>5 B CENTS 3 Dlfl fi43 MOTOR DRIVE FOR MACHINE TOOLS WITH A CHAPTER ON WIRING FOR MOTOR-DRIVEN MACHINERY MACHINERY'S REFERENCE BOOR NO. 115 PUBLISHED BY MACHINERY. NEW YORK MACHINERY'S REFERENCE SERIES EACH NUMBER IS A UNIT IN A SERIES ON ELECTRICAL AND STEAM ENGINEERING DRAWING AND MACHINE DESIGN AND SHOP PRACTICE NUMBER 115 ELECTRIC MOTOR DRIVE FOR MACHINE TOOLS CONTENTS Application of Motors to Machine Tools Wiring on Motor-driven Machinery - 3 - - Copyright, 1913, The Industrial Press, Publishers of MACHINERY, 140-144 Lafayette Street, New York City - 29 CHAPTER I APPLICATION OF MOTORS TO MACHINE TOOLS* For the shop where electric power is already installed, all kinds machine tools may be purchased completely equipped with individual motors. When, however, it is desired to institute a change in a shop that has been employing belts and shafting, and to substitute electric power, it becomes necessary to consider each of the belt-driven of tools separately, so as to secure as nearly as possible the that are obtained with the tools built for motor drive. same results At the same time excessive expenditures in the alterations must be avoided. It is the purpose of this article to outline the principles of motor application, and to suggest methods by which the belt-driven tools may be accommodated to motor drive. The first problem to consider is that of the transmission of the In large plants, covering acres of ground, alternating current is employed in order to permit the use of high voltages with the corresponding saving in the copper used for wiring. In plants consisting of but a few buildings, grouped fairly close together, the use of direct current possesses advantages in variable speed possibilities that far outweigh the gain to be secured by the use of the high-voltage It is, therefore, the general practice at the alternating current. present time to use 230-volt direct current for the operation of plants of the nature of machine shops, in which a large part of the load will consist of motors driving tools requiring variable speed. Where long transmissions make the distribution of power by alternating current a necessity, a motor-generator may be installed at the point of distribution for the purpose of supplying direct current to the This is often the system employed in the variable-speed motors. case of railway shops which are spread out over a considerable territory and contain a large proportion of constant-speed tools. Here the transmission current is 440 volts, alternating, and the constantspeed motors are operated on this current, while the motor-generator supplies 230-volt direct current for the operation of the variablespeed motors. Types of Motors power. In the first place the three types of direct-current motors should be thoroughly defined, so that the proper type may be selected for the particular tool to which the motor is to be applied. These three types are series-wound, shunt-wound, and The series-wound motor is compound-wound motors. one in which the . Mainly from an article by Georgo II. winding is in armature circuit, armature passes field series with, or forms a direct continuation of, the so that all of the current that passes through the Hall in MACHINERY, June, 1912. 347581 No. 4 llo-^MOTOR DRIVE The amount of current drawn from the line also through the fields. by a motor depends upon the work, or horsepower, which the motor It therefore follows that in the series motor the is developing. strength of the fields will depend upon the load which is placed on the aotor, and as the speed of the motor depends inversely upon the field strength, the speed of the series motor will be inversely proportional to the load. Since the speed of a motor also depends upon the voltage that is impressed upon the armature, the speed of a series motor may be controlled by introducing resistance in series with the armature, and this is accomplished by means of a controller which is used also for starting the motor. The use of the controller enables the operator to start the motor slowly under light loads, and also prevents too great a flow of current when starting under heavy loads. The characteristics of the series motor are heavy starting torque and a speed dependent upon the load. The shunt-wound motor is one in which the field winding is connected across the main lines, or is said to be in shunt with the armature circuit. The amount of current passing through the fields proportional to their resistance, and, except in the case variable-speed motor which will be treated later, remains This results in a practically constant under all conditions of load. is inversely of the constant-speed motor whose output, in horsepower, is dependent upon The the current, in amperes, which passes through the armature. characteristic of the shunt-wound motor is approximately constant speed under all conditions of load. The compound-wound motor is one having both a shunt and a The shunt field is connected to the main line series field winding. as in a shunt motor, while the series field is in series with the armature and carries all of the current passing through it as in the series motor. The field of an average compound motor is composed of about eighty per cent of shunt winding and twenty per cent of series winding, although this proportion may be varied to suit the class of work for which the motor is to be used. The speed of a is more nearly constant than that of a series motor, but the drop in speed from no load to full load is considerably more than in a shunt motor, owing to the action of the series part of the The characteristics of the compound motor partake of winding. those of both the series and the shunt motors in about the same degree as the relative proportion of the two windings composing the compound motor field. Selection of Direct- current Motors for Factory Use* The prospective purchaser should ascertain accurately the desired speed or speeds of the machine to be driven, and the maximum horsepower as well as the average horsepower required to do the work. The speed or speeds of the driven machine may be ascertained by tests conducted with an experimental motor, or from data furnished by the Often builder of the machine, where such information is available. * Abstract of an article by Earle D. tember, 1911. Jackson in the "Engineering Magazine," Sep- APPLICATION OF MOTORS TO MACHINE TOOLS 5 motor drive is to replace a steam drive, or individual motor drives are to replace an existing motor-driven group drive, in which cases the speeds are easily determined. the Horsepower Required to do the work should be determined The purchaser may rent an experimental power required, which is probably the The group drive gensolve the problem. testing be done, as the amount of power The horsepower required as accurately as possible. motor and ascertain the most satisfactory way to requires that this required under actual conditions erally for a group of machines of difand sizes is problematical, and the information cannot be obtained from the machine manufacturers as can often be done in It should be rememthe case of an individually driven machine. bered in this connection that from the input to the test motor as measured with a wattmeter, or with a voltmeter and ammeter, should be subtracted the test-motor losses, as the motor to be purchased ferent kinds rated on horsepower output or brake-horsepower. Money spent the accurate determination of the amount of power required is wisely expended a fact often overlooked by the factory manager. Machine-tool builders, motor manufacturers, and central stations is in are often called upon to supply the information as to how large a motor should be. Without accurate data, the machine-tool builder often overestimates the horsepower required for driving his tools, in order to be on the safe side, with the result that the motors run at one-quarter duced to efficiency. one-half load day The electrical and day in losses, together out, at greatly re- with interest and depreciation on the unnecessary extra investment, may amount to It certainly behooves a considerable sum in a large installation. the machine-tool builder to have on hand (and, of course, many of them do) accurate data acquired from carefully conducted tests, covering the performance of his motor-driven machines under all conditions of load and speed. The motor manufacturer often has in his own establishment in- dividual maciiine-tool drives and group drives similar to those of the prospective purchaser, in which event he can supply the necessary information as to the size of the motor. Many up-to-date central amount of data on power required for difmotor drives, derived from actual tests under working conditions, which are always available to a prospective power consumer. The piece-worker requires a relatively larger motor for the same tool than does the operator working by the day. In the former case, heavy cuts at the higher speeds will be the rule, together with quicker starting and more continuous running of the motor, as the pieceworker crowds his machine to the limit, and must be provided with ample motor capacity. Nothing is more discouraging to a workman than to find out that the motor will not perform all the work he stations also have a vast ferent requires of it, or is continually giving trouble. No. 6 115 MOTOR DRIVE Group Drives* A few years ago when the electric motor drive began to take a prominent place in manufacturing plants, many factories changed from the old method of belting the engine to a large drive shaft, which was connected by belts to long lines of shafting throughout the plant, to the individual motor drive having a separate motor attached to each machine. The owners soon discovered that this made a very expensive installation, and this form of drive, although -the most flexible, is gradually giving way to the group drive for light machine shop work. In the group drive a motor drives a short length This arof lineshafting which, in turn, drives the machine tools. rangement makes the first cost considerably less than that of the individual motor drive, and if planned systematically it is almost as flexible as the latter method. The best arrangement for the group drive is to divide the machine shop into small units, having a motor for each department or The lineshafting should be as short as each kind of machines. possible and the motors placed in accessible positions, so that they can be watched and easily replaced in case of a breakdown. A small platform makes an excellent mounting for a motor, as it can be easily Experience has proved inspected and removed if found necessary. that motors suspended from the ceiling do not receive as careful attention, and a further disadvantage of this method of mounting lies in the fact that the motors are difficult to replace when set up in this way. With the proper equipment, a motor can be removed from a platform and a new motor installed in less than fifteen minutes. By carefully planning a group drive system, all the lineshafting can be run at the same speed and a standard size motor adopted for the entire shop. This does away with the necessity of carrying a number of different sized motors in stock and standardizes the motor equipment of a factory. impossible to obtain reliable data for figuring the proper to drive machine tools. During the installation of mechanical equipment in an automobile engine factory, the machine shop was carefully laid out and a copy of the drawing, together with the sizes of machine tools, kind of work, speed and other technical information were sent to the different machine tool builders with the request that they give the exact power requirements for their machines when operating on the group drive system. The replies were carefully It is often size of motors tabulated and after a careful analysis, it was shown that machine tool builders were giving the same results for group drive as for the individual drive, overlooking the fact that some of the machines would be idle and others consuming only a small amount of power at the time when the remaining machines were absorbing the maximum amount of power. These .conditions all tend to equalize one another, so that the average power used by each machine would be considerably less for the group drive than the maximum power demanded for the individual drive. From an article by Harry C. Spillman in MACHINERY, June, 1913. APPLICATION OF MOTORS TO MACHINE TOOLS No. 8 115 MOTOR DRIVE Careful tests which have been made since the machine shop was placed in operation show that the shop takes less than one-fifth of the power recommended by the machine tool builders, or in other words, they were figuring over five times too high for the group drive. The accompanying shows that the table gives lineshafting the and results of the countershafting tests. consume It also thirty per cent of the total power, and the total friction losses absorb seventytwo per cent of the total power. This makes a forty-two per cent loss of power from the countershafting to the machine tools, and only twenty per cent of the total power is utilized in doing work. The In the table electrical loss shows eight per cent of the total power. Total average power per there are two items mentioned as follows: machine, deducting idle machines; total average power per machine, These items include all the mechanical including idle machines. power of that department, such as lineshafting, countershafting, machine friction and power consumed in doing work on the machines. In the first case this total power is equally divided among all the machines which are in operation. In the second case it is divided equally among all the machines, both running and idle. The electrical losses are omitted in all cases. Having determined the speeds of the driven machines and the horsepower required to do the work under all conditions, a knowledge of the various types of direct-current motors is the next essential in order that a motor may be selected which will fulfill the conditions required of it in the most acceptable manner. Selection of Motors To determine the type classes of tools in the of motor to be employed for the different machine shop, the character of the power re- quirements of the tools should be carefully analyzed. In the case of lathes, boring mills, milling machines, etc., in which the work of cutting is continuous, it will be seen that the tool is required to run at a speed which can be adjusted to the character of the work being machined, and when so adjusted will remain practically constant. the tool is usually started before the work of actual cutting that no excess of power is needed to start. The foregoing requirements correspond to the characteristics of the shunt motor, and for this class of work this motor should invariably be used. Also, begins,, so In the case of planers, shapers, slotters, etc., the work is intermittent, being far greater at some portions of the stroke than at others, and for this class of work the compound motor is best suited. The same type of motor is also used for the operation of punches, shears and other tools having heavy flywheels, as the motor will slow down at the period of greatest load, which is just after the The actual cut is effected through the completion of the stroke. inertia of the flywheel, and the maximum load on the motor is that of accelerating the flywheel and bringing it back to normal speed after it has carried the tool through the work. APPLICATION OF MOTORS TO MACHINE TOOLS 9 When operating hoists and cranes, the motor must be started under the full weight of the load to be handled and at the same time slowly enough to prevent the shock of too sudden acceleration. These requirements are best met by the series motor with a controller having a heavy starting resistance, as it provides high torque at low speeds. This type of motor is also used for auxiliary purposes, such as raising the cross-rails of planers and boring mills, traversing the carriages of large lathes, and elevating the tables of horizontal boring mills. Types of Motors for Different Requirements The general classification of direct-current motors now included in the standard product of nearly all motor manufacturers is as follows: Approximately constant speed, no load to full load j Semi-constant speed, full load Adjustable speed, proximately adjustment, no load to ( Compound motor. remaining apfor one load Shunt motor. Shunt-commutating pole motor. \ constant no j to /- \ full J ' load Adjustable speed, semi-constant for one adjustment, no load to full load ( J Shunt motor, with adjustable field resistance. Shunt-commutating pole motor with adjustable field resistance. Compound motor, with shunt field resistance adjustable - ( Varying speed, varying with the load Series motor, j ) Series-commutating pole motor. Constant-speed shunt motors are, of course, used for the operation of groups of machines that are driven by a common countershaft, but for individual drive the constant-speed motor is little used, as one of the greatest advantages of individual drive is the ability to vary the speed of the tool to suit the requirements of each piece being machined. This naturally brings up the question as to where the line should be drawn between tools that should be arranged for group drive and those which may advantageously be equipped with individual motors. No fixed rules can be laid down in answer to this question, but, in general, it is customary to group the smaller tools, as the initial expense of separate equipments for such tools bench tool grinders, emery wheels, and sensitive drills, In the exceeds the cost of the tools themselves. tool-room, also, the value of individual equipment is questionable, as the work on each tool is intermittent and there is not the demand for the high efficiency from the tools that obtains in the case of tools used in the manufacturing departments. If the product of a given tool is especially valuable, or forms a very important part of the shop's output, the first cost of the drive is of minor consideration, and an individual equipment which will secure the greatest output is warranted. as drills, often equals or 10 No. 115 MOTOR DRIVE Variable- speed Motors Variable-speed motors, in the generally accepted use of the term, are, strictly speaking, adjustable-speed motors, in that the speed may be adjusted by means of a controller. There are two methods common in complished. practice by which this adjustment of speed may be acThese are known, respectively, as armature regulation and fieki control. The first method consists of introducing resistance in series with the armature circuit, thereby reducing the voltage that is impressed on the armature. With constant field strength, as in a shunt motor, the speed of the motor will be directly in proportion to the impressed If the load on a motor remains constant, the speed will voltage. be inversely proportional to the resistance inserted in the circuit, as the torque is in proportion to the current in amperes, and the From the voltage equals the amperes divided by the resistance. foregoing it will be seen that if the motor load varies, the voltage and, therefore, the motor speed will, with a fixed resistance, vary with the load. of the motor when armature control is the torque, or turning effort, is proportional to the amperes drawn by the motor, while the horsepower is a function of the of the volts and the amperes. Thus a motor developing a * product Now, consider the output employed; given horsepower draws from the line a definite amount of current and produces a torque corresponding to that horsepower. If, now, we cut the speed in half, by halving the impressed voltage, while the torque remains the same, the product of the volts by the amperes will be but one-half, and the motor will be delivering but one-half its former horsepower, although it will be drawing just as much current as when delivering the full horsepower. Thus it will be seen that this method of control is uneconomical and gives a speed varying with the load, while the demand of most machine tools is for a drive that will give a desired speed regardless of the load. In employing the method described it is almost impossible to secure slow motor speeds with very light loads. For this reason this method of control is but little used in connection with machine tools. The second method, that of field control, is most generally used for motors employed in the operation of machine tools. With the voltage impressed on the armature constant, the speed of a motor be inversely proportional to the strength of the fields. This strength is directly proportional to the ampere-turns in the field, and as the actual turns of wire must remain constant, the ampere-turns may be easily regulated by inserting resistance in series with the field winding and thus decreasing the current in amperes will field passing through the field. The torque of the motor is, in this case, proportional to the field strength, and, as the field strength varies inversely as the speed increases, the horsepower of the motor will remain practically constant. Considering the average class of tools, such as lathes, boring mills, we can readily see that the foregoing motor characteristics etc., APPLICATION OF MOTORS TO MACHINE TOOLS 11 correspond to the requirements. When the cutting tool is run at a high speed, the cut taken by the tool is light, and when taking heavy cuts, the speed is slow, thus calling for a practically constant horsepower throughout the working range of the tool. As the field current is but a small proportion of the total current used by the motor, the total current consumption of motors using this type of control is practically in proportion to the work being done, so that this is an economical method. The speed, also, being regulated field strength, is independent of the load, so that for a given controller position it will be practically constant regardless of the power developed. As a matter of fact, the shunt motor with constant by the field strength will vary about 5 per cent from no load speed to full load speed. Open or Enclosed Motors The question whether to employ the open or enclosed motor often The metal covers of closed motors reduce the efficiency and arises. capacity of the motor by preventing free circulation of air around the active elements of the motor. Working conditions will usually decide whether it is possible to use the open motor, which is, of course, the desirable practice, or whether the presence of excessive dust makes it necessary to enclose the moving parts of the motor The partially or semi-enclosed motor should partially or completely. not be placed in a concealed position for the reason that it is then certain to be neglected in an ordinary factory. The perforated covers and wire screens will close up by dust and dirt, and as the result the semi-enclosed motor becomes virtually a totally enclosed motor with a semi-enclosed rating and consequent trouble. General Considerations Vertical motors are made in a number of sizes, but are only to be makes it apparent that they possess great advantages over the standard or horizontal type, as vertical motors are troublesome to keep in running order and They are not generally kept in stock by require greater attention. local dealers, and the motor, as well as repair parts, must be replaced from the factory stock at the risk of the usual delay in shipment. Manufacturers' standard sizes and speeds of motors should be chosen recommended when the nature of the drive possible, in preference to motors of special sizes and speeds, as prices, time of delivery, and general performance of the former In will be found to be more favorable than those of special design. many cases, it will be found impossible to select from the standard wherever and speeds of a single motor manufacturer only, all the motors which are required, and in this case there is no valid reason why the order should not be divided up and the motors purchased from the builders whose standard product meets the required conditions. The direct-current voltage now practically standardized for factory use is 220 volts. This voltage is both economically and operatively superior for direct-current motor systems to that of 110 volts somesizes times employed. No. 12 115 MOTOR DRIVE Types of Drives Having determined the horsepower and selected the type or types of direct-current motors desired, the best means to employ in driving the machines is the next problem that is confronted. In considering a belt drive, a greater pulley reduction than 5 to 1 is not to be recommended. Idlers to increase the arc of contact, or countershafts between the motor and the driven machine to reduce the initial speed of the driver, are doubtful expedients, unless the amount of power used is very small. It is an easy matter to design a belt 6>ive of this kind in which 20 to 30 per cent of the power of the motor is wasted between the motor and the driven machine. Direct-connected drives, gear drives, and silent chains constitute a list of positive drives from which it should be possible to select a satisfactory method of driving a machine from a motor, in which The safety, reliability, and economy of operation are all present. direct-connected drive is the ideal drive, as it eliminates all interIn a great many cases, howmediate power-absorbing apparatus. ever, the use of the direct-connected drive necessitates the employment of a special motor. It is unfortunate, in this respect, that machine-tool builders and motor manufacturers often disregard each other when it comes to the selection of standard speeds for their respective machines, although they are collaborating more than they The silent chain as a means of driving machines did formerly. The early types of silent chains were is coming into wider use. rapidly depreciated, and in many installations were far In point of efficiency, the silent-chain drive "silent." stands next to the direct-connected drive. The main objection to the gear drive is its excessive noise, but this may be overcome to a large expensive, from being degree by the use of a rawhide pinion. Specifications Specifications should be drawn which state in detail the number of motors required, the horsepower of each motor, the desired motor speed or speeds, together with the speed or speeds of the corresponding driven machine, and the name or description of the machine, giving the number of hours of its probable use per day; whether the motor is to be of the open, semi-enclosed, or enclosed type; the line voltage; details of the motor drive, including pulleys, gears, chains and sprockets, of both driver and driven machine; and whether the motor foundations are to be included in the contract price. Specifications should be submitted to at least three reputable motor manufacturers for quotations, giving cost complete in the case of each separate motor, weights and mechanical sizes of motors offered, efficiencies at one-quarter, all one-half, three-quarters, load, commutation at all and full loads, for speed regulation from no load to full loads and speeds, temperature rise, overload ranges of speed called for, capacity, times of delivery, and description of all starting and field or other rheostats to be furnished, as well as complete description Each one of the foregoing items should be known, of each motor. APPLICATION OP MOTORS TO MACHINE TOOLS if intelligent comparison and may also call for a test of each selection are to be made. The 13 speci- motor purchased, to be made by the purchaser or his engineer after the motors are in place and before final acceptance, to demonstrate whether or not all of the required conditions have been fulfilled. fications TABLE I. Frame TYPICAL LINE OF VARIABLE-SPEED SHUNT MOTOR RATINGS No. 14 115 MOTOR DRIVE any time of the day the amount of power used. These instruments, moreover, can be moved from place to place, until every motor in the shop has been included, thus acquiring valuable data for shop This is especially valuable immediately after a drive is inrecords. stalled as a means of ascertaining whether or not a motor of proper size and characteristics has been selected. Application of Motors to Machine Tools Considering the application of motors to specific tools, we can The first class best divide the problems presented into two classes. comprises those tools in which the removal of metal is continuous, The second class contains such as lathes and drilling machines. those tools in which the removal of metal is intermittent, as with and slotters. For use with machine tools of the first class, variable-speed shunt motors will be employed, and the next point to be considered is the planers, shapers BELT DRIVE Fig. 1. Comparison of Belt MOTOR DRIVE Machinery and Motor Drive of Engine Lathe speed range for which they must be adapted. For a given horsepower the size of the motor will be inversely proportional to the minimum speed, and as the use of gearing or chain drives places a practical limit on the maximum speed, the minimum speed, and consequently The best the size of the motor, will depend upon the speed range. idea of the actual results that can be obtained with field controlled motors may be secured from a table showing the outputs and speed ranges of a standard line of such motors. Although different makes vary somewhat in their ratings from those given in Table I, this gives a correct average of the various lines upon the market. With a wide motor speed range, a larger part of the working range of the tool is, of course, covered than with a more limited range, but as it is impracticable to cover the entire working range of such a tool as a lathe or boring mill by a corresponding motor range, it is customary to use one or more mechanical speed changes augment the electrical range. The problem is, therefore, to select a motor speed range that will give satisfactory results without in- to APPLICATION OF MOTORS TO MACHINE TOOLS 15 Actual experience has elaborate mechanical changes. under average conditions, a motor speed range of 2% to 1, or 3 to 1, together with two mechanical speed changes, will cover practically any range of speed that is obtainable with a cone-pulley drive on any of the ordinary types of machine tools. To show just how this works out, we will take an actual case of an engine lathe provided with a five-step cone pulley. In making too volving shown that, applications to old lathes it is desirable to retain the back-gearing, while the cone is removed from the spindle sleeve and two gears mounted thereon as shown in Pig. 1. The motor is placed above the headstock, on a bracket, and is geared to an intermediate shaft run- ning directly below. This shaft carries two gears, A and B, either of which may be meshed with its corresponding spindle gear E or F. The engraving shows a comparison of the spindle speeds obtained with the original belt-drive and those that may be secured by the Machinery Fig. 2. Plate and Brackets for Supporting Motor application of a 3 to 1 motor. Not only is the range of spindle speeds increased, but whereas in the belt range of 75 to 580 revolutions we obtained but five distinct speeds, with the motor and a twenty-step controller we obtain a range of 75 to 675 revolutions with forty running speeds, varying by about 6 per cent. This calculation considers only the range of speeds obtained without the backgearing of the lathe and the range is, of course, repeated at correspondingly lower speeds by the introduction of the single or double different back-gearing with which the lathe is provided. Just here it may be well to point out one of the greatest advantages It will be noticed that the belt drive, which of the motor drive. gave a range of 75 to 580 revolutions, did so in five steps varying by If the lathe is running on, let us say, at least 60 per cent per step. the fourth step it may be found that the cutting speed, owing to the size of the work or the condition of the tool, is not as high as could To jump to the next speed, however, be used to best advantage. increases the cutting speed over 60 per cent, which will be too much, No. 16 115 MOTOR DRIVE and the work will consequently be done on the fourth step, although be 30 or 40 per cent below that at which the best economy would obtain. With a motor drive giving speed increments of 6 per cent or less, the work can at all times be done at practically the best speed, and the increase of output that will be thus secured will be this may readily appreciated. Another typical case shown where the advantage of the motor drive is in the facing of a large surface such as a flange. The ordinary practice is to adjust the speed properly for the cut at the largest diameter and then cover the entire surface at this speed, clearly is although, as the tool approaches the center, and the cutting diameter will be too low. To be sure, an becomes smaller, the cutting speed Machinery Tig. 3. Motor Equipment of Horizontal Boring Machine shift his belt from time to time as the progresses, but this is practicable only after a reduction in speed of the 60 per cent made necessary by the large intervals between With the motor drive, requiring only the slight the cone steps. energetic lathe hand can work movement of the controller handle to adjust the speed, the operator will continually "notch-up" his controller, so that the entire surface will be covered at practically maximum speed. In making number are this application to belt-driven lathes, if a considerable it will be found economical to make a pattern alike, and cast a bracket that can be attached neatly to the headstock. This bracket will be provided with bearings for carrying the intermediate shaft below the motor. As this entails expensive pattern work, it will be cheaper, if the number of similar lathes is small, APPLICATION OF MOTORS TO MACHINE TOOLS 17 No. 18 115 MOTOR DRIVE wr ought-iron brackets to support a plate on which the motor can be placed. This plate will require a very simple pattern which can be readily changed to suit different sizes of motors for various tools with which it can be employed. Fig. 2 gives a general idea of such a bracket, and indicates the method of supporting it over the headstock of a lathe. The same scheme works out very satisfactorily for applying motors to other types of tools, although certain modifications may be needed in order to obtain the best results. Fig. 3 shows a horizontal boring machine which has been equipped in a manner similar to that of the lathe. The cone is replaced by the two gears C and D, but in to use Fig. 6. Motor applied to a Vertical Milling Machine this case the pinions A and B are fast on the intermediate shaft, while the gears C and D are free to slide on a feather in the spindle quill, so as to be engaged at will with their corresponding pinions. The intermediate shaft, in this case, is carried in brackets in front of the motor rather than beneath it. Fig. 4 shows how this type of drive, with underneath intermediate shaft, may be applied to a radial drill, and the same arrangement will be found readily applicable to upright drills. The halftone Fig. 5 shows the application of a motor drive to a The arrangement is extremely simple, consisting large boring mill. of replacing the driving pulley with a chain sprocket, and driving APPLICATION OF MOTORS TO MACHINE TOOLS 19 from the motor which is set at any convenient near-by point. The two pinions for the gear changes are seen in front of the original driving gears of the mill. For operating milling machines the most successful applications The motor may be placed on a floor are made with chain drives. base attached to the base of the machine, or it may be bracketed onto the top of the machine, illustrations of both of these arrangements being shown in Figs. 6 and 7. The latter motor position is preferable, as the chips from the machine necessitate the use of a fully enclosed Fig. 7. motor if it shown are is Motor Equipment of Universal Milling Machine placed below the table of the machine. The examples mainly as suggestions, as the construction and offered speeds of each particular tool will call for separate consideration. Horsepower Required Having decided upon the desirable speed range and the mechanical details of the application, followed, as so many the next problem is the selection of a this point no positive rules can be For the factors enter into the consideration. motor of suitable power. Upon 20 No. 115 MOTOR DRIVE operation of a lathe for general work a 5-horsepower motor might be fully adequate, while for driving the same size of lathe for manufacturing purposes, and using only high-speed steel at maximum cutting speeds, a 10- or even a 15-horsepower motor might be needed. For running a milling machine, for example, it is obvious that a much smaller motor could be employed if the machine were to be used only for finishing work, with light cuts, than would be needed on the same machine if it were to be used for heavy roughing work. Any tabulated data, therefore, based on the size of the tool, must necessarily give averages only, and should be modified by one's best judgment, based on the actual conditions obtaining. TABLE II. AVERAGE POWER REQUIREMENTS OF ENGINE LATHES Character of Swing, Inches 12 16 18 20 24 Work Character of Work APPLICATION OF MOTORS TO MACHINE TOOLS 21 Application of Motors to Planers, Shapers, etc. The second class of tools comprises those in which the cutting stroke alternates with a non-cutting return stroke, as in the case of planers, shapers and Blotters. Here the successive operations of the shown in Pig. 8. The highest points in the As the those which occur when reversing takes place. return stroke is taken at two or three times the speed of the cutting stroke, the power required to accelerate the bed of the planer or the head of the slotter to its return speed usually constitutes the greatest power demand, while a somewhat lower point is reached on the reverse to cut. It is not, however, necessary to power the tool to tool occur in cycles, as cycle are TABLE Swing, Inches 18 24 36 42 IV. AVERAGE POWER REQUIREMENTS OF DRILLING MACHINES Upright, to to iy2 to 2 to 1 1 No. 22 MOTOR DRIVE 115 and often a range 1% found such wide speed ranges as the shunt-wound motors, since any considerable weakening of the shunt field so changes the relation of the shunt to the series winding as to cause the motor to attain the nature of a series ficient for nearly all cases satisfactory. of to 1 will be Compound-wound motors are not used for motor, which is undesirable. In some new planers on the market, pneumatic or magnetic clutches are used for reversing, but in equipping old tools it will be found -REVERSE TO RETURN -REVERSE TO CUT RETURN L CUT Machinery Fig. 8. Cycle of Operations of Planer A practicable to retain the cross-belt drive with belt shipper. diagram of such an application is shown in Fig. 9. The motor is mounted on the top of the planer housings, and geared to a counter- more shaft which carries the driving pulleys. The use of the flywheel on is most desirable, as it greatly relieves the motor on the peak loads. By mounting it on the motor shaft, instead of on the motor shaft Fig. 9. Motor Equipment of a Planer the slower running countershaft, the flywheel effect is much increased. It is also well to provide the driving pulleys with extra heavy rims for the additional flywheel effect that they will produce. On Blotters it will usually be found convenient to place the motor on a bracket on the side of the frame, and employ a gear drive, while shapers may be either geared or chain-driven, or belt-driven by using an idler as in Fig. 10. shown APPLICATION OF MOTORS TO MACHINE TOOLS The remarks regarding the power requirements tools apply 23 for constant-cutting with equal force to this class of machines. The figures in Table VII are based on the use of two tool-heads and a return speed having a ratio to the cutting speed of about 3 to 1. If more than two heads are used, or if the planer has a longer bed than that given, the horsepower should be somewhat increased. In addition to the motors employed for operating the tools of the above classes, there are a number of uses for auxiliary motors as will Fig. 10. Motor Equipment of Belt-driven Shaper be noticed in some of the illustrations. In Pig. 3 is shown an auxiliary motor used for raising and lowering the table of a horizontal boring machine, while Pigs. 9 and 11 show similar motors employed for elevating and lowering the cross-rails of a large planer and boring On large lathes auxiliary motors are often used mill, respectively. for moving the tailstock along the bed, and they may also be arranged for turning the turret heads on heavy turret lathes. Series motors only are used for these purposes, as they are always started under full load, and have their speed regulated by armature No rules can be laid down for the power of these auxiliary motors, but the requirements are comparatively small, from 2 to 5 control. horsepower covering all of the above cases except for the very largest tools. The time of duty is very short. The drives are invariably by means of gearing to the operating shaft, one set of reducing gears frequently being needed to reduce the speed of the motor sufficiently. These motors should never be belted, for if the load should be thrown off, by breaking the belt, they will run up to a dangerously high speed, and may be badly damaged. Another type of auxiliary motor is shown 24 No. in Fig. 11, where large boring mill. 115 MOTOR DRIVE is used to operate the slotting attachment of a Such a motor should be compound wound and the it data relative to Blotters are applicable for such motors. TABLE Width between VII. AVERAGE POWER REQUIREMENTS OF PLANERS APPLICATION OP MOTORS TO MACHINE TOOLS 25 supplied as a separate unit which is connected to the drum by wiring. The controller should be mounted on the tool at any point to best suit the convenience of the operator. In the case of long lathes a good arrangement is to mount a handle on the lathe apron, and this, by means of gears and shafts can readily be arranged to operate the controller when mounted on the end of the lathe bed. The resistance, if separate, should be mounted near the controller in order to economize in wiring, but it should be so placed as to be exposed to the air and at the same time protected from dirt and Do not cover up the resistance or place it cuttings from the tool. inside of the tool frame, but select some place above the table of the tool, away from the path of the chips. Methods of Applying Motors to Machine Tools In a paper on the Economy of the Electric Drive in the Machine Shop, read at the April, 1910, meeting of the American Society of Mechanical Engineers, Mr. A. L. De Leeuw reviewed the conditions which must be considered in connection with the equipment of a machine shop with electric drive. In conclusion he gave a general idea of the mode of application of motors to machine tools, the selection of motors for different classes of tools, and the lines along which economical results may be expected. The following abstract of these conclusions will undoubtedly be of interest to mechanics in general. Bench and Speed Lathes Bench lathes should be driven from a countershaft attached to the wall or bench and driven in turn by a motor. Any kind of motor The except a series-wound or heavily compounded motor will do. object of the motor drive is to get the machine in the best possible location without regard to the location of the lineshafting. A number of these machines may be driven by a common lineshaft, which in driven by a motor. Speed lathes should be driven from a countershaft located under the In the latter case a variablelathe, or by a direct-connected motor. speed motor is to be preferred, if direct current is available. Motor drive is recommended when the machine is used in the assembling department, as the machines may then be placed where they are most needed; the crane service would also interfere with countershafts. There will be no material gain, if the machines are to be used for ordifrurn is nary shop operations. Engine Lathes Various methods of driving engine lathes by motors are in use. Some makers furnish motor-driven engine lathes as standard equipment. Some have a headstock with a limited number of speeds, and depend on a variable-speed motor to fill out the speeds of the lathe. Others apply a constant-speed motor, or one with a limited amount of variatIn general, the use to which this ion, to an all-geared headstock. class of machines is put in the shop would naturally lead to group No. 26 115 MOTOR DRIVE There is no material advantage in the individual motor drive, the machines are used for regular manufacturing operations, except where the location demands individual drive. drive. if Heavy Engine Heavy engine a lathes, direct-connected Lathes, Forg-e Lathes, Etc. and lathes motor. of similar types should be driven The motor should be by direct-current, as these machines are too heavy to permit a convenient all-gear drive. no direct current is available and there is only one machine of its If and this is used for an occasional job only, an alternating-current motor could be used, leaving a wide gap in the speeds. If these machines are used for manufacturing purposes, it would pay to install a small synchronous connector. The speed range in the motor class in the shop, does not need to exceed two to one, though a wider range is better if obtainable without complications or great expense. The position of the motor should be low, as the vibrations in the motor-support have a decided influence on the capacity of the machine, as well as on the rebill. The output of this class of machines may easily be increased from 20 to 25 per cent by motor drive. Further advantages of the motor drive are the possibility of placing the machine in the line of the routing of heavy work, and of placing it immediately under the pair be reached with a belt-driven gallery, if the construction of the shop lends itself to this arrangement, but the same convenience as that of the motor drive cannot be obtained. traveling crane. This latter object may machine by placing the headstock under the Axle and Wheel Lathes the greatest importance that axle lathes and car and driving wheel lathes should have the highest possible efficiency, and the most It is of These machines are mostly used in locomotive and car repair shops, where time saved does not mean merely the saving of wages, but each day gained means an added day in the convenient location. earning capacity of the engine or car. It is, therefore, important that these machines be motor-driven whenever installed in a railroad repair shop, though this does not mean that they should not be so driven if used for manufacturing. Direct current should be used. The economy of the motor drive should not be figured in increased output, but in reduction of time required to repair an engine or car. Chucking Lathes Generally speaking, there is little reason why a chucking lathe should be motor-driven. Most chucking lathes are provided with the necessary mechanism to shift speeds quickly. A few types handling large work may be motor-driven to advantage, though practically the only advantage lies in the fact that small gradations in speed can be thus obtained. Such machines, therefore, require a variablespeed motor. Automatic Screw Machines Small automatic screw machines are generally group-driven. Large machines may be individually motor-driven to good advantage. The APPLICATION OP MOTORS TO MACHINE TOOLS 27 larger sizes have generally one or two speeds for one piece of work, though these speeds may be varied when the machine is reset for a new piece of work. The speed given to the machine must naturally be proportional to the largest diameter to be turned, or in other This will reduce the speed for words, to the size of stock used. some of the operations, such as drilling and reaming, far below the economical speed. The amount of time saved by the application of the variable-speed motor may be considerable. Where the construction of the machine permits, two motors, one for feed and one for speed, would give still better results. In all cases variable-speed motors should be used. Drill Presses and Boringr Machines The only reason why the sensitive drill should be individually motor-driven is that it is often usec in an assembling department, where height of ceiling and crane service would make a belt drive 1 . awkward Most sensitive drills have, in themselves, or impossible. the speeds required for their work, so that any type of motor The motor may either be directly applied to the will be adaptable. machine or may drive a countershaft on a stand; or it may be placed on the floor by the side of the machine, in case the machine carries its own set of cones or other variable-speed device. Generally speaking, the upright drill is used for manufacturing There operations and does not require frequent changes of speed. are, however, many exceptions, for instance, where upright drills are used to do all the operations on a piece by means of a jig. In this all case frequent changes of tools, and, therefore, of speeds, are required, and an individual motor drive, whether direct-connected to the ma- chine or operating on the countershaft, is of the greatest benefit. No great benefit can be derived from a constant-speed motor with this Radial 'drills may be considered to present the type of machine. same requirements as upright drills. There is an additional reason why radial drills should be motor-driven they are often used in the neighborhood of the assembling floor. When the work for boring machines is specialized and the machines perform only one operation, there is no good reason why motor drive should be preferred to belt drive. Where, however, the machine is used for a multiplicity of operations, such as drilling, boring, reaming and facing, a motor drive is beneficial if a variable-speed motor is used. The range of speed of the motor should be as wide as possible, so that no gears may have to be shifted for the entire set of operations on a single hole. Especially where a boring machine is used for facing, this variable speed will be found highly economical. Grinders Grinders, in general, require so many various movements driven from countershafts that it is hardly possible to apply a single motor directly to the machine; the best that can be done is to attach the countershaft to the machine and drive the former from a motor standing on No. 28 115 MOTOR DRIVE the floor or on a bracket attached to the machine. In isolated cases would be well to have one or more motors, each controlling a single it operation, attached directly to the machine. Planers, Shapers, Blotters Planers in general are not benefited by the application of a motor, the motor only complicates the difficulties of a planer drive. However, large planers which must be placed under a crane give better results when motor-driven on account of the facility of handling the work. Another possible advantage when using a variable-speed motor and controlling the speed of the motor at the end of the stroke is that much higher return speeds can be obtained in connection with any desired cutting speed. What is true of planers is also true of shapers and slotters. Local conditions may make it advisable to drive them individually by motor, but generally speaking, there are no great advantages to be gained with this drive. as Milling Machines The larger sizes of knee-and-column type machines, will give the best results if the motor if motor-driven, of the variable-speed type, are used for gang work. This is is especially where these machines due to the fact that the speed of the mills is dependent on the largest cutter in the gang, while the feed is dependent on the smallest cutter, not counting the limitations due to the nature of the work. It is therefore important that the speed should be as close to the permissible limit as possible. When applied to this type of milling machine, the motor should be as low down as possible, as vibrations in the machine have a marked effect on the quality of the finish. In practically all cases the planer type of milling machine should be motor-driven, in order that it may be located under a crane. It is not so very important, however, whether the motor is of the constant-speed or variablespeed type. Punches, Bending- Bolls, Shears, etc. This class of machinery, used largely for boiler, bridge, structural iron and ship-building work, is generally placed in high shops and under cranes, and in locations and directions most convenient for the routing of the work. The shops in which it is placed are generally large and contain a relatively small amount of machinery, so that the amount of transmission gearing required is large in proportion to the amount of machinery. It is for this reason advisable in almost all cases to drive this class of machinery by an electric motor, which, of course, does not need to be of the variable-speed type. CHAPTER II WIRING ON MOTOR-DRIVEN MACHINERY Electrical wiring on the motor-driven machines furnished by even the best manufacturers is too often poorly arranged and inefficiently installed. This is because the wiring is not considered when the is designed. Its installation is usually left to some workman does the best he can. The wiring and arrangement of the control apparatus should be laid out in the drafting-room. This chapter discusses the best methods of machine wiring, describes the materials used, and gives concrete directions, rules and tables for wiring motordriven machinery. One industrial corporation which purchases many motor-driven machines incorporates the following clauses in the specifications for all such equipments: machine who 1. The machine manufacturer shall mount the motor and ling devices on the machine so that they shall and shall wire between them as hereinafter noted. control- form a part thereof, The controlling apparatus shall be conveniently arranged for 2. manipulation by the machine operator. All wiring shall be installed in accordance with the regulations 3. of the National Electrical Code^ All wiring shall be carried in wrought-iron conduit or in metal 4. conduit fittings. These shall be firmly attached to the frame of the machine. 5. So far as possible, all "live" bare metal parts shall be enclosed with metal covers. It was found desirable to makes these requirements because of the awkward practice prevailing in this respect among machine builders. the builder of the motor-driven machine, although he Frequently, mounted the motor and arranged the drive between the machine and the motor, would fail to mount the motor-starter or conIf he did mount it on the machine, in the troller on the machine. great majority of cases he would either provide no wiring between the motor and the controller, or install the wiring in such a careless, unbusinesslike manner that it would have to be reinstalled. Usually, the machine builder makes an extra charge for arranging the wiring in accordance with the above specifications; but it was found that the work was done better and more cheaply by the builder than carefully by the wire-men at the plants where the machines were installed. At the present time, when motor-driven machinery is so generally used, machine builders are paying more attention to the electrical details; but there some much to be desired. In the following will be given information that may be of value to manufacturers is still practical 30 No. 115 MOTOR DRIVE desiring to arrange and install the wiring on their machines as efIt is believed that good wiring will be appreficiently as possible. ciated by the purchaser. Rule No. 1 in the specifications given states that when the machine direct-driven the motor and controller should be considered as a Obviously, they are just as much so as is a part of the machine. If possible, the complete equipment should be shipped so that, gear. after setting up, it will only be necessary for the plant electrician to is run a pair of wires to put the machine in service. For large machines, which must be dismantled for transportation, the motor and controlling equipment must be shipped separately, and it may be necessary to dismount the conduit carrying the electrical conductors; but if the wiring has been properly connected and the conduit strapped to the machine in the erecting shop, it can easily be reinstalled. Thus, cranes, which have complicated wiring, can be taken apart, shipped, reerected and rewired with very little difficulty. The desirability of the requirements of Rule No. 2 is so obvious as to need no discussion. Rule No. 3 requires that all wiring be installed in accordance with National Electrical Code regulations. Standard fire insurance policies require that the electrical work in all plants having insurance proIt has tection be installed in accordance with these regulations. taken many years to mold the regulations into their present excellent form, and they are revised constantly to keep abreast with the advances in the art. It is therefore essential that machines which are to be installed in plants carrying fire insurance, be wired in accordance with the Code. Even if insurance is not carried, it is advisable to follow these rules, as they outline a substantial and safe method A copy of The National Electrical Code will be supplied of wiring. free to any one making request to the local Fire Underwriters' Inspection Bureau or to the Underwriters' Laboratories, Chicago, 111. Rule No. 4 requires that wiring be installed in wrought-iron conduits or in metal conduit fittings. It costs several times as much to run wiring in metal conduit (the properties of conduit are given in Table XII) as to arrange it without mechanical protection. However, it is only the first cost of conduit wiring that is high. When placed in conduit the wiring is done once for all; there is no future trouble from broken wires, grounds or short circuits, due to abraded insulation. When arranged with conduit wiring, the machine is easier to keep clean and looks neater. The conduit fittings (which will be described later) are used at points where wires issue from the conduit or where a turn in the conduit run is necessary and it is not desired to bend the conduit. In general construction, they somewhat resemble screwed pipe fittings, but they are always arranged with removable covers so that the wire is easily accessible. Conduit and fittings are attached to machine frames with either pipe straps (Table XV) or machine screws, as will be described. Rule No. 5 requires that all "live" bare metal parts be enclosed within metal covers. It is usually feasible to enclose "these parts. WIRING ON MOTOR-DRIVEN MACHINERY 31 Such enclosure prevents metallic chips from forming grounds or short and renders shock to attendants impossible. With the voltages at which machine motors are usually operated, a shock is not often fatal, but one hears of cases where men have been killed from contact with 220-volt circuits. At any rate, an electrical shock is unpleasant, and if there is a possibility of receiving one the attendant is likely to be cautious and waste time. Fire risk is reduced by enclosing "live" parts. Although the Underwriters do not require enclosure The electrical manufacturers appreciate the dethey commend it. mand for enclosed apparatus, and it is now possible to buy standard starters and controllers, for nearly all applications, that are well protected and so arranged that conduit wiring can be readily installed. circuits Wire for Motor Application wire to use for transmitting electrical energy (in lowvoltage work such as that involved in industrial-plant wiring) is determined by two requirements, viz., the cross-sectional area must be large enough to carry the current required without getting too hot, but must not be so large as to cause an excessive drop in voltage The size of However, the dispressure and consequent energy loss. tances involved in wiring machinery are so short that the latter requirement may be disregarded altogether. The only demand is, then, that the wire be big enough to obviate excessive heating. electrical The National Electrical Code specifies that all concealed wires shall be rubber-insulated and, in addition, that all wires carried in conduit All standard rubber-covered wires shall have a double-braid covering. used for voltages above 10 and below 600 have the same thickness of insulation. Copper wire is almost universally used for interior wirTherefore, if the voltage of the motor is below 600, wire for the ing. installation should be specified, for example, thus: No. 6 National Code Standard, 0-600 volts, double-braid, stranded, copper size of wire, and whether it is to be solid or stranded, is determined, as will be explained, by the horsepower output of the Electrical wire. The motor. So that wire in service will not be dangerously overheated, the Underwriters have specified a certain safe current-carrying capacity for each size of wire and for wires having different insulating maIn Table are given the safe current-carrying capacities for terials. all sizes of rubber-covered wire that the machine builder is likely to use. The sizes listed are all commercial ones and are, as a rule, readily obtainable. When the current or amperes taken by any motor is known, the size of wire to be used can be ascertained from Table X. Although Nos. 18 and 16 wires are listed in the table, the Underwriters do not permit the use, for applications such as herein treated, of any wire smaller than No. 14. It will be noted that the wires between No. 18 and No. 8, inclusive, are tabulated as "solid" and those Solid wire is that having a solid larger than No. 8 as "stranded." conductor, while the conductor in stranded wires is twisted up from several or many wires of relatively small diameter. Stranded wires are sometimes called cables. It is the usual practice in conduit work X No. 32 115 MOTOR DRIVE to specify that wires larger than No. 8 be stranded, because, if solid, they are too stiff to be handled and pulled into the conduit readily. Solid wires can be obtained, if desired, in sizes much larger than No. 8 and these are much used in "open-work" wiring. The numbers of wires in a strand given represent the practice of some manufacturers, but other manufacturers have different standards. They vary little, however, from those shown. As a rule, it is not desirable to specify the "number of wires in strand" when ordering, as the dealer may TABLE X. SPECIFICATIONS FOR WIRE AND CONDUIT ON MOTOR-DRIVEN MACHINERY Double-braid, Rubber-covered, to 600 Volts, N. E. C. S. Copper Wire, N. E. C. S. Wrought-iron Conduit WIRING ON MOTOR-DRIVEN MACHINERY are averages and may vary somewhat from name-plate ratings. Different makes of motors of the same horsepower have different ef- with alternating-current motors, and both these appreciably affect the amount ficiencies and, figures given in Table XI different power factors, of current taken. The indicate the current in each wire. That is, they show the number of amperes flowing through each of the two wires to a direct-current or to a single-phase alternating-current motor, through each of the four wires to a two-phase alternatingcurrent motor, or through each of the three wires to a three-phase alternating-current motor. Having found the current, in amperes, taken by a motor, the size of wire to be used cannot be selected without first considering another TABLE Motor of H.P. XI. APPROXIMATE FULL-LOAD CURRENT TAKEN BY ELECTRIC MOTORS (IN AMPERES) No. 34 115 MOTOR DRIVE about 25 amperes when operating at full load. To allow for a 25 per cent excess current, in accordance with the Code rule, an estimate is made thus: 31 amperes (about). 25X1.25 Referring to Table X, a No. 8 (solid) wire which has a safe carrying capacity of 33 amperes is the smallest that can be used. = The insulation on rubber-covered wire deteriorates very rapidly under the action of heat, so if it is necessary to install conductors where they will be subjected to high temperatures, wire having "slowburning" insulation should be used. Such wire, if enclosed, must be (according to the Code) in "lined" conduit. This conduit is described under the following heading. Conduit for Motor Application Wiring Wrought-iron conduit is merely standard-weight steel, or possibly in some cases wrought-iron pipe, which has been thoroughly cleaned to remove burrs and scale, and then either enameled or coated with zinc. Conduit which meets the requirements of the National Electrical Code and which has been approved by an Underwriters' inspector, is called National Electrical Code standard conduit or N. E. C. S. In Table XII are given the principal dimensions of comconduit. mercial N. E. C. S. conduit, elbows and couplings. Conduit is furnished only in lengths of ten feet. Electrical conduit is threaded with standard pipe threads and standard-weight screwed pipe fittings will fit it. In addition to the "unlined" conduit, described above, a "lined" conduit is manufactured which has a relatively thick insulating lining. The lined conduit is seldom used as it is more expensive than the unlined and the latter has given entire satisfaction. The insulating lining appears to be unnecessary, as the rubber insulation on standard wire provides excellent protection. Although its use would be prohibited by the Underwriters, there is really no objection to using commercial wrought-iron pipe instead of conduit for wiring machines. Such pipe should be carefully cleaned inside and out and every precaution taken to make sure that there are no burrs or slivers on the inside of the pipe which might cut insulation on wires. After the pipe is painted, it is almost impossible to distinguish it from conduit. Conduit elbows are formed from conduit to the dimensions indicated in Table XII. The smaller sizes of conduit can be bent cold to any desired contour, but it requires some skill to do the bending. Conduitbending machines are obtainable and their installation pays if there Both power- and hand-operated types are is much wiring to be done. manufactured. Couplings for conduit are exactly the same as screwed couplings for standard-weight pipe, except that the former are either enameled or coated with zinc and have a better finish. After determining the proper size of wire to use for supplying energy to a given motor, the size of conduit to carry it can be selected from Table X. The sizes theretabulated, for the different sizes of wire, have been chosen as the result of much experience with conduit wiring. They are sufficiently large to allow wires to be drawn in or WIRING ON MOTOR-DRIVEN MACHINERY 35 S5 o M O .2 1 I' "! ?* s-g m RS ^s bccs a O If 8 T-< TH OJ'OJ CO iC t- OS O i! si 1?3 2s 5 tS I* < G^'^oOr-<CDOCO'TC<} OOOCOCOO^OiCO II s 10 10 1O OCO5OO5CCOOOOtO .I'o!*'*c ;w S5 No. 36 MOTOR DRIVE 115 out without the application of excessive force. It is a common error to choose a conduit size so small that the wires must be pulled in with blocks 'and tackle. If this is done, the insulation be injured and withdrawal may be impossible. is likely to Conduit Fittings and Sundries Where wires emerge from conduit ends, the Code requires that provision be made so that a possible burr on the inside of the conduit will not abrade the insulation on the wires when they are being drawn TABLE Thomas and XIII. DIMENSIONS OF CONDUIT BUSHINGS All Dimensions taken from Samples. Dimensions in Inches Betts Bushings. All Size of Conduit H* Uf 2U in or out. as Conduit ends may be protected either by a bushing, such shown in the engraving accompanying Table XIII, or by a fitting, of one of the types shown in Fig. 14, equipped with a porcelain cover, The bushing should be used when the conduit terminates Pig. 12. within an enclosed outlet, junction, or panel box (see Pig. 13) which may be made of either cast or sheet iron. The dimensions given in Table XIII will prove useful in indicating what clearances are required for screwing the bushing on the end of the conduit and will also assist in determining the locations for the conduit holes. Outlet boxes usually have unthreaded holes for the conduit, as indicated in Pig. 13, but where a waterproof installation is essential, WIRING ON MOTOR-DRIVEN MACHINERY TABLE XIV. DIMENSIONS OF CONDUIT LOCK-NUTS -H T kMachtnery.N.Y. Thomas and Betts Lock-nuts. All Size of Conduit All Dimensions taken from Samples. Dimensions in Inches 37 No. 38 115 MOTOR DRIVE When the holes are unthreaded, a locknut (shown with Table XIV) is run on the end of the conduit and, after the bushing is screwed to position, the lock-nut is turned up snugly against the side of the box, binding the conduit firmly in position. It should be understood that the dimensions given in Tables XIII and XIV for bushings and lock-nuts are accurate for only one manufacturer's line. There are several different makes available, but all will measure approximately the same as those shown. the holes should be threaded. The application of conduit fittings can best be shown by an In Pig. 15 example. is illustrated a motor- driven open-side planer with the wirbetween the ing starter and the motor neatly carried in conAt the motor duit. terminal the con- ductors issue through a fitting, which is of the type shown in Pig. 14 at C, equipped with the cover shown in Fig. 12 at B. FRAME OF MACHINE PLAN VIEW The con- are so duit fittings made that any style of cover of a given pipe size will iron , sponding SCREW HOLDING BOX TO MACHINE any fit cast- of corre- pipe size. fitting The covers are held on with brass screws. 17 Fig. is arrangement SECTION A-A Fig. 13. Outlet Xachtnerv.y.Y. Box Mounted on Machine In shown an of fit- tings that might be used with the of starting type panel shown in Fig. 15, if the motor were located below instead of above It will be noted that where "elbow" fittings (G and H, the panel. Fig. 14) are arranged with metal covers, they are effectively used at turns in the conduit run, instead of bends or wrought-iron elbows. Fig. A 18 illustrates further applications of conduit-fitting elbows. very convenient feature of the fittings shown in Fig. 14 is the By means of this provision of a headless set-screw in the throat. set-screw it is possible to secure a conduit end firmly in a fitting even if the threading on the conduit is faulty or if, because of a WIRING ON MOTOR-DRIVEN MACHINERY 39 does not set up tightly in the fitting, when In this type of fitting, conduit can be secured The set-screw provides ample atwithout being threaded at all. tachment, if conduit and fittings are firmly fastened to a supporting Nor is it necessary to surface, as they usually are on machinery. An unthread conduit running into fittings like that in Fig. 16. threaded end of a conduit length is inserted in the nipple, the nut is The threaded portion of the tightened, and the conduit is secured. bend in the conduit, it in its proper position. nipple and tapered. These fittings possess several advantageous Being of sheet-steel, they are unbreakable. The fact that is split points. Fig. 14. Types of Cast-iron Conduit Fittings each fitting has several "knock-out" holes makes possible a great of combinations from a comparatively small stock of fittings number and covers. Supporting Conduit Wiring Obviously, conduit carrying conductors should be so securely supported that there can be no chance of its being displaced under reasonable conditions. Pipe straps, formed from sheet-steel and then gal- shown with Table XV, are most frequently used and 18. The dimenXV making clearance al- vanized, such as those for supporting conduit, as shown in Pigs. 15, 17 sions given in Table will be found useful in lowances and in determining the locations for the tapped holes for the round headed machine screws, with which the straps are fastened. The dimensions in Table XV are accurate only for the lines of certain manufacturers, but will be approximately correct for all makes. Another good method of supporting conduit runs is by fastening the fitting to the machine frame with machine screws, as shown in Figs. 13 and 19. The screws pass through a hole drilled in the bottom of the fitting and down into a hole tapped in the machine frame. No. 40 115 MOTOR DRIVE DRIVEN PULLEY MOTOR STARTING PANEL CONDUIT FITTING Machinery.}?.?. Fig. 15. Open-side Planer with Well-arranged Wiring KNOCK-OUT" , PRESSED STEEL BOX HOLE6 SCREW FOR I \ HOLDING ON COVER 4 HOULDER >NDUIT EXPANSION SLOT END OF HEADED OVER SIDE ELEVATION Fig. 16. SECTION A-A FRONT ELEVATION Machinery, N. Y. Details of Typical Pressed-steel Fitting WIRING ON MOTOR-DRIVEN MACHINERY 41 support a complete conduit installation by this avoid the use of pipe straps. This sort of a job presents a neat appearance. It is often feasible to method and thereby entirely Motors Arranged When for Conduit Wiring- that the "motor shall be arranged for conduit motor manufacturers will provide, without extra charge, a metal ter- it is specified certain wiring," . minal box, with a removable cover, around the motor terminals. A motor so arranged CONDUCTORS FROM SOURCE OF SUPPLY shown in Fig. 18. Such a terminal box is NOTE: permits FUSES ARE NOT ORDINARILY REQUIRED ON A PANEL TO BE MOUNTED ON A of possible and through MACHINE the best installation, its pres- ence a conduit fitting, like that at the motor in Pig. 15, can be dispensed with. A hole is provided in the minal FRAME OF MACHINE box and ter- the conduit is terminated with a bushing in the hole. Switches It is required by the National Machinery,N.TT. Fig. 17. A Neatly Wired Starting Panel Electrical Code that every motor and starting box be CONDUCTOR3 TO MOTOR protected by a doublepole cut . out (f uses or and controlled by an indicating switch that plainly indicates whether the circuit is open or closed. For motors exceeding in capacity horsepower, a double-pole switch is required, but a circuit breaker) % may be used for smaller ones. It is always advishowever, to use the double-pole type, as through its use both sides of a circuit are rendered dead when tha switch is open. single-pole switch able, For handling currents up to 20 amperes, or thereabout, the best switch to use is of the indicating-snap type, shown in Fig. 20. This type can readily be obtained as either single-pole, for direct-current and single-phase alternating-current motors, or triple-pole for threeAll "live" parts are effectively enclosed in a formed sheet-metal cover (Fig. 20) which is lined with an insulating material. phase motors. By unscrewing the composition handle, the cover can be quickly re- No. 42 moved for 115 MOTOR DRIVE making connections. Wires enter switch the through holes in the back of the porcelain base. A revolving dial, bearing the legends "On" and "Off," indicates whether the switch is open or closed. An in indicating-snap switch mounted on a conduit fitting as shown All 21 makes a rugged and safe switching combination. Fig. wires and turers make conduit "live" parts are Some manufaccompletely enclosed. designed for carrying switches; fittings especially TABLE XV. DIMENSIONS OF PIPE STRAPS All Dimensions taken from Samples. All Dimensions in Inches i i il f I! No. 2 2* 0.20 0.20 0.20 0.22 0.22 0.22 0.22 0.22 0.25 in. 8X 8X 8x 10X 10X if .it I? a-c | $0.40 \ 0.45 0.50 0.75 10X1 10x1 ioxu To 72 40 29 21 18 14 12 2.75 but an equivalent fitting may be assembled, as shown in Fig. 14 at K, with the components A and J, or with J and any other piece shown in Fig. 14. For handling currents above 20 amperes, open-knife switches are used. The open type is used because (so far as the writer These is aware) no enclosed knife switch is regularly manufactured. open switches are best mounted close to the motor starter. Controllers and starters, as will be outlined later, can be purchased with the line switches mounted directly on them, as indicated in Figs. 15 and 17. Such combinations are called starting or controlling panels. commonly WIRING ON MOTOR-DRIVEN MACHINERY 43 these examples of knife-line-switch and controller applications, it was evidently deemed unnecessary by the designer to enclose the switches and controllers. If enclosure is desirable (and as many In view all of there are few cases where it, it is not) a cover for a PIPE STRAP--' CONDUIT FITTING WROUGHT-IRON CONDUIT CONTAINING CONDUCTORS TO MOTOR SOURCE OF SUPPLY Machinery,??. Fig. 18. knit'e- Y Machine Equipped with Drum Controller switch can readily be constructed from sheet or cast metal as suggested in Fig. 22. As will be described subsequently, circuit-breakers are often used on motor-driven machines, making switches unnecessary. While a cut-out is required by the Code to protect every motorit is not advisable to mount this on the ma- controller combination, . / WROUGHT SCREWS FOR FASTENING IRON WROUGHT \ CONDUIT HOLE DRILLED BY WIRE-MAN Fig. chine. As a circuit to the at A in Fig. IRON CONDUIT 19. ,N. Y. Satisfactory Method of Supporting Fittings is best located at the point where the branchmachine taps from the main supply circuit, as shown 23. Hence the machine manufacturer should not be rule, it expected to provide a cut-out. A cut-out is ordinarily required at A. 44 No. 115 MOTOR DRIVE inasmuch as the branch wires are usually smaller than the main wires and the Code requires the installation of a cut-out wherever there is a decrease in wire size. INDICATOR WINDOW PORCELAIN BASE FORMED METAL COVER' \ PO RCELAIN BASE FORMED METAL COVER SIDE ELEVATION PLAN VIEW Machinery.*. Fig. 20. Y. Indicating Snap Switch Motor Controllers and Starters Motor starters as regularly furnished by the motor manufacturers are of the open type shown in line-cut Fig. 15. By "open type" is WROUGHT-IRON CONDUIT ENCLOSING COVER CONDUIT FITTING CONDUIT CARRYING CONDUCTORS TO MOTOR MOTOR GAUZE ENCLOSING COVERS THIS CONDUIT TO BE INSTALLED BY PURCHASER ENCLOSING CASE FOR CHAIN DRIVE * A^ Machinery. X.Y. Fig. 21. A Motor-driven Shaper with Completely Enclosed Wiring "live" parts protected by a These open starters have given and will give entire satis- meant a type which does not have cover. its WIRING ON MOTOR-DRIVEN MACHINERY 45 faction in places where it is reasonably clean. But some purchasing concerns orefer to have, in so far as possible, all electrical apparatus enclosed, and it is believed that, all things considered, this is usually the most economical method, although the first cost of enclosed equipment is a trifle higher. An enclosed starter is shown in Fig. 21. It consists merely of a standard open starter fitted with a cover which encloses all "live" parts, and has a semi-circular slot for the operating Most of the electrical manufacturing concerns have standhandle. ardized and are prepared to furnish enclosing covers for their control equipment. Such a cover makes it difficult for the unauthorized to Fig. 22. Enclosing Cover for Knife-switch tamper with the adjustment of the starter, keeps it clean, eliminates liability to shock and prevents grounds or short circuits due to flying metal chips. The purchaser of an enclosing cover for a starter should insist that it enclose not only the dial-contacts, but also the terminals on the starter. Certain manufacturers will furnish a cover that will shroud the dial and not the terminals, unless specifically directed as above; all bare current-carrying parts should be enclosed. In Fig. 24 is detailed an excellent enclosing cover that can be apInstead of being slotted for the operating plied to standard starters. handle as is the one shown in Fig. 21, a better construction is used. An auxiliary operating handle and arm is mounted on the cover; on the end of this arm is an insulating fork which engages the controller arm when the cover is in its normal position, and thus transmits the movements of the operating handle to the controller arm. The absence of a slot in the cover makes the starter dust-proof. The terminals are completely enclosed and a removable piece that can be taken out altogether, for the admittance of wires, or drilled for conduit, is pro- No. 46 115 MOTOR DRIVE vided above the terminals. When this cover is applied to the standard controller the old controller handle is removed. Sometimes a circuit-breaker is substituted for the switch on a A circuit-breaker is one type starting panel, as shown in Pig. 25. of cut-out. It opens a circuit automatically when a current, of a value for which it is set, flows through it. It can also be opened manually by releasing a catch. Circuit-breakers, of reliable types, are considerably higher in first cost than a switch-fuse combination, but in the long run they are more economical. The reasons for this are: First, fuse renewals, which are relatively expensive, are not required; and second, the cost of labor wasted while fuses are being replaced, is saved. The panel construction in Fig. 25 is shown without enclosing covers so that its will be apparent; but it is made with covers which expose only the circuit-breaker and starting-rheostat operating handles. ' ENTRANCE SWITCH AND CUT-OUT At! MAIN SUPPLY CIRCUIT BRANCH CUT-OUT PROTECTING .MACHINE MOTOR I BRANCH CIRCUIT TO MACHINE LINE SWITCH - STARTER ED j Machinery.N.T. Fig. 23. Some manufacturers Wiring Diagram for Motor-driven Machines enclose panels like that of Fig. 25 in sheet-metal boxes having hinged doors, but this is not a satisfactory arrangement for machinery applications, because, to operate the starter This or manipulate the switch, the attendant must open the door. is awkward and, in case of accidents, when the motor should be stopped The consequence is that the without delay, prevents quick action. door is usually left open or is taken off altogether. As previously mentioned, motors on machines are frequently protected by branch-fuses located at the supply circuit as shown at A in Fig. 23, and a circuit-breaker or a starting panel provides additional However, the circuit-breaker should be set to trip on a protection. smaller current than will rupture the fuses. The circuit-breaker takes the brunt of an overload and operates instantaneously, saving the cost of fuse renewals. As the economies of circuit-breaker applications are becoming better understood they are becoming more popular. Some steel WIRING ON MOTOR-DRIVEN, large industrial corporations specify them on every motor starting or controlling panel. Drum controllers with external resistances are deservedly becoming In Fig. 18 is very popular, particularly for variable-speed control. shown drum-controller applications. The drum controller receives its name from the fact that contact is made between stationary fingers and rotating segments mounted on a drum. All the parts can be made very rugged and can be so arranged as to be readily removable The resistance is arranged in a separate for renewal and repair. frame which can be provided with an enclosing cover and arranged for conduit wiring as shown in Pig. only the contact-making mechanism. 18. The drum usually contains It is believed that a drum con- SUPPORTING LUGS .! DETAIL OF INSULATING FORK FORKED PIECE OF INSULATING FIBER ENGAGING CONTROLLER HANDLE iNTROLLER ARM WITH HANDLE REMOVED u SECTIONAL FRONT ELEVATION SIDE ELEVATION Machinery, N.Y. Tig. 24. A Good Enclosing Cover Design way to one of the dial type, which has contact buttons arranged on the face of an insulating panel and a swinging arm to make electrical contact with them. Often the drum controller is mounted conveniently near the motor troller is preferable in every at the head of the lathe. The controlling handle, whereby the lathe started, stopped, or has its speed varied, is attached to and travels with the apron, and hence is always handily located for operation. is The handle engages with a longitudinally when slotted shaft so arranged The shaft extends nearly the entire length of the lathe and motion is transmitted from it to the controller drum by means of sprockets and a chain. It will be noted that the cover of the drum controller can be easily removed that the handle is turned the shaft turns. by unscrewing a couple of swing nuts. ' 48 * ' ' ' N'oV 115 MOTOR DRIVE Enclosing Motors 1 Motors can be furnished either open, semi-enclosed or fully enclosed. fully enclosed motor of a given horsepower and speed costs more than a semi-enclosed or an open one, because a large frame is needed for the enclosed type. The power capacity of a motor depends largely on its ability to dissipate the heat generated within it, and if it is enclosed, the heat is dissipated with difficulty. To reduce the quantity of heat generated, the parts must be proportioned more generously; hence the necessity for larger frames for enclosed motors. Motors seldom need to be fully enclosed unless they are to operate in very dirty places, or in other special cases. A gauze enclosure such as that indicated in Fig. 21 is satisfactory for most machinery applications. A IRON FOOT LINE TERMINALS CIRCUIT BREAKER _- NO-VOLTAGE RELEASE COIL MOTOR TERMINALS Fig. 25. Machinery, X.Y. A Circuit-breaker Starting Panel Gauze or wire-netting enclosing covers reduce the rating of a motor very little, if any. The use of such covers is advocated on motors for nearly all machine drives. The Code specifies that the frames of all motors operating at potentials in excess of 550 volts shall be either permanently grounded or else insulated by wooden frames or otherwise. The use of a wooden frame or any other insulating arrangement is not usually feasible, so the almost universal practice is to bolt the motor frame into good electrical contact with the frame of the machine. It devolves upon the purchaser of the machine to see that it is well grounded, either through the conduit conveying the conductors to the machine (the Code requires that the conduit of all conduit wiring systems be grounded) or through a specially provided ground wire connected to The Underwriters require that special permission be obtained before motors with grounded frames are installed. the machine. THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW AN INITIAL FINE OP 25 CENTS WILL BE ASSESSED FOR FAILURE TO RETURN THIS BOOK ON THE DATE DUE. THE PENALTY WILL INCREASE TO SO CENTS ON THE FOURTH DAY AND TO $1.OO ON THE SEVENTH DAY OVERDUE. JUN NQV i LD 21-100m-7,'39(402s) YC 53944 UNIVERSITY OF CALIFORNIA LIBRARY MACHINERY'S DATA SHEET SERIES MACHINERY'S Data Sheet Books include the well-known series of Data Sheets originated by MACIUJNI v, and issued monthly as supplements to the publication; of these Data Sheets over 500 have been published, and 6,000,000 copies sold. Revised and greatly amplified, they are now presented in book form, kindred subjects being grouped together. The price of each book is 25 cents (one shilling) delivered anywhere in tho world. CONTENTS OF DATA SHEET No. 1. Screw Threads. United States, Whitworth, Sharp V- and British Association Threads; Briggs Pipe Thread; Oil W.-M Casing Gages; Tin and Metric Fire Hose Connections; AmuThreads; Machine, Wood, L; ew, and Caretc. Bolt Threads, riage -1 No. 2. Screws, Bolt and !., .. illister-head, Headless, Collar-hear an<1 Hcxi, ^on-head Screws; Standard and Sp-e':il Nuts; T-nuts, T-bolts and Washers; Thumb Screws and Nuts; Machine Screw Heads; Wood Screws; Tap Drills. No. 3. Taps and Dies. Hand, Machine, Tapper and Machine Screw Taps; Taper Die Taps; Sellers Hobs; Screw Machine Taps; Straight and Taper Boiler Taps; Stay-bolt, Washout, and Patch-bolt Taps; Pipe Taps and Hobs; Threading Dies. No. 4. Reamers, Sockets, Drills and Milling Hand Reamers; Shell Reamers and ArCutters. bors; Pipe Reamers; Taper Pins and Reamers; Brown & Sharpe, Morse and Jarno Taper Sockets and Reamers; Drills; Wire Gages; Milling Cutters; Setting Angles for Milling Teeth in End Mills and Angular Cutters, etc. No. 5. Spur Gearing. Diametral and Circular Pitch; Dimensions of Spur Gears; Tables of Pitch Diameters; Odontograph Tables; Rolling Mill Gearing; Strength of Spur Gears: Horsepower Transmitted by Cast-iron and Rawhide Pinions; Design of Spur Gears; Epicyclic Gearing. No. 6. Bevel, Spiral and Worm Gearing. Rules and Formulas for Bevel Gears; Strength of Bevel Gears; Design of Bevel Gears: Rules and Formulas for Spiral Gears; Diagram for Cutters for Spiral Gears; Rules and Formulas fov Worm Gearing, etc. No. 7. Shafting, Keys ana Keyways. Horsepower of Shafting; Strength of Shafting; Forcing, Driving, Shrinking and Running Fits; Woodruff Keys; Standard Keys; Gib Keys; Milling Keyways; Duplex Keys. No. 8. Bearings, Couplings, Clutches, Crane Chain and Hooks. Pillow Blocks; Babbitted Bearings; Ball and Roller Bearings; Clamp Couplings; Flange Couplings; Tooth Clutches; Crab Couplings; Cone Clutches; Universal Joints; Crane Chain; Crane Hooks; Drum Scores. No. 9. Springs, Slides and Machine Details. Formulas and Tables for Spring Calculations; Machine Slides; Machine Handles and Levers; Collars; Hand Wheels; Pins and Cotters; Turn-buckles. No. 10. Motor Drive, Speeds and Feeds, Change Power required for Gearing, and Boring Bars. Machine Tools; Cutting Speeds and Feeds for Carbon and High-speed Steel; Screw Machine Speeds and 1 ,-eds- Heat Treatment of High-speed Steel Tools; 'i.-prTurning; Change Gearing for Bars and Tools. the Lathe; Bori g. '.OOFS No. 11. Milling Machine Indexinj Clamping Devices and Planer Jacks. Tables for vl tiling Machine Indexing; Change Gears for Milling Spirals; Angles for sitting Indexing Head when Milling Clutches; Jig Clamping Devices. No. 12. Pipe and Pipe Fittings. Pipe Threads Gages; Cast-iron Fittings; Bron/e F.'ttings; Pipe Flanges; Pipe Bends; Pipe Clumps and Hangers. No. 13. Boilers and Chimneys. Fit;. Spacing and Bracing for Boilers; Strength of BoiKT Joints; Riveting; Boiler Setting; Chimneys. No. 14. Locomotive and Railway Data. Locomotive Boilers; Bearing Pressures for Locomotive Journals; Locomotive Classifications; R:iil Sections; Frogs, Switches and Cross-overs; Tin-, Tractive Force; Inertia of Trains; Brake Lever and No. 15. Steam and Gas Engines. -Saturated Steam; Steam Pipe .Sizes; Steam Engine Design; Volume of Cylinders; Stu'h'ng Boxes; Setting Corliss Engine 'Valve Gears; Condenser and Air Pump Data: Horsepower of Gasoline Engines; Automobile Engine Crankshafts, etc. 16. Mathematical Tables. No. Squares of Mixed Numbers; Functions of Fractions; Circumference and Diameters of Circles; Tables for SpacFormulas ing off Circles; Solution of Triangles' for Solving Regular Polygons; Geometrical Pro: gression, Mechanics and Strength of Materials. Centra ugal Force; Center of GravMotion; Friction; Pendulum; Falling Bodies; No. Work; ity; etc. 17. En.-rjry; Strength of Materials; Strength of Flat Plates; Strength of Thick Cylinders, etc. No. 18. Beam Formula and Structural Design. Beam Formulas, Sectio ,al Moduli of Structural Shapes; Beam Charts; Net Areas of Structural Angles; Rivet Spacing; Splices for Channels and Ibeams; Stresses in Roof Trusses, etc. No. 19. Belt, Rope and Chain Drives. Dimensions of Pulleys; Weights of Pulleys; Horsepower of Belting; Belt Velocity; Angular Belt Drives; Horsepower transmitted by Ropes; Sheaves for Rope Drive; Bending Stresses in Wire Ropes; Sprockets for Link Chains; Formulas and Tables for Driving Chain. No. 20. Wiring Diagrams, Heating and Ventilaand Miscellaneous Tables. Typical Motor tion, Wiring Diagrams; Resistance of Round Copper Wire; Current Densities for Various Contacts and Materials; Centrifugal Fan and Blower Capacities; Hot Water Main Capacities; Decimal EquivaMetric Conversion Tables. Weights and lents, Specific Gravity of Metals, Drafting-room Con. ventions, etc. M VCHINERY, the leading journal in the machine-building field, the originator of Subscription, $2.00 the 25-cent Reference and Data Books. Published monthly. yearly. Foreign subscription, $3.00. The Industrial Press, Publishers of MACHINERY, New York City, U. 140-144 Lafayette Street, S. A.