Lathe Machine Assignment 4g6751

LATHE MACHINE

SUBMITTED BY: RAKESH KUMAR(1120259) BHIMSAIN(1120258) SECTION D-2

INTRODUCTION

A lathe is a machine tool which rotates the workpiece on its axis 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 symmetryabout an axis of rotation. 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 material can be held in place by either one or two centers, at least one of which can be moved horizontally to accommodate varying material 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 dogs.

DIAGRAM OF LATHE MACHINE

Explanation of the standard components of most lathes: • Bed: Usually made of cast iron. Provides a heavy rigid frame on which all the main components are mounted.

• Ways: Inner and outer guide rails that are precision machined parallel to assure accuracy of movement. • Headstock: mounted in a fixed position on the inner ways, usually at the left end. Using a chuck, it rotates the work. • Gearbox: inside the headstock, providing multiple speeds with a geometric ratio by moving levers. • Spindle: Hole through the headstock to which bar stock can be fed, which allows shafts that are up to 2 times the length between lathe centers to be worked on one end at a time. • Chuck: 3-jaw (self centering) or 4-jaw (independent) to clamp part being machined. • Chuck: allows the mounting of difficult workpieces that are not round, square or triangular.

• Tailstock: Fits on the inner ways of the bed and can slide towards any position the headstock to fit the length of the work piece. An optional taper turning attachment would be mounted to it. • Tailstock Quill: Has a Morse taper to hold a lathe center, drill bit or other tool. • Carriage: Moves on the outer ways. Used for mounting and moving most the cutting tools. • Cross Slide: Mounted on the traverse slide of the carriage, and uses a handwheel to feed tools into the workpiece. • Tool Post: To mount tool holders in which the cutting bits are clamped. • Compound Rest: Mounted to the cross slide, it pivots around the tool post.

• Apron: Attached to the front of the carriage, it has the mechanism and controls for moving the carriage and cross slide. • Feed Rod: Has a keyway, with two reversing pinion gears, either of which can be meshed with the mating bevel gear to forward or reverse the carriage using a clutch. • Lead Screw: For cutting threads. • Split Nut: When closed around the lead screw, the carriage is driven along by direct drive without using a clutch. • Quick Change Gearbox: Controls the movement of the carriage using levers. • Steady Rest: Clamped to the lathe ways, it uses adjustable fingers to the workpiece and align it. Can be used in place of tailstock or in the middle to long or unstable parts being machined.

• Follow Rest: Bolted to the lathe carriage, it uses adjustable fingers to bear against the workpiece opposite the cutting tool to prevent deflection.

LATHE RIES: • Four-jaw chuck: • Used mainly for holding irregular shapes. • Collet chuck: • Primarily used for small round work pieces • Three-jaw chuck: • Used with a variety of diameters of round stock. It is a self centering chuck. it is used to hold only round jobs. • Faceplate: • A faceplate, drive dog, and mandrel may be used to turn workpieces such as gearblanks.

Tools used on LATHE machine TOOL HOLDERS AND TOOL POSTS Lathe tool holders are designed to securely and rigidly hold the tool bit at a fixed angle for properly machining a workpiece . Tool holders are designed to work in conjunction with various lathe tool posts, onto which the tool holders are mounted. Tool holders for high speed steel tool bits come in various types for different uses. These tool holders are designed to be used with the standard round tool post that usually is supplied with each engine lathe. This tool post consists of the post, screw, washer, collar, and rocker, and fits into the T-slot of the compound rest.

Standard tool holders for high-speed steel cutting tools have a square slot made to fit a standard size tool bit shank. Tool bit shanks can be 1/4-inch, 5/16-inch, 3/8-inch, and greater, with all the various sizes being manufactured for all the different lathe manufacturer's tool holder models. Some standard tool holders for steel tool bits are the straight tool holder, right and left offset tool holder, and the zero rake tool holder designed for special carbide tool bits. Other tool holders to fit the standard round tool post include straight, left, and right parting tool holders, knurling tool holders, boring bar tool holders, and specially formed thread cutting tool holders. The turret tool post is a swiveling block that can hold many different tool bits or tool holders. Each cutting tool can quickly be swiveled into cutting position and clamped into place using a quick clamping handle. The turret tool post is used mainly for high-speed production operations. The heavy-duty or open-sided tool post (Figure 717) is used for holding a single carbide-tipped tool bit or tool holder. It is used mainly for very heavy cuts that require a rigid tool holder.

The quick-change tool system (Figure 7-18) consists of a quick-change dovetail tool post with a complete set of matching dovetailed tool holders that can be quickly changed as different lathe operations become necessary. This system has a quick-release knob on the top of the tool post that allows tool changes in less than 5 seconds, which makes this system valuable for production machine shops.

WORK HOLDING DEVICES lathe Many different devices, such as chucks, collets, faceplates, drive plates, mandrels, and

lathe centers, are used to hold and drive the work while it is being machined on a lathe. The size and type of work to be machined and the particular operation that needs to be done will determine which work holding device is best for any particular job. Another consideration is how much accuracy is needed for a job, since some work holding devices are more accurate than others. Operational details for some of the more common work holding devices follow. The universal scroll chuck, usually has three jaws which move in unison as an adjusting pinion is rotated. The advantage of the universal scroll chuck is its ease of operation in centering work for concentric turning. This chuck is not as accurate as the independent chuck, but when in good condition it will center work within 0.002 to 0.003 inches of runout. The jaws are moved simultaneously within the chuck by a scroll or spiral-threaded plate. The jaws are threaded to the scroll and move an equal distance inward or outward as the scroll is rotated by the adjusting pinion. Since the jaws are individually aligned on the scroll, the jaws cannot

usually be reversed. Some manufactures supply two sets of jaws, one for internal work and one for external work. Other manufactures make the jaws in two pieces so the outside, or gripping surface may be reversed. which can be interchanged. The universal scroll chuck can be used to hold and automatically center round or hexagonal workpieces. Having only three jaws, the chuck cannot be used effectively to hold square, octagonal, or irregular shapes. The independent chuck, generally has four jaws which are adjusted individually on the chuck face by means of adjusting screws. The chuck face is scribed with concentric circles which are used for rough alignment of the jaws when chucking round workpieces. The final adjustment is made by turning the workpiece slowly by hand and using a dial indicator to determine it's concentricity. The jaws are then readjusted as necessary to align the workpiece within the desired tolerances. The jaws of the independent chuck may be used as illustrated or may be reversed so that the steps face in the opposite direction; thus workpieces can be gripped either externally or internally. The

independent chuck can be used to hold square, round, octagonal, or irregularly shaped workpieces in either a concentric or eccentric position due to the independent operation of each jaw. Because of its versatility and capacity for fine adjustment, the independent chuck is commonly used for mounting odd-shaped workpieces which must be held with extreme accuracy. A combination chuck combines the features of the independent chuck and the universal scroll chuck and can have either three or four jaws. The jaws can be moved in unison on a scroll for automatic centering or can be moved individually if desired by separate adjusting screws. The drill chuck, is a small universal chuck which can be used in either the headstock spindle or the tailstock for holding straight-shank drills, reamers, taps, or small diameter workpieces. The drill chuck has three or four hardened steel jaws which are moved together or apart by adjusting a tapered sleeve within which they are contained. The drill chuck is capable of centering tools and small-diameter workpieces to within 0.002 or 0.003 inch when firmly tightened.

The collet chuck is the most accurate means of holding small workpieces in the lathe. The collet chuck consists of a spring machine collet and a collet attachment which secures and regulates the collet on the headstock spindle of the.

Lathe Cutting Tools a.General. A machine tool is no more efficient than its cutting tool. There is nothing in shop work that should be given more thoughtful consideration than cutting tools. Time is always wasted if an improperly shaped tool is used. The cutting action of the tool depends on its shape and its adjustment in the holding device. Lathe cutter bits may be considered as wedges which are forced into the material to cause compression, with a resulting rupture or plastic flow of the material. The rupture or plastic flow is called cutting. To machine metal efficiently and accurately, it is necessary that the cutter bits have keen, well-ed cutting edges, and that they be ground for the particular metal being machined and the type of cut desired. Cutter bits are made from several

types of steel, the most common of which are described in the following subparagraphs. (1) Carbon Steel. Carbon steel, or tool steel is high in carbon content, hardens to a high degree of hardness when properly heated and quenched. The carbonsteel tool will give good results as long as constant care is taken to avoid overheating or "bluing," since the steel will lose its temper or hardness at a relatively low heat becoming ineffective as a cutting tool. For low-speed turning, high carbon steels give satisfactory results and are more economical than other materials. (2) High-Speed Steel. High-speed steel is alloyed with tungsten and sometimes with chromium, vanadium, or molybdenum. Although not as hard as properly

tempered carbon steel, the majority of lathe cutting tools are made of high-speed steel because it retains its hardness at extremely high temperatures. Cutter hits made of this material can be used without damage at speeds and feeds which heat the cutting edges to a dull red. (3) Stellite. These cutter bits will withstand higher cutting speeds than high-speed steel cutter bits. Stellite is a nonmagnetic alloy which is harder than common high-speed steel. The tool will not lose its temper, even though heated red hot from the friction that is generated by taking a cut. Stellite is more brittle than highspeed steel. To prevent breaking or chipping, it requires just enough clearance to permit the tool to cut freely. Stellite is also used for machining hardened steel, cast iron, bronze, etc. (4) Tungsten Carbide. Tungsten carbide is used to tip cutter bits when maximum speed and efficiency is required for materials which are difficult to machine. Although expensive, these cutter bits are highly efficient for machining cast iron, alloyed cast iron, copper, brass, bronze, aluminum, Babbitt

metal, and such abrasive nonmetallic materials as fiber, hard rubber, and bakelite. Cutter bits of this type require very rigid and are usually held in open-side toolposts. They require special grinding wheels for sharpening, since tungsten carbide is too hard to be redressed on ordinary grinding abrasive wheels. (5) Tantalum Carbide and Titanium Carbide. These cutting tools are similar to tungsten carbide tools but are used mostly for machining steel where extreme heavy cuts are taken and heat and pressure tend to deform the cutting edge of the other types of cutting tools.

LATHE OPERATIONS:

• Turning: This operation is one of the most basic machining processes. That is, the part is rotated while a single point cutting tool is moved parallel to the axis of rotation. Turning can be done on the external surface of the part as well as internally (boring). The starting material is generally a workpiece generated by other processes such as casting, forging, extrusion, or drawing. Tapered turning

a) from the compound slide b) from taper turning attachment c) using a hydraulic copy attachment d) using a C.N.C. lathe e) using a form tool f) by the offsetting of the tailstock - this method more suited for shallow tapers Spherical generation The proper expression for making or turning a shape is to generate as in to generate a form around a fixed axis of revolution. a) using hydraulic copy attachment b) C.N.C. (computerised numerically controlled) lathe c) using a form tool (a rough and ready method) d) using bed jig (need drawing to explain Hard turning Hard turning is a turning done on materials with a Rockwell C hardness greater than 45. It is typically performed after the workpiece is heat treated. The process is intended to replace or limit traditional grinding operations. Hard turning, when applied for purely stock removal purposes, competes favorably with rough grinding. However, when it is applied for finishing where form and dimension are critical, grinding is superior. Grinding produces higher dimensional accuracy of roundness and cylindricity. In addition, polished surface

finishes of Rz=0.3-0.8z cannot be achieved with hard turning alone. Hard turning is appropriate for parts requiring roundness accuracy of 0.5-12 micrometres, and/or surface roughness of Rz 0.8– 7.0 micrometres. It is used for gears, injection pump components, hydraulic components, among other applications.

(turning) • Facing: It is part of the turning process. It involves moving the cutting tool at right angles to the axis of rotation of the rotating workpiece. This can be performed by the operation of the cross-slide, if one is fitted, as distinct from the longitudinal feed (turning). It is frequently the first operation performed in the production of the workpiece, and often the last- hence the phrase “ending up”.

(facing) • Parting: This process is used to create deep grooves which will remove a completed or part-complete component from its parent stock.

(parting) •

Grooving: It is like parting, except that grooves are cut to a specific depth by a form tool instead of severing a completed/part-complete component from the stock

Grooving can be performed on internal and external surfaces

(grooving) • Screw cutting : Both standard and non-standard screw threads can be turned on a lathe using an appropriate cutting tool. (Usually having a 60, or 55° nose angle • Chamfering: Chamfering removes the burrs and sharp edges, and thus makes the handling safe. Chamfering can be done by a form tool having angle equal to chamfer which is generally kept at 45°.

(chamfered piece)