THE "HOW-TO-DO-IT" BOOKS
PRACTICAL MECHANICS FOR BOYS
THE "HOW-TO-DO-IT" BOOKS
PRACTICAL MECHANICS FOR BOYS
In language which every boy can understand and so arranged that he may readily carry out any work from the instructions given.
WITH MANY ORIGINAL ILLUSTRATIONS
By J. S. ZERBE, M.E.
CARPENTRY FOR BOYS ELECTRICITY FOR BOYS
M. A. DONOHUE & COMPANY
CHICAGO :: NEW YORK
COPYRIGHT, 1914, BY THE NEW YORK BOOK COMPANY
Made in U. S. A.
INTRODUCTORY Page 1
I. ON TOOLS GENERALLY Page 7
Varied Requirements. List of Tools. Swivel Vises. Parts of Lathe. Chisels. Grinding Apparatus. Large Machines. Chucks. Bench Tools. Selecting a Lathe. Combination Square. Micrometers. Protractors. Utilizing Bevel Protractors. Truing Grindstones. Sets of Tools. The Work Bench. The Proper Dimensions. How Arranged.
II. HOW TO GRIND AND SHARPEN TOOLS Page 26
Importance of the Cutting Tool. The Grinder. Correct Use of Grinder. Lathe Bitts. Roughing Tools. The Clearance. The Cutting Angle. Drills. Wrong Grinding. Chisels. Cold Chisels. System in Work. Wrong Use of Tools.
III. SETTING AND HOLDING TOOLS Page 34
Lathe Speed. The Hack-saw. Hack-saw Frame. The Blade. Files. Grindstones. Emery and Grinding Wheels. Carelessness in Holding Tools. Calipers. Care in Use of Calipers. Machine Bitts. The Proper Angle for Lathe Tools. Setting the Bitt. The Setting Angle. Bad Practice. Proper Lathe Speeds. Boring Tools on Lathe. The Rake of the Drill. Laps. Using the Lap. Surface Gages. Uses of the Surface Gage.
IV. ON THE FIRST USE OF THE FILE Page 48
The First Test. Filing an Irregular Block. Filing a Bar Straight. Filing Bar with Parallel Sides. Surfacing Off Disks. True Surfacing. Precision Tools. Test of the Mechanic. Test Suggestions. Use of the Dividers. Cutting a Key-way. Key-way Difficulties. Filing Metal Round. Kinds of Files. Cotter-file. Square. Pinion. Half-round. Round. Triangular. Equalizing. Cross. Slitting. Character of File Tooth. Double Cut. Float-cut. Rasp Cut. Holding the File. Injuring Files. Drawing Back the File.
V. HOW TO COMMENCE WORK Page 61
Familiarity with Tools. File Practice. Using the Dividers. Finding Centers. Hack-saw Practice. Cutting Metal True. Lathe Work. First Steps. Setting the Tool. Metals Used. The Four Important Things. Turning Up a Cylinder. Turning Grooves. Disks. Lathe Speeds.
VI. ILLUSTRATING SOME OF THE FUNDAMENTAL DEVICES Page 68
Belt Lacing. Gears. Crown Wheel. Grooved Friction Gearing. A Valve which Closes by the Water Pressure. Cone Pulleys. Universal Joint. Trammel for Making Ellipses. Escapements. Simple Device to Prevent a Wheel or Shaft from Turning Back. Racks and Pinions. Mutilated Gears. Simple Shaft Coupling. Clutches. Ball and Socket Joints. Tripping Devices. Anchor Bolt. Lazy Tongs. Disk Shears. Wabble Saw. Crank Motion by a Slotted Yoke. Continuous Feed by Motion of a Lever. Crank Motion. Ratchet Head. Bench Clamp. Helico-volute Spring. Double helico-volute. Helical Spring. Single Volute Helix Spring. Flat Spiral, or Convolute. Eccentric Rod and Strap. Anti-dead Center for Lathe.
VII. PROPERTIES OF MATERIALS Page 79
Elasticity. Traction. Torsion. Flexure. Tenacity. The Most Tenacious Metal. Ductility. Malleability. Hardness. Alloys. Resistance. Persistence. Conductivity. Equalization. Reciprocity. Molecular Forces. Attraction. Cohesion. Adhesion. Affinity. Porosity. Compressibility. Elasticity. Inertia. Momentum. Weight. Centripetal Force. Centrifugal Force. Capillary Attraction. The Sap of Trees. Sound. Acoustics. Sound Mediums. Vibration. Velocity of Sound. Sound Reflections. Resonance. Echos. Speaking Trumpet. The Stethoscope. The Vitascope. The Phonautograph. The Phonograph. Light. The Corpuscular Theory. Undulatory Theory. Luminous Bodies. Velocity of Light. Reflection. Refraction. Colors. The Spectroscope. The Rainbow. Heat. Expansion.
VIII. HOW DRAUGHTING BECOMES A VALUABLE AID Page 95
Lines in Drawing. Shading. Direction of Shade. Perspectives. The Most Pronounced Lines. Direction of Light. Scale Drawings. Degree, and What it Means. Memorizing Angles. Section Lining. Making Ellipses and Irregular Curves. Focal Points. Isometric and Perspective. The Protractor. Suggestions in Drawing. Holding the Pen. Inks. Tracing Cloth. Detail Paper. How to Proceed. Indicating Material by Section Lines.
IX. TREATMENT AND USE OF METALS Page 112
Annealing. Toughness and Elasticity. The Process. Tempering. Tempering Contrasted with Annealing. Materials Used. Gradual Tempering. Fluxing. Uniting Metals. Alloying Method. Welding. Sweating. Welding Compounds. Oxidation. Soldering. Soft Solder. Hard Solder. Spelter. Soldering Acid. The Soldering Iron.
X. ON GEARING, AND HOW ORDERED Page 121
Spur and Pinion. Measuring a Gear. Pitch. Diametral Pitch. Circular Pitch. How to Order a Gear. Bevel and Miter Gears. Drawing Gears. Sprocket Wheels.
XI. MECHANICAL POWER Page 128
The Lever. Wrong Inferences from Use of Lever. The Lever Principle. Powers vs. Distance Traveled. Power vs. Loss of Time. Wrongly-Directed Energy. The Lever and the Pulley. Sources of Power. Water Power. Calculating Fuel Energy. The Pressure or Head. Fuels. Power from Winds. Speed of Wind and Pressure. Varying Degrees of Pressure. Power from Waves and Tides. A Profitable Field.
XII. ON MEASURES Page 139
Horse Power. Foot Pounds. Energy. How to Find Out the Power Developed. The Test. Calculations. The Foot Measure. Weight. The Gallon. The Metric System. Basis of Measurement. Metrical Table, Showing Measurements in Feet and Inches.
XIII. USEFUL INFORMATION FOR THE WORKSHOP Page 148
Finding the Circumference of a Circle. Diameter of a Circle. Area of a Circle. Area of a Triangle. Surface of a Ball. Solidity of a Sphere. Contents of a Cone. Capacity of a Pipe. Capacity of Tanks. To Toughen Aluminum. Amalgams. Prevent Boiler Scaling. Diamond Test. Making Glue Insoluble in Water. Taking Glaze Out of Grindstone. To Find Speeds of Pulleys. To Find the Diameters Required. To Prevent Belts from Slipping. Removing Boiler Scale. Gold Bronze. Cleaning Rusted Utensils. To Prevent Plaster of Paris from Setting Quickly. The Measurement of Liquids with Spoons.
XIV. SIMPLICITY OF GREAT INVENTIONS AND OF NATURE'S MANIFESTATION Page 152
Invention Precedes Science. Simplicity in Inventions. The Telegraph. Telephone. Transmitter. Phonograph. Wireless Telegraphy. Printing Telegraph. Electric Motor. Explosions. Vibrations in Nature. Qualities of Sound. The Photographer's Plate. Quadruplex Telegraphy. Electric Harmony. Odors. Odophone. A Bouquet of Vibrations. Taste. Color.
XV. WORKSHOP RECIPES AND FORMULAS Page 160
Adhesives for Various Uses. Belt Glue. Cements. Transparent Cement. U. S. Government Gum. To Make Different Alloys. Bell-metal. Brass. Bronzes. Boiler Compounds. Celluloid. Clay Mixture for Forges. Modeling Clay. Fluids for Cleaning Clothes, Furniture, etc. Disinfectants. Deodorants. Emery for Lapping Purposes. Explosives. Fulminates. Files, and How to Keep Clean. Renewing Files. Fire-proof Materials or Substances. Floor Dressings. Stains. Foot Powders. Frost Bites. Glass. To Frost. How to Distinguish. Iron and Steel. To Soften Castings. Lacquers. For Aluminum and Brass. Copper. Lubricants. Paper. Photography. Plasters. Plating, Coloring Metals. Polishes. Putty. Rust Preventives. Solders. Soldering Fluxes. Steel Tempering. Varnishes. Sealing Wax.
XVI. HANDY TABLES Page 178
Table of Weights for Round and Square Steel. Table of Weight of Flat Steel Bars. Avoirdupois Weight. Troy Weight. Apothecaries' Weight. Linear Measure. Long Measure. Square Measure. Solid or Cubic Measure. Dry Measure. Liquid Measure. Paper Measure. Table of Temperatures. Strength of Various Metals. Freezing Mixtures. Ignition Temperatures. Power and Heat Equivalents.
XVII. INVENTIONS AND PATENTS, AND INFORMATION ABOUT THE RIGHTS AND DUTIES OF INVENTORS AND WORKMEN, Page 188
The Machinist's Opportunities. What is an Inventor? Idea Not Invention. What an Invention Must Have. Obligation of the Model Builder. Paying for Developing Devices. Time for Filing an Application. Selling an Unpatented Invention. Joint Inventors. Joint Owners Not Partners. Partnerships in Patents. Form of Protection Issued by the Government. Life of a Patent. Interference Proceedings. Concurrent Applications. Granting Interference. Steps in Interference. First Sketches. First Model. First Operative Machine. Preliminary Statements. Proving Invention. What Patents Are Issued For. Owner's Rights. Divided and Undivided Patents. Assignments. How Made. What an Invention Must Have. Basis for Granting Patent in the United States. Reasons for Granting Abroad. Original Grants of Patents. International Agreement. Application for Patents. Course of Procedure. Costs. Filing a Matter of Secrecy.
LIST OF ILLUSTRATIONS
FIG. PAGE 1. Bench vise 8 2. Pipe grip for vise 9 3. Swivel vise 10 4. Speed lathe 11 5. Calipers 12 6. Engine lathe 13 7. Center gage 14 8. Pocket screw and wire gage 15 9. Handy bench vise 16 10. Combination square 17 11. Uses of the combination square 18 12. A quick adjusting micrometer 19 13. Universal bevel protractor 20 14. Uses of universal bevel protractor 21 15. Grindstone truing device 22 16. Set of tools and case 23 17. The work bench 24 18. Hook tool 28 19. Parting tool 28 20. Knife tool 28 21. Right-hand side tool 28 22. Internal tool 28 23. Left-hand side tool 28 24. Tool for wrought iron 29 25. Tool for cast iron 29 26. End view of drill 31 27. Side view of drill 31 28. Hack-saw frame 35 29. Hack-saw blade 35 30. Plain hook tool 38 31. Plain straight tool 38 32. Proper angles for tools 39 33. Angles for tools 39 34. Angles for tools 39 35. Set of the bitt 40 36. Correct angle 41 37. Wrong angle 41 38. Too low 42 39. Improper set 42 40. Internal set 43 41. Set for brass 43 42. Surface gage 44 43. Uses of surface gage 46 44. Rounded surface 49 45. Winding surface 49 46. Hexagon nut 51 47. Laying off hexagon nut 51 48. Cutting key-way 52 49. Key-seat rule 54 50. Filing metal round 54 51. Filing metal round 54 52. Making a round bearing 55 53. Making a round bearing 55 54. Cross section of file 56 55. Files 58 56. Correct file movement 59 57. Incorrect file movement 60 58. Belt lacing 69 59. Belt lacing 69 60. Belt lacing 69 61. Belt lacing 69 62. Bevel gears 71 63. Miter gears 71 64. Crown wheel 71 65. Grooved friction gears 71 66. Valve 71 67. Cone pulleys 71 68. Universal joint 71 69. Trammel 73 70. Escapement 73 71. Device for holding wheel 73 72. Rack and pinion 73 73. Mutilated gears 73 74. Shaft coupling 73 75. Clutches 75 76. Ball and socket joints 75 77. Fastening ball 75 78. Tripping devices 75 79. Anchor bolt 75 80. Lazy tongs 75 81. Disc shears 75 82. Wabble saw 76 83. Continuous crank motion 76 84. Continues feed 76 85. Crank motion 76 86. Ratchet head 76 87. Bench clamp 76 88. Helico-volute spring 77 89. Double helico-volute 77 90. Helical spring 77 91. Single volute-helix 77 92. Flat spiral or convolute 77 93. Eccentric rod or strap 77 94. Anti dead-centers for lathes 77 95. Plain circle 95 96. Ring 96 97. Raised surface 96 98. Sphere 96 99. Depressed surface 96 100. Concave 97 101. Forms of cubical outlines 98 102. Forms of cubical outlines 98 103. Forms of cubical outlines 98 104. Forms of cubical outlines 98 105. Shading edges 99 106. Shading edges 99 107. Illustrating heavy lines 100 108. Illustrating heavy lines 100 109. Lines on plain surfaces 101 110. Lines on plain surfaces 101 111. Illustrating degrees 102 112. Section lining 103 113. Drawing an ellipse 104 114. Perspective at angles 106 115. Perspective of cube 107 116. Perspective of cube 107 117. Perspective of cube 107 118. Protractor 108 119. Using the protractor 109 120. Section-lining metals 110 121. Spur gears 122 122. Miter gear pitch 123 123. Bevel gears 124 124. Laying of miter gears 125 125. Sprocket wheel 128 126. Simple lever 129 127. Lever action 130 128. The pulley 132 129. Change of direction 133 130. Change of direction 133 131. Steam pressure 135 132. Water pressure 135 133. Prony brake 141 134. Speed indicator 142
PRACTICAL MECHANICS FOR BOYS
The American method of teaching the mechanical arts has some disadvantages, as compared with the apprentice system followed in England, and very largely on the continent.
It is too often the case that here a boy or a young man begins work in a machine shop, not for the avowed purpose of learning the trade, but simply as a helper, with no other object in view than to get his weekly wages.
Abroad, the plan is one which, for various reasons, could not be tolerated here. There he is bound for a certain term of years, and with the prime object of teaching him to become an artisan. More often than otherwise he pays for this privilege, and he knows it is incumbent on him "to make good" right from the start.
He labors under the disadvantage, however, that he has a certain tenure, and in that course he is not pushed forward from one step to the next on account of any merit of his own. His advancement is fixed by the time he has put in at each part of the work, and thus no note is taken of his individuality.
Here the boy rises step after step by virtue of his own qualifications, and we recognize that one boy has the capacity to learn faster than another. If he can learn in one year what it requires three in another to acquire, in order to do it as perfectly, it is an injury to the apt workman to be held back and deterred from making his way upwardly.
It may be urged that the apprentice system instills thoroughness. This may be true; but it also does another thing: It makes the man a mere machine. The true workman is a thinker. He is ever on the alert to find easier, quicker and more efficient means for doing certain work.
What is called "Efficiency" in labor methods, can never obtain in an apprenticeship system for this reason. In a certain operation, where twelve motions are required to do a certain thing, and a minute to perform the twelve operations, a simplified way, necessitating only eight motions, means a difference in saving one-third of the time. The nineteen hundred fewer particular movements in a day's work, being a less strain on the operator, both physically and mentally, to say nothing whatever of the advantages which the proprietor of the shop would gain.
I make this a leading text in the presentation of this book; namely, that individual merit and stimulus is something of such extreme importance that it should be made the keynote for every boy who tries to become a mechanic.
The machinist easily occupies a leading place in the multitude of trades and occupations. There is hardly an article of use but comes to the market through his hands. His labor is most diverse, and in his employment doing machine work he is called upon to do things which vary widely in their character.
These require special knowledge, particular tools, and more frequently than otherwise, a high order of inventive ability to enable him to accomplish the task.
The boy should be taught, at the outset, that certain things must be learned thoroughly, and that habits in a machine shop can be bad as well as good. When he once becomes accustomed to putting a tool back in its rightful place the moment he is through with it, he has taken a long step toward efficiency.
When he grasps a tool and presents it to the work without turning it over several times, or has acquired the knack of picking up the right tool at the proper place, he is making strides in the direction of becoming a rapid and skilled workman.
These, and many other things of like import, will require our attention throughout the various chapters.
It is not the intention of the book to make every boy who reads and studies it, a machinist; nor have we any desire to present a lot of useful articles as samples of what to make. The object is to show the boy what are the requirements necessary to make him a machinist; how to hold, handle, sharpen and grind the various tools; the proper ones to use for each particular character of work; how the various machines are handled and cared for; the best materials to use; and suggest the numerous things which can be done in a shop which will pave the way for making his work pleasant as well as profitable.
It also analyzes the manner in which the job is laid out; how to set the tools to get the most effective work; and explains what is meant by making a finished piece of workmanship. These things, properly acquired, each must determine in his own mind whether he is adapted to follow up the work.
Over and above all, we shall try to give the boy some stimulus for his work. Unless he takes an interest in what he is doing, he will never become an artisan in the true sense of the word.
Go through the book, and see whether, here and there, you do not get some glimpses of what it means to take a pleasure in doing each particular thing, and you will find in every instance that it is a satisfaction because you have learned to perform it with ease.
I do not know of anything which has done as much to advance the arts and manufactures, during the last century, as the universal desire to improve the form, shape and structure of tools; and the effort to invent new ones. This finds its reflection everywhere in the production of new and improved products.
In this particular I have been led to formulate a homely sentence which expresses the idea: Invention consists in doing an old thing a new way; or a new thing any way.
ON TOOLS GENERALLY
Judging from the favorable comments of educators, on the general arrangement of the subject matter in the work on "Carpentry for Boys," I am disposed to follow that plan in this book in so far as it pertains to tools.
In this field, as in "Carpentry," I do not find any guide which is adapted to teach the boy the fundamentals of mechanics. Writers usually overlook the fact, that as the boy knows nothing whatever about the subject, he could not be expected to know anything about tools.
To describe them gives a start in the education, but it is far short of what is necessary for one in his condition. If he is told that the chisel or bit for a lathe has a diamond point, or is round-nosed, and must be ground at a certain angle, he naturally wants to know, as all boys do, why it should be at that angle.
So in the setting of the tools with relation to the work, the holding and manipulation of the file, of the drill for accurate boring, together with numerous little things, are all taken for granted, and the boy blunders along with the ultimate object in sight, without having the pathway cleared so he may readily reach the goal.
VARIED REQUIREMENTS.—The machinist's trade is one which requires the most varied tools of all occupations, and they are by all odds the most expensive to be found in the entire list of vocations.
This arises from the fact that he must work with the most stubborn of all materials. He finds resistance at every step in bringing forth a product.
LIST OF TOOLS.—With a view of familiarizing the boy with this great variety the following list is compiled, from which we shall select the ones essential in the initial equipment of a small shop.
VISES.—One small, good vise is infinitely preferable to two bad ones. For ordinary work a 3-inch jaw is preferable, and it should be firmly mounted on the bench. So many kinds are now made that it would be a costly thing to purchase one for each special use, therefore the boy will find it profitable to make some attachments for the ordinary vise.
SWIVEL VISES.—A swivel vise is always a good tool, the cost being not excessive over the ordinary kind. Then a pair of grips for holding pipe, or round material which is to be threaded, can readily be made.
The drawing (Fig. 2) shows a serviceable pair of grips, made to fit the jaws of a vise, and will be acceptable in much of the work. Then, the vise should be provided with copper caps for the jaws to be used when making up articles which would otherwise be injured by the jaws.
Let us get a comprehensive view of the different kinds of tools necessary in a fully equipped shop.
PARTS OF LATHE.—The first thing of importance is the lathe, and of these there is quite a variety, and among the accompaniments are the slide rest, mandrel, back gear, division plate, angle plate, cone plate and various chucks.
There must also be change wheels, studs and quadrant plates, self-acting feed for surfacing and cross slide, and clamping nuts.
Drilling machines, both hand and power, hand and ratchet braces and breast-drill stocks.
CHISELS.—Chisels of various kinds, for chipping and cross-cutting; round-nosed, centering, set punches, tommies and drifts.
Back, tee and centering square; bevels, spirit level, inside and outside calipers, straight edges, rules and surface plates.
Gages for boring, scribing blocks, steel and brass scribes, stocks and dies, screw-plates, taps for bolts, reamers.
Files for various descriptions, countersinks, frame and hack saws.
GRINDING APPARATUS.—Emery wheel, cloth and paper, paper, flour emery, polishing powders, laps and buffs, and polishing sticks.
Forge, anvils, tongs, swages, punches, bolt tools, hot and cold chisels, blow-pipe, soldering iron, hard and soft solders, borax, spirits of salts, oil, resin and spelter.
To this may be added an endless variety of small bench tools, micrometers, protractors, arbors, collets, box tools and scrapers.
LARGE MACHINES.—The list would not be complete without the planer, shaper and milling machine, with their variety of chucks, clamps and other attachments, too numerous to mention.
The foregoing show what a wonderful variety of articles are found in a well-equipped shop, all of which can be conveniently used; but to the boy who has only a small amount of money, a workable set is indicated as follows:
A small lathe, with an 8-inch swing, can be obtained at a low cost, provided with a countershaft complete.
CHUCKS.—With this should go a small chuck, and a face-plate for large work, unless a large chuck can also be acquired. This, with a dozen tools of various sizes, and also small bits for drilling purposes.
The lathe will answer all purposes for drilling, but small drilling machines are now furnished at very low figures, and such a machine will take off a great deal of duty from the lathe.
As the lathe is of prime importance, never use it for drilling, if you have a driller, as it always has enough work to do for tuning up work.
BENCH TOOLS.—Of bench tools, a 3-inch vise, various files, center punch, two hammers, round and A-shaped peons, hack saw, compasses, inside and outside calipers, screw driver, cold chisels, metal square, level, straight edge, bevel square, reamers, small emery wheel and an oil stone, make a fairly good outfit to start with, and these can be added to from time to time.
Everything in the machine shop centers about the lathe. It is the king of all tools. The shaper and planer may be most efficient for surfacing, and the milling machine for making grooves and gears, or for general cutting purposes, but the lathe possesses a range of work not possible with either of the other tools, and for that reason should be selected with great care.
SELECTING A LATHE.—The important things about a lathe are the spindle bearings and the ways for the tool-holder. The least play in either will ruin any work. Every other part may be defective, but with solidly built bearing-posts and bearings, your lathe will be effective.
For this reason it will not pay to get a cheap tool. Better get a small, 6-inch approved tool of this kind, than a larger cheap article. It may pay with other tools, but with a lathe never.
Never do grinding on a lathe. The fine emery, or grinding material, is sure to reach the bearings; it matters not what care is exercised. There is only one remedy for this—overhauling.
COMBINATION SQUARE.—A tool of this kind is most essential, however small. It can be used as a try-square, and has this advantage, that the head can be made to slide along the rule and be clamped at any point. It has a beveling and a leveling device, as well.
The combination square provides a means for doing a great variety of work, as it combines the qualities of a rule, square, miter, depth gage, height gage, level and center head.
The full page illustration (Fig. 11) shows some of the uses and the particular manner of holding the tool.
MICROMETERS.—Tools of this description are made which will accurately measure work in dimensions of ten-thousandths of an inch up to an inch.
The illustration (Fig. 12) shows an approved tool, and this is so constructed that it can instantly be changed and set by merely pressing the end of the plunger as shown.
PROTRACTORS.—As all angles are not obtainable by the square or bevel, a protractor is a most desirable addition to the stock of tools. As one side of the tool is flat it is convenient for laying on the paper when drafting, as well as for use on the work.
The protractor has a graduated disk, and is adjustable so it can be disposed at any angle.
All special tools of this kind are serviceable, and the boy should understand their uses, even though he is not able for the time being to acquire them. To learn how they are applied in daily use is an education in itself.
UTILIZING BEVEL PROTRACTOR.—Examine the full-page illustration (Fig. 14), and see how the bevel protractor is utilized to measure the angles of work, whether it is tapering heads or different kinds of nuts, or end and side surfacing, and it will teach an important lesson.
TRUING GRINDSTONES.—Devices for truing up grindstones are now made, and the illustration (Fig. 15) shows a very efficient machine for this purpose. It can be applied instantly to the face of the stone, and it works automatically, without interfering with the use of the stone.
It is frequently the case that an emery wheel will become glazed, due to its extreme hardness. This is also caused, sometimes, by running it at too high a speed. If the glazing continues after the speed is reduced, it should be ground down an eighth of an inch or so. This will, usually, remedy the defect.
SETS OF TOOLS.—A cheap and convenient set of precision tools is shown in Fig. 16, which is kept in a neat folding leather case. The set consists of a 6-inch combination square, complete center punch, 6-inch flexible steel rule center gage, 4-inch calipers, 4-inch outside caliper with solid nut, 4-inch inside caliper with solid nut, and a 4-inch divider with a solid nut.
THE WORK BENCH.—This is the mechanic's fort. His capacity for work will depend on its arrangement. To the boy this is particularly interesting, and for his uses it should be made full three inches lower than the standard height.
A good plan to judge of the proper height is to measure from the jaws of the vise. The top of the jaw should be on a level with the elbows. Grasp a file with both hands, and hold it as though in the act of filing across the work; then measure up from the floor to the elbows, when they are held in that position.
THE PROPER DIMENSIONS.—This plan will give you a sure means of selecting a height that is best adapted for your work. The regulation bench is about 38 inches high, and assuming that the vise projects up about 4 inches more, would bring the top of the jaws about 42 to 44 inches from the floor. It is safe to fix the height of the bench at not less than 34 inches.
This should have a drawer, preferably near the right-hand end of the bench. The vise should be at the left side, and the bench in your front should be free of any fixed tools.
HOW ARRANGED.—Have a rack above the bench at the rear, for the various tools when not in use, and the rear board of the bench should be elevated above the front planks several inches, on which the various tools can be put, other than those which are suspended on the rack above.
The advantage of this is, that a bench will accumulate a quantity of material that the tools can hide in, and there is nothing more annoying than to hunt over a lot of trash to get what is needed. It is necessary to emphasize the necessity of always putting a tool back in its proper place, immediately after using.
HOW TO GRIND AND SHARPEN TOOLS
It is singular, that with the immense variety of tools set forth in the preceding chapter, how few, really, require the art of the workman to grind and sharpen. If we take the lathe, the drilling machine, as well as the shaper, planer, milling machine, and all power-driven tools, they are merely mechanism contrived to handle some small, and, apparently, inconsequential tool, which does the work on the material.
IMPORTANCE OF THE CUTTING TOOL.—But it is this very fact that makes the preparation of that part of the mechanism so important. Here we have a lathe, weighing a thousand pounds, worth hundreds of dollars, concentrating its entire energies on a little bit, weighing eight ounces, and worth less than a dollar. It may thus readily be seen that it is the little bar of metal from which the small tool is made that needs our care and attention.
This is particularly true of the expensive milling machines, where the little saw, if not in perfect order, and not properly set, will not only do improper work, but injure the machine itself. More lathes are ruined from using badly ground tools than from any other cause.
In the whole line of tools which the machinist must take care of daily, there is nothing as important as the lathe cutting-tool, and the knowledge which goes with it to use the proper one.
Let us simplify the inquiry by considering them under the following headings:
1. The grinder.
2. The grinding angle.
THE GRINDER.—The first mistake the novice will make, is to use the tool on the grinder as though it were necessary to grind it down with a few turns of the wheel. Haste is not conducive to proper sharpening. As the wheel is of emery, corundum or other quickly cutting material, and is always run at a high rate of speed, a great heat is evolved, which is materially increased by pressure.
Pressure is injurious not so much to the wheel as to the tool itself. The moment a tool becomes heated there is danger of destroying the temper, and the edge, being the thinnest, is the most violently affected. Hence it is desirable always to have a receptacle with water handy, into which the tool can be plunged, during the process of grinding down.
CORRECT USE OF GRINDER.—Treat the wheel as though it is a friend, and not an enemy. Take advantage of its entire surface. Whenever you go into a machine shop, look at the emery wheel. If you find it worn in creases, and distorted in its circular outline, you can make up your mind that there is some one there who has poor tools, because it is simply out of the question to grind a tool correctly with such a wheel.
Coarse wheels are an abomination for tool work. Use the finest kinds devised for the purpose. They will keep in condition longer, are not so liable to wear unevenly, and will always finish off the edge better than the coarse variety.
LATHE BITS.—All bits made for lathes are modifications of the foregoing 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 will fit against each other perfectly flat.
A pair of such disks, if absolutely true, will hold together by the force of cohesion, even in a dry state, or they will, as it were, float against each other.
TRUE SURFACING.—Prior to about 1850 the necessity of true surfacing was not so important or as well known as at the present time. About that period Sir J. Whitworth, an eminent English engineer and mechanic, called the attention of machinists to the great advantage arising from true surfaces and edges for all types of machinery, and he laid the foundation of the knowledge in accurating surfacing.
PRECISION TOOLS.—Due to his energy many precision tools were made, all tending to this end, and as a result machines became better and more efficient in every way.
It had this great advantage: It taught the workman of his day how to use the file and scraper, because both must be used conjunctively to make an absolutely flat plate.
Contrary to general beliefs, shapers and planers do not make absolutely accurate surfaces. The test of this is to put together two plates so planed off. There is just enough unevenness to permit air to get between the plates. If they were perfectly true they would exclude all air, and it would be a difficult matter to draw them apart.
TEST OF THE MECHANIC.—To make them perfectly flat, one plate has chalk rubbed over it, and the two plates are then rubbed together. This will quickly show where the high spots are, and the file and scraper are then used to cut away the metal.
In England the test of the mechanic used to be determined by his ability to file a piece of metal flat. It was regarded as the highest art. This is not the most desirable test at the present time, and it is recognized that a much severer test is to file a narrow piece exactly flat, and so that it will not have a trace of roundness, and be square from end to end.
TEST SUGGESTIONS.—In a shop which does not have the advantage of a planer or shaper, there are so many articles which must be filed up, that it is interesting to know something of how the various articles are made with a file.
To file a hexagon, or six-sided nut will be a good test with a file. To do this a little study in geometrical lines will save a vast amount of time. In beginning the work, measure the radius with a divider, and then step off and make six marks equidistant from each other on the round surface.
USE OF THE DIVIDERS.—The distance between each of these points is equal to the radius, or half the diameter, of the round bar. See Fig. 46, which shows this. The marks should be scribed across the surface, as shown in Fig. 47, where the lines show the ends of the facets of the outside of the nut.
Do not let the file obliterate the lines at the rough cutting, but leave enough material so you can make a good finish at the line.
CUTTING A KEY-WAY.—Another job you may have frequent occasion to perform, is to cut a way for a key in a shaft and in a wheel hub. Naturally, this will be first roughed out with a cold chisel narrower than the key is to be, and also slightly shallower than the dimensions of the key.
A flat file should be used for the purpose, first a heavy rough one, for the first cutting. The better way is to have the key so it can be frequently tried while the filing process is going on, so that to fit the key in this way is a comparatively easy task.
KEY-WAY DIFFICULTIES.—But the trouble commences when the groove is filed for the depth. Invariably, the mistake will be made of filing the width first, so the key will fit in. As a result, in deepening the groove the file will contact with the walls, and you have a key-way too wide for the key.
To avoid this, file the depth, or nearly so, and then with a fine file cut in the corners in the direction indicated by the dart, Fig. 48.
A proper key is square in cross section. In such a case the depth of the key-way, at each side wall, is just half the width of the key-way.
An excellent key-seat rule can be made by filing out two right-angled pieces, as shown in Fig. 49, which can be attached to the ordinary six-inch metal rule, and this will enable you to scribe the line accurately for the key-way on the shaft.
FILING METAL ROUND.—It is sometimes necessary to file a piece of metal round. This is a hard job, particularly where it is impossible to scribe the end of the piece. Suppose it is necessary to file up a bearing surface, or surfaces, intermediate the ends of a square bar.
You have in that case four sides to start from, the opposite sides being parallel with each other, so that you will have two dimensions, and four equal sides, as shown in Fig. 50.
The first step will be to file off accurately the four corners 1, 2, 3, 4, so as to form eight equal sides or faces, as shown in Fig. 51. If you will now proceed to file down carefully the eight corners, so as to make sixteen sides, as in Fig. 52, the fourth set of corners filed down will make the filed part look like the illustration Fig. 53 with thirty-two faces.
This may be further filed down into sixty-four faces, and a few cuts of the finishing file will take off the little ridges which still remain. By using emery cloth, and wrapping it around the bearing portion, and changing it continually, while drawing it back and forth, will enable you to make a bearing which, by care, will caliper up in good shape.
KINDS OF FILES.—Each file has five distinct properties; namely: the length, the contour, the form in cross section, the kind of teeth, and the fineness of the teeth.
There are nine well-defined shapes for files. These may be enumerated as follows:
No. 1. The cotter file. The small kind is called a verge or pivot file.
No. 2. Square file, which may be tapering from end to end, or have parallel sides throughout.
No. 3. Watch pinion file. This may have its sides parallel or tapering, to make a knife-shaped file.
No. 4. Clock-pinion; which may be used for either nicking, piecing, or squaring-off purposes.
No. 5. Round, with parallel sides for gulleting purposes, or rat-tail when it tapers.
No. 6. Triangular, or three equally-sided body for saw filing.
No. 7. Equalizing file. This is parallel when used for making clock-pinions or endless screws; or for slitting, entering, warding, or making barrel holes, when the body of the file tapers.
No. 8. Cross, or double-round, half-file.
No. 9. Slitting file; which has parallel sides only. A cant file.
CHARACTER OF THE FILE TOOTH.—Files are distinguished principally by the character of the oblique, or cross grooves and ridges which do the cutting and abrading when the file is drawn across the surface.
This is really more important than the shape, because the files, by their cuttings, are adapted for the various materials which they are to be used upon.
The files are classified as Double Cut, of which there are the rough, middle, bastard, second cut, smooth, and dead smooth.
The Float Cut, which is either rough, bastard or smooth; and
The Rasp Cut, either rough, bastard or smooth.
Several types are illustrated in Fig. 55, which show the characteristics of the various cuts.
The rasps are used principally for soft material, such as wood or for hoofs, in horse shoeing, hence they need not be considered in connection with machine-shop work.
HOLDING THE FILE.—The common mistake on the part of the beginner is to drag the file across the work at an angle. The body of the file should move across straight and not obliquely.
Note this movement in Fig. 56 where the dash shows the correct movement of the file with relation to the work. Also observe that the file cutting ridges are not straight across the file, but at an angle to the direction of the dart.
INJURING FILES.—Now the frequent practice is to use the file as shown in Fig. 57, in which case it is moved across obliquely. The result is that the angle of the file cut is so disposed that the teeth of the file do not properly aid in the cutting, but in a measure retard the operation.
File teeth are disposed at an angle for the purpose of giving them a shearing cut, which is the case when the file moves across the work on a line with its body.
To use a file as shown in Fig. 57 injures the file without giving it an opportunity to cut as fast as it would when properly used.
DRAWING BACK THE FILE.—In drawing back a file it is always better to allow it to drag over the work than to raise it up. It is frequently the case that some of the material will lodge in the teeth, and the back lash will serve to clear out the grooves.
This is particularly true in filing copper, aluminum, lead, and like metals, but it is well to observe this in all cases.
HOW TO COMMENCE WORK
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 the chapter 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.
ILLUSTRATING 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.
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 brass, 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 passes 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.
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 substitute 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.
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.
Fig. 76. BALL AND SOCKET JOINTS.—The most practical form of ball and socket joints is simply a head in which is a bowl-shaped cavity the depth of one-half of the ball. A plate with a central opening small enough to hold in the ball, and still large enough at the neck to permit the arm carrying the ball to swing a limited distance, is secured by threads, or by bolts, to the head. The first figure shows this.
Fig. 77 illustrates a simple manner of tightening the ball so as to hold the standard in any desired position.
Fig. 78. TRIPPING DEVICES.—These are usually in the form of hooks, so arranged that a slight pull on the tripping lever will cause the suspended articles to drop.
Fig. 79. ANCHOR BOLT.—These are used in brick or cement walls. The bolt itself screws into a sleeve which is split, and draws a wedge nut up to the split end of the sleeve. As a result the split sleeve opens or spreads out and binds against the wall sufficiently to prevent the bolt from being withdrawn.
Fig. 80. LAZY TONGS.—One of the simplest and most effective instruments for carrying ice, boxes or heavy objects, which are bulky or inconvenient to carry. It grasps the article firmly, and the heavier the weight the tighter is its grasp.
Fig. 81. DISC SHEARS.—This is a useful tool either for cutting tin or paper, pasteboard and the like. It will cut by the act of drawing the material through it, but if power is applied to one or to both of the shafts the work is much facilitated, particularly in thick or hard material.
Fig. 82. WABBLE SAW.—This is a most simple and useful tool, as it will readily and quickly saw out a groove so that it is undercut. The saw is put on the mandrel at an angle, as will be seen, and should be run at a high rate of speed.
Fig. 83. CRANK MOTION BY A SLOTTED YOKE.—This produces a straight back-and-forth movement from the circular motion of a wheel or crank. It entirely dispenses with a pitman rod, and it enables the machine, or the part of the machine operated, to be placed close to the crank.
Fig. 84. CONTINUOUS FEED BY THE MOTION OF A LEVER.—The simple lever with a pawl on each side of the fulcrum is the most effective means to make a continuous feed by the simple movement of a lever. The form shown is capable of many modifications, and it can be easily adapted for any particular work desired.
Fig. 85. CRANK MOTION.—By the structure shown, namely, a slotted lever (A), a quick return can be made with the lever. B indicates the fulcrum.
Fig. 86. RATCHET HEAD.—This shows a well-known form for common ratchet. It has the advantage that the radially movable plugs (A) are tangentially disposed, and rest against walls (B) eccentrically disposed, and are, therefore, in such a position that they easily slide over the inclines.
Fig. 87. BENCH CLAMP.—A pair of dogs (A, B), with the ends bent toward each other, and pivoted midway between the ends to the bench in such a position that the board (C), to be held between them, on striking the rear ends of the dogs, will force the forward ends together, and thus clamp it firmly for planing or other purposes.
Fig. 88. HELICO-VOLUTE SPRING.—This is a form of spring for tension purposes. The enlarged cross-section of the coil in its middle portion, with the ends tapering down to the eyes, provides a means whereby the pull is transferred from the smaller to the larger portions, without producing a great breaking strain near the ends.
Fig. 89. DOUBLE HELICO-VOLUTE.—This form, so far as the outlines are considered, is the opposite of Fig. 88. A compression spring of this kind has a very wide range of movement.
Fig. 90. HELICAL SPRING.—This form of coil, uniform from end to end, is usually made of metal which is square in cross-section, and used where it is required for heavy purposes.
Fig. 91. SINGLE VOLUTE HELIX-SPRING.—This is also used for compression, intended where tremendous weights or resistances are to be overcome, and when the range of movement is small.
Fig. 92. FLAT SPIRAL, OR CONVOLUTE.—This is for small machines. It is the familiar form used in watches owing to its delicate structure, and it is admirably adapted to yield to the rocking motion of an arbor.
Fig. 93. ECCENTRIC ROD AND STRAP.—A simple and convenient form of structure, intended to furnish a reciprocating motion where a crank is not available. An illustration of its use is shown on certain types of steam engine to operate the valves.
Fig. 94. ANTI-DEAD CENTER FOR FOOT-LATHES.—A flat, spiral spring (A), with its coiled end attached to firm support (B), has its other end pivotally attached to the crank-pin (C), the tension of the spring being such that when the lathe stops the crack-pin will always be at one side of the dead-center, thus enabling the operator to start the machine by merely pressing the foot downwardly on the treadle (D).
PROPERTIES OF MATERIALS
A workman is able to select the right metals because he knows that each has some peculiar property which is best adapted for his particular use. These with their meaning will now be explained.
ELASTICITY.—This exists in metals in three distinct ways: First, in the form of traction. Hang a weight on a wire and it will stretch a certain amount. When the weight is removed the wire shrinks back to its original length.
Second: If the weight on the wire is rotated, so as to twist it, and the hand is taken from the weight, it will untwist itself, and go back to its original position. This is called torsion.
Third: A piece of metal may be coiled up like a watch spring, or bent like a carriage spring, and it will yield when pressure is applied. This is called flexure.
Certain kinds of steel have these qualities in a high degree.
TENACITY.—This is a term used to express the resistance which the body opposes to the separation of its parts. It is determined by forming the metal into a wire, and hanging on weights, to find how much will be required to break it. If we have two wires, the first with a transverse area only one-quarter that of the second, and the first breaks at 25 pounds, while the second breaks at 50 pounds, the tenacity of the first is twice as great as that of the second.
To the boy who understands simple ratio in mathematics, the problem would be like this:
25 x 4 : 50 x 1, or as 2 : 1.
THE MOST TENACIOUS METAL.—Steel has the greatest tenacity of all metals, and lead the least. In proportion to weight, however, there are many substances which have this property in a higher degree. Cotton fibers will support millions of times their own weight.
There is one peculiar thing, that tenacity varies with the form of the body. A solid cylindrical body has a greater strength than a square one of the same size; and a hollow cylinder more tenacity than a solid one. This principle is well known in the bones of animals, in the feathers of birds, and in the stems of many plants.
In almost every metal tenacity diminishes as the temperature increases.
DUCTILITY.—This is a property whereby a metal may be drawn out to form a wire. Some metals, like cast iron, have absolutely no ductility. The metal which possesses this property to the highest degree, is platinum. Wires of this metal have been drawn out so fine that over 30,000 of them laid side by side would measure only one inch across, and a mile of such wire would weigh only a grain, or one seven-thousandth of a pound.
MALLEABILITY.—This is considered a modification of ductility. Any metal which can be beaten out, as with a hammer, or flattened into sheets with rollers, is considered malleable. Gold possesses this property to the highest degree. It has been beaten into leaves one three-hundred-thousandth of an inch thick.
HARDNESS.—This is the resistance which bodies offer to being scratched by others. As an example, the diamond has the capacity to scratch all, but cannot be scratched by any other.
ALLOYS.—Alloys, that is a combination of two or more metals, are harder than the pure metals, and for this reason jewelry, and coins, are usually alloyed.
The resistance of a body to compression does not depend upon its hardness. Strike a diamond with a hammer and it flies to pieces, but wood does not. One is brittle and the other is tough.
The machinist can utilize this property by understanding that velocity enables a soft material to cut a harder one. Thus, a wrought iron disc rotating rapidly, will cut such hard substances as agate or quartz.
RESISTANCE.—All metals offer more or less resistance to the flow of an electric current. Silver offers the least resistance, and German silver the greatest. Temperature also affects the flow. It passes more easily over a cold than a warm conductor.
PERSISTENCE.—All metals on receiving heat, will retain it for a certain length of time, and will finally cool down to the temperature of the surrounding atmosphere. Some, like aluminum, retain it for a long time; others, as iron, will give it off quickly.
CONDUCTIVITY.—All metals will conduct heat and cold, as well as electricity. If one end of a metal bar is heated, the heat creeps along to the other end until it has the same temperature throughout. This is called equalization.
If a heated bar is placed in contact with another, the effect is to increase the temperature of the cold bar and lower that of the warm bar. This is called reciprocity.
MOLECULAR FORCES.—Molecular attraction is a force which acts in such a way as to bring all the particles of a body together. It acts in three ways, dependent on the particular conditions which exist.
First: Cohesion. This exists between molecules which are of the same kind, as for instance, iron. Cohesion of the particles is very strong in solids, much weaker in liquids, and scarcely exists at all between the particles in gases.
Second: Adhesion is that property which exists between the surfaces of bodies in contact. If two flat surfaces are pressed together, as for instance, two perfectly smooth and flat pieces of lead, they will adhere. If, for instance, oil should be put on the surfaces, before putting them together, they would adhere so firmly that it would be difficult to pull them apart.
Third: Affinity. This is another peculiarity about materials. Thus, while cohesion binds together the molecules of water, it is chemical affinity which unites two elements, like hydrogen and oxygen, of which water is composed.
POROSITY.—All matter has little hollows or spaces between the molecules. You know what this is in the case of a sponge, or pumice stone. Certain metals have the pores so small that it is difficult to see them except with a very powerful glass. Under great pressure water can be forced through the pores of metals, as has been done in the case of gold. Water also is porous, but the spaces between the molecules are very small.
COMPRESSIBILITY.—It follows from the foregoing statement, that if there are little interstices between the molecules, the various bodies can be compressed together. This can be done in varying degrees with all solids, but liquids, generally, have little compressibility. Gases are readily reduced in volume by compression.
ELASTICITY.—This is a property by virtue of which a body resumes its original form when compressed. India rubber, ivory and glass are examples of elasticity; whereas, lead and clay do not possess this property. Air is the most elastic of all substances.
INERTIA.—This is a property of matter by virtue of which it cannot of itself change its state of motion or of rest.
Newton's first law of motion is, in substance, that matter at rest will eternally remain at rest, and matter in motion will forever continue in motion, unless acted on by some external force.
A rider is carried over the head of a horse when the latter suddenly stops. This illustrates the inertia of movement. A stone at rest will always remain in that condition unless moved by some force. That shows the inertia of rest.
MOMENTUM.—This is the term to designate the quantity of motion in a body. This quantity varies and is dependent on the mass, together with the velocity. A fly wheel is a good example. It continues to move after the impelling force ceases; and a metal wheel has greater momentum than a wooden wheel at the same speed, owing to its greater mass.
If, however, the wooden wheel is speeded up sufficiently it may have the same momentum as the metal one.
WEIGHT.—All substances have what is called weight. This means that everything is attracted toward the earth by the force of gravity. Gravity, however, is different from weight. All substances attract each other; not only in the direction of the center of the earth, but laterally, as well.
Weight, therefore, has reference to the pull of an object toward the earth; and gravity to that influence which all matter has for each other independently of the direction.
CENTRIPETAL FORCE.—This attraction of the earth, which gives articles the property of weight, is termed centripetal force—that is, the drawing in of a body.
CENTRIFUGAL FORCE.—The direct opposite of centripetal, is centrifugal force, which tends to throw outwardly. Dirt flying from a rapidly moving wheel illustrates this.
CAPILLARY ATTRACTION.—There is a peculiar property in liquids, which deserves attention, and should be understood, and that is the name given to the tendency of liquids to rise in fine tubes.
It is stated that water will always find its level. While this is true, we have an instance where, owing to the presence of a solid, made in a peculiar form, causes the liquid, within, to rise up far beyond the level of the water.
This may be illustrated by three tubes of different internal diameters. The liquid rises up higher in the second than in the first, and still higher in the third than in the second. The smaller the tube the greater the height of the liquid.
This is called capillary attraction, the word capillary meaning a hair. The phenomena is best observed when seen in tubes which are as fine as hairs. The liquid has an affinity for the metal, and creeps up the inside, and the distance it will thus move depends on the size of the tube.
THE SAP OF TREES.—The sap of trees goes upwardly, not because the tree is alive, but due to this property in the contact of liquids with a solid. It is exactly on the same principle that if the end of a piece of blotting paper is immersed in water, the latter will creep up and spread over the entire surface of the sheet.
In like manner, oil moves upwardly in a wick, and will keep on doing so, until the lighted wick is extinguished, when the flow ceases. When it is again lighted the oil again flows, as before.
If it were not for this principle of capillary attraction, it would be difficult to form a bubble of air in a spirit level. You can readily see how the liquid at each end of the air bubble rounds it off, as though it tried to surround it.
SOUND.—Sound is caused by vibration, and it would be impossible to convey it without an elastic medium of some kind.
Acoustics is a branch of physics which treats of sounds. It is distinguished from music which has reference to the particular kinds.
Sounds are distinguished from noises. The latter are discordant and abrupt vibrations, whereas the former are regular and continuous.
SOUND MEDIUMS.—Gases, vapors, liquids and solids transmit vibrations, but liquids and solids propagate with greater velocity than gases.
VIBRATION.—A vibration is the moving to and fro of the molecules in a body, and the greater their movement the more intense is the sound. The intensity of the sound is affected by the density of the atmosphere, and the movement of the winds also changes its power of transmission.
Sound is also made more intense if a sonorous body is near its source. This is taken advantage of in musical instruments, where a sounding-board is used, as in the case of the piano, and in the violin, which has a thin shell as a body for holding the strings.
Another curious thing is shown in the speaking tube, where the sound waves are confined, so that they are carried along in one line, and as they are not interfered with will transmit the vibrations to great distances.
VELOCITY OF SOUND.—The temperature of the air has also an effect on the rate of transmission, but for general purposes a temperature of 62 degrees has been taken as the standard. The movement is shown to be about 50 miles in 4 minutes, or at the rate of 1,120 feet per second.
In water, however, the speed is four times greater; and in iron nearly fifteen times greater. Soft earth is a poor conductor, while rock and solid earth convey very readily. Placing the ear on a railway track will give the vibrations of a moving train miles before it can be heard through the air.
SOUND REFLECTIONS.—Sound waves move outwardly from the object in the form of wave-like rings, but those concentric rings, as they are called, may be interrupted at various points by obstacles. When that is the case the sound is buffeted back, producing what is called echoes.
RESONANCE.—Materials have a quality that produces a very useful result, called resonance, and it is one of the things that gives added effect to a speaker's voice in a hall, where there is a constant succession of echoes. A wall distant from the speaker about 55 feet, produces an almost instantaneous reflection of the sound, and at double that measurement the effect is still stronger. When the distance is too short for the reflecting sound to be heard, we have resonance. It enriches the sound of the voice, and gives a finer quality to musical instruments.
ECHOES.—When sounds are heard after the originals are emitted they tend to confusion, and the quality of resonance is lost. There are places where echoes are repeated many times. In the chateau of Simonetta, Italy, a sound will be repeated thirty times.
SPEAKING TRUMPET.—This instrument is an example of the use of reflection. It is merely a bell-shaped, or flaring body, the large end of which is directed to the audience. The voice talking into the small end is directed forwardly, and is reflected from the sides, and its resonance also enables the vibrations to carry farther than without the use of the solid part of the instrument.
The ear trumpet is an illustration of a sound-collecting device, the waves being brought together by reflection.
THE STETHOSCOPE.—This is an instrument used by physicians, and it is so delicate that the movements of the organs of the body can be heard with great distinctness. It merely collects the vibrations, and transmits them to the ears by the small tubes which are connected with the collecting bell.
THE VITASCOPE.—Numerous instruments have been devised to determine the rate of vibration of different materials and structures, the most important being the vitascope, which has a revolvable cylinder, blackened with soot, and this being rotated at a certain speed, the stylus, which is attached to the vibrating body, in contact with the cylinder, will show the number per second, as well as the particular character of each oscillation.
THE PHONAUTOGRAPH.—This instrument is used to register the vibration of wind instruments, as well as the human voice, and the particular forms of the vibrations are traced on a cylinder, the tracing stylus being attached to a thin vibrating membrane which is affected by the voice or instrument.
THE PHONOGRAPH.—This instrument is the outgrowth of the stylus forms of the apparatus described, but in this case the stylus, or needle, is fixed to a metallic diaphragm, and its point makes an impression on suitable material placed on the outside of a revolvable cylinder or disc.
Light.-Light is the agent which excites the sensation of vision in the eye. Various theories have been advanced by scientists to account for the phenomenon, and the two most noted views are the corpuscular, promulgated by Sir Isaac Newton, and the undulatory, enunciated by Huygens and Euler.
The corpuscular theory conceives that light is a substance of exceedingly light particles which are shot forth with immense velocity. The undulatory theory, now generally accepted, maintains that light is carried by vibrations in ether. Ether is a subtle elastic medium which fills all space.
Luminous bodies are those like the sun, which emit light. Rays may diverge, that is, spread out; converge, or point toward each other; or they may be parallel with each other.
VELOCITY OF LIGHT.—Light moves at the rate of about 186,000 miles a second. As the sun is about 94,000,000 miles from the earth, it takes 8-1/2 minutes for the light of the sun to reach us.
REFLECTION.—One of the most important things connected with light is that of reflection. It is that quality which is utilized in telescopes, microscopes, mirrors, heliograph signaling and other like apparatus and uses. The underlying principle is, that a ray is reflected, or thrown back from a mirror at the same angle as that which produces the light.
When the rays of the sun, which are, of course, parallel, strike a concave mirror, the reflecting rays are converged; and when the rays strike a convex mirror they diverge. In this way the principle is employed in reflecting telescopes.
REFRACTION.—This is the peculiar action of light in passing through substances. If a ray passes through water at an angle to the surface the ray will bend downwardly in passing through, and then again pass on in a straight line. This will be noticed if a pencil is stood in a glass of water at an angle, when it will appear bent.
Refraction is that which enables light to be divided up, or analyzed. In this way white light from the sun is shown to be composed of seven principal colors.
COLORS.—If the light is passed through a prism, which is a triangularly shaped piece of glass, the rays on emerging will diverge from each other, and when they fall on a wall or screen the colors red, orange, yellow, green, blue, indigo and violet are shown.
The reason for this is that the ray in passing through the prism has the different colors in it refract at different angles, the violet bending more than the red.
THE SPECTROSCOPE.—The ability to make what is thus called a spectrum, brought forth one of the most wonderful instruments ever devised by man. If any metal, or material, is fused, or put in such a condition that a ray of light can be obtained from it, and this light is passed through a prism, it will be found that each substance has its own peculiar divisions and arrangements of colors.
In this way substances are determined by what is called spectrum analysis, and it is by means of this instrument that the composition of the sun, and the planets and fixed stars are determined.
THE RAINBOW.—The rainbow is one of the effects of refraction, as the light, striking the little globular particles of water suspended in the air, produces a breaking up of the white light into its component colors, and the sky serves as a background for viewing the analysis thus made.
HEAT.—It is now conclusively proven, that heat, like light, magnetism and electricity, is merely a mode of motion.
The mechanical theory of heat may be shown by rubbing together several bodies. Heat expands all substances, except ice, and in expanding develops an enormous force.
EXPANSION.—In like manner liquids expand with heat. The power of mercury in expanding may be understood when it is stated that a pressure of 10,000 pounds would be required to prevent the expansion of mercury, when heated simply 10 degrees.
Gases also expand. While water, and the different solids, all have their particular units of expansion, it is not so with gases, as all have the same coefficient.