MACHINE TOOLS

LATHE TURRET

By:Mohammad Yousefi

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ابزار های ماشین

تراش دستگاه گیر ابزار

محمدی: ساسان دکتر استاد

: یوسفی محمد کننده تهیه

PREFACE

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A turret machine tool has a slide table mounted on a machine base for movement toward and

away from a workpiece to be machined. A turret head is indexably mounted on the slide table,

and a plurality of multispindle heads mounted on the turret head at spaced angular intervals in

an indexing direction of the turret head, each of the multispindle heads having a plurality of

spindles disposed therein. A plurality of machine tools mounted on respective ends of the

spindles, and a plurality of spindle gears are mounted on the spindles, respectively. A driven

gear is mounted in each of the multispindle heads in mesh with the spindle gears through a train

of gears. A drive gear is axially movably disposed in the turret head for movement into and out

of mesh with the driven gear in one of the multispindle heads which has been indexed. A

plurality of gear shafts are supported in a cantilevered fashion by each of the multispindle heads

and project toward the turret head, the train of gears and the driven gear being mounted on the

gear shafts. The multispindle heads can be highly accurately installed on the turret head, and

the train of gears can easily be serviced. The turret machine tool is relatively light in weight, and

can be manufactured relatively inexpensively.

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1.turret lathe

The turret lathe, as we know it today, is a comparatively modern machine, and was developed

from an ordinary engine lathe by the addition of revolving tool-holding devices called turrets.

The turret was at first made of circular form, and rotated upon a vertical pivot which had a

binding nut whereby it could be held in any desired position. The circumference of the circular

turret was drilled and reamed for four tools projecting horizontally from it at angles of 90 degrees

with each other. Later the number of tool holes was increased to six, and the turret was

frequently made of hex-gonal form.

The turret was at first located upon a lathe carriage in place of the tool block, and properly set in

line with the lathe center by means of the cross-feed screw. The lateral feed, upon which the

device depends for its action, was obtained by the operation of the feeding mechanism in the

apron attached to the carriage.

The object sought to be accomplished by the addition of this device to the lathe was that of

carrying various drilling, reaming, counterboring, and similar tools by which several operations

could be performed upon a piece of work without removing it from the chuck, or without any

further change of tools than that of revolving the turret. The tools, when once adjusted, required

no further alteration as the several pieces of work were completed and removed from the chuck,

and other pieces substituted for a like series of operations. By this means the work could be

performed much more rapidly, the producing value of the machine being correspondingly

increased.

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2.Types of turret lathes, and their nomenclature

2.1 The archetypical turret lathe: horizontal, manual

The archetypical turret lathe, and the first in order of historical appearance, is the horizontal-bed, ` usually understood in context to refer to this type. The formative decades for this class of machine were the 1840s through 1860s, when the basic idea of mounting an indexable turret on a bench lathe or engine lathe was elaborated upon, developed, and disseminated into factory|factories.

2.2 Semi-automatic turret lathes

Sometimes machines similar to those above, but with power feeds and automatic turret-indexing at the end of the return stroke, are called "semi-automatic turret lathes". This nomenclature distinction is blurry and not consistently observed. The term "turret lathe" encompasses them all. During the 1860s, when semi-automatic turret lathes were developed, they were sometimes called "automatic". What we today would call "automatics", that is, fully automatic machines, had not been developed yet.

2.3Automatic turret lathes

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During the 1870s through 1890s, the mechanically automated "automatic" turret lathe was developed and disseminated. These machines can execute many part-cutting cycles without human intervention. Thus the duties of the operator, which were already greatly reduced by the manual turret lathe, were even further reduced, and productivity increased. These machines use cams to automate the sliding and indexing of the turret and the opening and closing of the chuck (engineering)chuck. Thus, they execut the part-cutting cycle somewhat analogously to the way in which an elaborate cuckoo clock performs an automated theater show. Christopher Miner Spencer built the first one, which he patented in 1873. Unfortunately, his patent attorney failed to protect the most significant part, the cam drum, which Spencer called the "brain wheel.

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3.Classification of Turret Lathes

To obtain a comprehensive view of the various forms of turret lathes, including engine lathes so

modified as to adapt them to turret-lathe work, they may be divided into five classes as follows:

(1) Engine lathes adapted to serve as turret lathes by having a hand-revolved turret mounted

upon the carriage in place of the usual tool-block or compound rest.

(2) Engine lathes adapted to serve as turret lathes by having a hand-revolved turret mounted

upon a laterally moving slide, supported upon a. shoe or saddle fitting the V's of the bed.

(3) The turret lathe proper, specially designed and built as such, with a turret revolved and fed

by hand, supported by and pivoted upon a slide, which is in turn supported by a shoe or saddle

fitted to the Va of the bed.

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(4) A turret lathe designed and built in a similar manner to that last described, and in which there

is a power feed for the cuts. It is so arranged that the turret is revolved automatically. This lathe

is frequently called a semi-automatic turret lathe.

(5) A complete automatic turret lathe having a power feed for the cuts; a quick return of the

turret slide, operated by power; with the turret automatically revolved at the end of its run.

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The lathes described in the third, fourth, and fifth classes are usually provided with a carriage

called a cross-slide, carrying one cutting tool in front and frequently another tool at the back,

inverted so as to cut without reversing the direction of revolution of the work.

A very useful modification of the type described in the third class is called the monitor lathe,

probably from the fancied resemblance of its turret to the turret of the type of warship called a

"monitor". In this lathe the slide upon which the turret is supported and pivoted is moved back

and forth by means of a horizontal hand lever, and is therefore very rapid in its operation. From

the fact that this constitutes a rapid hand feed for the turret, this type is adapted for light work or

work upon soft metals. For this class of work it is a very rapid and efficient machine. Fig. 292

shows one of these machines. The lever A is for operating the turret slide B, carrying the turret

C, which was first revolved by hand but later by a ratchet device located in its base and

actuated by a pawl during the latter portion of the movement of the slide in withdrawing the

cutting tools from the work. The lever D is for operating the cross-slide E, carrying a cutting-off

tool and frequently a forming tool also.

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4.SPECIAL FEATURES

Three piece face gear coupling allows tool disc to be indexed without lifting. It also ensures high repeat positioning accuracy an rigidity.

'Parallel Index' cam mechanism allows fast and smooth indexing of heavy tool disc's. Computer generated cam profiles ensure shock-free indexing action.

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Totally enclosed, robust mechanism, with oil bath lubrication.

Electrical elements are conveniently located in a separate area, free from oil and coolant.

PRINCIPLE OF WORKING    Electric motor drives the cam shaft through a system of gears. Cam shaft indexes the follower shaft through a 'parallel index' drive mechanism. Cam shaft is also geared to the 'drum cam' which controls clamping and release of the 3 piece coupling.    One revolution of cam shaft completes one indexing cycle of 'unclamping - indexing - clamping'. Absolute position encoder gives feedback of the turret position. Proximity switch inspects the clamped position of the turret.

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5.Examples and Specifications:

Specifications:

Height of center: 80mm

Number of tools: 8, 10, 12

Tool change time (adjustment): 0.4 sec

Tool change and locking time (adjustment): 0.8 sec

Hydraulic Working pressure: 40 kg/cm²

Pulling force of hydraulic cylinder: 4100 kg

Radial load of tool end: 900 kg

Axial load of tool front end: 780 kg

Axial load of tool rear end: 350 kg

Turret rotating movement of inertia: 15386 kgxcm²

Opposite side width of disc: 300 mm

N.W. (without tool disc): 73 kgs

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Specifications:

Height of center: 125mm

Number of tools: 8, 10, 12

Tool change time (adjustment): 0.2 sec

Tool change and locking time (adjustment): 0.5 sec

Hydraulic Working pressure: 45 kg/cm²

Pulling force of hydraulic cylinder: 10360 kg

Radial load of tool end: 2500 kg

Axial load of tool front end: 3900 kg

Axial load of tool rear end: 1500 kg

Turret rotating movement of inertia: 63360 kgxcm²

Opposite side width of disc: 420 mm

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N.W. (without tool disc): 130 kgs

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REFERENCES

www.mtsdriventools.co.uk/img/tool-turret

www.centroidcnc.com/images/8_position_cnc_turret

news.thomasnet.com/images/large/552/552509

www.precisionengineer.co.uk/cooldrill.html

www.allproducts.com/.../hydraulic_turret_06.html

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