This section is from the "Modern Machine Shop Construction, Equipment, And Management" book, by Oscar E. Perrigo. Also see Amazon: Modern Machine Shop Construction, Equipment, And Management.
The question of friction of the two systems of transmitting power, that is, from the engine by shafting and belting, or the loss of power by generating an electric current with which to drive motors, is one which has provoked much discussion. Probably it will be found in practice to be about as follows: Where the distance is short, shafting and pulleys are much the more economical. For distances of two or three hundred feet there will be little difference in the two systems. For much greater distances the advantages are in favor of the electric method.
The plan of power transmission here selected is to drive from the balance wheel of the engine to a 72-inch pulley on the main line of shafting, giving a shaft speed of 240 revolutions per minute. This shaft is in lengths of 20 feet, supported by hangers every 10 feet, and with a hanger on each side of main driving pulleys. The three lengths in the center are 5 inches in diameter and the remaining portion each way from these three lengths is 3« inches in diameter to the end.
Cut-off couplings are provided on the main shaft at the points shown in the drawings, for the purpose of stopping either section of the shaft in case of accident. In the same manner, the shaft in the gallery over the main line has a cut-off coupling at each end of the section, upon which the main pulley is located.
The smaller sizes of shafting are now usually made on the odd sixteenth of an inch diameter, but the even sizes are here given for convenience. The shafts are provided with roller bearings, and all pulleys with the exception of the large main driving pulleys are of the pressed sheet steel form, as being the lightest pulley made for strength, convenience, and transmission of power.
From the end of the main shaft toward the front of the building, power is taken for the machines in the tool room. From near the center, power is carried by a vertical belt to the gallery floor above. This shaft is 3« inches in diameter for the central 20-foot length and the remainder is 3 inches in diameter. Upon the central length, as well as on the main line below, are pulleys 48 inches in diameter and 14 inches face. The central length is supported by four hangers - one at each end, and one on each side of the main pulley.
In all cases the couplings are to be placed on the side of the hanger away from the source of power, so as to be secure in case of the failure of a coupling.
The dynamos for lighting as well as those for driving the motors may be located in the engine room and driven by belts from the main line by friction pulleys, or they may be located under the main line shafting.
It should be remembered that for a belt of high velocity it will be much better to run it horizontally than vertically, and that it will transmit much more power under the former condition. If it is desired to locate the dynamos in the engine room and run them by horizontal belts, a countershaft may be located near the floor, just inside the engine room and driven by a belt from the main line.
An independent engine may be used to drive the motors. In this case the power of the main engine would be considerably reduced. The main line shaft furnishes power for all machines on that side of the main floor.
The machines on the opposite side of the main floor may be those which it is desired to drive by individual motors, while in the gallery above, the line shaft, in say three or four sections, may be driven by suitable motors.
The same method may be desirable in the pattern shop and also in the tool room, if preferred, although it is more adaptable in the pattern shop where power is not used continuously.
The power for driving the machines in the carpenter shop may be transmitted by belt from the main line through a belt box occupying the space between the machine shop and the carpenter shop to the line shaft in the latter. Or, a motor may be located in the carpenter shop.
If a steam hammer is used in the forge shop the steam supply should be carried in a pipe passing through an underground brick conduit, as carrying it around through the machine shop and carpenter shop would necessitate a long line of piping.
A motor will be most convenient for operating the blast fan, drop hammers, cutting-off machines, power hack saws, etc.
For the foundry, steam may be carried under ground, across the yard in a brick conduit, as the most direct way, to the engine running the heating apparatus, and another for the cupola blower and the tumbling barrels. Here again motors will be very convenient, as one may be directly connected to the heating apparatus fan and another used for the cupola blower and the tumbling barrels, as well as to run the elevator which supplies the cupola platform with its fuel and stock.
The boilers, and at least all pipes over 1« inches in diameter, conveying live steam, should be protected with a good non-conducting covering. Probably the best preparation for this purpose is a mixture of carbonate of magnesia and asbestos, only a sufficient quantity of the latter being used as a bond, to hold the mixture together. The proportions may be, eight parts of magnesia and two parts of asbestos, with a sufficient quantity of water to form a plastic mass.
The thickness of this covering will depend on the amount of exposure to cold air to which the boilers or steam pipes are subjected. From one to two inches is ordinarily used, according to circumstances.