Practical Mechanics for Boys Part 6

CUTTING METALS TRUE.--When you saw off the end of such a bar for trial purposes, use a square, after the cut is made, and note how much it is out of true in both directions. It is a curious fact that most mechanics are disposed to saw or cut crooked in one direction, either to the right or to the left. In tests made it is found that this defect is persisted in.

It is practice only which will remedy this, and it would be well for the boy to learn this for himself as early in his career as possible, and correct the tendency to veer in either direction.

The test of sawing around a round bar is also commended. After a few trials you will be surprised to see how your judgment will improve in practice.

LATHE WORK.--Learn the uses of the chuck. As you have, probably, economized as much as possible, a universal chuck is not available, hence the first experience will be with an independent chuck, where the three dogs move independently of each other. This will give you some work to learn how you can get the job true.

Now, before attempting to cut the material, thoroughly learn all the parts of the feed mechanism, and how to reverse, as well as to cross feed. Learn the operation of the operative parts so that your hand will instinctively find them, while the eye is on the work.

FIRST STEPS.--See to it that your tools are sharp, and at the first trials make light cuts. Practice the feeds by manually moving the tool holder, for surface cutting as well as for cross cutting.

SETTING THE TOOL.--Set the cutting tool at various angles, and try the different tools, noting the peculiarities of each, at the different speeds. Do not, by any means, use refractory metals for your first attempt. Mild steel is a good test, and a light gray iron is admirable for practice lessons.

METALS USED.--Bra.s.s is good for testing purposes, but the difficulty is that the tendency of the boy, at first, is to try to do the work too rapidly, and bra.s.s encourages this tendency. Feed slowly and regularly until you can make an even finish.

Then chuck and re-chuck to familiarize yourself with every operative part of the lathe, and never try to force the cutting tool. If it has a tendency to run into the work, set it higher. If, on the other hand, you find, in feeding, that it is hard to move the tool post along, the tool is too high, and should be lowered.

THE FOUR IMPORTANT THINGS.--Constant practice of this kind will soon enable you to feel instinctively when the tool is doing good work. While you are thus experimenting do not forget the speed. This will need your attention.

Remember, you have several things to think about in commencing to run the lathe, all of which will take care of themselves when it becomes familiar to you. These may be enumerated as follows:

First: The kind of tool best to use.

Second: Its proper set, to do the best work.

Third: The speed of the work in the lathe.

Fourth: The feed, or the thickness of the cut into the material.

TURNING UP A CYLINDER.--The first and most important work is to turn up a small cylinder to a calipered dimension. When it is roughed down ready for the finish cut, set the tool so it will take off a sufficient amount to prevent the caliper from spanning it, and this will enable you to finish it off with emery paper, or allow another small cut to be taken.

TURNING GROOVES.--Then follow this up by turning in a variety of annular grooves of different depths and widths; and also V-shaped grooves, the latter to be performed by using both the longitudinal and transverse feeds. This will give you excellent practice in using both hands simultaneously.

The next step would be to turn out a bore and fit a mandrel into it.

This will give you the opportunity to use the caliper to good advantage, and will test your capacity to use them for inside as well as for outside work.

DISCS.--A job that will also afford good exercise is to turn up a disc with a groove in its face, and then chuck and turn another disk with an annular rib on its face to fit into the groove. This requires delicacy of measurement with the inside as well as the outside calipers.

The groove should be cut first, and the measurement taken from that, as it is less difficult to handle and set the tool for the rib than for the groove.

LATHE SPEEDS.--Do not make the too common mistake of running the mandrel at high speeds in your initial tests. It is far better to use a slow speed, and take a heavy cut. This is good advice at all times, but it is particularly important with beginners.

CHAPTER VI

ILl.u.s.tRATING SOME OF THE FUNDAMENTAL DEVICES

There are numerous little devices and shop expedients which are desirable, and for which the boy will find uses as he progresses.

We devote this chapter to hints of this kind, all of which are capable of being turned out or utilized at various stages.

LACING BELTS.--To properly lace a belt is quite an art, as many who have tried it know. If a belt runs off the pulley it is attributable to one of three causes: either the pulleys are out of line or the shafts are not parallel or the belt is laced so it makes the belt longer at one margin than the other.

In Fig. 58 the lacing should commence at the center hole (A) of one belt end and lace outwardly, terminating at the hole (B) in the center of the other belt end, as shown in Fig. 58.

In Fig. 59 the lacing commences at A, and terminates at the hole (B) at the edge. This will be ample for all but the widest belts.

Fig. 60 is adapted for a narrow belt. The lacing commences at one margin hole (A), and terminates at the other margin hole (Z).

Fig. 61 shows the outside of the belt.

Fig. 62. GEARS.--This is something every boy ought to know about. Fig.

62 shows a pair of intermeshing bevel gears. This is the correct term for a pair when both are of the same diameter.

[Ill.u.s.tration: _Inside Fig. 58. Belt Lacing_ _Outside Fig. 58. Belt Lacing_ _Fig. 59. Belt Lacing_ _Fig. 60. Belt Lacing_ _Fig. 61. Belt Lacing_]

MITER GEARS.--In Fig. 63 we have a pair of miter gears, one being larger than the other. Remember this distinction.

Fig. 64. CROWN WHEEL.--This is a simple manner of transmitting motion from one shaft to another, when the shafts are at right angles, or nearly so, without using bevel or miter gears.

Fig. 65. GROOVED FRICTION GEARING.--Two grooved pulleys, which fit each other accurately, will transmit power without losing too much by friction. The deeper the grooves the greater is the loss by friction.

Fig. 66. A VALVE WHICH CLOSES BY THE WATER PRESSURE.--The bibb has therein a movable valve on a horizontal stem, the valve being on the inside of the seat. The stem of the handle has at its lower end a crank bend, which engages with the outer end of the valve stem. When the handle is turned in either direction the valve is unseated. On releasing the handle the pressure of the water against the valve seats it.

Fig. 67. CONE PULLEYS.--Two cone pulleys of equal size and taper provide a means whereby a change in speed can be transmitted from one shaft to another by merely moving the belt to and fro. The slightest change is available by this means.

Fig. 68. UNIVERSAL JOINT.--A wheel, with four projecting pins, is placed between the U-shaped yokes on the ends of the approaching shafts. The pins serve as the pivots for the angles formed by the two shafts.

Fig. 69. TRAMMEL FOR MAKING AN ELLIPSE.--This is a tool easily made, which will be of great service in the shop. In a disc (A), preferably made of bra.s.s, are two channels (B) at right angles to each other. The grooves are undercut, so that the blocks (C) will fit and slide in the grooves and be held therein by the dove-tailed formation. Each block is longer than the width of the groove, and has an outwardly projecting pin which pa.s.ses through a bar (D). One pin (E) is movable along in a slot, but is adjustable at any point so that the shape of the ellipse may be varied. The end of the bar has a series of holes (G) for a pencil, so that the size of the ellipse may also be changed.

[Ill.u.s.tration: _Fig. 62. Bevel Gears_ _Fig. 63. Miter Gears_ _Fig. 64. Crown Wheel_ _Fig. 65. Grooved Friction Gears_ _Fig. 66. Valve_ _Fig. 67. Cone Pulleys_ _Fig. 68. Universal Joint_]

Fig. 70. ESCAPEMENTS.--Various forms of escapements may be made, but the object of all is the same. The device is designed to permit a wheel to move intermittingly or in a step by step movement, by the swinging motion of a pendulum. Another thing is accomplished by it. The teeth of the escapement are cut at such an angle that, as one of the teeth of the escapement is released from one tooth of the escapement wheel, the spring, or the weight of the clock, will cause one of the teeth of the escapement wheel to engage the other tooth of the escapement, and give the pendulum an impulse in the other direction. In the figure, A is the escapement, B the escapement wheels and _a_, _b_, the pallets, which are cut at suitable angles to actuate the pendulum.

Fig. 71. SIMPLE DEVICE TO PREVENT A WHEEL OR SHAFT FROM TURNING BACK.--This is a subst.i.tute for a pawl and ratchet wheel. A is a drum or a hollow wheel and B a pulley on a shaft, and this pulley turns loosely with the drum (A). Four tangential slots (C) are cut into the perimeter of the pulley (B), and in each is a hardened steel roller (D). It matters not in what position the wheel (B) may be, at least two of the rollers will always be in contact with the inside of the drum (A), and thus cause the pulley and drum to turn together. On reversing the direction of the pulley the rollers are immediately freed from binding contact.

Fig. 72. RACKS AND PINIONS.--The object of this form of mechanism is to provide a reciprocating, or back-and-forth motion, from a shaft which turns continually in one direction. A is the rack and B a mutilated gear. When the gear turns it moves the rack in one direction, because the teeth of the gear engage the lower rack teeth, and when the rack has moved to the end its teeth engage the teeth of the upper rack, thus reversing the movement of the rack.

Fig. 73. MUTILATED GEARS.--These are made in so many forms, and adapted for such a variety of purposes, that we merely give a few samples to show what is meant by the term.

[Ill.u.s.tration: _Fig. 69. Trammel_ _Fig. 70. Escapement_ _Fig. 71. Device for Holding Wheel_ _Fig. 72. Rack and Pinion_ _Fig. 73. Mutilated Gears_ _Fig. 74. Shaft Coupling_]

Fig. 74. SIMPLE SHAFT COUPLING.--Prepare two similarly formed discs (A, B), which are provided with hubs so they may be keyed to the ends of the respective shafts. One disc has four or more projecting pins (C), and the other disc suitable holes (D) to receive the pins.

Fig. 75. CLUTCHES.--This is a piece of mechanism which is required in so many kinds of machinery, that we show several of the most approved types.