague to use electric motors to invent the first electric trolley system in 1887–88 in Richmond VA, the electric elevator and control system in 1892, and the electric subway with independently powered centrally controlled cars, which were first installed in 1892 in Chicago by the South Side Elevated Railway where it became popularly known as the "L". Sprague's motor and related inventions led to an explosion of interest and use in electric motors for industry, while almost simultaneously another great inventor was developing its primary competitor, which would become much more widespread. The development of electric motors of acceptable efficiency was delayed for several decades by failure to recognize the extreme importance of a relatively small air gap between rotor and stator. Efficient designs have a comparatively small air gap. [17] [a]
The St. Louis motor, long used in classrooms to illustrate motor principles, is
extremely inefficient for the same reason, as well as appearing nothing like a modern motor.
Application of electric motors revolutionized industry. Industrial processes were no longer limited by power transmission using line shafts, belts, compressed air or hydraulic pressure. Instead every machine could be equipped with its own electric motor, providing easy control at the point of use, and improving power transmission efficiency. Electric motors applied in agriculture eliminated human and animal muscle power from such tasks as handling grain or pumping water. Household uses of electric motors reduced heavy labor in the home and made
higher standards of convenience, comfort and safety possible. Today, electric motors stand for more than half of the electric energy consumption in the US.
Emergence of AC motors
In 1824, the French physicist François Arago formulated the existence of rotating magnetic fields, termed Arago's rotations, which, by manually turning switches on and off, Walter Baily demonstrated in 1879 as in effect the first primitive induction motor.[20][21] [22][23] In the 1880s, many inventors were trying to develop workable AC motors[24] because AC's advantages in long distance high voltage transmission were counterbalanced by the inability to operate motors on AC. Practical rotating AC induction motors were independently invented by Galileo Ferraris and Nikola Tesla, a working motor model having been demonstrated by the former in 1885 and by the latter in 1887. In 1888, the Royal Academy of Science of Turin published Ferraris's research detailing the foundations of motor operation while however concluding that "the apparatus based on that principle could not be of any commercial importance as motor."
In 1888, Tesla presented his paper A New System for Alternating Current Motors and Transformers to the AIEE that described three patented twophase four-stator-pole motor types: one with a four-pole rotor forming a non-selfstarting reluctance motor, another with a wound rotor forming a selfstarting induction motor, and the third a true synchronous motor with separately
excited DC supply to rotor winding. One of the patents Tesla filed in 1887, however, also described a shorted-winding-rotor induction motor. George Westinghouse promptly bought Tesla's patents, employed Tesla to develop them, and assigned C. F. Scott to help Tesla, Tesla leaving for other pursuits in 1889.
The constant speed AC induction motor was found not to be suitable for street cars[24] but Westinghouse engineers successfully adapted it to power a mining operation in Telluride, Colorado in 1891.[45][46][47] Steadfast in his promotion of three-phase development, Mikhail Dolivo-Dobrovolsky invented the three-phase cage-rotor induction motor in 1889 and the three-limb transformer in 1890. This type of motor is now used for the vast majority of commercial applications.
However, he claimed that Tesla's motor was not practical because of two-phase pulsations, which prompted him to persist in his three-phase work. [50]
Although Westinghouse achieved its first practical induction motor in 1892 and
developed a line of polyphase 60 hertz induction motors in 1893, these early Westinghouse motors were two-phase motors with wound rotors until B. G. Lamme developed
a
rotating
bar
winding
rotor.[37] The General
Electric
Company began developing three-phase induction motors in 1891.[37] By 1896, General Electric and Westinghouse signed a cross-licensing agreement for the barwinding-rotor design, later called the squirrel-cage rotor.[37] Induction motor improvements flowing from these inventions and innovations were such that a 100 horsepower (HP) induction motor currently has the same mounting dimensions as a 7.5 HP motor in 1897.
Rotor
Main article: Rotor (electric)
In an electric motor the moving part is the rotor which turns the shaft to deliver the mechanical power. The rotor usually has conductors laid into it which carry currents that interact with the magnetic field of the stator to generate the forces that turn the shaft. However, some rotors carry permanent magnets, and the stator holds the conductors. Devices such as magnetic solenoids and loudspeakers that convert electricity into motion but do not generate usable mechanical power are respectively referred to as actuators and transducers. Electric motors are used to produce linear force or torque (rotary).
Stator Main article: Stator
The stationary part is the stator, usually has either windings or permanent magnets. The stator is the stationary part of the motor’s electromagnetic circuit. The stator core is made up of many thin metal sheets, called laminations. Laminations are used to reduce energy losses that would result if a solid core were used.
Air gap
In between the rotor and stator is the air gap. The air gap has important effects, and is generally as small as possible, as a large gap has a strong negative effect on the performance of an electric motor.
Windings Main article: Windings Windings are wires that are laid in coils, usually wrapped around a laminated soft iron magnetic core so as to form magnetic poles when energized with current.Electric machines come in two basic magnet field pole
configurations: salient-pole machine and nonsalient-pole machine. In the salientpole machine the pole's magnetic field is produced by a winding wound around the pole below the pole face. In the nonsalient-pole, or distributed field, or round-rotor, machine, the winding is distributed in pole face slots. [51] A shaded-pole motor has a winding around part of the pole that delays the phase of the magnetic field for that pole.
Some motors have conductors which consist of thicker metal, such as bars or sheets of metal, usually copper, although sometimes aluminum is used. These are usually powered byelectromagnetic induction.
Commutator Main article: Commutator (electric)
A toy's small DC motor with its commutator A commutator is a mechanism used to switch the input of certain AC and DC machines consisting of slip ring segments insulated from each other and from the electric motor's shaft. The motor's armature current is supplied through the stationary brushes in contact with the revolving commutator, which causes required current reversal and applies power to the machine in an optimal manner as the rotor rotates from pole to pole.
[52][53]
In absence of such current reversal, the motor would brake to a stop. In light
of significant advances in the past few decades due to improved technologies in electronic controller, sensorless control, induction motor, and permanent magnet motor fields, electromechanically commutated motors are increasingly being displaced by externally commutated induction and permanent-magnet motors.
6. HANDLE
A handle is a part of, or attachment to, an object that can be moved or used
by
hand.
The
design
of
each
type
of
handle
involves
substantial ergonomicissues, even where these are dealt with intuitively or by following tradition. Handles for tools are an important part of their function, enabling the user to exploit the tools to maximum effect.
USESE
A sheath or coating on the handle that provides friction against the hand, reducing the gripping force needed to achieve a reliable grip.
Designs such as recessed car-door handles, reducing the chance of accidental operation, or simply the inconvenience of "snagging" the handle.
Sufficient circumference to distribute the force comfortably and safely over the hand. An example where this requirement is almost the sole purpose for a handle's existence is the handle that consists of two pieces: a hollow wooden cylinder about the diameter of a finger and a bit longer than one hand-width, and a stiff wire that passes through the center of the cylinder, has two right angles, and is shaped into a hook at each end. This handle permits comfortable carrying, with otherwise bare hands, of a heavy package, suspended on a tight string that passes around the top and bottom of it: the string is strong enough to support it, but the pressure the string would exert on fingers that grasped it directly would often be unacceptable.
One major category of handles are pull handles, where one or more hands grip the handle or handles, and exert force to shorten the distance between the hands and their corresponding shoulders. The three criteria stated above are universal for pull handles.
Many pull handles are for lifting, mostly on objects to be carried.Horizontal pull handles are widespread, including drawer pulls, handles on latchless doors and the outside of car doors. The inside controls for opening car doors from inside are usually pull handles, although their function of permitting the door to be pushed open is accomplished by an internal unlatching linkage. Two kinds of pull handles may involve motion in addition to the hand-focused motions described:
Pulling the starting cord on a small internal-combustion engine may, besides moving the hand toward the shoulder, also exploit simultaneously pushing a wheeled vehicle away with the other hand, stepping away from the engine, and/or standing from a squat.
Some throwing motions, as in a track-and-field hammer throw, involve pulling on a handle against centrifugal force (without bringing it closer), in the course of accelerating the thrown object by forcing it into circular motion.
7.GNEVA MECHANISM
Gneva mechanism, also called Geneva Stop, one of the most commonly used devices for producing intermittent rotary motion, characterized by
alternate periods of motion and rest with no reversal in direction. It is also used for indexing (i.e., rotating a shaft through a prescribed angle).
In the Figure the driver A carries a pin or roller R that fits in the four radial slots in the follower B. Between the slots there are four concave surfaces that fit the surface S on the driver and serve to keep the follower from rotating when they are fully engaged. In the position shown, the pin is entering one of the slots, and, on further rotation of the driver, it will move into the slot and rotate the follower through 90°. After the pin leaves the slot, the driver will rotate through 270° while the follower dwells— i.e., stands still. The lowest practical number of slots in a Geneva mechanism is 3; more than 18 are seldom used. If one of the slot positions is uncut, the number of turns that the driver can make is limited. It is said that the Geneva mechanism was invented by a Swiss watchmaker to prevent the overwinding of watch springs. For this reason it is sometimes called a Genevastop.
8. BENCH VICE
A vise (American English) or vice (British English) is a mechanical apparatus used to secure an object to allow work to be performed on it. Vises have two parallel jaws, one fixed and the other movable, threaded in and out by a screw and lever.
Woodworking
Woodworker's vise with entirely wooden jaws
Woodworking vises are attached to a workbench, typically flush with its work surface. Their jaws are made of wood or metal, the latter usually faced with wood, called cheeks, to avoid marring the work.[1] The movable jaw may include a retractable dog to hold work against a bench dog.
"Quick-release" vises employ a split nut that allows the screw to engage or disengage with a half-turn of the handle. When disengaged the movable jaw may be moved in or out throughout its entire range of motion, vastly speeding up the process of adjustment. Common thread types are Acme and buttress.
Engineer's
Engineer's bench vise made of cast iron - image inset shows soft jaws
A small machine vise used in a drill press
A machine vise that can be rotated
An engineer's vise, also known as a metalworking vise or fitter's vise, is used to clamp metal instead of wood. It is typically made of cast steel or malleable cast iron. Cheaper vises may be made of brittle cast iron. The jaws are often separate and replaceable, usually engraved with serrated or diamond teeth. Soft jaw covers made of aluminum, lead, or plastic may be used to protect delicate work.
An engineer's vise is bolted onto the top surface of a workbench, [2] with the face of the fixed jaws just forward of its front edge. The vise may include other features such as a small anvil on the back of its body.
Woodworking
Woodworker's vise with entirely wooden jaws
Woodworking vises are attached to a workbench, typically flush with its work surface. Their jaws are made of wood or metal, the latter usually faced with wood,
called cheeks, to avoid marring the work.[1] The movable jaw may include a retractable dog to hold work against a bench dog.
"Quick-release" vises employ a split nut that allows the screw to engage or disengage with a half-turn of the handle. When disengaged the movable jaw may be moved in or out throughout its entire range of motion, vastly speeding up the process of adjustment. Common thread types are Acme and buttress.
Engineer's
Engineer's bench vise made of cast iron - image inset shows soft jaws
A small machine vise used in a drill press
A machine vise that can be rotated
An engineer's vise, also known as a metalworking vise or fitter's vise, is used to clamp metal instead of wood. It is typically made of cast steel or malleable cast iron. Cheaper vises may be made of brittle cast iron. The jaws are often separate and replaceable, usually engraved with serrated or diamond teeth. Soft jaw covers made of aluminum, lead, or plastic may be used to protect delicate work.
An engineer's vise is bolted onto the top surface of a workbench, [2] with the face of the fixed jaws just forward of its front edge. The vise may include other features such as a small anvil on the back of its body.
8. GEAR
A gear or cogwheel is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part to transmit torque, in most cases with teeth on the one gear being of identical shape, and often also with that shape on the other gear. [1]Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine. Geared devices can change the speed, torque, and direction of a power source. The most common situation is for a gear to mesh with another gear; however, a gear can also mesh with a non-rotating toothed part, called a rack, thereby producing translation instead of rotation.
The gears in a transmission are analogous to the wheels in a crossed belt pulley system. An advantage of gears is that the teeth of a gear prevent slippage.
When two gears mesh, and one gear is bigger than the other (even though the size of the teeth must match), a mechanical advantage is produced, with
the rotational speeds and the torques of the two gears differing in an inverse relationship.
In transmissions with multiple gear ratios—such as bicycles, motorcycles, and cars—the term gear, as in first gear, refers to a gear ratio rather than an actual physical gear. The term describes similar devices, even when the gear ratio is continuous rather than discrete, or when the device does not actually contain gears, as in a continuously variable transmission.[2]
History of the differential gear[edit] Main article: differential (mechanical device) § History The earliest known reference to gears was circa A.D. 50 by Hero of Alexandria, [3]
but they can be traced back to the Greek mechanics of the Alexandrian school in
the
3rd
century
BCE
and
were
greatly
developed
by
the
Greek polymath Archimedes (287–212 BCE).[4] The Antikythera mechanism is an example
of
a
very
early
and
intricate
geared
device,
designed
to
calculate astronomicalpositions. Its time of construction is now estimated between 150 and 100 BC.
Single stage gear reducer. Ma Jun (c. 200–265 AD) re-invented the differential gear as part of a southpointing chariot. History of other gears[edit]
The water-powered grain-mill, the water-powered saw mill, fulling mill, and other applications of watermill often used gears.
The first mechanical clocks was built in AD 725.
The 1386 Salisbury cathedral clock may be the world's oldest working mechanical clock.
The definite velocity ratio that teeth give gears provides an advantage over other drives (such as traction drives and V-belts) in precision machines such as watches that depend upon an exact velocity ratio. In cases where driver and follower are proximal, gears also have an advantage over other drives in the reduced number of parts required; the downside is that gears are more expensive to manufacture and their lubrication requirements may impose a higher operating cost.
External vs internal gears
Internal gear An external gear is one with the teeth formed on the outer surface of a cylinder or cone. Conversely, an internal gear is one with the teeth formed on the inner surface of a cylinder or cone. For bevel gears, an internal gear is one with the pitch angle exceeding 90 degrees. Internal gears do not cause output shaft direction reversal.
Spur
Spur gear
Spur gears or straight-cut gears are the simplest type of gear. They consist of a cylinder or disk with the teeth projecting radially, and although they are not straight-sided in form (they are usually of special form to achieve constant drive ratio, mainly involute), the edge of each tooth is straight and aligned parallel to the axis of rotation. These gears can be meshed together correctly only if they are fitted to parallel shafts.
Helica
Helical gears Top: parallel configuration\ Bottom: crossed configuration
Helical or "dry fixed" gears offer a refinement over spur gears. The leading edges of the teeth are not parallel to the axis of rotation, but are set at an angle. Since the gear is curved, this angling causes the tooth shape to be a segment of a helix. Helical gears can be meshed in parallel or crossed orientations. The former refers to when the shafts are parallel to each other; this is the most common orientation. In the latter, the shafts are non-parallel, and in this configuration the gears are sometimes known as "skew gears".
The angled teeth engage more gradually than do spur gear teeth, causing them to run more smoothly and quietly.[8] With parallel helical gears, each pair of teeth first make contact at a single point at one side of the gear wheel; a moving curve of contact then grows gradually across the tooth face to a maximum then recedes until the teeth break contact at a single point on the opposite side. In skew gears, teeth suddenly meet at a line contact across their entire width causing stress and noise. Skew gears make a characteristic whine at high speeds. Whereas spur gears are used for low speed applications and those situations where noise control is not a problem, the use of helical gears is indicated when the application involves high speeds, large power transmission, or where noise abatement is important.[9] The speed is considered to be high when the pitch line velocity exceeds 25 m/s.[10]
A disadvantage of helical gears is a resultant thrust along the axis of the gear, which needs to be accommodated by appropriate thrust bearings, and a greater degree of sliding friction between the meshing teeth, often addressed with additives in the lubricant Skew gears For a 'crossed' or 'skew' configuration, the gears must have the same pressure angle and normal pitch; however, the helix angle and handedness can be different. The relationship between the two shafts is actually defined by the helix angle(s) of the two shafts and the handedness, as defined:[11]
for gears of the same handedness for gears of opposite handedness Where
is the helix angle for the gear. The crossed configuration is less
mechanically sound because there is only a point contact between the gears, whereas in the parallel configuration there is a line contact.[11] Quite commonly, helical gears are used with the helix angle of one having the negative of the helix angle of the other; such a pair might also be referred to as having a right-handed helix and a left-handed helix of equal angles. The two equal but opposite angles add to zero: the angle between shafts is zero—that is, the shafts are parallel. Where the sum or the difference (as described in the equations above) is not zero the shafts are crossed. For shafts crossed at right angles, the helix angles are of the same hand because they must add to 90 degrees. 3D Animation of helical gears (parallel axis) 3D Animation of helical gears (crossed axis)
Double helical
Double helical gears Main article: Double helical gear Double helical gears, or herringbone gears, overcome the problem of axial thrust presented by "single" helical gears, by having two sets of teeth that are set in a V shape. A double helical gear can be thought of as two mirrored helical gears joined together. This arrangement cancels out the net axial thrust, since each half of the gear thrusts in the opposite direction resulting in a net axial force of zero. This arrangement can remove the need for thrust bearings. However, double helical gears are more difficult to manufacture due to their more complicated shape.
For both possible rotational directions, there exist two possible arrangements for the oppositely-oriented helical gears or gear faces. One arrangement is stable, and the other is unstable. In a stable orientation, the helical gear faces are oriented so that each axial force is directed toward the center of the gear. In an unstable orientation, both axial forces are directed away from the center of the gear. In both arrangements, the total (or net) axial force on each gear is zero when the gears are aligned correctly. If the gears become misaligned in the axial direction, the unstable arrangement generates a net force that may lead to disassembly of the gear train, while the stable arrangement generates a net corrective force. If the direction of rotation is reversed, the direction of the axial thrusts is also reversed, so a stable configuration becomes unstable, and vice versa.
Spiral bevels[edit]
Spiral bevel gears Main article: Spiral bevel gear Spiral bevel gears can be manufactured as Gleason types (circular arc with non-constant tooth depth), Oerlikon and Curvex types (circular arc with constant tooth depth), Klingelnberg Cyclo-Palloid (Epicycloide with constant tooth depth)
or Klingelnberg Palloid. Spiral bevel gears have the same advantages and disadvantages relative to their straight-cut cousins as helical gears do to spur gears. Straight bevel gears are generally used only at speeds below 5 m/s (1000 ft/min), or, for small gears, 1000 r.p.m.[12]
Hypoid[edit]
Hypoid gear Hypoid gears resemble spiral bevel gears except the shaft axes do not intersect. The pitch surfaces appear conical but, to compensate for the offset shaft, are in fact hyperboloids of revolution.[13][14] Hypoid gears are almost always designed to operate with shafts at 90 degrees. Depending on which side the shaft is offset to, relative to the angling of the teeth, contact between hypoid gear teeth may be even smoother and more gradual than with spiral bevel gear teeth, but also have a sliding action along the meshing teeth as it rotates and therefore usually require some of the most viscous types of gear oil to avoid it being extruded from the mating tooth faces, the oil is normally designated HP (for hypoid) followed by a number denoting the viscosity. Also, the pinion can be designed with fewer teeth than a spiral bevel pinion, with the result that gear ratios of 60:1 and higher are
feasible using a single set of hypoid gears.[15] This style of gear is most common in driving mechanical differentials, which are normally straight cut bevel gears, in motor vehicle axles. Crown[edit]
Crown gear Main article: Crown gear
Crown gears or contrate gears are a particular form of bevel gear whose teeth project at right angles to the plane of the wheel; in their orientation the teeth resemble the points on a crown. A crown gear can only mesh accurately with another bevel gear, although crown gears are sometimes seen meshing with spur gears. A crown gear is also sometimes meshed with an escapement such as found in mechanical clocks. Worm[edit]
Worm gear
4-start worm and wheel Main article: Worm drive Main article: Slewing drive Worm gears resemble screws. A worm gear is usually meshed with a spur gear or a helical gear, which is called the gear, wheel, or worm wheel.Worm-andgear sets are a simple and compact way to achieve a high torque, low speed gear ratio. For example, helical gears are normally limited to gear ratios of less than 10:1 while worm-and-gear sets vary from 10:1 to 500:1.[16] A disadvantage is the potential for considerable sliding action, leading to low efficiency.
A worm gear is a species of helical gear, but its helix angle is usually somewhat large (close to 90 degrees) and its body is usually fairly long in the axial direction. These attributes give it screw like qualities. The distinction between a worm and a helical gear is that least one tooth persists for a full rotation around the helix. If this occurs, it is a 'worm'; if not, it is a 'helical gear'. A worm may have as few as one tooth. If that tooth persists for several turns around the helix, the worm appears, superficially, to have more than one tooth, but what one in fact sees is the same tooth reappearing at intervals along the length of the worm. The usual screw nomenclature applies: a one-toothed worm is called single thread or single start; a worm with more than one tooth is called multiple thread or multiple start. The helix angle of a worm is not usually specified. Instead, the lead angle, which is equal to 90 degrees minus the helix angle, is given. In a worm-and-gear set, the worm can always drive the gear. However, if the gear attempts to drive the worm, it may or may not succeed. Particularly if the lead angle is small, the gear's teeth may simply lock against the worm's teeth, because the force component circumferential to the worm is not sufficient to overcome friction. Worm-and-gear sets that do lock are called self locking, which can be used to advantage, as for instance when it is desired to set the position of a mechanism by turning the worm and then have the mechanism hold that position. An example is the machine head found on some types of stringed instruments. If the gear in a worm-and-gear set is an ordinary helical gear only a single point of contact is achieved.[15][18] If medium to high power transmission is desired, the tooth shape of the gear is modified to achieve more intimate contact by making both
gears partially envelop each other. This is done by making both concave and joining them at a saddle point; this is called a cone-drive.[19] or "Double enveloping" Worm gears can be right or left-handed, following the long-established practice for screw threads.
9. MERITS It reduces the manual work. Quick operation Accuracy is more Low cost machine Its used multipurpose device like Grinding, screw driving.
10. APPLICATIONS
Used automobile workshops like carburetor holes Used small scale industries In welding shop for grinding For performing the operations in huge part which cannot be done in ordinary machines. Since it’s portable. In such places where frequent change in operation are required.
