US672557A - Grinding-machine. - Google Patents

Description

No. 672,557. Patented Apr. 23, 19m.

A. JOHNSTON.

GRINDING MACHINE.

(Application filed Jan. 22, 1900.)

(No Model.) 7 Sheets-Sheet l.

No. 672,557. Patented Apr. 23, l90l. A. JOHNSTON.

GRINDING MACHINE.

(Application filed Jan. 22, 1900.) 1N0 Model. 1

7 Sheets-Sheet 2.

ff'vlzasscmsms V'EFERS ca. PHUTO-U'KNCL, wxsumsma. D c.

Patented Apr. 23, l90l. A. JOHNSTON.

GRINDING MACHINE (Application filed Jan. 22. 1900.

7 SheeIs-Sheet 3.

(No Model.)

1 lllg l lllllnlllllllllli n nms PETERS co. P oqwnsnmuron n c No. 672,557. Patented Apr. 23, 190i. A. JOHNSTON.

GRINDING MACHINE.

(Application filed Jam 7 Sheets-$he-et 44 (No Model.)

No. 672,557. Patented Apr. 23, I90I.

A. JOHNSTON.

GRINDING MACHINE.

(Application filed Jan. 22, 1900.) (No Model.) 7 ShaetsSheet 5.

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W m NEE-U2: 6 2%] I III [I V/ m -II 4 WI-u I I Inn I I I y Patented Apr. 23, 19m.

A. JOHNSTON.

GRINDINGMACHINE.

(Application filed Jan. 22, 1900.)

7 Sheets-Sheet 6.

(No Model.)

Wi /v6.5.5 es.

Patented Apr. 23, mm.

A. JOHNSTON.

GRINDING MACHINE.

(Application filed Jan. 22, 1900') 7 Sheets-Sheet 7.

. (No Model.

\% hp 6%) 7 My 2 is a front elevation.

view. Fig. 4 is a vertical sectional view 1 throughythe basin of the frame and the recipro'cating carriage on line 4 4 of Fig. 3. Fig.

I 1 To all whom it may concern.-

Be'it known that I, ALLEN resident of Ottumwa, lowafhave invented a new and useful Improvement in Grinding-Machines, which invention is fully set forth in en the following specificationr l H This invention has reference to improvements in grinding and polishing machines,

UNITED STATES WATENT OFFICE.-

ALLEN JOHNSTON, OTTUMWA, IOWA.

GRINDING-#MACHINE.

SPECIFICATION forming part of Letters Patent N 0. 672,557, dated April 23, e 1901. Application filed January 22, 1900. Serial No. 2,370. \110 model.)

JOHNSTON, a

particularly to such as are employed in the whitening of the blades of tableknives. i a 1 p My presentinvention consists in certain jimprovementsfupon'themachine of my Patent.No.55'Z,825, dated April 7, 1896, the principal features of said improvements being the i X provision of mechanism operated automatice ally at predetermined intervals for truing the Q actingsurface ofthegrindin gwheel and for i advancing said wheel to compensate for wear on its acting surface, and, furthermore, to so locate and construct the parts of the mechanism that wear. generally, andparticularly that Qdueto the loose grinding material (from the sulfface of the grinding-wheel) coming in con- ;tact; with bearing-surfaces,will be avoided, or atleast reduced to a minimum.

' My inventionfalso embraces other important features, all of which will be best understood b y reference tothe accompanying drawings, wherein Figure 11 is a vertical sectional view. Fig. Fig. 3 is a top plan 5 is a rear'elevation. Fig. 6 is a sectional I view on line 6 6 of Fig. 1 looking to the left.

Fig. 7 is a vertical sectional View on line '7 7 of Fig-1. Fig. 8 is a sectional view on line 5 ,8 8 of Fig. 2.

Fig 8 is a detail perspective view of the upper end of rod 45. Fig. 9 is a :vertical longitudinal sectional view through the knife-holder, which is mounted on the carriage. Fig. 10 is a horizontal longitudinal sectional view through the knife-holder. Fig.'1l is a plan view of the knife-holder,

partly broken away and with other parts omitted.

Fig. .12 is a sectional view on line 12 12 i of Fig. 10.

A brief explanation of the scheme of oper- 'tions in said grindingsurface.

modus operandi of the parts about to be more fully explained in the detailed description. The knife to be ground is placed by the op erator in a knife holder, Figs. 9 to 12, which slides transversely on a carriage to bring the blade of the knife into contact with the sur= face of the grinding wheel. The carriage is given a limited longitudinal reciprocatory movement, so as to present different partsof the surface of the knife-blade to diiferent parts of the grinding-surface and prevent uneven grinding or grooving due to imperfec- By pressing on a treadle the operator advances the knifeholder to the grinding-surface and places under tension a spring which acts on the holder to hold the knife in contact with the grinding-surface with yielding pressure. The same operation throws into gear the means for re ciprocating the carriage, and after the knife has been acted upon for a predetermined pe-.

riod of ti me the reciprocation ceases, the knife-,

holder is withdrawn from its advanced position, and the operator puts in another knife. Upon depression of the treadle these operations are repeated. After the machine has been thus started and automatically stopped a predetermined number of timesin the present case tenor, in other words, after ten knives (or both sides of five knives) have been acted uponmeans are auto maticallybrou ght into operation for truin g the grinding-surface. Means are also provided for automatically advancing the grinding-wheel to compensate for the wear on the grinding-surface.

Referring to the drawings, A represents the base of the frame, upon which is mounted the basin B.

C is a grinding wheel, of annular or ring form, carried bya shaft 0, which is mounted in bearings c 0. At its outer end and within bearings c the shaft is surrounded by a sleeve d, within which are located ball-bearings d d, which receive the end thrust of the shaft. At its outer end sleeve 01 is provided with exterior screw-threads which are engaged by interior screw-threads on a ratchet-wheel e, said wheel having a hub e projectinginto the hearing 0' and having a flange e thereabout projecting into a corresponding groove in a fill- 'ing 6 of Babbitt metal within the bearing,

whereby the ratchet-wheel is permitted to rotate, butlongitudinal movement thereof; prevented. By turning the ratchet-wheel in the proper direction the shaft and with it the grinding-wheel C, may be advanced'toward the front of the machine to compensate for wear on the grinding-surface. Means for automatically rotating the ratchet-wheel will be described hereinafter.

The shaft 0 carries fast and loose pulleys (3 and O respectively, by the former of which it is driven from anysuitable source of power.

F is ashaft having a hearing at one end-in the base A and at its other end in-a spider F,

extending upwardly from the footof said basetothe under side of the basin B." This a shaft carries a fast pulleyf and a loose pul- "@ley'f", having an elongated hub f 1 A belt F (see Figs. land 5, not shown in Fig.3) passes from shaft O. over the pulleys ff, said belt being of'such width as to at all times partially l overlap the rim of thelooseipulley, even when the belt i s'shifted to such position as'to drive fthe fixed pulley, aud with it the shaft F. In' this, manner-while thepulleyfisfdriven only when the belt isshifted thereon, asshown in Fig. 1,,the. loose pulley iscontinuously rotated. I

p p 'Thedevice for truinglthe grinding-surface andthe meansforsautomatically operating thesame may bem'ost clearly understood by -reference'toFigsQl, 2, 3, 5, and 6. Gris acap @or cover which fits over the grinding-wheel and is secured .to the basin B. Said cap is "enlarged at G to permit the necessary movementof the swingingarm g, which carriesthe "diamond or other hard point g, which is -fadaptedto be moved laterally across and act carrying at'its rear projecting'end a crank arm h, through which said shaft is adaptedupon the surface of the grindingwheel to true I the same. The arm 9 is secured to a shaft 9 hearing in one sideof the cap or cover G and torecei've its oscillatory movement. for imparting the. translatory movement to the truing-point g. Arm it receives its movement from apitman h, which has a forked lower end h embracing the hub 12 of gear-Wheel I,

loosely mounted on: the shaft F. Said gearwheel is provided with a heart-shaped camgroove 2' engaged by a roller h on the pitman h. It will thus be apparent that upon rotation of thegearwheel I the heart-shaped cam will act to impart to the pitman h a longitudinal reciprocatory movement, which through the intermediary of the arm h will be transformed into oscillatory movement in the shaft g As it is not necessary that the truing device should be. continuously in operation, means are provided whereby it is brought into action intermittently. To this end the gearwheel I is adapted to be driven by a belt j, passing from the hub of loose pulley f over a, pulley j', carried by a shaft j said shafthearing at one end in thespider F and at its other end in the base A and carrying a pinion is, adapted to engage said gear I. At one point on its periphery, hoWever,-the teeth of the 'gear-wheel-I are omitted, 'and when this part of the gear-wheel comesopposite the pin ion is its movement is arrested, a brake-shoe Z, actuated by a spring Z, (see Fig. 1,) bearing against the teeth of the gear-wheel I with sufficient friction to preventmovement thereof due to momentum, but at the same time allowing the same to be rotated when the teeth of the pihionk are in actual engagement with the teeth on the gear-wheel. It willthus be seen that after the truing point has been traversed across the grinding-surface and back again itis arrested until the gearwheel :I. is moved a sufficient distance to again bring.

the teeth thereof into engagement with the pinion Zc,lwhich latteris continuously rotated by the'pulleyf, as will beclearly understood.-

The means foreffecting themovement of the gear-weeel I for the purpose of again engaging the teeth thereof with the pinion will be described later.

Referring now to Figs. 1], 3,, 4, and 7 rep- I resents a reciprocatory carriage which. carries the knife-holdelgto be described herelnafter. This carriage consists of a hollow elongated part at one end and ofIa T-shaped extension-at the potherend. The extremity of the elongated end'passes. through and is adapted to. slide in; asuitable opening in the vertical wall of the basin "B, while the ex? tremities ofthe armsof,the-Tfsh'aped' ends. of the carriage haveprojectionstherethrough which are engaged by horizo'ntalpinsm 'm,

loo

whicharesupported' by suitable uprights from the bottom of the. basin B, Fig.;7.

The carriage Lreceives its longitudinal reciprocation through the followingmechanism: Atits forward extremity the shaft F (seeFigs,

land 2) is provided. with an eccentricpine, which engages an opening in the rectangular block 0, which latter is adapted toslid'e-ver-. tically in a suitable way formed in the lower end of a vertically-disposedlever 0, said lever being pivoted at 0 and its upper end. projectrr o ing through a vertical opening 1) in the. bottom of basin Band engaging a recess 19 in the under side of, the carriage L, It will be obvious that the oscillatory movement imparted to the lever O by the eccentric-pin o and the block 0 will in turn impart a corresponding shaft Q, passing througha horizontal bearing in the upper part of base A just below the basin B, said shaft bearing'at its outer extremity a'heart-shaped cam 1 against which bears a roller r, carried by one arm of a bellcrank lever B, pivoted to the under side of basin B atr'- A screw-threaded bolt 8 passes through a corresponding opening in the extremity of the horizontal arm on the bellcrank lever and at its upper end supports a vertically-movable bar S, which passes upwardly through a sleeve 3, formed on the bottom of the basin B. A set-nut 3 serves to secure the bolt 8 in any desired position of adjustment. At its upper extremity bar S supports a cap t, having a central opening in which is located a bearing-ball said ball resting against the end surface of the bar, but being confined in its movement by the wall of the opening through the cap. Thetail-piece l or extremity of the knife-holder (to be more fully described hereinafter) bears against the ball 15 during the longitudinal reciprocation of. said knife-holder with the carriage L. i From the foregoing description it will be understood that the rotation of the heart-shaped cam g acts through bell-crank lever R to slowly raise and lower the bar S and that the p knife-holderfollowingthis movement of the 1 q barwill be gradually tilted in conformity with i 25 the convexity which it is desired to impart j tothe surface of the knife-blade.

The knife-holder is most clearly shown in 1 Figs. 9 to 12 of the drawings. It consists of 'a plate 1, to one side of which is secured the hollowfra ne 2 by the. screws 3 3. From the i under sidexof the frame 2 projects a tailpiece M 4, which, when the knife-holder is in place on the carriage, rests agaiustball t, as already described. When placed in the holder the blade of the knife rests against the fiat face a C iof the plate 1, while the handle thereof engages between a spring 5 and a cross-pin 6, y constitutingparts of the extension 7 of the holder, which is adjusiably secured to the frame 2 by means of a set-bolt 8. A hook 9 on the holder closely engages the groove of the bolster of theknife to hold the latter tightly in place, as clearly shown in Fig. 10 of the drawings. To the under side of the forward end of the frame2, contiguous to the plate 1, 1. j issecured a recessed block 13. This block is held in place by screws 14 14 (see Figs. 9 and 10), engaging through slots therein, which slots permitthe desired adjustment of said block. Pin15,--thefunction of which will be more fully described hereinafter, has a head 16 engaging in the recess of the block 13, as clearly shown in Fig. 12, the stem of said pin projecting rearwardly loosely through an 55 opening in said block. j t .On the .T-shaped part of the carriage L is i an elevated part 17, (see Figs. 1, 4, 7, and 12,) having a longitudinal recess therein, in which is. a plate 19, secured by set-bolts 18. This platehas two openings therethrough,in which are adjustably secured rods 20, projecting forwardly toward the acting face of the grimling-wheel, as most clearly shown in Fig. 1.

1 These rods constitute the bearing for the forward end of the knife-holder in its movements toward and from the grinding-wheel, the under edgeof the plate 1 resting directly on the upper surface of said rods. To prevent lateral movement of the holder on these rods, I provide vertical pins 21, en gaging against the inner faces of the rods 20 20, respectively, as clearly shown in Figs. 7, 9, and 12.

For advancing the knife-holder and holding the knife in contact with the grindingwheel with yielding pressure and for automatically withdrawing the same after the knife has been subjected to the grinding action for a predetermined period and for arresting the reciprocatory movement of the carriage'I provide the following mechanism: A treadle 22 extends forwardly to the front of base A from a shaft 23, mounted in bearings on the inner face of the spider F. A coiled spring 24 about the shaft 23 acts to raise the treadle when the same is released in a manner about to be described. A beltshifting arm 84, projecting upwardly from shaft 23, has pins 25 25 at its upper extremity engaging on opposite sides of the belt F as most clearly shown in Fig. 3.

As clearly shown in Figs. 1 and 4, a shaft 26 extends longitudinally through the hollow part of the carriage L. The projecting inner end of the shaft is provided with a lateral opening thereth rough, in which isadjustably secured a pin or finger 27,"(see Figs. 1, 4, and 12,) having a recess 28 in its upper extremity, in which the pointed end of thepin 15, heretofore referred to, engages, as most clearly shown in Fig. 12. The rear side of the finger bears against the cylindrical surface '29 of a rod secured in the frame 2. The other end of the shaft 26 projects thr'oughthe end of car riage L, bearing in the vertical wall of the basin B, and carries acrank-arm 30, which pivotally connects with the "upper end of the rod 31, which telescopes intothehollowendof the rod 32, the latter being pivoted at its lower end to the treadle 22. The rod 31 has a series of openings through its lower end, in any one of which maybe engaged a pin 33, which projects at opposite ends throughslots in the wall of the hollow upper end of the rod 32. A coiled spring 34 rests at its lower end against the projecting ends of the pin 33, and its upper end bears against the under side of a nut 35, screw-threaded onto the rod 32. With the parts as thus described it will be seen that when the operator depresses the treadle 22 the spring 34 will, when placed under sufficient tension, move the rod 31 downwardly and through the crank-arm rotate the shaft 26, causing the finger 27, through its connection with the knife-holder by means of the pin 15, to advance said holder until the surface of the knife-blade is brought in contact with the grinding-wheel. There is sufficient freedom of movement between the pin 15 and the knife-holder, on the one hand, and the pin 15 and the finger 27, on the other hand, to enable the knife-holder to be thus advanced without lifting the same from the rods 20 or the bearing-ball .t'. In order to too hold the tailpiece of the holder firmly in contact with its bearing-ball, I provide a spring 40, (see Fig. 7,) secured at its upper end to u the cover G and at its lower end bearing in a conical recess 41 in the upper surface of the frame 2, forming a part of the knife-holder, said recess being most clearly shown in Figs. 10, 11, and 12 of the drawings. The knifeholder, of course, has such freedom of movement as to permit the fiat face of the knife carried thereby to automatically aline itself I with the flat grinding-surface when advanced to contact therewith. It will be understood that upon depression of the treadle in the manner above referred to the belt-shifter acts to move the belt F onto the fast pulley f, thus throwing into operation the mechanism for reciprocating the carriage and for tilting the knife-holder during its reciprocation with the carriage To maintain the treadle in its de-' pressed'condit-ionfor a. length of time suificient toaccomplish the desired grinding of the surface of the knife-blade, I provide a vertically-disposed rod 45, pivotally connect-- ed at its lower end. to the treadle 22 (see Fig. 1 2) and at itsupper end formed with a notch? 46, the horizontal shoulder of which upon de-,

- pressionis adapted toengage under the peripheraledge of a wheel 47 ,a spring 48, lo- I cated in a recess in thebase A, acting against ,apin bearing on .therod 451 to force the upper end'of saidrod outwardly, so*that its notch will engage the wheel 47 in the manner. described. (See Fig. 8.) Arranged equidis-i taut-about the-'perip'hery'of the wheel 47 are scr ews"49,th'e heads of which project from said wall andare adapted toact on the in-.

clinedsurface50, just below the notch 46 in the upper-end of the bar 45, to force the horizontal sho'ulfderof said bar out of engagement; withflthe wheel, and thus permit the treadle 22 to be raised through the action .of

' the coiled springs 24 and 34,already referred to. When the treadlejis raised, the bar is movedupwardly to the position shown in dotted linesinFig. 8, the belt F is shifted from the fast pulley f, the shaft 26 is rotated,

moving the finger 27, and the knife-holder S is moved to the position shown in Fig. 1. An

other knife is now inserted by the operator, who again depresses the treadle, and the op-' erations as above described are repeated. As has already been explained, after ten knives are thus ground the truing device is brought into action and from time'to time the grind ing-wheel is advanced to compensate for wear thereon. The. means for operating the truing device have already been described to the point where that part of the surface of the gear-wheel I having no teeth thereon is brought to a position opposite the pinion k, and it only remains to be explained how this gear-wheel is advanced to bring the teeth thereof into engagement with the pinion. The wheel 47,-already described,'is secured to one'end of shaft 60, which has hearings in the base-A. (See Figs. 2, 6, and 8). On the shaft is also mounted a cam 61, which bears against one end of a spring-actuated slide 62.

(See Figs. 5 and 6.) This slidev carries a pawl 63 in engagement with the teeth of gear-wheel I. For every knife ground the wheel 47 is moved a distance equal to the space between two of the screws 49 thereon, or, in other words, one-tenth of a rotation; This movement of wheel 47 is effected by a pawl 64 (see Fig. 2) engaging the ratchet-teeth 65, which extend entirely around one side of thepe- Fig. 8, said pawl being actuated by an ec-' centric-pin 66,(see Figs. 1 and 2, the pawl 64 being omitted from the former figure,) projecting from the face of cam g 60, and consequently the cam 61, carried thereby, is given a similar movement, and

it will therefore be seen that ten knives will be actedupon during the'timerequiredto impart a complete rotation tosaid cam. During this time the cam intermittently moves the slide 62 to the left, Fig. 6, untilsaid slide drops off of the highest part of the cam-surface and under the action of its spring is moved to the right. In this movement-the riphery of said wheel, as clearly shown in The shaft pawl 63 moves the gear-wheel I a distance sufficient to engage the. teeth thereon with the constantly-rotating pinion 7a, and the mechanism for moving the truing device is thuscaused to operate in the manner already set forth.

The shaft 60 carries at its rear extremity an eccentric 70, secured to the shaft by a screw 7.1 and engaging an opening eccentric ally located in the end thereof. 1 Upon loosening this screw 71 the eccentric may be adjusted on the shaft to vary its throw. The eccentric 70 actuates atpawl '72, which engages a ratchet-wheel e, heretofore referred to, turning the same from time to timeto' move shaft C longitudinally in its hearings to compensate for wear on the grinding-surface.-

80 is a pipe through which vwater may befed to the grinding-surface.

The complete cycle of operation of-the machine will,it isthought,be readily understood from the description above given.

Grinding and polishing being analogous operations,all references to the former will be understood to apply also to the latter.

Having thus fully described myinvention,

what I claim as new, and desire tosecure by v and adapted to act upon said surface to true the same, and mechanismffor actuating said arm automatically and intermittently after certain predetermined movements of the work-holder.

2. In a grinding-machine, the combination with a grinding-Wheel having a flat grindingsurface, of a movable work-holder, means for rocking the work-holder to laterally oscillate the article being ground, means for reciprocating the work-holder longi tu din ally to move the article being ground along the grindingsurface, a swinging arm mounted to move in a plane parallel with the grinding-surface, and carrying a truing-point which is adapted to traverse and act upon the grinding-surface to true the same, and mechanism actuating said arm operated automatically and intermittently after certain predetermined movements of the work-holder.

3. In combination, a grinding-wheel, a movable work-holder, means for rocking the workholder to laterally oscillate the article being ground, means for reciprocating the workholder longitudinally to move the article beingground along the grinding-surface,- a truing device adapted to be moved across and in contact with the grinding-surface to true the same, gearing and connections for transmitting motion to said truing device, means for automatically throwing said gearing out of operative relation with the driving parts of the machine after the truing device has operated for a predetermined period of time, and means for automatically throwing the same into such operative relation when the machine is operated for a predetermined period.

t 4. The combination with a grinding-wheel,

of a movable work-holder, means for rocking the work-holder to laterally oscillate the article being ground, means for reciprocatingthe work-holder longitudinally to move the article being ground along the grinding-surface, a

truing device for the grinding-wheel, actuating mechanism for the truing device, and mechanism for automatically and intermittently throwing said actuating mechanism into gear with the driving parts of the machine.

5. In combination, a grinding-wheel, a movable work-holder and mechanism for imparting movement thereto to present the work to the grinding-surface, a truin g device for said wheel, a driving-pinion for the truing device and means for rotating the same, a gear-wheel meshing with said pinion, the teeth of said wheel being omitted at one point whereby rotation of the wheel is arrested when this point comes opposite to the pinion, and means operating automatically to move the gearwheel to bring the teeth thereof into engagement with the teeth of the pinion after the grinding-wheel has done a predetermined amount of work.

6. Inagrinding-machine, a grinding-wheel, a truing device for said wheel, a driving-pinion for the truing device and means for rotating the same, a gear-wheel meshing with said pinion, the teeth of said wheel being omiited at one point whereby rotation of the wheel is arrested-when this point comes opposite to the pinion, a carriage, a holder on said carriage for the article to be ground, mechanism for reciprocating the carriage, means for throwing said mechanism into operation, means for automatically throwing said mechanism out of operation, and means operating automatically to move the gear-wheel into ongagement with the teeth of the pinion after the mechanism for reciprocating the carriage has been thrown into and out of operation a predetermined number of times.

7. In a grinding-machine, a grinding-wheel, a movable work-holder and mechanism for operating the same to present the work to the grinding-surface, a shaft for the grindingwheel, and means actuated automatically during the operation of the machine for moving said shaft longitudinally in its bearings to advance the wheel to compensate for wear on its grinding-su rface.

8. In agrinding-machine, a basin in which the grinding-wheel operates, a reciprocatory carriage mounted in said basin in front of the grinding-wheel, an arm for reciprocating said carriage projecting upwardly through an opening in the bottom of the basin beneath the carriage and mechanism for actuating said arm.

9. In a grinding-machine, a basin in which the grinding-wheel operates, a reciprocating carriage and means for operating the same, a work-holder mounted to move laterally on the carriage to present the work to and withdraw it from the grinding-surface, means for imparting such lateral movement to the workholder, means mounted in the basin and pro jecting through the bottom thereof for supporting the outer end of the work-holder and raising and lowering the same to rock the work-holder and thereby grind the work to the desired convexity of surface, and mechanism exterior to the basin for operating said means.

10. In a grinding-machine, a basin. in which the grinding-Wheel operates, a reciprocating carriage and means for operating the same, a work-holder mounted to move laterally on the carriage to present the work to and withdraw it from the grinding-surface, means for imparting such lateral movement to the workholder, a vertically-disposed rod mounted in a suitable bearing on the bottom of the basin and depending outside of the same, an anti- IIO friction-bearing at the upper end of said rod I carriage havingalongitudinal passage thereholder, mechanism for rocking the worklongitudinally to move the article being.

ground along the grinding-surface, said mechanism being adapted to be thrown intooperation by the operator and to be automatically thrown out of operation, a truing device for the grinding-wheel, and automatically-operated mechanism for actuating the truing device after the work-holder has been thrown into and out of operation a predetermined number of times.

13. In a grinding-machine, the combinaiion with a grinding-wheel, ofa movable workholder, mechanism for rocking the workholder to laterally oscillate the article being ground and for reciprocating the work-holder longitudinally to move the article being ground along the grinding-surface, said mechanism being adapted to be thrown into operation by the operator and to be automatically thrown out of operation, a truing device for the grinding-wheel, automatically-operated mechanism for actuating the truing device after the work-holder has been thrown into and out of operation a predetermined number of times, and automatically-operated means for advancing the grinding-wheel to compensate for wear on its grinding-surface.

In testimony whereof I have signed this specification in the presence of two subscribing witnesses.

ALLEN JOHNSTON.

Witnesses:

J. T. HACKWORTH, A. G. HARROW.

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