Turret Note

8/4/2019 Turret Note

http://slidepdf.com/reader/full/turret-note 1/24

Department of Production Engineering o u e emi utomatic an utomatic at es Vidya Academy of Science & Technology

1

Turret,Capstan and Automatic Lathes Introduction

Engine lathes are extremely useful and versatile, but they are not suitable for mass production. As aconsequence of the time required for changing and setting tools and for making measurements on the

workpiece, the actual chip producing time often is less than 50 % of the total cycle time.

Also, a skilled machinist is required for all the operations and such personnel are costly and often inshort supply. Consequently Turret, Capstan and Automatic lathes which reduce or eliminate theamount of skilled labour and reduce production time were developed and are widely used in quantity

manufacturing.

Difference Between Turret and Engine Lathes

Turret lathe is adapted to quantity production work, engine lathe is primarily used for miscellaneous

jobbing, tool room or single operation work. Another difference between an engine lathe and turret isthat the tailstock is replaced by a (usually) hexagon turret upon which are bolted various toolholders

for knee turning, roller box turning, drilling, boring and recessing.

Unlike engine lathe, a turret lathe can hold a number of cutting tools at a time. In engine lathe one toolcuts at a time whereas in turret, a number of tools can operate on the job simultaneously. Tools may be

permanently set up in the turret in the sequence in which they need be used.

Extreme rigidity in the holding of work and tools is built into the turret lathe to permit multiple land

combined cuts. Using a turret lathe instead of an engine lathe can often cut machining time by 25 to75% and handling time by 2550%.

Unlike an engine lathe a turret lathe has

(i) A front tool post which holds four tools that may be indexed by 90°. so that every 1001 can operateupon the workpiece in a regular order and

(ii) A rear tool post mounted upon the carriage which holds another tool e.g., for cutting off operation.

If large number of pieces are to be manufactured, every time positioning and changing of tools for each

job on an engine lathe not only involves a good deal of time but may also result in workpieces of nonidentical dimensions.

Frequent tool changing is not needed on a turret lathe, because several tools can be mounted on the

hexagonal turret and tool post and can be preset as per the requirements of various operations to be

carried out on workpieces on mass scale.

Unlike engine lathe, the feed movement of each tool set on hexagonal turret is regulated by stops andfeed trips. The tools operate on the workpiece for a predetermined amount (e.g., length etc.).

The original cost of a turret lathe is considerably higher than that of the engine lathe. Tooling is

expensive and setup time will run from 12 hours on small jobs up to 8 hours for a complex job.Machining time on turret lathe, as compared with an engine lathe, is not shortened. Feeds and speed

remain the same for all types of lathes.




The time saving on turret lathe is principally because of the combined cuts and because so muchmachining can be done with only one chucking of the part. For example, the cross slide tools may be

turning one diameter while toe turret tools are boring and turning other diameters. Unlike engine lathe,a semiskilled operator can operate a turret lathe or a Capstan lathe after the same has been set up by a

skilled worker.

Main parts of Turret Lathes

The main parts of a horizontal turret lathe are:

(i) Bed

(ii) Head stock, spindle, chuck etc.,

(iii) Carriage

(iv) Turret.

(i) Bed

The bed is a long, box like casting fitted with rectangular ways upon which are mounted the carriage,and turret. It also supports the headstock. The bed provides strength and rigidity to other parts. It

ensures proper alignment of parts also.

(ii) Headstock The headstock is a large casting located on the left end of the bed. It houses the

transmission mechanism (gears etc.) which operates the spindle at various speeds. These speeds arecontrolled by the built in speed selector.

A modern turret lathe uses either an electric head with a multiple speed motor mounted directly on thespindle or an all geared head is used.The operator needs only to set the dial to the diameter of work,

and the spindle speed selector will automatically shift to the correct speed.

(iii) Carriage: The carriage is fitted over the ways of the bed. Mounted on it is the tool post. The frontof the carriage includes the apron which contains the feed mechanism.

The carriage has reversible power longitudinal feeds ranging from 0'125 to 4'5 mm and also reversible power cross feeds ranging from 0'050 to 2'25 mm per revolution of the spindle.Most models have

longitudinal and cross-feed positive stops which act to disengage the feed according to thespecification the work.




3

(iv)Turret :The turret is a hexagon on square shaped tool holder mounted on the saddle or carriage onthe bed ways. The main ram turret usually is six sided, and provision is made for mounting tools on

each of the six faces. The turret can be rotated about a vertical axis to bring each tool into operating position, and the entire unit can be moved longitudinally, either manually or by power, to provide feed

for the tools.

The cross slide turret also can be rotated manually about a vertical axis to bring each of the four toolsinto operating position. On most machines the turret can be moved transversely, either manually or by power, by means of the cross slide and longitudinally through power or manual operation of the

carriage.

In most cases, a rear tool post also is added to the back end of the cross slide; this often carries a parting tool. The tools held in the turret may be used to perform certain operations on a workpiece,

while at the same time, other tools held in the square tool post mounted on the carriage do other operations.

The workpiece having been previously chucked correctly, with these basic features of a turret lathe, a

number of tools can be set up on the machine and then quickly be brought successively into working position so that a complete part can be machined without the necessity for further adjustment or

changing tools or making measurements.

Operations such as roughing, knifing, tapping, boring etc., can be performed merely by rotating thehexagon turret and presenting to the workpiece a different tool secured in the turret, in order of

sequence.

Turret Head Indexing Mechanism - Turret head indexing mechanism is an arrangement that indexesthe turret head automatically when it is brought back away from the spindle nose or chuck after the

first operation is completed. That means, automatically the present tool in the turret head will rotate

away and the next tool will come in its place for the next operation.

Turret Head Indexing Mechanism

A - Spring D - Pin G - Index Plate

B - Cam E - Turret Spindle H - Turret

C - Pawl F - Ratchet Wheel I - Plunger




4

As the turret head reaches the backward position that is away from the chuck holding the workpiece,the plunger actuating cam lifts the plunger from the slot S of the index plate and thus unlocks it so that,

now, the turret head is free to rotate. As the saddle is still moving, the ratchet wheel comes in contactwith the projecting pin of the pawl.

The pin pushes and rotates the ratchet wheel which results in the indexing of turret. When the turret

head has reached its extreme right position, ratchet wheel has also been rotated through 60° and the plunger has again set in one of the slots of the index plate

Bar Feeding Mechanism - When workpieces are to be machined from the bar stock on, capstan or turret lathes, it is necessary that some arrangement must be there for feeding the bar stock forward (for

the next piece) after each finished workpiece is parted off. The bar may be pushed forward manually by hand.

But this arrangement takes more time, because the spindle and the long bar must come to a dead stop before any adjustment can be made. The other method of bar feeding which pushes the bar forward

immediately after the collet chuck releases the work without stopping the machine.

Bar Feeding Mechanism

A - Rotating sleeve C - Headstock E - Pulley

B - Spindle D - Guide Bar F - Stand

This method consumes less time as compared to manual bar feeding and the bar can be fed without

stopping the machine. The method, however, suits to small machines only. The rotating sleevemounted on the guide bar carries the rear end of the bar stock. The other end of the bar stock passes

through the spindle to project outside the collet chuck.

Under the action of wire rope and weight, the sleeve and bar stock have a tendency to move to right i.e.towards the headstock and thus out from the collet chuck. After the finished piece has been parted off,the chuck opens and thus the bar stock automatically moves forward and rests against the bar stop

fitted on the turret




5

Types of Turret Lathes - Different types of turret lathes are:

(i) Horizontal turret lathe

a) Ram type

b) Saddle type

(ii) Vertical turret lathes

(iii) Numerically controlled (N/C) turret lathes.

Horizontal turret lathe and a vertical turret lathe. Depending upon the turret layout, turret lathes areclassified as machines with horizontal or vertical axis of turret rotation.

Ram Type Horizontal Turret Lathes - This machine is a light to medium duty turret lathe and is

quick and easy to handle. The turret is mounted on a ram which slides in ways machined on the saddle.The complete saddle can be positioned forward or back to bring the turret head close lathe work, and

then it is locked in place.

Collets may be used for feeding bar stock and conventional chucks may be employed if each part is to

be loaded by hand. Air or hydraulically operated power chucks may be used for speed in loading andcontrol of pressure on the workpiece.

Power feed is available for the turret (ram) and in both (X and Z) directions on the cross slide, though

hand feed may be used. Speed may be from 50 to 4000 RPM depending on the size of lathe. Larger lathes have lower speeds. Trip stops are there to stop the feeding motion of the turret at any predetermined point.

Saddle Type Turret Lathes

Saddle type turret lathe is a heavy duty machine, there is no ram, rather the turret head is mounteddirectly on the saddle and the saddle slides on the ways of the machine.




6

This makes a more rigid turret, avoiding the overhang which occurs when a ram type turret is advancedto the work and the possible sagging out of line. Power feed is standard on turret and both axes of the

cross slide. Speed may be from 20 to 1500 RPM depending upon the size of the machine.

Vertical Turret Lathes

Vertical turret lathes are designed for considerably larger and heavier work than is commonlyassociated with either type of horizontal turret lathes. Vertical lathes are utilized solely for complex

chucking work, particularly for boring operations, and are not adapted to bar work.

Vertical turret lathe closely resembles a vertical boring mill. It commonly has a rotating table ranging

from 600 to 1200 mm in diameter, which is equipped with both removable chuck jaws and T-slots for clamping the work.

The main tool head is mounted on the cross rail 'c' along which it travels horizontally and with which it

travels vertically. The five sided turret is mounted on a ram R which travels vertically in the cross railtool head. This turret can be easily and quickly indexed from hole to hole and clamped with a lever

Tools are clamped in the tool holes of the turret by the same type of holders as those used in horizontal

turret lathes. Frequently, a second tool holder also is mounted on the cross rail. Each motion for successive tools can be controlled by means of stops so that duplicate work pieces can be machined

with one tooling setup.

Tooling Equipment For Vertical Turret Lathe

All the cross rail tool heads and the side tool head have power feeds in the forward and reverse

directions, as well as rapid traverse motions for tool approach and return motions. A five sided turret isavailable so the operations must be completed by five indexing of the turret. This necessitates multiple

tool setting arranged as follows:

1. There are four tools in the holder No.1, first tool, left rough faces the top and then with a vertical

feed rough turn the rim. The next two tools finish top and radius corner and the fourth tool skins thevanes which are at an angle.

2. Operation, 2, involves three tools to rough face: the boss at three different heights.




7

3. Operation number 3, finish machines the same faces;

4. Operation 4, one tool finish turns the outside rim with a vertical traverse, while the comers of theinside boss are radiused and chamfered by the two remaining tools.

5. The 5th operation is to rough and finish bore and to size the top recess of the bore

Numerically Controlled NC Turret Lathes

Such lathes are now available in considerable variety and have proven to be far more productive than

manually operated machines.

Some N/C machines have only a bed turret, while others have both a bed turret and a cross slide turret.When properly programmed and tooled, these machines can economically produce a few to a few

thousand parts.

Size and Specification of Turret Lathes:-

(i) Maximum diameter of bar that can be passed through the machine spindle,

(ii) Swing diameter of the workpiece,

(iii) Spindle speeds,

(iv)Feeds,

(v) Chuck size,

(vi)Drive motor capacity,

(vii) Cost, etc.

Work Holding Devices of Turret Lathes

Turret is a mass production machine. In order to keep set up time to minimum, the work holding

devices should be accurate, easy and quick to operate, and should ensure rigidity against heavy cuts.Commonly used work holding devices are:

(a) Collet chucks,

(b) Jaw chucks,

(c) Arbors, and

(d) Fixtures.




8

a) Collet chucks:- Collet chucks are widely used to clamp bar stock in machining on turret lathes.Their main feature is a collet, which is a steel sleeve with split tapered portion forming jaws, Clamps

bar 3 when tube 4 together with collet 2 is shifted to the left until the jaws of the collet are contracted by inner tapered hole of spindle 1.

The drawback of this arrangement is an axial bar displacement in clamping, which decreases the

accuracy of axial bar positioning. Illustrates a collet chuck in which, on clamping bar, collet 1 ismoved to the right and the outer taper of collet is contracted under the action of the inner taper of stop

nut 2. screwed on spindle 3. The conventional collet taper angle is 30°.

Collet chuck may be hand operated or air operated.

(b) Jaw Chucks:- Jaw chucks are used 10 bold irregular shaped individual work pieces. Various jaw

chucks employed for the said purpose are:

(i) Three jaw self centering chuck,

(ii) Four jaw independent chuck,

(iii) Two jaw box chuck,

(iv)Power chucks.

Jaw chucks (i) and (ii) have been described in the chapter on Lathe. Two jaw box chucks is used for

holding specially the work pieces having parallel flat sides.

Power chucks are operated by air pressure, or hydraulic pressure. Air chucks are commonly used

because of easy availability of compressed air in the workshops, ease of their operation and proper grip

strength.

(c) Arbors:- Arbors may be sometimes used for holding small workpieces having accurately drilled

holes in them. Threaded type and expanding type arbors are in use.

(d) Fixtures:- Special fixtures may be employed to hold jobs which cannot otherwise, be held incollets, jaw chucks or arbors.

Turret Tools

On a turret, the workpieces are machined, (i) either from the bar stock, or un in the form of separate

castings or forgings held in jaw chucks or on face plates. Typical tools for bar work include

(i) Box tools, and

(ii) Hollow mills (for reducing the diameter of the bars of stock to the required size).

(iii) Special designs of turning tools or turners are used extensively on flat turret lathes,

(iv)Forming tools are used when there is an irregular surface to be machined,




9

(v) Drills and reamers,

(vi) Dies, when the part must be threaded,

(vii) Cutting off tools for severing finished parts, and

(viii) Many tools of special design.

In general, cutting off and forming tools are mounted on a cross-slide between the turret and

headstock, whereas box tools, hollow mills, dies, etc., arc carried in the turret. For chuck work, theturret tool equipment often includes tools such as:

(i) Drills

(ii) Boring bars

(iii) Reamers

(iv) Facing cutters

(v) Taps

(vi) Dies, etc

A box tool held on the turret is commonly used for turning operations, As a box tool operates on the

unsupported end of the bar projecting from the chuck, it is equipped with some form of backrestopposite the turning tool for supporting the work; it usually encloses or surrounds the turned part to

some extent, and, for that reason, is known as a box tool.

Tool Holding Devices

Tool holders for holding turret tools may be mounted on turret faces or on cross slide tool post. Tool

holders used to clamp various types of single point tools in the tool holes of turret.

Straight Turning Cutting Off Boring

Adjustable Straight Turning Vertical Slide




10

Tool Holders for Holding Single Point Tools

When mounting tool on the main turret of a conventional horizontal turret lathe, a standard type of adapter that is fastened directly to the turret face is used. The adapter holds one turning tool and one

boring tool, thus enabling two operations to be performed at one position of the turret.

Method of Mounting Tool to the Main Turret

A - Turning Tool C - Adapter

B - Work piece D - Turret Face

Special adapters are available that hold three or four tools for performing three or four operations

simultaneously, particularly when the turret is capable of moving horizontally in two directions. The Tslot principle of mounting, shown on the two form tool adapters is used for most tools that operate

from cross slide, regardless of how the adapter is designed.

Flat Form Tool of Dovetail Design

A - Lock for Mounting in Slide C - Dovetail E - T - Slot mounting

B - Lock for Dovetail D - Form Cutting Edge

Circular Form Tool




11

A - Adjustable Screw C - Form Cutting Edge

B - Serrated Faces For Looking D - T -Slot Mounting

List of Turret Attachments

Different attachments when fitted on the turret lathe increase its usefulness and a wide variety of works

may be done on lathe and more efficiently. A few attachments commonly used on turret lathe are:(i) Bar stops,

(ii) Roller support turning attachment.(iii) Box tool Holder.

(iv)Multiple tool holder.(v) Knee tool holder.

(vi) Slide Tool.(vii) Screw cutting self-opening die head.

(viii) Collapsing Tap.(ix) Taper attachment

Turret Bar Stop

When same component is to be produced on mass scale from the bar stock, every time the same length

of the bar is to be measured and projected out from the collet chuck. This is a cumbersome and timeconsuming process. A simple solution is to make use of a bar feeding arrangement and a bar stop.

Every time, a piece is finished and cut off, the collet opens and the bar moves forward out from thechuck and its end rests against the bar stop fitted on the turret machine. This ensures constant length of

bar projecting from the collet chuck every time for each component to be machined.

Turret Roller Support Turning Attachment

This attachment is frequently used when workpiece overhang is excessive.

Roller Support Turning Attachment

A - Adjustable Carrier for Roller B - Roller C - Cross Slide Mounting

Such an attachment is mounted on a cross slide opposite to the direction of the cutting forces, to

prevent bending of the workpiece during machining, the rollers can be adjusted to accommodate a

range of workpiece diameters.




12

Supports similar to the type, but in which the Work is supported in a Vee instead of by rollers, havealso been successfully used, but supports that utilize rollers are preferred.

Turret Box Tool Holder

Roller support can be extended for use for axial turning, as from a turret. Tools used for this procedure

combine support with one or more cutting tools, Tools that incorporate both support and cutters areoften called box tools, A box tool that incorporates two supporting rollers.

A Box Tool Holder

A - Cutting Tool B - Roller C - T - Slot Mounting

In turning with this type of tool, the rotating workpiece passes between the rollers and the cutter. The

cutter is set slightly ahead of the rollers, which allows the rollers to begin their function of providing

support as turning progresses. Both rollers and the cutter can be adjusted, permitting considerable sizevariation for any given tool.

Turret Knee Tool Holder

A knee tool holder is used for combined turning and boring or combined turning and drillingoperations. Fig. shows an adjustable knee tool for turning and drilling short lengths at the same time.

Knee Tool Holder




13

Turret Multiple Tool Holder

A multiple tool holder permits several operations to be carried out from the same position. This toolholder may be bolted direct on the turret face.

Different turning and boring tools may be held in different holes of the multiple tool holders, for

carrying out such operations simultaneously.

The pilot bar at the top of multiple tool holders lends additional support to the tool and prevents any

vibration or deflection while the tool is caring out cutting action.

Turret Slide Tool

The slide tool can hold tools for boring, drilling, reaming, recessing, and grooving operations.

Slide Tool

The slide can be moved up and down by means of a hand wheel provided at the top. The movement of

slide is similar to that of the shaper tool head.

Turret Screw Cutting Opening Die Head

It is a very useful attachment for cutting external threads. The die head bolted on the face of the turret

accommodates the die which can be adjusted by means of the screws. When the required thread lengthhas been attained, further feeding of the head is stopped and die opens automatically to clear the

threaded workpiece. The head is then withdrawn.

Self Opening Die Head




14

Turret Collapsing Tap

It is employed for cutting internal threads. A usual Solid tap, if used for cutting threads, need bereversed to take the tap out of the threaded hole at the end of threading operation, But in case of a

collapsing tap, its cutting edges are made to collapse into the body of the tap, when threading iscomplete and the tap can be brought out of the work piece very easily.

Turret Taper Attachments

A taper attachment for the universal, carriage is a separate tool bolted to the T-slots on the near of thecross side, The rear tool block can be used for taper turning without affecting normal use of the square

turret at the front of the cross slide.

Turret Lathe Operations

Operations performed on turret lathe are same as those performed on an engine lathe, except that twoor more operations may be carried out simultaneously on the turret lathe. Various operations

performed on turret lathe are:

(i) Cylindrical turning

(ii) Form turning(iii) Taper turning

(iv) Facing(v) Boring

(vi) Drilling(vii) Reaming

(viii) Threading(ix) Recessing

(x) Chamfering(xi) Knurling

(xii) Parting off.

The above named operations are carried out using

(a) Turret tools described in article(b) Turret tool holders described in article

(c) Turret attachments described in article

Knurling Operation on Turret Lathe




15

Turret Lathe Tooling Layout:-

(i) Set up time(ii) Work handling time

(iii) Machine Controlling time,(iv) Cutting time

(v) Tool cost(vi) Setup labor cost

(vii) Lathe operator labor cost(viii) Number of parts to be manufactured.

Factors (i) to (iv) affect the arrangement of the tools in the turret and tool holders. Factors (v) to (viii)relate to the cost of producing parts on the turret lathe and thus determine whether turret should be

used for the said purpose or not.

(i) Set up time is the time required for a skilled tool setter to set the various cutting tools and work holders in the turret lathe, adjust them to produce the desired dimensions on the workpiece, and set the

various stops. Set up time should be as short as possible for maximum production. This may be

achieved by using standard too] holders and tools.

(ii) Work handling time is the time required for putting work into and removing it from the turret lathe.Power chucks and automatic bar feeding may help in reducing work handling time.

(iii) Machine controlling time is that required to manipulate the controls which reverse and rotate the

turrets, change speeds and so on. Machine controlling time may be reduced by combining operations ina single turret position, etc.

(iv)Cutting time is that during which chips are produced cutting time can be reduced by working at

optimum speeds and feeds and by making simultaneous cuts.

The next step is to:

(i) Prepare the finished drawing of the part to be manufactured.

(ii) Select tool holders and tools such as drills, boring bars reamers etc., for the necessary machiningoperations.

(iii) Decide length of travel of the tools and position of stops.(iv) Select proper cutting speeds and feeds for each operation.

(v) Set the work, tool holders and tools on the turret lathe.

Turret Tooling for a Threaded Adapter




16

A - Tap C - Ream R E - Drill

B - Recess D - Bore A F - Start Drill

The various operations are:

1. The bar stock is advanced against the combination stock stop and start drill and is clamped in the

collet chuck. The start drill is advanced and the end of the workpiece centered.

2. The turret rotates; drill at 2 takes the position earlier occupied by start, drill 1. Drill 2 drills the bolein the bar stock (workpiece) up to the required length.

3. Turret rotates, boring bar, 3, takes the horizontal position and bores thread diameter. The boring bar in a slide tool is used.

4. Turret rotates, reamer 4, occupies horizontal position opposite to the workpiece and the already

drilled hole is reamed to size.

5. Turret rotates, and the recessing tool comes in front of the workpiece and a groove for thread

clearance is recessed. For this operation a quick acting slide tool is used with a recessing cutter mounted in a boring bar.

6. Turret again rotates and the tap 6 comes in front of the workpiece and the internal threads are cut.

After operation 6, a parting tool held in the rear tool post does the cutting off operation and the

threaded adapter separates from the bar stock. The collet chuck opens, bar stock is advanced again andoperational steps from 1 to 6 above repeat to produce the next workpiece.

Capstan Lathe Introdution - The capstan lathe is so called because of the hexagon shaped tool carrier the capstan, which replaces the tail stock of the centre lathe. The capstan (tool head) is mounted on the

capstan slide, which in turn is mounted on a suitable rest or saddle, which is fitted on the lathe bed.

Capstan Lathe Parts

A - HeadStock C - Capstan Slide E - Bed

B - Capstan D - Adjustment For Capstan Stops




17

Tool Posts and Capstan Head

A - Back Tool Post C - Chuck

B - Front Tool Post D - Turning Tool

Arrangement of Typical Capstan Layout

A - Front Tool Box B - Back Tool Post C - Capstan Tools

The workpiece is held in the chuck at the headstock. The capstan can usually carry six cutting tools.

The construction of capstan is such that it has a comparatively short stroke, permits rapidmanipulation, especially since the capstan head rotates automatically at the end of the withdrawal

stroke, thereby positioning a new or different tool in its holder with a minimum of lost time, ready for performing the next operation.

Stops can be set to limit movement of the tools, and on repetitive work much time is saved by workingto these preset stops.Capstan lathe is particularly useful for batch production work, as it is a multi-

operation machine, and can be set up to carry out a sequenced series of cutting operations. Themachine is ideal for production of small parts.

Specifications of capstan lathe. Either, the total length of the bed and the height of the spindle centre

above the bed or, the working length of the bed and the swing. Cutting tools, attachments and work holding devices number of cutting tools attachments and work devices are used interchangeably on

turret and lathes. Operations performed on a capstan lathe are similar to those carried out on a turretlathe.




18

Operation involved for the Manufacture of a Bolt on the Capstan Lathe

Operation No. Description

1 The bar stock a is pushed against the stop b

2 Rough turning is carried out using cutting tools c and a steady rest d.

3 Finish Turning is being done

4 Chamfering operation is being carried out

5 Threads are being cut

6 Parting off operation to separate the finished component from the bar stock a

Automatic Lathe Introduction

Next in progression from the Capstan lathes come the Automatic lathes, one form of which, indeed, is

a Capstan which has been modified by a form of plug board automation and limit switches to operatethrough its cycle.

In fully automatic lathes, once the machine is set up, all the movements related to the manufacturing

cycle and also the loading of blanks and the unloading of machined parts are performed without theoperator's participation. In semiautomatic machines, the two latter movements are accomplished by the

operator.

To explain further, lathes that have their tools automatically fed to the work and withdrawn after the

cycle is complete are known as Automatic lathes. Since most lathes of this type require that theoperator place the part to be machined in the lathe and remove it after the work is complete, they are

perhaps incorrectly called automatic lathes.

On an automatic lathe, the bar stock is entered through the main spindle and clamped by a colletdevice. Automatic lathes machine independently one piece after the other from the bar.




19

All movements and actions take place automatically e.g., feed and return travel of the turret carriage,changing over of the turret bead, loosening feeding and chucking of the bright drawn bar. Therefore

one worker can operate several automatic lathes.

Work feeding: Fully automatic lathes are provided with magazine feed so that a number of parts can be machined, one after the other, with little attention from the operator.

Tool feeding: Most machines, especially those holding the work between centers, have front and rear

tool slides. Others adapted for chucking jobs, have an end tool slide located in the same position as theturret on the turret lathe. These machines may also have the two side tool slide.

In another construction, there is a flat table in front of the chucking spindle, on which can be mountedtool slides at any angle or in any position. Each tool slide has individual feed and receives its power

from individual drive shafts at the end of the machine. As a rule, automatic lathes are multiple toolmachines

Classification of Automatic Lathes - Automatic lathes can be classified as follows:

(i) Single spindle automatics,

(ii) Multi spindle automatics,

(iii) Bar stock machines,

(iv) Chucking machines,

(v) Horizontal spindle machines,

(vi) Vertical spindle machines.

Single spindle automatics have only one spindle and they machine one component at a time.

Multi spindle automatics have more then one spindles (4 to 8). These machines are either of parallel

action type or of progressive action type. Multi spindle machines have higher production rate ascompared to single spindle machines.

Bar stock machines use-work material in the form of bar and produce components such as bushes,nuts, screws, rings etc.

Chucking machines hold castings or forgings in the chuck or in special fixtures for machining them.

Horizontal spindle machines have their spindle in the horizontal position.

Vertical spindle machines have their spindle in vertical position. They occupy less floor space as

compared to horizontal spindle machines.

The majority of these machines are operated mechanically by trips and cams, which, with the gearing,control the spindle speeds, strokes and other aspects of the cycle.

Single Spindle Chucking Automatics - Single spindle chucking automatics are designed for efficient

production of parts which must be held in a chuck. All tool movements, and speed and feed changesare controlled automatically. Parts are usually loaded and unloaded manually.




20

These machines are built with numerical controls or with electromechanical or hydraulic controlsystems.Single spindle chucking automatics vary in size from 150 mm to 600 mm chucking capacity.

The drive from the motor is to the spindle via change gears and from thence, through feed changegears, to tbe control shaft which operates the turret by means of a drum earn having the same number

of lobes as there are turret faces, which vary from four to six. Driven from this shaft, at right angles, is

the cross slide earn shaft, having single lobe drum cams driving the front and rear slides

Fitted at an accessible place on the central shaft are various trips. Two, set to operate when the turret is

in the back position, work gear change mechanisms, so that a limited range of speeds and feeds may beemployed at each turret position. Alternate speeds and feeds are obtained by using different change

gears.

Turret and cross slide feed strokes are altered by adjustable trips on the central shaft operating a clutch,which disengages the feed drive from the work spindle and brings in a constant fast speed drive to the

central shaft, so that although the turret has a constant stroke, the feed stroke can be tripped in at anytime.

Single spindle machines can be set up in a reasonably short time, to perform turning operations, of a

simple nature with a minimum of tooling and so are invaluable for small batch work.Cycle times, whilst being high when compared with the more sophisticated multispindle automatics,

even then the machining costs are reduced where the operator works two machines grouped together to perform the two operations usually required to produce both sides of a finished blank.

Multi Spindle Bar Automatics - Because of bar loading limitations, multi spindle bar automatics are

horizontal spindle machines, having from four to eight workspindles of from 15 mm to 120 mmcapacity. Instead of the tools being mounted in a revolving turret; on this machine, the spindles are

mounted in a turret called a spindle carrier

Each spindle carries a bar of material. The end working tools are mounted on a reciprocating slide.

Cross slides are also provided for profile work and stock cut off. One machining stage is performed ateach spindle position, and each workpiece passes consecutively through all positions, I to IV.

Method of Multiple Spindle Turning on a Four Spindle Machine




21

Thus, one revolution of the spindle cylinder (carrier) is required to machine a workpiece, if theautomatic has one loading position. To explain further, in multispindle automatics, the work is divided

so that a portion of it is performed at each of the several (say, 4, 5, 6 or 8) stations or positionssimultaneously, thereby short terming the time required to finish one part.

Each time the tools are withdrawn and the spindle carrier indexes one station, a finished workpiece is,

cut off and a new piece is started. Bars of stock are loaded into each spindle when it has been indexed,to the first position. It automatic stock feeding is used, it is done in the lower spindle position at the

rear of the machine.

In operation, the spindle carrier is indexed by steps to bring the bar of stock in each of the work spindles successively in line with the various tools held on the tool slides. All tools in the successive

positions are at work OD different bars at the same time. Multispindle bar automatics are intended to produce parts from bar stock of different profiles.

Performed oil the machine are the following operations:

(i) Rough, finish and form turning

(ii) Facing,

(iii) Drilling and reaming,

(iv) Boring, counter boring and countersinking,

(v) Cutting internal and external threads, etc.

In place of collet when multi spindle automatics are provided with hydraulic or air operated chucks for

holding individual pieces, the machine is known as Multispindle automatic chucking machine. It issimilar to multiple spindle bar automatic except for the stock holding equipment.

Advantages of Automatic Lathes - Automatic lathes have the following advantages:

Minimized production time.

Large scale production of identical components.

Part accuracy is more than that obtained on other types of lathes.

One worker can look after more than one machines at a time.

Applications of Automatic Lathes - Automatic lathes are ideally suited for medium to long production runs. In many instances, the automatic cycle enables the operator either to handle additional

machines or to perform other work.

Single spindle automatics are intended to produce complex shape parts in batch and mass production.Multispindle automatics are high production machines. Production quantities mav range from 3000 to

over 100,000 parts




22

Automatic Screw Machines - Automatic screw machines were developed for the high speed production of large numbers of identical precision parts. The machine tool has been designed to

perform the maximum number of operations, either simultaneously, or in a very repid sequence.

As the name implies, making screws was one of the earliest uses of automatic screw machines.An automatic screw machine is essentially a turret lathe designed to use only bar stock.

Most automatic screw machines not only feed in an entire bar of stock, but also are provided with a

magazine so that bars can be fed through the machine automatically.

Single Spindle Automatic Screw Machines - A Single spindle automatic screw machine has a cross

slide that carries tools both front and rear. A turret mounted in a vertical position on a slide haslongitudinal movement.

Cutting tools are mounted around the turret in a vertical plane in line with the machine spindleand all the operations such as turning, drilling, boring, threading etc., can be done on round, square or

hexagonal bar work of small diameter. Disk cams control the cross slide and dogs engage various triplevers to control the operation of the machine

Swiss Type Screw Machines - The swiss type screw machine was developed for precision turning of

small parts to tolerances of 0'005 mm to 0'0125 mm. Swiss type machine differs widely in design andfunction from other types of screw machines.

The swiss type screw machine does not have a turret. Instead, the cutting tools are held and

moved in radial slides.The stock is held and rotated by an accurately made collet located at the back of the machine and additionally supported by a closefitting guide bushing

Machining of stock is carried out with single point cutting tools. Because of their location, the

tools cut close to the headstock bushing so that the workpiece is not subjected too much deflection.

Cams move the tools into cutting position and provide feed into the work in a radial direction only.Four cams feed the cutting tools, in and out, perpendicular to the work. This controls the diameter.

Fifth cam moves the work along endwise under the cutting tools.

The time required for setting the tooling usually is an hour or two, and an operator can handleseveral machines, once they have been properly tooled.

Swiss Type Screw Machine

A - Micrometer Adjustment C - Cam

B - Infeed Cam Arm D - Tool Bit




23

Parts Made Out From Swiss Type Screw Machines

Specification of Turret Lathe

Bar Stock Capacity

Chuck Size

Drive motor capacity

Swing over ways

Speed

Difference between Engine lathe and Capstan & Turret lathe

1. According to Automation

Non automatic Semi Automatic

2. According to Construction

Holds single Tool on tool postHolds large number of cutting tools; upto four in

indexable tool post on the front slide, one in the rear slide

Equipped with tail stock at the right end of the bed Tailstock is replaced by a hexagonal indexable turret

Head stock is simplHead stock is heavier &Wider range of speeds.

Require 3 hp motor. Require 15 hp motor for similar size of engine lathe

3. According to Operation

Feed movement of tool regulated manuallyFeed movement of tool regulated by stops and feed

trips

Only one operation can be done at a time on W/PPossible to perform more than one operation at atime .

4. According to Production

Suitable for Job oriented

production Suitable for batch production

High skilled labor is required Semi skilled labor is required




5. According to Machining & Setup time

Work & Tool setup time is more Work & Tool setup time is less

Machining time is moreFacility of combination cut reduces the machining

time

6. According to Cost

High labor cost Less labor cost

Less Equipment cost High Equipment cost

Difference between Capstan and Turret lathe

Capstan lathe Turret lathe

Turret of a capstan lathe is mounted on ramwhich slides on the saddle

Turret of a turret lathe is mounted on saddlewhich slides directly on the bedways

Saddle is clamped on bed ways after adjusting the

length of the w/p.Saddle slides on bed ways

Non rigid construction and light & medium duty

machines Relatively more robust and heavy duty machines

Capstan lathes generally deal with short or long

rod type blanks held in collet

Turret lathes mostly work on chucking type jobs

held in the quick acting chucks

Hexagonal turret can be moved back and forth

very rapidly and easilyDifficult to move back and forth

Turret Note

Documents

Transcript of Turret Note