A metal lathe or metalworking lathe is a large class of lathes A lathe is a machine tool which spins the workpiece to perform various operations such as cutting, sanding, knurling, drilling, or deformation with tools that are applied to the workpiece to create an object which has symmetry about an axis of rotation designed for precisely machining Conventional machining, one of the most important material removal methods, is a collection of material-working processes in which power-driven machine tools, such as lathes, milling machines, and drill presses, are used with a sharp cutting tool to mechanically cut the material to achieve the desired geometry. Machining is a part of the relatively hard materials. They were originally designed to machine metals A metal is a chemical element that is a good conductor of both electricity and heat and forms cations and ionic bonds with non-metals. In chemistry, a metal is an element, compound, or alloy characterized by high electrical conductivity. In a metal, atoms readily lose electrons to form positive ions (cations). Those ions are surrounded by; however, with the advent of plastics A plastic material is any of a wide range of synthetic or semi-synthetic organic amorphous solids[citation needed] used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce costs. Monomers of plastic are either natural or synthetic and other materials, and with their inherent versatility, they are used in a wide range of applications, and a broad range of materials. In machining jargon Jargon is terminology which is especially defined in relationship to a specific activity, profession, or group. The philosophe Condillac observed in 1782 that "Every science requires a special language because every science has its own ideas." As a rationalist member of the Enlightenment he continued, "It seems that one ought to, where the larger context is already understood, they are usually simply called lathes, or else referred to by more-specific subtype names (toolroom lathe, turret lathe, etc.). These rigid machine tools A machine tool is a powered mechanical device, typically used to fabricate metal components of machines by machining, which is the selective removal of metal. The term machine tool is usually reserved for tools that used a power source other than human movement, but they can be powered by people if appropriately set up. Many historians of remove material from a rotating A rotation is a movement of an object in a circular motion. An object rotates around a center of rotation. A three-dimensional object rotates always around an imaginary line called an axis as the Euler's rotation theorem shows. If the axis of rotation is within the body, the body is said to rotate upon itself, or spin—which implies relative workpiece via the (typically linear) movements of various cutting tools, such as tool bits The term tool bit generally refers to a non-rotary cutting tool used in metal lathes, shapers, and planers. Such cutters are also often referred to by the set-phrase name of single-point cutting tool. The cutting edge is ground to suit a particular machining operation and may be resharpened or reshaped as needed. The ground tool bit is held and drill bits Drill bits are cutting tools used to create cylindrical holes. Bits are held in a tool called a drill, which rotates them and provides torque and axial force to create the hole. Specialized bits are also available for non-cylindrical-shaped holes.
Construction
The design of lathes can vary greatly depending on the intended application; however, basic features are common to most types. These machines consist of (at the least) a headstock, bed, carriage, and tailstock. Better machines are solidly constructed with broad bearing surfaces (slides or ways) for stability, and manufactured with great precision. This helps ensure the components manufactured on the machines can meet the required tolerances and repeatability.
Headstock
Headstock with legend, numbers and text within the description refer to those in the imageThe headstock (H1) houses the main spindle (H4), speed change mechanism (H2,H3), and change gears (H10). The headstock is required to be made as robust as possible due to the cutting forces involved, which can distort a lightly built housing, and induce harmonic A harmonic of a wave is a component frequency of the signal that is an integer multiple of the fundamental frequency, i.e. if the fundamental frequency is f, the harmonics have frequencies 2f, 3f, 4f, . . . etc. The harmonics have the property that they are all periodic at the fundamental frequency, therefore the sum of harmonics is also periodic vibrations that will transfer through to the workpiece, reducing the quality of the finished workpiece.
The main spindle is generally hollow to allow long bars to extend through to the work area. This reduces preparation and waste of material. The spindle runs in precision bearings and is fitted with some means of attaching workholding devices such as chucks or faceplates. This end of the spindle usually also has an included taper, frequently a Morse taper, to allow the insertion of tapers and centers A lathe center is a tool that has been ground to an included angle of 60 ° and is used to accurately position a workpiece about its axis.[citation needed]. On older machines the spindle was directly driven by a flat belt pulley A pulley, also called a sheave or a drum, is a mechanism composed of a wheel on an axle or shaft that may have a groove between two flanges around its circumference. A rope, cable, belt, or chain usually runs over the wheel and inside the groove, if present. Pulleys are used to change the direction of an applied force, transmit rotational motion, with lower speeds available by manipulating the bull gear. Later machines use a gear box driven by a dedicated electric motor. A fully geared head allows the operator to select speeds entirely through the gearbox.
Bed
The bed is a robust base that connects to the headstock and permits the carriage and tailstock to be aligned parallel with the axis of the spindle. This is facilitated by hardened and ground ways which restrain the carriage and tailstock in a set track. The carriage travels by means of a rack and pinion A rack and pinion is a type of linear actuator that comprises a pair of gears which convert rotational motion into linear motion. The circular pinion engages teeth on a linear "gear" bar – the rack. Rotational motion applied to the pinion will cause the rack to move to the side, up to the limit of its travel. For example, in a rack system, leadscrew A leadscrew , also known as a power screw or translation screw, is a screw designed to translate radial motion into linear motion. Common applications are machine slides (such as in machine tools), vises, presses, and jacks of accurate pitch, or feedscrew.
Types of beds include inverted "V" beds, flat beds, and combination "V" and flat beds. "V" and combination beds are used for precision and light duty work, while flat beds are used for heavy duty work.[citation needed]
When a lathe is installed, the first step is to level it, which refers to making sure the bed is not twisted or bowed. There is no need to make the machine exactly horizontal, but it must be entirely untwisted to achieve accurate cutting geometry. A precision level is a useful tool for identifying and removing any twist. It is advisable also to use such a level along the bed to detect bending, in the case of a lathe with more than four mounting points. In both instances the level is used as a comparator rather than an absolute reference.
Feed and lead screws
The feedscrew (H8) is a long driveshaft A drive shaft, driving shaft, propeller shaft, or Cardan shaft is a mechanical component for transmitting torque and rotation, usually used to connect other components of a drive train that cannot be connected directly because of distance or the need to allow for relative movement between them that allows a series of gears to drive the carriage mechanisms. These gears are located in the apron of the carriage. Both the feedscrew and leadscrew A leadscrew , also known as a power screw or translation screw, is a screw designed to translate radial motion into linear motion. Common applications are machine slides (such as in machine tools), vises, presses, and jacks (H7) are driven by either the change gears (on the quadrant) or an intermediate gearbox known as a quick change gearbox (H6) or Norton gearbox. These intermediate gears allow the correct ratio and direction to be set for cutting threads or worm gears A worm drive is a gear arrangement in which a worm meshes with a worm gear (which is similar in appearance to a spur gear, and is also called a worm wheel). The terminology is often confused by imprecise use of the term worm gear to refer to the worm, the worm gear, or the worm drive as a unit. Tumbler gears (operated by H5) are provided between the spindle and gear train along with a quadrant plate that enables a gear train of the correct ratio and direction to be introduced. This provides a constant relationship between the number of turns the spindle makes, to the number of turns the leadscrew makes. This ratio allows screwthreads to be cut on the workpiece without the aid of a die Taps and dies are cutting tools used when creating screw threads. A tap is used to cut the female portion of the mating pair . A die is used to cut the male portion of the mating pair (e.g. a bolt). The process of cutting the threads in a hole is called "tapping" the hole. The process of cutting with a die is called "threading".
Some lathes have only one leadscrew that serves all carriage-moving purposes. For screw cutting, a half nut is engaged to be driven by the leadscrew's thread; and for general power feed, a key engages with a keyway cut into the leadscrew to drive a pinion along a rack A rack and pinion is a type of linear actuator that comprises a pair of gears which convert rotational motion into linear motion. The circular pinion engages teeth on a linear "gear" bar – the rack. Rotational motion applied to the pinion will cause the rack to move to the side, up to the limit of its travel. For example, in a rack that is mounted along the lathe bed.
The leadscrew will be manufactured to either imperial Imperial units or the imperial system is a system of units, first defined in the British Weights and Measures Act of 1824, later refined and reduced. The system came into official use across the British Empire. By the late 20th century most nations of the former empire had officially adopted the metric system as their main system of measurement or metric The metre , symbol m, is the base unit of length in the International System of Units (SI). Originally intended to be one ten-millionth of the distance from the Earth's equator to the North Pole, its definition has been periodically refined to reflect growing knowledge of metrology. Since 1983, it is defined as the distance travelled by light in standards and will require a conversion ratio to be introduced to create thread forms from a different family. To accurately convert from one thread form to the other requires a 127-tooth gear, or on lathes not large enough to mount one, an approximation may be used. Multiples of 3 and 7 giving a ratio of 63:1 can be used to cut fairly loose threads. This conversion ratio is often built into the quick change gearboxes.
The precise ratio required to convert a lathe with an Imperial (inch) leadscrew to metric (millimeter) threading is 100 / 127 = 0.7874... . The best approximation with the fewest total teeth is very often 37 / 47 = 0.7872... . This transposition gives a constant -0.020 percent error over all customary and model-maker's metric pitches (0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.60, 0.70, 0.75, 0.80, 1.00, 1.25, 1.50, 1.75, 2.00, 2.50, 3.00, 3.50, 4.00, 4.50, 5.00, 5.50 and 6.00mm).
Carriage
Carriage with legend, numbers and text within the description refer to those in the imageIn its simplest form the carriage holds the tool bit The term tool bit generally refers to a non-rotary cutting tool used in metal lathes, shapers, and planers. Such cutters are also often referred to by the set-phrase name of single-point cutting tool. The cutting edge is ground to suit a particular machining operation and may be resharpened or reshaped as needed. The ground tool bit is held and moves it longitudinally (turning) or perpendicularly (facing) under the control of the operator. The operator moves the carriage manually via the handwheel (5a) or automatically by engaging the feed shaft with the carriage feed mechanism (5c). This provides some relief for the operator as the movement of the carriage becomes power assisted. The handwheels (2a, 3b, 5a) on the carriage and its related slides are usually calibrated, both for ease of use and to assist in making reproducible cuts. The carriage typically comprises a top casting, known as the saddle (4), and a side casting, known as the apron (5).
Cross-slide
The cross-slide (3) rides on the carriage and has a feedscrew that travels perpendicular to the main spindle axis. This permits facing operations to be performed, and the depth of cut to be adjusted. This feedscrew can be engaged, through a gear train, to the feed shaft (mentioned previously) to provide automated 'power feed' movement to the cross-slide. On most lathes, only one direction can be engaged at a time as an interlock mechanism will shut out the second gear train.
Compound rest
The compound rest (or top slide) (2) is usually where the tool post is mounted. It provides a smaller amount of movement (less than the cross-slide) along its axis via another feedscrew. The compound rest axis can be adjusted independently of the carriage or cross-slide. It is used for turning tapers, to control depth of cut when screwcutting or precision facing, or to obtain finer feeds (under manual control) than the feed shaft permits. Usually, the compound rest has a protractor marked in its base (2b), enabling the operator to adjust its axis to precise angles.
The slide rest can be traced to the fifteenth century. In 1718 the tool-supporting slide rest with a set of gears was introduced by a Russian inventor Andrey Nartov and had limited usage in the Russian industry.[1] In the eighteenth century the slide rest was also used on French ornamental turning lathes. The suite of gun boring mills at the Royal Arsenal The Royal Arsenal, Woolwich, originally known as the Woolwich Warren, carried out armaments manufacture, ammunition proofing and explosives research for the British armed forces. It was sited on the south bank of the River Thames in Woolwich in south-east London, England, Woolwich Woolwich is a district in south London, England, located in the London Borough of Greenwich. The area is identified in the London Plan as one of 35 major centres in Greater London, in the 1780s by the Verbruggan family also had slide rests. The story has long circulated that Henry Maudslay invented it, but he did not (and never claimed so). The legend that Maudslay invented the slide rest originated with James Nasmyth, who wrote ambiguously about it in his Remarks on the Introduction of the Slide Principle, 1841; later writers misunderstood, and propagated the error. Maudslay did help to disseminate the idea widely. It is highly probable that he saw it when he was working at the Arsenal as a boy. In 1794, whilst he was working for Joseph Bramah Joseph Bramah , born Stainborough Lane Farm, Wentworth, Yorkshire, England, was an inventor and locksmith. He is best known for having invented the hydraulic press. Along with William George Armstrong, he can be considered one of the two fathers of hydraulic engineering, he made one, and when he had his own workshop used it extensively in the lathes he made and sold there. Coupled with the network of engineers he trained, this ensured the slide rest became widely known and copied by other lathe makers, and so diffused throughout British engineering workshops. A practical and versatile screw-cutting lathe incorporating the trio of leadscrew, change gears, and slide rest was Maudslay's most important achievement.
The first fully documented, all-metal slide rest lathe was invented by Jacques de Vaucanson Jacques de Vaucanson was a French inventor and artist with a mechanical background who is credited with creating the world's first true robots, as well as for creating the first completely automated loom around 1751. It was described in the Encyclopédie Encyclopédie, ou dictionnaire raisonné des sciences, des arts et des métiers was a general encyclopedia published in France between 1751 and 1772, with later supplements, revised editions, and translations. As of 1750 the full title was Encyclopédie, ou Dictionnaire raisonné des sciences, des arts et des métiers, par une société de gens de a long time before Maudslay invented and 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.
Toolpost
The tool bit The term tool bit generally refers to a non-rotary cutting tool used in metal lathes, shapers, and planers. Such cutters are also often referred to by the set-phrase name of single-point cutting tool. The cutting edge is ground to suit a particular machining operation and may be resharpened or reshaped as needed. The ground tool bit is held is mounted in the toolpost (1) which may be of the American lantern style, traditional four-sided square style, or a quick-change style such as the multifix arrangement pictured. The advantage of a quick change set-up is to allow an unlimited number of tools to be used (up to the number of holders available) rather than being limited to one tool with the lantern style, or to four tools with the four-sided type. Interchangeable tool holders allow all tools to be preset to a center height that does not change, even if the holder is removed from the machine.
Tailstock
Tailstock with legend, numbers and text within the description refer to those in the imageThe tailstock A tailstock, also known as a foot stock, is a device often used as part of an engineering lathe, wood-turning lathe, or used in conjunction with a rotary table on a milling machine is a toolholder directly mounted on the spindle axis, opposite the headstock. The spindle (T5) does not rotate but does travel longitudinally under the action of a leadscrew and handwheel (T1). The spindle includes a taper to hold drill bits Drill bits are cutting tools used to create cylindrical holes. Bits are held in a tool called a drill, which rotates them and provides torque and axial force to create the hole. Specialized bits are also available for non-cylindrical-shaped holes, centers A lathe center is a tool that has been ground to an included angle of 60 ° and is used to accurately position a workpiece about its axis.[citation needed] and other tooling. The tailstock can be positioned along the bed and clamped (T6) in position as required. There is also provision to offset the tailstock (T4) from the spindles axis, this is useful for turning small tapers.
The image shows a reduction gear box (T2) between the handwheel and spindle, this is a feature found only in the larger center lathes, where large drills may necessitate the extra leverage.
Types of metal lathes
There are many variants of lathes within the metalworking Metalworking is the process of working with metals to create individual parts, assemblies, or large scale structures. The term covers a wide range of work from large ships and bridges to precise engine parts and delicate jewellery. It therefore includes a correspondingly wide range of skills, processes, and tools field. Some variations are not all that obvious, and others are more a niche area. For example, a centering lathe is a dual head machine where the work remains fixed and the heads move towards the workpiece and machine a center drill hole into each end. The resulting workpiece may then be used "between centers" in another operation. The usage of the term metal lathe may also be considered somewhat outdated these days, plastics and other composite materials are in wide use and with appropriate modifications, the same principles and techniques may be applied to their machining as that used for metal.
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