been determined practically that in the ordinary manufacturing establishment the mean effective power is but 30 per cent. of the total aggregate effective power which is required when all the tools are running at maximum load. This percentage is termed the load factor. In the case of belt-drive there is, then, 100 h.p. assumed loss for 100 h.p. effective load; that is, an efficiency of 50 per cent. Applying the load factor as above, it is found that there is but 30 mean h.p. to use and that it requires 100 h.p. to transmit it, thus giving the real efficiency as only 23 per cent, With the individual motor drive the loss varies with the load, Taking the same load factor, and as

suming 30 per cent. as representing the loss incurred by the 30 h.p. effective load, there is but 9 h.p. loss against 100 h.p. with the belt drive. Thus, with individual drive, there is generated 39 h.p., of which 30 is effective, giving an efficiency of 77 per cent. against 23 per cent. by the shafting and belting method."

2. Cost of Buildings.-Heavy overhead shafting is not required for the electric drive, hence the buildings may be made lighter and cheaper in construction, as settlingwill not throw parts of the equipment out of alignment and cause serious friction losses, vibration, etc.

3. Cost of Equipment. The relative expense of equipping a factory with electric motors or with belting and shafting is usually greater in the former case, so that the saving in operation expenses, or increased earning power must more than offset the increased interest and depreciation. On the other hand the lower cost of the lighter building construction balances more or less the cost of the motors.

4. Arrangement of Machinery.

The use of electric motors enables the machinery to be placed in almost any desired position. It is not necessary that they should be parallel or arranged in rows, or placed at any particular angle with each other, whereas for belting and shafting the machinery must be arranged in a very particular manner, and very often it has to be placed where the light is poor, or accessibility and other important features must be

sacrificed. A great advantage obtained due to the flexibility of the electrically driven machines is that portable equipments are easily made up and operated, so that the tool is frequently brought

to the object to be worked on, in place of bringing the work to the tool. (Figs. 6 and 7.)

5. Clear Head Room. - The elimination of overhead belting and shafting through the use of motors gives a clear head room, which enables overhead cranes to be freely used; a fact which results in a great saving of time and labor in the bringing of the work to the tools or removing finished pieces, the value of which is apparent when one considers the time and labor necessary to bar along heavy machinery on rollers. The clear head room also gives better illumination and ventilation. In fact the saving in cost for proper illumination may amount to as much or even more than the saving in tool operating power; since general illumination may be largely resorted to. Fig. 8 shows the appearance of a machine shop operated by belting and shafting, and Fig. 9 is an illustration of a plant where the tools are operated electrically, the great advantages regarding head room and illumination being well brought out by these two examples.

6. Cleanliness. The dripping of oil from overhead shafting is a constant source of annoyance, and the dirt thrown out from belting is an even worse enemy to cleanliness. The agitation of dust by belting and shafting keeps it in constant circulation, so that it penetrates everything and everywhere. This is a very important matter in printing and textile work.

7. Health of Employees. - On account of the better ventilation and illumination, and reduction in dust and dirt, it is shown by actual experience that the general health of those who work with electrically driven machinery is improved. In the Government

printing office at Washington, it was found that the sick list was decreased about 20 to 40 per cent. after the electric drive was introduced.

8. Convenience for Detached Buildings. The electrical method enables power to be supplied easily and economically to detached

FIG. 8.

A loss of power in transmission

An example of a great investment in shafts, pulleys and belts. amounting to over 60 per cent.

manufacturing establishment into a series of detached buildings is an almost absolute safeguard against total destruction by fire; and is thus a practical guarantee of continuous earning powers. If however electric power were not employed, it would be necessary to have long belting systems, involving great losses,

buildings or sections, which is not possible with belt or steam transmission; therefore, the buildings, like the machinery within them, can be located for general convenience, and not with special regard to supplying them with power. This subdivision of a plant or

FIG. 9. Electrically Driven. No belts, shafting or pulleys. Allows a clear headway for crane service; a more convenient and economical arrangement of machines, and better lighting.

and extra heavy wall construction, or a series of small power plants calling for a larger force of men; and considerably less economical in operation than one central power house.

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9. Freedom for Growth. For similar reasons, with electric drive it is a simple matter to extend a building, or add another in any direction, whereas with belting, the shafting must be installed originally large enough to allow for extension; or else it must be replaced later; in which case the operation of the existing line shafts would be interfered with.

10. Shut downs Less Frequent and Less Serious. An accident in an electrically driven plant usually has a local effect only, simply shutting down one or a few machines, while with belting and shafting the breaking or slipping off of a belt, or the failure of a friction clutch, may require the shutting-down of a whole plant or a large section thereof. In a large establishment a delay of even a few minutes represents a considerable item in wages, and in addition the interruption of the work is demoralizing. It might be argued that the central station may break down; this is however just as likely to happen with one form of power transmission as another.

11. Speed Control. The variation of speed that is possible with the electric drive, and the convenience as well as the wide ranges of control, are great advantages with most kinds of machine work. The operator can drive the tool to its limit of capacity, and can, on the other hand, instantly relieve it of strain. With mechanical drive the methods of speed control are more limited and require more time to operate than with electric motors. The shifting of the belt on a cone pulley, or the throwing in and out of different sets of gears, takes more effort than the simple turning of a controller handle, which can be placed right at the work, and is thus not so likely to be carried out by the operator to gain slightly in the efficiency or rapidity of his work. The curves given in Fig. Io show the time required to perform a certain piece of machine work, the speed control being by electrical and mechanical means, The cutting speed in the case of the electric drive being kept absolutely constant and at its maximum value throughout the operation, whereas that of the mechanical drive could not be adjusted as closely as this, but had to vary between control values. The saving in time thus obtained is considerable and correspondingly reduces the shop cost of the article.