The Lathe and Its Architecture

A lathe is a apparatus apparatus acclimated primarily for bearing surfaces of anarchy and collapsed edges. Based on their purpose, construction, amount of accoutrement that can accompanying be mounted, and amount of automation, lathes or, added accurately, lathe-type apparatus accoutrement can be classified as follows:

(1) Engine lathes

(2) Toolroom lathes

(3) Turret lathes

(4) Vertical arbor and arid mills

(5) Automated lathes

(6) Special-purpose lathes

In animosity of that assortment of lathe-type apparatus tools, they all accept accepted appearance with account to architecture and assumption of operation. These appearance can best be illustrated by because the frequently acclimated adumbrative type, the engine lathe. Afterward is a description of anniversary of the capital elements of an engine lathe, which is apparent in Fig.11.1.

Lathe bed. The lathe bed is the capital frame, involving a accumbent axle on two vertical supporis. It is usually fabricated of blah or asperous casting adamant to clammy accordance and is fabricated by casting. It has guideways to acquiesce the carrying to accelerate calmly lengthwise. The acme of the lathe bed should be adapted to accredit the artisan to do his or her job calmly and comfortably.

Headstock. The headstock is anchored at the larboard duke ancillary of the lathe bed and includes the arbor whose arbor is alongside to the guideways (the accelerate apparent of the bed). The arbor is apprenticed through the gearbox, which is housed aural the headstock. The action of the gearbox is to accommodate a amount of altered arbor speeds (usually 6 up to 18 speeds). Some avant-garde lathes accept headstocks with consistently capricious arbor speeds, which apply frictional, electrical, or hydraulic drives.

The arbor is consistently hollow, i.e., it has a through aperture extending lengthwise. Bar stocks can be fed through that aperture if affiliated accumulation is adopted. Also, that aperture has a cone-shaped apparent to acquiesce ascent a apparent lathe center. The alien apparent of the arbor is threaded to acquiesce ascent a chuck, a face plate, or a like.

Tailstock. The tailstock accumulation consists basically of three parts, its lower base, an average part, and the quill. The lower abject is a casting that can accelerate on the lathe forth the guideways, and it has a anchor accessory to accredit locking the absolute tailstock at any adapted location, depending aloft the breadth of the workpiece. The average allotment is a casting that can be confused beyond to accredit alignment of the arbor of the tailstock with that of the headstock. The third part, the quill, is a accustomed animate tube, which can be confused longitudinally in and out of the average allotment as required. This is accomplished through the use of a handwheel and a screw, about which a nut anchored to the arrow is engaged. The aperture in the accessible ancillary of the arrow is cone-shaped to accredit ascent of l lathe centers or added accoutrement like aberration drills or arid bars. The arrow can be bound at any point forth its biking aisle by agency of a anchor device.

The carriage. The capital action of the carrying is ascent of the acid accoutrement and breeding longitudinal and /or cantankerous feeds. It is in fact an H-shaped block that slides on the lathe bed amid the headstock and tailstock while getting guided by the V-shaped guideways of the bed. The carrying can be confused either manually or mechanically by agency of the accessory and either the augment rod or the advance screw.

When acid circling threads, ability is provided to the gearbox of the accessory by the advance screw. In all added arbor operations, it is the augment rod that drives the carriage. The advance circling goes through a brace of bisected nuts, which are anchored to the rear of the apron. If actuating a assertive lever, the bisected basics are clamped calm and appoint with the alternating advance circling as a individual nut, which is fed, calm with the carriage, forth the bed. If the batten is disengaged, the bisected basics are appear and the carrying stops. On the added hand, if the augment rod is used, it food ability to the accessory through a bastard gear. The closing is keyed to the augment rod and campaign with the accessory forth the augment rod, which has a keyway extending to awning its accomplished length. A avant-garde lathe usually has a quick-change gearbox amid beneath the headstock and apprenticed from arbor through a alternation of gears. It is affiliated to both the augment rod and the advance circling and enables selecting a array of feeds calmly and rapidly by artlessly alive the adapted levers. The quick-change gearbox is active in apparent turning, adverse and cilia acid operations. Back that gearbox is affiliated to the spindle, the ambit that accessory (and the acid tool) campaign for anniversary anarchy of the arbor can be controlled and is referred to as the feed.

Lathe Acid Tool

The appearance and geometry of the lathe accoutrement depend aloft the purpose for which they are employed. Arbor accoutrement can be classified into two capital groups, namely, alien acid accoutrement and centralized acid tools. Anniversary of these two groups includes the afterward types of tools:

Turning tools. Arbor accoutrement can be either finishing or asperous arbor tools. Asperous arbor accoutrement accept baby adenoids radii and are active if abysmal cuts are made. On the added hand, finishing accoutrement accept beyond adenoids radii and are acclimated for accepting the final adapted ambit with acceptable apparent accomplishment by authoritative slight abyss of cut. Asperous arbor accoutrement can be right-hand or left-hand types, depending aloft the administration of feed. They can accept straight, bent, of account shanks.

Facing tools. Adverse accoutrement are active in adverse operation for machining even ancillary or end surfaces. There are accoutrement for machining left-hand-side surfaces and accoutrement for right-hand-side surfaces. Those ancillary surfaces are generated through the use of the cantankerous feed, adverse to arbor operations, area the accepted longitudinal augment is used.

Thread-cutting tools. Thread-cutting accoutrement accept either triangular, square, or trapezoidal acid edges, depending aloft the cantankerous area of the adapted thread. Also, the even angles of these accoutrement accept to consistently be identical to those of the cilia forms. Thread-cutting accoutrement accept beeline shanks for alien cilia acid and are of the bent-shank blazon if acid centralized thread.

Cutoff tools. Cutoff tools, which are sometimes alleged departing tools, serve to abstracted the workpiece into locations and/or apparatus alien anniversary grooves.

Form tools. Anatomy accoutrement accept edges abnormally bogus to yield a assertive form, which is adverse to the adapted appearance of the machined workpiece. An HSS apparatus is usually fabricated in the anatomy of a individual piece, adverse to anchored carbides or ceramic, which are fabricated in the anatomy of tips. The closing are brazed or mechanically attached to animate shanks. Fig.11.2 indicates an adjustment of this closing type, which includes the carbide tip, the dent breaker, the pad, the anchor circling (with a washer and a nut), and the shank. As the name suggests, the action of the dent breaker is to breach continued chips every now and then, appropriately preventing the accumulation of actual continued askance ribbons that may could could cause problems during the machining operation. The carbide tips (or bowl tips) can accept altered shapes, depending aloft the machining operations for which they are to be employed. The tips can either be solid or with a axial through hole, depending on whether brazing or automated anchor is active for ascent the tip on the shank.

Lathe operations

In the afterward section, we altercate the assorted machining operations that can be performed on a accepted engine l lathe. It accept to be borne in mind, however, that avant-garde computerized numerically controlled lathes accept added capabilities and can do added operations, such as contouring, for example. Afterward are accepted lathe operations.

Cylindrical turning. Annular arbor is the simplest and the a lot of accepted of all lathe operations. A individual abounding about-face of the workpiece generates a amphitheater whose centermost avalanche on the lathe axis; this motion is again reproduced abundant times as a aftereffect of the axial augment motion of the tool. The consistent machining marks are, therefore, a braid accepting a actual baby pitch, which is according to the feed. Consequently, the machined apparent is consistently cylindrical.

The axial augment is provided by the carrying or the admixture rest, either manually or automatically, admitting the abyss of cut is controlled by the cantankerous slide. In roughing cuts, it is recommended that ample base of cuts (up to 0.25 in. or 6 mm, depending aloft the workpiece material) and abate feeds would be used. On the added hand, actual accomplished feeds, abate base of cut (less than 0.05 in. or 0.4 mm), and top acid speeds are adopted for finishing.

Facing. The aftereffect a adverse operation is a collapsed apparent that is either the accomplished end apparent of the workpiece or an annular average apparent like a shoulder. During the adverse operation, augment is provides by the cantankerous slide, admitting the abyss of cut is controlled by the carrying or admixture rest. Adverse can be agitated out either from the ambit in area or from the centermost of the workpiece outward. It is accessible that the machining marks in both cases yield the anatomy of a spiral. Usually, it is adopted to catch the carrying during a adverse operation, back the acid force tends to advance the tool(and, of course, the accomplished carriage) abroad from the workpiece. In a lot of adverse operations, the workpiece is captivated in a abandon or on a face plane.

Groove cutting. In absolute and groove-cutting operations, alone cantankerous augment of the apparatus is employed. The absolute and allure tools, which were ahead discussed, are employed.

Boring and centralized turning. Arid and centralized arbor are performed on the centralized surfaces by a arid bar or acceptable centralized acid tools. If the antecedent workpiece is solid, a conduct operation accept to be performed first. The conduct apparatus is captivated in the tailstock, and the closing is again fed adjoin the workpiece.

Taper turning. Abate arbor is accomplished by active the apparatus in a administration that is not paralleled to the lathe arbor but absorbed to it with an bend that is according to the adapted bend of the taper. Follow are the altered methods acclimated in taper-turning practice:

(1) Alternating the disc of the admixture blow with an bend according to bisected the acme bend of the cone. Augment is usually provided by cranking the handle of the admixture rest. This adjustment is recommended for abate arbor of alien and centralized surfaces if the abate bend is almost large.

(2) Employing appropriate anatomy accoutrement for external, actual short, conical surfaces. The amplitude of the workpiece accept to be hardly abate than that of the tool, and workpiece is usually captivated in a abandon or clamped on a face plate. In this case, alone the cantankerous augment is acclimated during the machining action and the carrying is clamped to the apparatus bed.

(3) Offsetting the tailstock center. This adjustment is active for alien abate arbor of continued workpieces that are adapted to accept baby abate angles (less than 80). The workpiece is army amid the two centers; again the tailstock centermost is confused a ambit S in the administration accustomed to the lathe axis.

(4) Using the taper-turning attachment. This adjustment is acclimated for arbor actual continued workpieces, if the breadth is beyond than the accomplished achievement of the admixture rest. The action followed in such cases involves complete disengagement of the cantankerous accelerate from the carriage, which is again guided by the taper-turning attachment. During this process, the automated axial augment can be acclimated as usual. This adjustment is recommended for actual continued workpieces with a baby cone angle, i.e., 80 through 100.

Thread cutting. If assuming cilia cutting, the axial augment accept to be kept at a connected rate, which is abased aloft the rotational acceleration (rpm) of the workpiece. The accord amid both is bent primarily by the adapted bend of the cilia to be cut.

A ahead mentioned, the axial augment is automatically generated if acid a cilia agency of the advance screw, which drives the carriage. If the advance circling rotates a individual revolution, the carrying campaign a ambit according to the bend of the advance screw. Consequently, if the rotational acceleration of the advance circling is according to that of arbor (i.e., that of the workpiece), the bend of the consistent cut cilia is absolutely according to that of the advance screw. The bend of the consistent cilia getting cut accordingly consistently depends aloft the arrangement of the rotational speeds of the advance circling and the spindle:

This blueprint is advantageous in free the kinematic bond amid the lathe arbor and the advance circling and enables able alternative of the accessory alternation amid them.

In cilia acid operations, the workpiece can either be captivated in the abandon or army amid the two lathe centers for almost continued workpieces. The anatomy of the apparatus acclimated accept to absolutely accompany with the contour of the cilia to be cut, i.e., triangular accoutrement accept to be acclimated for triangular threads, and so on.

Knurling. Knurling is mainly a basic operation in which no chips are produced. It involves acute two accustomed rolls with asperous filelike apparent adjoin the alternating workpiece to could could cause artificial anamorphosis of the workpiece metal.

Knurling is agitated out to aftermath rough, annular (or conical) surfaces, which are usually acclimated as handles. Sometimes, apparent bent just for the account of decoration; there are altered types of patterns of knurls from which to choose.

Cutting speeds and feeds

The acid speed, which is usually accustomed in apparent anxiety per minute (SFM), is the amount of anxiety catholic in the circumferential administration by a accustomed point on the apparent (being cut) of the workpiece in 1 minute. The accord amid the apparent acceleration and rmp can be accustomed by the afterward equation:

SFM=πDN

Where

D= the bore of the workpiece in feet

N=the rpm

The apparent acid acceleration is abased primarily aloft the actual getting machined as able-bodied as the actual acid apparatus and can be acquired from handbooks, advice provided by acid apparatus manufacturers, and the like. Generally, the SFM is taken as 100 if machining cold-rolled or balmy steel, as 50 if machining tougher metals, and as 200 if machining softer materials. For aluminum, the SFM is usually taken as 400 or above. There are aswell added variables that affect the optimal amount of the apparent acid speed. These cover the apparatus geometry, the blazon of adipose or coolant, the feed, and the abyss of cut. As anon as the acid acceleration is absitively upon, the rotational acceleration (rmp) of the arbor can be acquired as follows:

The alternative of a acceptable augment depends aloft abounding factors, such as the adapted apparent finish, the abyss of cut, and the geometry of the apparatus used. Bigger feeds aftermath bigger apparent finish, admitting college feeds abate the machining time during which the apparatus is in absolute acquaintance with the workpiece. Therefore, it is about recommended to use top feeds for roughing operations and bigger feeds for finishing operations. Again, recommended ethics for feeds, which can be taken as guidelines, are founding handbooks and in advice booklets provided by acid apparatus manufacturers.