Contenido

Actualmente se utilizan en la industria del mecanizado varios tipos de tornos, cuya aplicación depende de la cantidad de piezas a mecanizar por serie, de la complejidad de las piezas y de la dureza de las piezas.

Parallel lathe

The parallel lathe or mechanical is the type of lathe that evolved from the old lathes when new equipment was incorporated that managed to turn it into one of the most important machine tools that have ever existed. However, currently this type of lathe is being relegated to carrying out unimportant tasks, to be used in apprentice workshops and maintenance workshops to carry out specific or special jobs.

For mass and precision manufacturing they have been replaced by copying, revolver, automatic and CNC lathes. To operate these lathes well, the expertise of very well-qualified professionals is required, since manual handling of their carriages can often cause errors in the geometry of the turned parts.

copying lathe

Copying lathe is a type of lathe that, operating with a hydraulic and electronic device, allows the turning of parts according to their characteristics following the profile of a template that reproduces a replica equal to the guide.

This type of lathe is used for turning parts that have different diameter steps, that have been previously forged or cast, and that have little excess material. These lathes are also widely used in woodworking and artistic marble to shape the embellishing columns. Preparation for machining on a copy lathe is very simple and fast and that is why these machines are very useful for machining batches or series of parts that are not very large.

The technological conditions of machining are common to those of other lathes, it is only necessary to provide a tool that allows good chip evacuation and an effective lubrication and cooling system for the cutting edge of the tools using plenty of cutting oil or coolant.

revolver lathe

The revolver lathe is a variety of lathe designed to machine parts on which the simultaneous work of several tools is possible in order to reduce the total machining time. The pieces that present this condition are those that, starting from bars&action=edit&redlink=1 "Bar (material) (not yet written)"), have a final shape of a bushing or similar. Once the bar is securely held with clamps or a claw plate, the machined interior part is drilled, bored, threaded or reamed and at the same time it can be turned, faced, slotted, threaded and cut with external turning tools.

The revolver lathe has a carriage with a rotating turret in which the different tools that carry out the machining of the piece are inserted. Parts can also be machined individually, fixing them to a hydraulically operated claw plate.

automatic lathe

A type of lathe whose work process is entirely automated is called an automatic lathe. The feeding of the bar necessary for each piece is also done automatically, from a long bar that is inserted through a tube that has the head and is held by hydraulic clamping clamps.

These lathes can be single spindle or multi-spindle:.

• - Single spindle machines are basically used for machining small parts that require large production series.

• - When it comes to machining larger pieces, automatic multi-spindle lathes are used where part of the machining of the piece is carried out in a programmed manner on each spindle. As the spindles change position, the final machining of the part is very fast because all the spindles machine the same part simultaneously.

The setup of these lathes is very laborious and that is why they are mainly used for large production series. The movement of all tools is automated by a system of eccentrics and electronic regulators that regulate the cycle and limit stops.

A type of automatic lathe is known as "moving headstock" or "Swiss type" (Swiss type), in which the axial displacement is given by the lathe headstock. In these machines, the head moves back with the clamp open, closes the clamp and generates the forward movement of the bar to machine the part while the tools do not move axially. Moving head lathes also have the peculiarity of having a steady rest or barrel that guides the bar at the same height as the tools. For this reason, it is capable of machining pieces of great length compared to their diameter. The diameter range of a moving headstock lathe currently reaches 38 millimeters in bar diameter, although they tend to be machines with smaller diameters. These types of lathes can operate with cams or CNC and are capable of working with very tight tolerances.

Vertical lathe

The vertical lathe is a variety of lathe, with a vertical axis, designed to machine large pieces, which are subject to the jaw plate or other operators and which, due to their dimensions or weight, would make their fixation on a horizontal lathe difficult.

Vertical lathes do not have a tailstock but the only holding point for the pieces is the horizontal plate on which they are supported. The manipulation of the pieces to fix them on the plate is done using bridge cranes or hoists.

CNC lathe

The CNC lathe is a computer numerical control controlled lathe.

It offers great production capacity and precision in machining due to its functional structure and the trajectory of the turning tool is controlled by a built-in computer, which processes the execution orders contained in software that has previously been created by a programmer knowledgeable in lathe machining technology. It is a machine that is profitable for machining large series of simple parts, especially revolution parts, and allows curved surfaces to be precisely machined by coordinating the axial and radial movements for the advancement of the tool.

The rotation speed of the workpiece head, the advance of the longitudinal and transverse carriages and the execution dimensions of the part are programmed and, therefore, free of errors attributable to the machine operator.[14]​.

Other types of lathes

In addition to the lathes used in the mechanical industry, lathes are also used for woodworking, ornamentation with marble or granite.

The name lathe is also applied to other rotating machines such as the potter's wheel or the dental lathe. These machines have a totally different application and operating principle than the lathes described in this article.

The lathe has five main components:

• - Bench: serves as support for the other units of the lathe. In its upper part it has guides along which the moving headstock or tailstock and the main carriage move.

• - Fixed headstock: contains the gears or pulleys that drive the workpiece and the feed units. It includes the motor, spindle, speed selector, feed unit selector and feed direction selector. It also serves to support and rotate the workpiece that rests on the spindle.

• - Tailstock: the tailstock is the element that is used to serve as support and be able to place the pieces that are turned between points, as well as other elements such as drill chucks or drill bits to make holes in the center of the axes. This tailstock can be moved and fixed in various positions along the bench.

• - Portable carriage: consists of the main carriage, which produces the tool movements in the axial direction; and the transverse carriage, which slides transversely on the main carriage in a radial direction. In parallel lathes there is also an adjustable upper carriage, made up of three pieces: the base, the charriot and the tool-carrying turret. Its base is supported on a rotating platform to direct it in any direction.

• - Rotating head or chuck: its function is to hold the piece to be machined. There are several types, such as the independent four-jaw chuck or the universal chuck, mostly used in the mechanical workshop, just as there are magnetic and six-jaw chucks.

Certain accessories are required, such as workpiece holders, holders, and tool holders. Some common accessories include:

• - Universal claw chuck: holds the workpiece in the head and transmits movement.

• - Clamps: Holds the workpiece in the head across an already finished surface. They are machined for a specific diameter and are not valid for others.

• - Centers or points: they support the workpiece in the headstock and tailstock.

• - Driving bolt: It is fixed on the lathe chuck and on the workpiece and transmits movement to the piece when it is mounted between centers.

• - Fixed support or fixed rest: supports the extended end of the workpiece when the tailstock cannot be used.

• - Mobile support or mobile steady rest: is mounted on the carriage and allows long workpieces to be supported near the cutting point.

• - Tool holder turret with multiple alignment.

• - Drag plate: to tie down pieces that are difficult to hold.

• - Independent claw plate: it has 4 claws that act independently of each other.

Las herramientas de torneado se diferencian en dos factores, el material del que están constituidas y el tipo de operación que realizan. Según el material constituyente, las herramientas pueden ser de acero rápido, metal duro soldado o plaquitas de metal duro (widia) intercambiables.

La tipología de las herramientas de metal duro está normalizada de acuerdo con el material que se mecanice, puesto que cada material ofrece unas resistencias diferentes. El código ISO para herramientas de metal duro se recoge en la tabla más abajo.

Cuando la herramienta es de acero rápido o tiene la plaquita de metal duro soldada en el portaherramientas, cada vez que el filo se desgasta hay que desmontarla y afilarla correctamente con los ángulos de corte específicos en una afiladora. Esto ralentiza bastante el trabajo porque la herramienta se tiene que enfriar constantemente y verificar que el ángulo de incidencia del corte este correcto. Por ello, cuando se mecanizan piezas en serie lo normal es utilizar portaherramientas con plaquitas intercambiables, que tienen varias caras de corte de usar y tirar y se reemplazan de forma muy rápida.

Characteristics of carbide inserts

The quality of the carbide inserts (widia) is selected taking into account the material of the part, the type of application and the machining conditions.

The variety of insert shapes is large and standardized. Likewise, the variety of materials used in modern tools is considerable and is subject to continuous development.[15]​.

The main tool materials for turning are shown in the following table.

The suitability of the different types of inserts depending on the material to be machined are indicated below and are classified according to an ISO/ANSI Standard to indicate the applications in relation to the resistance and toughness they have.

Format code for hard metal inserts

As there is so much variety in geometric shapes, sizes and cutting angles, there is a standardized coding made up of four letters and six numbers where each of these letters and numbers indicates a specific characteristic of the corresponding insert type.

Insert code examples: SNMG 160408 HC.

The first two figures indicate the length of the cutting edge of the insert in millimeters.

The next two figures indicate the thickness of the insert in millimeters.

The last two figures indicate the tip radius of the insert in tenths of a millimeter.

Principales especificaciones técnicas de los tornos convencionales:[16]​.

Ability

• - Height of points;.

• - distance between points;.

• - diameter admitted on bed or turning, measured from the center of the spindle at the beginning of the bed.

• - diameter admitted on neckline;.

• - diameter admitted on transversal carriage;.

• - width of the bench;

• - length of the neckline in front of the smooth plate.

Fixed head

• - Norton box.

• - Diameter of the main spindle hole or bar pitch;

• - nose of the main spindle; or secondary spindle nose.

• - Morse taper") of the main spindle;.

• - range of head speeds (usually in rpm);.

• - number of speeds.

Cars

• - Cross carriage travel;

• - journey of the "charriot" or upper carriage;

• - maximum dimensions of the tool.

• - range of longitudinal advances;.

• - range of transversal advances.

• - automatic feed path (longitudinal carriage).

• - automatic feed path (cross slide).

Threaded

• - Range of metric steps;.

• - Whitworth step range;.

• - range of modular steps;.

• - Diametral Pitch step range;

• - pitch of the master spindle.

moving head

The moving head is made up of two pieces, which are generally cast "Casting (metallurgy)"). One of them, the support, rests on the main guides of the lathe, on which it can be fixed or moved from the end opposite the headstock. The other piece is located on top of the previous one and has a spindle that is operated with a crank for the longitudinal movement of the tailstock, fitting it with the appropriate pressure in a blind conical hole, called centering point, made on the end of the piece opposite to the fixed head.[17]​.

Engines

• - Power "Power (physical)") of the main engine (usually in kW);

• - power of the coolant motor pump (in kW).

Lunettes

Not all types of lathes have the same technical specifications. For example, vertical lathes do not have a tailstock and only the parts subjected to air are machined. Machine threading with a Norton Box is only available on parallel lathes.

• - Cutting motion: usually imparted to the part that rotates rotationally about its main "Axis (mechanical)") axis. This movement is produced by an electric motor that transmits its rotation to the main spindle through a system of pulleys or gears. The main spindle has different clamping systems attached to its end (claw plates, clamps, auxiliary chucks or others), which hold the part to be machined. Traditional lathes have a fixed range of rotation speeds, however, in modern Numerical Control lathes the rotation speed of the headstock is variable and programmable and adapts to the optimal conditions that the machining allows.

• - Feed movement: is the movement of the cutting tool in the direction of the axis of the piece being worked. In combination with the rotation imparted to the spindle, it determines the space traveled by the tool for each revolution the piece makes. This movement may also not be parallel to the axis, thus producing cones. In that case, the chariot is rotated, adjusting the required angle on a graduated scale, which will be half of the desired cone. Conventional lathes have a fixed range of feeds, while Numerical Control lathes the feeds are programmable according to the optimal machining conditions and empty movements are carried out at high speed.

• - Depth of pass"): movement of the cutting tool that determines the depth of material removed in each pass. The amount of material that can be removed depends on the profile of the cutting tool used, the type of material machined, the cutting speed, power "Power (physical)") of the machine, feed, etc.

• - Verniers of the carriages: to regulate the turning work, the lathe carriages have built-in verniers in the shape of a graduated drum, where each division indicates the displacement of the carriage, whether longitudinal, transversal or charriot. The measurement is made manually by the machine operator, so a very expert person is required to manipulate it if it is to achieve dimensions with very close tolerances. Numerical control lathes no longer have verniers, but rather the dimensions of the piece are entered into the program and these are achieved automatically.

Displacement

This operation consists of the external or internal machining to which parts that have cylindrical machining are subjected. To be able to carry out this operation, the depth of passage and, therefore, the diameter of the cylinder is regulated with the transverse carriage, and the length of the cylinder is regulated with the parallel carriage. The parallel carriage advances automatically according to the desired work progress. In this procedure, the surface finish "Roughness (mechanical)") and the tolerance "Tolerance (manufacturing)") obtained can be a factor of great relevance. To ensure quality in the turning, the lathe must have its alignment and concentricity well adjusted.

The turning can be done with the piece held in the air held in the jaw plate, if it is short, or with the piece held between points and a drive pin, or supported on a fixed or mobile steady rest if the piece is large and heavy. To perform the cylindering of parts or axles held between points, it is necessary to previously make the centering points on the axes.

When the turning is carried out in the hollow of the piece, it is called boring.

Facing

The facing operation consists of frontal machining perpendicular to the axis of the parts that is carried out to produce a good coupling in the subsequent assembly of the turned parts. This operation is also known as bordering. The problem with facing is that the cutting speed on the edge of the tool decreases as it advances towards the center, which slows down the operation. To improve this aspect, many modern lathes incorporate speed variators in the headstock so that the rotation speed of the piece can be increased.

Grooved

grooving consists of machining cylindrical grooves of variable width and depth in the pieces that are turned, which have many different uses. For example, to house an O-ring, for thread exit, for pressure washers, etc. In this case, the tool has already formed the width of the slot and by acting with the transverse carriage the desired depth is given. Pulley channels are a clear example of turned grooves.

Threading on the lathe

There are two systems for performing threading on lathes, on the one hand the traditional one used by parallel lathes), using the Norton Box, and on the other hand, the one that is carried out with CNC lathes, where the thread data is fully programmed and the Norton box is no longer needed to do it.

To carry out threading with a tool, the following must be taken into account:.

• - The threads can be external (screws) or internal (nuts), and their magnitudes must be consistent so that both elements can be screwed.

• - The elements that appear in the table are those that must be taken into account when making a thread on a lathe:.

To carry out threading, the following tasks must be previously carried out:

• - Previously turn to the diameter of the thread.

• - Prepare the tool according to the angles of the thread fillet.

• - Establish the cutting depth that the thread must have until the appropriate profile is achieved.

One of the tasks that can be performed on a parallel lathe is to make threads of various pitches and sizes, both external on shafts and internal on nuts. To do this, universal parallel lathes incorporate a mechanism called Norton Box, which facilitates this task and avoids assembling a train of gears every time you want to make a thread.

The Norton box is a mechanism composed of several gears that was invented and patented in 1890, which was incorporated into parallel lathes and provided a solution to the manual gear change to set the pitches of the pieces to be threaded. This box can consist of several movable gear trains or a tilting train and a gear cone. The box connects the movement of the lathe headstock with the tool carriage that has a built-in square thread spindle.

The best achieved system includes a gearbox with several reducers. In this way, with the manipulation of several levers, different tool carriage advance speeds can be set, allowing a wide variety of thread pitches to be made, both metric and Whitworth. There are oil bath and dry ones, with gears carved in one way or another, but basically it is a gearbox.

The figure shows how a screw is machined from a hexagonal bar. To do this, the following operations are carried out:

1. • The body of the screw is cylindered, leaving the hexagonal head in its original measurements.

2. • The entrance of the thread is chamfered and the tip of the screw is faced.

3. • The throat is slotted where the thread ends next to the head of the screw.

4. • The body of the screw is threaded, resulting in the finished piece.

This same process can be done starting from a long bar, finally cutting off the machined part.

Knurled

Knurling is a process of cold forming the material using knurls that press the piece while it rotates. This deformation produces an increase in the starting diameter of the piece. Knurling is performed on pieces that have to be handled by hand, which are generally threaded to prevent slipping that would occur if they had a smooth surface.

Knurling is done on lathes with tools called knurls, with different pitch and pattern.

An example of knurling is that of the 50 euro cent coins, although in this case the knurling is so that the blind can better identify the coin.

Strain knurling can be performed in two ways:.

• - Radially, when the knurled length on the piece matches the thickness of the knurled wheel to be used.

• - Longitudinally, when the length exceeds the thickness of the knurled wheel. For this second case, the knurled wheel must always be beveled at its ends.

Cone turning

A cone "Cone (geometry)") or a truncated cone of a generation body is defined by the following concepts:

• - Larger diameter.

• - Smaller diameter.

• - Length.

• - Angle of inclination.

• - Conicity.

Different lathes machine cones in different ways.

• - In CNC lathes there is no problem because, by properly programming their dimensions, the transverse and longitudinal carriages move in a coordinated manner, giving rise to the desired cone.

• - In copying lathes there is no problem either because the copying template allows the probe to move through it and the carriages act in a coordinated manner.

• - To machine cones on conventional parallel lathes it can be done in two different ways. If the length of the cone is small, the cone is machined with the charriot inclined according to the angle of the cone. If the length of the cone is very large and the axis is machined between points, then the tailstock is moved the appropriate distance according to the dimensions of the cone.

To calculate the angle of inclination of the car, proceed as follows:

where is the largest diameter, is the smallest diameter and is the length of the cone.

Spherical turning

Spherical turning, for example that of ball joints "Ball joint (mechanical)"), does not have any difficulty if it is carried out on a Numerical Control lathe because, by programming its measurements and the corresponding radial machining function, it will be carried out perfectly.

If the lathe is a high-production automatic lathe, it works with a bar and the ball joints are not large, the ball joint is achieved with a transverse carriage where the tools are sharpened with the profile of the ball joint.

Making ball joints manually on a parallel lathe presents some difficulty in achieving accuracy. In that case it is advisable to have a template of the sphere and machine it manually and finish it with a file "File (tool)") or scraper to give the final adjustment.

Mowing or bucking

The turning operation that is carried out when working with a bar is called mowing and at the end of the machining of the corresponding piece it is necessary to cut the bar to separate the piece from it. For this operation, very narrow tools are used with a projection according to the diameter of the bar and allowing the transverse carriage to reach the center of the bar. It is a very common operation in bar-fed revolver and automatic lathes and mass production.

Chamfering

Chamfering is a very common turning operation that consists of killing both the exterior and interior edges to avoid cuts with them and in turn facilitate the subsequent work and assembly of the pieces. The most common chamfer is usually 1 mm by 45°. This chamfer is made by attacking the edges directly with a suitable tool.

Eccentric machining

An eccentric is a part that has two or more cylinders with different centers or axes of symmetry, as occurs with engine crankshafts or camshafts. An eccentric is a body of revolution and therefore machining is carried out on a lathe. To machine an eccentric it is first necessary to make the centering points of the different eccentric axes at the ends of the piece that will be fixed between two points.

Spiral machining

A spiral is a thread carved into a flat disk and machined on a lathe, by appropriately moving the cross slide. To do this, the transmission that will be placed between the headstock and the feed spindle of the transverse carriage must be calculated according to the pitch of the spiral thread. It is a rare operation in turning. An example of a spiral thread is the one inside the jaw plates of lathes, which allows the opening and closing of the jaws.

Boring

Many pieces that are turned require drilling with drill bits in the center of their axes of rotation. Normal drill bits are used for this task, which are clamped at the tailstock in a drill chuck or directly in the tailstock housing if the diameter is large. The technological conditions for drilling are normal according to the characteristics of the material and type of drill bit used. Deep drilling processes deserve special mention where the process is already very different, especially the constitution of the drill bit used.

Not all lathes can perform all of these operations indicated, but this depends on the type of lathe used and the accessories or equipment it has.

Reamed.

Reaming is a finishing process used to increase the size of an existing hole, improve its surface finish, and produce a very precise hole diameter.[18]​.

Los parámetros de corte fundamentales que hay que considerar en el proceso de torneado son los siguientes:.

• - Elección del tipo de herramienta más adecuado.

• - Sistema de fijación de la pieza.

• - Velocidad de corte (V) expresada en metros/minuto.

• - Diámetro exterior del torneado.

• - Revoluciones por minuto (rpm) del cabezal del torno.

• - Avance en mm/rev, de la herramienta.

• - Avance en mm/mi de la herramienta.

• - Profundidad de pasada.

• - Esfuerzos de corte.

• - Tipo de torno y accesorios adecuados.

cutting speed

Cutting speed is defined as the "linear speed" of the periphery of the part that is in contact with the tool. The cutting speed, which is expressed in meters per minute (m/min), has to be chosen before starting machining and its appropriate value depends on many factors, especially the quality and type of tool used, the depth of the pass, the hardness and machinability of the material being machined and the feed speed used. The main limitations of the machine are its range of speeds, the power of the motors and the rigidity of the fixation of the piece and the tool.

By determining the cutting speed, the revolutions per minute that the lathe head will have can be determined, according to the following formula:

Where V is the cutting speed, n is the rotation speed of the part to be machined and D is the diameter of the part.

Cutting speed is the main factor that determines tool life. A high cutting speed allows machining to be carried out in less time but accelerates tool wear. Tool manufacturers and machining manuals offer indicative data on the appropriate cutting speed of tools for a given tool duration, for example, 15 minutes. Sometimes it is desirable to adjust the cutting speed for a different tool life, for which the cutting speed values ​​are multiplied by a correction factor. The relationship between this correction factor and the life of the tool in cutting operation is not linear.[19]​.

Excessive cutting speed may result in:.

• - Very rapid wear of the tool's cutting edge.

• - Plastic deformation of the cutting edge with loss of machining tolerance.

• - Poor machining quality; surface finish "Roughness (mechanical)") inefficient.

Cutting speed too low may result in:.

• - Formation of a contribution edge on the tool.

• - Negative effect on chip evacuation.

• - Low productivity.

• - High machining cost.

Workpiece rotation speed

The rotation speed of the lathe headstock is usually expressed in revolutions per minute (rpm). In conventional lathes there is a limited range of speeds, which depend on the rotation speed of the main motor and the number of speeds of the machine's gearbox. In numerical control lathes, this speed is controlled with a feedback system that usually uses a frequency converter and any speed can be selected within a range of speeds, up to a maximum speed.

The rotation speed of the tool is directly proportional to the cutting speed and inversely proportional to the diameter of the workpiece.

Feed speed

The feed or feed rate in turning is the relative speed between the piece and the tool, that is, the speed with which the cut progresses. The feed of the cutting tool is a very important factor in the turning process.

Each tool can adequately cut at a range of feed rates per revolution of the part, called feed per revolution (f). This range depends fundamentally on the diameter of the piece, the depth of the pass, and the quality of the tool. This speed range is determined experimentally and is found in tool manufacturers' catalogs. Furthermore, this speed is limited by the rigidity of the workpiece and tool clamping and by the power of the machine's feed motor. The maximum chip thickness in mm is the most important limiting indicator for a tool. The cutting edge of the tools is tested to have a certain value between a minimum and maximum chip thickness.

The feed rate is the product of the feed per revolution and the rotation speed of the piece.

As with the tool rotation speed, in conventional lathes the feed speed is selected from a range of available speeds, while numerical control lathes can work at any feed speed up to the maximum feed speed of the machine.

Effects of ground speed.

• - Decisive for chip formation.

• - Affects power consumption.

• - Contributes to mechanical and thermal stress.

The high forward speed gives rise to:.

• - Good chip control.

• - Shorter cutting time.

• - Less tool wear.

• - Higher risk of tool breakage.

• - High surface roughness of the machining.

Low forward speed results in:.

• - Longer chip.

• - Improvement of machining quality.

• - Accelerated tool wear.

• - Longer duration of machining time.

• - Higher machining cost.

Specific cutting force

The cutting force is a necessary parameter to be able to calculate the power necessary to carry out a certain machining. This parameter is a function of the tool feed, the depth of pass, the cutting speed, the machinability of the material, the hardness of the material, the characteristics of the tool and the average thickness of the chip. All these factors are included in a coefficient called K. The specific cutting force is expressed in N/mm².[20]​.

Cutting power

The cutting power P necessary to carry out a specific machining operation is calculated from the value of the chip removal volume, the specific cutting force and the performance of the machine. It is expressed in kilowatts (kW).

This specific cutting force F is a constant that is determined by the type of material being machined, tool geometry, chip thickness, etc.

In order to obtain the correct power value, the value obtained has to be divided by a certain value (ρ) that takes into account the efficiency of the machine. This value is the percentage of the motor power that is available in the tool placed in the spindle.

where.

• - P is the cutting power (kW).

• - A is the diameter of the piece (mm).

• - f is the feed speed (mm/min).

• - F is the specific cutting force (N/mm²).

• - ρ is the performance or efficiency of the machine.

• - Design and limitations of the piece: size, turning tolerances, tendency to vibrations, clamping systems, surface finish, etc.

• - Turning operations to be performed: external or internal turning, facing, grooving, roughing, finishing, optimization to perform several operations simultaneously, etc.

• - Stability and machining conditions: intermittent cuts, part overhang, shape and condition of the part, condition, power and drive of the machine, etc.

• - Availability and selection of the type of lathe: possibility of automating machining, being able to perform several operations simultaneously, series of parts to be machined, quality and quantity of coolant, etc.

• - Material of the piece: hardness, condition, resistance, machinability, bar, casting, forging, dry or coolant machining, etc.

• - Availability of tools: quality of tools, tool clamping system, access to tool distributor, tool technical service, technical advice.

• - Economic aspects of machining: machining optimization, tool life, tool price, machining time price.

Special aspects of boring tools: the largest possible bar diameter must be selected and good chip evacuation must be ensured. Select the smallest possible overhang of the bar. Select tools with the greatest possible tenacity.[15]​.

Turning has evolved so much that it is no longer just about removing material at high speed, but the parameters that make up the process have to be closely controlled to ensure the final results of economy, quality and precision. In particular, the way of treating the chip has become a complex process, where all the technological components of machining are involved, so that it can have the size and shape that does not disturb the work process. If this were not the case, masses of long, fibrous chips would quickly accumulate in the machining area, forming tangled and uncontrollable skeins.

The shape the chip takes is mainly due to the material being cut and can be either ductile or brittle and brittle.

The feed at which you work and the depth of the pass usually largely determine the shape of the chip. When these variables are not enough to control the shape of the chip, it is necessary to choose a tool that incorporates an effective chip breaker.

Today dry turning is completely viable. There is a recent trend to carry out dry machining whenever the quality of the tool allows it.

Concern arose during the 90s, when studies carried out in automotive component manufacturing companies in Germany highlighted the high cost of refrigeration and especially its recycling.

However, dry machining is not suitable for all applications, especially for drilling, threading and boring to ensure chip evacuation.

It is also not advisable to dry turn pasty or too soft materials such as aluminum or low carbon steel since it is very likely that the cutting edges will become dull with the material they cut, producing poor surface finish, dispersions in the measurements of the piece and even breakage of the cutting edges.

In the case of machining short chip materials such as gray cast iron, coolant is beneficial as a cleaning agent, preventing the formation of toxic dust clouds.

The coolant is essential when turning abrasive materials such as stainless steel, inconells, etc.

In dry turning, the machinery must be prepared to absorb without problems the heat produced in the cutting action.

To avoid overheating of spindles, etc., internal oil or air cooling circuits are usually incorporated.

With few exceptions and unlike milling, dry turning has not become widespread but it has made companies question using coolant only in the necessary operations and with the necessary flow rate..

It is necessary to carefully evaluate operations, materials, parts, quality requirements and machinery to identify the benefits of eliminating the refrigerant contribution.

For a lathe to function correctly and guarantee the quality of its machining, it is necessary that it periodically undergo a review and tune-up where all its functions will be adjusted and verified.

The most important tasks carried out in the overhaul of the lathes are the following:

Other functions such as the precision of the verniers are carried out more sporadically, mainly when the machine is new.

When working on a lathe, you must observe a series of requirements to ensure that you do not have any accident that could cause any piece to be thrown off the plate or chip if it is not cut properly. For this, most lathes have a protection screen. But also of utmost importance is preventing being caught by the rotational movement of the machine, for example by clothing or long hair.

Ante la diversidad de tornos que existe, también existen diferentes perfiles de los profesionales torneros dedicados a estas máquinas, entre los que se puede establecer la siguiente clasificación:[21]​.

Numerical control lathe programmers

Numerical control (CNC) lathes first require a technical programmer to develop the execution program that the lathe has to carry out for the machining of a specific part. In this case, it must be a good knowledge of the factors involved in machining on the lathe, such as the following:

• - Lathe features.

• - Features and availability of tools.

• - Fastening of the pieces.

• - Type of material to be machined and its machining characteristics.

• - Use of refrigerants.

• - Number of pieces to be machined.

• - Surface finish. Rugosity.

• - Allowable machining tolerance.

In addition, you must know well the technological parameters of turning, which are:.

• - Optimum cutting speed at which turning should be carried out.

• - Optimum machining advance.

• - Depth of pass").

• - Spinning speed (RPM) of the head.

• - Tool change system.

To all these requirements must be added a correct interpretation of the part plans and the programming technique used in accordance with the equipment that the lathe has.[22]​.

Preparers of automatic and computer numerical control (CNC) lathes

In industries where several large-production automatic lathes or computer numerical control (CNC) lathes have been installed, there must be a professional in charge of fine-tuning these machines every time there is a change in the parts to be machined because fine-tuning an automatic or numerical control lathe is a fairly complex task.

Once the lathe has been prepared for a specific job, the subsequent control of the machine's work is usually entrusted to a person with less technical preparation who only has to ensure that the quality of the machined parts is met within the required tolerance and roughness qualities. Sometimes an operator is able to attend to several automatic lathes, if they have an automated part feeding system using bars or automatons.

• - Mechanic-Turner.

• - Machine tool.

• - Harassing.

• - Machining.

• - Embossing on the lathe.

• - Machine Tool Research Foundation Archived July 14, 2013 at the Wayback Machine.

• - Spanish Association of Machine Tool Manufacturers.

• - Spanish Machine Tool Biennial.

• - Directory of Exhibitors of the Spanish Machine Tool Biennial.

• - Wand made with a lathe (My Popular Mechanics).

• - Types of lathe machines used in industries.

old lathes

The existence of lathes has been attested since at least 850 BC. C., with representations in Assyrian and Egyptian reliefs. The oldest preserved image is found in the tomb of the Egyptian high priest Petosiris (century BC),[9]​ where an arch lathe operated by two people is shown. For centuries, these lathes worked according to the “violin bow” system, until in the Middle Ages the pedal lathe with a flexible pole spread in Europe, which allowed the rotation to be activated with the foot and freed the operator's hands. In the century new technical improvements appeared, such as belt transmission and the connecting rod-crank mechanism, which made continuous movement of the shaft possible and paved the way for modern mechanical lathes.[9]​.

mechanical lathes

With the beginning of the Industrial Revolution in England, during the , the first precision mechanical lathes were developed capable of shaping metal parts with a degree of accuracy unknown until then, which marked a turning point in the history of mechanical manufacturing. Before that time, lathes were mainly made of wood and were operated by hand or with pedals, limited to carpentry work or artisanal modeling. Starting in 1750, engineers and inventors such as Jacques de Vaucanson in France began to adapt mechanical principles of control and transmission of motion to metal lathes, introducing the concept of the sliding tool carriage, considered the direct antecedent of the modern lathe.[11]​.

Around 1794–1800, the British engineer Henry Maudslay perfected this design by inventing the slide-rest lathe, a lathe with a cast iron bed, threaded spindle and moving carriage with automatic feed, which allowed screws and metal cylinders to be cut with uniform precision. Almost simultaneously, in the United States, David Wilkinson "David Wilkinson (machinist)") patented a similar model with automatic feeds in 1798. driven by guide screws, which expanded the possibilities of industrial machining.[10]​[11]​.

These developments gave rise to the heavy industrial metal lathe, a robust, stable and repeatable machine that allowed for the first time the mass production of standardized components, laying the foundations for modern engineering and manufacturing systems with interchangeable parts that would dominate the century.[10]​[12]​ In 1820, Thomas Blanchard invented the copying lathe. In the 1840s the revolver lathe was developed.

In 1833, Joseph Whitworth set up on his own in Manchester. Their designs and creations fundamentally influenced other manufacturers of the time. In 1839 he patented a "parallel lathe" for turning and threading with a bed of flat guides and an automatic cross slide, which was widely accepted. Two lathes that incorporate elements of his patents are preserved today. One of them, built in 1843, is kept in the Science Museum in London. The other, built in 1850, is kept in the Birmingham Museum. In 1850 it was located in the San Blas Ironworks in Sabero, León, an iron factory belonging to the Palentina-Leonesa Mines Society, a lathe for turning the rolling cylinders of the rolling mills, is currently exhibited in the Museum of Steel and Mining of Castilla - León in Sabero in the same place where it was located more than 160 years ago.

But in 1839 it was J. G. Bodmer") who had the idea of ​​building vertical lathes. At the end of the century, this type of lathes were manufactured in different sizes and weights. The design and patent in 1890 of the Norton box"), incorporated into parallel lathes, provided a solution to the manual change of gears to set the pitches of the pieces to be threaded.[13]​.

Introduction of computer numerical control

The numerical control lathe is an example of programmable automation. It was designed to accommodate variations in product configuration. Its main application focuses on medium production volumes of simple parts and medium and low production volumes of complex parts. One of the most important examples of programmable automation is numerical control in the manufacturing of metal parts. Numerical control (NC) is a form of programmable automation in which processing equipment is controlled through numbers, letters and other symbols. These numbers, letters and symbols are encoded in an appropriate format to define a program of instructions to perform a specific task. When the task at hand changes, the program of instructions is changed. The ability to change the program makes NC suitable for low to medium production volumes, since it is easier to write new programs than to make changes to processing equipment.

The first development in the area of ​​numerical control was made by the American inventor John T. Parsons (Detroit, 1913-2007), together with his employee Frank L. Stulen, in the 1940s. The concept of numerical control involved the use of data in a reference system to define the contour surfaces of a helicopter propellers.

Contenido

Actualmente se utilizan en la industria del mecanizado varios tipos de tornos, cuya aplicación depende de la cantidad de piezas a mecanizar por serie, de la complejidad de las piezas y de la dureza de las piezas.

Parallel lathe

The parallel lathe or mechanical is the type of lathe that evolved from the old lathes when new equipment was incorporated that managed to turn it into one of the most important machine tools that have ever existed. However, currently this type of lathe is being relegated to carrying out unimportant tasks, to be used in apprentice workshops and maintenance workshops to carry out specific or special jobs.

For mass and precision manufacturing they have been replaced by copying, revolver, automatic and CNC lathes. To operate these lathes well, the expertise of very well-qualified professionals is required, since manual handling of their carriages can often cause errors in the geometry of the turned parts.

copying lathe

Copying lathe is a type of lathe that, operating with a hydraulic and electronic device, allows the turning of parts according to their characteristics following the profile of a template that reproduces a replica equal to the guide.

This type of lathe is used for turning parts that have different diameter steps, that have been previously forged or cast, and that have little excess material. These lathes are also widely used in woodworking and artistic marble to shape the embellishing columns. Preparation for machining on a copy lathe is very simple and fast and that is why these machines are very useful for machining batches or series of parts that are not very large.

The technological conditions of machining are common to those of other lathes, it is only necessary to provide a tool that allows good chip evacuation and an effective lubrication and cooling system for the cutting edge of the tools using plenty of cutting oil or coolant.

revolver lathe

The revolver lathe is a variety of lathe designed to machine parts on which the simultaneous work of several tools is possible in order to reduce the total machining time. The pieces that present this condition are those that, starting from bars&action=edit&redlink=1 "Bar (material) (not yet written)"), have a final shape of a bushing or similar. Once the bar is securely held with clamps or a claw plate, the machined interior part is drilled, bored, threaded or reamed and at the same time it can be turned, faced, slotted, threaded and cut with external turning tools.

The revolver lathe has a carriage with a rotating turret in which the different tools that carry out the machining of the piece are inserted. Parts can also be machined individually, fixing them to a hydraulically operated claw plate.

automatic lathe

A type of lathe whose work process is entirely automated is called an automatic lathe. The feeding of the bar necessary for each piece is also done automatically, from a long bar that is inserted through a tube that has the head and is held by hydraulic clamping clamps.

These lathes can be single spindle or multi-spindle:.

• - Single spindle machines are basically used for machining small parts that require large production series.

• - When it comes to machining larger pieces, automatic multi-spindle lathes are used where part of the machining of the piece is carried out in a programmed manner on each spindle. As the spindles change position, the final machining of the part is very fast because all the spindles machine the same part simultaneously.

The setup of these lathes is very laborious and that is why they are mainly used for large production series. The movement of all tools is automated by a system of eccentrics and electronic regulators that regulate the cycle and limit stops.

A type of automatic lathe is known as "moving headstock" or "Swiss type" (Swiss type), in which the axial displacement is given by the lathe headstock. In these machines, the head moves back with the clamp open, closes the clamp and generates the forward movement of the bar to machine the part while the tools do not move axially. Moving head lathes also have the peculiarity of having a steady rest or barrel that guides the bar at the same height as the tools. For this reason, it is capable of machining pieces of great length compared to their diameter. The diameter range of a moving headstock lathe currently reaches 38 millimeters in bar diameter, although they tend to be machines with smaller diameters. These types of lathes can operate with cams or CNC and are capable of working with very tight tolerances.

Vertical lathe

The vertical lathe is a variety of lathe, with a vertical axis, designed to machine large pieces, which are subject to the jaw plate or other operators and which, due to their dimensions or weight, would make their fixation on a horizontal lathe difficult.

Vertical lathes do not have a tailstock but the only holding point for the pieces is the horizontal plate on which they are supported. The manipulation of the pieces to fix them on the plate is done using bridge cranes or hoists.

CNC lathe

The CNC lathe is a computer numerical control controlled lathe.

It offers great production capacity and precision in machining due to its functional structure and the trajectory of the turning tool is controlled by a built-in computer, which processes the execution orders contained in software that has previously been created by a programmer knowledgeable in lathe machining technology. It is a machine that is profitable for machining large series of simple parts, especially revolution parts, and allows curved surfaces to be precisely machined by coordinating the axial and radial movements for the advancement of the tool.

The rotation speed of the workpiece head, the advance of the longitudinal and transverse carriages and the execution dimensions of the part are programmed and, therefore, free of errors attributable to the machine operator.[14]​.

Other types of lathes

In addition to the lathes used in the mechanical industry, lathes are also used for woodworking, ornamentation with marble or granite.

The name lathe is also applied to other rotating machines such as the potter's wheel or the dental lathe. These machines have a totally different application and operating principle than the lathes described in this article.

The lathe has five main components:

• - Bench: serves as support for the other units of the lathe. In its upper part it has guides along which the moving headstock or tailstock and the main carriage move.

• - Fixed headstock: contains the gears or pulleys that drive the workpiece and the feed units. It includes the motor, spindle, speed selector, feed unit selector and feed direction selector. It also serves to support and rotate the workpiece that rests on the spindle.

• - Tailstock: the tailstock is the element that is used to serve as support and be able to place the pieces that are turned between points, as well as other elements such as drill chucks or drill bits to make holes in the center of the axes. This tailstock can be moved and fixed in various positions along the bench.

• - Portable carriage: consists of the main carriage, which produces the tool movements in the axial direction; and the transverse carriage, which slides transversely on the main carriage in a radial direction. In parallel lathes there is also an adjustable upper carriage, made up of three pieces: the base, the charriot and the tool-carrying turret. Its base is supported on a rotating platform to direct it in any direction.

• - Rotating head or chuck: its function is to hold the piece to be machined. There are several types, such as the independent four-jaw chuck or the universal chuck, mostly used in the mechanical workshop, just as there are magnetic and six-jaw chucks.

Certain accessories are required, such as workpiece holders, holders, and tool holders. Some common accessories include:

• - Universal claw chuck: holds the workpiece in the head and transmits movement.

• - Clamps: Holds the workpiece in the head across an already finished surface. They are machined for a specific diameter and are not valid for others.

• - Centers or points: they support the workpiece in the headstock and tailstock.

• - Driving bolt: It is fixed on the lathe chuck and on the workpiece and transmits movement to the piece when it is mounted between centers.

• - Fixed support or fixed rest: supports the extended end of the workpiece when the tailstock cannot be used.

• - Mobile support or mobile steady rest: is mounted on the carriage and allows long workpieces to be supported near the cutting point.

• - Tool holder turret with multiple alignment.

• - Drag plate: to tie down pieces that are difficult to hold.

• - Independent claw plate: it has 4 claws that act independently of each other.

Las herramientas de torneado se diferencian en dos factores, el material del que están constituidas y el tipo de operación que realizan. Según el material constituyente, las herramientas pueden ser de acero rápido, metal duro soldado o plaquitas de metal duro (widia) intercambiables.

La tipología de las herramientas de metal duro está normalizada de acuerdo con el material que se mecanice, puesto que cada material ofrece unas resistencias diferentes. El código ISO para herramientas de metal duro se recoge en la tabla más abajo.

Cuando la herramienta es de acero rápido o tiene la plaquita de metal duro soldada en el portaherramientas, cada vez que el filo se desgasta hay que desmontarla y afilarla correctamente con los ángulos de corte específicos en una afiladora. Esto ralentiza bastante el trabajo porque la herramienta se tiene que enfriar constantemente y verificar que el ángulo de incidencia del corte este correcto. Por ello, cuando se mecanizan piezas en serie lo normal es utilizar portaherramientas con plaquitas intercambiables, que tienen varias caras de corte de usar y tirar y se reemplazan de forma muy rápida.

Characteristics of carbide inserts

The quality of the carbide inserts (widia) is selected taking into account the material of the part, the type of application and the machining conditions.

The variety of insert shapes is large and standardized. Likewise, the variety of materials used in modern tools is considerable and is subject to continuous development.[15]​.

The main tool materials for turning are shown in the following table.

The suitability of the different types of inserts depending on the material to be machined are indicated below and are classified according to an ISO/ANSI Standard to indicate the applications in relation to the resistance and toughness they have.

Format code for hard metal inserts

As there is so much variety in geometric shapes, sizes and cutting angles, there is a standardized coding made up of four letters and six numbers where each of these letters and numbers indicates a specific characteristic of the corresponding insert type.

Insert code examples: SNMG 160408 HC.

The first two figures indicate the length of the cutting edge of the insert in millimeters.

The next two figures indicate the thickness of the insert in millimeters.

The last two figures indicate the tip radius of the insert in tenths of a millimeter.

Principales especificaciones técnicas de los tornos convencionales:[16]​.

Ability

• - Height of points;.

• - distance between points;.

• - diameter admitted on bed or turning, measured from the center of the spindle at the beginning of the bed.

• - diameter admitted on neckline;.

• - diameter admitted on transversal carriage;.

• - width of the bench;

• - length of the neckline in front of the smooth plate.

Fixed head

• - Norton box.

• - Diameter of the main spindle hole or bar pitch;

• - nose of the main spindle; or secondary spindle nose.

• - Morse taper") of the main spindle;.

• - range of head speeds (usually in rpm);.

• - number of speeds.

Cars

• - Cross carriage travel;

• - journey of the "charriot" or upper carriage;

• - maximum dimensions of the tool.

• - range of longitudinal advances;.

• - range of transversal advances.

• - automatic feed path (longitudinal carriage).

• - automatic feed path (cross slide).

Threaded

• - Range of metric steps;.

• - Whitworth step range;.

• - range of modular steps;.

• - Diametral Pitch step range;

• - pitch of the master spindle.

moving head

The moving head is made up of two pieces, which are generally cast "Casting (metallurgy)"). One of them, the support, rests on the main guides of the lathe, on which it can be fixed or moved from the end opposite the headstock. The other piece is located on top of the previous one and has a spindle that is operated with a crank for the longitudinal movement of the tailstock, fitting it with the appropriate pressure in a blind conical hole, called centering point, made on the end of the piece opposite to the fixed head.[17]​.

Engines

• - Power "Power (physical)") of the main engine (usually in kW);

• - power of the coolant motor pump (in kW).

Lunettes

Not all types of lathes have the same technical specifications. For example, vertical lathes do not have a tailstock and only the parts subjected to air are machined. Machine threading with a Norton Box is only available on parallel lathes.

• - Cutting motion: usually imparted to the part that rotates rotationally about its main "Axis (mechanical)") axis. This movement is produced by an electric motor that transmits its rotation to the main spindle through a system of pulleys or gears. The main spindle has different clamping systems attached to its end (claw plates, clamps, auxiliary chucks or others), which hold the part to be machined. Traditional lathes have a fixed range of rotation speeds, however, in modern Numerical Control lathes the rotation speed of the headstock is variable and programmable and adapts to the optimal conditions that the machining allows.

• - Feed movement: is the movement of the cutting tool in the direction of the axis of the piece being worked. In combination with the rotation imparted to the spindle, it determines the space traveled by the tool for each revolution the piece makes. This movement may also not be parallel to the axis, thus producing cones. In that case, the chariot is rotated, adjusting the required angle on a graduated scale, which will be half of the desired cone. Conventional lathes have a fixed range of feeds, while Numerical Control lathes the feeds are programmable according to the optimal machining conditions and empty movements are carried out at high speed.

• - Depth of pass"): movement of the cutting tool that determines the depth of material removed in each pass. The amount of material that can be removed depends on the profile of the cutting tool used, the type of material machined, the cutting speed, power "Power (physical)") of the machine, feed, etc.

• - Verniers of the carriages: to regulate the turning work, the lathe carriages have built-in verniers in the shape of a graduated drum, where each division indicates the displacement of the carriage, whether longitudinal, transversal or charriot. The measurement is made manually by the machine operator, so a very expert person is required to manipulate it if it is to achieve dimensions with very close tolerances. Numerical control lathes no longer have verniers, but rather the dimensions of the piece are entered into the program and these are achieved automatically.

Displacement

This operation consists of the external or internal machining to which parts that have cylindrical machining are subjected. To be able to carry out this operation, the depth of passage and, therefore, the diameter of the cylinder is regulated with the transverse carriage, and the length of the cylinder is regulated with the parallel carriage. The parallel carriage advances automatically according to the desired work progress. In this procedure, the surface finish "Roughness (mechanical)") and the tolerance "Tolerance (manufacturing)") obtained can be a factor of great relevance. To ensure quality in the turning, the lathe must have its alignment and concentricity well adjusted.

The turning can be done with the piece held in the air held in the jaw plate, if it is short, or with the piece held between points and a drive pin, or supported on a fixed or mobile steady rest if the piece is large and heavy. To perform the cylindering of parts or axles held between points, it is necessary to previously make the centering points on the axes.

When the turning is carried out in the hollow of the piece, it is called boring.

Facing

The facing operation consists of frontal machining perpendicular to the axis of the parts that is carried out to produce a good coupling in the subsequent assembly of the turned parts. This operation is also known as bordering. The problem with facing is that the cutting speed on the edge of the tool decreases as it advances towards the center, which slows down the operation. To improve this aspect, many modern lathes incorporate speed variators in the headstock so that the rotation speed of the piece can be increased.

Grooved

grooving consists of machining cylindrical grooves of variable width and depth in the pieces that are turned, which have many different uses. For example, to house an O-ring, for thread exit, for pressure washers, etc. In this case, the tool has already formed the width of the slot and by acting with the transverse carriage the desired depth is given. Pulley channels are a clear example of turned grooves.

Threading on the lathe

There are two systems for performing threading on lathes, on the one hand the traditional one used by parallel lathes), using the Norton Box, and on the other hand, the one that is carried out with CNC lathes, where the thread data is fully programmed and the Norton box is no longer needed to do it.

To carry out threading with a tool, the following must be taken into account:.

• - The threads can be external (screws) or internal (nuts), and their magnitudes must be consistent so that both elements can be screwed.

• - The elements that appear in the table are those that must be taken into account when making a thread on a lathe:.

To carry out threading, the following tasks must be previously carried out:

• - Previously turn to the diameter of the thread.

• - Prepare the tool according to the angles of the thread fillet.

• - Establish the cutting depth that the thread must have until the appropriate profile is achieved.

One of the tasks that can be performed on a parallel lathe is to make threads of various pitches and sizes, both external on shafts and internal on nuts. To do this, universal parallel lathes incorporate a mechanism called Norton Box, which facilitates this task and avoids assembling a train of gears every time you want to make a thread.

The Norton box is a mechanism composed of several gears that was invented and patented in 1890, which was incorporated into parallel lathes and provided a solution to the manual gear change to set the pitches of the pieces to be threaded. This box can consist of several movable gear trains or a tilting train and a gear cone. The box connects the movement of the lathe headstock with the tool carriage that has a built-in square thread spindle.

The best achieved system includes a gearbox with several reducers. In this way, with the manipulation of several levers, different tool carriage advance speeds can be set, allowing a wide variety of thread pitches to be made, both metric and Whitworth. There are oil bath and dry ones, with gears carved in one way or another, but basically it is a gearbox.

The figure shows how a screw is machined from a hexagonal bar. To do this, the following operations are carried out:

1. • The body of the screw is cylindered, leaving the hexagonal head in its original measurements.

2. • The entrance of the thread is chamfered and the tip of the screw is faced.

3. • The throat is slotted where the thread ends next to the head of the screw.

4. • The body of the screw is threaded, resulting in the finished piece.

This same process can be done starting from a long bar, finally cutting off the machined part.

Knurled

Knurling is a process of cold forming the material using knurls that press the piece while it rotates. This deformation produces an increase in the starting diameter of the piece. Knurling is performed on pieces that have to be handled by hand, which are generally threaded to prevent slipping that would occur if they had a smooth surface.

Knurling is done on lathes with tools called knurls, with different pitch and pattern.

An example of knurling is that of the 50 euro cent coins, although in this case the knurling is so that the blind can better identify the coin.

Strain knurling can be performed in two ways:.

• - Radially, when the knurled length on the piece matches the thickness of the knurled wheel to be used.

• - Longitudinally, when the length exceeds the thickness of the knurled wheel. For this second case, the knurled wheel must always be beveled at its ends.

Cone turning

A cone "Cone (geometry)") or a truncated cone of a generation body is defined by the following concepts:

• - Larger diameter.

• - Smaller diameter.

• - Length.

• - Angle of inclination.

• - Conicity.

Different lathes machine cones in different ways.

• - In CNC lathes there is no problem because, by properly programming their dimensions, the transverse and longitudinal carriages move in a coordinated manner, giving rise to the desired cone.

• - In copying lathes there is no problem either because the copying template allows the probe to move through it and the carriages act in a coordinated manner.

• - To machine cones on conventional parallel lathes it can be done in two different ways. If the length of the cone is small, the cone is machined with the charriot inclined according to the angle of the cone. If the length of the cone is very large and the axis is machined between points, then the tailstock is moved the appropriate distance according to the dimensions of the cone.

To calculate the angle of inclination of the car, proceed as follows:

where is the largest diameter, is the smallest diameter and is the length of the cone.

Spherical turning

Spherical turning, for example that of ball joints "Ball joint (mechanical)"), does not have any difficulty if it is carried out on a Numerical Control lathe because, by programming its measurements and the corresponding radial machining function, it will be carried out perfectly.

If the lathe is a high-production automatic lathe, it works with a bar and the ball joints are not large, the ball joint is achieved with a transverse carriage where the tools are sharpened with the profile of the ball joint.

Making ball joints manually on a parallel lathe presents some difficulty in achieving accuracy. In that case it is advisable to have a template of the sphere and machine it manually and finish it with a file "File (tool)") or scraper to give the final adjustment.

Mowing or bucking

The turning operation that is carried out when working with a bar is called mowing and at the end of the machining of the corresponding piece it is necessary to cut the bar to separate the piece from it. For this operation, very narrow tools are used with a projection according to the diameter of the bar and allowing the transverse carriage to reach the center of the bar. It is a very common operation in bar-fed revolver and automatic lathes and mass production.

Chamfering

Chamfering is a very common turning operation that consists of killing both the exterior and interior edges to avoid cuts with them and in turn facilitate the subsequent work and assembly of the pieces. The most common chamfer is usually 1 mm by 45°. This chamfer is made by attacking the edges directly with a suitable tool.

Eccentric machining

An eccentric is a part that has two or more cylinders with different centers or axes of symmetry, as occurs with engine crankshafts or camshafts. An eccentric is a body of revolution and therefore machining is carried out on a lathe. To machine an eccentric it is first necessary to make the centering points of the different eccentric axes at the ends of the piece that will be fixed between two points.

Spiral machining

A spiral is a thread carved into a flat disk and machined on a lathe, by appropriately moving the cross slide. To do this, the transmission that will be placed between the headstock and the feed spindle of the transverse carriage must be calculated according to the pitch of the spiral thread. It is a rare operation in turning. An example of a spiral thread is the one inside the jaw plates of lathes, which allows the opening and closing of the jaws.

Boring

Many pieces that are turned require drilling with drill bits in the center of their axes of rotation. Normal drill bits are used for this task, which are clamped at the tailstock in a drill chuck or directly in the tailstock housing if the diameter is large. The technological conditions for drilling are normal according to the characteristics of the material and type of drill bit used. Deep drilling processes deserve special mention where the process is already very different, especially the constitution of the drill bit used.

Not all lathes can perform all of these operations indicated, but this depends on the type of lathe used and the accessories or equipment it has.

Reamed.

Reaming is a finishing process used to increase the size of an existing hole, improve its surface finish, and produce a very precise hole diameter.[18]​.

Los parámetros de corte fundamentales que hay que considerar en el proceso de torneado son los siguientes:.

• - Elección del tipo de herramienta más adecuado.

• - Sistema de fijación de la pieza.

• - Velocidad de corte (V) expresada en metros/minuto.

• - Diámetro exterior del torneado.

• - Revoluciones por minuto (rpm) del cabezal del torno.

• - Avance en mm/rev, de la herramienta.

• - Avance en mm/mi de la herramienta.

• - Profundidad de pasada.

• - Esfuerzos de corte.

• - Tipo de torno y accesorios adecuados.

cutting speed

Cutting speed is defined as the "linear speed" of the periphery of the part that is in contact with the tool. The cutting speed, which is expressed in meters per minute (m/min), has to be chosen before starting machining and its appropriate value depends on many factors, especially the quality and type of tool used, the depth of the pass, the hardness and machinability of the material being machined and the feed speed used. The main limitations of the machine are its range of speeds, the power of the motors and the rigidity of the fixation of the piece and the tool.

By determining the cutting speed, the revolutions per minute that the lathe head will have can be determined, according to the following formula:

Where V is the cutting speed, n is the rotation speed of the part to be machined and D is the diameter of the part.

Cutting speed is the main factor that determines tool life. A high cutting speed allows machining to be carried out in less time but accelerates tool wear. Tool manufacturers and machining manuals offer indicative data on the appropriate cutting speed of tools for a given tool duration, for example, 15 minutes. Sometimes it is desirable to adjust the cutting speed for a different tool life, for which the cutting speed values ​​are multiplied by a correction factor. The relationship between this correction factor and the life of the tool in cutting operation is not linear.[19]​.

Excessive cutting speed may result in:.

• - Very rapid wear of the tool's cutting edge.

• - Plastic deformation of the cutting edge with loss of machining tolerance.

• - Poor machining quality; surface finish "Roughness (mechanical)") inefficient.

Cutting speed too low may result in:.

• - Formation of a contribution edge on the tool.

• - Negative effect on chip evacuation.

• - Low productivity.

• - High machining cost.

Workpiece rotation speed

The rotation speed of the lathe headstock is usually expressed in revolutions per minute (rpm). In conventional lathes there is a limited range of speeds, which depend on the rotation speed of the main motor and the number of speeds of the machine's gearbox. In numerical control lathes, this speed is controlled with a feedback system that usually uses a frequency converter and any speed can be selected within a range of speeds, up to a maximum speed.

The rotation speed of the tool is directly proportional to the cutting speed and inversely proportional to the diameter of the workpiece.

Feed speed

The feed or feed rate in turning is the relative speed between the piece and the tool, that is, the speed with which the cut progresses. The feed of the cutting tool is a very important factor in the turning process.

Each tool can adequately cut at a range of feed rates per revolution of the part, called feed per revolution (f). This range depends fundamentally on the diameter of the piece, the depth of the pass, and the quality of the tool. This speed range is determined experimentally and is found in tool manufacturers' catalogs. Furthermore, this speed is limited by the rigidity of the workpiece and tool clamping and by the power of the machine's feed motor. The maximum chip thickness in mm is the most important limiting indicator for a tool. The cutting edge of the tools is tested to have a certain value between a minimum and maximum chip thickness.

The feed rate is the product of the feed per revolution and the rotation speed of the piece.

As with the tool rotation speed, in conventional lathes the feed speed is selected from a range of available speeds, while numerical control lathes can work at any feed speed up to the maximum feed speed of the machine.

Effects of ground speed.

• - Decisive for chip formation.

• - Affects power consumption.

• - Contributes to mechanical and thermal stress.

The high forward speed gives rise to:.

• - Good chip control.

• - Shorter cutting time.

• - Less tool wear.

• - Higher risk of tool breakage.

• - High surface roughness of the machining.

Low forward speed results in:.

• - Longer chip.

• - Improvement of machining quality.

• - Accelerated tool wear.

• - Longer duration of machining time.

• - Higher machining cost.

Specific cutting force

The cutting force is a necessary parameter to be able to calculate the power necessary to carry out a certain machining. This parameter is a function of the tool feed, the depth of pass, the cutting speed, the machinability of the material, the hardness of the material, the characteristics of the tool and the average thickness of the chip. All these factors are included in a coefficient called K. The specific cutting force is expressed in N/mm².[20]​.

Cutting power

The cutting power P necessary to carry out a specific machining operation is calculated from the value of the chip removal volume, the specific cutting force and the performance of the machine. It is expressed in kilowatts (kW).

This specific cutting force F is a constant that is determined by the type of material being machined, tool geometry, chip thickness, etc.

In order to obtain the correct power value, the value obtained has to be divided by a certain value (ρ) that takes into account the efficiency of the machine. This value is the percentage of the motor power that is available in the tool placed in the spindle.

where.

• - P is the cutting power (kW).

• - A is the diameter of the piece (mm).

• - f is the feed speed (mm/min).

• - F is the specific cutting force (N/mm²).

• - ρ is the performance or efficiency of the machine.

• - Design and limitations of the piece: size, turning tolerances, tendency to vibrations, clamping systems, surface finish, etc.

• - Turning operations to be performed: external or internal turning, facing, grooving, roughing, finishing, optimization to perform several operations simultaneously, etc.

• - Stability and machining conditions: intermittent cuts, part overhang, shape and condition of the part, condition, power and drive of the machine, etc.

• - Availability and selection of the type of lathe: possibility of automating machining, being able to perform several operations simultaneously, series of parts to be machined, quality and quantity of coolant, etc.

• - Material of the piece: hardness, condition, resistance, machinability, bar, casting, forging, dry or coolant machining, etc.

• - Availability of tools: quality of tools, tool clamping system, access to tool distributor, tool technical service, technical advice.

• - Economic aspects of machining: machining optimization, tool life, tool price, machining time price.

Special aspects of boring tools: the largest possible bar diameter must be selected and good chip evacuation must be ensured. Select the smallest possible overhang of the bar. Select tools with the greatest possible tenacity.[15]​.

Turning has evolved so much that it is no longer just about removing material at high speed, but the parameters that make up the process have to be closely controlled to ensure the final results of economy, quality and precision. In particular, the way of treating the chip has become a complex process, where all the technological components of machining are involved, so that it can have the size and shape that does not disturb the work process. If this were not the case, masses of long, fibrous chips would quickly accumulate in the machining area, forming tangled and uncontrollable skeins.

The shape the chip takes is mainly due to the material being cut and can be either ductile or brittle and brittle.

The feed at which you work and the depth of the pass usually largely determine the shape of the chip. When these variables are not enough to control the shape of the chip, it is necessary to choose a tool that incorporates an effective chip breaker.

Today dry turning is completely viable. There is a recent trend to carry out dry machining whenever the quality of the tool allows it.

Concern arose during the 90s, when studies carried out in automotive component manufacturing companies in Germany highlighted the high cost of refrigeration and especially its recycling.

However, dry machining is not suitable for all applications, especially for drilling, threading and boring to ensure chip evacuation.

It is also not advisable to dry turn pasty or too soft materials such as aluminum or low carbon steel since it is very likely that the cutting edges will become dull with the material they cut, producing poor surface finish, dispersions in the measurements of the piece and even breakage of the cutting edges.

In the case of machining short chip materials such as gray cast iron, coolant is beneficial as a cleaning agent, preventing the formation of toxic dust clouds.

The coolant is essential when turning abrasive materials such as stainless steel, inconells, etc.

In dry turning, the machinery must be prepared to absorb without problems the heat produced in the cutting action.

To avoid overheating of spindles, etc., internal oil or air cooling circuits are usually incorporated.

With few exceptions and unlike milling, dry turning has not become widespread but it has made companies question using coolant only in the necessary operations and with the necessary flow rate..

It is necessary to carefully evaluate operations, materials, parts, quality requirements and machinery to identify the benefits of eliminating the refrigerant contribution.

For a lathe to function correctly and guarantee the quality of its machining, it is necessary that it periodically undergo a review and tune-up where all its functions will be adjusted and verified.

The most important tasks carried out in the overhaul of the lathes are the following:

Other functions such as the precision of the verniers are carried out more sporadically, mainly when the machine is new.

When working on a lathe, you must observe a series of requirements to ensure that you do not have any accident that could cause any piece to be thrown off the plate or chip if it is not cut properly. For this, most lathes have a protection screen. But also of utmost importance is preventing being caught by the rotational movement of the machine, for example by clothing or long hair.

Ante la diversidad de tornos que existe, también existen diferentes perfiles de los profesionales torneros dedicados a estas máquinas, entre los que se puede establecer la siguiente clasificación:[21]​.

Numerical control lathe programmers

Numerical control (CNC) lathes first require a technical programmer to develop the execution program that the lathe has to carry out for the machining of a specific part. In this case, it must be a good knowledge of the factors involved in machining on the lathe, such as the following:

• - Lathe features.

• - Features and availability of tools.

• - Fastening of the pieces.

• - Type of material to be machined and its machining characteristics.

• - Use of refrigerants.

• - Number of pieces to be machined.

• - Surface finish. Rugosity.

• - Allowable machining tolerance.

In addition, you must know well the technological parameters of turning, which are:.

• - Optimum cutting speed at which turning should be carried out.

• - Optimum machining advance.

• - Depth of pass").

• - Spinning speed (RPM) of the head.

• - Tool change system.

To all these requirements must be added a correct interpretation of the part plans and the programming technique used in accordance with the equipment that the lathe has.[22]​.

Preparers of automatic and computer numerical control (CNC) lathes

In industries where several large-production automatic lathes or computer numerical control (CNC) lathes have been installed, there must be a professional in charge of fine-tuning these machines every time there is a change in the parts to be machined because fine-tuning an automatic or numerical control lathe is a fairly complex task.

Once the lathe has been prepared for a specific job, the subsequent control of the machine's work is usually entrusted to a person with less technical preparation who only has to ensure that the quality of the machined parts is met within the required tolerance and roughness qualities. Sometimes an operator is able to attend to several automatic lathes, if they have an automated part feeding system using bars or automatons.

• - Mechanic-Turner.

• - Machine tool.

• - Harassing.

• - Machining.

• - Embossing on the lathe.

• - Machine Tool Research Foundation Archived July 14, 2013 at the Wayback Machine.

• - Spanish Association of Machine Tool Manufacturers.

• - Spanish Machine Tool Biennial.

• - Directory of Exhibitors of the Spanish Machine Tool Biennial.

• - Wand made with a lathe (My Popular Mechanics).

• - Types of lathe machines used in industries.