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GENERAL EFFICIENCY IN MANUFACTURING OPERATIONS
Changes and improvements. The modern factory. Manufacturing conditions of the
present time. Economy a necessity. Arrangement of departments. Character of the work in different departments. Transferring stock. Economy of power. Various systems. Necessary conditions. Location of shafting. Roller bearings. Arrangement of machines. Machines on benches. Efficiency of machines. High speed steel. Design of machines. Design of the cutting tools. Transportation of stock and materials. Shop tracks. Elevators. Trucks. Cars. Overhead trolleys. Distribution of small tools. Overhead carriers. Vertical carriers. Economy of the pay roll. Cheapness not necessarily economy. Classifying employees. Classifying the work. Time accounts.
EVERYTHING in nature lives, moves, and has its being by a well-defined system of natural laws which govern all animate and inanimate things, and all tend towards the evolution and development of life and matter into an innumerable variety of more complete and perfect forms.
In our world of business, trade, and manufacture, we shall do wisely if we strive to imitate nature in these respects, to the end that whatever plans we may devise, whatever changes we may effect, or whatever processes we may develop, they shall be for the better and more perfect use of the means at our command, and in fact and in truth we may so labor
“that each to-morrow Finds us farther than to-day,”
that each step we take may be a real improvement, a real advancement to better and more perfect conditions of whatever we manage and control.
And in so doing we shall do well to remember that change is not always progress. That a narrow-minded and short-sighted view of matters, facts, and conditions often lead men, seeing the successful changes effected by their more broad-minded fellows, to endeavor to imitate them by simply making changes. Often to the detriment rather than the betterment of existing conditions.
Hence we should proceed with a well considered and well planned
system, supported alike by theory and experience, since such a system will have all the chances in its favor and consequently always make for success, more or less certain, of course, according to the conditions of the case, while without systematic proceeding to a betterment of conditions will but invite the failure that usually follows.
These conditions and observations are applicable to nearly all positions in life, but in this chapter we propose to consider briefly their relation to the equipment of the modern factory in the effort to decrease its expense and to increase its efficiency in the regular routine work of manufacturing.
As no particular line of goods to be manufactured is taken up the subject will be treated in a general way by referring to such matters as are common to all or nearly all factories whenever possible to so consider the matter.
While the present time is by no means the “day of small things,” but on the contrary the day of very large enterprises, it is yet true that the percentage of profits in comparison to the amounts invested and the number of workmen employed are relatively considerably less than formerly. It might be said with truth in almost all manufacturing operations that the percentage of actual waste fifteen years ago was greater than the net profits of to-day. It therefore behooves us to so arrange and conduct manufacturing operations that every item of unnecessary waste may be eliminated, every ounce of material utilized, and every hour of the employees' time expended in useful work, and properly accounted for.
And not only is this true, but also that as every square foot of floor space costs a certain amount of outlay in the interest upon the real estate and buildings, as well as their maintenance and insurance, and the expense for light, heat, and power, we must see to it that every available foot of floor space is occupied and utilized with profit, and every machine kept as constantly employed on profitable work as possible, since every occupied foot of floor space and every working machine must bear, not only its own proportion of these burdens of expense, but also a proportion of those of the unused space and the idle machines.
In laying out and locating the various departments composing the factory, we must first carefully consider what the product is to be and the various operations which will be necessary to its manufacture.
Then we will consider the different classes of machines needed to properly perform these operations. This will give us the needed facts in determining the number of departments required, while the number of machines needed of each class, to properly balance the production, and the space they are to occupy, will determine the floor space to be occupied by each of the different departments.
The character of the work done in each department, from the raw
material to the finished product, will determine the location of the departments in relation to each other, since the material or stock in progress through the factory should be moved on in one continuous course with little or no retrograde movement, as every unnecessary movement adds to the expense of manufacturing, and also interferes with other stock being moved in its onward way towards completion. This is a point too often lost sight of, or its application to existing or future conditions very much underestimated; the result being an unnecessary expense, perhaps small, but continuous.
Much discussion has been indulged in as to the relative merits and economy of driving machines by long lines of shafting belted from the engine; shorter lines driven by electric motors; or motors for driving individual machines.
All of these systems are good in their place and may be used with economical results in the same factory. The special points in favor of each are usually as follows: Heavy machines, requiring considerable
if placed near the engine, may probably be driven by the system of shafting and belting very economically, while if placed at quite a distance, say one hundred feet or more, it will be more economical to operate them individually by motors; or, if several are located closely together as a group, to drive them from a short line shaft operated by a motor.
We may say, therefore, that it is more economical to transmit power to distances of over one hundred feet by electricity than by shafting and belting. Large machines that are not in nearly constant use should be motor driven, as power is only used when the machine is in actual operation, while in the use of line shafting it must be kept in order, and we must use the power necessary to drive it continuously, even if there is only one machine of the group in operation.
Where machines are driven from a long line shaft, it should be run at sufficient speed to permit the use of pulleys of moderate diameters. Slow running shafts require to be of comparatively large diameter and the pulleys much larger and heavier, consequently the friction is greater and the power must be increased in proportion. If a shaft 3 inches* in diameter is located in the center of the room, driving machines on both sides, its speed being 150 R. P. M. and requiring pulleys from 18 to 36 inches in diameter to drive the machines, it will be found much more economical to replace it by two shafts of 2 inches diameter, and running 300 R. P. M., on each side of the room and carrying pulleys from 9 to 18 inches in diameter. The aggregate weights of the two shafts and their pulleys will be much less than that of the
* Regular sizes of shafting are“ on the odd sixteenth,” that is als, etc. The even inch is here given for convenience only.
one large shaft, the belts may be shorter, narrower, and lighter, and consequently the power much less.
The weights upon line shafts will be materially reduced by the use of the pressed steel pulleys. This will apply to all pulleys of ten inches and larger. A still further economy will result by driving each of these two shafts by a motor. This would also permit the stopping of either of them in case of an accident, without interfering with the other.
In cases where the factory is of several floors and the power transmitted by vertical belts, the driven pulleys should be of the friction clutch form for the purpose of throwing out any one shaft without stopping any of the others. All shafting of two inches or over should be provided with roller bearings, preference being given to those of the flexible type. An automatic system of lubrication for shafting has become a necessity and will be a great saving of power. The simple form of a reservoir beneath the bearing, from which the oil is drawn through a piece of felt, and returned by way of grooves at each end of the box, is an excellent and economical device, although there are many others equally as efficient.
The location and relative arrangement of machines is a matter of much importance. If the department contains a variety of quite small and medium sized machines, the smaller ones may be well arranged on benches along the walls where the light is always good. The bench may be very useful for holding stock and material in process of manufacture. This method will leave the central portion of the room for larger machines set up on the floor, and still leave ample passageways in a building of the usual width, say forty feet. This would allow, on each side, a bench two feet wide, another two feet for the operator, behind whom would be a passageway six feet wide, and still leave a 20-foot space in the center for larger machines, and a central space for a passageway, car track, etc.
Frequently machines set on wall benches may be driven from a very light shaft located only three or four feet above the bench, thus eliminating about 50 per cent of the lengths of the machine-driving belts, and still leaving them long enough for good service. Machines of the same general type and doing the same class of work, or consecutive operations upon it, should be grouped together, for convenience in handling the stock in its continuous progress.
The degree of efficiency of machines operating on cutting metals may be very materially increased by careful experiment and study of speeds, the best qualities of tool steel for the particular purpose, and the form of the tools. It is not good economy to force cutting speeds to the highest limit, even with the best high-speed steel. The point to be determined is the highest economical speed for the metal operated upon, the form of the piece being
made, and the particular machine used for the work. And however much we may experiment in this matter we shall probably never arrive at any fixed rule of say so many
minute for machine steel, so many for cast iron, steel, brass, bronze, etc.
Much will depend on the design of the machine, the manner of holding the tool, as well as the method of holding the piece to be machined; the whole combining to give rigidity and prevent vibration, both laterally and in the direction of motion, as even the slightest vibration of tool or work will reduce the possible cutting speed.
Neither shall we arrive at any fixed angle of side clearance or top rake for a cutting tool, inasmuch as that it depends to a considerable extent on the form and rigidity of the machine used, the nature of the cut, etc.
The operations of milling, drilling, and tapping, as well as nearly all similar operations, will require the same observation and experiment to arrive at the best, most efficient, and economical speeds, in view of the individual conditions governing the work.
Where the work is heavy enough to warrant it, there should be shop tracks, let in flush with the floor level, upon which should run shop cars of such dimensions and weights as their loads may demand, and of such form as may be necessary to adapt them to the particular form and character of the stock and material to be handled. For this purpose they may be
provided with racks, shelves, trays, boxes, crates, etc., as may be needed; these accessories being readily removable so that others may
be substituted. factory of several floors, the elevators connecting them should be provided with similar tracks, so that cars may be conveniently run upon them and taken to any desired floor.
There should be a number of switches, at least one to each line of tracks, where cars may pass each other, so as to avoid lost time. At one end of the room a cross track may be laid, forming connections with the principal tracks by curves, or by turntables at the intersections.
When the character of the stock and material to be moved is not of sufficient weight to require tracks, the cars may be replaced by trucks of proper dimensions, their wheels being provided with rubber tires to avoid jar and noise. Both of these methods of transportation may be advisable, say a track through the center of the rooms and trucks serving the machines at the sides. The accessories for trucks and cars should, of course, be interchangeable.
Where there are no belts or other obstructions in the way, overhead trolleys may be arranged for transporting light stock and materials, with economy. These trolleys may run upon overhead I-beams, or beams of special form adapted to their use. These may also be used on the elevators