Grinding Machines

ENGIN.

LIBRARY

'

Grinding

Machines

8

CO

o

_SHAW

PITMAN'S

TECHNICAL

PRIMER

SERIES

Edited by R. E.

NEALE,

B.Sc., Hons. (Lond.) A.C.G.I.,A.M.I.E.E.

GRINDING

MACHINES

PITMAN'S

TECHNICAL

PRIMERS

EditedbyB.E.NEALE,B.Sc. (Hons.), A.C.G.I.,A.M.I.E.E. IN each book of the series the fundamental principles of some

sub-division of engineering technology are treated in a practical

manner, providing the studentwith ahandysurveyofthe particular

branchoftechnology with which heisconcerned. Each2s.6d. net.

THE STEAMLOCOMOTIVE. 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-ELECTRICDEVELOPMENT. ByJ.W.MEARES, M.Inst.C.E.

THEELECTRIFICATION OFRAILWAYS. By H. F._TREWMAN, M.A.

CONTINUOUSCURRENTARMATUREWINDING. ByF.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.

THEELECTRIC FURNACE. By FRANKJ. MOFFETT, B.A.,M.I.EE

SMALL SINGLE-PHASE TRANSFORMERS. ByE.T.PAINTON.B.Sc:.

PNEUMATICCONVEYING ByE. G. PHILLIPS, M.I.E.E.,A.M.I.Mech.E.

BOILER INSPECTIONANDMAINTENANCE. By R. CLAYTON.

ELECTRICITY IN STEEL WORKS. By W. MACFARLANE, B.Sc.

MODERNCENTRAL STATIONS. By C. W. MARSHALL, B.Sc.

STEAM LOCOMOTIVE CONSTRUCTION AND MAINTENANCE. By

E. L. AKRONS, M.I.Mech.E., M.l.Loco.E.

HIGHTENSION SWITCHGEAR. By H. E. POOLE, B.Se.,AC.G.I.

HIGHTENSIONSWITCHBOARDS. BytheSameAuthor.

POWERFACTORCORRECTION. ByA. E. CLAYTON, B.Sc., A.K.C.

TOOLAND MACHINE SETTING. By P. GATES.

TIDAL POWER. By A. STRUBEN, O.B.E., A.M.I.C.E.

SEWERS AND SEWERAGE, ByH.G.WHYATT,M.Inst.C.E. M.R.S.I

ELEMENTSOF ILLUMINATING ENGINEERING. By A. I>. TROTTER

M.Inst.C.E.

COAL-CUTTING MACHINERY. By G. E. F. EAGAR, M.Iast.Min.E.

GRINDINGMACHINESANDTHEIRUSE. ByT.R.SHAW,M.I.Mech.E.

ELECTRO-DEPOSITICN OF COPPER. ByC.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.

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HIGH-TENSION TRANSFORMERS. By W.T.TAYLOR, M.Inst.CE.

GRINDING

MACHINES

AND

THEIR

USE

THE

MAINPRINCIPLES,

EQUIPMENT AND METHODS

OF PRECISION GRINDING BASED

ON LONG

EXPERIENCE

IN

THE

DESIGN, CONSTRUCTION,

AND

APPLICATION OF GRINDING MACHINES

FOR

STUDENTS, MECHANICS, DESIGNERS,

AND

PRACTISING ENGINEERS

BY

THOS.

R.

_SHAW,

MJ.Mech.E.

A AUTHOR OF

"PRECISIONGRINDING MACHINES"; "MACHINETOOLS"; ETC.

LONDON

SIR

ISAAC

PITMAN

&

_SONS,

LTD.

PARKER

_STREET,

_KINGSWAY,

W.C.2

BATH,

MELBOURNE,

TORONTO,

NEW

YORK

KENYON

S

PATENT

Engineer

INTERSTRANDED COTTON

Litor

DRIVING

ROPE

For

Main,

Counter

2f

Machine

Drives

ffi Ourexperience,which extends

^jj over 50 years and embraces

installations from JH.P. to 6,000 H.P.,isat_yourservice.

Consult

our

Technical

_Dept

Thecompletetransmission designed,

suppliedanderected.

ENDLESS

ROPES

FOR

GRINDING

MACHINES

A SPECIALITY. MINIMUM STRETCH MAXIMUM LIFE.

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_Kenyon

&

Sons,

Ltd,

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CHESHIRE.

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PREFACE

THE

_object of this

book

has

been

to

_embody

in concise

form

the

main

_principles of

_workshop

precision grinding,

and

inthe pages following will be

found

the results of

_many

_{years' experience} in the design

and

construction of _grinding

machines

and

close observation of their _practical utility.

The

_subject matter is the basis of a series of

lectures

on

_grinding

machines

_given

_by

theauthor at the

_Royal

Technical _College, Salford.

The

author _hopes, however, that the

book

will _prove

helpful,not onlyto the technical student, butalso

to the _fully trained _engineer, because _precision

grinding plays such

an

important part in all

engineering

work

that every engineer should be

aware

ofits_{possibilities.} Itis

_hoped

the

book

will

not merely be perused

and

_put aside, but that it

will be studied _carefully

and

a desire thus be stimulated for closer _acquaintance with actual grinding practice.

In the space available it has not

been

_possible to _{give complete} details of machines,

and

the reader

who

desires fuller information

on

these points is referred to _Grinding

_Machinery

_by

J. J.

Guest,

and

Precision _Grinding

_{Machines by}

the author.

The

authordesires_{to place}

on

recordhis indebt-edness to the various firms

who

have

_kindly

VI

PREFACE

assisted

him

with information _regarding their

machines,

and by

the loan ofblocks ; also to the

Norton

Co., U.S.A., for _permiss'on to

make

extracts

from

their _{interesting trade publication,}

Grits

and

Grinds.

THOS.

R.

SHAW.

CONTENTS

PAGE

PREFACE

...

V

CHAPTER

I

GRINDING

WHEELS

...

1

Grindingas_{a cutting process} Abrasives, naturaland

artificial Abrasives for various materials

Jtfanu-factureofabrasivewheels Vitrified,silicate,and

elas-tic wheels Grain and grade Selection of _grades

Loading Glazing Effect of multiplicity of cutting

points Speedof wheels.

CHAPTER

II

CYLINDRICAL GRINDING

MACHINES

. .

.15

Useofthe grindingmachine Relationofturning to grinding Necessity for_{wide range} of work speeds.

TJie Universal Grinder Variety of uses Universal

head Tailstock Tableandslides Extrafinefeed

Taper grinding, etc. Disc and face grinding

Internal grinding. Plain GrindingMachines Crank

shaft grinding Formgrinding

Cam

grinding Roll grinding Centreless grinding. Internal Grinding

Machines Planetary typespindle.

CHAPTER

III

PLANE

SURFACE GRINDING

MACHINES

. . 46

Typeofmachines Vertical-spindlemachine

Piano-type machines Blanchard machine Continuous

readingcaliperattachment Wheelspeedforsurface grinding Selection of wheels _Mounting wheels Safety Lubricantfor _{surface grinding.}

Vlll

CONTENTS

PAGE

CHAPTER

IV

CONSTRUCTIONAL DETAILS OF GRINDING

MACHINES

. . . 67

Importanceof rigidity -Wheelhead Wheelspindle

construction Vertical _spindle Water _supply.

Internal Spindles Adapter type spindles Tube

type spindles. Automatic cross feed Reversing mechanisms.

CHAPTER V

CARE

AND

OPERATION OF GRINDING

WHEELS

AND

MACHINES

. . . * . 96

Grinding limits and allowances Wheel _mounting

Wheelbalance Preventionofdistortion Centresin

work Table travel and wheel width Wheel and

work _speeds Wear of _grinding wheels Special

drivers.

ILLUSTRATIONS

FIG. PAGE

1. Micro -photographof chipsfroma properly

operating grinding wheel.

2. Nortongrade chart

....

8

3. Illustrating wheel contact in different

classes of

work

. . 10

4. Churchill universal grinding machine . 20

5.

Brown and

_Sharpe universal

work

head 22

6. Tailstock of Churchill universal grinding machine

...

24

7. _Settingofwheelslideforextrafinefeed . 27

8. _Truing centres on universal grinder . 28

9. _Grinding angular face with wheel slide

swivelled . .

...

29

10. Grinding taper

by

angular adjustment of

table 30

11. Expandingarborfor discgrinding . . 30

12. Internal spindle drive . . .

.32

13. Norton _plain grinding machine . . 34

14. Typical wheel faces forform grinding . 36

15.

Cam

grinding attachment

...

38

16. Heald internal grinding machine . . 42

17. Churchill cylinder grinder in operation . 44

18. Heald rotary surface grinder . . 47

19. Surface grinding with cup wheel . . 48

20. _{Vertical -spindle surf}ace-grinder . . 50

21. _{Grinding sad} irons on vertical-spindle sur-facegrinder . . . .

.52

22. Blanchard grinding machine

...

54

23. Tablepositions

and

three-pointcolumn sup-portofBlanchardgrinder

...

54

X

ILLUSTRATIONS

FIO. PAGE

25. Pathsof_magnetismin_{Blanchard magnetic}

chuck . . .

.57

26. Section throughtableofBlanchardgrinder,

showingelectrical_parts . .

.58

27. _Supports for continuous _{reading caliper}

Blanchardgrinder . . .

.59

28. Continuous reading caliper. Blanchard

grinder

...

60

29. Cross-section of _plain grinder . . 68 30. Under-side of sliding table

...

70 31.

Wheel

headof Churchilluniversal grinder 74

32.

Wheel

spindle

and

bearingsof

Brown

and

Sharpe universal grinder . .

.76

33.

Wheel

headof Blanchardvertical-spindle

grinder

...

77

34. Churchill adapter-type internal spindle 81

35. Heald _tube-type internal spindle . 83 36.

Brown

and

_Sharpe internal spindle . 86 37. Detachablespindle forChurchill planetary

type internal grinder . .

.87

38. Churchill micrometer feed disc

.89

39.

Wheel

feed

mechanism

of Churchill plain

grinder

...

91

40.

Brown

and

_{Sharpe automatic} cross-feed. 92

41. "

Load and

fire "reversemechanism.

Per-sons-Arter rotary surface grinder . 94

42. _Taper

and

flanged spindle noses . . 99

43. Quick-acting driver . . .

.109

44.

_Expanding

holder onlive_spindle .

.111

45. _{Special running} driver for pins .

.112

TABLES

TABLE PAGE

I. Wheels for Blanchard surface grinder . 64

II. _Grinding limits for cylindrical pieces 96

III. _{Limit gauges}forlathe-

work

. 98

GRINDING

MACHINES

AND

THEIR

USE

CHAPTER

I

GRINDING

WHEELS

THE

forerunner of the

modern

_grinding

machine

was

_{the grindstone,}

which

has

been

in use

from

time

immemorial

and

still finds _useful

applica-tions.

Between

the

modern

_grinding

machine

and

the _{grindstone there} is, however, nothing in

com-mon.

The

art of "precision

"

grindinglias

made

great advances since the beginning of the

twen-tiethcentury, largely

owing

tothe

demands

ofthe

automobile manufacturer,

and

_{precision grinding}

machines are _capable of _dealing with materials

and

_{obtaininga degree}of_{accuracyquite}

_beyond

the

powers

ofa grindstone. Mechanically, the grind-ing

machine

is a

machine

tool of the highest quality

and

thereis

an

enormous

difference

between

the _grindstone a solid block of soft natural stone

and

the

modern

abrasive wheel

which

is

made

artificially

from

particles of extremely

hard

material.

When

the wheel is _properly chosen

and

usedthese_{particles actually}cutthe

work and

do

not "_grind" or "abrade" it in _{the ordinary} sense of these words.

Grindingis a Cutting Process.

The

_operationof

grinding, in

which

metal or other substance is

removed

_by

contact with a _{rapidly revolving} grinding wheel, is

an

_{actual cutting process.}

The

-MACBINKS?C

-

THEIR

USE

cutting tools are hard, sharp particles of abrasive

extending

from

the working face of the wheels.

When

these small, sharp tools harder

_{than any}

substance theyare called

_upon

to cut are

moved

FIG. 1. MICRO -PHOTOGRAPH or CHIPS FROM A

PROPERLY OPERATING GRINDING WHEEL.

at _{high speed} into contact with the material to be ground, each particlecuts its

own

minute

chip

from

the work.

The

modern

_grinding wheel, properly selected

and

usedinthe

modern

grinding machine, is _{just as surely} a _{milling cutter as} ifit

WHEELS

material

removed

is seen to resemble the _chips

from

other

machine

tools, being, forinstance, very similar to those

_produced

_by

a _{milling cutter or} lathe tool, see _Fig. 1.

Abrasives.* These areof

two

kinds,natural

and

artificial.

The

natural abrasives

_{emery and}

corun-dum

are both mineral substances, similarin

com-position,exceptthat

emery

isnotas_pureas

corun-dum

butcontainsa_{largepercentage}of iron,

which

is undesirable in a _grinding wheel as it has

no

abrasive qualities.

Initially the principal abrasive available

was

emery, that

most

in repute, as being the purest,

coming

from

Naxos. Deposits of nearly pure

corundum

have

since

been

found,

and

this isthe naturalmaterial

now

most

inuse.

The

best_gradeof

corundum

is

found

inCanada,

and

has a _{higher percentage} of

aluminium

oxide

than

_{has emery.}

Under

_{the pressure} of _grinding

the grains of

corundum

fracture, thus presenting

new

_{cutting edges or points to the} work. Since both

_{emery and}

corundum

are natural _products, they cannot be obtained free

from

all_impurities.

Artificialabrasiveshave, to_{a verylarge extent,}

superseded natural abrasives in the

manufacture

of _{grinding wheels,} because

_improvements

in the design

and

construction of _grinding

machines

created the

demand

for better

and more

reliable

grinding wheels

which

could be used

on

them.

The

excellenceof_{the grinding} wheelasobtainable to-dayis

_{undoubtedly due}

to _{the requirements} of

the grinding machine.

* _{Forfurtherinformation onthis}

subjectseeAbrasives,

4

GRINDING MACHINES

AND

THEIR USE

The

artificial abrasives used are aluminous

abrasives

and

carbide of silicon.

Both

of these are_products ofintense heat in

an

electricfurnace.

Aluminous

abrasives are

made

from

bauxite, a hydrate of alumina,

which

is

found

at

_Baux,

France,

and

in several _parts of the southern

United

States;

and

siliconcarbideis

made

from

a

mixture of coke, sand, salt

and

sawdust.

Abrasives

Used

_for Various Materials.

The

extreme

hardness

and

brittleness of carbide of

silicon is

an

essential element in the successful

grinding of metals of low tensile strength, such as

cast_{iron, brass,bronze,}

and

_copper. Itisalsoused

for _{grinding granite, pearl,} earthenware, firebrick,

glazed sanitary ware,

wood,

cork, leather,

and

a

variety of other articles.

Wheels

made

from

this

abrasive

_by

different

makers

bear various

names

including Crystolon,

Carborundum,

Carbolite, etc.

An

abrasive _{material perfectly}

_adapted

to the grinding of materials of hightensile strength, such

as steel

and

malleable iron, differs in essential

characteristics

from

one suitable for the _grinding

of cast iron

and

brass.

For

materials of _high

tensile _strength

an

abrasive

must

be

hard

and

sharp

and

possess greater toughness

than

is

required for the successful _grinding of

weaker

materials.

Such

extreme hardness

and

_sharpness as is

found

in carbide of silicon is not essentialor

even

desirable in

an

abrasivefor_{the grinding}of steel

and

malleable iron.

The

aluminous abrasives are thereforeusedforthese metals,

under

trade

names

of

_Alundum,

Aloxite, etc.

For

_{the grinding of}steel,then,

an

abrasive

must

GRINDING

WHEELS

hardness

which

will _permit it to _{penetrate easily} into the material to be ground. (2)

An

irregular

crystallization producing the property of

sharp-ness. ₍₃₎

A

_degree of _toughness

which

will

per-mit the _{crystals of} thegrain to stand

up

and

not break

down

or fracture too _rapidly

under

the

strain_placed

_upon

them

_by

the _high resistance of

a

_tough

material _{during a grinding operation.}

Such

wheels _{cut rapidly}

and

freely,

but

atsuch

a rate

and

in such a

_way

that excessive heat is

not generated.

They

are used for all classes of

steel _{grinding, varying}

from

fine _precision

and

tool-room

work

to _snagging of

_heavy

_castings.

Bonding

of Abrasive Wheels.

The

-manu-facture of abrasive wheels involves _{the processes}

by means

of

which

the _grainsofabrasive material are

bonded

_{together into} masses _{of specified sizes}

and

_shapes

and

_{desired degrees} of coarseness

and

hardness. Three different processes are used:

vitrified, silicate

and

elastic.

Of

these, the

vitrified process is

_by

far the

most

_important,

as itis _{possible to}obtain a

much

greaterrangeof gradesor degreesofhardnessin

an

abrasive wheel

by

this

method

than

_by

_any

other. Itis,therefore, possible to

manufacture

grinding wheels

by

the

vitrified _process that are

_adapted

to _{a very great}

variety of grinding operations.

The

_bonding materials used in the vitrified

process consist principally of fusible clays.

The

bonding clays are

mixed

with the abrasive grains

inthe_{properproportions}

and

the

mass

is

formed

or

moulded

into the desired size

and

_shape. It is

then thoroughly dried

and

_placed in a vitrifying

6

GRINDING MACHINES

AND

THEIR USE

sufficiently high to fuse or _vitrify the bonding

clays.

When

this vitrificationis_completethekiln

iscooled_gradually

and

then

_{opened and}

unloaded.

The

wheels are then finished or turned to exact

size

on

_{specially designed} lathes

_by

means

of

rotary steel- ordiamond-dressers.

The

arborhole

is

sometimes

bushed

to the desired size

and

each wheelis _{tested carefully} forbalance

and

_strength.

Silicate wheels, as the

name

indicates, are

made

by

using a

bonding

material

composed

of silicate

of soda.

The

_proper

amount

of this material is

mixed

with _{the abrasive grain}

and

_tamped

into

an

iron

mould

of _{approximately the shape}

and

dimensions of the wheel wanted. It is then

baked

for

about

20hr. at a _{comparatively low} temperature, high

enough

tocausethesilicate

bond

to harden.

The

wheel is then _ready for the truing room,

and from

this _point

onwards

it is

treated as a vitrified wheel.

With

a

few

_exceptions all wheels 30in. in

dia-meter and

overare

_{manufactured by}

this _process.

Wheels

_up

to 60 in. in diameter are

_commonly

made

forcutlery grinding.

Silicate wheels are used

where

a wheel is

requiredthathas a

somewhat

softergrinding action

than

awheelofthe _{corresponding}grain

and

grade

manufactured

_by

the vitrified _process.

_They

are

used _chiefly

on

_dry tool _grinding

and

similar

work. There is also the

advantage

that wheels

urgently required can be completed in three

days

by

thesilicate _process.

In the elastic _{process the abrasive} is

mixed

hot

with shellac,

run

into _trays,

and

allowed to cool.

Itis then

broken

_up

into its _{original size}

and

the grains (eachof

which

is

now

coatedwithshellac)are

GRINDING

WHEELS

putintohot moulds,rolledwithhotrollers,allowed

to cool,

and

then

packed

in _quartz

and baked

in

ovensat_{a temperature}of500 to600 Fahrenheit.

The

_subsequent treatment is the

same

as for

vitrified

and

silicate wheels.

Itis _{possible to}

make

wheels

_by

this _{process as}

thin as _-Jg-in., these being used chiefly for

saw

sharpening, grinding

between

the teeth of gears,

sharpening

moulding

cutters

and

_wood-working

tools, cutting-off small stock, slotting

and

roll

grinding.

Owing

to the hardness of

_many

_high-speed

steels it is _impossible to cut-off small _pieces of

stock forlathe

and

_planer tools in the usual

way.

The

elasticw^heels are _veryusefulfor this_^purpose

and

small _cutting-off machines, fitted with such wheels, are

made

for tool

room

use.

Cutter Grinding. In order to _keep cutters as well as othertoolsin_{properly sharpened}condition

in the easiest

and

quickest way, a cutter grinding

machine

should beused. Thisis_generallyasmall

machine

_having universal

movements

so that all

kinds of _{cutters, reamers, etc.,}

_may

_{be ground.}

Cup,saucer

and

dished grindingwheelsina_variety

of _shapes

and

sizes are

made

for use in such machines.

Grain (or Grit)

and

Grade.

The

grain

and

grade ofawheelrefer_{respectively to}thesizeof_grain

and

hardness.

The

_{grain or} grit

number

indicatesthe

number

of

meshes

_perlineal_{inch through}

which

the grain has passed.

The

sizes of _{grain in use are}

numbered

from

4to200 ; finer

than

200it iscalled

flour,

and

designated

by

letters, F,

FF,

FFF.

8

GRINDING MACHINES

AND

THEIH USE

The

_grade of a wheel is _{usually designated}

_by

letters,

and

means

the degree of hardness of the

wheel.

An

_{ideal grinding} wheel is one that

com-bines correct

_temper

of_{abrasive grain}(i.e. a grain that will fracture after the _{cutting point} has

M

VerySoft Soft Medium MediumHard Hard }rtre/ne/yHard

FIG. 2.

NORTON GRADE

CHART

become

dulled,thus_presentinga

new

_cuttingpoint

to _{the work) with a}

bond

_{just sufficiently}

hard

to hold the_grain untilit_{has performed}its

maximum

amount

of _cutting, the _{grain then being} released so as to_present

new

cuttingpoints tothework.

GRINDING

WHEELS

allowsthe_{grain to}break

_away

beforeithas

become

dulled, resulting inrapid wear,

and

toohard

when

the

bond

holds the _grain after it has

become

dulled.

In

thelatterconditionthewheel

becomes

glazed, resulting in slow cutting

and

heating of the work.

A

series of _grades is _just as essential as a

series of _{grains to permit} of the

_many

_varying

combinations required inpractice.

Wheels

are _graded

from

soft to hard, different

methods

of indicating grade being used

by

different _grindingwheel manufacturers.

The

Norton

method

_employs

the letters of the alphabetfor vitrified

and

silicate wheels.

For

elastic

and

rubberwheels,

numbers

nareused

to _designate hardness.

The

Norton

_grade list

is

shown

in

_{diagram form}

_{in Fig.}2.

Elastic wheels are _graded as follows

SOFT

1, li, 2, 2}; 3, 4, 5, 6

HARD.

Selectionof Grades.

The

factors that influence the selection ofthe _{grades are physical properties}

ofthemetalto_{be ground, shape}

and

conditionof

the surface to _{be ground, speed} of wheel, rigidity of the machine,

and

the

method

of _grinding.

Soft wheels are used

on hard

materials like

hardened steel.

On

softer materials, like mild

steel

_{and wrought}

iron, harder grades

can

be

used.

The

_{area of surface to}be

_ground

incontact with the wheel is of the

utmost

_importance in deter-mining the grade tobe used.

A

_strongly

bonded

wheel

must

be used ifthere is _{point-contact} with

the work, as

when

_grinding a ball. If there is a broadcontact,

where

the

work

brings alarge part

10

GRINDING MACHINES

AND

THEIR

USE

ofthe wheel_{into operation,} softer _grades

must

be used.

Vibration _{in grinding}

machines

necessitates the useofharderwheels.

A

softer_grade ofwheelcan be used _efficiently

on

_rigid machines.

Reference to _Fig. 3 will illustrate the _practical influence of wheel contact

_upon

the choice of a wheel.

A

wheel is

shown

in contact with four

different varieties of _work, all of

which

_may

be

(C) (d)

FIG. 3. ILLUSTRATING

WHEEL

CONTACT INDIFFERENT CLASSES OF

WORK

supposedtobeofthe

same

material,

and

thedepth

of cut,

much

exaggerated, beingthe

same

in each

case. In case _(a) the

work

_ground

is a shaft of

small _{diameter and, the wheel contact being very} small, aharder grade of wheelis _required

than

in

case ₍₆₎

where

a _{larger shaft} is _being

_{ground and}

where

thewheel contactis_{proportionately}

greater.

To

_{continue the comparison,}

_diagram

(c)

shows

the

wheel_grindingaflatsurface,

and

at _(d)thewheelis

engaged

in _{internal grinding.} In these successive cases _practice

demands

that the wheel shall be progressively softer in

bond

or grade,

and

this is

GRINDING

WHEELS

some

_proofof_{consistency in the action}of_grinding

wheels.

As

awheel wears

down

thesurface_speedof the wheelis decreased(ifthe r.p.m.

remain

constant),

and

also, because of the smaller diameter of the

wheel,

which

results in a smaller arc of contact

between

wheel

and

work, the grain

depth

of

cutwill be _{correspondingly increased. Similarly,}

it is true that as the

work

diameter is increased larger chips will be cut

from

the

work

and

the thickness ofthese _chips, orthe _grain

_depth

of cut,

must be

lessened. These statements

assume

that, in_{analysing the} effectof a_particularfactor,

all other factors

remain

constant. _Accordingly, a _{wheel should appear harder} as the diameter of

the

work

increases, or softer as it decreases;

similarly,awheel should appearsofterasthewheel

diameterdecreases

and

harderas it increases.

Loading. If a wheelis forced into the

work

so deeply

and

so quickly that the material to

be

ground

is

crowded

intothe

_open

_{spaces,filling}

them

beforethe

bond

can be

worn

_{away by}

friction,the

wheelissaidtobeloaded.

With

too

_{deep and}

_rapid feed loadingwilloccur

whatever

_may

be

_{the speed}

of the wheel, but it will occur

most

_frequently

when

_{the speed} is too slow.

The

_clogged surface

must

be

removed

_by

_{dressing before the} wheel

can

beusedtocut asitshoulddo. Inthis

we

have an

analogy withthefile

and

the _milling cutter.

Glazing.

A

glazed wheel is one the _cutting

particles of

which

have

become

dull or

worn

down

even

with the bond, the

bond

being so

hard

that

12

GRINDING

MACHINES

AND

THEIR USE

between

the _{cutting particles,}

and

to _permit the cuttingparticles to escape

when

dulled.

A

wheel

of the_{right grade}

and

_grain

_may

_glaze if

run

too

fast,

and

a wheel

run

attherightspeed

may

glaze

if it istoo

hard

forthe work.

One remedy

for _loadingisto increase_{the speed.}

A

remedy

for_glazingisto decreasethe _speed. If

the _{speeds are right use} a softer wheel in either

case.

_{Loading and}

_glazing

make

_necessary

exces-sive_dressing,

and

_{excessive dressing}wears a wheel

away

faster than _grinding.

The

Effect of a Multiplicity of Cutting Points in Grinding.* "

The

lathe _performs its

work

usually with a single pointed tool.

The

_grinding

machine employs

atool in the

form

of a _grinding wheel

which seldom

has less

than

50,000 points,

and

when

_{using alarger}

and

wider_grinding wheel there are often

from

500,000 to _{800,000 cutting} points.

The

volume

of

work

that the lathe is

capable of doing

depends

upon

the strength

and

durabilityofthesinglepointedtool.

The

_grinding

wheel has a

marked

_advantage

overthe lathe tool inthis respectforthereasonthat,

when

the

maxi-mum

strength

and

durabilityofa_singlepoint

on

the grindingwheelis_reached,thewheel can be revolved at a _{greater or}lesser _speedin order to obtainthe

maximum

_strength

and

durability ofall the other cutting points

upon

the face ofthe wheel.

"

Grinding wheels are revolved for

no

reason other

than

to distribute the

work

_among

the

entire

number

of _{cutting points.} If it

were

physically possible to

make

thewheel with agrain so strong, so durable, thatit

would

stand

_up

under

GRINDING

WHEELS

13

the cutfor_{a long}time, there

would

be

no

occasion

for_{revolving the wheel.} It could be used_{in just} the

same

manner

asalathetool.

When

we

revolve thewheel atasufficient _speedtosecure the

maxi-mum

work

each _point is _capable of _performing without wearing

away

too _rapidly,

we

then

have

the correct _speed for that wheel.

"

While

the_{hard grades or strong}wheels_are per-forming a given

amount

of

work

in _{a given time}

at_relativelyslow_speed,they

do

sowith_relatively

greater pressure

on

the work. Soft wheels revolving at high speed can perform the

same

amount

of

work

with less _pressure, because with the greaterspeed each pointis_{required to cut}less

eachtime thatit

comes

_{in contact,}

and

is enabled to_performthe

same work

in_{a given} time'because

it

comes

incontact

more

_{times during thatperiod.} "

For

_{cylindrical grinding}

we

therefore select the

maximum

revolutionthat is safe _{against breaking}

the softer _grades of wheels,

and

use such of the

softer _grades as are suitable for certain material

when

these wheels arerevolvedatthat

number

of

revolutions _{per minute.}

When

we

need

to use harder _{or stronger} wheels for other materials or other forms of work,

we

select _{such grades} as are suitable

when

revolved at the

same

revolution as

the softer wheels."

Speedo!Wheels.

The

surface_speedat

which

to run _grinding wheels remains _practically constant regardless of the material being ground,

and

for

cylindrical

work

varies

from

5,500 to 7,000ft. _per

min.

The

best _average surface _speed of _grinding

wheels

made

from

artificial abrasives, is

about

14

GRINDING MACHINES

AND

THEIR USE

and

the useful_{speed range} is

from

_{6,500 to 5,500} ft._{per min.}

Below

this_speedexcessivewheel

wear

is _{veryprobable,}

and

_grindingmachines should be arranged sothattheeffectivelife ofthewheelfalls

within this _range.

The

effective life of the wheel

is that _portion outside the

minimum

diameter

which

can be used

_owing

to the limitations of the machine, orthe

method

of_mounting.

A

variation

of 500ft. _{per min.}

makes

no

material difference,

and

it isbestnotto_{change the speed}ofthewheel in _{order to get}avariation inresults,

but

rather to

change the speed of rotation of the work. It is

of the

utmost

_importance, however, that the speed of the wheel be maintained during the cutting operation,

no

matter

what

the speed

may

be,

and

thedriveshouldbesufficiently

power-ful to _{prevent slowing}

down

_during

_momentary

heavy

cutting.

Not

onlyiswheel

wasted by

_being

allowedto slow

down, but what

is

more

_important,

the wheel face is _destroyed

and

more

_frequent

truing-

up

is _necessary.

When

thewheel has

been worn

down

sothatthe peripheralspeed falls below_{the satisfactory} work-ing speed, thespeedofthewheel

must

beincreased so that the _{proper speed} can be maintained ;

otherwise, the farther the wheel wears the softer

itwill_appearto_{become, although}itisnot_actually

so, this effect _being

_produced

_by

the reduced

peripheral speed.

When

worn

down

below

the speed range given

on

the

machine

thewheel should be transferred to a smaller

machine

and

so

CHAPTER

II

CYLINDRICAL GRINDING MACHINES

Use

of the Grinding Machine.

The

_cylindrical

grinding

machine

has

become

fullyrecognizedasa

machine

essential in _every

_workshop

for _reducing

the costof_cylindricalwork. It

was

_{originated to}

assistthelathe in_{producingcylindrical}work,

and

to

make

_{the process}less_{expensive not simply}to replace filing.

Those

who

would

produce

cylin-drical

work

efficiently

must

recognize the factthat

different _{cases require} different _degrees of

refine-ment

_and,

whether

the

work

_requires a,Jow or a very high degree of refinement, the _grinding

machine

is the _only

means

for _{performing such}

work

in

an

efficient

and

economical

manner.

The

lathe

was

_{originally the only}

machine

for

producing cylindrical work.

The

cylindrical

grinding

machine

was

introduced to perform the

finishing operation

and

to give a

more

nearly

perfect cylinder

than

could be

produced

by

the lathe alone.

The

_grinding

machine

_produces precision

work

not perfect

work

but,

when

required, the accuracy

can be

made

so

much

higher

than

when

using the lathe, that the

cylin-drical _grinding

machine

is _rightly

known

as the

precision machine,

when

compared

with the lathe

which

it_supplements.

The

_replacement of a steel tool

_by

a _grinding wheel

was

first

_adopted

to deal with the

_problem

of

hardened

work

the correction of distortion

due

to the _process of _hardening. In its _early

16

GRINDING MACHINES

AND

THEIR USE

days, the process whilst giving higher accuracy

and

better finish

than

_turning

was

so tedious that it

was

confined to those cases

where

the requirements warranted the expense, such as the spindles of

machine

tools. Since that time the operation of_grinding has obtained _{ever-increasing} recognition. 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, further

emphasized

the importance of _{the process.}

It is well

known

to all

_engaged

in the

manu-facture of precision

machines

and

tools that the lathe is _incapable of _{producing highly} accurate

work

in

an

efficient

_{manner, even}

in the softer

metals,

and

in _operating

_upon

hardened

surfaces

it fails _{altogether. Grinding,} therefore,

means

cheapercostofallwork,

and

cheaper turning

than

is_possiblewithout theuseof_{the grinding}machine.

The

aim

of_{every engineer} is to obtain the best

work

in the shortest time

and

at the lowest cost.

In the case _{of cylindrical}

work

this ideal can be reached,

whether

itis _necessaryforthe_{part to} be exacttofinelimits oferroror not,

by

the combina-tion of _very

_rough

_{turning with} finish _grinding.

The

realreasonfor

_removing

metalisnotto secure so

_many

_pounds

_{of chips,}

but

to_accomplishcertain finished results and,

where

the grindingwheel will

enable this to be

done

more

_cheaply

than

the

steel _cutting tool,it is false

_economy

not to allow

itto

do

so.

Proper Relation of Turning to Grinding.

The

proper relation of _turning

and

_grinding

lathe,the

amount

ofstock

removed

inthe grinding

machine, the

number

and depth

of the cuts, etc.,

can only

be

determined after scientific

investiga-tion ofeach _{piece to} befinished.

No

rule can be

laid

down

establishing this relation definitely

and

for all cases.

Sometimes

it is

more

profitable to grinddirect

from

theblack without turningatall ;

most

times it is not.

Tradition tells the lathe _operator that if he

turns his

work

_very close to size it will _require

lesstimeforgrinding. Thisis_true,butitdoesnot follow that thetotalcostofthe

two

_operationswill

then be a

minimum.

It

_may

be,

and

often is

truethat

_by

so _{turning the}

w

r

orkthat_{the grinding} requires

more

time, the total cost is _reduced, for

it has

been

_proved that in

_any

_{metal-removing}

operationswhichincludefinishing,apointisreached

when

_{the grinding}

machine

in

some form

or other

will

remove

metal faster

than

other _types of cutting tools.

Necessityfora

Wide Range

of

Work

Speeds. In

cylindrical grinding

w

r

ork a given size of

machine

has to handle a great variety of different classes

and

differentkindsofwork,

which

_naturally

intro-duces as

_many

differentdiameters ofwork.

With

a given gradeofwheel, in order to

keep

thesurface speed ofthe

work

constantso thatthiswheelwill

have

_practically the

same

_cutting action

on

all

these different diameters, it

becomes

_{necessary to} introduce a _speed-

_change

device

between

the source of

_{power which}

revolves the

work and

the

work

itself. This _usually takes the

form

of

gearing or belting,

and

a considerable range is

18

GRINDING

MACHINES

AND

THEIR USE

allwork,

from

thesmallest tothe_{largest sizes}

which

can be

_ground

_by

themachine.

The

_{speed changes thus}

made

_possible, secure properactionofthewheel

when

_grinding,

and

take care eitherof

_change

inthe diameterof thework, changeinthediameterofthewheel,changeinthe composition of the material _{being ground,} or

change

inthefinishdesired

on

thework.

It has often been claimed that it is _impossible

to obtain first-class results

when

_grinding

work

which

is driven

_by

_{gears. Certainly} it _is, to _say

the least, very difficult to

do

this

when

_{using the}

ordinary

form

oftooth.

_Experiments

were,

there-fore,

made

with various forms of teeth,

and

a

form

has

been

devised

which

gives the requisite sweet motion,

and

is so successfulthatitis _easily

possible togrind a mirrorfinish.

THE

UNIVERSAL GRINDER

The

_{universal grinding}

machine

is, as its

name

implies, capable of_{performing almost} all _grinding

operations, including external work, parallel, or of

any

angle ortaper; internal

work

; flat

work

held

on

a _faceplate or in a

chuck

;

and

sharpening

certain classes of cutters.

The

life

and

usefulness of _every

machine

tool

depends

largely

on

thecare

and

skillof_the opera-tor,

and

this statement applies in

an enhanced

degree to the universal grinder.

The

highest standard of _accuracy is _expected in its _product,

and

this _{can only be secured}

when

the

machine

itself is accurate

and

in _perfect

_working

order.

This calls for the

utmost

care in several

UNIVERSAL GRINDER

The

_design

must

_embody

_{every possible}

advan-tage,so as to

combine

rigiditywitheaseof

manipu-lation, the

power

to withstand

undue

wear,

and

such _proportions as to distribute unavoidable

wear

so as to

have

theleast _possible effect

on

the qualityofthework.

The

_{workmanship must}

be ofthe _highest class

to secure _{the degree} of _accuracy in the various

parts, without,

which

the

machine

failsin thevery

objectofitsexistence.

The

materials of

which

the

machine

is built

must

be of the _{best quality,}

and

the material for

each _{individual part}

must

be best suited to the

duty which

it hasto _perform.

Fig.4

shows

a

view

of a12in.

x

36irr:

_machine

made by

the Churchill

Machine

Tool Co., Ltd., Manchester, complete with various attachments forming the standard equipment.

The

machine

carries a _grinding wheel 12 in. diameter

_by

1_Jin. face. Churchill _grinders are built

on

the

almost _{universal principle} of a fixed wheel-head

and moving

table, i.e. the

work

_being

_ground

is

carried _past a _{grinding wheel running} in fixed bearings. This

method

is _generally

_acknowledged

to _{be capable}of_producingthe

most

accurate

work

with theleast effort

on

_{the part}ofthe_operator.

The

more

_{rigidlythe grinding}wheel can beheld,

the less vibration there is

on

_{the machine,} conse-quentlybetter

work

can beexpected,

and

the

wear

and

tear

on

the

machine

areminimized.

Thus

with the construction illustrated in Fig. 4 the wheel

head

can be carried

on

afixed_partofthe bed,

and

has the necessary rigidity for carrying large

and

heavy

grindingwheels withoutvibration.

As

this part of the

machine

also carries the cross feed

mechanism,

there is less _liability to torsional

deflection, thereby ensuring a sensitive control to

the feed atalltimes. _{Further, in order to}transmit the

_power

_{necessary to revolve}the _grindingwheel tothe best _advantage, itis

done

_{through a single}

belt

and

_pulley,

and

_{not through a long}

drum,

as

is _necessary

when

the wheel travels.

The

_{long table, long} in _proportion to thewheel

slide, keeps the

ways

uniform

and even

as it

travels to

and

fro over

them

(even if

wear

takes

place),

and

preservesthealignment.

Another

_advantagein_{having the position}ofthe cut _stationary is that the _operator

can

see it

without

_{moving from}

_{his position.}

With

the

_moving

wheel, there is _{the objection}that_{the operator has} to followthe_grindingwheel

_up

and

down

the bed. This

on

_long

work becomes

a_{laborious operation,} as the _operator is

bound

to follow the wheel to adjust the

work

rests

when

_{opposite the} cut.

A

featureofthebedsofthese_machines,

and

one generally adopted, is the _three-point bearing

upon

which

the

bed

rests. This

makes

the

machine

self-setting

and

independentoftheirregularities of

foundations. All _operations of _planing

and

scraping the

ways

are carried out with the

bed

resting

on

the three points,

and

so arethe erecting

and

_testing, hence, once the

machine

is built to

work

_{rightly thealignments}are maintained.

Universal Head.

For

external

grinding, the

work

is carried

between

the centres of the

work-head

and

thetailstock,

and

isrotated

_{by means}

of

the

dead

centre _pulley.

The work

revolves

on

dead

centres the _only

method

of _{ensuring truly}

work-head

_may

be swivelled in _{a complete} circle,

allowing the grindingwheelto be presentedto the

work

in

_any

desired_position.

For

live_{spindle work,} the

dead

_{centre pulley}is

removed.

The

_spindle nose is threaded so that various attachments

can

be

mounted.

In the Churchillmachines_{the spindle}noseconsists of

two

parallel surfaces of different diameters

and

one

threaded_portion.

The

threaded_portionforms the

driver,

and

the

two

parallel portions, being both

accurately

ground and

perfectlycylindrical,ensure

all fixtures

which

_may

be fitted _{being perfectly}

interchangeable

and

true running.

A

sectional

_drawing

of a

Brown

&

_Sharpe

universal

head

is

shown

in_Fig. 5.

When

it isdesiredto_grind

work on dead

centres,

the spindleis held

from

_revolving

_by

_{a pin}

w

r

hich enters the rim ofthe pulley

keyed

tothe _spindle. This lock is also useful

when

_removing

the

dead

centre pulley

from

the _{spindle nose,}

and

_putting

on

a _{face plate or} chuck.

Tailstock.

A

view

ofthe tailstock

and

one

end

of the table of a Churchill

machine

is

shown

in

Fig. 6.

The

tailstock _spindle is _{provided with spring}

tension to allowfor _expansionofthe

work

_during grinding.

The

spindle is _fully enclosed

and

operated

by

a conveniently placed lever at the

rear.

A

suitable

_clamp

_provides for locking the

spindleinposition

when

necessary, but thisshould only be used

when

the

work

is_heavy.

The

tailstock

body

is _split

and

fittedwith

an

adjustingscrewfor taking

up

wear. It is furnishedwith a convenient

clamp

with knurled

thumb-screw

for _{holding the}

diamond

tool

when

the grinding wheel is _being

trued,alsoashield_{to protect the spindle}

from

water

and

_grit.

The

_grinding wheel can thus

be

trued

up

without

_removing

the

work from

the centres.

A

special feature is the

method

of _securingthe

head

and

tailstock in position

on

the table, (see

also Fig. 29). Instead of_beinglocated

_by

_tongue

pieces

which

fit in the central T-slot of the table

and

w^hichtend to

wear

loose

and become

unreliable _alignmentissecured

on

these

machines

directly

from

the front edge of the

upper

table,

which

can be

made

and

maintained truewith the

least_{possible trouble.}

The

_clampingiseffected

_by

bolts set _{diagonally, so that they pull}

the,,heads

down

and back

into_position,yetallow the

utmost

freedom of

movement when

released.

Table

and

Slides.

The work

table swivels

on

a

hardened

central stud

and

can besetat

an

_angle tothe

_ways

for_{tapergrinding.}

The

_adjustmentis

made by

a screw at the

end

of the table,

and

a

scale is fitted

_showing

the _{angle in degrees}

and

inches per foot. _Locking devices secure the table

in

_any

_{position through} its _range of swivel adjustment.

The

table travelis automatic

and

controlled

_by

adjustable

hardened

steel _dogs

on

front of table operating against the reversing lever.

The

dogs

slide

on

a steel rack fixed

on

the table,

and

their _position

can

be

_changed

while the

machine

is_running

_by

_simply

pressinga

thumb

latch

which

engages withthe rack. Thereisalsoafine

adjust-ment

_provided

_{by means}

of a screw

and

thumb

nut for use

when

_grinding

_up

to shoulders.

The

26

GRINDING MACHINES

AND

THEIR

USE

drawn

back

when

desired,allowing the table to be

run beyond

the_{reversingpoints}withoutdisturbing the adjustment of _{the dogs.}

The

spring plunger automatically assumesits

normal

_position

when

the tableisreturned.

The

base of the swivel slide

which

carries the wheel is _{graduated through} halfits circumference,

and

readsto_{90 degrees}either side of zero.

When

the slide is set at zero the line of

motion

is at

rightangles to the

ways

ofthetable,

and

when

the

slide is set at 90 _degrees the

two

motions are

parallel.

The

_satisfactory

_working

ofthe

_{machine depends}

to a _large extent

on

the care _given to the cross

slide,

which must be

kept clean

and

welloiled. If

allowed _{to get} stiff

and

_dirty the slide will lose

that _{sensitive responsiveness}

which

is so essential

to accurate _sizing.

Remember

that the slide is

required to

move

exactly in accordance with the

working

ofthe feed_{pawl, that}

and

it

must advance

by

any

desired

amount

down

to 0-000125in.

(won

m

-)>this beingthe

movement

produced

by

a

single toothof the feed ratchet.

Such

exactitude

is_onlypossible

when

theslideisin

_good

order

and

working

smoothly.

Obtaining Extra Fine Feed.

When

grinding gauges, or other

work

requiring a closer limit of accuracy

than

the finest feed of _{the machine, the}

following

method

will

be

found

convenient.

The

bottom

wheel slide is swivelled to

an

_angle of 60 degrees

from

zero, the wheel

head and

top swivel being set in their

normal

_positions as

shown

in

Fig. 7,

the table, the feed

motion

now

moves

the wheel

along aline at

an

_angleof30_degrees.

As

aresult

the actual feed is half that indicated

_by

-he graduations

on

the handwheel,

and

thefinest feed

FIG. 7. SETTING OF

WHEEL

SLIDE TO OBTAIN

EXTRA

FINE

FEED

FOR GAUGES, ETC.

is

now

_T

eoTHii

n

- _(0-0000625

in.), corresponding to

8^5-0 i*1- reduction in diameter, instead of

Bt

* (tttin. (401OUin. reduction in diameter). This planwill

often be

found

of assistance in _handling

work

where

the _{greatest possible accuracy} is _required.

Taper Grinding, Etc.

The

_{adaptability of} the universal _giinding

machine

is further

_{shown by}

28

GRINDING

MACHINES

AND

THEIR

USE

Figs.'8 to 10. Centres can readily

be ground

by

settingtheuniversal

head

to

an

_angleof30_degrees

(see Fig. 8)

and

traversing the revolving centres

past the wheel. Iffor

_any

reason it

were

desired

FIG. 8. TRUING CENTRES ON UNIVERSAL GRINDER

to avoid _disturbing the _setting of the universal head,

an

alternative

method

of_grindingthecentres

would

be to swivel the wheel _{slide, and,} with the wheel face _parallelto the line of motion, traverse thewheel

_{by means}

ofthecrossfeed. Inthiscase thetablewould,ofcourse,

remain

stationary,being only

moved by

hand

the slight

amount

necessary to

_{put on}

thecut. Obviouslythis

method

involves

THE

UNIVERSAL

a

_good

deal

more

trouble

than

thatfirst_described,

and would

therefore _{only be}

_employed

_in

excep-tional cases. This

method

is also illustrated

_by

Fig.9,

which shows

thewheel

head

swivelled

round

to grind the bevel face of a_{piece carried}

on dead

FIG. 9. GRINDING

ANGULAR

FACE WITH

WHEEL

SLIDE SWIVELLED

centres. _Fig. 10 illustrates the

method

of

grindingtaper

work

by

settingoverthetop table.

Disc

and Face

Grinding.

An

expanding chuck usually forms part ofthe

equipment and

is

found

useful for disc _grinding, such as thin _milling

cutters, saws, washers, etc.

An

_example

from

FIG. 10. GRINDING TAPER

BY ANGULAR

ADJUSTMENT OF TABLE

Fig. 11. This

chuck

holds the

work

by means

of a bushing

expanded

inthe hole in the centreofthe piece to be ground.

The work

is held

by

the bushing C,

which

is

_expanded

_by

thescrew

B

and

drawn

_{tightly against the}face plate

by

turning the

knob

A. Differentsizesof_bushingsare_easily

and

quickly inserted tofitvarious sizes ofholes inthe work.

This face _{plate, together} with the four-

_jaw

chuck,

when

usedincombination withthe universal

head

of the_grinding machine, is _extremely useful

in_handlinga _{wide range} offlat

and

_{angular work,}

which

would

otherwise be _impossible.

In _{face grinding} the headstock is set

round

through 90degrees ; the table forsuchwork*ls, of

course, set to traverse half the diameter of the

work.

A

note

_may

here _{be given} as to face grinding

on

the universal.

As

thearea ofcontact

between

wheel

and

work

is

much

_{greater in face grinding}

than_{in cylindricalgrinding,}

more

heatis_generated,

with a tendency to crack

hardened

thin _pieces. Therefore a softer _grade of wheel should be used

than

for _cylindrical

work

of the

same

material,

and

there should be a _{plentiful supply} of _cooling

lubricant. Ifafine _{adjustment has}tobe

made

to obtain flatness of surface, it will be found

much

easiertoeffectit

_{by means}

ofthe tablescrew

than

by

disturbing the headstock setting.

Internal Grinding.

The

_equipment

of the universal grinder also _{includes provision}for

inter-nal grinding. Fig. 12

shows

the

arrangement

used

on

the Churchill machines.

A

_range of spindles

32

GRINDING MACHINES

AND

THEIR

USE

and

lengths of holes.

Each

_spindle is

self-con-tained

and immediate

_{change can be}

made

from

one _{spindle to another,} the _{supporting bracket}

A

FIG. 12. INTERNAL SPINDLE DRIVE: CHURCHILL

UNIVERSAL GRINDER A SupportingBracket.

B Crossslide.

C Independent speedpulley.

D

Positionofpulleywhenexternal grinding.

on

the

end

of the cross slide

B

_{being split}

and

clamped

for _easy

and

_{rigid locking.}

The

wheel

head

slideis,ofcourse, swivelled

round

_{to bring the}