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to do the work to advantage. As a consequence, a machine was built with sufficient strength to do the work. When this was found to save money and increase the product, other jobs were transferred to the machine. As time went on it was realized that the setting of the machine, and adjusting it when necessary, consumed a vast amount of time. This
necessary, the head can be swiveled in a vertical plane through 360 degrees, enabling the workman to mill angular portions of a piece of work without altering the setting of the piece. This is made not only possible but practicable by the automatic cross-feed, whereby the saddle of the machine may be fed in either direction automatically.
Other attachments—such as the universal milling, the high-speed (Fig. 2), and many more too numerous to mention-are furnished if desired, making possible a wide range of work.
The plain milling machine is ordinarily furnished with a vise for holding such work as can be machined to advantage
FIG. 1. caused a change in the design and led to the adoption of proper graduations, which enable the machine to be adjusted to any desired amount.
Milling machines are made for many different purposes, and are of innumerable types.
For general use, however, they are made for manufacturing purposes and for the tool room. The former type is generally known as the plain milling machine, and the latter as the universal milling machine. The plain machine is sometimes used for tool-room purposes, and the universal is at times used for manufacturing purposes, but in general the above classification holds. The universal milling machine is fur
FIG. 2. nished with a vise provided with an arrangement whereby it can be swiveled to when held between the jaws. When any desired angle. The base is provided pieces of work are held in this manner with tongues which fit in slots in the they usually rest on pins, or on a shelf table. A set of index centers is fur arranged for the purpose; or pins are nished for use in milling work; these provided to enter some hole in the piece, have centers between which the work thus locating the work in reference to is held, or it can be held in a chuck that one or more holes. With other machines, screws on the end of the spindle of the generally, the jaw of the vise will have index head.
one pin that will enter a hole in the piece When desired, there is furnished at to be machined, and some portion of the extra cost) a vertical spindle milling piece will rest on another pin. head, as shown in Fig. 1. This makes As the back jaw of the vise is stationit possible to do vertical milling; or, if ary, it is customary to put the pins in
the detachable jaw, which is fastened to cause, if large numbers of a piece are to the stationary part of the vise. Were the be machined, a fixture, even though expins placed in the movable jaw, it would pensive, which will make it possible to not be possible to produce accurate work, do the whole work for one-half the cost as the slide of the vise, being movable, that would be involved in the use of a would not assume the same position ver cheap fixture, is many times cheaper in tically if screwed up under varying ten the end. sion.
It should be borne in mind that cast When the work rests on a shelf, as iron is comparatively cheap when made shown in Fig. 3, the shelf should, if pos up into machines and tools, because it sible, be located on the fixed jaw; but can be cast in the desired form. Moresometimes, in order to support the work over, if used in sufficient quantities, it properly, the shelf must be placed on both insures rigidity and freedom from chatjaws, as shown in Fig. 4. This will an tering, provided other conditions are swer if extreme accuracy is not essen what they should be. Therefore plenty tial. When it is necessary to produce of this metal should be put where accurate work, the movable jaw may be strength is essential—it insures accurate connected with the fixed jaw by means work and allows heavier cuts and coarser of pins, as shown at A, Fig. 4; these feeds. pins must be a close, sliding fit in the jaw. For most work it is advisable to run However, in case the work is to be done the milling cutters against the work, as in quantities sufficiently large to warrant shown in Fig. 5. However, there are the outlay, it is advisable to make a fix- jobs where better results follow if the ture specially de
cutters are run signed for hold
on to the work, ing this particu
as shown in Fig. lar piece.
6; the action of For the dupli
the cutters in cation of parts,
this case tends fixtures are spe
to hold the piece cially made for
of work down to holding almost
the seating, inevery piece of
suring accuracy. work; for not
Again, if the cutonly can the
ters were run as work be held to machine more closely shown in Fig. 5, certain pieces of work to gage than when a vise is used, but would, when the cutters are in action, be the cost of putting in and taking out is pulled out of almost any fixture that less.
could be used. Now, if we reverse the When considering the advisability of cutters and run them in the manner ilmaking special fixtures of any kind, lustrated in Fig. 6, the cutters themwhether for use on a milling or other ma selves will bear upon the work in such a chine, the designer should first take into way as to hold it down. consideration the cost of the fixture, and Frequently heavy fixtures are built to decide whether or not it will save its cost insure strength and rigidity while a in doing the number of pieces to be ma heavy cut is being taken with a cutter chined. This may be determined from having a small arbor hole. As a consethe difference in cost of machining or in quence, the arbor springs, and the result accuracy of the product. There are some in this case is that the work is no more jobs that cannot be held in the vise at accurate than if it were held in a light, all; for such, it is necessary to make fix weak fixture. tures, and in these cases no comparison If a cut is wide, necessitating a cutter can be made.
more than one inch in length, it is genIn the designing of fixtures, the main erally considered advisable to cut the point for consideration must be simplicity teeth spirally, as shown in Fig. 7. If the of construction and operation, not nec cut is several inches wide, the cutter is essarily cheapness of construction, be best made in two parts, or, rather, two
cutters should be made with the teeth cut with opposite spirals, that is, one set of teeth a right-hand spiral and the other a left-hand spiral. Should one cutter be sufficient to do the work, it is necessary to cut its teeth spirally in one direction alone. When of only one spiral, however, the tendency of the cutter in action is to pull the arbor out of the spindle hole, and to draw the adjusting nut on the spindle so hard against the collar between it and the box that a great amount of friction is created. If cut on the opposite spiral, the pressure would be all the other way. This result is, of course, preferable to the other; but if we make two cutters and give them opposite spirals, they balance each other, and so relieve the machine of strain.
When shank (end) mills are made, which have no means of support the outer end, it is especially necessa ry give attention to this matter, as the spiral shape of the cutter tends to cause it to be pulled out of the collet, or spindle, unless it is cut with a spiral that will force it in rather than draw it out.
When using a modern manufacturing milling machine having automatic feeds in all directions, it is possible to mill a long piece of work on one side, and then mill the end at right angles to the side, without disturbing the setting. This is
done by milling the side the entire length, and then throwing out the lateral feed and throwing in the vertical feed. The work will then be fed up past the cutter.
The vertical milling attachment is furnished with both plain and universal machines, but is used more commonly on the latter. With it the top of a piece of work can be milled, the spindle being used in a vertical position. It may then be turned to any angle, and a surface at an angle with the top or one side can be milled. When using this attachment, for milling angles, the automatic device for feeding the saddle is used instead of the lateral feed which moves the table. The advantages derived from the use of the vertical milling attachment are so numerous that
a great deal of space would be required to describe them adequately.
The foregoing illustrates in a measure a few of the many ways in which
the modern millFIG. 6.
ing machine is
related to modern methods for the production of the most accurate kind of work, not only with
to offer a simple explanation in answer to them.
Wireless telegraphy consists in the generation of ether waves or vibrations, and the power to receive the same by some intelligible method without any visible connection between the generator and receiver.
Three things, then, have to be considered if we wish to comprehend properly the whole system-namely, ether vibrations, the generator or transmitter, and the receiver.
What are ether vibrations or waves ?
fluid body. The size of the generated wave would vary according to the size and force of the projected pebble.
We have vibrations in another substance familiar to all of us, namely, air, which gives an entirely different result, and which we familiarly recognize as sound. Pure air is invisible, but we can analyze it. It is a mechanical mixture of simple chemical gases, subject to wellrecognized natural laws, and can be affected by a series of forces producing various results. By a simple mechanical contrivance known as the siren, the air
can be thrown into vibration, and the all our senses imperceivable and by all number of vibrations accurately deter chemical and other means undemonmined corresponding to the tone pro strable. We know it does exist, else duced. If we cause forty vibrations per we could not explain the above-mentioned second, we get a sound, the lowest the phenomena. We can measure its wave ear can perceive; if we increase this to lengths, their rapidity and their velocity, 44,000 per second, we get the highest but the substance itself eludes us. tone within the range of the human ear. Just as air, so can ether be thrown into The tone or note familiar to us in the vibration, and the result of that vibration mosquito is due to the flapping of its gives rise to heat, light, electricity, wings 3,000 times per second. It is magnetism, X-rays, and Hertzian and probable that some of the lower animals Marconi waves. The different phenomena perceive tones higher and lower in range depend upon the length and rapidity of than the human ear is capable of. the ether vibration. This vibration may Sound waves
are longer or shorter be produced by purely mechanical or by according to the method of production, chemical means. The Indians used the and have to do with the quality of the former means in lighting their fires by tones produced. We have seen
the rubbing together cedar sticks or using a
flint. The mechanical friction produced by rubbing a match is enough to excite sufficiently rapid ether vibration to ignite it. If, on the other hand, you rub a glass rod with a piece of fur, you get electricity; or even in stroking a cat's back in a dry winter's atmosphere the same result is obtained. Chemically, if we apply heat to a piece of charcoal and it begins to glow, its ether is vibrating about 40,000,000,000 times per second ; while sunlight is probably caused by 500,000,000,000,000 quadrillions of vibrations per second, and the vibration of
the Hertzian wave is only 230,000,000 VIEW OF MARCONI STATION, BROOMFIELD
times per second. ROAD, CHELMSFORD, ENGLAND.
The waves differ in length just as the
water or air waves. Those of light are rapidity of a wave or vibration in water about one forty-thousandth of an inch or in a fluid body. Sound or air vibration long, those of the Hertzian wave three travels much faster, or about 1,140 feet and a half feet, while those of Marconi per second, owing to its greater elasticity vary from several hundred to as many and to other physical qualities.
thousand, depending on the power in There are a number of other natural their production. The velocity of the phenomena familiar i all of us, which projection of the ether vibration is the do not admit of explanation by any of same for all of these ether phenomena, the qualities recognizable by us in air, namely, about 186,000 miles per second. and which are in fact operable in its The next question comes: How are the absence. These are heat, light, electric
Hertzian and Marconi waves generated ? ity, magnetism, X-rays, and Hertzian The lightning's flash generates ether and Marconi waves.
waves. The electric discharge between In order to explain all the phenomena two Leyden jars, or that between the connected with these natural forces, terminals of an ordinary induction coil, physicists have had to assume the exist will generate these ether vibrations; and ence of a substance to which has been it is the latter method which is in use for given the name of “ether.” It pervades short distances for wireless telegraphic all bodies and all space. Earth and sky work. For long distances it is necessary alike are permeated by this substance, to to contract special batteries for the