US2836939A - Machine for producing spherical surfaces - Google Patents

Description

June 3, 1958 A. H. WHITE MACHINE FOR PRODUCING SPHERICAL .SURFACES Filed March 21, 1956 7 Sheets-Sheet l June 3, 1958 A. H. WHITE 2,836,939

MACHINE FOR PRODUCING SPHERICAL SURFACES Filed March 21, 1956 v Sheets-Sheet 2 /v PEA/72m June 3, 1958 A. H. WHITE 2,836,939

' MACHINE FOR PRODUCING SPHERICAL SURFACES Filed March 21, 1956 7 Sheets-Sheet 3 A an/m flaw/v17 Mrs June 3, 1958 A. H. WHITE 2,836,939

MACHINE FOR PRODUCING SPHERICAL SURFACES Filed March 21, 1956 7 Sheets-Sheet 4 M1 X I3 R U j 49 A. H. WHITE 2,836,939

7 Sheets-Sheet 5 R mm am m V 0 0o ov m June 3, 1958 MACHINE FOR PRODUCING SPHERICALv SURFACES Filed March 21, 1956 i I I MIL v June 3, 1958 wHlTE 2,836,939

MACHINE FOR PRODUCING SPHERICAL SURFACES Filed March 21, 1956 '7 Sheets-Sheet 6 June 3, 1958 A. H. WHITE MACHINE FOR PRODUCING SPHERICAL SURFACES 7 Sheets-Sheet '7 Filed March 21, 1956 WVEAIIVIQ #1? 174m A b/may MHTE Ar-raatrvf7 Unite States MACHINE FOR PRODUEZNG SPHERE'CAL SURFACES Arthur Howard White, Stourhridge, Engiaud Application March 21, 1956, Serial No. 57255? Claims priority, application Great Eritain March 24, 1955 11 Claims. (Cl. Si -131) This invention is concerned with a new machine for producing spherical surfaces such, for example, as partspherical ends or heads on rods and spindles, or partsphericai concave seatings, by any machining process such as milling, grinding, lapping or the like.

One method used at present for producing a spherical end on a rod is to use a form tool ground to the required radius and fed in a right angles to the axis of rotation of the work-piece. This method sufiers from a number of obvious disadvantages. The feed must be stopped at exactly the right point from the axis of rotation or the sphere will be oblate. One tool Will produce a sphere of only one diameter. The rotation of the component gives a cutting speed which varies from a maximum at the top diameter to zero at the axis. Furthermore, the truth of the sphere, even if the feed-in is correct, is dependent wholly on the accuracy of the form tool, and any irnperfections in its edge will leave rings or grooves on the Work. Again, if the tool is a formed grinding wheel, the load on its bearings is wholly transverse to its axis of rotation and any play in the bearings will give rise to trouble.

Another method, more generally used, overcomes some, but not all, of the disadvantages of that described above. This is to move the tool in an are about the centre of the desired sphere whilst the work is rotated about an axis passing through that centre. However, there is still present the disadvantage of varying cutting speed, and there is now the added drawback that the tool or grinding wheel has only point contact with the Work and will consequently wear rapidly. The resultant groove in the tool or wheel will then, it is true, give line contact with the work, but this will then be incorrect for any subsequent work with a different radius of curvature. If it were possible to maintain the surface of the tool truly fiat, the spherical surface would present under a microscope a spiral of minute fiat surfaces. As the tool-holder must move in an arcuate path, it is di ficult, if not impossible, to fit at the same time a progressive inward eed.

In this second method, the accuracy of the sphere is dependent on the freedom from play of the pivot about which the tool-holder moves. Yet this pivot must be free enough to allow smooth and steady movement, as any interruption or hesitation in the travel of the tool will produce a ring or groove on the work. Where tool is a grinding wheel, the grinding load produces opposite sideway loads, on the two bearings of the grinding spindle. All these are potential sources of vibration which give rise to errors in the truth of the sphere produced.

it is known in the glass industry to advance a rotating work-piece, such as a lens, towards a rotating grinding wheel, the axis of which makes an angle with that of the work. However, it is evident that this method cannot be used to produce surfaces of more than a hemisphere; furthermore, and this is a particularly important point, it is virtually impossible to make the surface with 2,335,939 Patented June 3, 1958 a centre at an accurately predetermined point relative to the workpiece.

According to the present invention, a spherical surface is produced on a work-piece by rotating it about an axis and advancing towards it a tool rotating about a second axis intersecting but not parallel to the first, the line of advance of the tool being along the second axis. The

entre of the surface produced will be the point of intersection of the two axes and its sphericity will be virtually prefect. The tool may have a single cutting point or may be a circular edge or a cutter with a series of teeth arranged in a circle, with its centre on and its plane perpendicular to its axis of rotation.

If the surface to be produced is to include a part passing through the axis of rotation of the work-piece, as would be the case in a ball end on a rod, then the ad- Vance must stop at the point where the circular path of the tool just passes through the axis of rotation of the work-piece. Then, as the axial position of the work is fixed during machining and the tool advances along a fixed line to a predetermined point, it is possible to control very accurately the size and position of the surface produced.

Where the sphere is to be ground, the tool may be a iollow cylindrical grinding wheel, the inner edge of which makes contact with the work along a circle which will be termed the grinding line. If a concave surface is to be produced, the square end of a solid cylindrical wheel is used.

It will be appreciated that the active cutting edges, whether a single rotating tool, the teeth of a milling cutter, or the abrasive particles in a grinding wheel, move in a direction, which is generally transverse to the direction of movement of the surface of the work. This prevents a continuous ridge or groove being formed in the Work by any irregularity in the tool. Furthermore this means that, in grinding, an extremely high finish can be obtained, which is not limited by the grain size of the wheel. In fact, the finish can be many times better than the grit of wheel used, a result which is unapproachable by any other method. The slower the rotation of the work relative to that of the wheel, the better the finish for a given grain size of wheel used.

In one machine according to the invention for carrying out the above method, there are provided on a bed two heads bearing rotating spindles, one carrying the work and the other carrying a grinding or cutting tool. The two axes of rotation lie in a common plane and one of the heads, preferably the cutting or grinding head, can be moved in an are about an axis perepndicular to that plane, and preferably intersecting the axis of rotation of the tool spindle. The Work head can be displaced horizontally in a direction perpendicular to its own axis of rotation, for reasons which will become apparent later.

A stop may be provided on the work head which can be swung into line with the chuck carrying the work, and enables the work to be quickly set to the right position axially. On the grinding head a diamond dressing tool may be provided, swinging in a plane perpendicular to the axis of rotation of the grinding wheel, and this plane forms a fixed datum for determining the grinding line, irrespective of wear of the Wheel.

The machine preferably includes means for automatically advancing the grinding head rapidly up to the work, feeding'it in slowly, and then providing a dwell at the end of the stroke to give a very fine finish to the work. During the dwell of the grinding wheel, the rotation of the work may be slowed right down.

The invention will now be described more fully with reference to the accompanying drawings, in which;

is fixed by therelationship:

shape of the head, the required va Figure l shows'diagrammatically examples of the dis position of the work and wheel in the application of the invention to grinding;

Figure 2 shows a front elevation of a machine for carrying out the method of the invention; 7 V p Figure 3 is a scrap section onthe line .3 '3 of Figure 2; Figure 4 shows-to a larger scale a section of the work head on the line .44 of Figure 3; V

Figure '5 shows in detail the reduction in the headstock spindle;

Figure 6 is a scrap View from the left in Figure 1;

Figure 7 is a section to a larger scale of the upper half of the grinding spindle assembly, taken on the line 7-7 in Figure ,6; a W g a a Figure 8 is a scrap sectional elevation of the grinding gear embodied of the grinding head looking head and part of the associated advancing mechanism 7 for the Slide; 7 n r Figure 9 is a sectional eleva'tion of the lower part of the grindinglhead.. showing the feed-in mechanism{ and Figure 1-0 is a plan viewof the feed-in mechanism 'with- I in the grinding head; Z

Referring first to Figure 1(a), thereis shown a hollow cylindrical grinding wheel 1 'forminga part-spherical en-. larged end;2 on a rod 3. The rod is rotated about its own axis A, and the wheel is independently rotated at a higher speed about its axis B. It will be seen that the inner edge of 'theendof the wheel.1 engages the surface of the s'phereon a circle which we have called the grind-l ing line, and that, since both the work and the wheel are rotating about different axes, the sphere must inevitably b'e' 'true, with its centre on the intersection-C of the two axes, when thewheel has been fed inyalong its own 7 axisB sufliciently fair for it to corneinto contact with the whole of the surface of the'end 2;

Normally, the end 2 will have previously been :rnachined or ground I roughlyto a spherical shape bya form tool or wheel, and

the m ethod according tothe'inventionwill only be used to give a final truing cut. 1 J

. In order to ensure that no u means matter a givenradius .of spherical surface and V a given diameter of grinding :wheel, the angle a between A i a where D is the diameterjof the inner edge of the wheel and R is the radius of the sphere to be produced."

nground'portion is left on .theend 2 adjacent the axis of therod 3, it will be seen that the feed-in of the wheel 1 must end at such a point" that the grinding line just intersects'the axis A. This;

e setting angle,

7 V 4 radii the overhang with s impossibly great. instead, the point F 'is fixed, ,and the axis A can be offset laterally from it. This also enables the distance K'from the'plane of the grinding 7 line to the point F to be fixed independently of the work which, as will be seen, makes it possible to determine extremely accurately the point at which the feed-in of the wheel stops and hence the finaldiameter of the work. The otfset of the axis A from F is indicated at O and is given by the relationship:

Figure l(b)' shows the set-up for grindingia ball head large in comparison with the diameter of the rod, and

in Figure its is shown the grinding of a dome of large 7 Whilst in Figure l we'have shown throughout a grinding wheel 1, it will be understood that it may equally well be replaced'by a milling cutter, or even by a'single 7 7 tool rotating about the axis B. If a single tool is used,

however, the rotation of the -wor k must be very slow in comparison to thatjof thetool if a reasonable finish is 'to' be obtained, and the ingly long tir'ne.- V v 1 An example of a practicalmachine fol-carrying out the invention, and embodying a number of refinements,

is shown in the remainder of the-drawings; Referring to Figure 2,'the machine comprisesa bed 10,, on which is mounted a headstock il for rotating the work and a table 12 on which the grinding head is mounted;

' The headstock- 11 is mounted ontransverse slides,

one 3/ and one flat, on the bed 10, so -that it can be moved horizontally in a direction transverse tothegaxis; fot the headstock spindleiS (Figure 3;),"on the .end'of V which is a collet chuck 14 forcarrying the work.

The transverse position of the headstock is controlled by a lead screwactuated by a handle 15 which has a micrometer scale (not shown) and enables the ofisetiO of the axis of rotation of the workti; e. the headstock J spindle) 'from the focal point to be'controlled very accurately. A lever 16 serves toropen 'and close the chuck14. a V V The bed .10 has its upper surface formed as a quadrant at 17, and the table'12 is pivoted on a spigot projecting alarge spherical 'end is required,or only a dome repre.

senting a small fraction of 'asphere. The setting'angle a .must beat least half the angle subtended at the centre betweenthe edgegof the sphereand the axis A, which angle iscalled 0. Aconvenient rule to adopt is to make b' /26+5; which gives the cutting edge ofjthe wheel a reasonablearc of travel clear'fof the work, to prevent its clogging, Forfexample, in Figure l, *in,which. the

end .Zis slightly less'thana hemisphere, 0 is 89, making 11:45

from u and R For adjustment'of Now if this point F: -we reT-to bejri'z ade coincident with C,

, I V V the setting angle, axis B of 1 the grinding heel '1 can be turned about a focal point P,

In these circumstances, a'is fixed by; the

luejof 1) is determifled vertically upwards from the centre of the quadranttthe axis of'the spigot if extended upwards, would pass near the collet chuck, and its point of intersection with. the 1 horizontal plane. ofthe headstock spindle 13 represents thefocal point F of Figure .1. An arcuate rack or gear segment iS on the bed 10 is engaged by a pinion 19 scale to within 15 secondsaofar c.

that it is rigid with the base during actual grinding.

The actual gr-indingl spindle 21 is formed by an V l integral extension of' the s haft of anelectric motor built intoa housing 22 on a slide 23. This slide 23 is mounted V on 'slideways of generous dimensions .on the table.12, 'so asto be'i 'movable towardsand away from the focal point; The grinding spindle is in exactly. the sainej horizontal plane as'the work spindle 13 audits '7 passes through the focal point'F (i. e; the intersection a1axis aboutwhich thetable a with thatplane of the vertic 12 can be turned).

mall radius work would be I job would take a correspond-.

The headstock 11 carries a stop on the end of an arm 26 pivoted on a spindle 27. A handle 28 enables the stop to be swung down in front of the chuck 14 and it may be provided with a micrometer screw to enable it to be moved in the direction of the axis of the headstock spindle. This stop enables the work to be set rapidly in the correct axial position with respect to the focal point F, due allowance being made for the amount to be ground off.

The interior of the headstock 11 is shown in Figures 4 and 5. At 29 and 30 respectively are the V and flat slides on which it is carried on the base. it will be seen that the lever 16 is secured to a shaft 31 carrying lugs 32 on which pins engage an annular groove in a sleeve 33 rotating with the headstock spindle 13, to control the axial position of the sleeve. This sleeve 33 has a conical surface engaging a pair of pivoted bell-crank levers 34, which in their turn engage the end of a tube 35 running coaxially within the spindle 13 and acting on a split sleeve 36 containing the jaws 37 of the collet chuck. It will be understood that angular movement of the lever 16 opens and closes the jaws of the chuck. The work, of which a typical example is shown at 38, is held in the jaws 37 by means of a split bush 39, which enables the shank of the work to be gripped even though there is a ball head on each end. An axially sliding plunger as within the sleeve 36 is urged outwards by a coil spring 41 and tends to push the works outwards. This simplifies setting the axial position of the work, as it is clamped in the chuck whilst being urged gently against the stop 25, which is then swung out of the way.

The spindle 13 runs in opposed conical bearings 42 and 43, and carries, keyed to it, a spider 4a (Figure 5) the fingers of which extend between balls 45 forming an epicyclic reduction gear between a sun wheel in the form of a V pulley 46 and an annulus 47 formed with a V pulley groove d8. Both the sun and annulus are free to turn on the spindle 13 and the engaging pressure is derived from angularly spaced coil springs 49, the thrust being taken by a ball race 50.

The pulleys 46 and 47 are connected by belts 51 and 52 respectively to separate electric motors contained in the base it). During normal grinding the right-hand pulley 48 is stationary and only the left-hand pulley 4% is driven, so that the spindle 13 is driven at a lower speed through the reduction gear formed by the balls 45. When a very low rotational speed of the spindle is required, during the dwell as will be described later, the second motor is started up to drive the annulus 4-7 in the opposite direction but at a slightly lower speed than the I pulley 46, and only the difference in speeds is transmitted to the balls 4531 Turning now to the grinding head, Figures 6 and 7 show the upper part of the housing 22, in which is mounted an electric motor 55, its shaft 56 being mounted in special bearings lubricated by oil mist from a special pressure lubricator which has been indicated at 57 in Figure 2 but has been omitted from the remainder of the drawings for clarity. This enables the shaft 56 to run up to speeds as high as 24,000 R. P. M.

On the end of the shaft 56 there is screwed a boss 53 carrying a cup-shaped grinding wheel 59. A bracket so carries a transparent guard 61 to protect the operator from coolant flung oh the wheel.

As mentioned earlier, the housing 22 and slide -3 are movable with res ect to the table 12 in the direction of the axis of the grinding spindle. There are two separate mechanisms for effecting the inward movement, one for providing a rapid advance up to the work and a finer one for producing a slow feed-in during the actual grinding operation. The first of these mechanisms is shown in Figure 8 and comprises an air cylinder 62 under the control of a solenoid-operated valve actuated from a push button on the bed 10. The cylinder itself is pivoted to the table 12 and its movable piston advances a link '15 63 to tilt a motion plate do, forming a toggle linkage with a further link 65 pivoted at 66 to the slide 23, thus advancing the slide rapidly and taking the wheel 59 to Within a few thousandths of an inch of the work. Figure 9 shows the linkage in the fully advanced position.

The pivot or about which the plate 64 turns is substantially stationary during the rapid advancing motion described above, but is not mounted directly on the table 12. On the contrary, it is carried on the top end of a lever 68, of which the upper arm is only one fifth of the length of the lower arm. The second of the mechanisms referred to above, for giving a slow progressive feed-in, is connected via a link 69 to the lower end of the lever 68 and comprises a slide 79 movable on a sub-assembly.

'71 within the table 12 and urged to the right in Figure 9 by a compressed air cylinder '72. The rate of movement is controlled by an oil dashpot 73, the piston of which is connected to a piston rod '74 screwed into the slide 70. The flow of oil from one side of the piston to the other takes place through pipes leading to a metering valve 76 (shown more clearly in Figure 10), which can be readily adjusted by hand.

Referring now to Figure 10, a link 77 pivotally mounted at one end on the subassernbly 71 forms at its other end a pivot for a lever '78, which is itself pivoted at its mid-point to the top of the slide 74). At its free end the lever 78 carries a striker plate 79, which is kept with its face square to the line of movement of the slide by means of a member t) forming a parallel linkage with the lever '78. It will be seen that the five-to-one magnification of the lever 63 combined with the two-toone ratio of the lever 73 gives a linear movement of the striker plate 79 which is ten times that of the slide 23.

A carriage Si! is mounted for sliding movement on the sub-assembly 71 in a direction parallel with that of the movement of the slide 79. its position is adjusted by means of a lead screw under the control of a hand wheel 83 which is provided with a micrometer dial 34 (Figure 9). A stop formed by an electric micro-switch 35 is mounted rigidly on top of the carriage 81 in the path of the striker plate 7? and a second micro-switch 86 on a carrier 3? is mounted for sliding movement on the carriage. A spiined shaft 88 actuated by a knob 29 with a micrometer setting dial 9d enables the position of the switch 86 to be altered with respect to the carriage 3i irrespective of the overall position of the carriage. Adjustable bolts 91 below the micro-switches form positive dead stops to bring the striker plate '79 to a halt immediately after the corresponding micro-switch has been actuated.

As stated earlier, operation of a push button on the base iii opens a solenoid-controlled valve to admit air to the cylinders 62 and 72. This is effected through a pipe 92. The quick advance produced by the cylinder 62 is continued as a slow feed-in by the cylinder 72 until the striker plate 79 engages the micro-switch 86, initiating the action of an electronic timer which, after a predetermined time delay, admits air to a pipe 93 connected to the exhaust sides of the cylinders to actuate them in a reverse direction until the plate 79 engages the stop 91 and the other micro-switch 85. The micro-switch is in series with the starting button and prevents the next cycle of operations being started by the operator unless the slide 23 is fully retracted.

A T-junction 94 in the pipe 93 branches ofi to an air cylinder 95, which applies air pressure to the fluid in the hydraulic circuit of the dashpot 73 to prevent cavitalien behind the piston on the reversal of direction.

it will be seen that the total distance of the slow feedin is controlled by the knob 5%, which fixes the distance apart of the two micro-switches. The feed-in may be varied over a range from one thousandth up to one quarter of an inch. Once the overall feed-in has been set (this depends on the amount of material to be removed), the wheel to the points at which it starts vantage that the. spherical stroyed during the course 05 and ends in relation to the focal point; This is deter mined "by the requirement-that the front. face of the wheel59'at the end of the stroke should be rthe distance K of Figure lfrom the focal point i A diamond dressing tool 96 is carried on an arm 97 pivoted to a carrier Fe (Figures 2 and 3) on the table 12 to move in an arc in a vertical plane under the influence of a control handle The diamond'is traversed'across the faceo f the wheeld'e with the slide 23in its fully retracted position. i

The final forward position of the wheel, i. e. its position during the dwellyshc uldbe such that the face of the wheel is the fixed distance K from the focal point P. If there were no slow feedin, this would simply be fixed by the foremost position of the rapid advance, but, with the 'additional'slow feedin, this final position. will be the total rapid advance. it includes a micrometer screw which enables the plane of the diamond .to be set by a predetermined ount beyond that plane (in a direction away from the V V V to the feed-in set by the ltnob Then, provided the knob fi'is not disturbed, this serves as a datum for all subsequent operations on the particular batch of work be'ing ground, as, whcn the grinding wheel 59 wears, the Wheel Slis turned by the operator: to advance the carriage a l a few thousandths of an inch and the wheel is trimmed by the diamond in the fully retracted. position.

Then, on the next feed-in the wheel stops withits newly dressed face at exactly the planerat which the previous face stopped before. V V i The'length of time or the feed-in and of the dwell will dep hid upon the size, material and centre angle of the sphere to be ground, also on the grade and grit of the wheel and the amount of material left on the worlrpiece for removal.

During the dwell the speed be brought right down.

of rotation of the work may 4 R. l M. during a dwell or" about one minute. By' this. means it has be found possible to achieve an extremely high surface inches, which is better than could be achieved'by ordinary lapping. This is chiefly attributable to the fact that thedirection of movement of the cutting edges on the be attached to the arm 92- of the total a slot) which distance is made equal 7 sh, of as little as one and ahall micro forward of the foremost position of the rapid advance by said first spindle for retaining a'work-piece, asecond rotatable spindle, cutting means carried on said second spindle; "sa'd cutting means-being displaced "from the axis of d second spindle and defining a circular path about said axisg said first andsecond's pindles lying in a commoii plane, means] for causing relative angular movement between said spindles about an axi s'perpendicular" to said plane, means for advancing said second spindle along itsown axis of rotation up to the point where said circular path intersects the axis of rotation of: said first spindle: V 7

2. Apparatus for producing a spherical surface on a work-piececomprising a bed, a hcadstoclcon said bed, a' first rotatable spindle, said first spindle being mounted for" about a horizontal axis in said'headstock, world 1 n g means on said first spindle, a table, s'aid table being mounted on said bed for angular 'r'novem'dnt' about" a vertical axis, a slide on said table, said'slicle being rccip rocable horizontally in a direct'ion passing through; said vertical axis, a second rotatable spindle, said second spindle being mounted for rotation on said slide about a a horizontal axis intersecting said vertical axis,;a cutting tool mounted on said second spindle and definingin its' rotation a circular path, means for causing rotationof.

said first and second spindles and means for advancing;

cage, and including ineans for driving said'annulus'in direction opposite to that of said sun wheel.

5. Apparatus according to claim 2, wherein said means for advancingtthe slide comprises a first means for pro-T ducing a rapid'advancc, in conjunction with a second means for producing an additional slow feed-in.

V g In one example the work is rotated at 25 R. l. M. during the feed-in and then at only i the axis of rotation of said motor spindle being horizontal, f

tool (in this case'the abrasive particles in the grinding wheel) is substantially transverse to that of the surface of the work itself. 7

It will be appreciated that the load on the bearings of' w "axial, so that there is no the grinding spindle is tendency forsideways play to develop. 7 Itshould also be noted that the truthof the sphere is not ailected by any. rror'in the concentricity of the 'collet chuck, since I V the centre of the sphere willelwa'ys lie on th'eaxis of rotationofi the worlgirrespective of the position of the axis of the-work itself. 1 g V V V To'ov ercorne difiiculties in getting coolant to penetrate inside the cup grinding wheel, theiwheel may be of a special impregnated self-lubricating;kind. Themachine described may also be used for lapping, and has the ad rm of the work is not dethe lapping operationl I claim: 7 a V V V 1. Appairatusfor producing a'spherical surface on a V work-piece comprising a first rotatable spindle, means on f iusaid Spindle,

6. A machine for producing a spherical surface on a bed for angular movement about a vertical axis, a worl f carrying spindle mounted for rotation about a horizontal i axis in said headstock perpendicular to'the direction of sliding of said headstock on the bed, a first elcctric'rnotor, means for driving said work-carrying spindle from said first motor, .a' slide mounted for sliding movement on said} table in a hori sontal direction passing through said verti-g cal axis, an electric motor on said slide having a spindle,

motor spindle, said grinding wheel defining a circular pathi vanc ing said slide slowly, and meansfor stopping the ad Vance at the point where said circular path intersects the axis of said work carrying spindle. i i a 7. Amachine according to claim 6, wherein said meansfor stopping the advance of the. slide is adjustableinf position; V a i ."8..A machine. for producing a spherical surface on:

c'agefsaid first spindle being connected to said planetj 7' a work-piece comprising a bed, a headstockmoufitedf on said bed, a work-carrying spindle mouhte'd'for rotation;

in said headstock, power. means for driving said Worki:

on 1 said table, a grinding sp'indle mounted 'for rotation" said spindles having their axes intersecting and lying in slide, lpower means Tfordriving said grinding;

a' common planegthe axis'of said pivotal con-if nection intersecting that of said grinding spindle, and being furthermore perpendicular to said common plane, means for clamping said pivotal connection, a grinding wheel carried on said grinding spindle, said grinding wheel having a plane end face and a cylindrical surface, the intersection of said face and surface defining a line herein termed the grinding line, means for advancing said slide with respect to said table in a direction parallel with the axis of rotation of said grinding spindle, and means for halting its advance at the point where said grinding line intersects the axis of rotation of said work-carrying spindle.

9. A machine as claimed in claim 8, including a diamond dresser, said diamond dresser being mounted on said slide for movement in a plane which is perpendicular to the axis of said grinding spindle and is a fixed distance from the axis of said pivotal connection.

10. A machine as claimed in claim 8, wherein said means for advancing said slide comprise a first pneumatic motor on said table, a toggle linkage, pivotal connections between said motor and linkage and between said linkage and said slide, a second pneumatic motor on said table, and a lever interconnecting said second motor and said toggle linkage.

l1. A machine as claimed in claim 8 wherein the axes of said work-carrying and grinding spindles lie in a horizontal plane and the axis of said pivotal connection is vertical.

References Cited in the file of this patent UNITED STATES PATENTS 1,617,167 Schramm Feb. 8, 1927 1,994,529 Meyer 1. Mar. 19, 1935 2,286,361 Goddu June 16, 1942 2,424,271 Galloway July 22, 1947 2,629,975 Desenberg Mar. 3, 1953

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