Lathe Machine

Lathe Machine

What is lathe -

A lathe (/leɪð/) is a machine tool that rotates a workpiece about an axis of rotation to perform various operations such as cutting, sanding, knurling, drilling, deformation, facing, and turning, with tools that are applied to the workpiece to create an object with symmetry about that axis.

Uses -

Lathes are used in woodturning, metalworking, metal spinning, thermal spraying, parts reclamation, and glass-working. Lathes can be used to shape pottery, the best-known design being the Potter's wheel. Most suitably equipped metalworking lathes can also be used to produce most solids of revolution, plane surfaces and screw threads or helices. Ornamental lathes can produce three-dimensional solids of incredible complexity. The workpiece is usually held in place by either one or two centers, at least one of which can typically be moved horizontally to accommodate varying workpiece lengths. Other work-holding methods include clamping the work about the axis of rotation using a chuck or collet, or to a faceplate, using clamps or dog clutch.

lathe machines 

History -

The lathe is an ancient tool. The earliest evidence of a lathe dates back to Ancient Egypt around 1300 BC.^[1] There is also tenuous evidence for its existence at a Mycenaean Greek site, dating back as far as the 13th or 14th century BC.^[2]

Clear evidence of turned artifacts have been found from the 6th century BC: fragments of a wooden bowl in an Etruscan tomb in Northern Italy as well as two flat wooden dishes with decorative turned rims from modern Turkey.^[3]

During the Warring States period in China, c. 400 BCE, the ancient Chinese used rotary lathes to sharpen tools and weapons on an industrial scale.^[4]

The first known painting showing a lathe dates to the 3rd century BC in ancient Egypt.^[5]

The lathe was very important to the Industrial Revolution. It is known as the mother of machine tools, as it was the first machine tool that led to the invention of other machine tools.^[6] The first fully documented, all-metal slide rest lathe was invented by Jacques de Vaucanson around 1751. It was described in the Encyclopédie.

An important early lathe in the UK was the horizontal boring machine that was installed by Jan Verbruggen in 1772 in the Royal Arsenal in Woolwich. It was horse-powered and allowed for the production of much more accurate and stronger cannon used with success in the American Revolutionary War in the late 18th century. One of the key characteristics of this machine was that the workpiece was turning as opposed to the tool, making it technically a lathe. Henry Maudslay, who later developed many improvements to the lathe, worked at the Royal Arsenal from 1783, being exposed to this machine in the Verbruggen workshop.^[8] A detailed description of Vaucanson's lathe was published decades before Maudslay perfected his version. It is likely that Maudslay was not aware of Vaucanson's work, since his first versions of the slide rest had many errors that were not present in the Vaucanson lathe.In 1718 Russian engineer Andrey Nartov invented one of the first lathes with a mechanical cutting tool-supporting carriage and a set of gears (also known as a compound rest or slide rest) with the first to invent such a lathe probably being Leonardo da Vinci.

Parts -

A lathe may or may not have legs also known as a nugget, which sit on the floor and elevate the lathe bed to a working height. A lathe may be small and sit on a workbench or table, not requiring a stand.

Almost all lathes have a bed, which is (almost always) a horizontal beam (although CNC lathes commonly have an inclined or vertical beam for a bed to ensure that swarf, or chips, falls free of the bed). Woodturning lathes specialized for turning large bowls often have no bed or tail stock, merely a free-standing headstock and a cantilevered tool rest.

At one end of the bed (almost always the left, as the operator faces the lathe) is a headstock. The headstock contains high-precision spinning bearings. Rotating within the bearings is a horizontal axle, with an axis parallel to the bed, called the spindle. Spindles are often hollow and have exterior threads or an interior Morse taper on the "inboard" (i.e., facing to the right / towards the bed) by which work-holding accessories may be mounted to the spindle. Spindles may also have exterior threads or an interior taper at their "outboard" (i.e., facing away from the bed) end, or may have a hand-wheel or other accessory mechanism on their outboard end. Spindles are powered and impart motion to the workpiece.

The spindle is driven either by foot power from a treadle and flywheel or by a belt or gear drive to a power source. In most modern lathes this power source is an integral electric motor, often either in the headstock, to the left of the headstock, or beneath the headstock, concealed in the stand.

In addition to the spindle and its bearings, the headstock often contains parts to convert the motor speed into various spindle speeds. Various types of speed-changing mechanism achieve this, from a cone pulley or step pulley, to a cone pulley with back gear (which is essentially a low range, similar in net effect to the two-speed rear of a truck), to an entire gear train similar to that of a manual-shift automotive transmission. Some motors have electronic rheostat-type speed controls, which obviates cone pulleys or gears.

The counterpoint to the headstock is the tailstock, sometimes referred to as the loose head, as it can be positioned at any convenient point on the bed by sliding it to the required area. The tail-stock contains a barrel, which does not rotate, but can slide in and out parallel to the axis of the bed and directly in line with the headstock spindle. The barrel is hollow and usually contains a taper to facilitate the gripping of various types of tooling. Its most common uses are to hold a hardened steel center, which is used to support long thin shafts while turning, or to hold drill bits for drilling axial holes in the work piece. Many other uses are possible.^[9]

Metalworking lathes have a carriage (comprising a saddle and apron) topped with a cross-slide, which is a flat piece that sits crosswise on the bed and can be cranked at right angles to the bed. Sitting atop the cross slide is usually another slide called a compound rest, which provides 2 additional axes of motion, rotary and linear. Atop that sits a toolpost, which holds a cutting tool, which removes material from the workpiece. There may or may not be a leadscrew, which moves the cross-slide along the bed.

Woodturning and metal spinning lathes do not have cross-slides, but rather have banjos, which are flat pieces that sit crosswise on the bed. The position of a banjo can be adjusted by hand; no gearing is involved. Ascending vertically from the banjo is a tool-post, at the top of which is a horizontal tool-rest. In woodturning, hand tools are braced against the tool rest and levered into the workpiece. In metal spinning, the further pin ascends vertically from the tool rest and serves as a fulcrum against which tools may be levered into the workpiece.

Accessories-

Unless a workpiece has a taper machined onto it which perfectly matches the internal taper in the spindle, or has threads which perfectly match the external threads on the spindle (two conditions which rarely exist), an accessory must be used to mount a workpiece to the spindle.

A workpiece may be bolted or screwed to a faceplate, a large, flat disk that mounts to the spindle. In the alternative, faceplate dogs may be used to secure the work to the faceplate.

A workpiece may be mounted on a mandrel, or circular work clamped in a three- or four-jaw chuck. For irregular shaped workpieces it is usual to use a four jaw (independent moving jaws) chuck. These holding devices mount directly to the lathe headstock spindle.

In precision work, and in some classes of repetition work, cylindrical workpieces are usually held in a collet inserted into the spindle and secured either by a draw-bar, or by a collet closing cap on the spindle. Suitable collets may also be used to mount square or hexagonal workpieces. In precision toolmaking work such collets are usually of the draw-in variety, where, as the collet is tightened, the workpiece moves slightly back into the headstock, whereas for most repetition work the dead length variety is preferred, as this ensures that the position of the workpiece does not move as the collet is tightened.

A soft workpiece (e.g., wood) may be pinched between centers by using a spur drive at the headstock, which bites into the wood and imparts torque to it.

A soft dead center is used in the headstock spindle as the work rotates with the centre. Because the centre is soft it can be trued in place before use. The included angle is 60°. Traditionally, a hard dead center is used together with suitable lubricant in the tailstock to support the workpiece. In modern practice the dead center is frequently replaced by a live center, as it turns freely with the workpiece—usually on ball bearings—reducing the frictional heat, especially important at high speeds. When clear facing a long length of material it must be supported at both ends. This can be achieved by the use of a traveling or fixed steady. If a steady is not available, the end face being worked on may be supported by a dead (stationary) half center. A half center has a flat surface machined across a broad section of half of its diameter at the pointed end. A small section of the tip of the dead center is retained to ensure concentricity. Lubrication must be applied at this point of contact and tail stock pressure reduced. A lathe carrier or lathe dog may also be employed when turning between two centers

Modes of use -

When a workpiece is fixed between the headstock and the tail-stock, it is said to be "between centers". When a workpiece is supported at both ends, it is more stable, and more force may be applied to the workpiece, via tools, at a right angle to the axis of rotation, without fear that the workpiece may break loose.

When a workpiece is fixed only to the spindle at the headstock end, the work is said to be "face work". When a workpiece is supported in this manner, less force may be applied to the workpiece, via tools, at a right angle to the axis of rotation, lest the workpiece rip free. Thus, most work must be done axially, towards the headstock, or at right angles, but gently.

When a workpiece is mounted with a certain axis of rotation, worked, then remounted with a new axis of rotation, this is referred to as "eccentric turning" or "multi-axis turning". The result is that various cross sections of the workpiece are rotationally symmetric, but the workpiece as a whole is not rotationally symmetric. This technique is used for camshafts, various types of chair legs.

HYDRO-STATICS

INTRODUCTION -

             hydrostatics is the branch of fluid mechanics that studies "fluids at rest and the pressure in a fluid or    exerted by a fluid on an immersed body".^[1]

It encompasses the study of the conditions under which fluids are at rest in stable equilibrium as opposed to fluid dynamics, the study of fluids in motion. Hydrostatics are categorized as a part of the fluid statics, which is the study of all fluids, incompressible or not, at rest.

Hydrostatics is fundamental to hydraulics, the engineering of equipment for storing, transporting and using fluids. It is also relevant to geophysics and astrophysics (for example, in understanding plate tectonics and the anomalies of the Earth's gravitational field), to meteorology, to medicine (in the context of blood pressure), and many other fields.

Hydrostatics offers physical explanations for many phenomena of everyday life, such as why atmospheric pressure changes with altitude, why wood and oil float on water, and why the surface of still water is always level.

HISTORY -

     Some principles of hydrostatics have been known in an empirical and intuitive sense since antiquity, by the builders of boats, cisterns, aqueducts and fountains. Archimedes is credited with the discovery of Archimedes' Principle, which relates the buoyancy force on an object that is submerged in a fluid to the weight of fluid displaced by the object. The Roman engineer Vitruvius warned readers about lead pipes bursting under hydrostatic pressure.^[2]

The concept of pressure and the way it is transmitted by fluids was formulated by the French mathematician and philosopher Blaise Pascal in 1647.

HYDRO-STATICS IN ANCIENT GREECE AND ROME 

 Pythagorean Cup -

      The "fair cup" or Pythagorean cup, which dates from about the 6th century BC, is a hydraulic technology whose invention is credited to the Greek mathematician and geometer Pythagoras. It was used as a learning tool.

The cup consists of a line carved into the interior of the cup, and a small vertical pipe in the center of the cup that leads to the bottom. The height of this pipe is the same as the line carved into the interior of the cup. The cup may be filled to the line without any fluid passing into the pipe in the center of the cup. However, when the amount of fluid exceeds this fill line, fluid will overflow into the pipe in the center of the cup. Due to the drag that molecules exert on one another, the cup will be emptied.

                                                                      Pythagorean Cup 

Heron's fountain - 

Heron's fountain is a device invented by Heron of Alexandria that consists of a jet of fluid being fed by a reservoir of fluid. The fountain is constructed in such a way that the height of the jet exceeds the height of the fluid in the reservoir, apparently in violation of principles of hydrostatic pressure. The device consisted of an opening and two containers arranged one above the other. The intermediate pot, which was sealed, was filled with fluid, and several cannula (a small tube for transferring fluid between vessels) connecting the various vessels. Trapped air inside the vessels induces a jet of water out of a nozzle, emptying all water from the intermediate reservoir.

                                                                        Heron's fountain

Pascal's contribution in hydro-statics -

Pascal made contributions to developments in both hydrostatics and hydrodynamics. Pascal's Law is a fundamental principle of fluid mechanics that states that any pressure applied to the surface of a fluid is transmitted uniformly throughout the fluid in all directions, in such a way that initial variations in pressure are not changed.

                                                                         Pascal's Principle

Hydro-static pressure -

In a fluid at rest, all frictional and inertial stresses vanish and the state of stress of the system is called hydrostatic. When this condition of V = 0 is applied to the Navier–Stokes equations, the gradient of pressure becomes a function of body forces only. For a barotropic fluid in a conservative force field like a gravitational force field, the pressure exerted by a fluid at equilibrium becomes a function of force exerted by gravity.

The hydrostatic pressure can be determined from a control volume analysis of an infinitesimally small cube of fluid. Since pressure is defined as the force exerted on a test area (p = F/A, with p: pressure, F: force normal to area A, A: area), and the only force acting on any such small cube of fluid is the weight of the fluid column above it, hydrostatic pressure can be calculated according to the following formula:

${\displaystyle p(z)-p(z_{0})={\frac {1}{A}}\int _{z_{0}}^{z}dz'\iint _{A}dx'dy'\,\rho (z')g(z')=\int _{z_{0}}^{z}dz'\,\rho (z')g(z'),}$

where:

• p is the hydrostatic pressure (Pa),
• ρ is the fluid density (kg/m³),
• g is gravitational acceleration (m/s²),
• A is the test area (m²),
• z is the height (parallel to the direction of gravity) of the test area (m),
• z₀ is the height of the zero reference point of the pressure (m).

For water and other liquids, this integral can be simplified significantly for many practical applications, based on the following two assumptions: Since many liquids can be considered incompressible, a reasonable good estimation can be made from assuming a constant density throughout the liquid. (The same assumption cannot be made within a gaseous environment.) Also, since the height h of the fluid column between z and z₀ is often reasonably small compared to the radius of the Earth, one can neglect the variation of g. Under these circumstances, the integral is simplified into the formula:

${\displaystyle p-p_{0}=\rho gh,}$

where h is the height z − z₀ of the liquid column between the test volume and the zero reference point of the pressure. This formula is often called Stevin's law.^[3][4] Note that this reference point should lie at or below the surface of the liquid. Otherwise, one has to split the integral into two (or more) terms with the constant ρ_liquid and ρ(z′)_above. For example, the absolute pressure compared to vacuum is:

${\displaystyle p=\rho gH+p_{\mathrm {atm} },}$

where H is the total height of the liquid column above the test area to the surface, and p_atm is the atmospheric pressure, i.e., the pressure calculated from the remaining integral over the air column from the liquid surface to infinity. This can easily be visualized using a pressure prism.

Hydrostatic pressure has been used in the preservation of foods in a process called pascalization

Atmospheric pressure -

Statistical mechanics shows that, for a gas of constant temperature, T, its pressure, p will vary with height, h, as:

${\displaystyle p(h)=p(0)e^{-{\frac {Mgh}{kT}}}}$

where:

• g is the acceleration due to gravity
• T is the absolute temperature
• k is Boltzmann constant
• M is the mass of a single molecule of gas
• p is the pressure
• h is the height

This is known as the barometric formula, and maybe derived from assuming the pressure is hydrostatic.

If there are multiple types of molecules in the gas, the partial pressure of each type will be given by this equation. Under most conditions, the distribution of each species of gas is independent of the other species.

Buoyancy -

Anybody of arbitrary shape which is immersed, partly or fully, in a fluid will experience the action of a net force in the opposite direction of the local pressure gradient. If this pressure gradient arises from gravity, the net force is in the vertical direction opposite that of the gravitational force. This vertical force is termed buoyancy or buoyant force and is equal in magnitude, but opposite in direction, to the weight of the displaced fluid. Mathematically,

${\displaystyle F=\rho gV}$

where ρ is the density of the fluid, g is the acceleration due to gravity, and V is the volume of fluid directly above the curved surface.^[6] In the case of a ship, for instance, its weight is balanced by pressure forces from the surrounding water, allowing it to float. If more cargo is loaded onto the ship, it would sink more into the water – displacing more water and thus receive a higher buoyant force to balance the increased weight.

Discovery of the principle of buoyancy is attributed to Archimedes.

Hydro-static force on submerged surfaces -

The horizontal and vertical components of the hydrostatic force acting on a submerged surface are given by the following:^[6]

${\displaystyle {\begin{aligned}F_{\mathrm {h} }&=p_{\mathrm {c} }A\\F_{\mathrm {v} }&=\rho gV\end{aligned}}}$

where:

• p_c is the pressure at the centroid of the vertical projection of the submerged surface
• A is the area of the same vertical projection of the surface
• ρ is the density of the fluid
• g is the acceleration due to gravity
• V is the volume of fluid directly above the curved surface      

AIR COMPRESSOR

Introduction -

An air compressor is a device that converts power (using an electric motor, diesel or gasoline engine, etc.) into potential energy stored in pressurized air ( compressed air). By one of several methods, an air compressor forces more and more air into a storage tank, increasing the pressure. When the tank's pressure reaches its engineered upper limit, the air compressor shuts off. The compressed air, then, is held in the tank until called into use.^[1] The energy contained in the compressed air can be used for a variety of applications, utilizing the kinetic energy of the air as it is released and the tank depressurizes. When tank pressure reaches its lower limit, the air compressor turns on again and re-pressurizes the tank. An air compressor must be differentiated from a pump because it works for any gas/air, while pumps work on a liquid.

     AIR  COMPRESSOR 

Classification -

        Compressors can be classified according to the pressure delivered:

1. Low-pressure air compressors (LPACs), which have a discharge pressure of 150 psi or less
2. Medium-pressure compressors which have a discharge pressure of 151 psi to 1,000 psi
3. High-pressure air compressors (HPACs), which have a discharge pressure above 1,000 psi^[2]

        They can also be classified according to the design and principle of operation:

1. Single-stage reciprocating compressor
2. Two-stage reciprocating compressor
3. Compound compressor
4. Rotary-screw compressor
5. Rotary vane pump
6. Scroll compressor
7. Turbo compressor
8. Centrifugal compressor      

Applications -

       

                 Air compressors have many uses, including: supplying high-pressure clean air to fill gas         cylinders, supplying moderate-pressure clean air to a submerged surface supplied diver, supplying   moderate-pressure clean air for driving some office and school building pneumatic HVAC control   system valves, supplying a large amount of moderate-pressure air to power pneumatic tools, such   as jackhammers, filling high pressure air tanks (HPA), for filling tires, and to produce large volumes of   moderate-pressure air for large-scale industrial processes (such as oxidation for petroleum coking or   cement plant bag house purge systems).^[6]

 Most air compressors either are reciprocating piston type, rotary vane or rotary screw. Centrifugal   compressors are common in very large applications, while rotary screw, scroll,^[7] and reciprocating air     compressors are favored for smaller, portable applications.

 There are two main types of air-compressor pumps: oil-injected and oil-less. The oil-less system has more   technical development, but is more expensive, louder and lasts for less time than oil-lubed pumps. The oil-   less system also delivers air of better quality.

 Air compressors are designed to utilize a variety of power sources. While gas/diesel-powered and electric   air compressors are among the most popular, air compressors that utilize vehicle engines, power-take-off,   or hydraulic ports are also commonly used in mobile applications.^[8]

Maintenance - 

 To ensure all compressor types run efficiently with no leaks, it is imperative to perform routine       maintenance, such as monitoring and replacing air compressor fittings.^[10] It is suggested that air   compressor owners perform daily inspections of their equipment, such as:

• Checking for oil and air leaks
• Checking the differential pressure in the compressed air filter
• Determining whether or not the oil in the compressor should be changed
• Verifying safe operating temperature
• Draining condensation from air receiver tanks

 References -

1.  "How Do Air Compressors Work?". Popular Mechanics. 2015-03-18. Retrieved 2017-01-12.
2. ^ "CLASSIFICATION OF AIR COMPRESSORS". www.tpub.com. Retrieved 2017-01-12.
3. ^ "Air Compressor Types and Controls". Natural Resources Canada.
4. ^ "Compressor Selection Basics: Positive Displacement versus Dynamic Compression". Retrieved 2017-01-12 – via The 5th Utility.
5. ^ "Types of Air Compressors". The Engineering ToolBox.