Book: Elements of Machine Work: 01 History and Origin of Machine Tools

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CHAPTER I. HISTORY AND ORIGIN OF MACHINE TOOLS

EQUIPMENT FOR TEACHING AND MANUFACTURING. MATERIALS USED FOR MACHINE CONSTRUCTION. READING DRAWINGS.

HISTORY AND ORIGIN OF MACHINE TOOLS.

1. Simple tools. — The hammer, cold chisel, file, and hand drill are the simple tools of machine construction, and are operated by hand.

Primitive tools. — To the hand drill belongs the distinction of being the first machine with revolving parts used by primitive man. Machine tools, as the lathe, planer, milling and drilling machines, etc., operate cutting tools by power.

2. Evolution of the lathe. — The lathe is the most general and useful of all machine tools and is used to produce cylindrical surfaces.

The date of its origin is lost in antiquity. The first lathes consisted of two short posts driven into the ground, and a nail driven into each formed the centers on which the work revolved, operated by a rope, treadle and sapling, or lath, and from the latter name the term lathe is derived.

To Henry Maudslay of England, belongs the credit of inventing the slide rest and applying it to the lathe about 1794; and later, to other machines. Planing machines came next, and did for plane surfaces what the lathe had done for cylindrical surfaces. Then followed milling machines, grinding machines, screw machines, gear cutters, etc. The improvements in machine tools during the past fifty years have been greater than in all the preceding years.

EQUIPMENT FOR TEACHING AND MANUFACTURING.

3. Machine laboratories for teaching the principles of machine construction should be equipped with the following classes of machine tools: hand and engine lathes, planing, shaping, milling, grinding, slotting, drilling, cutting-off, screw and turret machines. To properly equip and use these machine tools requires a great variety of small tools, lathe, planer and shaper tools, milling cutters, drills, reamers, taps, dies, rules, calipers, dividers, chucks, surface gages, cylindrical gages, templets, jigs, hammers, chisels, files, center punches, scratch awls, gravers, a variety of small hand turning tools, etc., and to grind tools properly it is necessary to have a water emery tool grinder, a grindstone, a cutter grinder, and a twist drill grinder.

4. Machine manufacturing plants or shops. — A plant for the construction of machines in lots comprises several departments. Each is fitted with regulation machine tools, and also many special machines, jigs, fixtures, and various small tools for the duplication of the various parts, the equipment differing with the class of machines built. Likewise there are departments for pattern making, forging, hardening, and tempering, and foundries for producing castings. Separate and specially equipped departments are also maintained for designing, draughting, inspecting, testing, painting, storing, shipping, and a machine shop for repairing machines and tools.

6. Tool and stock rooms are necessary for teaching or manufacturing tools and to provide for a proper storage of small tools; also a check system for the intelligent distribution and accounting of tools, and such machinery as will be necessary to keep these tools in good repair, and a storeroom for materials and supplies.

MATERIALS USED FOR MACHINE CONSTRUCTION.

6. Materials for machines and tools are principally cast iron, steel, wrought iron, and alloys of copper. Such substances as slate, glass, carbon, porcelain, and mica are largely used in the construction of electrical apparatus and machinery, The base for all steel and iron products is " pig " iron, obtained directly from the ore.

7. Ores of iron are magnetite 72.4%, hematite 70%, limonite 60% iron. The blast-furnace process produces pig iron from which the earthy impurities of the ore have been removed; but pig contains carbon, silicon, sulphur, phosphorus, and perhaps other elements. In the foundry, pig is recast into cast iron. In the puddling process, blast-furnace pig is made into wrought iron by burning out practically all the impurities. In the Bessemer converter and in the open-hearth furnace, machine steel is made from blast-furnace pig, utilizing also wrought-iron and steel scrap. In the crucible process wrought iron or machine steel are made into carbon or tool steel and high-speed steel.

8. Cast iron contains 2.3% or more of carbon and is made by remelting pig and scrap cast iron (broken or old castings). It is not malleable or ductile like wrought iron, nor can it be hardened and tempered, yet it may be chilled to make it very hard. When fractured it shows a crystalline surface similar to granite. It is molded into castings of any form, and is used where weight or mass is more important than strength, as in frames of machines. The strength of iron castings is increased by the addition of vanadium.

9. Wrought iron, commercially pure iron, is made by burning out the carbon and other impurities from pig iron. The iron is left in a pasty mass which is refined by rolling and hammering. When broken it has a fibrous appearance resembling wood. It is soft, tenacious, malleable, and ductile. It can be welded and forged, but not molded like cast iron. It cannot be hardened and tempered but may be case-hardened.

Wrought iron is used in machine construction in the form of bars, shafting, finished rods, wire, sheets, forgings, etc.

10. steel. — The term steel is indefinite unless qualified. Steel containing less than 0.5% of carbon is called machine steel; that containing from 0.5% to 1.5% of carbon is called carbon or tool steel.

11. Machine steel is made by taking carbon and other impurities from pig iron by means of the Bessemer converter or the open-hearth furnace. Large quantities of all kinds of scrap are also worked up into steel by these processes. Machine steel covers all kinds of steel between wrought iron and carbon steel. It is obtainable in same form as wrought iron. Both steel and wrought iron are often galvanized to prevent rusting.

12. Carbon or tool steel is made by adding carbon to wrought iron or to machine steel by the crucible melting process. It is used for fine-edge cutting tools that must be hardened and tempered, such as taps, dies, reamers, drills, lathe and planer tools, etc. See High-speed Steel, § 229.

It is difficult to weld carbon steel to carbon steel, but it may be welded to machine steel or wrought iron. It is obtainable in bars, disks, wire, sheets, etc., annealed or unannealed.

The quantity and condition of associated carbon make the distinction between iron and steel. The distinction between the different grades of steel is due more to the variation of carbon content than to differences in other elements.

13. Carbon or temper in steel is designated in one-hundredths of one per cent; thus 25-point carbon means 25 hundredths of one per cent carbon.

50 to 60 point carbon is best for hot working.
60 to 70 point carbon for tools of dull edge.
70 to 80 point carbon for cold sets and similar tools.
80 to 100 point carbon for chipping chisels, drills, knives, center punches.
100 to 110 point carbon for large lathe tools, dies, punches, drills.
110 to 150 point carbon for lathe tools, scrapers, reamers, and all tools requiring a very fine cutting edge.

A practical test to distinguish carbon steel from good machine steel is to heat it to a light red and cool in water. If it becomes glass hard, as indicated by file test, it is tool steel; if only partially hardened, it is machine steel.

14. Vanadium, nickel, and chrome alloy steels give the greatest strength with the least weight and are used for moving machine parts that are subject to severe strains or sudden shocks. Vanadium-chrome steel in high and low carbon grades, is used for automobile parts. It forges and machines more readily than nickel-chrome steels.

Nickel-chrome steel is made in high and low carbon grades and used for gears, springs, and general structural work.

Nickel-steel is used for shafting, rods, bolts, etc., of marine engines, and light plate work.

16. Hand and drop forgings are made when shapes are desired which are not readily machined from the bar. In manufacturing a large number of pieces of the same shape they are uniformly and economically produced in dies under a drop hammer. Drop forgings are also obtainable in copper and bronze.

16. Steel castings. — The molten product of Bessemer converter or open-hearth furnace may be run into molds and form steel castings in the same way as iron castings. They must be annealed. Vanadium steel, nickel steel, manganese steel, and chrome steel castings are used to resist severe stress and wear and where hard, reliable, and strong castings are desired.

The strength of steel castings is increased by the addition of vanadium.

17. Halleable-iron castings are made by annealing special iron castings by packing them in a box with oxide of iron and maintaining at a red heat in an oven from three to six days, then cooling slowly. They can be case-hardened.

18. Cold-rolled steel and wrought iron. — Open-hearth steel of low carbon and wrought iron are obtainable cold rolled in shafts, rods, plates, etc., with smooth, bright surfaces, in accurate sizes. Each is used without further preparation for shafting, piston rods, pump rods, engine guides, etc. The process of cold rolling greatly improves the physical properties of steel and iron; it increases the tenacity and elevates the elastic limit under tensile and transverse stresses.

19. Cold-drawn steel and wrought iron in bars, rods, and wire, round, square, hexagonal, etc., are used as stock for screw machines and turret lathes, for making screws, bolts, studs, shafting keys, etc. Steel wire is cold drawn through diamond dies as small as .003" in diameter.

20. Finished Bessemer steel rods and wire, finished to accurate sizes to fractional parts of an inch or to wire gage, are obtainable in various cross-sections. They are copper-coated to prevent corrosion.

21. Carbon or tool-steel rods and wire, cold drawn, finished to accurate sizes are obtainable for small tools.

22 Music (piano) wire, cold drawn is obtainable finished in sizes according to different music wire gages, or in thousandths of an inch. It has a spring temper, is very resilient and largely used for springs and various mechanical devices; it can be hardened and tempered.

23. Copper. — Is a red metal and the most ancient known. It can be cast, rolled, forged, and machined. It is very malleable and ductile, and is a good conductor of heat and electricity. It is used either alone or alloyed with other metals to form brass, bronze, composition, etc. It is hardened by rolling or hammering.

24. Alloys (composition). — The chief ingredients of copper alloys are copper, zinc, and tin, With small percentages of other metals. In general, an alloy of copper and zinc is brass; copper and tin, bronze; and copper, zinc, and tin, composition metal also bronze.

25. Brass is composed of about 70% copper and 30% zinc (spelter). Rich gold metal for electrical apparatus is made of 90% copper and 10% zinc. Brass is readily machined. It can be made harder by the addition of two or three per cent of tin, or more malleable by the same proportion of lead; tin whitens it, lead reddens it. Brass is used in machine construction in the form of castings, rods, sheets, tubing, and wire. Brass and copper wire are obtainable as fine as .002" in diameter.

26. Bronze is tough and durable and is used in the form of castings for bearings and parts of engines and machinery subject to shock, great strain and wear. It is also used for bells, telescopes, ordnance, screw propellers, ornaments, etc. There are various kinds of bronzes: phosphor btonze, Tobin bronze, manganese bronze, aluminium bronze, etc.

Bronze for bearings in machines and small engines is composed of about 85% copper, 13% tin, and 2% zinc. Gun metal is variously composed of from 90% to 95% copper with from 5% to 10% of tin.

27. Phosphor bronze is an alloy of phosphorus, tin, and copper. It is very tough and will stand great wear. Many spiral and worm gears are of phosphor bronze.

28. Manganese bronze is an alloy of manganese and copper. As it does not corrode easily, it is much used for propeller wheels.

29. Aluminium bronze is an alloy of aluminium and copper. An alloy of from 5% to 12% aluminium with 95% to 88% copper is very strong, elastic, and ductile. It can be hammered, rolled, and forged at a red heat, and is in many ways similar to mild steel. It is practically non-corrosive.

30. Babbitt metal is a soft white alloy of very variable composition, as eight parts tin to one copper and one antimony; nine parts tin, one copper, etc. It is used to line boxes for bearings to reduce friction in all kinds of machinery. See § 327.

31. Lead is a very malleable metal, of a bluish gray color, and is obtainable in sheets, pipes, and blocks.

32. Tin is a highly malleable metal resembling silver, largely used in coating sheet iron, and with copper to form alloys.

33. Zinc is a whitish, brittle metal much used in combination with copper to form alloys, and for galvanizing.

34. Aluminium is a light bluish white, soft, malleable metal of extreme lightness and brilliant luster. It does not corrode; can be soldered, forged or rolled hot or cold, and machined and annealed by bringing to a dull red heat and cooling slowly. It shrinks greatly in casting. It is used for gear cases for automobiles, parts of mathematical instruments, and alloyed with copper for journal bearings.

36. Vanadium. — A silver-white primary metallic element which has wrought wonders in the manufacture of steel, iron, copper, brass, aluminium, and lead. A small amount of vanadium alloyed with any of these metals has the triple effect of cleansing, strengthening and toughening the material.

36. Platinum is a very rare metal and very ductile. It is used for connecting filaments in incandescent lamps, sparking devices for gas engines, etc.

37. Wood is used considerably in the construction of some classes of machinery, for tables, frames, etc.

READING DRAWINGS.

38. Drawing is a universal language, a scientific method of communication between designers, draughtsmen, and constructors. One should learn to make mechanical drawings and to read them just as he does printed matter.

The principles and conventions used in drawing, with special reference to those known as working drawings, are here given.

Methods of representing objects. — There are three general methods, the perspective, isometric, and projection drawing.