References

This are a all the references that we took from internet while we are in the process of doing our assignment :-

http://www.mini-lathe.com/Mini_lathe/Operation/Facing/facing.htm

http://en.wikipedia.org/wiki/Lathe_(metal)

http://en.wikipedia.org/wiki/Turning

http://www.mini-lathe.com/Mini_lathe/lathe_safety.htm

http://www.sherline.com/grinding.htm

http://itdc.lbcc.edu/cps/machineTool/machiningOperations/machiningOperationsALT/machiningOperations.htm

http://www.mini-lathe.com/Mini_lathe/Operation/Drilling/drilling.htm

http://www.mini-lathe.com/Mini_lathe/Introduction/introduction.htm

Lathe Safety

As in the lathe machine operations, like any power tools, can be dangerous if used improperly. If you are new to metal working, get in the habit right from the start of rigorously following good safety practices. Here are some tips:

• Always wear eye protection to prevent any sharp, hot metal chips spin off from the lathe machine to injured our eye.
• Short sleeve shirts needed to be worn to prevent get caught on the rotating work.
• Shoes are advice to be worn especially leather work shoes to protect your feet from sharp metal chips.
• Wrist watches, necklaces and chains are needed to be removed to prevent get caught on rotating work and might even damaged your hand.
• Tie back long hair so it can’t get caught in the rotating work.
• Double check the condition of the machine before starts using the lathe machine.
• Chuck key is immediately remove after use to prevent users to play with it.
• Fingers are need to be clear from the rotating work and cutting tools.
• Keep hands away from spinning chuck.
• Never use a file with bare tang – tang could be forced back into your wrist or palm. Inexpensive wooden handles are readily available for common file sizes

Internal Lathe Operations

Drilling Operations

The alignment between the headstock and tailstock of the lathe enables you to drill holes that are precisely centered in a cylindrical piece of stock. The next step is to start the drill hole using a center drill - a stiff, stubby drill with a short tip. If you try to drill a hole without first center drilling, the drill will almost certainly wander off center, producing a hole that is oversized and misaligned.

The picture below shows the drilling tools for lathe machine.

Preparing to Drill

Before drilling you need to make sure that the drill chuck is firmly seated in the tailstock. With the chuck arbor loosely inserted in the tailstock bore, crank the tailstock bore out about 1/2". Lock the tailstock to the ways, then thrust the chuck firmly back towards the tailstock to firmly seat the arbor in the Morse taper of the tailstock. (The chuck is removed from the tailstock by cranking the tailstock ram back until the arbor is forced out).

Choose a center drill with a diameter similar to that of the hole that you intend to drill. Insert the center drill in the jaws of the tailstock chuck and tighten the chuck until the jaws just start to grip the drill. Since the goal is to make the drill as stiff as possible, you don't want it to extend very far from the tip of the jaws. Twist the drill to seat it and dislodge any metal chips or other crud that might keep the drill from seating properly. Now tighten the chuck. It's good practice to use 2 or 3 of the chuck key holes to ensure even tightening (but all three may be impossible to reach given the tight confines of the 7x10).

Slide the tailstock along the ways until the tip of the center drill is about 1/4" from the end of the workpiece and tighten the tailstock clamp nut. The locking lever for the tailstock ram should be just snug - not enough to impede the movement of the ram, but enough to ensure that the ram is as rigid as possible.

Center Drilling

Turn on the lathe and set the speed to around 600 RPM. Use the tailstock crank to advance the drill slowly into the end of the workpiece and continue until the conical section of the center drill is about 3/4ths of the way into the workpiece. This is as far as you need to go with the center drill since its purpose is just to make a starter hole for the regular drill. Back the center drill out and stop the lathe.

Drilling the Hole

Loosen the tailstock clamp nut and slide the tailstock back to the end of the ways. Remove the center drill from the chuck and insert a regular drill and tighten it down in the chuck. Slide the tailstock until the tip of the drill is about 1/4" from the workpiece and then lock the tailstock in place. Place a few drops of cutting fluid on the tip of the drill, then start the lathe and drill into the workpiece as before, at 400 to 600 RPM.

After advancing the drill about twice its diameter, back it out of the hole and use a brush to remove the metal chips from the tip of the drill. Add a few more drops of cutting fluid if necessary, then continue drilling, backing the drill out to remove chips about every 2 diameters of depth.

Measuring Drilling Depth

Unless you are drilling completely through a fairly short workpiece you will generally need a way to measure the depth of the hole so that you can stop at the desired depth. One of the first accessories I made on the lathe is a simple depth gauge - just a small cylinder of brass with a locking screw which slides on a piece of 1/16" drill rod about 3" long. It's quite handy for checking the depth of holes. You can use a shop rule to set the brass slider to the desired depth and then lock it in place with the little set screw.

Drilling Deep Holes, Blind Holes and Large Holes

In the world of metalwork, a "deep" hole is any hole more than about 3 times the drill diameter. A blind hole is one in which you are not drilling all the way through the workpiece. The critical thing when drilling such holes is to frequently back the drill completely out of the hole to allow the chips to escape from the hole. You need to do this repeatedly each time you advance the drill by about twice its diameter. Failure to follow this procedure will cause the chips to bind in the hole, weld to the drill and create a hole with an uneven and rough diameter. Cutting fluid will also help to keep the chips from binding to the drill or the sides of the hole.

Large holes are relative to the size of the machine and for the mini-lathe, I consider a hole larger than 3/8" to be "large". If you try to drill a large hole, say 1/2" starting with a 1/2" drill, you may not get a nice clean hole because too much material is being removed at one time. It is better to drill the hole in stages, starting, say, with a 5/16" drill, then a 3/8" and so forth, until you work up to the 1/2" drill for the final pass. This way, the large drill is removing only a small amount of material around the perimeter of the hole and will have a much easier job to do.

External Lathe Operation

Facing Operation

• a process of removing metal from the end of a work piece to produce a flat surface

• Work piece is cylindrical but using a 4 jaw chuck able to face rectangular or odd-shaped work to form cubes and other non-cylindrical shapes.

Preparing the Facing Cut

The tumbler gear lever should be in the neutral position to prevent the leadscrew does not rotate. During the facing operation, the leadscrew should be clamp half to prevent the saddle from being forced back from the end of the workpiece by the force of the cutting operation.

To run the operation properly, the work should be properly centered by the jaws touch the surface of the work. The workpiece is then twist in the jaws to seat it.

Beginning the Facing Cut

1. Use the compound crank to advance the tip of the tool until it just touches the end of the workpiece.Use the cross feed crank to back off the tool until it is beyond the diameter of the workpiece.

2. Turn the lathe on and adjust the speed to a few hundred RPM - about 10 O'clock setting of the speed control knob. Now slowly advance the cross feed crank to move the tool towards the workpiece.

3. When the tool touches the workpiece it should start to remove metal from the end.

The Roughing Cut

• Use the compound crank to advance the tool towards the chuck about .010" (ten one-thousandths of an inch, or one one-hundredth of an inch).
  

• If the compound is set at a 90 degrees to the cross slide (which is how I usually set mine) then each division you turn the crank will advance the tool .001 (one one-thousandth of an inch) toward the chuck.

• If the compound is set at some other angle, say 30 degrees, to the cross slide, then it will advance the tool less than .001 for each division. The exact amount is determined by the trigonometric sine of the angle. Since the sine of 30 degrees is .5 the tool would advance .0005 (five ten-thousandths or 1/2 of one one-thousandth of an inch) for each division in this example.

Cutting on the Return Pass

• crank the tool back towards you after it reaches the center of the workpiece you will notice that it removes a small amount of metal on the return pass. This is because the surface is not perfectly smooth and it is removing metal from the high spots.
  

• If you need to remove a lot of metal, to reduce the workpiece to a specific length, for example, you can take advantage of this return cut to remove more metal on each pass by advancing the tool a small ways into the workpiece on the return pass. Since the tool must plunge into the face of the workpiece, this works best with a fairly sharp pointed tool.

The Finishing Cut

• Depending on how rough the end of the workpiece was to begin with and how large the diameter is, you may need to make 3 or more passes to get a nice smooth finish across the face. These initial passes are called roughing passes and remove a relatively large amount of metal.

• a final finishing cut to remove just .001 to .003" of metal and get a nice smooth surface.

• The finishing cut can also be made at higher RPM (say 1500 RPM) to get a smoother finish.

Straight Turning Operation

1. Turning is the process whereby a centre lathe is used to produce "solids of revolution". I

• When turning, a piece of material (wood, metal, plastic even stone) is rotated and a cutting tool is traversed along 2 axes of motion to produce precise diameters and depths.
  

• Turning can be either on the outside of the cylinder or on the inside (also known as boring) to produce tubular components to various geometries. Although now quite rare, early lathes could even be used to produce complex geometric figures, even the platonic solids; although until the advent of C.N.C it had become unusual to use one for this purpose for the last three quarters of the twentieth century.

2. Facing is part of the turning process.

It involves moving the cutting tool across the face (or end) of the workpiece and is 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".

The bits of waste metal from turning operations are known as chips (North America), or swarf in Britain. In some locales they may be known as turnings.

The turning processes are typically carried out on a lathe, considered to be the oldest machine tools, and can be of four different types such as straight turning, taper turning, profiling or external grooving. Those types of turning processes can produce various shapes of materials such as straight, conical, curved, or grooved workpiece. In general, turning uses simple single-point cutting tools. Each group of workpiece materials has an optimum set of tools angles which have been developed through the years.

Aluminium, copper alloys, steels, stainless steels, high-temperature alloys, refractory alloys, titanium alloys, cast irons, thermoplastics, thermosets, etc… are examples of different type of materials used

Material removal rate

The material removal rate (MRR) in turning is the volume of material removed per unit time in mm³/min. For each revolutionof the workpiece, a ring-shaped layer of material is removed.

MRR = pi×D_avg×d×f×N where

D_avg: Average diameter
N: Rotational speed of the workpiece
f: Feed
d: Depth of cut

The forces acting on a cutting in turning are important in the design of machine tools. The machine tool and its components must be able to withstand these forces without causing significant deflections, vibrations, or chatter during the operation. There are three principal forces during a turning process: cutting force, thrust force and radial force.

• The cutting force acts downward on the tool tip allowing deflection of the workpiece upward. It supplies the energy required for the cutting operation.
• The thrust force acts in the longitudinal direction. It is also called the feed force because it is in the feed direction of the tool. This force tends to push the tool away from the chuck.
• The radial force acts in the radial direction and tends to push the tool away from the workpiece.

Although it requires less-skilled labor, the engine lathes do need skilled labor and the production is somewhat slow. Moreover, it can be accelerated by using a turret lathe (In a turret lathe, a longitudinally feedable, hexagon turret replaces the tailstock. The turret, on which six tools can be mounted, can be rotated about a vertical axis to bring each tool into operating position, and the entire unit can be moved longitudinally, either mannually or by power, to provide feed for the tools) and automated machines.

External Facing Operation

Lathe Classification by size

• Largest diameter is classified as lathe.

• Commonly called the swing of a lathe. Second factor is the total length between the centers with a tailstock at the end of the ways.

• size of the lathe is from lathe from 6-in diameter swing to over a 100-in diameter swing.

• The lathe most commonly used in industry have a 10 to 30 inches diameter swing

Size and specification of lathe

Size of lathe is usually specified by :-

• height of the center measured from the lathe bed.

• swing of a work piece diameter over bed. this is the maximum diameter of work that can be rotated on a lathe

• maximum distance between the center; maximum length of a work piece that can be mounted between the lathe center

• the length of a bed; indicated the approximate floor space occupied by a lathe

For example, if a lathe size indicated by 400mm * 864mm * 1900mm means maximum diameter of a work piece is 400mm, 864mm is the length between the lather center and 1900 mm is the length of the lathe bed.

Lathe construction features and functions

Lathe Machine consists of

• bed
• headstock
• tailstock
• carriage assembly
• quick change gearbox

Bed made out of gray or ductile cast iron or fabricated from steel by welding. Bed is divided to 2 types, first is the outer way and another one is the inner way.

In the Inner way, headstock and tailstock located in it. By the longitudinal movement for the carriage assembly and towards the centerline of the lather. The bed is needed to clean to avoid damaging to the machine.

Headstock

• mounted on the left side of the lathe machine.

• the function of the headstock is to turn the work piece and where it is suppost to hold the attachments mount.

• the spindle is mounted on the bearings on the headstock and it is hardened and specially ground to fit different type of devices. Spindle speed is controlled by varying the geometry of the drive train

• 3 jaw chucks, collets and centers can be held in the spindle

• To reverse the headstock movement, the lead screw and feed rod will change the direction of the movement of the carriage.

Tailstock

• support the end of the longer work piece
  

• holds cutting tools for internal machining operations

• spindle is graduated to control the depth of the drilling operations.

• fastened into the position by tailstock clamp

• the spindle in the tailstock can be adjusted longfitudinally by rotating hand wheel and locked by tailstock spindle lock

The figure above shows the adjustment for the tailstock and it is made in 2 parts

It allow the top part to move toward or backward from the operator

• For turning tapered parts or aligning the tailstock spindle true with headstock spindle.
• Must be realigned exactly on center when turning a cylindrical part

Carriage Assembly

• move along longitudinally

• H- shaped casting fitted on the outer set of ways

• cross slide mounted on the top of the saddle and moves the cutting tool laterally across the bed by cross feed hand wheel that has a micrometer collar that allows the cutting tools to remove metal.

• Compound Resta mounted on the cross slide and support the tool post and able to swiveled to any angle for taper turning or cross - feed hand wheel.

• Aprona mounted beneath the front of saddle and houses the carriage and cross - slide control mechanisms. The apron hand wheel is used to move the carriage assembly by rack and gears.

Gearbox

• Mounted on the left side of bed and below the headstock

• Houses gears and other mechanisms that transmit various feed rates from the headstock spindle to either of lead screw or feed rod

• Lead screw advances the carriage during threading operations, feed rod moves the carriage during turning, boring and facing operations.

TOOLS AND EQUIPMENT

GENERAL PURPOSE CUTTING TOOLS

The lathe cutting tool or tool bit must be made of the correct material and ground to the correct angles to machine a workpiece efficiently. The most common tool bit is the general all-purpose bit made of high-speed steel. These tool bits are generally inexpensive, easy to grind on a bench or pedestal grinder, take lots of abuse and wear, and are strong enough for all-around repair and fabrication. High-speed steel tool bits can handle the high heat that is generated during cutting and are not changed after cooling. These tool bits are used for turning, facing, boring and other lathe operations. Tool bits made from special materials such as carbides, ceramics, diamonds, cast alloys are able to machine workpieces at very high speeds but are brittle and expensive for normal lathe work. High-speed steel tool bits are available in many shapes and sizes to accommodate any lathe operation.

SINGLE POINT TOOL BITS

Single point tool bits can be one end of a high-speed steel tool bit or one edge of a carbide or ceramic cutting tool or insert. Basically, a single point cutter bit is a tool that has only one cutting action proceeding at a time. A machinist or machine operator should know the various terms applied to the single point tool bit to properly identify and grind different tool bits (Figure 7-4).

The shank is the main body of the tool bit.

The nose is the part of the tool bit which is shaped to a point and forms the corner between the side cutting edge and the end cutting edge. The nose radius is the rounded end of the tool bit.

The face is the top surface of the tool bit upon which the chips slide as they separate from the work piece.

The side or flank of the tool bit is the surface just below and adjacent to the cutting edge.

The cutting edge is the part of the tool bit that actually cuts into the workpiece, located behind the nose and adjacent to the side and face.

The base is the bottom surface of the tool bit, which usually is ground flat during tool bit manufacturing.

The end of the tool bit is the near-vertical surface which, with the side of the bit, forms the profile of the bit. The end is the trailing surface of the tool bit when cutting.

The heel is the portion of the tool bit base immediately below and supporting the face.

Angles of Tool Bits

The successful operation of the lathe and the quality of work that may be achieved depend largely on the angles that form the cutting edge of the tool bit (Figure 7-4). Most tools are hand ground to the desired shape on a bench or pedestal grinder. The cutting tool geometry for the rake and relief angles must be properly ground, but the overall shape of the tool bit is determined by the preference of the machinist or machine operator. Lathe tool bit shapes can be pointed, rounded, squared off, or irregular in shape and still cut quite well as long as the tool bit angles are properly ground for the type of material being machined. The angles are the side and back rake angles, the side and end cutting edge angles, and the side and end relief angles. Other angles to be considered are the radius on the end of the tool bit and the angle of the tool holder. After knowing how the angles affect the cutting action, some recommended cutting tool shapes can be considered.

Rake angle pertains to the top surface of the tool bit. There are two types of rake angles, the side and back rake angles (Figure 7-4). The rake angle can be positive, negative, or have no rake angle at all. The tool holder can have an angle, known as the tool holder angle, which averages about 15°, depending on the model of tool holder selected. The tool holder angle combines with the back rake angle to provide clearance for the heel of the tool bit from the workpiece and to facilitate chip removal. The side rake angle is measured back from the cutting edge and can be a positive rake angle or have no rake at all.

Rake angles cannot be too great or the cutting edge will lose strength to support the cutting action. The side rake angle determines the type and size of chip produced during the cutting action and the direction that the chip travels when leaving the cutting tool. Chip breakers can be included in the side rake angle to ensure that the chips break up and do not become a safety hazard.

Side and relief angles, or clearance angles, are the angles formed behind and beneath the cutting edge that provide clearance or relief to the cutting action of the tool. There are two types of relief angles, side relief and end relief. Side relief is the angle ground into the tool bit, under the side of the cutting edge, to provide clearance in the direction of tool bit travel. End relief is the angle ground into the tool bit to provide front clearance to keep the tool bit heel from rubbing. The end relief angle is supplemented by the tool holder angle and makes up the effective relief angle for the end of the tool bit.

Side and cutting edge angles are the angles formed by the cutting edge with the end of the tool bit (the end cutting edge angle), or with the side of the tool bit (the side cutting edge angle). The end cutting edge angle permits the nose of the tool bit to make contact with the work and aids in feeding the tool bit into the work. The side cutting edge angle reduces the pressure on the tool bit as it begins to cut. The side rake angle and the side relief angle combine to form the wedge angle (or lip angle) of the tool bit that provides for the cutting action (Figure 7-4).

A radius ground onto the nose of the tool bit can help strengthen the tool bit and provide for a smooth cutting action.

Shapes of Tool Bits

The overall shape of the lathe tool bits can be rounded, squared, or another shape as long as the proper angles are included. Tool bits are identified by the function they perform, such as turning or facing. They can also be identified as roughing tools or finishing tools. Generally, a roughing tool has a radius ground onto the nose of the tool bit that is smaller than the radius for a finishing or general-purpose tool bit. Experienced machinists have found the following shapes to be useful for different lathe operations.

A right-hand turning tool bit is shaped to be fed from right to left. The cutting edge is on the left side of the tool bit and the face slopes down away from the cutting edge. The left side and end of the tool bit are ground with sufficient clearance to permit the cutting edge to bear upon the workpiece without the heel rubbing on the work. The right-hand turning tool bit is ideal for taking light roughing cuts as well as general all-around machining.

A left-hand turning tool bit is the opposite of the right-hand turning tool bit, designed to cut when fed from left to right. This tool bit is used mainly for machining close in to a right shoulder.

The round-nose turning tool bit is very versatile and can be used to turn in either direction for roughing and finishing cuts. No side rake angle is ground into the top face when used to cut in either direction, but a small back rake angle may be needed for chip removal. The nose radius is usually ground in the shape of a half-circle with a diameter of about 1/32 inch.

The right-hand facing tool bit is intended for facing on right-hand side shoulders and the right end of a workpiece. The cutting edge is on the left-hand side of the bit, and the nose is ground very sharp for machining into a square corner. The direction of feed for this tool bit should be away from the center axis of the work, not going into the center axis.

A left-hand facing tool bit is the opposite of the right-hand facing tool bit and is intend to machine and face the left sides of shoulders.

The parting tool bit, Figure 7-6, is also known as the cutoff tool bit. This tool bit has the principal cutting edge at the squared end of the bit that is advanced at a right angle into the workpiece. Both sides should have sufficient clearance to prevent binding and should be ground slightly narrower at the back than at the cutting edge. Besides being used for parting operations, this tool bit can be used to machine square corners and grooves.

Thread-cutting tool bits, Figure 7-7, are ground to cut the type and style of threads desired. Side and front clearances must be ground, plus the special point shape for the type of thread desired. Thread-cutting tool bits can be ground for standard 60° thread forms or for square, Acme, or special threads. Thread-cutting forms are discussed in greater detail later in this chapter.

SPECIAL TYPES OF LATHE CUTTING TOOLS

Besides the common shaped tool bits, special lathe operations and heavy production work require special types of cutting tools. Some of the more common of these tools are listed below.

Tungsten carbide, tantalum carbide, titanium carbide, ceramic, oxide, and diamond-tipped tool bits (Figure 7-8). and cutting tool inserts are commonly used in high-speed production work when heavy cuts are necessary and where exceptionally hard and tough materials are encountered. Standard shapes for tipped tool bits are similar to high-speed steel-cutting tool shapes. Carbide and ceramic inserts can be square, triangular, round, or other shapes. The inserts are designed to be indexed or rotated as each cutting edge gets dull and then discarded. Cutting tool inserts are not intended for reuse after sharpening.

Specially formed thread cutter mounted in a thread cutter holder (Figure 7-9). This tool is designed for production high-speed thread cutting operations. The special design of the cutter allows for sharp and strong cutting edges which need only to be resharpened occasionally by grinding the face. The cutter mounts into a special tool holder that mounts to the lathe tool post.

The common knurling tool, Figure 7-10, consists of two cylindrical cutters, called knurls, which rotate in a specially designed tool holder. The knurls contain teeth which are rolled against the surface of the workpiece to form depressed patterns on the workpiece. The common knurling tool accepts different pairs of knurls, each having a different pattern or pitch. The diamond pattern is most widely used and comes in three pitches: 14, 21, or 33. These pitches produce coarse, medium, and fine knurled patterns.

Boring tool bits, Figure 7-11, are ground similar to left-hand turning tool bits and thread-cutting tool bits, but with more end clearance angle to prevent the heel of the tool bit from rubbing against the surface of the bored hole. The boring tool bit is usually clamped to a boring tool holder, but it can be a one-piece unit . The boring tool bit and tool holder clamp into the lathe tool post.

There is no set procedure to grinding lathe tool bit angles and shapes, but there are general guidelines that should be followed. Do not attempt to use the bench or pedestal grinder without becoming fully educated as to its safety, operation, and capabilities. In order to effectively grind a tool bit, the grinding wheel must have a true and clean face and be of the appropriate material for the cutting tool to be ground. Carbide tool bits must be ground on a silicon carbide grinding wheel to remove the very hard metal.

High-speed steel tool bits are the only tool bits that can effectively be ground on the bench or pedestal grinder when equipped with the aluminum oxide grinding wheel which is standard for most field and maintenance shops. Before grinding, shaping, or sharpening a high-speed steel tool bit, inspect the entire grinder for a safe setup and adjust the tool rests and guards as needed for tool bit grinding (Figure 7-12).

Set the tool rest 1/8 inch or less from the wheel, and adjust the spark arrestor 1/4 inch or less. Each grinder is usually equipped with a coarse-grained wheel for rough grinding and a fine-grained wheel for fine and finish grinding. Dress the face of the grinding wheels as needed to keep a smooth, flat grinding surface for the tool bit. When grinding the side and back rake angles, ensure the grinding wheel has a sharp corner for shaping the angle. Dip the tool bit in water occasionally while grinding to keep the tool bit cool enough to handle and to avoid changing the property of the metal by overheating. Frequently inspect the tool bit angles with a protractor or special grinding gage. Grind the tool bit to the recommended angles in the reference for tool bit geometry (Table 7-l in Appendix A). After grinding to the finished shape, the tool bit should be honed lightly on an oilstone to remove any burrs or irregular high spots. The smoother the finish on the cutting tool, the smoother the finish on the work. Figure 7-13 shows the steps involved in grinding a round nose tool bit to be used for turning in either direction. As a safety note, never use the side of the grinding wheel to grind a tool bit, as this could weaken the bonding of the wheel and cause it to crack and explode.

Lathe ToolBits

·A lathe toolbit is shown in the figure below, with a few terms defined.

· In general, as the rake angle increases (positive), the cutting forces are reduced, the surface finish improves, and tool life increases.

· The side edge cutting angle has two effects outlined below,

· The End Relief Angle prevents friction on the flank of the tool. The holder for the bit is often angled, and the end relief angle must be larger than the tool holder angle to prevent rubbing.

· The side relief angle has a function similar to the end relief, This angle must exceed the feed helix angle.

· Increasing the nose radius improves the surface finish. But this reaches a limit.

8.2 OPERATIONS ON A LATHE

· Operations on a lathe include,

Introduction to Lathe

Lathe Machine

• machine tool which spins a block of material to perform various operations such as cutting, sanding , knurling, drilling or deformation with tools that are applied to the work piece to create an object which has symmetry about an axis or rotation.

• usually lathe is used in wood turning, metal working, metal spinning and glass working.

• lathe also can be used to shape pottery and lathe is the best known design being the potter's wheel.

Above figure is the parts that are in a lathe machine.

• Bed is mainly support the whole machine

• Carriage is assembly that moves the tool post and cutting tool along the ways

• Carriage Hand wheel is a wheel with a handle used to move the carriage by hand by means of a rack and ponion drive

• A chuck is a clamping device for holding work in the lathe

• Apron is the front part of the carriage assembly on which carriage hand wheel is mounted

• Cross slide is a platform that moves perpendicular to the lathe axis under control of the cross slide hand wheel

• Cross slide hand wheel is a wheel with handle used to move the cross slide in and out.

• Halfnut lever is the lever to engage the carriage with leadscrew to move the carriage under power

• lead screw is a precision screw that runs the length of the bed. it is used to drive the carriage under power for turning and thread cutting operations.

• swing is a dimension representing the largest diameter work piece that a lathe can rotate

• tailstock is a cast iron assembly that can be slide along the ways and be locked in place. used to hold long work in place or mount a drill chuck for drilling into end of the work

• Ram is a piston type shaft that can be moved in and out of the tailstock by turning the tailstock hand wheel.

• Tool is a cutting tool used to remove metal from the work piece and usually made of high speed steel or carbide.

• ways is a precision ground surfaces along top of the bed on which saddle rides. the ways are precisely aligned with the centerline of the lathe

Fig 1. This picture above shows the current lathe machine that we are using in this days

Fig 2. Lathe Machine with the work piece ready for cutting

Fig 3.

Woodworking lathes

• oldest variety.

• All other varieties are descended from these simple lathes.
  

• An adjustable horizontal metal rail - the tool rest - between the material and the operator accommodates the positioning of shaping tools, which are usually hand-held. With wood, it is common practice to press and slide sandpaper against the still-spinning object after shaping to smooth the surface made with the metal shaping tools.

There are also woodworking lathes for making bowls and plates, which have no horizontal metal rail, as the bowl or plate needs only to be held by one side from a metal face plate. Without this rail, there is very little restriction to the width of the piece being turned. Further detail can be found on the wood turning page.

Metalworking lathes

• metal is removed from the workpiece using a hardened cutting tool, which is usually fixed to a solid moveable mounting called the "toolpost", which is then moved against the workpiece using handwheels and/or computer controlled motors.

• The toolpost is operated by leadscrews that can accurately position the tool in a variety of planes. The toolpost may be driven manually or automatically to produce the roughing and finishing cuts required to turn the workpiece to the desired shape and dimensions, or for cutting threads, gear, etc.
  

• Cutting Fluid may also be pumped to the cutting site to provide cooling, lubrication and clearing of swarf from the workpiece. Some lathes may be operated under control of a computer for mass production of parts.

Metalworking lathes are commonly provided with a variable ratio gear train to drive the main leadscrew. This enables different pitches of threads to be cut. Some older gear trains are changed manually by using interchangeable gears with various numbers of teeth, while more modern or elaborate lathes have a quick change box to provide commonly used ratios by the operation of a lever.

The workpiece may be supported between a pair of points called centres, or it may be bolted to a faceplate or held in a chuck. A chuck has movable jaws that can grip the workpiece securely.

Cue lathes

• Cue lathes function similar to turning and spinning lathes allowing for a perfectly radially-symmetrical.

• They can also be used to refinish cues that have been worn over the years.

Glass working lathes

• similar in design to other lathes, but differ markedly in how the workpiece is modified.

• slowly rotate a hollow glass vessel over a fixed or variable temperature flame.
  

• The source of the flame may be either hand-held, or mounted to a banjo/cross slide that can be moved along the lathe bed.
  

• The flame serves to soften the glass being worked, so that the glass in a specific area of the workpiece becomes malleable, and subject to forming either by inflation or by deformation with a heat resistant tool. Such lathes usually have two headstocks with chucks holding the work, arranged so that they both rotate together in unison.
  

• Air can be introduced through the headstock chuck spindle for glassblowing. The tools to deform the glass and tubes to blow (inflate) the glass are usually handheld.

Metal spinning lathes

• a disk of sheet metal is held perpendicularly to the main axis of the lathe, and tools with polished tips (spoons) are hand held, but levered by hand against fixed posts, to develop large amounts of torque/pressure that deform the spinning sheet of metal.

• Metal spinning lathes are almost as simple as wood turning lathes. Typically, metal spinning lathes require a user-supplied rotationally symmetric mandrel, usually made of wood, which serves as a template onto which the workpiece is moulded

Given the advent of high speed, high pressure, industrial die forming, metal spinning is less common now than it once was, but still a valuable technique for producing one-off prototypes or small batches where die forming would be uneconomical.

Reducing Lathe

Many types of lathes can be equipped with accessory components to allow them to reproduce an item: the original item is mounted on one spindle, the blank is mounted on another, and as both turn in synchronized manner, one end of an arm "reads" the original and the other end of the arm "carves" the duplicate.

Reducing lathes are used in coin-making, where a plaster original. Duplicated and reduced on the reducing lathe, generating a master die.

Rotary lathes

A lathe in which softwood logs are turned against a very sharp blade and peeled off in one continuous or semi-continuous roll. Invented by Immanuel Nobel. The first such lathes were set up in the United States in the mid-19th century.

Watchmaker's lathes

• Delicate but precise metalworking lathes, usually without provision for screw cutting

• still used by horologists for work such as the turning of balance shafts. A handheld tool called a graver is often used in preference to a slide mounted tool. The original watchmaker's turns was a simple dead centre lathe with a moveable rest and two loose headstocks. The workpiece would be rotated by a bow, typically of horse hair, wrapped around it.