grinding machines

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GrindingMachines

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PITMAN'S TECHNICAL PRIMER SERIESEdited by R. E. NEALE, B.Sc., Hons. (Lond.)

A.C.G.I., A.M.I.E.E.

GRINDING MACHINESAND THEIR USE


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PITMAN'S TECHNICAL PRIMERSEdited by B. E. NEALE, B.Sc. (Hons.), A.C.G.I., A.M.I.E.E.

IN each book of the series the fundamental principles of somesub-division of engineering technology are treated in a practicalmanner, providing the student with a handy survey of the particularbranch of technology with which he is concerned. Each 2s. 6d. net.THE STEAM LOCOMOTIVE. By E. L. AKRONS, M.I.Mech.E.BELTS FOR POWER TRANSMISSION. By W. G. DUNKLEY. B.So.WATER-POWER ENGINEERING. By F. F. FERGUSSON, A.M.I.C.E.PHOTOGRAPHIC TECHNIQUE. By L. J. HIBBERT, F.R.P.S.HYDRO-ELECTRIC DEVELOPMENT. By J. W. MEARES, M.Inst.C.E.THE ELECTRIFICATION OF RAILWAYS. By H. F. TREWMAN, M.A.CONTINUOUS CURRENT ARMATURE WINDING. By F. M. DENTON.MUNICIPAL ENGINEERING. By H. PERCY BOULNOIS, M.Inst.C.E.FOUNDRYWORK. By BEN SHAW and JAMES EDGAR.PATTERNMAKING. By BEN SHAW and JAMES EDGAR.THE ELECTRIC FURNACE. By FRANK J. MOFFETT, B.A., M.I.E ESMALL SINGLE-PHASE TRANSFORMERS. By E. T. PAINTON. B.Sc:.PNEUMATIC CONVEYING By E. G. PHILLIPS, M.I.E.E., A.M.I.Mech. E.BOILER INSPECTION AND MAINTENANCE. By R. CLAYTON.ELECTRICITY IN STEEL WORKS. By W. MACFARLANE, B.Sc.MODERN CENTRAL STATIONS. By C. W. MARSHALL, B.Sc.STEAM LOCOMOTIVE CONSTRUCTION AND MAINTENANCE. ByE. L. AKRONS, M.I.Mech.E., M.l.Loco.E.HIGH TENSION SWITCHGEAR. By H. E. POOLE, B.Se., A C.G.I.HIGH TENSION SWITCHBOARDS. By the Same Author.POWER FACTOR CORRECTION. By A. E. CLAYTON, B.Sc., A.K.C.TOOL AND MACHINE SETTING. By P. GATES.TIDAL POWER. By A. STRUBEN, O.B.E., A.M.I.C.E.SEWERS AND SEWERAGE, By H. G. WHYATT, M.Inst.C.E. M.R.S.IELEMENTS OF ILLUMINATING ENGINEERING. By A. I>. TROTTERM.Inst.C.E.COAL-CUTTING MACHINERY. By G. E. F. EAGAR, M.Iast.Min.E.GRINDING MACHINES AND THEIR USE. By T. R. SHAW, M.I.Mech.E.ELECTRO-DEPOSITICN OF COPPER. By C. W. DENNY, A.M.I.E.E.DIRECTIVE WffiELESS TELEGRAPHY. By L. H. WALTER, M.A.TESTING OF CONTINUOUS-CURRENT MACHINES. By C. F. SMITH,D.Sc., M.I.E.E.ELECTRICAL TRANSMISSION OF ENERGY. By W. M. THORNTON, D.Sc.STEAM ENGINE VALVES AND VALVE GEAR. By E. L. AKRONS,M.I.Mech.E.MECHANICAL HANDLING OF GOODS. By C. H. WOODFIELD.INDUSTRIAL AND POWER ALCOHOL. By R. C. FARMER, D.Sc.HIGH-TENSION TRANSFORMERS. By W. T. TAYLOR, M.Inst.C E.LONDON: SIR ISAAC PITMAN & SONS, LTD.


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KENYON S PATENT EngineerINTERSTRANDED COTTON LitorDRIVINGROPEFor Main, Counter2f Machine Drivesffi Our experience, which extends^jj over 50 years and embracesinstallations from J H.P. to 6,000H.P., is at your service.

Consult our Technical DeptThe complete transmission designed,

supplied and erected.

ENDLESS ROPESFOR GRINDING MACHINESA SPECIALITY.

MINIMUM STRETCH MAXIMUM LIFE.

Win. Kenyon & Sons, Ltd,DUKINFIELD, CHESHIRE.By mentioning this book when replying, you will oblige


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VI PREFACEassisted him with information regarding theirmachines, and by the loan of blocks ; also to theNorton Co., U.S.A., for permiss'on to makeextracts from their interesting trade publication,Grits and Grinds.

THOS. R. SHAW.MANCHESTER.


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CONTENTSPAGE

PREFACE ....... VCHAPTER IGRINDING WHEELS ..... 1

Grinding as a cutting process Abrasives, natural andartificial Abrasives for various materials Jtfanu-facture of abrasive wheels Vitrified, silicate, and elas-tic wheels Grain and grade Selection of gradesLoading Glazing Effect of multiplicity of cuttingpoints Speed of wheels.

CHAPTER IICYLINDRICAL GRINDING MACHINES . . .15Use of the grinding machine Relation of turning to

grinding Necessity for wide range of work speeds.TJie Universal Grinder Variety of uses Universalhead Tailstock Table and slides Extra fine feedTaper grinding, etc. Disc and face grindingInternal grinding. Plain Grinding Machines Crankshaft grinding Form grinding Cam grinding Rollgrinding Centreless grinding. Internal GrindingMachines Planetary type spindle.

CHAPTER IIIPLANE SURFACE GRINDING MACHINES . . 46

Type of machines Vertical-spindle machine Piano-type machines Blanchard machine Continuousreading caliper attachment Wheel speed for surfacegrinding Selection of wheels Mounting wheelsSafety Lubricant for surface grinding.


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Vlll CONTENTSPAGE

CHAPTER IVCONSTRUCTIONAL DETAILS OF GRINDINGMACHINES . . . . . . 67Importance of rigidity -Wheel head Wheel spindleconstruction Vertical spindle Water supply.Internal Spindles Adapter type spindles Tubetype spindles. Automatic cross feed Reversingmechanisms.

CHAPTER VCARE AND OPERATION OF GRINDING WHEELS ANDMACHINES . . . . . * . 96

Grinding limits and allowances Wheel mountingWheel balance Prevention of distortion Centres inwork Table travel and wheel width Wheel andwork speeds Wear of grinding wheels Specialdrivers.INDEX . 113


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ILLUSTRATIONSFIG. PAGE1 . Micro-photograph of chips from a properlyoperating grinding wheel.2. Norton grade chart .... 83. Illustrating wheel contact in different

classes of work . . 104. Churchill universal grinding machine . 205. Brown and Sharpe universal work head 226. Tailstock of Churchill universal grindingmachine ...... 247. Setting of wheel slide for extra fine feed . 278. Truing centres on universal grinder . 289. Grinding angular face with wheel slide

swivelled . . ... 2910. Grinding taper by angular adjustment of

table 3011. Expanding arbor for disc grinding . . 3012. Internal spindle drive . . . .3213. Norton plain grinding machine . . 3414. Typical wheel faces for form grinding . 3615. Cam grinding attachment ... 3816. Heald internal grinding machine . . 4217. Churchill cylinder grinder in operation . 4418. Heald rotary surface grinder . . 4719. Surface grinding with cup wheel . . 4820. Vertical-spindle surface-grinder . . 5021. Grinding sad irons on vertical-spindle sur-face grinder . . . . .5222. Blanchard grinding machine... 5423. Table positions and three-point column sup-

port of Blanchard grinder ... 5424. Section of Blanchard magnetic chuck . 56


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X ILLUSTRATIONSFIO. PAGE25. Paths of magnetism in Blanchard magneticchuck . . . . . .5726. Section through table of Blanchard grinder,

showing electrical parts . . .5827. Supports for continuous reading caliperBlanchard grinder . . . .5928. Continuous reading caliper. Blanchard

grinder ...... 6029. Cross -section of plain grinder . . 6830. Under-side of sliding table ... 7031. Wheel head of Churchill universal grinder 7432. Wheel spindle and bearings of Brown and

Sharpe universal grinder . . .7633. Wheel head of Blanchard vertical-spindle

grinder ...... 7734. Churchill adapter-type internal spindle 8135. Heald tube-type internal spindle . 8336. Brown and Sharpe internal spindle . 8637. Detachable spindle for Churchill planetary

type internal grinder . . .8738. Churchill micrometer feed disc .8939. Wheel feed mechanism of Churchill plain

grinder ...... 9140. Brown and Sharpe automatic cross-feed . 9241. Load and fire reverse mechanism. Per-

sons-Arter rotary surface grinder . 9442. Taper and flanged spindle noses . . 9943. Quick-acting driver . . . .10944. Expanding holder on live spindle . .11145. Special running driver for pins . .112

TABLESTABLE PAGE

I. Wheels for Blanchard surface grinder . 64II. Grinding limits for cylindrical pieces 96III. Limit gauges for lathe- work . 98IV. Grinding wheel speeds. . . . 106


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GRINDING MACHINESAND THEIR USECHAPTER I

GRINDING WHEELSTHE forerunner of the modern grinding machinewas the grindstone, which has been in use fromtime immemorial and still finds useful applica-tions. Between the modern grinding machine andthe grindstone there is, however, nothing in com-mon. The art of precision grinding lias madegreat advances since the beginning of the twen-tieth century, largely owing to the demands of theautomobile manufacturer, and precision grindingmachines are capable of dealing with materialsand obtaining a degree of accuracy quite beyond thepowers of a grindstone. Mechanically, the grind-ing machine is a machine tool of the highestquality and there is an enormous difference betweenthe grindstone a solid block of soft naturalstone and the modern abrasive wheel which ismade artificially from particles of extremely hardmaterial. When the wheel is properly chosenand used these particles actually cut the work anddo not grind or abrade it in the ordinarysense of these words.

Grinding is a Cutting Process. The operation ofgrinding, in which metal or other substance isremoved by contact with a rapidly revolvinggrinding wheel, is an actual cutting process. The

1


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-MACB INKS? C - THEIR USEcutting tools are hard, sharp particles of abrasiveextending from the working face of the wheels.When these small, sharp tools harder than anysubstance they are called upon to cut are moved

FIG. 1. MICRO-PHOTOGRAPH or CHIPS FROM APROPERLY OPERATING GRINDING WHEEL.at high speed into contact with the material tobe ground, each particle cuts its own minute chipfrom the work. The modern grinding wheel,properly selected and used in the modern grindingmachine, is just as surely a milling cutter as if itwere made of steel. Under the microscope the


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GRINDING WHEELS 3material removed is seen to resemble the chipsfrom other machine tools, being, for instance, verysimilar to those produced by a milling cutter orlathe tool, see Fig. 1.

Abrasives.* These are of two kinds, natural andartificial. The natural abrasives emery and corun-dum are both mineral substances, similar in com-position, except that emery is not as pure as corun-dum but contains a large percentage of iron, whichis undesirable in a grinding wheel as it has noabrasive qualities.

Initially the principal abrasive available wasemery, that most in repute, as being the purest,coming from Naxos. Deposits of nearly purecorundum have since been found, and this is thenatural material now most in use.The best grade of corundum is found in Canada,and has a higher percentage of aluminium oxidethan has emery. Under the pressure of grindingthe grains of corundum fracture, thus presentingnew cutting edges or points to the work. Sinceboth emery and corundum are natural products,

they cannot be obtained free from all impurities.Artificial abrasives have, to a very large extent,

superseded natural abrasives in the manufactureof grinding wheels, because improvements in thedesign and construction of grinding machinescreated the demand for better and more reliablegrinding wheels which could be used on them.The excellence of the grinding wheel as obtainableto-day is undoubtedly due to the requirements ofthe grinding machine.

* For further information on this subject see Abrasives,by A. B. Searle, uniform with this volume.


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4 GRINDING MACHINES AND THEIR USEThe artificial abrasives used are aluminous

abrasives and carbide of silicon. Both of theseare products of intense heat in an electric furnace.Aluminous abrasives are made from bauxite, ahydrate of alumina, which is found at Baux,France, and in several parts of the southernUnited States ; and silicon carbide is made from amixture of coke, sand, salt and sawdust.

Abrasives Used for Various Materials. Theextreme hardness and brittleness of carbide ofsilicon is an essential element in the successfulgrinding of metals of low tensile strength, such ascast iron, brass, bronze, and copper. It is also usedfor grinding granite, pearl, earthenware, firebrick,glazed sanitary ware, wood, cork, leather, and avariety of other articles. Wheels made from thisabrasive by different makers bear various namesincluding Crystolon, Carborundum, Carbolite, etc.An abrasive material perfectly adapted to thegrinding of materials of high tensile strength, suchas steel and malleable iron, differs in essentialcharacteristics from one suitable for the grindingof cast iron and brass. For materials of hightensile strength an abrasive must be hard andsharp and possess greater toughness than isrequired for the successful grinding of weakermaterials.Such extreme hardness and sharpness as isfound in carbide of silicon is not essential or even

desirable in an abrasive for the grinding of steel andmalleable iron. The aluminous abrasives aretherefore used for these metals, under trade namesof Alundum, Aloxite, etc.For the grinding of steel, then, an abrasive mustpossess the following properties: (1) A degree of


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GRINDING WHEELS 5hardness which will permit it to penetrate easilyinto the material to be ground. (2) An irregularcrystallization producing the property of sharp-ness. (3) A degree of toughness which will per-mit the crystals of the grain to stand up and notbreak down or fracture too rapidly under thestrain placed upon them by the high resistance ofa tough material during a grinding operation.Such wheels cut rapidly and freely, but at sucha rate and in such a way that excessive heat isnot generated. They are used for all classes ofsteel grinding, varying from fine precision andtool-room work to snagging of heavy castings.Bonding of Abrasive Wheels. The -manu-

facture of abrasive wheels involves the processesby means of which the grains of abrasive materialare bonded together into masses of specified sizesand shapes and desired degrees of coarseness andhardness. Three different processes are used:vitrified, silicate and elastic. Of these, thevitrified process is by far the most important,as it is possible to obtain a much greater range ofgrades or degrees of hardness in an abrasive wheelby this method than by any other. It is, therefore,possible to manufacture grinding wheels by thevitrified process that are adapted to a very greatvariety of grinding operations.The bonding materials used in the vitrifiedprocess consist principally of fusible clays. Thebonding clays are mixed with the abrasive grainsin the proper proportions and the mass is formed ormoulded into the desired size and shape. It isthen thoroughly dried and placed in a vitrifyingkiln. The kiln is brought to a temperature


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6 GRINDING MACHINES AND THEIR USEsufficiently high to fuse or vitrify the bondingclays. When this vitrification is complete the kilnis cooled gradually and then opened and unloaded.The wheels are then finished or turned to exactsize on specially designed lathes by means ofrotary steel- or diamond-dressers. The arbor holeis sometimes bushed to the desired size and eachwheel is tested carefully for balance and strength.

Silicate wheels, as the name indicates, are madeby using a bonding material composed of silicateof soda. The proper amount of this material ismixed with the abrasive grain and tamped intoan iron mould of approximately the shape anddimensions of the wheel wanted. It is thenbaked for about 20 hr. at a comparatively lowtemperature, high enough to cause the silicate bondto harden. The wheel is then ready for thetruing room, and from this point onwards it istreated as a vitrified wheel.With a few exceptions all wheels 30 in. in dia-meter and over are manufactured by this process.Wheels up to 60 in. in diameter are commonlymade for cutlery grinding.Silicate wheels are used where a wheel is

required that has a somewhat softer grinding actionthan a wheel of the corresponding grain and grademanufactured by the vitrified process. They areused chiefly on dry tool grinding and similarwork. There is also the advantage that wheelsurgently required can be completed in three daysby the silicate process.In the elastic process the abrasive is mixed hotwith shellac, run into trays, and allowed to cool.It is then broken up into its original size and thegrains (each of which is now coated with shellac) are


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GRINDING WHEELS 7

put into hot moulds,rolled with hot rollers, allowed

to cool, and then packed in quartz and baked inovens at a temperature of 500 to 600 Fahrenheit.The subsequent treatment is the same as forvitrified and silicate wheels.

It is possible to make wheels by this process asthin as -Jg- in., these being used chiefly for sawsharpening, grinding between the teeth of gears,sharpening moulding cutters and wood-workingtools, cutting-off small stock, slotting and rollgrinding.Owing to the hardness of many high-speedsteels it is impossible to cut-off small pieces ofstock for lathe and planer tools in the usual way.The elastic w^heels are very useful for this ^purposeand small cutting-off machines, fitted with suchwheels, are made for tool room use.

Cutter Grinding. In order to keep cutters aswell as other tools in properly sharpened conditionin the easiest and quickest way, a cutter grindingmachine should be used. This is generally a smallmachine having universal movements so that allkinds of cutters, reamers, etc., may be ground.Cup, saucer and dished grinding wheels in a varietyof shapes and sizes are made for use in suchmachines.

Grain (or Grit) and Grade. The grain and gradeof a wheel refer respectively to the size of grain andhardness. The grain or grit number indicates thenumber of meshesper

lineal inch throughwhich the

grain has passed. The sizes of grain in use arenumbered from 4 to 200 ; finer than 200 it is calledflour, and designated by letters, F, FF, FFF.

2-15363)


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8 GRINDING MACHINES AND THEIH USEThe grade of a wheel is usually designated byletters, and means the degree of hardness of thewheel. An ideal grinding wheel is one that com-bines correct temper of abrasive grain (i.e. a grainthat will fracture after the cutting point has

M

VerySoft

Soft

Medium

Medium Hard

Hard

}rtre/ne/y HardFIG. 2. NORTON GRADE CHART

become dulled, thus presenting a new cutting pointto the work) with a bond just sufficiently hard tohold the grain until it has performed its maximumamount of cutting, the grain then being releasedso as to present new cutting points to the work.A grinding wheel is too soft when the bond


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GRINDING WHEELSallows the grain to break away before it has becomedulled, resulting in rapid wear, and too hard whenthe bond holds the grain after it has becomedulled. In the latter condition the wheel becomesglazed, resulting in slow cutting and heating ofthe work.A series of grades is just as essential as aseries of grains to permit of the many varyingcombinations required in practice.Wheels are graded from soft to hard, differentmethods of indicating grade being used bydifferent grinding wheel manufacturers.The Norton method employs the letters of thealphabet for vitrified and silicate wheels.For elastic and rubber wheels, numbersnare usedto designate hardness. The Norton grade listis shown in diagram form in Fig. 2.

Elastic wheels are graded as followsSOFT 1, li, 2, 2}; 3, 4, 5, 6 HARD.Selection of Grades. The factors that influence

the selection of the grades are physical propertiesof the metal to be ground, shape and condition ofthe surface to be ground, speed of wheel, rigidityof the machine, and the method of grinding.Soft wheels are used on hard materials likehardened steel. On softer materials, like mildsteel and wrought iron, harder grades can beused.The area of surface to be ground in contact withthe wheel is of the utmost importance in deter-

mining the grade to be used. A strongly bondedwheel must be used if there is point-contact withthe work, as when grinding a ball. If there is abroad contact, where the work brings a large part


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10 GRINDING MACHINES AND THEIR USEof the wheel into operation, softer grades must beused.

Vibration in grinding machines necessitates theuse of harder wheels. A softer grade of wheel canbe used efficiently on rigid machines.Reference to Fig. 3 will illustrate the practicalinfluence of wheel contact upon the choice of awheel. A wheel is shown in contact with fourdifferent varieties of work, all of which may be

(C) (d)FIG. 3. ILLUSTRATING WHEEL CONTACT IN DIFFERENTCLASSES OF WORKsupposed to be of the same material, and the depthof cut, much exaggerated, being the same in eachcase. In case (a) the work ground is a shaft ofsmall diameter and, the wheel contact being verysmall, a harder grade of wheel is required than incase (6) where a larger shaft is being ground andwhere the wheel contact is proportionately greater.To continue the comparison, diagram (c) shows thewheel grinding a flat surface, and at (d) the wheel isengaged in internal grinding. In these successivecases practice demands that the wheel shall beprogressively softer in bond or grade, and this is


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GRINDING WHEELS 11some proof of consistency in the action of grindingwheels.As a wheel wears down the surface speed of thewheel is decreased (if the r.p.m. remain constant),and also, because of the smaller diameter of thewheel, which results in a smaller arc of contactbetween wheel and work, the grain depth ofcut will be correspondingly increased. Similarly,it is true that as the work diameter is increasedlarger chips will be cut from the work andthe thickness of these chips, or the grain depth ofcut, must be lessened. These statements assumethat, in analysing the effect of a particular factor,all other factors remain constant. Accordingly,a wheel should appear harder as the diameter ofthe work increases, or softer as it decreases ;similarly, a wheel should appear softer as the wheeldiameter decreases and harder as it increases.

Loading. If a wheel is forced into the work sodeeply and so quickly that the material to beground is crowded into the open spaces, filling thembefore the bond can be worn away by friction, thewheel is said to be loaded. With too deep and rapidfeed loading will occur whatever may be the speedof the wheel, but it will occur most frequentlywhen the speed is too slow. The clogged surfacemust be removed by dressing before the wheel canbe used to cut as it should do. In this we have ananalogy with the file and the milling cutter.

Glazing. A glazed wheel is one the cuttingparticles of which have become dull or worn downeven with the bond, the bond being so hard thatit does not wear away fast enough to leave spaces


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12 GRINDING MACHINES AND THEIR USEbetween the cutting particles, and to permit thecutting particles to escape when dulled. A wheelof the right grade and grain may glaze if run toofast, and a wheel run at the right speed may glazeif it is too hard for the work.One remedy for loading is to increase the speed.A remedy for glazing is to decrease the speed. Ifthe speeds are right use a softer wheel in eithercase. Loading and glazing make necessary exces-sive dressing, and excessive dressing wears a wheelaway faster than grinding.The Effect of a Multiplicity of Cutting Points

in Grinding.* The lathe performs its workusually with a single pointed tool. The grindingmachine employs a tool in the form of a grindingwheel which seldom has less than 50,000 points,and when using a larger and wider grinding wheelthere are often from 500,000 to 800,000 cutting

points. The volume of work that the lathe iscapable of doing depends upon the strength anddurability of the single pointed tool. The grindingwheel has a marked advantage over the lathe toolin this respect for the reason that, when the maxi-mum strength and durability of a single point on thegrinding wheel is reached, the wheel can be revolvedat a greater or lesser speed in order to obtain themaximum strength and durability of all the othercutting points upon the face of the wheel. Grinding wheels are revolved for no reasonother than to distribute the work among theentire number of cutting points. If it werephysically possible to make the wheel with a grainso strong, so durable, that it would stand up under

* H. W. Dunbar in Grits and Grinds.


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GRINDING WHEELS 13the cut for a long time, there would be no occasionfor revolving the wheel. It could be used in justthe same manner as a lathe tool. When we revolvethe wheel at a sufficient speed to secure the maxi-mum work each point is capable of performingwithout wearing away too rapidly, we then havethe correct speed for that wheel. While the hard grades or strong wheels are per-forming a given amount of work in a given timeat relatively slow speed, they do so with relativelygreater pressure on the work. Soft wheelsrevolving at high speed can perform the sameamount of work with less pressure, because withthe greater speed each point is required to cut lesseach time that it comes in contact, and is enabledto perform the same work in a given time' becauseit comes in contact more times during that period. For cylindrical grinding we therefore select themaximum revolution that is safe against breakingthe softer grades of wheels, and use such of thesofter grades as are suitable for certain materialwhen these wheels are revolved at that number ofrevolutions per minute. When we need to useharder or stronger wheels for other materials orother forms of work, we select such grades as aresuitable when revolved at the same revolution asthe softer wheels.

Speed o Wheels. The surface speed at which torun grinding wheels remains practically constantregardless of the material being ground, and forcylindrical work varies from 5,500 to 7,000 ft. permin. The best average surface speed of grindingwheels made from artificial abrasives, is about6,000 ft. per min. for external cylindrical grinding,


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14 GRINDING MACHINES AND THEIR USEand the useful speed range is from 6,500 to 5,500ft. per min. Below this speed excessive wheel wearis very probable, and grinding machines should bearranged so that the effective life of the wheel fallswithin this range. The effective life of the wheelis that portion outside the minimum diameterwhich can be used owing to the limitations of themachine, or the method of mounting. A variationof 500 ft. per min. makes no material difference,and it is best not to change the speed of the wheelin order to get a variation in results, but rather tochange the speed of rotation of the work. It isof the utmost importance, however, that thespeed of the wheel be maintained during thecutting operation, no matter what the speedmay be, and the drive should be sufficiently power-ful to prevent slowing down during momentaryheavy cutting. Not only is wheel wasted by beingallowed to slow down, but what is more important,the wheel face is destroyed and more frequenttruing-up is necessary.When the wheel has been worn down so that theperipheral speed falls below the satisfactory work-ing speed, the speed of the wheel must be increasedso that the proper speed can be maintained ;otherwise, the farther the wheel wears the softerit will appear to become, although it is not actuallyso, this effect being produced by the reducedperipheral speed. When worn down below thespeed range given on the machine the wheel shouldbe transferred to a smaller machine and soutilized. (See table of Wheel Speeds, page 106.)


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CHAPTER IICYLINDRICAL GRINDING MACHINES

Use of the Grinding Machine. The cylindricalgrinding machine has become fully recognized as amachine essential in every workshop for reducingthe cost of cylindrical work. It was originated toassist the lathe in producing cylindrical work, andto make the process less expensive not simply toreplace filing. Those who would produce cylin-drical work efficiently must recognize the fact thatdifferent cases require different degrees of refine-ment and, whether the work requires a,Jow or avery high degree of refinement, the grindingmachine is the only means for performing suchwork in an efficient and economical manner.The lathe was originally the only machine forproducing cylindrical work. The cylindricalgrinding machine was introduced to perform thefinishing operation and to give a more nearlyperfect cylinder than could be produced by thelathe alone. The grinding machine producesprecision work not perfect work but, whenrequired, the accuracy can be made so muchhigher than when using the lathe, that the cylin-drical grinding machine is rightly known as theprecision machine, when compared with the lathewhich it supplements.The replacement of a steel tool by a grindingwheel was first adopted to deal with the problemof hardened work the correction of distortiondue to the process of hardening. In its early

15


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16 GRINDING MACHINES AND THEIR USEdays, the process whilst giving higher accuracyand better finish than turning was so tediousthat it was confined to those cases where therequirements warranted the expense, such as thespindles of machine tools. Since that time theoperation of grinding has obtained ever-increasingrecognition. It was soon found to be indispen-sable for the production of interchangeable work,and did much to raise the standard of manu-facturing accuracy, which, in turn, furtheremphasized the importance of the process.

It is well known to all engaged in the manu-facture of precision machines and tools that thelathe is incapable of producing highly accuratework in an efficient manner, even in the softermetals, and in operating upon hardened surfacesit fails altogether. Grinding, therefore, meanscheaper cost of all work, and cheaper turning thanis possible without the use of the grinding machine.The aim of every engineer is to obtain the bestwork in the shortest time and at the lowest cost.In the case of cylindrical work this ideal can bereached, whether it is necessary for the part to beexact to fine limits of error or not, by the combina-tion of very rough turning with finish grinding.The real reason for removing metal is not to secureso many pounds of chips, but to accomplish certainfinished results and, where the grinding wheel willenable this to be done more cheaply than thesteel cutting tool, it is false economy not to allowit to do so.

Proper Relation of Turning to Grinding. Theproper relation of turning and grinding opera-tions, i.e. the amount of stock removed by the


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CYLINDRICAL GRINDING MACHINES 17lathe, the amount of stock removed in the grindingmachine, the number and depth of the cuts, etc.,can only be determined after scientific investiga-tion of each piece to be finished. No rule can belaid down establishing this relation definitely andfor all cases. Sometimes it is more profitable togrind direct from the black without turning at all ;most times it is not.

Tradition tells the lathe operator that if heturns his work very close to size it will requireless time for grinding. This is true, but it does notfollow that the total cost of the two operations willthen be a minimum. It may be, and often istrue that by so turning the wrork that the grindingrequires more time, the total cost is reduced, forit has been proved that in any metal-removingoperations which include finishing, a point is reachedwhen the grinding machine in some form or otherwill remove metal faster than other types ofcutting tools.

Necessity for a Wide Range of Work Speeds. Incylindrical grinding wrork a given size of machinehas to handle a great variety of different classesand different kinds of work, which naturally intro-duces as many different diameters of work. Witha given grade of wheel, in order to keep the surfacespeed of the work constant so that this wheel willhave practically the same cutting action on allthese different diameters, it becomes necessary tointroduce a speed-change device between thesource of power which revolves the work and thework itself. This usually takes the form ofgearing or belting, and a considerable range isprovided to maintain constant surface speed on


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18 GRINDING MACHINES AND THEIR USEall work, from the smallest to the largest sizes whichcan be ground by the machine.The speed changes thus made possible, secureproper action of the wheel when grinding, and takecare either of change in the diameter of the work,change in the diameter of the wheel, change in thecomposition of the material being ground, orchange in the finish desired on the work.It has often been claimed that it is impossibleto obtain first-class results when grinding workwhich is driven by gears. Certainly it is, to saythe least, very difficult to do this when using theordinary form of tooth. Experiments were, there-fore, made with various forms of teeth, and aform has been devised which gives the requisitesweet motion, and is so successful that it is easilypossible to grind a mirror finish.

THE UNIVERSAL GRINDERThe universal grinding machine is, as its name

implies, capable of performing almost all grindingoperations, including external work, parallel, or ofany angle or taper ; internal work ; flat work heldon a faceplate or in a chuck ; and sharpeningcertain classes of cutters.The life and usefulness of every machine tool

depends largely on the care and skill of the opera-tor, and this statement applies in an enhanceddegree to the universal grinder. The higheststandard of accuracy is expected in its product,and this can only be secured when the machineitself is accurate and in perfect working order.This calls for the utmost care in severaldirections.


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THE UNIVERSAL GRINDER 19The design must embody every possible advan-tage, so as to combine rigidity with ease of manipu-

lation, the power to withstand undue wear, andsuch proportions as to distribute unavoidablewear so as to have the least possible effect on thequality of the work.The workmanship must be of the highest classto secure the degree of accuracy in the variousparts, without ,which the machine fails in the veryobject of its existence.The materials of which the machine is builtmust be of the best quality, and the material foreach individual part must be best suited to theduty which it has to perform.

Fig. 4 shows a view of a 12 in. x 36 irr: machinemade by the Churchill Machine Tool Co., Ltd.,Manchester, complete with various attachmentsforming the standard equipment. The machinecarries a grinding wheel 12 in. diameter by1 J in. face. Churchill grinders are built on thealmost universal principle of a fixed wheel-headand moving table, i.e. the work being ground iscarried past a grinding wheel running in fixedbearings. This method is generally acknowledgedto be capable of producing the most accurate workwith the least effort on the part of the operator.The more rigidly the grinding wheel can be held,the less vibration there is on the machine, conse-quently better work can be expected, and the wearand tear on the machine are minimized. Thus withthe construction illustrated in Fig. 4 the wheelhead can be carried on a fixed part of the bed, andhas the necessary rigidity for carrying large andheavy grinding wheels without vibration. As thispart of the machine also carries the cross feed


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THE UNIVERSAL GRINDER 21mechanism, there is less liability to torsionaldeflection, thereby ensuring a sensitive control tothe feed at all times. Further, in order to transmitthe power necessary to revolve the grinding wheelto the best advantage, it is done through a singlebelt and pulley, and not through a long drum, asis necessary when the wheel travels.The long table, long in proportion to the wheelslide, keeps the ways uniform and even as ittravels to and fro over them (even if wear takesplace), and preserves the alignment.Another advantage in having the position of thecut stationary is that the operator can see itwithout moving from his position. With the movingwheel, there is the objection that the operator hasto follow the grinding wheel up and down the bed.This on long work becomes a laborious operation,as the operator is bound to follow the wheel toadjust the work rests when opposite the cut.A feature of the beds of these machines, and onegenerally adopted, is the three-point bearing uponwhich the bed rests. This makes the machine

self-setting and independent of the irregularities offoundations. All operations of planing andscraping the ways are carried out with the bedresting on the three points, and so are the erectingand testing, hence, once the machine is built towork rightly the alignments are maintained.

Universal Head. For external grinding, thework is carried between the centres of the work-head and the tailstock, and is rotated by means ofthe dead centre pulley. The work revolves ondead centres the only method of ensuring trulycylindrical work. Both the wheel-head and the


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THE UNIVERSAL GRINDER 23work-head may be swivelled in a complete circle,allowing the grinding wheel to be presented to thework in any desired position.For live spindle work, the dead centre pulley isremoved. The spindle nose is threaded so thatvarious attachments can be mounted. In theChurchill machines the spindle nose consists of twoparallel surfaces of different diameters and onethreaded portion. The threaded portion forms thedriver, and the two parallel portions, being bothaccurately ground and perfectly cylindrical, ensureall fixtures which may be fitted being perfectlyinterchangeable and true running.A sectional drawing of a Brown & Sharpeuniversal head is shown in Fig. 5.When it is desired to grind work on dead centres,the spindle is held from revolving by a pin wrhichenters the rim of the pulley keyed to the spindle.This lock is also useful when removing the deadcentre pulley from the spindle nose, and puttingon a face plate or chuck.

Tailstock. A view of the tailstock and one endof the table of a Churchill machine is shown inFig. 6.The tailstock spindle is provided with springtension to allow for expansion of the work duringgrinding. The spindle is fully enclosed andoperated by a conveniently placed lever at therear. A suitable clamp provides for locking thespindle in position when necessary, but this shouldonly be used when the work is heavy. The tailstockbody is split and fitted with an adjusting screw fortaking up wear. It is furnished with a convenientclamp with knurled thumb-screw for holding the3-{5363)


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THE UNIVERSAL GRINDER 25diamond tool when the grinding wheel is beingtrued, also a shield to protect the spindle from waterand grit. The grinding wheel can thus be truedup without removing the work from the centres.A special feature is the method of securing thehead and tailstock in position on the table, (seealso Fig. 29). Instead of being located by tonguepieces which fit in the central T-slot of thetable and w^hich tend to wear loose and becomeunreliable alignment is secured on these machinesdirectly from the front edge of the upper table,which can be made and maintained true with theleast possible trouble. The clamping is effected bybolts set diagonally, so that they pull the,, headsdown and back into position, yet allow the utmostfreedom of movement when released.

Table and Slides. The work table swivels ona hardened central stud and can be set at an angleto the ways for taper grinding. The adjustment ismade by a screw at the end of the table, and ascale is fitted showing the angle in degrees andinches per foot. Locking devices secure the tablein any position through its range of swiveladjustment.The table travel is automatic and controlled byadjustable hardened steel dogs on front of table

operating against the reversing lever. The dogsslide on a steel rack fixed on the table, andtheir position can be changed while the machineis running by simply pressing a thumb latch whichengages with the rack. There is also a fine adjust-ment provided by means of a screw and thumbnut for use when grinding up to shoulders. Thereversing lever has a spring plunger which can be


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26 GRINDING MACHINES AND THEIR USEdrawn back when desired, allowing the table to berun beyond the reversing points without disturbingthe adjustment of the dogs. The spring plungerautomatically assumes its normal position when thetable is returned.The base of the swivel slide which carries thewheel is graduated through half its circumference,and reads to 90 degrees either side of zero. Whenthe slide is set at zero the line of motion is atright angles to the ways of the table, and when theslide is set at 90 degrees the two motions areparallel.The satisfactory working of the machine dependsto a large extent on the care given to the crossslide, which must be kept clean and well oiled. Ifallowed to get stiff and dirty the slide will losethat sensitive responsiveness which is so essentialto accurate sizing. Remember that the slide isrequired to move exactly in accordance with theworking of the feed pawl, that and it must advanceby any desired amount down to 0-000125 in.(wonm -)> this being the movement produced by asingle tooth of the feed ratchet. Such exactitudeis only possible when the slide is in good order andworking smoothly.

Obtaining Extra Fine Feed. When grindinggauges, or other work requiring a closer limit ofaccuracy than the finest feed of the machine, thefollowing method will be found convenient. Thebottom wheel slide is swivelled to an angle of 60degrees from zero, the wheel head and top swivelbeing set in their normal positions as shown inFig. 7,Instead of traversing the wheel directly towards


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THE UNIVERSAL GRINDER 27the table, the feed motion now moves the wheelalong a line at an angle of 30 degrees. As a resultthe actual feed is half that indicated by -hegraduations on the handwheel, and the finest feed

FIG. 7. SETTING OF WHEEL SLIDE TO OBTAINEXTRA FINE FEED FOR GAUGES, ETC.is now Te oTHi in - (0-0000625 in.), corresponding to8^5-0 i*1 - reduction in diameter, instead of Bt *(ttt in.( 401OU in. reduction in diameter). This plan willoften be found of assistance in handling workwhere the greatest possible accuracy is required.Taper Grinding, Etc. The adaptability of theuniversal giinding machine is further shown by


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28 GRINDING MACHINES AND THEIR USEFigs.' 8 to 10. Centres can readily be ground bysetting the universal head to an angle of 30 degrees(see Fig. 8) and traversing the revolving centrespast the wheel. If for any reason it were desired

FIG. 8. TRUING CENTRES ON UNIVERSAL GRINDERto avoid disturbing the setting of the universalhead, an alternative method of grinding the centreswould be to swivel the wheel slide, and, with thewheel face parallel to the line of motion, traversethe wheel by means of the cross feed. In this casethe table would, of course, remain stationary, beingonly moved by hand the slight amount necessaryto put on the cut. Obviously this method involves


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THE UNIVERSAL GRINDER 29a good deal more trouble than that first described,and would therefore only be employed in excep-tional cases. This method is also illustrated byFig. 9, which shows the wheel head swivelled roundto grind the bevel face of a piece carried on dead

FIG. 9. GRINDING ANGULAR FACE WITH WHEELSLIDE SWIVELLEDcentres. Fig. 10 illustrates the method ofgrinding taper work by setting over the top table.

Disc and Face Grinding. An expanding chuckusually forms part of the equipment and is founduseful for disc grinding, such as thin millingcutters, saws, washers, etc. An example fromBrown & Sharpe practice is shown in section


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FIG. 10. GRINDING TAPER BY ANGULAR ADJUSTMENTOF TABLE

FIG. 11. EXPANDING ARBOR FOR Disc GRINDING


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THE UNIVERSAL GRINDER 31Fig. 11. This chuck holds the work by means ofa bushing expanded in the hole in the centre of thepiece to be ground. The work is held by thebushing C, which is expanded by the screw B anddrawn tightly against the face plate by turning theknob A. Different sizes of bushings are easily andquickly inserted to fit various sizes of holes in thework.This face plate, together with the four-jawchuck, when used in combination with the universalhead of the grinding machine, is extremely usefulin handling a wide range of flat and angular work,which would otherwise be impossible.In face grinding the headstock is set roundthrough 90 degrees ; the table for such work*ls, ofcourse, set to traverse half the diameter of thework.A note may here be given as to face grindingon the universal. As the area of contact betweenwheel and work is much greater in face grindingthan in cylindrical grinding, more heat is generated,with a tendency to crack hardened thin pieces.Therefore a softer grade of wheel should be usedthan for cylindrical work of the same material,and there should be a plentiful supply of coolinglubricant. If a fine adjustment has to be made toobtain flatness of surface, it will be found mucheasier to effect it by means of the table screw thanby disturbing the headstock setting.

Internal Grinding. The equipment of theuniversal grinder also includes provision for inter-nal grinding. Fig. 12 shows the arrangement usedon the Churchill machines. A range of spindlesis made capable of dealing with various diameters


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32 GRINDING MACHINES AND THEIR USEand lengths of holes. Each spindle is self-con-tained and immediate change can be made fromone spindle to another, the supporting bracket A

FIG. 12. INTERNAL SPINDLE DRIVE : CHURCHILLUNIVERSAL GRINDERA Supporting Bracket.B Cross slide.C Independent speed pulley.D Position of pulley when external grinding.

on the end of the cross slide B being split andclamped for easy and rigid locking. The wheelhead slide is, of course, swivelled round to bring theinternal spindle into position. An independent


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PLAIN GRINDING MACHINES 33speed pulley C is used to drive the internal grindingspindle, and this is always in position on the top ofthe main wheel head. This construction avoidsusing the main spindle as a countershaft, and thusprolongs its life. It also avoids the necessity forremoving the wheel and guard. Both externaland internal spindles always remain in theirworking positions, the arrangement being suchthat the use of either does not interfere with theother. When the machine is used for externalgrinding the speed pulley C and its bracket areturned half-round to leave the drive clear to themain spindle.

PLAIN GRINDING MACHINES*The universal grinding machine fulfilled most

requirements for a time, but production on amanufacturing basis called for a more powerfulmachine of a more or less specialized character,and this machine, called the plain grinder,meets all requirements as to accuracy and finish,and enables all plain cylindrical work to be handledeconomically, which is not possible on the ordinaryuniversal machine. Plain grinding machinesare designed expressly for high production,and on account of their rigidity they arecapable of turning out very accurate work.Frequently a grinder is used exclusively for theproduction of some particular machine part orduplicate pieces. Under such conditions it ispossible to select a wheel graded in every way to

* For fidler information on this subject the reader isreferred to the author's book Precision Grinding Machines.(Scott, Greenwood & Son.)


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34 GRINDING MACHINES AND THEIR USEmeet the grinding requirements of the particularwork to be done. Machines are made having acapacity of 72 in. swing.A representative type by the Norton GrindingCo., U.S.A., is shown in Fig. 13.

(Alf. Herbert, Ltd., Coventry)FIG. 13. NORTON PLAIN GRINDING MACHINE

Crankshaft Grinding. The finishing of crank-shaft pins and bearings, both for single- andmultiple-throw crankshafts, is a class of workpeculiarly applicable to the grinding machine,owing to the high degree of accuracy and finishdemanded. One of the difficulties encounteredin any method of machining crankshafts is tosecure alignment of the crankpins in relation toeach other, owing to the gradual release of variousstresses in the shaft forgings whilst the machiningis proceeding step by step. It is for this reasonthat the grinding machine has been so successful


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PLAIN GRINDING MACHINES 35on this work, the removal of the surplus materialby grinding being a more gradual operation, andone that does not impart further stresses to theshaft.The method adopted in such grinding is to use agrinding wheel equal in width to the full width of acrank pin or bearing, no traverse being used. Thefillets on the pins are formed directly by the wheel,the corners of the latter being rounded to thedesired radius by a special truing device.The crankshaft is carried in holders adjustablefor any stroke, and provided with accurate indexmechanism for four or six throws.The procedure in crankshaft grinding is generallyas follows

1. Rough-grind journals.2. Rough-grind pins.3. Finish-grind pins.4. Finish-grind journals.

The grinding of the journals should always bethe final operation because it is important theyshould be in line. It must always be borne inmind that every operation of removing metalcauses a change of alignment, and crankshafts arevery susceptible to this.Form Grinding. Form grinding consists in

producing irregular or straight surfaces by the useof a wide grinding wheel, which is fed directly intothe work without using the traverse. This methodis used very frequently on some classes of work,especially for studs and other pieces of shortlength and, as already mentioned, the pins of acrankshaft.Wheels up to 4 in. or 5 in, wide can be used


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36 GRINDING MACHINES AND THEIR USE

advantageously, but beyond this width there isdifficulty in obtaining wheels of uniform gradethroughout the full width, and there is also thegreater difficulty in obtaining rigidity of work.

Radius, Straight and Taper Combined. R uPto^

Large Radius and Taper Combined. Two Tapers

Straight and Radius. R=upto 3

Uniform Curve.FIG. 14. TYPICAL WHEEL FACES FOR FORM GRINDINGA typical instance of such work is the grinding

of the taper shanks of twist drills, which isperformed very successfully.It is not necessary that the face of the grindingwheel always be straight. Various curved formscan be ground, and to make the wheel face to the


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PLAIN GRINDING MACHINES 37desired outline it is necessary to use a separateattachment fixed to the table of the grind-ing machine with a slide carrying a diamondtool. This slide is traversed against a formercorresponding with the profile desired.Some examples of wheel faces that have beenused for form grinding are shown in Fig. 14.Cam Grinding. The subject of cam grinding is

interesting in view of the methods which have to beadopted to produce with fine limits of inaccuracythe particular contour or shape desired. In thecase of the aeroplane engine camshaft, it is commonto have 24 cams formed integrally on one shaft,and owing to the extremely high speed of rotationthese cams must be finished with the greatestaccuracy. Fig. 15 shows a cam grindingattachment for cams integral with the shaft.There are two methods which may be employedin grinding a cam to its finished shape (a) byoscillating or swinging either the work or the wheel,or (6) by a sliding action of either the work or thewheel.The first method is the one generally adopted,and it gives the greater accuracy owing to its more

sensitive control.The shaft is earned on centres on an oscillatingtable. The oscillation at each revolution of thework is controlled positively by a hardened steelmaster cam in contact with a roller, and althougha cam-shaft may have any number of cams, onlyone master cam is used, having two forms, oneeach for the inlet and exhaust. It is commonpractice to add a third form for the purpose ofgrinding the air pump eccentric. This does not


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PLAIN GRINDING MACHINES 39in any way affect the principle involved. The twoor three forms, as the case may be, are always madefrom one piece of tool steel, generated, hardened,and ground to the correct shape, and with exactrelationship between the inlet and exhaust, so thatno variation can possibly occur in actual use. Totake care of the varying number of engine cylindersand their respective cams a dividing plate formspart of the attachment. This plate is accuratelydivided corresponding to the number of cylindersused. This method of combined master cam ispeculiar to the Churchill machines, and has provedparticularly successful in meeting the exactrequirements of the engine builders.A further interesting adaptation of this methodof grinding has been the finishing of the outsides ofthe webs of crankshafts for automobile and aircraftengines, thereby eliminating a large percentage ofthe tedious and expensive hand work otherwiseentailed. All the faces are ground at one operation,and, apart from the large saving of time, the crank-shaft produced by this method is in much betterbalance than one finished by hand methods.Another example is the grinding of the externalcontour of turbine blades.

Roll Grinding. Chilled iron rolls are used to rollall kinds of sheet metal for the engineering trades,and they are used as calendar rolls in the textiletrade, and as rolls for flour mills and allied trades.In almost every case a different type of finish isrequired, but in all cases the results demanded arevery exacting, particularly where rolls with cam-bered surfaces are concerned. The grinding of aparallel roll is a comparatively simple matter once

4 (5363)


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40 GRINDING MACHINES AND THEIR USEcertain conditions are compiled with, such as thecorrect mounting of the roll, the rigidity of themachine, and correct grade of grinding wheel, butthe grinding of cambered surface rolls is much moredifficult, particularly where rolls up to 30 in.diameter and 6 or 8 ft. long have to be groundwith a diameter at the centre of the roll one ortwo thousandths greater than the diameters atthe ends, the rest of the surface being spherical.It will readily be realized that very sensitivecontrol mechanism is needed to regulate the move-ments of the wheel during the cambering operation.

It is essential that the roll be supported on itsown necks, and a special design of roll support isused for this purpose. A truly cylindrical rollcannot be ground unless the roll necks are alsocylindrical, and the design of the supports is suchthat the roll necks themselves can be ground to atrue cylinder whilst rotating in the supports. Evenif the roll necks are elliptical or oval to startwith, they can be ground cylindrical whilst runningin the supports. The fact that this can be donegreatly simplifies the operation of roll grinding.

Centreless Grinding. The grinding of shortpieces of work, such as studs and rollers, withoutthe use of supporting centres is a methodthat has been adopted with varying degreesof success, and for work that comes within therange it is a very economical method of grinding.The machine is of very simple construction asthere are no headstocks. In some machines thegrinding wheel is tapered and in others a ring wheelis used having a plane surface, the work travellingin a path parallel to that plane, but, as in the case


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INTERNAL GRINDING MACHINES 41of the tapered wheel, contact between the wheeland work is utilized for revolving and feeding thework.The process of centreless grinding has also beenapplied to bars and rods, and such machines havegenerally been made by the users themselves, inparticular, those specializing in the making ofchains.

INTERNAL GRINDING MACHINESThere are two methods of internal grinding, the

oldest and commonest being that in which thework is rotated and carried on a live spindle ; theHeald grinder shown in Fig. 16 is representativeof this type. The other type is that in which thework is stationary and the grinding wheel spindlehas a planetary motion. This method of grindingis suitable for work of an unbalanced nature, orfor work that cannot conveniently be rotated.

Internal grinding is a commercial operation, andthe factors governing production are much thesame as in external grinding. The wheel diameteris limited by the size of hole to be ground and bearsno direct proportion to it. For holes of less than6 in. diameter the ratio of wheel diameter to holediameter will be from 0-6 : 1 to 0-9 : 1. Providedthat a suitably rigid spindle is employed, thegrinding wheel diameter has very little effect onproduction, but it would be absurd to grind a 4 in.or 6 in. hole, using a 1 in. diameter wheel, becauseproduction would be limited by the weakness ofthe spindle that would have to be employed tocarry such a small wheel. On holes of 9 in.diameter and upwards, the wheel diameter isaffected not so much by the diameter of holes as by


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42 GRINDING MACHINES AND THEIR USEthe length, and also by the strength of spindle.There would be no gain in grinding, say, a 12 in.hole with an 8 in. diameter wheel if the spindlecarrying the wheel were designed to carry onlya 4 in. wheel. In such a case, production would be

FIG. 16. HEALD INTERNAL GRINDING MACHINEgoverned by the rigidity of the spindle, otherconditions being equal, such as wheel grade,surface speed, width, and traverse.The grinding wheel surface speed for internal

grinding has little effect on production, but such astatement requires a good deal of qualification.


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INTERNAL GRINDING MACHINES 43Internal grinding has reached what might betermed an advanced stage in the works of theChurchill Co., and the results obtained have hada direct effect on the design of machines, and moreparticularly on the design of internal grindingspindles. It has been found that the effectivespeed range of a good grinding wheel is very muchgreater in internal grinding than in any otherform of grinding, and ranges from about 1,000 ft.to 4,000 ft. per min. Much successful grindingis done at a surface speed of from 1,500 to 2,500 ft.per min., but such results have only been madepossible by spindle construction embodying theutmost

rigidityfor the particular work in view.Rigidity is, indeed, ofmore importance than actualwheel speed.

Planetary Type Spindle Machine. For thesecond type of internal grinding there is a greatdiversity of work to be operated upon includingthe grinding of holes in large castings, the bore ofengine cylinders, liners, etc. For such serviceMessrs. Churchill have designed a machine inwhich the table carrying the work is stationaryand does not traverse (see Fig. 17). With thisarrangement there is no limitation to the externalshape of work which may be dealt with. Forinstance, taking the ordinaryknee type of horizontalmilling machine, it is possible to grind the spindlehole, and also the hole for the overarm at onesetting, ensuring absolute parallelism of the spindlewith the overarm.The grinding head of this machine is verticallyadjustable on a column which reciprocates on the

bed, the length of stroke being variable, depending


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44 GRINDING MACHINES AND THEIR USEon the length of cylinder or hole to be ground.The grinding wheel spindle is driven at the highspeed necessary for the grinding wheel, and hasalso an independent rotary motion, provided withvarying throw, eccentrically adjustable whilst

FIG. 17. CHURCHILL CYLINDER GRINDER INOPERATIONwork is proceeding for the purpose of adjustingand feeding the wheel to the internal cylindricalsurface of the work.The grinding wheel spindle is self-contained anddetachable from the main spindle, and may easilybe removed and another size substituted. A full


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INTERNAL GRINDING MACHINES 45range of spindles is made so that the smallestholes may be ground, and up to the maximumcapacity of the machine.Where this method of finishing holes is adopted,it becomes a vital factor in the design of machineparts, designs being modified so that they can bedealt with on this machine, resulting in accuratealignment of holes, interchangeable work, andcorresponding cheapness of production. Themachine might be termed of the generative class, inasmuch as on some classes of work itgenerates the alignment of relative partsautomatically. The holes in many parts ofmachines can be finish-ground hi correct align-ment with previously finished locating surfaces orslides, correct alignment being thus secured witha minimum of correction by hand work.


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CHAPTER IIIPLANE SURFACE GRINDING MACHINES

THE production of plane surfaces by grinding isrecognized as a cheap and efficient manufacturingprocess. On certain classes of work it will give agreater production than either milling or planing.

Types of Surface Grinding Machines. Thereare two methods of surface grinding one usingthe periphery of the grinding wheel, and the otherthe edge or side of the wheel. The wheel in thelatter case is of cup form and carried on either avertical or horizontal spindle, the more widely usedbeing the vertical spindle type. The two methodsare further sub-divided according to the manner inwhich the work is moved, machines being madewith the work carried on a reciprocating table,or on a circular revolving table. Four classes ofmachines may be classified briefly as follows

(1) Horizontal-spindle surface grinding machine,in which the work is reciprocated under thegrinding wheel.

(2) Horizontal-spindle ring and surface grind-ing machine. In this machine the work is carriedon a circular revolving table, generally made in theform of a magnetic chuck, and is rotated under thegrinding wheel. A machine of this class, made bythe Heald Machine Co., U.S.A., is illustrated inFig. 18.(3) Vertical-spindle ring and surface grindingmachine, in which the grinding wheel is of cup

46


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02


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48 GRINDING MACHINES AND THEIR USEform, carried on a vertical spindle, and the workis carried on a circular rotating table, generallyin the form of a magnetic chuck, and is rotatedunder the wheel.

(4) Vertical-spindle surface grinding machine,in which the wheel is of cup form carried on a

FIG. 19. SURFACE GRINDING WITH CUP-WHEELvertical spindle, and the work is carried on atable reciprocating under the wheel (see Fig. 19).The first and fourth types are the most commonlyused, and are intended for the grinding of flatsurfaces of all kinds, and in all materials.The second and third types are intended forthe grinding of the sides of disc work, such ascircular knives and saws, piston rings, disc valves,etc., using the rotary table. The second type ofmachine, with horizontal spindle, leaves the workwith a concentric finish, whereas the third type ofmachine, with the cup wheel, leaves the work with


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PLANE StJfcFACE GRINDING MACHINES 49a radial finish, which in some classes of workis objectionable, particularly, for instance, inpiston rings, where the concentric finish ispreferred.So far as production is concerned the vertical-spindle machine will give a greater output than thehorizontal-spindle machine. Both machines canbe arranged to grind flat, concave, or convexsurfaces, and it is impossible to recommend onemachine in preference to the other without takinginto account the work intended to be ground onthe machine.The vertical-spindle surface grinding machinewith the cup wheel, which covers the full widthof work at each stroke of the table, as Fig. 19,comes under Class (4), and has a distinct advantagein this respect over the horizontal-spindle machineusing the periphery of the wheel, which wouldhave to be traversed transversely in order to covera work surface wider than the width of wheel.By the cup wheel work can be ground at onesetting up to about 85 per cent, of the full diameterof the grinding wheel, and of a length governed onlyby the length of table travel.

Quite apart from the question of heat distribu-tion, the vertical-spindle machine has the greaterproductive capacity, and for grinding wide surfacesor groups of small articles this type of machine hasthe advantage of the horizontal-spindle machine.The vertical-spindle surface grinding machine isadopted in all classes of engineering works, andwherever flat surfaces have to be produced, as inmachine tool work, for instance, there is no methodthat can be compared with it for cheapness ofproduction.


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50 GRINDING MACHINES AND THEIR USEThe Churchill Machine. This machine, Fig. 20,

is designed on the unit system of constructionthe body, upright, driving bracket, wheel head,

FIG. 20. VERTICAL-SPINDL.E SURFACE GRINDER

spindle-driving bracket, change speed gear box,and feed-control apron all being built as separateunits to simplify construction and assembling ofthe parts. The spindle and all shafts and pulleys


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PLANE SURFACE GRINDING MACHINES 51run in ball journal bearings. Another specialfeature is the balancing of the spindle. This isarranged so that the spindle is pulled away fromthe work. This prevents any tendency to lostmotion, and ensures perfect solidity of cut.The wheel head is carried on square gibbedslides of great length on the upright, and has anautomatic down-feed with trip motion, whichranges from 0-000125 in. at each stroke of thetable. An important factor which cannot beignored is the dissipation and distribution of theheat generated by the grinding wheel, and for thispurpose the spindle is made hollow, and the coolantcompound passing to the inside of the grindingwheel is thrown by centrifugal force between thewheel and the work, keeping them cool andwashing them clear of grit.Where this type of machine is used for grindingsmall articles in groups, the general practice is tocover the face of the table or the magnetic chuck ascompletely as possible, the object being to grind asmany articles as possible at the one setting. Thisis not, however, always the most efficient methodfrom a production point of view. Assuming thearticles to be placed in one row, the full length ofthe table, then the time required per piece is thetime required to grind one article. This produc-tion can approximately be doubled by adoptingthe method indicated in Fig. 21, which is to arrangetwo small groups, the centre of each group beingspaced apart a length equal to the diameter ofthe grinding wheel. Instead of using one side ofthe wheel only, as is the case when a large numberof articles is ground, both sides A, B, of the wheelare used, and the travel of the table is only that


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52 GRINDING MACHINES AND THEIR USEnecessary to cover one group. The illustrationmakes it clear that whilst the travel of the tableis set for grinding one group only, two groups are

FIG. 21. GRINDING SAD IRONS ON VERTICAL-SPINDLESURFACE GRINDERground in the same time, both sides of the wheelbeing used at once. For example, in one case aChurchill machine ground four sad irons from theblack to a fine finish in 1J minutes, removingapproximately -^ in. of metal. The dimensions


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PLANE SURFACE GRINDING MACHINES 53of the irons were 6 in. X 4 in., and the grindingwheel was 14 in. diameter.Piano-Type Machines. To deal with large

surfaces, vertical spindle surface grinding machinesare also arranged on the planing machine principle,i.e. with a grinding wheel supported on a cross-slide, this in turn being carried on two uprightsbetween which slides a reciprocating table. Inthis case the head has an automatic cross travelon the cross slide at each reversal of the table.Comparing the two types of machines, it wouldappear that for surfaces up to about 10 in. wide thestandard vertical-spindle machine is the quickerproducer, but on broader surfaces the piano-typemachine is the quicker, as harder grinding wheelscan be used with a smaller arc of contact andgreater depth of cut as compared with the othertype of machine, in which the limiting factor ofproduction for cast iron surfaces is obtaining asoft wheel of exactly the right grade.The Blanchard Machine. The machine illus-

trated by Fig. 22 comes under Class 3. (p. 46). Itis made by the Blanchard Machine Co., U.S.A.The upright carrying the wheel head is a boxcasting resting on three adjustable points, thisarrangement enabling the head to be set verticaland square with the chuck when grinding work ofuniform thickness, or slightly inclined whengrinding a convex or concave surface. The threesupporting points are shown at A, Fig. 23. Thespindle construction is shown later in Fig. 33. Allwork is held for grinding on the rotary table, whichis 26 in. in diameter. This table is mounted on a


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FIG. 22. BLANCHARD GRINDERBelt drive with 16 in. wheel

FIG. 23. TABLE POSITIONS AND THREE-POINT COLUMNSUPPORT OF BLANCHARD GRINDER


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PLANE SURFACE GRINDING MACHINES 55sliding carriage so that it may be moved out clearof the wheel when placing or removing work.Only the rotary motion is used for grinding, andthis is power-driven through a gear box giving avariety of speeds. The sliding carriage is operatedby hand.The rotary work table is a magnetic chuck withgreat gripping power. Tapped holes are providedin the face so that fixtures can be permanentlyscrewed in place if desired. The chuck, therefore,combines the advantage of a plain and a magneticwork support.The chuck is designed especially for the machineand is built by the Blanchard Machine Co. in itsown shops. Its construction differs from othermagnetic chucks in that the poles and body areall in one piece of forged steel. This climatesall joints from the outside and face of the chuck,thus making the chuck waterproof. The coils areformer wound and are impregnated by the vacuumprocess. The completed chuck is a solid mass withno open spaces in its interior.As will be seen by examination of the cresssection of the chuck Fig. 24, the face is divided intonarrow, concentric ring poles, so that even a smallpiece of work will touch two or more poles, nomatter where placed on the face. Brass in theform of narrow strips is used to fill the grooves thatseparate the poles and is driven firmly in place.This chuck has only steel and brass in the workingface and will keep a true surface and not chargewith grit. The steel walls of the chuck body areall connected together at the bottom by a heavyplate of steel, both surfaces of the joint beingground flat to ensure good contact.

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PLANE SURFACE GRINDING MACHINES 57Each coil establishes a magnetic flux as shownby the arrows in Fig. 25 and, as the current in

adjacent coils is opposite in direction, themagnetism in any one of the walls between coils,whether induced by the coil inside or outside that

Work

IT Chuck

FIG. 25. PATHS OF MAGNETISM IN BLANC-HARDMAGNETIC CHUCK

wall, flows all in the same direction. If there were nobrass rings or grooves in the face of the chuck themagnetism would find an ample path in the faceof the chuck itself, and would not flow out of theface into the work and back again, as is necessaryto secure magnetic holding of the work.The arrangement of the electrical circuit is shownin Fig. 26, where S is the switch ; C the cable ;B the brushes ; R the contact rings ; and T thechuck terminals. Spring plungers P on thecontact rings connect these rings to the terminals.

Continuous Reading Caliper Attachment. Thisattachment, supplied with the Blanchard machines,


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PLANE SURFACE GRINDING MACHINES 59is a very convenient means for measuring thework and letting the operator know the exactsize whilst the grinding is proceeding, thus elim-inating the loss of time which occurs when work is

FIG. 27. -SUPPORTS FOR CONTINUOUS READINGCALTPER. (BLANCHARD GRINDER)stopped and the piece removed for measurement.The caliper operates by direct contact with thework and is entirely independent of wheelwear.

Fig. 27 shows the supporting arm, and Fig. 28a section through the tube and its adjustments.


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PLANE SURFACE GRINDING MACHINES 61

slowing the table motion, even when many smallpieces are being ground.The attachment is aligned to swing the buttonparallel to the table surface, so that correctreadings can be taken at any convenient place onthe work. The caliper swings out of the way forplacing or removing work without disturbing itssetting. It can be removed from the machine,when not needed, without disturbing its alignmentparallel to the table, as the pivoted base need notbe removed. The clamp bolt E is provided so thatthe pillar may be removed if desired.The wear of the contact button introduces aslight error which, if unconnected, would cause thework to be left more and more over size. Bychecking a piece now and then with micrometersand correcting the variation from size by slightadjustments of the button, this error is renderedentirely negligible. A fine adjustment of the tubecarrying the contact button is made by handle C,clamping of the tube being effected by handle B.With the exception of a few screws, all the partsover the work table, including the arm, are ofbronze, avoiding errors that might otherwise becaused by the magnetic pull of the table. As thecontact button rests on the work, it is not affectedby magnetic pull, and to secure durability it ismade of hardened tool steel.Wheel Speed for Surface Grinding. The bestwheel surface speed for all-round surface grinding

is about 4,000 ft. per min ; but there is not thesame margin of wheel speed for surface grinding asthere is in external and internal cylindrical grind-ing ; that is, if a wheel is working successfully at


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62 GRINDING MACHINES AND THEIR USE4,000 ft. per min., it cannot be varied up or downfrom this speed without affecting production.Consequently the vertical spindle machine, with thecup wheel has a great advantage in this respect,the cup wheel, retaining its diameter as itwears down, whereas, in the case of the hori-zontal spindle machine, the wheel diameter isreduced by wear and its cutting speed is re-duced proportionately (unless the r.p.m. bealtered).

Selection of Wheels for Surface Grinding. Thegrade of the wheel for surface grinding demandsfar closer attention and more accurate selectionthan is necessary in any other type of grinding.The only remedy for a wheel that is too hard ortoo soft is to change it for a wheel of the correctgrade, and to adhere to this when once it has beendetermined.

In the surface grinding operation there is con-siderably more wheel buried in the work during theactual cutting time than there is with the samediameter wheel on a cylindrical piece of work.Hence for surface grinding it is usually safe to saythat the wheels must be very much softer than forcylindrical grinding and that the wheels should besomewhat coarser to allow room for chips beingremoved whilst the particles of wheel are buriedin the work. The same principle, of course,applies to cylindrical work ; as the diameter ofwork gets larger and larger, the wheel isburied deeper in the part being ground than onsmaller diameters, and therefore a somewhatsofter and coarser wheel is required for the largerdiameters.


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PLANE SURFACE GRINDING MACHINES 63The width of the surfaces presented to the

wheel also has to be considered. Soft and coarsewheels are used for broad surfaces hard and finewheels -for narrow surfaces.

Table I by the Blanchard Co. is a guide for theselection of wheels, and will enable a close approx-imation to be made. The table lists only wheelsmade by two firms, because the company's dataare only reasonably complete for these twomakes.Mounting Wheels for Surface Grinding. Either

fusible or Portland cement can be used to securethe wheel in the ring, no clamping devices beingnecessary. Fusible cement is amply strong andhas the advantage that the wheels can be used atonce. Portland cement requires 48 hours to set.To use Fusible Cement. Clean the inside of thering and the end of the wheel farthest from thewire bands. Set the ring on a level bench, placethe wheel centrally in it, with the wire bands awayfrom the ring, and pour in melted cement to fill thespace between wheel and ring.To use Portland Cement. Mix equal parts ofPortland cement and sand with water to a thinpaste. Wet the wheel thoroughly all over andspread a thin layer of the cement paste on the endfarthest from the wire bands.

Clean all dirt and grease from the inner surfacesof the iron ring and place the wheel centrally inthe ring, cemented end down. Then fill the spacebetween the wheel and the ring with cement paste,using a thin piece of metal to ram it in place.Remove all surplus cement from the outside ofthe ring and wheel and grease the ring. Then


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64 GRINDING MACHINES AND THEIR USE

TABLE IWHEELS FOR BLANCHARD SURFACE GRINDER

1


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PLANE SURFACE GRINDING MACHINES 65cover the wheel entirely with wet cloths and placeit in a covered box or barrel.Wheels should be allowed to set two days ormore, varying with the brand of cement used.

If not already done by the maker, the inside ofthe wheel should be covered with paraffin waxpainted on hot, to prevent annoyance from spray.

Safety. A grinding wheel should not be used ona vertical spindle unless protected against burstingstresses by means of a band of flat steel, or unlessthe wheel has been reinforced by the makers withbands of wire. The wheel should be mountedwith these bands away from the retaining ring.When the wheel is worn down to within J in. ofa band, the band should either be cut off or pushedup against the band above. Unless the wheel isbadly cracked, cut the band off and do the samewith the second band when it is within J in. ofthe face of the wheel. If the wheel has severalcracks, extending part or all the way from face toring, it is advisable to push the bands up and notremove them until there is no longer room forthem on the wheel.

Lubricant for Surface Grinding. A good cuttinglubricant for general work isWater . . .50 gallons.Soda . . . 5 to 7 pounds.Machine oil . . 1 to 2 quarts.

The oil improves the finish of the work and helpsto prevent rusting, and to prevent the work dryingwhite.


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66 GRINDING MACHINES AND THEIR USEThe use of grinding compounds as used in cylin-

drical grinding machines is not recommended.Troubles frequently met with in using compoundsare (1) Foaming so as to overflow the tank ;(2) the chips, being slightly magnetized, have atendency to become a solid mass, clogging the feedpipe. The soda in the recipe shown on page 65dissolves this mass and leaves the pipe clear.


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CHAPTER IVCONSTRUCTIONAL DETAILS OF GRINDINGMACHINES

Importance o Rigidity. There is probably nomachine tool in use the value of which is moredependent on rigidity than is that of the grinderAlso this is one of the essentials that is not alwaysapparent at the outset, but to the practical man it isof particular importance. The tendency of work-ing parts to vibrate, thus impairing the accuracyand finish of the work, is resisted by the rigidityof the machine, which ensures alignments beingmaintained. Without rigidity a successfulmachine is impossible.

Present-day manufacturing demands bothquality and quantity, and the more rapidly amachine is operated the more prone are its parts tovibrate, so that rigidity becomes vital to success-ful production. Running at high speed, revolvingwork, and abrupt reversal of table at ends oftraverse, all conduce to vibration, and so, too, dothe forces on the wheel when cutting. Vibrations ofthe work during operation cannot always beattributed to lack of rigidity in the machine.There are numerous minor causes that give riseto vibration, but it is generally easy to locate andremedy such sources of trouble. Where, however,a machine is incapable of taking cuts at speeds andfeeds consistent with modern good practice, thefault usually lies in either the design or theconstruction of the machine, or in both.

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GRINDING MACHINES AND THEIR USEAnother factor contributing to the success of a

grinder is the alignment of the various parts andmechanisms. Any error in alignment is invariablycommunicated to, and very often multiplied in,the work, and where this is of a fine characterthe slightest errors aresufficient to impair itsquality. As the chiefvalue of the grinder liesin its ability to producework within very closelimits of inaccuracy,alignments assume aparamount importance,and if they are notdependable then theutility of the machineis restricted.Plain grindingmachines are subjectedto a much heavier classof work than is theuniversal grinder ; hencethe design of the work

FIG. 29. CROSS-SECTION OF head, tailstock, and sup-PLAIN GRINDER porting steadies differsin the two styles ofmachines. Fig. 29 shows an example of theconstruction of these parts in a plain grinder.It will be seen that the work centres are located

directly above a solid wall of metal, which extendsto the floor ; and the outward thrust of the wheelagainst the work is brought to bear upon th^ frontwall of the base.A grinding machine table is guided and supported


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CONSTRUCTIONAL DETAILS 69by one V and one flat way. The long guideresulting therefrom ensures an accurate andstraight line movement, but it is essential that theguiding surface be made a true straight line in thefirst instance. The top table of a plain grinderis of a special form most suitable for keeping waterfrom the front mechanism, and also for providinga face which can easily be made straight. On thisface depends the truth of the machine, for when theheads are moved from one position to another toaccommodate different jobs, it is essential that theymaintain a straight line and that the work head andtailstock centres exactly coincide. The clampingbolts are so arranged as to pull the heads on to thealigning faces, as in the universal grinders alreadydescribed. The strong ribbing of the slidingtable is shown clearly in the view of the under side(Fig. 30). This construction entirely overcomesthe tendency of the table to sag when at the endof the traverse.The Wheel Head. The construction of the wheelhead calls for very special care, both in design and

workmanship. Any lack of rigidity in this por-tion of a grinding machine makes it unable to meetthe demands of work both as to quality andquantity.The wheel head must be heavy enough to carrythe largest and the broadest wheel with which themachine may possibly be fitted, and also to over-come any possible want of balance in the wheelitself. For the same reasons the spindle and itsbearings should be of ample proportions to with-stand the above forces without requiring frequentadjustments. It should be emphasized that the


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CONSTRUCTIONAL DETAILS 71work produced on a grinding machine is only areproduction of the grinding wheel itself. Forcylindrical work the grinding wheel must be aperfect cylinder, otherwise good work cannot beproduced, and, unless a grinding wheel head hasthe rigidity necessary to overcome possible adverseconditions in the wheel itself, it is impossible tomake a wheel perfectly cylindrical, and failure isthe result. It is for this reason that a grindingmachine cannot very well be improvised. Manyattempts have been made to convert the lathe intoa grinding machine by means of attachments,but such attempts can only meet with verymoderate results owing to the lack of the necessaryrigidity.The grinding wheel spindle and its bearings areexamples of the highest class of workmanship, andthere is no other detail on any machine tool fromwhich such exacting duties are required. Efficientlubrication is the first consideration. The highspeed, combined with large diameters and thenecessarily close running fit, make the lubricationof vital importance.Before being sent out by the makers, the spindleof a grinding machine is usually tested and tunedup to correct running fit. The adjustments shouldnot be tampered with, and any adjustmentrequired to take up wear should be undertaken bysome responsible person with a knowledge of theconstruction of the bearing, and the conditionsunder which the spindle should run. Spindles areknown to have run for two years without requiringadjustment.To be in good running condition the bearingshould be at a temperature of 100-120 F. To6 (5363)


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72 GRINDING MACHINES AND THEIR USEmaintain the temperature constant a grindingwheel is usually left running all day long, even whenall other motions are stopped.Unless proper attention is given to the lubrica-tion, the best spindle will quickly be ruined. Afilm of oil should be maintained, so that there isnever metal to metal contact between the spindleand bearing. A medium heavy-bodied oil shouldbe used, of such viscosity that it will not run awayat 100-120 F. The oil should be perfectlyclean, and the oil-well should be drainedoccasionally.

Wheel Spindle Construction. In order to main-tain the close fit necessary on the spindle bearings,they are designed taper on the outside so as to beeasily adjusted by movement parallel to thespindle axis. This adjustment has the advantageof giving perfect control with long life and pre-serves as nearly as possible the original align-ment, which is of the utmost importance with thewide grinding wheels now in use.Where split taper bushes are used, they have atendency to close in on the spindle at the planeof severance, independent of the action of drawing-in by means of the adjusting nuts. This is anobjectionable feature in the spindle of a grindingmachine, as it is essential to the true and steadyr

grinding machines

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