Machine Lab Assignment

7/31/2019 Machine Lab Assignment

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Report

on

Types of Lathes

Submitted by

Neethu M. Raja(1RV10ME058)

Nikhil Jain(1RV10ME059)

Nikhil P N(1RV10ME060)

Nitish Prabhu(1RV10ME061)

Manav P(1RV10ME062)

Parimesh Panda(1RV10ME063)


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Introduction

A metal lathe or metalworking lathe is a large class of lathes designed for precisely machining

relatively hard materials. They were originally designed to machine metals; however, with the

advent of plastics 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, where the largercontext 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 remove

material from a rotating workpiece via the (typically linear) movements of various cutting tools,such as tool bits and drill bits.

Types of metal lathes

There are many variants of lathes within the metal working 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 machinea 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 The usage of the term metal lathe may also be considered somewhat outdated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 appropriatemodifications, the same principles and techniques may be applied to their machining as that used

for metal.
http://en.wikipedia.org/wiki/File:Metal_lathe.pnghttp://en.wikipedia.org/wiki/File:London007.jpghttp://en.wikipedia.org/wiki/File:Metal_lathe.pnghttp://en.wikipedia.org/wiki/File:London007.jpg


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Two-speed back gears in a cone-head lathe. A typical center lathe.

The terms center lathe, engine lathe, and bench lathe all refer to a basic type of lathe that may

be considered the archetypical class of metalworking lathe most often used by the general

machinist or machining hobbyist. The name bench lathe implies a version of this class smallenough to be mounted on a workbench (but still full-featured, and larger than mini-lathes or

micro-lathes). The construction of a center lathe is detailed above, but depending on the year of

manufacture, size, price range, or desired features, even these lathes can vary widely between

models.

Engine LatheAn engine lathe is found in every machine shop. It is used mostly for turning, boring, facing, and

thread cutting. But it may also be used for drilling, reaming, knurling, grinding, spinning, and

spring winding. Since you will primarily be concerned with turning, boring, facing, and threadcutting, we will deal primarily with those operations in this chapter.


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The work held in the engine lathe can be revolved at any one of a number of different speeds,

and the cutting tool can be accurately controlled by hand or power for longitudinal feed and

crossfeed. (Longitudinal feed is the movement of the cutting tool parallel to the axis of the lathe;crossfeed is the movement of the cutting tool perpendicular to the axis of the lathe.)

Lathe size is determined by two measurements:

(1) The diameter of work it will swing (turn) over the ways and

(2) The length of the bed. For example, a 14-inch by 6-foot lathe will swing work up to 14 inches

in diameter and has a bed that is 6 feet long.


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Engine lathes vary in size from small bench lathes that have a swing of 9 inches to very large

lathes for turning large diameter work such as low-pressure turbine rotors. The 16-inch lathe isthe average size for general purposes and is the size usually installed in ships that have only one

lathe.

Principal Parts

Lathes from different manufacturers differ somewhat in construction, but all are built to performthe same general functions. As you read the description of each part, find its location on the lathe

in figure 9-1 and the figures that follow. (For specific details of features of construction and

operating techniques, refer to the manufacturers technical manual for your machine.)

Bed and Ways

The bed is the base or foundation of the parts of the lathe. The main feature of the bed is the

ways, which are formed on the beds upper surface and run the full length of the bed. The wayskeep the tailstock and the carriage, which slide on them, in alignment with the headstock.

Headstock

The headstock contains the headstock spindle and the mechanism for driving it. In the belt-

driven type, shown in figure 9-2, the driving mechanism consists of a motor-driven cone pulleythat drives the spindle cone pulley through a drive belt. The spindle can be rotated either directly

or through back gears.

When the headstock is set up for direct drive, a bull-gear pin, located under a cover to the right

of the spindle pulley, connects the pulley to the spindle. This connection causes the spindle toturn at the same speed as the spindle pulley.

When the headstock is set up for gear drive, the bull-gear pin is pulled out, disconnecting the

spindle pulley from the spindle. This allows the spindle to turn freely inside the spindle pulley.

The back-gear lever, on the left end of the headstock, is moved to engage the back-gear set witha gear on the end of the spindle and a gear on the end of the spindle pulley. In this drive mode,

the drive belt turns the spindle pulley, which turns the back-gear set, which turns the spindle.

Each drive mode provides four spindle speeds, for a total of eight. The back-gear drive speedsare less slower than the direct-drive speeds.

Tailstock

The primary purpose of the tailstock is to hold the dead center to support one end of the work

being machined. However, the tailstock can also be used to hold tapered shank drills, reamers,and drill chucks. It can be moved on the ways along the length of the bed and can be clamped in

the desired position by tightening the tailstock clamping nut. This movement allows for the

turning of different lengths of work. The tailstock can be adjusted laterally (front to back) to cuta taper by loosening the clamping screws at the bottom of the tailstock. (see fig. 9-1.)


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Crossfeed Slide

The crossfeed slide is mounted to the top of the carriage in a dovetail and moves on the carriage

at a right angle to the axis of the lathe. A crossfeed screw allows the slide to be moved toward or

away from the work in accurate increments.

Compound Rest

The compound rest mounted on the compound slide, provides a rigid adjustable mounting for the

cutting tool. The compound rest assembly has the following principal parts:

1. The compound rest SWIVEL, which can be swung around to any desired angle and clampedin position. It is graduated over an arc of 90 on each side of its center position for easier setting

to the angle selected. This feature is used for machining short, steep tapers, such as the angle on

bevel gears, valve disks, and lathe centers.

2. The compound rest, or TOP SLIDE, which is mounted on the swivel section on a dovetailedslide. It is moved by the compound rest feed screw.

This arrangement permits feeding the tool to the work at any angle (determined by the angular

setting of the swivel section). The graduated collars on the crossfeed and compound rest feed

screws read in thousandths of an inch for fine adjustment in regulating the depth of cut.

Capstan & Turret LatheA capstan lathe or a turret lathe is a production lathe used to manufacture any

number of identical pieces in the minimum time. These lathes are development of

engine lathes. The capstan lathe was first developed in the United States of America by

Pratt and Whitney sometimes in 1860.

Special characteristics of a capstan or turret lathe enable it to perform a series ofoperations such as drilling, turning, boring, thread cutting, reaming, chamfering, cuttingoff

and many other operations in a regular sequence to produce a large number of

identical pieces in a minimum time.

Differences between a Capstan Lathe and Turret and an Engine Lathe:1. The headstock of a turret lathe is similar to that of an engine lathe in construction

but possesses wider range of speeds, and is of heavier in construction.

2. Similar sizes of capstan and turret lathe and engine lathe, when an engine lathewill require a motor of 3h.p. to drive its spindle and other parts, a capstan andturret lathe will demand power as high as 15h.p. for high rate of production.

3. In a turret lathe, combination of cuts can be take. Two or more tools may be mounted onthe same face of the turret, making it possible to machine more than one surface at a time.This feature reduces total operational time.

4. A semi-skilled operator a capstan or turret lathe after the machine has been set up by askilled machinist. A skilled machinist may be requisitioned for setting up only for a largenumber of machines, where as actual production may be given by a semi-skilled operator.


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5. Capstan and Turret Lathe is fundamentally a production machine, capable of producinglarge number of identical pieces in a minimum time. The center lathe is suitable for oddjobs having different shapes and sizes.

6. Capstan and Turret lathes are not usually fitted with lead screws for cutting threads. Ashort length of lead screw called Chasing Screw are sometimes provided for cutting

threads by a chaser in a turret lathe.

A schematic diagram important parts of Turret Lathe

Toolroom Lathe

A toolroom lathe is a lathe optimized for toolroom work. It is essentially just a top-of-the-line

center lathe, with all of the best optional features that may be omitted from less expensive

models, such as a collet closer, taper attachment, and others. There has also been an implicationover the years of selective assembly and extra fitting, with every care taken in the building of a

toolroom model to make it the smoothest-running, most-accurate version of the machine that canbe built. However, within one brand, the quality difference between a regular model and its

corresponding toolroom model depends on the builder and in some cases has been partly

marketing psychology. For name-brand machine tool builders who made only high-quality tools,there wasn't necessarily any lack of quality in the base-model product for the "luxury model" to

improve upon. In other cases, especially when comparing different brands, the quality


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differential between (1) an entry-level center lathe built to compete on price, and (2) a toolroom

lathe meant to compete only on quality and not on price, can be objectively demonstrated bymeasuring TIR, vibration, etc. In any case, because of their fully ticked-off option list and (real

or implied) higher quality, toolroom lathes are more expensive than entry-level center lathes.

Gang-tool Lathe

A gang-tool lathe is one that has a row of tools set up on its cross-slide, which is long and flat

and is similar to a milling machine table. The idea is essentially the same as with turret lathes: toset up multiple tools and then easily index between them for each part-cutting cycle. Instead of

being rotary like a turret, the indexable tool group is linear.

Multispindle Lathe

Multispindle lathes have more than one spindle and automated control (whether via cams or

CNC). They are production machines specializing in high-volume production. The smaller types

are usually called screw machines, while the larger variants are usually called automatic

chucking machines, automatic chuckers, or simply chuckers. Screw machines usually work

from bar stock, while chuckers automatically chuck up individual blanks from a magazine.

Typical minimum profitable production lot size on a screw machine is in the thousands of partsdue to the large setup time. Once set up, a screw machine can rapidly and efficiently produce

thousands of parts on a continuous basis with high accuracy, low cycle time, and very little

human intervention. (The latter two points drive down the unit cost per interchangeable partmuch lower than could be achieved without these machines.)


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Rotary transfer machines might also be included under the category of multispindle lathes,

although they defy traditional classification. They are large, expensive, modular machine toolswith many CNC axes that combine the capabilities of lathes, milling machines, and pallet

changers.

CNC lathe / CNC turning center

CNC lathe with milling capabilities

Computer numerical controlled (CNC) lathes are rapidly replacing the older production lathes(multispindle, etc.) due to their ease of setting, operation, repeatability and accuracy. They are

designed to use modern carbide tooling and fully use modern processes. The part may be

designed and the tool paths programmed by the CAD/CAM process or manually by the

programmer, and the resulting file uploaded to the machine, and once set and trialled themachine will continue to turn out parts under the occasional supervision of an operator.

The machine is controlled electronically via a computer menu style interface, the program may

be modified and displayed at the machine, along with a simulated view of the process. The

setter/operator needs a high level of skill to perform the process, however the knowledge base is

broader compared to the older production machines where intimate knowledge of each machine

was considered essential. These machines are often set and operated by the same person, wherethe operator will supervise a small number of machines (cell).

The design of a CNC lathe varies with different manufacturers, but they all have some common

elements. The turret holds the tool holders and indexes them as needed, the spindle holds the

workpiece and there are slides that let the turret move in multiple axis simultaneously. Themachines are often totally enclosed, due in large part to Occupational health and safety (OH&S)

issues.


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With rapid growth in this industry, different CNC lathe manufacturers use different user

interfaces which sometimes makes it difficult for operators as they have to be acquainted withthem. With the advent of cheap computers, free operating systems such as Linux, and open

source CNC software, the entry price of CNC machines has plummeted.

Swiss-style Lathe

A view inside the enclosure of a CNC Swiss-style lathe

A Swiss-style lathe is a specific design of lathe providing extreme accuracy (sometimes holdingtolerances as small as a few tenths of a thousandth of an incha few microns). A Swiss-style

lathe holds the workpiece with both a collet and a guide bushing. The collet sits behind the guide

bushing, and the tools sit in front of the guide bushing, holding stationary on the Z axis. To cut

lengthwise along the part, the tools will move in and the material itself will move back and forthalong the Z axis. This allows all the work to be done on the material near the guide bushing

where it is more rigid, making them ideal for working on slender workpieces as the part is held

firmly with little chance of deflection or vibration occurring. This style of lathe is commonly

used under CNC control.

Most CNC Swiss-style lathes today use one or two main spindles plus one or two back spindles(secondary spindles). The main spindle is used with the guide bushing for the main machining

operations. The secondary spindle is located behind the part, aligned on the Z axis. In simple

operation it picks up the part as it is cut off, and accepts it for second operations, then ejects itinto a bin, eliminating the need to have an operator manually change each part, as is often thecase with standard CNC turning centers. This makes them very efficient, as these machines are

capable of fast cycle times, producing simple parts in one cycle (i.e., no need for a second

machine to finish the part with second operations), in as little as 1015 seconds. This makes

them ideal for large production runs of small-diameter parts.

Additionally, as many Swiss lathes incorporate a secondary spindle, or 'sub-spindle', they alsoincorporate 'live tooling'. Live tools are rotary cutting tools that are powered by a small motor

independently of the spindle motor(s). Live tools increase the intricacy of components that can

be manufactured by the Swiss lathe. For instance, automatically producing a part with a holedrilled perpendicular to the main axis (the axis of rotation of the spindles) is very economical

with live tooling, and similarly uneconomical if done as a secondary operation after machining

by the Swiss lathe is complete. A 'secondary operation' is a machining operation requiring a
http://en.wikipedia.org/wiki/File:CNC_Swiss_turn_001.jpg


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partially completed part to be secured in a second machine to complete the manufacturing

process. Generally, advanced CAD/CAM software uses live tools in addition to the mainspindles so that most parts that can be drawn by a CAD system can actually be manufactured by

the machines that the CAD/CAM software support.

Combination lathe (3-in-1 machine)

A combination lathe, often known as a 3-in-1 machine, introduces drilling or milling

operations into the design of the lathe. These machines have a milling column rising up abovethe lathe bed, and they utilize the carriage and topslide as the X and Y axes for the milling

column. The 3-in-1 name comes from the idea of having a lathe, milling machine, and drill press

all in one affordable machine tool. These are exclusive to the hobbyist and MRO markets, asthey inevitably involve compromises in size, features, rigidity, and precision in order to remain

affordable. Nevertheless, they meet the demand of their niche quite well, and are capable of high

accuracy given enough time and skill. They may be found in smaller, non-machine-oriented

businesses where the occasional small part must be machined, especially where the exacting

tolerances of expensive toolroom machines, besides being unaffordable, would be overkill forthe application from an engineering perspective.

Mini-Lathe and Micro-Lathe

Mini-lathes and micro-lathes are miniature versions of a general-purpose center lathe (engine

lathe). They typically have swings in the range of 3" to 7" (70 mm to 170 mm) diameter (in otherwords, 1.5" to 3.5" (30 mm to 80 mm) radius). They are small and affordable lathes for the home

workshop or MRO shop. The same advantages and disadvantages apply to these machines as

explained earlier regarding 3-in-1 machines.

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