CHAPTER VofPRACTICAL MECHANICS FOR BOYS
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The question is often asked: Where and how shall the novice commence work?
When the shop is equipped, or partially so, sufficient, at least, to turn out simple jobs, the boy will find certain tools which are strangers to him. He must become acquainted with them and not only learn their uses, but how to use them to the best advantage.
Familiarity with Tools.—Familiarity with the appearance of tools, and seeing them in the hands of others will not be of any value. Nothing but the immediate contact with the tool will teach how to use it.
File Practice.—The file is a good tool to pick up first. Select a piece of metal, six or eight inches long, and follow the instructions laid down in chapter 4 relating to the use of the file.
Practice with several kinds and with different varieties of material will soon give an inkling of the best kind to use with the metal you have. Use the straight edge and the square while the filing process is going on, and apply them frequently, to show you what speed you are making and how nearly true you are surfacing up the piece.
Using the Dividers.—Then try your hand using the dividers, in connection with a centering punch. As an example, take two pieces of metal, each about a foot long, and set the dividers to make a short span, say an inch or so, and step off the length of one piece of metal, and punch the last mark. Then do likewise with the other piece of metal, and see how nearly alike the two measurements are by comparing them.
You will find a variation in the lengths of the two measurements at the first trials, and very likely will not be able to make the two pieces register accurately after many trials, even when using the utmost care.
Sooner or later you will learn that you have not stepped paths along the two bars which were exactly straight, and this will account for the variations. In order to be accurate a line should be drawn along each piece of metal, and the dividers should step off the marks on that line.
Finding Centers.—By way of further experiment, it might be well to find the exact center of the ends of a square bar, putting in the punch marks and then mounting it in the lathe centers to see how accurately this has been done.
If either end is out of true the punch marks can be corrected by inclining the punch, so that when it is struck it will move over the point in the direction of its true center. This may be followed up by centering the end of a round bar so as to make it true. This will be found to be a more difficult job, unless you have a center head, a tool made for that purpose.
It is good practice, however, to make trials of all this work, as it will enable you to judge of measurements. It can be done with the dividers by using care in scribing the centers.
Hack-Saw Practice.—Practice with the hack-saw should be indulged in frequently. Learn to make a straight cut through a bar. Try to do this without using a square to guide you. One of the tests of a good mechanic is ability to judge a straight cut.
The following plan is suggested as a test for the eye. Use a bar of iron or steel one inch square, and make a cut an eighth of an inch deep across it; then turn it around a quarter, so as to expose the nest face, and continue the cut along the side, the same depth, and follow this up with the remaining two sides, and see how near the end of the first cut and the finish cut come together. The test will surprise you.
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.—Brass 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 brass 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.
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