Lathe machine

Lathe machine

Introduction_
A lathe is a tool that rotates the work piece about an axis of rotation to perform various operations such as cutting, sanding, knurling, drilling, deformation, facing, turning, with tools that are applied to the work piece to create an object with symmetry about that axis. Lathes are used in wood turning, 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 work piece is usually held in place by either one or two centers, at least one of which can typically be moved horizontally to accommodate varying work piece lengths. Other work-holding methods include clamping the work about the axis of rotation using a chuck or col-let, or to a face plate, using clamps or dogs. Examples of objects that can be produced on a lathe include candlestick holders, gun barrels, cue sticks, table legs, bowls, baseball bats, musical instruments [especially woodwind instruments], crankshafts, and camshafts.

History_
The lathe is an ancient tool, dating at least to ancient Egypt and known to be used in Assyria, India and ancient Greece. 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 lead to the invention of other machine tools. The origin of turning dates to around [1300 BCE] when the Ancient Egyptians first developed a two-person lathe. One person would turn the wood work piece with a rope while the other used a sharp tool to cut shapes in the wood. Ancient Rome improved the Egyptian design with the addition of a turning bow. In the Middle Ages a pedal replaced hand-operated turning, allowing a single person to rotate the piece while working with both hands. The pedal was usually connected to a pole, often a straight-grained sapling. The system today is called the "spring pole" lathe. Spring pole lathes were in common use into the early 20th century. Exact drawing made with camera obscure of horizontal boring machine by Jan Verbiage in Woolworth Royal Brass Foundry approx. [1778][Drawing 47 out of set of 50 drawings]. An important early lathe in the UK was the horizontal boring machine that was installed in [1772] in the Royal Arsenal in Woolworth. 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 work piece was turning as opposed to the tool, making it technically a lathe [see attached drawing]. Henry Maud slay who later developed many improvements to the lathe worked at the Royal Arsenal from 1783 being exposed to this machine in the Verbiage workshop. During the Industrial Revolution, mechanized power generated by water wheels or steam engines was transmitted to the lathe via line shafting, allowing faster and easier work. Metalworking lathes evolved into heavier machines with thicker, more rigid parts. Between the late 19th and mid-20th centuries, individual electric motors at each lathe replaced line shafting as the power source. Beginning in the [1950], servomechanisms were applied to the control of lathes and other machine tools via numerical control, which often was coupled with computers to yield computerized numerical control [CNC]. Today manually controlled and [CNC] lathes coexist in the manufacturing industries.

Description_

A lathe may or may not have legs, 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 snarf, or chips, falls free of the bed]. Wood turning lathes specialized for turning large bowls often have no bed or tail stock, merely a free-standing head stock and a cantilevered tool rest. At one end of the bed [almost always the left, as the operator faces the lathe] is a head stock. The head stock 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 and/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 and/or an interior taper at their "outboard" [I.e-Facing away from the bed] end, and/or may have a hand-wheel or other accessory mechanism on their outboard end. Spindles are powered and impart motion to the work piece. 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 head stock, to the left of the head stock, or beneath the head stock, concealed in the stand. In addition to the spindle and its bearings, the head stock 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 auto transmission. Some motors have electronic rheostat-type speed controls, which obviates cone pulleys or gears. The counterpoint to the head stock is the tail stock, 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 head stock 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. 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 tool post, which holds a cutting tool, which removes material from the work piece. There may or may not be a lead screw, which moves the cross-slide along the bed. Wood turning 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 wood turning, hand tools are braced against the tool rest and levered into the work piece. 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 work piece.

Accessories_
Unless a work piece 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 work piece to the spindle. A work piece may be bolted or screwed to a face plate, a large, flat disk that mounts to the spindle. In the alternative, face plate dogs may be used to secure the work to the face plate. A work piece may be mounted on a mandrel, or circular work clamped in a three- or four-jaw chuck. For irregular shaped work pieces it is usual to use a four jaw [independent moving jaws] chuck. These holding devices mount directly to the lathe head stock spindle. In precision work, and in some classes of repetition work, cylindrical work pieces are usually held in a col-let inserted into the spindle and secured either by a draw-bar, or by a col-let closing cap on the spindle. Suitable col-lets may also be used to mount square or hexagonal work pieces. In precision tool making work such col-lets are usually of the draw-in variety, where, as the col-let is tightened, the work piece moves slightly back into the head stock, whereas for most repetition work the dead length variety is preferred, as this ensures that the position of the work piece does not move as the col-let is tightened. A soft work piece [e.g., wood] may be pinched between centers by using a spur drive at the head stock, which bites into the wood and imparts torque to it. Live center [top]; dead center [bottom]. A soft dead center is used in the head stock spindle as the work rotates with the center. Because the center 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 tail stock to support the work piece. In modern practice the dead center is frequently replaced by a live center, as it turns freely with the work piece—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 concentric. 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. In wood turning, one variation of a live center is a cup center, which is a cone of metal surrounded by an annular ring of metal that decreases the chances of the work piece splitting. A circular metal plate with even spaced holes around the periphery, mounted to the spindle, is called an "index plate". It can be used to rotate the spindle to a precise angle, then lock it in place, facilitating repeated auxiliary operations done to the work piece. Other accessories, including items such as taper turning attachments, knurling tools, vertical slides, fixed and traveling steadies, etc., increase the versatility of a lathe and the range of work it may perform.

Modes of use_
When a work piece is fixed between the head stock and the tail-stock, it is said to be "between centers". When a work piece is supported at both ends, it is more stable, and more force may be applied to the work piece, via tools, at a right angle to the axis of rotation, without fear that the work piece may break loose. When a work piece is fixed only to the spindle at the head stock end, the work is said to be "face work". When a work piece is supported in this manner, less force may be applied to the work piece, via tools, at a right angle to the axis of rotation, lest the work piece rip free. Thus, most work must be done axially, towards the head stock, or at right angles, but gently. When a work piece 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 work piece are rotation ally symmetric, but the work piece as a whole is not rotation ally symmetric. This technique is used for camshafts, various types of chair legs.

Cost_
152703rs