PRACTICAL MECHANICS FOR BOYS TEXT

types (Figs. 18, 19, 20, 21, 22, 23). As this chapter deals with the sharpening methods only, the reader is referred to the next chapter, which deals with the manner of setting and holding them to do the most effective work. When it is understood that a cutting tool in a lathe is simply a form of wedge which peels off a definite thickness of metal, the importance of proper grinding and correct position in the lathe can be appreciated. ROUGHING TOOLS.--The most useful is the roughing tool to take off the first cut. As this type of tool is also important, with some modifications, in finishing work, it is given the place of first consideration here. [Illustration: _Fig. 24. Tool for Wrought iron._ _Fig. 25. Tool for Cast iron._] Fig. 24 shows side and top views of a tool designed to rough off wrought iron, or a tough quality of steel. You will notice, that what is called the top rake (A) is very pronounced, and, as the point projects considerably above the body of the tool itself, it should, in practice, be set with its cutting point above the center. THE CLEARANCE.--Now, in grinding, the important point is the clearance line (B). As shown in this figure, it has an angle of 10 degrees, so that in placing the tool in the holder it is obvious it cannot be placed very high above the center, particularly when used on small work. The top rake is ground at an angle of 60 degrees from the vertical. The arc of the curved end depends on the kind of lathe and the size of the work. The tool (Fig. 25), with a straight cutting edge, is the proper one to rough off cast iron. Note that the top rake (C) is 70 degrees, and the clearance 15 degrees. THE CUTTING ANGLE.--Wrought iron, or mild steel, will form a ribbon when the tool wedges its way into the material. Cast iron, on the other hand, owing to its brittleness, will break off into small particles, hence the wedge surface can be put at a more obtuse angle to the work. In grinding side-cutters the clearance should be at a less angle than 10 degrees, rather than more, and the top rake should also be less; otherwise the tendency will be to draw the tool into the work and swing the tool post around. DRILLS.--Holders for grinding twist drills are now furnished at very low prices, and instructions are usually sent with the machines, but a few words may not be amiss for the benefit of those who have not the means to purchase such a machine. Hand grinding is a difficult thing, for the reason that through carelessness, or inability, both sides of the drill are not ground at the same angle and pitch. As a result the cutting edge of one side will do more work than the other. If the heel angles differ, one side will draw into the work, and the other resist. [Illustration: _Fig. 26. End view._ _Fig. 27. Side view._] WRONG GRINDING.--When such is the case the hole becomes untrue. The sides of the bit will grind into the walls, or the bit will have a tendency to run to one side, and particularly if boring through metal which is uneven in its texture or grain. Figs. 26 and 27 show end and side views of a bit properly ground. If a bit has been broken off, first grind it off square at the end, and then grind down the angles, so that A is about 15 degrees, and be sure that the heel has sufficient clearance--that is, ground down deeper than the cutting point. CHISELS.--A machine shop should always have a plentiful supply of cold chisels, and a particular kind for each work, to be used for that purpose only. This may seem trivial to the boy, but it is really a most important matter. Notice the careless and incompetent workman. If chipping or cutting is required, he will grasp the first chisel at hand. It may have a curved end, or be a key-way chisel, or entirely unsuited as to size for the cutting required. The result is an injured tool, and unsatisfactory results. The rule holds good in this respect as with every other tool in the kit. _Use a tool for the purpose it was made for_, and for no other. Acquire that habit. COLD CHISELS.--A cold chisel should never be ground to a long, tapering point, like a wood chisel. The proper taper for a wood chisel is 15 degrees, whereas a cold chisel should be 45 degrees. A drifting chisel may have a longer taper than one used for chipping. It is a good habit, particularly as there are so few tools which require grinding, to commence the day's work by grinding the chisels, and arranging them for business. SYSTEM IN WORK.--Then see to it that the drills are in good shape; and while you are about it, look over the lathe tools. You will find that it is better to do this work at one time, than to go to the emery wheel a dozen times a day while you are engaged on the job. Adopt a system in your work. Don't take things just as they come along, but form your plans in an orderly way, and you will always know how to take up and finish the work in the most profitable and satisfactory way. WRONG USE OF TOOLS.--Never use the vise as an anvil. Ordinary and proper use of this tool will insure it for a lifetime, aside from its natural wear. It may be said with safety that a vise will never break if used for the purpose for which it was intended. One blow of a hammer may ruin it. Furthermore, never use an auxiliary lever to screw up the jaws. If the lever which comes with it is not large enough to set the jaws, you may be sure that the vise is not large enough for your work. CHAPTER III SETTING AND HOLDING TOOLS Some simple directions in the holding and setting of tools may be of service to the novice. Practice has shown the most effective way of treating different materials, so that the tools will do the most efficient work. A tool ground in a certain way and set at a particular angle might do the work admirably on a piece of steel, but would not possibly work on aluminum or brass. LATHE SPEED.--If the lathe should run at the same speed on a piece of cast iron as with a brass casting, the result would not be very satisfactory, either with the tool or on the work itself. Some compositions of metal require a high speed, and some a hooked tool. These are things which each must determine as the articles come to the shop; but there are certain well-defined rules with respect to the ordinary metals that should be observed. THE HACK SAW.--Our first observation should be directed to the hand tools. The hack saw is one of the most difficult tools for the machinist to handle, for the following reasons: First, of the desire to force the blade through the work. The blade is a frail instrument, and when too great a pressure is exerted it bends, and as a result a breakage follows. To enable it to do the work properly, it must be made of the hardest steel. It is, in consequence, easily fractured. [Illustration: _Fig. 28.--Hack Saw Frame._] [Illustration: _Fig. 29.--Hack Saw Blade._] Second. The novice will make short hacking cuts. This causes the teeth to stick, the saw bends, and a new blade is required. Take a long sweeping cut, using the entire length of the blade. Do not oscillate the blade as you push it through the work, but keep the tooth line horizontal from one end of the stroke to the other. The moment it begins to waver, the teeth will catch on the metal on the side nearest to you, and it will snap. Third. The handle is held too loosely. The handle must be firmly held with the right hand, and the other held by the fingers lightly, but in such a position that a steady downward pressure can be maintained. If loosely held, the saw is bound to sag from side to side during the stroke, and a short stroke accentuates the lateral movement. A long stroke avoids this. The hack saw is one of the tools which should be used with the utmost deliberation, combined with a rigid grasp of the handle. FILES.--For remarks on this tool see Chapter IV, which treats of the subject specially. GRINDSTONES, EMERY AND GRINDING WHEELS.--A good workman is always reflected by his grinding apparatus. This is true whether it has reference to a grindstone, emery, corundum wheel, or a plain oil stone. Nothing is more destructive of good tools than a grooved, uneven, or wabbly stone. It is only little less than a crime for a workman to hold a tool on a revolving stone at one spot. CARELESSNESS IN HOLDING TOOLS.--The boy must learn that such a habit actually prevents the proper grinding, not only of the tool he has on the stone, but also of the one which follows. While it is true that all artificially made grinders will wear unevenly, even when used with the utmost care, due to uneven texture of the materials in the stone, still, the careless use of the tool, while in the act of grinding, only aggravates the trouble. Another fault of the careless workman is, to press the bit against the stone too hard. This cuts the stone more than it wears off the tool, and it is entirely unnecessary. Furthermore, it heats up the tool, which should be avoided. CALIPERS.--A true workman, who endeavors to turn out accurate work, and preserve his tools, will never test the work with his calipers while the piece is turning in the lathe. A revolving cast iron disk will cut ruby, the hardest substance next to the diamond, so it is not the hardness of the material which resists wear, but the conditions under which it is used. CARE IN USE OF CALIPERS.--The calipers may be of the most hardened steel, and the work turned up of the softest brass, the latter, when revolving, will grind off the point of the tool, for the reason that the revolving piece constantly presents a new surface to the point of the calipers, and when tests are frequently made, it does not take long to change the caliper span so that it must be reset. As stated elsewhere, the whole energy of the lathe is concentrated on the bit or cutting tool, hence, in order to get the most effective work out of it requires care; first, in grinding; and, second, in setting. MACHINE BITS.--It does not always matter so much whether you use a square, pointed, or a round-nosed bit, provided it is properly ground and set in the tool holder. As a rule, the more brittle the metal the less the top rake or angle should be. In the chapter relating to the grinding of tools, references were made as to the most serviceable bits for the various metals. We are concerned here with the setting or holding of these articles. [Illustration: _Fig. 30. Plain Hook Tool_ _Fig. 31. Plain Straight Tool._] The two illustrations here given show a pair of plain bits, in which Fig. 30 represents a hook-shaped formation, and Fig. 31 a straight grind, without any top rake. The hooked bit would do for aluminum, or steel, but for cast iron the form shown in Fig. 31 would be most serviceable. Then the side bits, such as the round-nosed, Fig. 32 and the square end, Fig. 33, may be ground hooked, or with a top rake, or left flat. The too common mistake is to grind the lower or clearance side at too great an angle. Fig. 34 shows the correct angle, and the dotted line A illustrates the common tendency to grind the clearance. THE PROPER ANGLE FOR LATHE TOOLS.--Now there is a reason why the angle of from 10 to 15 should be maintained in the clearance. The point of the tool must have suitable support for the work it is required to do, so it will not chatter or yield in the slightest degree. A bit ground along the dotted line has a cutting edge which will spring down, and consequently break or produce a rough surface. [Illustration: _Fig. 32. Fig. 33. Fig. 34. Proper Angles for Tools_] Then, again, the angle of the clearance acts as a guide, or rather, a guard, to prevent the tool from going in too far, as will now be explained. SETTING THE BIT.--In order to understand the correct setting, examine the work A, in Fig. 35. A is a cylinder being turned up in the lathe, and B the cutting tool, which approaches it on a horizontal line, C, extending out from the center of the cylinder A. This setting is theoretically correct, and in practice has been found most advantageous. In this case let us assume that the clearance angle D is 15 degrees, as well as in the following figures. [Illustration: _Fig. 35. Set of the Bit_] Suppose we have a piece of tough steel, and the tool holder is raised so that the point of the tool is at the 15 degree line E, as shown in Fig. 36, in which case the clearance line D is at right angles to the line E. The line E is 15 degrees above the center line C. THE SETTING ANGLE.--Now, it is obvious that if the tool should be raised higher than the line E it would run out of work, because the clearance surface of the tool would ride up over the surface cut by the edge of the tool. If, on the other hand, the tool should be placed lower, toward the line C, the tendency would be to draw in the tool toward the center of the work A. In Fig. 37 the tool has its point elevated, in which case it must be lowered so the point will touch the work nearer the center line C. The foregoing arrangement of the tools will be found to be effective where the material is soft and not too tough as with aluminum. BAD PRACTICE.--Figs. 38 and 39 show illustrations of bad practice which should never be resorted to. Fig. 38 shows the tool, held in a horizontal position, but with its point below the center line C. With any rough metal the tool could not possibly work, except to act as a scraper, and if it should be used in that position on cast iron, the tool itself would soon be useless. [Illustration: _Fig. 36. Correct Angle_ _Fig. 37. Wrong Angle_] Fig. 39 is still worse, and is of no value for any purpose except in polishing brass, where it would be serviceable. It would make a sorry looking job with aluminum. Brass requires a tool with very little top rake, and the point should be set near the center line C. LATHE SPEED.--It is often a question at what speeds to run the lathe for different work. If you know the speeds of your lathe at low and high gear, you must also consider the diameter of the work at the cutting point. The rule is to have the bit cut from 15 to 20 feet per minute for wrought iron; from 11 to 18 feet for steel; from 25 to 50 for brass; and from 40 to 50 for aluminum. [Illustration: _Fig. 38. Too Low_ _Fig. 39. Improper Set_] As a result, therefore, if, at low speed, a piece 10 inches in diameter, runs at the proper speed to cut at that distance from the center, it is obvious that a piece 5 inches in diameter should ran twice as fast. This is a matter which time and practice will enable you to judge with a fair degree of accuracy. Observe this as a maxim: "Slow speed, and quick feed." BORING TOOLS ON LATHE.--The lathe is a most useful tool for boring purposes, better for some work than the drilling machine itself. The work which can be done better on a lathe than on a drilling machine, may be classified as follows: 1. When straight and true holes are required. 2. In long work, where the lathe is used to turn up the article, and where the drilling can be done at the same time. 3. Anything that can be chucked in a lathe. 4. Where the work is long and cannot be fixed in a drilling machine. The long bed of the lathe gives room for holding such work. [Illustration: _Fig. 40. Internal Set_ _Fig. 41. Set for Brass_] THE RAKE OF THE DRILL.--A boring tool requires some knowledge in setting. It should have a greater top rake than for the outside work, and the cutting edge should also be keener, as a rule. [Illustration: _Fig. 42.--Surface Gage._] In this class of work the material bored must be understood, as well as in doing outside work. The hooked tool, Fig. 40, is shown to be considerably above the center line, and at that point it will do the most effective cutting on steel. If, on the other hand, brass is operated on there should be no top rake, as illustrated in Fig. 41, thus assuring a smooth job. LAPS.--This is a tool which is very useful, particularly for grinding and truing up the cylinders of internal combustion engines, as well as for all kinds of bores of refractory material which cannot be handled with the cutting tool of the lathe. It is made up of a mandrel or rod of copper, with lead cast about it, and then turned up true, so that it is but the merest trifle larger than the hole it is to true up. USING THE LAP.--The roller thus made is turned rapidly in a lathe, and the cylinder to be trued is brought up to it and the roller supplied freely with emery powder and oil. As rapidly as possible the cylinder is worked over on the roller, without forcing it, and also turned, so as to prevent even the weight from grinding it unduly on one side. More or less of the emery will embed itself in the lead, and thus act as an abrasive. The process is called "lapping." SURFACE GAGES.--Frequently, in laying out, it is necessary to scribe lines at a given distance from some part of the work; or, the conditions are such that a rule, a caliper, or dividers will not permit accurate measurement to be made. For such purposes, what is called a surface gage was devised. This is merely a heavy base, provided with a pivoted upright on which is mounted a scribe that is held by a clamp so it may be turned to any angle. [Illustration: _Fig. 43.--Showing uses of the Surface Gage._] SURFACE GAGE.--The clamp holding the scriber is vertically movable on the pivoted upright. By resting the base of the surface gage on the line to be measured from, and swinging one point of the scriber to the place where the work is to be done, accuracy is assured. One end of the scriber is bent, so it can be adapted to enter recesses, or such places as could not be reached by the straight end. CHAPTER IV ON THE USE OF THE FILE The most necessary tool in a machine shop is a file. It is one of the neglected tools, because the ordinary boy, or workman, sees nothing in it but a strip or a bar with a lot of cross grooves and edges, and he concludes that the only thing necessary is to rub it across a piece of metal until he has worn it down sufficiently for the purpose. THE FIRST TEST.--The fact is, the file is so familiar a tool, that it breeds contempt, like many other things closely associated in life. Give the boy an irregular block of metal, and tell him to file it up square, and he will begin to realize that there is something in the handling of a file that never before occurred to him. He will find three things to astonish him: First: That of dimensions. Second: The difficulty of getting it square. Third: The character of the surface when he has finished it. FILING AN IRREGULAR BLOCK.--To file a block of an irregular character so that the dimensions are accurate, is a good test for an accomplished workman. The job is made doubly difficult if he is required to file it square at the same time. It will be found, invariably, that the sides will not be parallel, and by the time it is fully trued up the piece will be too small. See Figs. 44 and 45. Then, unless the utmost care is taken, the flat sides _will not_ be flat, but rounded. FILING A BAR STRAIGHT.--The next test is to get the boy to file a bar straight. He has no shaper or planer for the purpose, so that it must be done by hand. He will find himself lacking in two things: The edge of the bar will not be straight; nor will it be square with the side of the bar. [Illustration: _Fig. 44. Rounded Surface_ _Fig. 45. A Winding Face_] FILING BAR WITH PARALLEL SIDES.--Follow up this test by requiring him to file up a bar, first, with two exactly parallel sides, and absolutely straight, so it will pass smoothly between the legs of a pair of calipers, and then file the two other sides in like manner. SURFACING OFF DISKS.--When the foregoing are completed there is still another requirement which, though it appears simple, is the supreme test. Set him to work at surfacing off a pair of disks or plates, say one and a half inches in diameter, so that when they are finished they