Page images
PDF
EPUB

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 furnished with a vise provided with an arrangement whereby it can be swiveled to any desired angle. The base is provided. with tongues which fit in slots in the table. A set of index centers is furnished for use in milling work; these have centers between which the work is held, or it can be held in a chuck that screws on the end of the spindle of the index head.

When desired, there is furnished (at extra cost) a vertical spindle milling head, as shown in Fig. 1. This makes it possible to do vertical milling; or, if

[merged small][ocr errors]

when held between the jaws. When pieces of work are held in this manner they usually rest on pins, or on a shelf arranged for the purpose; or pins are provided to enter some hole in the piece, thus locating the work in reference to one or more holes. With other machines, generally, the jaw of the vise will have one pin that will enter a hole in the piece to be machined, and some portion of the piece will rest on another pin.

As the back jaw of the vise is stationary, it is customary to put the pins in

the detachable jaw, which is fastened to the stationary part of the vise. Were the pins placed in the movable jaw, it would not be possible to produce accurate work, as the slide of the vise, being movable, would not assume the same position vertically if screwed up under varying tension.

When the work rests on a shelf, as shown in Fig. 3, the shelf should, if possible, be located on the fixed jaw; but sometimes, in order to support the work properly, the shelf must be placed on both jaws, as shown in Fig. 4. This will answer if extreme accuracy is not essential. When it is necessary to produce accurate work, the movable jaw may be connected with the fixed jaw by means of pins, as shown at A, Fig. 4; these pins must be a close, sliding fit in the jaw. However, in case the work is to be done in quantities sufficiently large to warrant the outlay, it is advisable to make a fixture specially designed for holding this particular piece.

For the duplication of parts, fixtures are specially made for holding almost every piece of work; for not only can the

FIG. 3.

work be held to machine more closely to gage than when vise is used, but the cost of putting in and taking out is less.

When considering the advisability of making special fixtures of any kind, whether for use on a milling or other machine, the designer should first take into consideration the cost of the fixture, and decide whether or not it will save its cost in doing the number of pieces to be machined. This may be determined from the difference in cost of machining or in accuracy of the product. There are some jobs that cannot be held in the vise at all; for such, it is necessary to make fixtures, and in these cases no comparison can be made.

In the designing of fixtures, the main point for consideration must be simplicity of construction and operation, not necessarily cheapness of construction, be

cause, if large numbers of a piece are to be machined, a fixture, even though expensive, which will make it possible to do the whole work for one-half the cost that would be involved in the use of a cheap fixture, is many times cheaper in the end.

It should be borne in mind that cast iron is comparatively cheap when made up into machines and tools, because it can be cast in the desired form. Moreover, if used in sufficient quantities, it insures rigidity and freedom from chattering, provided other conditions are what they should be. Therefore plenty of this metal should be put where strength is essential-it insures accurate work and allows heavier cuts and coarser feeds.

For most work it is advisable to run the milling cutters against the work, as shown in Fig. 5. However, there are jobs where better results follow if the

[subsumed][ocr errors][merged small][merged small][merged small][merged small]

shown in Fig. 5, certain pieces of work would, when the cutters are in action, be pulled out of almost any fixture that could be used. Now, if we reverse the cutters and run them in the manner illustrated in Fig. 6, the cutters themselves will bear upon the work in such a way as to hold it down.

Frequently heavy fixtures are built to insure strength and rigidity while a heavy cut is being taken with a cutter having a small arbor hole. As a consequence, the arbor springs, and the result in this case is that the work is no more accurate than if it were held in a light, weak fixture.

If a cut is wide, necessitating a cutter more than one inch in length, it is generally considered advisable to cut the teeth spirally, as shown in Fig. 7. If the cut is several inches wide, the cutter is 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 on the outer end, it is especially necessary give attention to this matter, as

to

FIG 5.

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

them

a great deal of space would be required to describe adequately. The foregoing illustrates in a measure a few of the many ways in which the modern milling machine is related to modern methods for the production of the most accurate kind of work, not only with

FIG. 6.

[graphic][merged small][merged small]
[merged small][merged small][merged small][merged small][merged small][graphic][subsumed][merged small]

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 number of vibrations accurately determined corresponding to the tone produced. If we cause forty vibrations per second, we get a sound, the lowest the ear can perceive; if we increase this to 44,000 per second, we get the highest tone within the range of the human ear. The tone or note familiar to us in the mosquito is due to the flapping of its wings 3,000 times per second. It is probable that some of the lower animals perceive tones higher and lower in range than the human ear is capable of.

Sound waves are longer or shorter according to the method of production, and have to do with the quality of the tones produced. We have seen the

VIEW OF MARCONI STATION, BROOMFIELD ROAD, CHELMSFORD, ENGLAND.

rapidity of a wave or vibration in water or in a fluid body. Sound or air vibration travels much faster, or about 1,140 feet per second, owing to its greater elasticity. and to other physical qualities.

There are a number of other natural phenomena familiar all of us, which do not admit of explanation by any of the qualities recognizable by us in air, and which are in fact operable in its absence. These are heat, light, electricity, magnetism, X-rays, and Hertzian. and Marconi waves.

In order to explain all the phenomena connected with these natural forces, physicists have had to assume the existence of a substance to which has been given the name of "ether." It pervades all bodies and all space. Earth and sky alike are permeated by this cbstance, to

all our senses imperceivable and by all chemical and other means undemonstrable. We know it does exist, else we could not explain the above-mentioned phenomena. We can measure its wave lengths, their rapidity and their velocity, but the substance itself eludes us.

Just as air, so can ether be thrown into vibration, and the result of that vibration. gives rise to heat, light, electricity, magnetism, X-rays, and Hertzian and Marconi waves. The different phenomena depend upon the length and rapidity of the ether vibration. This vibration may be produced by purely mechanical or by chemical means. The Indians used the former means in lighting their fires by 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 times per second.

The waves differ in length just as the water or air waves. Those of light are about one forty-thousandth of an inch long, those of the Hertzian wave three and a-half feet, while those of Marconi vary from several hundred to as many thousand, depending on the power in their production. The velocity of the projection of the ether vibration is the same for all of these ether phenomena, namely, about 186,000 miles per second.

The next question comes: How are the Hertzian and Marconi waves generated? The lightning's flash generates ether waves. The electric discharge between two Leyden jars, or that between the terminals of an ordinary induction coil, will generate these ether vibrations; and it is the latter method which is in use for short distances for wireless telegraphic work. For long distances it is necessary to contract special batteries for the

[graphic]
« PreviousContinue »