Methods of holding tools between centres

 

When machining a piece of work on a lathe the former is usually mounted between the lathe centres. Having been mounted on the lathe the work is supported by the conical points of the live and dead centres.The work must therefore have centre holes in each end drilled by using a combined drill and a countersink. The size of the centre hole has to be proportioned to the weight of the work and the size of cut to be taken. By virtue of the clearance holes the work does not rest on the extreme points of the centres. This is important because otherwise the position of the work will be indefinite. Owing to this method of holding work between centres, the work can be removed from the lathe as often as may be desired. If the work has to be mounted again between centres for further treatment, it will rotate about the same axis as before.

The two lathe centres are mounted in two spindles: one - the live centre is held in the headstock spindle and turns together with the spindle and the work, the other - the dead centre is held in the tailstock spindle and in most cases does not turn and rubs against the workpiece. The point of the dead centre should be hardened to prevent its wearing during the operations performed on the lathe. Both lathe centres should

always be aligned, i. e. the points are to meet when the tailstock with its centre is moved up to the headstock centre. A turner tests the alignment of the centres by taking a cut and then measuring both ends of the cut by a micrometer. Having got the same measurements, the turner may be sure that the centres are aligned and he may proceed with the taming. The centre shown in Fig. 26 consists of a cone, on which the work to be treated is installed, and of a tapered shank, which fits corresponding taper holes in the headstock spindle and tailstock popper.

 

 

Fig. 26. Centre:

1 - cone; 2 - tapered shank

 

 

Fig. 27. Running Centre:

1 - centre; 2, 4 - ball bearings; 3 - tapered shank; 5 - ball thrust bearing

 

When works are machined at high speeds or when the former are too heavy a dead centre and the work will be heated up so as to cause excessive wear from friction. In such cases the so called "running centres" are used. Fig.27 shows a running centre inserted into the taper hole of the tailstock poppet. The centre rotates on ball bearings. The thrust exerted on the centre is taken by the available ball thrust bearing. The tapered shank fits the taper hole of the tailstock poppet.

 

Exercises

I. Use the following words and phrases in sentences of your own:

 

to countersink, to mount, live centre, dead centre, headstock, tailstock, to align, taper hole, to fit, tailstock poppet, running centre, to insert, speed, to exert

II. Retell the text giving answers to the following questions:

 

1. What is the most widely used method of holding work in the lathe? 2. By what parts of the centres is the work supported while being turned? 3. By what means are centre holes drilled in the work? 4. What would happen if the work rested on the extreme points of the centres? 5. Owing to what method of holding work in the lathe, can it be removed from the lathe as often as may be desired? 6. Where are the two lathe centres mounted on the lathe? 7. What kinds of centres are used

on Iathes? 8. Where is the live centre held and how does it operate? 9. Where is the dead centre held and does it turn or not?

 

III. Underline the suffixes and prefixes and translate into Russian the following groups of words of the same stem:

 

to combine, combined, combination, uncombined; to lubricate, lubrication, lubricant; to mount, to dismount, mounting, mountable, discountable

IV. Find in the text English equivalents for:

 

зенковка, предотвращать, шпиндель задней бабки, шпиндель передней бабки, вращающийся центр, хвостовик, неподвижный центр, подогревать, центрировать

V. Give derivatives from the following words and translate them into Russian:

to support, to live, to wear, point, to align, to insert, to fit

VI. Change the sentences using the predicates in the Past and Future tenses and translate them into Russian:

Example: Each end of the work must be countersunk.

Each end of the word had to be countersunk.

Each end of the work will have to be countersunk.

1. When being machined the work must be fastened between the lathe centres. 2. Countersinking must be done by means of a countersink. 3. The axial adjustment of the tailstock centre must be done carefully. 4. The poppet must be re-adjusted from time to time during the process of work. 5. The live centre of the lathe can turn together with the spindle and the work. 6. The dead centre of the lathe cannot turn. 7. Both centre points of the lathe must be aligned.

VII. Connect the following sentences using participle constructions and translate the sentences into Russian:

Example: A piece of work has been delivered to the shop.

The work was machined on the lathe.

Having been delivered to the shop, a work was machined on the lathe.

 

1.The work has been countersunk with a combined drill and countersink. The work is ready to be machined. 2. The tailstock reduced wear of the dead centre. It has been lubricated. 3. The turner has got different measurements. The turner has to change the position of the dead centre. 4. The worker has turned a special screw in the tailstock. The worker removed the tailstock centre from the tailstock spindle. 5. The point of the dead centre has been hardened. The point of the dead centre increased its wear-resistance. 6. The work has been mounted in the lathe. The work is turned.

VIII. Giving answers to the following questions describe the construction and principle of operation of the centre shown in Fig. 26:

1. What parts does the centre consist of? 2. Where is the work to be machined installed? 3. Where does the tapered shank of the centre fit? 4. What causes excessive wear of the dead centre and the work?

 

IX. Describe the construction of the running centre shown in Fig. 27.

HOLDING WORK IN A CHUCK

 

Short parts are usually held in a chuck. This method of holding work is of great importance since it is widely used with lathes. A chuck is a rotating vice which may be attached to the nose of the lathe spindle. There are three important varieties of lathe chucks, such as independent jaw chucks, concentric or self-centering chucks or contracting chucks.

 

 

Fig.28. Independent Four-Jaw Chuck 1,2,3,4 -jaws; 5 – screw

 

Fig. 28 shows an independent four-jaw chuck belonging to the group of simple chucks. The chuck has four jaws 1, 2, 3, 4 carried in radial slots in the chuck body. Each jaw of the chuck can he adjusted independently by means of its own screw 5. It others the possibility to fasten works of both cylindrical and non-cylindrical shape in such chucks. The body of the chuck is provided with a screwed hole to fit the spindle nose of the lathe. Fig. 29, a shows a concentric chuck.

 

 

Fig. 29. Concentric Chuck:

1 - chuck key; 2 - bevel gears; 8 - large bevel gear; 4 -

multi-turn spiral groove; 5 -jaws

 

 

 

The concentric chuck usually has three jaws which can be moved in and out¹ together by means of a chuck key; which is inserted into the opening of one of the three bevel gears (Fig.29, c) meshed with a large bevel gear (Fig. 29, c). A multiturn spiral groove (Fig. 29, d) is cut on the flat reverse side of the large bevel gear. The bottom projections of the jaws are inserted into the separate turns of the groove. When one of the bevel gears is turned by means of the chuck key its motion is transmitted to the large, bevel gear. The rotation of that large bevel gear causes simultaneous and uniform motion of all the three jaws along the slots of the chuck by means of the spiral groove. When the gear with the spiral groove is rotated in that or another direction² the jaws are either approached to or removed from the centre thus clamping or unclamping the work. The concentric or self-centering chuck is very convenient in operation as all its jaws are moved simultaneously. Consequently a work of cylindrical shape is clamped exactly along the spindle axis. This centering is done automatically, therefore such chucks are called "self-centering".

 

 

Fig. 30. Collet Chuck or Contracting Chuck:

1 - shank; 2 - collet; 3 - nut; 4 - collet opening

 

The jaws of the chuck are made of hardened and tempered steel to prevent their wear. The chucks are characterized by strong, all-steel construction³, and are designed to be mounted directly on the spindles of machines without any intermediate plate or adapter, thus ensuring utmost accuracy and rigidity. Fig. 30 shows a collet or a contracting chuck. Such chucks are applied for rapid fastening short works of small diameter. The tapered shank of the chuck is inserted into the taper hole of the headstock spindle. A collet with a cone is placed inside the groove of the chuck. The work to be treated is set into the hole of the collet. When the nut is screwed on the body of the chuck the collet is contracted and the work gets clamped. Magnetic chucks are adapted to work which is difficult to hold in chuck jaws, either on account of its shape or because the pressure of the jaws may distort the work. The magnetic chucks have no jaws, as the work is held by magnetic force instead of by mechanical means. Some workpieces are so shaped that they cannot be held in a chuck, and work of this kind is often clamped to a. faceplate. Most lathes are equipped with two faceplates: one small plate is used for driving workpieces turned between centres, and a large one is used to hold heavy or irregularly shaped pieces.

For finishing the external diameter of work which is already bored axially a mandrel is used. A mandrel is a bar with centre holes at each end. The mandrel is mounted between centres and enables the outside of a workpiece to be turned concentric with the inside and in general such work would have the whole finished first and the outside finished on a mandrel subsequently. The advantage of mounting work on a mandrel is that of being able to reverse the work on the centres so that the whole of the work exterior can be operated on by cutting tools.

¹. to move in and out - вдвигать и выдвигать

². in that or another direction - в том или ином направлении

³. all-steel construction - цельнолитая конструкция

 

Exercises

I. Use the following words and phrases in sentences of your own:

 

chuck, rotating vice, lathe spindle, independent jaw chuck, contracting chuck, chuck body, chuck key, to project, to reverse, motion, to transmit, to mesh, bevel gear, faceplate, mandrel

II. Answer the following questions:

 

1. Where are usually short parts held when being turned in a lathe? 2. What is a chuck? 3. V/hat types of chucks do you know'? 4. What purposes are chucks used for? 5. What kind of work are magnetic chucks adapted to? 6. How is the work held in a magnetic chuck? 7. How many faceplates are most lathes equipped with? 8. What kind of work is a mandrel used for? 9. What is. the advantage of mounting work on a mandrel?

III. Supply English equivalents for the following words and word combinations:

 

self-centering chuck, independent jaw chuck, collet chuck, radial slots, groove, spindle nose

IV Find in the text synonyms of the following words:

 

collet chuck, comfortably, with the help of, slot, to revolve

V. Give derivatives from the following words and translate them into Russian:

 

to divide, dependent, possible, cylinder, to open, to transmit, to ensure

VI. Read and translate the following text without using a dictionary and analyze the ing- forms and ed-forms:

 

The standard chucks generally furnished are mechanically operated by an automatic mechanism which gives the operator total freedom of both hands for handling the work. While the machine is running to cycle time¹ he simply places the work in the chuck which is held there by the work locator² then he releases the safety foot treadle³. There are no chucking levers or valves and gauges that require his attention and time. Standard chucks can be furnished with either two or three simple jaws and with the jaws contracting or expanding. Chucking pressures are the same at all positions and the pressures are adjustable for different types of work. All standard chucks are constructed entirely of steel having a solid steel body, and all the moving parts are made of hardened alloy steel to withstand wear.

¹. cycle time - цикл хронометрирования

². work locator - фиксатор

 

 

³. safety foot treadle – предохранительная ножная педаль

VII. Giving answers to the following questions describe the s independent four-jaw chuck shown in Fig. 28 and its a principle of operation:

 

1. What kind of chuck is shown in Fig. 28? 2. What group of chucks does the independent four-jaw chuck belong to? 3. How many jaws has the chuck? 4. Where are the four jaws of the chuck situated? 5. How can each jaw of the chuck be adjusted? 6. What possibility is offered by the independent adjustment of jaws? 7. What is the body of the chuck provided with?

VIII. Using the following words and word combinations describe the construction and principle of operation of the concentric chuck shown in Fig. 29:

 

a concentric chuck, to have three jaws, to move in and out, a chuck key, to be inserted, the opening, one of three bevel gears, to be meshed with a large bevel gear, on the flat reverse side, the large bevel gear, a multiturn spiral groove, to be cut, the motion of one of the bevel gears, to be transmitted, by means of the chuck, key, to move simultaneously and uniformly, the slots of the body, due to the spiral groove, rotating in that or another direction, the gear with the spiral grooves, to cause, approaching or removing, the jaws of the chuck, from the centre, due to this, the work, to be clamped or unclamped, the advantage, the concentric or self-centering chuck, in moving all jaws simultaneously

X. Describe the construction and principle of operation of the contracting chuck shown in Fig. 30.

II. HOLDING WORK IN A VICE

 

Vices are attachments which are mainly used for holding workpieces in machine and fitting shops. It should be noticed that a vice may also be used as an attachment for holding workpieces on a metal-cutting lathe.

Depending on the character of operation performed bench vices or parallel vices may be applied. Bench vices are made from forged steel and are of rugged construction. If their construction were not rugged, they could not be used when heavy-duty operations such as cutting, riveting, etc. are performed. A bench vice consists of two jaws: the movable jaw and the solid jaw. At the end of the solid jaw there is a lug for securing the vice to a bench. The extension rod of the jaw is built-in a wooden pillow. When a workpiece is clamped between the jaws they are moved together by means of a square-threaded screw. By unscrewing the screw the jaws are moved apart by a spring riveted to the solid jaw. In parallel vices the jaws move parallel to each other. It should be pointed out that parallel vices in their turn are subdivided into swivel vices and plain vices.

Fig. 31. Swivel Vice:

a - front view; b - cross-sectional view:, 1 - vice base*;- 2 - solid jaw; 3 - movable jaw;

4 - screw; 5 - fixed nut; 6 - handle; 7 - swivel plate; 8 - spindle; 9 - bolt; 10 - lever

 

A swivel vice (Fig. 31), being the most convenient vice in operation, consists of a vice base*, a solid jaw and a movable jaw. The motion of die movable jaw is provided by the rotation of a screw inserted into a fixed nut. When the screw is rotated by means of a handle the former will screw in and move the movable jaw to the workpiece to he clamped. The vice base is mounted on a swivel plate being connected with the latter by a spindle. A bolt is inserted into a T-groove. By turning a handle the bolt may be loosened and the vice may be turned in a desired direction.

Plain vices differ entirely from swivel vices in the absence of the swivel plate and that the vice base is bolted directly to a bench. The vice of such a type is made from grey iron, steel hardened plates with a nut being screwed to its jaws. Parallel vices are convenient for clamping workpieces., but as their jaws are of little strength they are non-suitable for heavy-duty operations.

* American - vice ground

 

Exercises

I. Use the following words and phrases in sentences of your own:

 

vices, attachment, bench vice, to rivet, rugged, parallel vices, heavy-duty operation, to secure, movable jaw, solid jaw, lug, pillow, extension rod, swivel vices, plain vices, front view, cross-sectional view, fixed nut, to loosen

II. Answer the following questions:

 

1. What are vices and what purposes are they used for? 2. On what lathes are vices used? 3. Depending on what features may bench or parallel vices be applied for holding workpieces? 4. What material are vices made of? 5. If the construction of the vices were not rugged, could they be used for heavy-duty operations? 6. What main parts does a bench vice consist of? 7. Why is the end of the solid jaw of the bench vice provided with a lug?

III. Find in the text English equivalents of:

 

 

тиски, вид спереди, проекция поворотных тисков в попе речном разрезе, поворотная плита, пружина, основание, завинчивать, неповоротные тиски, тавровый или Т-образный паз, закрепленная гайка, поворачивать, обеспечивать, приспособление

 

IV. Underline the suffixes and prefixes and translate into Russian the following words:

 

attachment, mainly, operation, movable, wooden, convenient, unscrew, disconnect, extension, rugged, performed

V. Translate the following sentences, paying attention to different meanings of should and would:

 

1. It is necessary that all fitting shops should be supplied with bench vices. 2. If the jaws of parallel vices had not been of low strength, the parallel vices would have found greater application in industry. 3. It is very important that workpieces being in the process should be firmly clamped in vices. 4. If fitting shops were not supplied with vices, how would workers clamp workpieces? 5. It is necessary that the vice should be fastened to a bench. 6. Great attention should be paid to the proper securing of the vice to the bench. 7. Providing all the requirements were met, the efficiency of the swivel vices would be increased. 8. If the bolt had been loosened enough, we should have been able to turn the swivel vices in a desired direction.

VI. Translate into English:

 

1.Следовало бы отметить, что неподвижные тиски не очень удобны для работы. 2. Важно, чтобы к губкам тисков привинчивали стальные закаленные пластинки. 3. Необходимо., чтобы на пластинках, привинчиваемых к губкам, была насечка. 4. Следовало бы указать, что параллельные тиски имеют существенный недостаток, заключающийся в малой прочности их губок. 5. Если бы губки параллельных тисков были более прочными, тиски могли бы использоваться для закрепления тяжелых деталей. 6. Если бы крепление стуловых тисков на верстаке обеспечивало надежность их установки, они двигались бы во время работы.

VII. (a) Read and translate the text without using a dictionary:

 

Vices are used in tool-rooms and as attachments on metal-cutting lathes for holding workpieces. Vices of rugged construction can hold heavy work, easily withstanding the most severs duty imposed on them. There are different types of vices such as plain vices and swivel vices. The jaws of all the vices are made of accurately ground tool steel. They may be moved together or apart by means of a handle. The plain vice is used for light milling operations and is fastened to the bench by means of a screw. The swivel vice may be turned through any angle as the base of the vice is held to the table with a swivel plate. Universal vice may

be used for general tool-room work. It can be swiveled up to 90° in the vertical plane and up to 360° in the horizontal plane.

(b) Answer the following questions:

 

1. Where are vices widely used? 2. What do they serve for? 3. What types of vices do you know? 4. What is the difference between plain and swivel vices? 5. By what means are the jaws of all vices moved together or apart? 6. What may the universal vice be used for?

VII. Using the following words and word combinations describe the principle of, operation of the swivel vices shown in Fig. 81:

 

a swivel vice, to be the most convenient vice, to consist, a base, a solid jaw, a movable jaw, the motion, the movable jaw, to be provided, the rotation, a screw inserted, a fixed nut, the screw, to be rotated, a handle, the vice base, to be mounted, a swivel plate, by means of a spindle, to loosen, the bolt, the vice, to be turned in any direction

 

CHAPTER III

MACHINE PARTS

 

WELDING

Welding is a process which provides a non-detachable joining of two like metal pieces¹ by heating them till melting condition or fusion without or with mechanical pressure. Fusion of two metal pieces may be brought about² by different types of welding, such as hammer welding, thermit welding, electric welding and gas welding.

Hammer welding is a process in which two metal pieces are joined and fused together by force from a hand or power hammer after having heated these pieces in a blacksmith's forge until they reached their plastic stage.

Thermit welding is a process consisting of a chemical reaction obtained by igniting finely divided aluminium and iron oxide. This type of welding is used in repairing rails, frames, etc.

Electric resistance welding is a process consisting of heating metals to be welded to their plastic temperature and then applying mechanical pressure for achieving a non-detachable joining of the metals.

Resistance welding processes form a group consisting of many types of welding. Selection of each type of welding depends on the kind and size of metals to be welded. Resistance welding embraces such processes as spot welding, butt welding, electric arc welding, etc.

Spot welding is a process in which two metals are held between electrodes passing a heavy current through the metals to be welded. The electrodes having been forced together by pressure join the surfaces of the metals in a spot, the size of which is about the same as that of the tip of the electrode. This kind of welding is suitable for welding parts of airplanes, refrigerators and automobiles.

In butt welding the parts to be welded are pressed together while heat is generated by passing a heavy current through the area of the joint. Butt welding may be applied for welding pipes, tubing, rods, etc.

 

 

Fig. 32. Electric Arc Welding:

1 - carbon electrode; 2 - additive;3 - plate; 4 - weld

 

Electric arc welding is a process in which surfaces to be joined are fused together by the heat of an electric arc. The electric arc was invented in 1802 by the famous Russian scientist V. V. Petrov, who demonstrated the possibility of utilizing its heat for fusing metals. Fig. 32 shows the process of electric arc welding. By bringing the work and the electrode together as conductors, an electric circuit is

established. When the conductors are separated, an electric arc is created in which the electrical energy is converted into heat, its temperature being as high as 7000°F³. An additive is placed into the flame of the electrical arc. An additive is a metal which is externally applied to the place of welding and melted to form a weld together with the material of the work. The electric arc melts both the edges of the parts to be melted and the additive used. The electrode having been removed from the place of welding, the molten metal cools, solidifies and forms a weld, joining the parts of the work.

In autogenous (gas) welding the source of heat is the gas flame obtained from a gas which is often acetylene. Acetylene mixed with oxygen in a torch when ignited gives a steady flame. The welding torch consists essentially of a gas mixing chamber and is designed in two types: the low-pressure injector type and the equal-pressure type. In the injector-type torch the acetylene is delivered at very low pressure and the oxygen enters the torch at high pressure and velocity expanding in the mixing chamber. Then the acetylene is drawn by suction created in the mixing chamber in a constant ratio to the oxygen. Autogenous welding is carried out in different ways and methods. According to the movement of the torch, welding may be divided into rightward welding and leftward welding. In rightward welding the torch moves ahead of the additive, and in leftward welding the additive moves in front of the torch. In practice rightward welding is mostly used. Gas welding may be used for cutting metals and repairing agricultural machines and implements.

¹. two like metal pieces - два однородных куска металла

². fusion of two metal pieces may be brought about - сплавление двух кусков металла может быть произведено (выполнено)

³. 7000°F=7000 degrees according to Fahrenheit ['fa:renhait] - 7000 градусов по Фаренгейту

 

Exercises

I. Use the following words and phrases in sentences of your own:

 

electrode, to weld, fusion, non-detachable joining, electric resistance welding, to ignite, iron oxide, arc welding, spot welding, torch, velocity, autogenous welding, to generate, current

II. Answer the following questions:

 

1. What is welding and what is it used for? 2. What types of welding do you know? 3. What is the source of heat for arc welding? 4. What is the source of heat for gas welding? 5. What gas is used in autogenous welding? 6. What methods of autogenous welding do you know? 7. What is spot welding? 8. What is butt welding used for? 9. What is hammer welding? 10. What does the selection of a given type of welding depend on? 11. What processes does resistance welding embrace?

III. Supply synonyms for the following words:

 

burner, to fuse, various, to get, to convert, ahead of, to utilize

 

 

IV. Underline the suffixes in the following words and state what part of speech they belong to:

 

detachable, fusion, mechanical, pressure, obtained, finely, resistance, molten, rightward, agricultural, implement, suitable, possibility

V. Give derivatives from the following words and translate them into Russian:

 

to obtain, chemistry, final, to achieve, to conduct, electrical, external, press, wide

VI. Change the following sentences using the subordinate clauses instead of participle and gerundial constructions and translate the following sentences into Russian:

Example: 1. Having fused two metal pieces we obtained a weld.

When we have fused two metal pieces we obtained a weld.

2. We heard of their having applied a new kind of additive to obtain firm joining.

We heard that they have applied a new kind of additive to obtain firm joining.

1. After having heated two metal pieces in a blacksmith's forge they reached their plastic stage. 2. Having heated the additive to its melting temperature it began to diffuse into the metals to be joined. 3. We heard of their having applied termite welding to provide a non-detachable joining of two like metal pieces. 4. The engineer informed them of the hammer welding of two metal pieces having been completed. 5. We know of Petrov's having invented the electric arc. 6. Having been asked to join these rods by butt welding, I had to prepare my instruments for this work. 7. Having found a new method of welding, we were able to join machine parts better and faster.

VII. Give English equivalents of the following words:

 

сварка встык, контактная сварка, термитная сварка, сплавлять, шов, соединение, выбор, электрод, ток, площадь, присадочный материал, зажигать, ремонтировать, газосмешивающая камера, затвердевать, остывать, скорость, пламя

VIII. Giving answers to the following questions describe the process of electric arc melding shown in Fig. 32:

 

1. What process is shown in Fig. 32? 2. How can an electric circuit be established in electric arc welding? 3. When is an electric arc created? 4. Where is the electrical energy converted into heat? 5. What is an additive? 6. Where is an additive to be placed? 7. What is melted by the electric arc? 8. When does the molten metal cool, solidify and form a weld, joining the parts of the work?