Lathe Machine

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Machine:

A machine is a tool that consists of one or more parts, and uses energy to achieve aparticular goal. Machines are usually powered by mechanical, chemical, thermal,or electrical means, and are frequently motorized. Historically, a powered tool alsorequired moving parts to classify as a machine; however, the advent of electronicstechnology has led to the development of powered tools without moving parts thatare considered machines.

Lathe Machine

Metal lathe or metal working lathe are generic terms for any of a large class oflathes designed for precisely machining relatively hard materials. They wereoriginally designed to machine metals; however, with the advent of plastics andother materials, and with their inherent versatility, they are used in a wide range ofapplications, and a broad range of materials. In machining jargon, where the largercontext is already understood, they are usually simply called lathes, or else referredto by more-specific subtype names (toolroom lathe, turret lathe, etc.). These rigidmachine tools remove material from a rotating workpiece via the (typically linear)movements of various cutting tools, such as tool bits and drill bits.

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Figure & Machine parts of a Lathe Machine

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HistoryThe lathe is an ancient tool, dating at least to ancient Egypt and knownand used in Assyria and ancient Greece.

The origin of turning dates to around 1300 BC when the AncientEgyptians first developed a two-person lathe. One person would turnthe wood work piece with a rope while the other used a sharp tool tocut shapes in the wood. Ancient Rome improved the Egyptian designwith the addition of a turning bow. In the Middle Ages a pedal replacedhand-operated turning, freeing both the craftsman's hands to hold thewoodturning tools. The pedal was usually connected to a pole, often astraight-grained sapling. The system today is called the "spring pole"lathe. Spring pole lathes were in common use into the early 20thcentury.

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Principal of Operation of Lathe Machine

In Lathe machine, the workpiece to be machined is held firmly &rotated about its axis, while the cutting tool is moved relative tothe workpiece.

Because of this reason Lathe machine is also known as turningmachine.

The cutting tool is made of the harder material than that of theworkpiece.

It is fed against the workpiece which in turn removes theundesirable material from the workpiece in the form of the chips .

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Basic Elements of Lathe Machine

The Lathe machine consist of following six basic elements :1. Bed2. Headstock3. Tailstock4. Carriage5. Lead Screw6. Feed Drive

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Parts description:The machine has been greatly modified for various applications however a familiarity with thebasics shows the similarities between types. These machines consist of, at the least, a headstock,bed, carriage and tailstock. The better machines are solidly constructed with broad bearingsurfaces (slides or ways) for stability and manufactured with great precision. This helps ensurethe components manufactured on the machines can meet the required tolerances andrepeatability.

the different parts of a lathe is given below:

The Bed:

The lathe bed is a mounting and aligning surface for the other machine components. Viewedfrom the operating position in front of the machine, the headstock is mounted on the left end ofthe bed and the tailstock on the right. The bed must be bolted to a base to provide a rigid andstable platform. The bed ways are a precision surface (or surfaces) on which the carriage slidesleft and right during machining operations. The ways are machined straight and flat and areeither bolted to the top of the bed or are an integrally machined part of the bed.

Carriage:

In its simplest form the carriage holds the tool bit and moves it longitudinally (turning) orperpendicularly (facing) under the control of the operator. The operator moves the carriagemanually via the handwheel (5a) or automatically by engaging the feed shaft with the carriagefeed mechanism (5c). This provides some relief for the operator as the movement of the carriagebecomes power assisted. The handwheels (2a, 3b, 5a) on the carriage and its related slides areusually calibrated, both for ease of use and to assist in making reproducible cuts.

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Headstock:

The headstock (H1) houses the main spindle (H4), speed change mechanism (H2,H3), andchange gears (H10). The headstock is required to be made as robust as possible due to the cuttingforces involved, which can distort a lightly built housing, and induce harmonic vibrations thatwill 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, thisreduces preparation and waste of material. The spindle then runs in precision bearings and isfitted with some means of attaching work holding devices such as chucks or faceplates. This endof the spindle will also have an included taper, usually morse, to allow the insertion of tapers andcenters. On older machines the spindle was directly driven by a flat belt pulley with the lowerspeeds available by manipulating the bull gear, later machines use a gear box driven by adedicated electric motor. The fully geared head allows the speed selection to be done entirelythrough the gearbox.

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Tailstock:

Tailstock with legend, numbers and text within the description refer to those in the image

The tailstock is a toolholder directly mounted on the spindle axis, opposite the headstock. Thespindle (T5) does not rotate but does travel longitudinally under the action of a leadscrew andhandwheel (T1). The spindle includes a taper to hold drill bits, centers and other tooling. Thetailstock can be positioned along the bed and clamped (T6) in position as required. There is alsoprovision 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 featurefound only in the larger center lathes, where large drills may necessitate the extra leverage.

Feed Rod and lead screw-Feed:

The feedscrew (H8) is a long driveshaft that allows a series of gears to drive the carriagemechanisms. These gears are located in the apron of the carriage. Both the feedscrew andleadscrew (H9) are driven by either the change gears (on the quadrant) or an intermediategearbox known as a quick change gearbox (H6) or Norton gearbox. These intermediate gearsallow the correct ratio and direction to be set for cutting threads or worm gears. Tumbler gears(operated by H5) are provided between the spindle and gear train along with a quadrant plate thatenables a gear train of the correct ratio and direction to be introduced. This provides a constantrelationship between the number of turns the spindle makes, to the number of turns the leadscrewmakes. This ratio allows screwthreads to be cut on the workpiece without the aid of a die.

The leadscrew will be manufactured to either imperial or metric standards and will require aconversion ratio to be introduced to create thread forms from a different family. To accuratelyconvert from one thread form to the other requires a 127-tooth gear, or on lathes not largeenough to mount one, an approximation may be used. Multiples of 3 and 7 giving a ratio of 63:1can be used to cut fairly loose threads. This conversion ratio is often built into the quick changegearboxes.

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Cross-slide:

The cross-slide stands atop the carriage and has a feedscrew that travels perpendicular to themain spindle axis. This permits facing operations to be performed, and the depth of cut to beadjusted. This feedscrew can be engaged, through a gear train, to the feed shaft (mentionedpreviously) to provide automated 'power feed' movement to the cross-slide. On most lathes, onlyone direction can be engaged at a time as an interlock mechanism will shut out the second geartrain.

Toolpost:

The tool bit is mounted in the toolpost which may be of the American lantern style, traditional 4sided square style, or in a quick change style such as the multifix arrangement pictured. Theadvantage of a quick change set-up is to allow an unlimited number of tools to be used (up to thenumber of holders available) rather than being limited to 1 tool with the lantern style, or 3 to 4tools with the 4 sided type. Interchangeable tool holders allow the all the tools to be preset to acenter height that will not change, even if the holder is removed from the machine.

Spindle:

Lathe spindles have 3 configurations. These main configurations are the threaded, cam-lock andtapered. The threaded model is the oldest configuration and is not tapered which makes thechuck rather difficult to attach. Cam-lock spindles contain cam studs on one end; it slides into aring of similar holes. The studs lock in place when a chuck key is turned. The thirdconfiguration, the tapered spindle, narrows at the tip and has a threaded collar with a built-inchuck key.

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Cross Slide:

The cross-slide is mounted to the top of the carriage to provide movement perpendicular to thelength of the bed for facing cuts. An additional motion assembly, the compound rest, with anadjustable angle, is often added to the top of the cross slide for angular cuts. The cutting toolsthat do the actual metal removal during turning are mounted in an adjustable tool holder clampedto the compound rest.

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Types of Operations Performed on Lathe Machine

1. Turning

2. Eccentric Turning

3. Taper Turning

4. Facing

5. Chamfering

6. Grooving

7. Parting

8. Knurling

9. Drilling

10. Boring

11. Thread Cutting

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Lathe Chucks

Self Centering Lathe Chucks

3 Jaws Self Centering Single Slot Lathe Chuck

3 Jaws Self Centering Double Slot Lathe Chuck

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