Tips and tricks
Practical treatise on milling and milling machines
PRACTICAL TREATISE ON MILLING AND MILLING MACHINES
BROWN & SHARPE MFG. Co; PROVIDENCE; 1914
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Practical treatise on milling and milling machines
CONTENTS
- Classification of Milling Machines
- Essentials of a Modern Milling Machine
- Erection and Care of Machine
- Spiral Head - Indexing and Cutting Spirals
- Attachments
- Cutters
- General Notes on Milling, together with Typical Milling Operations
- Milling Operations - Gear Cutting
- Milling Operations - Cam Cutting, Graduating and Miscellaneous Operations
INTRODUCTION
Milling is the process of removing metal with rotary cutters. It is employed extensively in machine shops today for forming parts of machinery, tools, etc., to required dimensions and shapes. A machine designed especially for this purpose was in existence as early as 1818, but little progress was made in the process until after the invention of the universal milling machine (shown on the opposite page) in 1861-62 by Mr. Joseph R. Brown, of J. R. Brown and Sharpe. This was owing chiefly to the difficulties of obtaining satisfactory cutters and of sharpening them. Shortly after this, however, improvements in the methods of making cutters, the invention by Mr. J. R. Brown of the form cutter which can be sharpened without changing the cutting contour and the introduction of the grinding wheel for sharpening cutters, removed the obstacles that had so seriously hindered the early development of milling.
As the field of milling widened, the demands upon the machine increased accordingly, and it became necessary to make certain improvements to adapt it to the new conditions. But it is a noteworthy fact that in all of the changes in design leading up to the modern heavy type of universal machine, shown on page 44, none of the fundamental ideas of the original machine have been lost. Parts have been strengthened to better withstand heavier service, and radical changes have been made in the method of driving the spindle and feeds to accommodate the machine to modern requirements. From a comparison of the original machine with a modern type, the important changes that have been made are readily noted.
The column has been carried well above the spindle, and an overhanging arm with a support for the outer end of cutter arbor has been added. To further stiffen the arbor, arm braces have been devised by the use of which the overhanging arm, cutter arbor, and knee are all rigidly tied together. These braces on the smaller sizes of machines consist of long slotted cross arms, while on the larger, or heavy service machines, a different and heavier type is employed. The table feed has been changed from the end of the feed screw and carried up through the centre of the knee and saddle, thus allowing the table to be swiveled through a much greater arc. Power feeds have been applied to the transverse and vertical table movements, and the old-style elevating screw for the knee that required cutting a hole through the floor has been replaced by a telescopic screw.
Improvements have been made on the spiral head to make it more rigid and convenient to operate; differential indexing replaces to a large extent the compound method, and refinements such as graduated index sectors, and an adjustable index crank have been added.
Such conveniences as permanent hand wheels instead of cranks, adjustable dials reading to thousandths of an inch on the feed shafts, and other improvements have been put on the machines from time to time.
When the milling machine came into more general use, and its possibilities in removing metal began to be appreciated, the demand arose for the ability to make heavier cuts. These demands soon demonstrated that the method of driving the feeds through belts and cone pulleys from the spindle of the machine to the feed mechanism, was inadequate. The first improvement was to substitute chain and sprockets for the belt and pulleys and to use removable change gears to provide a variation in the rate of feed. The next step was to place all the change gears in a feed box wherein by simply shifting levers, a wide variation of feeds could be obtained.
The main spindle drive has undergone radical changes. The original machine had a four-step cone pulley mounted directly on the spindle, and many of the smaller sizes of machines today are similarly built. In order to get more power and a greater range of speeds, back gears similar to those of a lathe were added.
Following these improvements came a radical change in the whole driving mechanism of the machine. The value of feeds that were independent of the spindle speeds had become well recognized, and with the introduction of high speed steel, from which cutters could be made that would take much heavier cuts at faster speeds, and coarser feeds than had ever before been the practice, there arose a demand for more powerful machines. The constant speed type of drive was therefore originated. In this type of machine any combination of table feed and spindle speed is available, because both spindle and feeding mechanisms are driven from the main shaft of the machine, which revolves at a constant high velocity at all times. The table feeds are therefore entirely independent of the spindle speeds. A powerful drive is also transmitted to the spindle from the driving pulley of large diameter and wide face on the main shaft of the machine through a train of heavy spur gearing in which are certain change gears that can be manipulated to give a wide range of spindle speeds. At the same time that the constant speed type of drive was evolved, the machine was redesigned and made stronger throughout in order to better fit it for the heavy cuts that had become the practice.
Later improvements have been the extension of the flat bearing surface on the front of the column to the top, the application of a friction clutch in the driving pulley with levers at the sides of the machine for operating it, the automatic fast feed for quick movement of the table, and other improvements of lesser importance.
It is not to be assumed that the constant speed type of drive has been developed to the exclusion of the cone type, for there are many pieces of work that can be done to good advantage on this machine. The modern cone type of machine embodies all of the previously mentioned improvements, except those relating particularly to the constant speed drive, and there is still, and probably always will be, a steady demand for this machine. Two other types of machines known as Plain and Vertical Spindle Milling Machines have kept pace with the development of the universal machine. Milling Machines of the Planer and Manufacturing types have also come into extensive use, the former producing a wide range of work that is of too large dimensions for the previously mentioned machines, and the latter manufacturing in large quantities small duplicate parts of machinery, tools, etc.
With the improvements that have been made on the machines and their equipment, milling has become indispensable in the modern shop. Interchangeable pieces can be easily made, and work is produced at a low cost because of the continuous operation and inexpensiveness of cutters for a given amount of production. We, therefore, recommend the milling machine to manufacturers desirous of obtaining the best results at the lowest cost on all classes of work to which the machine is adapted. And we trust that a careful reading of the following chapters will be of material assistance in understanding the process of milling and how to use the machines.
CHAPTER I
Classification of Milling Machines
The existing types of milling machines are so numerous, and their designs merge into one another to such an extent, that it is very difficult to classify them definitely. But, taken as a whole, they may be said to consist of two distinct groups, those adapted to a variety of work, and those restricted to the performance of a single operation, such as gear cutting, bolt head milling, thread milling, etc. While this latter group embraces some valuable and interesting machines, the class of work done is of a more or less special character, and little can be learned from it of the general process of milling. For this reason, and also from the fact that it would be practically impossible to treat of every type in the limited space of this book, the first group alone will be considered. The machines of this group are classified in a variety of ways by different writers. We prefer to divide them, according to general appearance and design, into three classes, comprising the column and knee type, manufacturing type, and planer type. Such a classification brings out the characteristics of the different machines, and their relation to one another.
Column and Knee Milling Machines
An illustration of a representative example of the column and knee type of milling machine is shown on the opposite page. This machine is the most recent of the three types named, having been in existence about fifty years. The rapid strides, however, that have been made within the past few years in the process of milling are largely due to its versatility and convenience. Even with the most expert cutter making, milling could never have obtained its important position in the field of machinery and tool manufacture had it not been for the column and knee type of construction.
The name, column and knee, is derived from the high, column like design of the main casting, and the likeness of the bracket which supports the table to a knee or angle iron. The knee is adjustable on the column so that the table can be set at different heights to accommodate work of varying size. It can also be fed upward, thus enabling vertical cuts to be taken. Provision is made for movement of the table horizontally in two directions: one, longitudinally, at right angles to the axis of the spindle; and the other, transversely, parallel to the axis of the spindle. The combination of these three movements is found only in the column and knee machine, and it is due to the advantages derived from this construction that the machine is superior to the manufacturing or planer type for general milling purposes.
This type of milling machine is shown in the illustration on the opposite page. It is a development of one of the earliest forms that was built particularly for use in, the manufacture of small parts of firearms, and has since been successively adopted for machining parts of sewing machines, typewriters and other machines and tools. The advantages it offers for this class of work are due to the stiff construction and convenience with which it can be operated. These make possible an exceptionally large production of first quality work - factors of great importance in commercial manufacturing.
There are many minor variations of this type of milling machine, but the general features are similar in all. In that shown on the opposite page, the spindle is supported in bearings located in an adjustable head that can be raised and lowered. The capacity of the machine is rather limited as regards work of widely varying heights. Furthermore, there is no transverse table feed, the only movement transversely being obtained by a slight adjustment of the spindle. These, however, cannot be considered disadvantages, as provision for work of widely varying heights is not required, because all work done is of comparatively small dimensions, and there is seldom any necessity for a transverse table movement.
Planer Milling Machine
The planer milling machine is designed for the heaviest classes of slab and gang milling. It bears a marked resemblance to the planer, from which it derives its name. The spindle is mounted in bearings carried in a vertically adjustable slide similar to that of a planer, and the table is in a corresponding position. This brief reference will enable one to easily distinguish these machines. And, as the class of work performed is identical in character, only heavier than that done on the column and knee type of machine, the same principles are involved.
Returning to the column and knee type, we can subdivide it into three classes, known as Plain, Universal, and Vertical Spindle Machines. In the first two the spindle is supported in horizontal, bearings that are fixed in the main casting of the machine instead of being adjustable vertically, as in the case of both manufacturing and planer types of machines. This is one of the points where the column and knee machine is radically different from either of the other types. As we have already explained, vertical adjustment in this type is obtained by the movement of the knee upon the column.
Plain Milling Machine. The word plain when applied to any milling machine is used to designate one in which the longitudinal travel of the table is fixed at right angles to the spindle. Both manufacturing and planer types are therefore essentially plain milling machines.
An illustration of a plain milling machine of the column and knee type is shown on page 19. In this machine, the table has the three movements: longitudinally, transversely, and vertically, that have already been mentioned. Some machines have both automatic and hand feeds for all three of the movements; others have longitudinal and transverse movements so controlled and the vertical is operated by hand; or the longitudinal movement alone is operated both automatically and by hand, and the transverse and vertical movements are made only by hand. Feed screws are used for operating all of the table movements in many of the smaller sizes and all of the larger machines, but in some of the smaller ones a rack and pinion are employed for the longitudinal movement. The smallest sizes of machines have no power feeds at all, and are called hand milling machines. (See illustration on page 46.) In these, the table and knee are moved by means of racks and pinions operated by levers. They are convenient for manufacturing purposes on some classes of small work, as they can be operated very rapidly.
It is the practice in the classes of work to which the medium and larger sizes of plain milling machines are adapted to take heavy cuts at fast speeds and coarse feeds. The rigid construction of the machine enables this to be successfully done, and it is in this ability that the chief value of the plain machine is found.
Universal Milling Machine. The Universal milling machine is justly regarded by many to be the most important machine tool employed today; for with it much of the work of the planer and shaper - heretofore considered indispensable machines in every shop -can be done with an appreciable saving of time. Spur, bevel and spiral gears, twist drills, and all kinds of straight and taper milling can also be economically produced.
It was first patented February 21st, 1865, by Mr. J. R. Brown, of the firm of J. R. Brown & Sharpe, who designed it for the purpose of milling the grooves in twist drills, but adopted it shortly after for producing small spirals used in the manufacture of sewing machines.
The cuts on pages 10 and 44 are representative of modern universal milling machines. This style of machine is essentially the same in construction as the plain milling machine, and the table has the same movements. But, in addition, the table swivels upon the saddle and can be set at an angle to the spindle in a horizontal plane. Also, it is fitted with a mechanism known as a spiral head, for use in spiral milling and indexing to obtain any required spacing on the periphery of work. The introduction of the swivel renders the table a little less stable than that of the plain machine, though in common practice heavy cuts are taken. It is apparent, however, that the offices of the two machines are in a way distinct. A universal machine is the better for general shop purposes, but where continuous heavy milling of straight cuts is to be done the plain machine is preferable.
Vertical Spindle Milling Machine. The vertical spindle milling machine embodies the principles of a drilling machine. The spindle and table are similarly located, and the cutter is mounted at the end of the spindle. The table on the milling machine, however, has a series of movements that are not found on the drilling machine. For such work as face milling, die-sinking, profiling, etc., the vertical spindle machine offers many advantages over the horizontal style. Some work can be fastened directly to the top of the table, eliminating the use of special fixtures necessary for the same kind of work on a horizontal spindle machine. Furthermore, the operator is enabled to see his work at all times during operation and more readily follow any irregularities in outline. This feature is especially valuable in profiling, cutting odd-shaped slots, etc.
Not all vertical spindle machines are of the column and knee type. There are several styles that have no provision for vertical adjustment of the table, Also some vertical spindle machines have two spindles instead of one, but those are more generally known as profiling machines.
But the combination of the vertical spindle and column and knee constructions has given the mechanical world an exceptionally valuable machine tool. With it, all of the advantages of the vertical spindle, together with those of the column and knee, are acquired. A modern example of this style is shown in the cut on the opposite page. A further convenience of this machine is found in the spindle head, which is adjustable vertically, and can be fed by power, thus enabling drilling to be conveniently done. With the adjustable spindle head and column and knee construction, it is apparent that work of a wide range of heights can be accommodated. Another style of vertical spindle machine, where the spindle is driven by a belt, is shown on page 36.
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Practical treatise on milling and milling machines
As the field of milling widened, the demands upon the machine increased accordingly, and it became necessary to make certain improvements to adapt it to the new conditions. But it is a noteworthy fact that in all of the changes in design leading up to the modern heavy type of universal machine, shown on page 44, none of the fundamental ideas of the original machine have been lost. Parts have been strengthened to better withstand heavier service, and radical changes have been made in the method of driving the spindle and feeds to accommodate the machine to modern requirements. From a comparison of the original machine with a modern type, the important changes that have been made are readily noted.
The column has been carried well above the spindle, and an overhanging arm with a support for the outer end of cutter arbor has been added. To further stiffen the arbor, arm braces have been devised by the use of which the overhanging arm, cutter arbor, and knee are all rigidly tied together. These braces on the smaller sizes of machines consist of long slotted cross arms, while on the larger, or heavy service machines, a different and heavier type is employed. The table feed has been changed from the end of the feed screw and carried up through the centre of the knee and saddle, thus allowing the table to be swiveled through a much greater arc. Power feeds have been applied to the transverse and vertical table movements, and the old-style elevating screw for the knee that required cutting a hole through the floor has been replaced by a telescopic screw.
Improvements have been made on the spiral head to make it more rigid and convenient to operate; differential indexing replaces to a large extent the compound method, and refinements such as graduated index sectors, and an adjustable index crank have been added.
Such conveniences as permanent hand wheels instead of cranks, adjustable dials reading to thousandths of an inch on the feed shafts, and other improvements have been put on the machines from time to time.
When the milling machine came into more general use, and its possibilities in removing metal began to be appreciated, the demand arose for the ability to make heavier cuts. These demands soon demonstrated that the method of driving the feeds through belts and cone pulleys from the spindle of the machine to the feed mechanism, was inadequate. The first improvement was to substitute chain and sprockets for the belt and pulleys and to use removable change gears to provide a variation in the rate of feed. The next step was to place all the change gears in a feed box wherein by simply shifting levers, a wide variation of feeds could be obtained.
The main spindle drive has undergone radical changes. The original machine had a four-step cone pulley mounted directly on the spindle, and many of the smaller sizes of machines today are similarly built. In order to get more power and a greater range of speeds, back gears similar to those of a lathe were added.
Following these improvements came a radical change in the whole driving mechanism of the machine. The value of feeds that were independent of the spindle speeds had become well recognized, and with the introduction of high speed steel, from which cutters could be made that would take much heavier cuts at faster speeds, and coarser feeds than had ever before been the practice, there arose a demand for more powerful machines. The constant speed type of drive was therefore originated. In this type of machine any combination of table feed and spindle speed is available, because both spindle and feeding mechanisms are driven from the main shaft of the machine, which revolves at a constant high velocity at all times. The table feeds are therefore entirely independent of the spindle speeds. A powerful drive is also transmitted to the spindle from the driving pulley of large diameter and wide face on the main shaft of the machine through a train of heavy spur gearing in which are certain change gears that can be manipulated to give a wide range of spindle speeds. At the same time that the constant speed type of drive was evolved, the machine was redesigned and made stronger throughout in order to better fit it for the heavy cuts that had become the practice.
Later improvements have been the extension of the flat bearing surface on the front of the column to the top, the application of a friction clutch in the driving pulley with levers at the sides of the machine for operating it, the automatic fast feed for quick movement of the table, and other improvements of lesser importance.
It is not to be assumed that the constant speed type of drive has been developed to the exclusion of the cone type, for there are many pieces of work that can be done to good advantage on this machine. The modern cone type of machine embodies all of the previously mentioned improvements, except those relating particularly to the constant speed drive, and there is still, and probably always will be, a steady demand for this machine. Two other types of machines known as Plain and Vertical Spindle Milling Machines have kept pace with the development of the universal machine. Milling Machines of the Planer and Manufacturing types have also come into extensive use, the former producing a wide range of work that is of too large dimensions for the previously mentioned machines, and the latter manufacturing in large quantities small duplicate parts of machinery, tools, etc.
With the improvements that have been made on the machines and their equipment, milling has become indispensable in the modern shop. Interchangeable pieces can be easily made, and work is produced at a low cost because of the continuous operation and inexpensiveness of cutters for a given amount of production. We, therefore, recommend the milling machine to manufacturers desirous of obtaining the best results at the lowest cost on all classes of work to which the machine is adapted. And we trust that a careful reading of the following chapters will be of material assistance in understanding the process of milling and how to use the machines.
CHAPTER I
Classification of Milling Machines
The existing types of milling machines are so numerous, and their designs merge into one another to such an extent, that it is very difficult to classify them definitely. But, taken as a whole, they may be said to consist of two distinct groups, those adapted to a variety of work, and those restricted to the performance of a single operation, such as gear cutting, bolt head milling, thread milling, etc. While this latter group embraces some valuable and interesting machines, the class of work done is of a more or less special character, and little can be learned from it of the general process of milling. For this reason, and also from the fact that it would be practically impossible to treat of every type in the limited space of this book, the first group alone will be considered. The machines of this group are classified in a variety of ways by different writers. We prefer to divide them, according to general appearance and design, into three classes, comprising the column and knee type, manufacturing type, and planer type. Such a classification brings out the characteristics of the different machines, and their relation to one another.
Column and Knee Milling Machines
An illustration of a representative example of the column and knee type of milling machine is shown on the opposite page. This machine is the most recent of the three types named, having been in existence about fifty years. The rapid strides, however, that have been made within the past few years in the process of milling are largely due to its versatility and convenience. Even with the most expert cutter making, milling could never have obtained its important position in the field of machinery and tool manufacture had it not been for the column and knee type of construction.
The name, column and knee, is derived from the high, column like design of the main casting, and the likeness of the bracket which supports the table to a knee or angle iron. The knee is adjustable on the column so that the table can be set at different heights to accommodate work of varying size. It can also be fed upward, thus enabling vertical cuts to be taken. Provision is made for movement of the table horizontally in two directions: one, longitudinally, at right angles to the axis of the spindle; and the other, transversely, parallel to the axis of the spindle. The combination of these three movements is found only in the column and knee machine, and it is due to the advantages derived from this construction that the machine is superior to the manufacturing or planer type for general milling purposes.
This type of milling machine is shown in the illustration on the opposite page. It is a development of one of the earliest forms that was built particularly for use in, the manufacture of small parts of firearms, and has since been successively adopted for machining parts of sewing machines, typewriters and other machines and tools. The advantages it offers for this class of work are due to the stiff construction and convenience with which it can be operated. These make possible an exceptionally large production of first quality work - factors of great importance in commercial manufacturing.
There are many minor variations of this type of milling machine, but the general features are similar in all. In that shown on the opposite page, the spindle is supported in bearings located in an adjustable head that can be raised and lowered. The capacity of the machine is rather limited as regards work of widely varying heights. Furthermore, there is no transverse table feed, the only movement transversely being obtained by a slight adjustment of the spindle. These, however, cannot be considered disadvantages, as provision for work of widely varying heights is not required, because all work done is of comparatively small dimensions, and there is seldom any necessity for a transverse table movement.
Planer Milling Machine
The planer milling machine is designed for the heaviest classes of slab and gang milling. It bears a marked resemblance to the planer, from which it derives its name. The spindle is mounted in bearings carried in a vertically adjustable slide similar to that of a planer, and the table is in a corresponding position. This brief reference will enable one to easily distinguish these machines. And, as the class of work performed is identical in character, only heavier than that done on the column and knee type of machine, the same principles are involved.
Returning to the column and knee type, we can subdivide it into three classes, known as Plain, Universal, and Vertical Spindle Machines. In the first two the spindle is supported in horizontal, bearings that are fixed in the main casting of the machine instead of being adjustable vertically, as in the case of both manufacturing and planer types of machines. This is one of the points where the column and knee machine is radically different from either of the other types. As we have already explained, vertical adjustment in this type is obtained by the movement of the knee upon the column.
Plain Milling Machine. The word plain when applied to any milling machine is used to designate one in which the longitudinal travel of the table is fixed at right angles to the spindle. Both manufacturing and planer types are therefore essentially plain milling machines.
An illustration of a plain milling machine of the column and knee type is shown on page 19. In this machine, the table has the three movements: longitudinally, transversely, and vertically, that have already been mentioned. Some machines have both automatic and hand feeds for all three of the movements; others have longitudinal and transverse movements so controlled and the vertical is operated by hand; or the longitudinal movement alone is operated both automatically and by hand, and the transverse and vertical movements are made only by hand. Feed screws are used for operating all of the table movements in many of the smaller sizes and all of the larger machines, but in some of the smaller ones a rack and pinion are employed for the longitudinal movement. The smallest sizes of machines have no power feeds at all, and are called hand milling machines. (See illustration on page 46.) In these, the table and knee are moved by means of racks and pinions operated by levers. They are convenient for manufacturing purposes on some classes of small work, as they can be operated very rapidly.
It is the practice in the classes of work to which the medium and larger sizes of plain milling machines are adapted to take heavy cuts at fast speeds and coarse feeds. The rigid construction of the machine enables this to be successfully done, and it is in this ability that the chief value of the plain machine is found.
Universal Milling Machine. The Universal milling machine is justly regarded by many to be the most important machine tool employed today; for with it much of the work of the planer and shaper - heretofore considered indispensable machines in every shop -can be done with an appreciable saving of time. Spur, bevel and spiral gears, twist drills, and all kinds of straight and taper milling can also be economically produced.
It was first patented February 21st, 1865, by Mr. J. R. Brown, of the firm of J. R. Brown & Sharpe, who designed it for the purpose of milling the grooves in twist drills, but adopted it shortly after for producing small spirals used in the manufacture of sewing machines.
The cuts on pages 10 and 44 are representative of modern universal milling machines. This style of machine is essentially the same in construction as the plain milling machine, and the table has the same movements. But, in addition, the table swivels upon the saddle and can be set at an angle to the spindle in a horizontal plane. Also, it is fitted with a mechanism known as a spiral head, for use in spiral milling and indexing to obtain any required spacing on the periphery of work. The introduction of the swivel renders the table a little less stable than that of the plain machine, though in common practice heavy cuts are taken. It is apparent, however, that the offices of the two machines are in a way distinct. A universal machine is the better for general shop purposes, but where continuous heavy milling of straight cuts is to be done the plain machine is preferable.
Vertical Spindle Milling Machine. The vertical spindle milling machine embodies the principles of a drilling machine. The spindle and table are similarly located, and the cutter is mounted at the end of the spindle. The table on the milling machine, however, has a series of movements that are not found on the drilling machine. For such work as face milling, die-sinking, profiling, etc., the vertical spindle machine offers many advantages over the horizontal style. Some work can be fastened directly to the top of the table, eliminating the use of special fixtures necessary for the same kind of work on a horizontal spindle machine. Furthermore, the operator is enabled to see his work at all times during operation and more readily follow any irregularities in outline. This feature is especially valuable in profiling, cutting odd-shaped slots, etc.
Not all vertical spindle machines are of the column and knee type. There are several styles that have no provision for vertical adjustment of the table, Also some vertical spindle machines have two spindles instead of one, but those are more generally known as profiling machines.
But the combination of the vertical spindle and column and knee constructions has given the mechanical world an exceptionally valuable machine tool. With it, all of the advantages of the vertical spindle, together with those of the column and knee, are acquired. A modern example of this style is shown in the cut on the opposite page. A further convenience of this machine is found in the spindle head, which is adjustable vertically, and can be fed by power, thus enabling drilling to be conveniently done. With the adjustable spindle head and column and knee construction, it is apparent that work of a wide range of heights can be accommodated. Another style of vertical spindle machine, where the spindle is driven by a belt, is shown on page 36.
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Practical treatise on milling and milling machines
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