US2396775A - Grinding machine - Google Patents

Description

March M. DE YOUNG 96,775

GRINDING MACHINE Fiied April 2, 1945 4 Sheets-Sheet 1 Km) cvwor Mqrfin DeYoum 5 Mfomeg Filed April 2, 1945 4 Sheets-Sheet 2' n wu o v 6 mD .m 1. wl a M Wlarch 19, 1946. M. DE YOUNG GRINDING MACHINE Filed April 2, 1945 4 Sheets-Sheet s Inuenfov 5 NWT m DeYoun U? %4 March 19, 1946.-

M. DE YOUNG GRINDING MACHINE Filed April 2, 1945 4 Sheets-Sheetfi 52 M91 Mqrf in DcYouY\9 Mfomegg Patented Mar. 19, 1946 U N-l TE D .STAT E S T O F-"F IE GRINDING 7 Martin 'De'Yo'ung, Grand Rapids, 'assignor 'to Gallmeyer '& "Livingston "Company, Grand Rapids, Mich, a -corporation "of Micliigan ApplicationAprilZ, 1945, Serial No. 586,129

(cum-'92) control .meohanism .of i-t'hepres'ent invention {is 8 "Claims.

The present invention relatesto the hydraulic operation and control of grinding machines. .I have heretofore obtained (Patent No.'.2, 378:,006, issued June 12, 1945,.-for Grinding'machineacontrol, in which .novel mechanism is disclosed :for hydraulically operating a (horizontal work-carrying table upon a suitable carrying Ebed therefor, with periodic reversals of movementof the table at preselected .points in its longitudinal movements which points are adjustable in accordance with the length of the work processed. Such prior invention also fullyshowsalhydraulic operation and control of a cross Yfeed carriage which carries the driven grinding wheel Iinmov-ements transversely of the table so as .to move the grinding wheel across the work being ,processed in periodic step by step movements,..substantially simultaneous with the reversal ofthe reciprocating movements of the work carrying table and for reversing the cross Tfeed carriage when the entire width of the workbeingprocessed has been acted upon .by the grinding wheel.

The present invention is directed -to Ithe'hydraulic operation and control for thedownfeed of the grinding wheel with relation to the work being processed. It'is aprimary-object-an'd,purpose .of the ,present invention to provide a novel, practical relativelysimple and very effective hydraulicallygoverned downfeed which maybe controlled to move "the .grinding wheel'downw'ardly diiierent distances which maybe preselected; and to render the same operative whenever a rinding out has been taken over the full .surface of the work which is being ground, and under either the condition in which the peripheral width of the grinding wheel .acting upon the work is equal to or greater than the width of the work as in plunge grinding or'if the width of the work is greater than .such peripheral width of the wheel; and to also selectively 'control the operation of the downfeed at the ends of all reciprocating movements of .the work .carrying tabie, or at only alternate reci-procations.

An understanding of the invention may be had from the following description vtakeninconnection with the accompanying drawings, in which,

Fig. 1 is a vertical section through the ggrinding machine to which .my invention is applied, showing the general structural .environmerit df the invention.

Fig. 2 is a diagrammatic view illustrative of the hydraulic circuits and the mechanism used for controlling the grinding wheel downfe'ed.

Fig. 3 is a fragmentary planpartly in section showing the work -carrying table and thamanually operable means for raising and lowering the grinding wheel and the "head on which his carried and to which the automatic I'hydraulic applied. S

:Fig. .i-is .aifragmentary'section ande'l'evation of the hydraulic .meohanism 'usedfor governing the extent or degree of .downieed and-ff or controlling .at which end or whether at both ends hi the table or wheel head .reoiprocatory movements such downfeed .is operated.

Fig. '5 is a sideelevation of thehydraulic "unit for the operation and control of thedownfeed, and

lRig. dis a front elevation thereof with parts broken away andinsectionfor abetter disclosure lot-structure.

like reference characters re'fer to like ,parts "in theidifierentfigures o'iithe drawings.

:As-shown linjFig. 11, the grinding machine "to which this inventionis applied includes a "horizontal work carrying table fl-,.mounted for length- .wise reciprocating -movements upon ways '2, and which in practice is hydraulically operated by means including piston cylinder apparatus indicatedat. 3 and located underneathlthe table, the detail: of whichis not concerned with the present invention... andiull disclosure of which is made in my:prior-filed application, together with the con- 'trdlthereior of a manually operable nature, jin- .dicatedat the front of 'theimac'hine, at '6, in Fig. "l.

The double pump 55 with ..a liquid (usually oil) .holdingtan'kili below the table, .the ,pumps being driven lay .a motor ll are also fully disclosed in said ,p'rior application.

.An upper .head fBis mounted for vertica'l adjustmentbymeans io'fsuitable guide ways '9 on 21.5 .a "hood "[5 at the forward end .of a housing It connected with-and forming a part of the cross- .ffeed carriage, and on which a horizontallbarllil .is permanentlysecured with adjustable blocks [8 -onlthe1bar whichlm'ay "be selectivelyset. at .difier :50 entpositionsin spaced relation toleac'hother.

.hliorizontal cylinder 19 withends 2B is connected and .moves with the .oross'feed carriage within which, (Fig. 2 a ,piston 1.2] is located. TFromopposite ends of the piston, tubularpiston 55 rods .22 v.an'cl I23 extend .away from each "other which are connected, respectively, to liquid car- ..ryingpipes or conduits "z iand '25 leading to oppo- .-site .sidesof a valve housingdfi. Within the-housing a-is a direction a-con-trol valve 2 thenstem 10f B0.which extending nutside =of the "housing has a downwardly projecting handle 28 attached which when a stop [8 comes thereto in the movements of the crossfeed carriage, swings the valve from a position, as shown in Fig. 2,'to a position in which the side edges of the valve 21 shown cross the ports in the valve housing with which the pipes 24 and 25 are connected. A pressure inlet wardly from the shaft 48, for manual operation to connect or disconnect the pawl from the ratchet teeth.

A vertical cylinder 43 is secured to the body or frame of the machine at its front, being closed at both ends and having a piston rod 44 extending therethrough and above and below the ends,

p pe 29 for carrying liquid under pressure is con- "5 nected to the valve housing 26 between the port.

entrances of pipes 24 and 25 at one side of the the position shown in Fig. 2, liquid forced under 7 pressure through the pipe 23 enters the valve housing 26 and is forced to the only port open for its escape in such position of the valve, and thence through the pipe 24 and through the openings 24a which are made in the tubular piston rod 22, into the cylinder at the right hand side of piston 21. The piston remains stationary and the cylinder is thereupon moved to the right. Such movement continues until the crossfeed carriage with which the cylinder 19 is connected has moved to bring one of the reversing blocks 18 against the handle 28 to turn valve 21 to open the port leading to the pipe 25. When this occurs the flow of liquid under pressure is carried through the tubular rod 23 and escapes through the like openings 24a. in rod 23 at the opposite side of the piston 2| thereby reversing the movement of the crossfeed. The structure thus described is disclosed in my prior filed application and is disclosed herein only so far as is necessary for an understanding of the structure and utility and mode of operation of the hereinafter described invention.

r The head 8 (Fig. 1) carries the cross feed carriage and is raised and lowered by the rotation of a nut 32 through which a vertical screw 3| extends into a sleeve 3|a at the upper end of which the nut 32 is located and which, at its periphery, is formed as a worm gear 33. A worm 34 at the end of an outwardly extending horizontal shaft 35 is mounted at the upper end of the sleeve am in mesh with the worm teeth 33 (Fig. 3). Said shaft at its outer end in front of and below the table has a hand wheel 36 permanently secured thereto for manual operation, whereby the crossfeed carriage head 8 may be raised and lowered manuall for the placing of work to be processed upon the table I and for moving the grinding wheel roughl into a close proximity to the surface which is to be ground.

It is the shaft 35 to which the operating mechanism of my invention is applied to automatically and hydraulically control the subsequent downfeed movements to lower the grinding wheel periodically, and at selected intervals with relation to the work, upon which the grinding wheel is operating. As shown in Fig. 5, the shaft 35 passes through a covering sleeve 31 at its outer end and at the inner face of the hand wheel 36 a disk or ring 38 with consecutive closely spaced ratchet teeth is secured. An arm 39 is loosely mounted at one end on and around the sleeve 31, extending radially outward to a point beyond the periphery of the ratchet 38. Through the outer end portion of the arm a short horizontal shaft 40 extends and is mounted for rocking movement therein. At its end adjacent the ratchet teeth 38 shaft 40 is formed with a downwardly extending pawl 4| (Fig. 6), the free end of which engages between consecutive teeth of the ratchet 38. At the other end a handle extends out-' said rod, within the cylinder, carrying a piston (Figs. 4 and 6). Upper and lower ports 46 .and 4! lead respectively to the upper and lower ends of the cylinder with which liquid carrying conduits 48 and 49 are respectively joined, as diagrammatically shown in Fig. 2. It is apparent that when liquid under pressure is introduced into the upper end of the cylinder the piston is forced downwardly, and any liquid below the piston will be forced out at the port 4?. When the liquid under pressure is carried by the pipe 49 to the cylinder below piston 45, it and its connected rod 44 will be moved upwardly and liquid above the piston will be forced outwardly through the port 46 and pipe 43.

At the lower end of the cylinder 43, a member 50 is fixedly secured at its upper end (Fig. 4). Said member is interiorly bored from its upper end (nearly through to its lowe end, and into the axial opening provided the lower end) portion of the rod 44 extends. The member 50 at diametrically opposed sides for the intermediate portion of its length is formed with vertical slots 5!. Said member 53 of a cylindrical form is exteriorly threaded. An upper and lower nut 52 are screwed onto said member 50, and through the lower end of the rod 44 a transverse pin 53 extends passing through the vertical slots 5! and having its end portions located between the spaced apart nuts 52. The nuts 52 are adjustable for spacing at difierent distances apart, and are held at any adjustable position by suitable set screws (Fig. 5). Accordingly, the stroke of the piston 45 and the piston rod 44 connected there- 'with is controlled by the adjusted space between the nuts 52 and may be changed to provide different lengths of stroke by changing the relative positions of the nuts 52 to each other.

A vertically extending bracket support 54 is secured to and extends upwardly from a block in which cylinde 43 is made, terminating a short distance below the plane of the shaft 35 (Fig. 5). A link 55 is pivotally connected to and'depends from the outer end portion of the arm 39, and at its lower end has a pivotal connection to the end of one arm 56 of a bell crank lever which i pivotally mounted between its ends at a face of and to one side of the upper end of the bracket 54. The other arm 51 of the bell crank lever extends downwardly and substantially at right angles to the arm 55 (Fig. 4). Two toggle links 58 and 59 are provided, pivotally connected together at meeting ends and to the upper end of a vertical link 60 which at its lower end has Pivotal con nection at the upper end of the rod 44. The other end of link 58 is pivotally connected to the arm 51 of the bell-crank lever and the other end of link 59 is pivotally connected to the bracket 54 at the same face thereof that the bell crank lever is mounted.

With this construction reciprocation of the rod 44 rocks the bell crank lever about its pivot. On downward movement of the rod 44 from the position shown in Fig. 4, if the pivot axis of link 58 to the toggle links 58 and 59 does not pass below a line connecting the pivots of links 58 and 59, respectively, to the bell crank lever and support, said bell crank lever will be rocked in one direction only with *a cor-responding movement er .the pawl ll in-one 'direction. 'But ifsaid'pivot passes below said dead-center line, the bellcra-rik lever will be initially rocked in one direction until said line "is reached andthen in the opposite direction aft-er passing across and "beyond in a downward direction. As the extent of movement'imparted to 'the bell-crahk lever by the reciprocating'm-ovemerits of the piston 'ii is c'ontrolledbytheposition for the 'nuts '52, it is apparent that shaft -35 may be turned either at *both reciprocations "of the rod 44 or at one-only thereof. In theformer case, the movement of rod M I will be su-ffioient "toc'arry the knee-or knuckle pivotalaxis of "the toggle lllffls"53-&Ild 59 below the -dea'd center-line. wane 'i-n 'the other "case, such movement will terminate above or at-the dead centerl-ine. a

*For the control of the pressure liquid to the "opposite ends of the cylinde -ca es--diagrammatically shown in Fig. 2 'a block 6B is provided with a cylindrical opening as therethrough =-and a second cylindrical opening paralleling it in which a-cylindrical valvett is rotatablymounted, the endsof the openings beingclosed by closure plates 62. In practical structure, as shown in Figs. -5 and 6, the block in which the vertical cylinder 534s made -is the same one in which the horizontal cylindrical chamber 63 and-also the opening to receive the-valve o l are made.

In said elongated chamber be, a valve of the shape shown with end andintermediate sections fiS-s'pacedfrom each other of a size tofitthe boring of the chamber "63 is provided, the over-all length of the valve being less than the distance between the closure ndplatest'z permitting a lengthwise movement of thevalve in the chamber 53. Around the reduced portions ofthe valve between said sections -65 are a central chamber '66, and two end chambers 61! and I 61a asshown. Liquid under pressure i conducted through an inlet conduit as-indicated at e nintothe central but said chamber will have been moved over to 50 llllCOVGT'flTldBOHIle-Ct with the diagrammatic conduit 48so that the pressureliquidunder suchcircumstances will be carried to the upper end of thecylinder' fi.

The'valve 64 has two series of. passages 59 and 'to-each other and in the same plane and extending-across the longitudinalaxis of the valve, while the passages H3, located outwardly toward the ends of the valve-64 from the passages 69, are located at right angles to passages 69, are parallel to each .other and alsoextend acrossthe longitudinal axis of the cylindrical valve 64. Midway in its length :said valve has a continuous annular exterior .groove H cut therein, with which a port through the lower side of the block 6! (Fig. 2) is in conjunction, with a pipe E2 in conjunction with said .port leading to the oil supply tanks for delivery of oil back to the tank after it has been used.

Apipe or conduit is connected with and "in conjunction with the previous described conduit 24 "connects with the block 6! and a'port through a "sidethereof which is in the same plane with one "of "the passages'lil throughvalve t l. Similarly a pipe or conduit 14 connects with the previously 7 describedconduit 25iandleads to aport inthe sheaths block- 6 the same plane withth'e ether or the passages 1!] through val-ve ii. B-tweenthoWalve 3 and the valve chamber 63 are two passages "l5 each with a branch-as shoWn -atl'fi. The ends of the passages are connected, respectively with plane-as the passagesl'fi therethrough.

10 therethrough, the passages 69 being parallel Communicating with the-groove Tl inthe valve -64, a.v passage 77 extends toward 'the' va'lve chamber -63, and has two branches l8 extending 'in opposite directions communicating with sa'id chamber "63 as -=shown. Ports are also made throu h lower sides" of the more t"l with which pipes 59 and 89 are-connectedsaid ports being 'in the same planes as the passages "6'9,-to therfdre connect with said passages when the valve-"El is disrupting the connection "previously describedras made by the passages :69 through the valve. Of course at an intermediate position of the valveGd none of the passages '69 or 19 will be effective to carry liquid and,'therefore, the entire unit which has been described will be cut off ando'peratively ineffective. As shown in Fig. 2 a handle)! for manually turning the control valve is supplied so that it may be moved to desired positions.

In Figs. 5 and 6 a member 83 provided at its inner side with a shroud 85 is adjustably mounted, at the rear side of the hand wheel 36, the

shroud bein of arc shape and located closely adjacent to and over a sector of the'ratchet ring 38. The wheel 36 has an annular T-slot therein for receiving the head of a securing bolt 85, for

adjustably securing said shroud at any desired position with reference to the ring 38. In the operatio of the shaft 35, with aconsequent turning of the hand wheel secured at its outer end, the shroud 8 1 will be carried to and intothepath of movement of the pawl '41 and will disconnect the pawl from the ratchet teeth andrender such pawl ineffective to move the shaft 35, even though thereafter the piston 85 be continuously reciprocated. Such structure is used :as a limit control of the downfeed by setting the member which carries the-shroudt l at a preselected position, such that when the selected amount of thedownward movement of the grinding wheel'has taken place, no further downfeed will occur irrespective of continuing operation of the machine.

With the parts in the pos'itionshown'iniFig. 2, and with pipes'ifi and 8l1 connected with the opposite sides of the reversing'valve mechanismfor the reciprocating tableas disclosed in my previouslyv'filed application, and with thei'pressure which operates one of the piston cylinder apparatus 3 (Fig. 1) to move the table I in one direction carried to and through the pipe 19, thence through the passages 69 and 15, the valve within the chamber as is moved/as shown totheright and there is'a how of liquid under pressure }from to the lower side of the piston 45 moving it in an upward direction. Liquid above the piston forced out at the-conduit 48 carried to the chamber 67a through the passages iii and H and the groove H and to the outlet conduit at 12. On the reverse movement of the table the pressure is directed through the pipe 89, passages 69 and to the opposite end of the chamber 63, with an interruption of the connection of the pipes 88 and48, reversing the movement of the piston 45 and with the exhaust of liquid from below the piston carried through the pipe 49. which will be connected I with the chamber at 6'? with the flow through the passages 78, ll, groove i! and pipe 12 back to the tank 6. Y

It is therefore apparent that with each reciprocatory movement of the work carrying table 1,

there is a corresponding reciprocation of the rod 44 and a swinging of the arm 39 about the axis of the shaft 35; and, as previously described, with the adjustment provided by the nuts 52, the dog 31 may be moved upwards (Fig. 2) at the end of one reciprocation of the table and moved downwardly at the end of'the other, to produce an effective downfeed at one end only of the work carried on the table attained. Also, as previously described, the extent of movement of piston 45 maybe controlled to get a downfeed at both ends of the work, that is, at each reciprocation of the table. Ihis is. the operation when the work to be processed, for example, is of a width which is not greater than the grinding face of the wheel bearing against it; and the valve 64 will be in the position shown in Fig. 2. When the work is wider than the peripheral face ofthe grinding .wheel It valve Bil is turned to bring one passage 16 and the pipe 13 in connection by one of the passages l0 through the valve, the other pipe M being similarly connected by the other passage Ii! with the other of the branch passages '15. In

. such case, the automatic movement of the valve 65 in the chamber $23 will be only at the time that the cross-feed is reversed, or when 'a stop 18 moving against the handle at 28 reverses the position of the valve 2?. The flow of the liquid under pressure conducted by the pipe 68 will be through the diagrammatic conduits 48 and 49 to opposite ends of the cylinder 43 in accordance with reversal of the crossfeed, irrespective of the number of reciprccations of the work carrying table I may have occur in covering the width of the work ground.

The construction which has been outlined and described has proven to be practical and very useful, and with it an automatic downfeed which is fully and completely controlled and capable of adjustment for all conditions has been made and very successfully produced and operated. The invention is defined in the appended claims and is to be considered comprehensive of all forms of structure coming within their scope.

I claim:

1. In a grinding machine having a horizontal reciprocable work carrying table to be reversed in its movements at preselected times, and having a head with a carriage thereon for carrying a grinding wheel, said carriage being mounted for reciprocatory movements transversely to the direction of movements of the work carrying table, means for raising and lowering said head including a shaft, the turning of which in opposite directions will raise and lower the head, hydraulic means including a hydraulic cylinder closed at both ends, a piston within the cylinder, means for supplying liquid under pressure alternately to opposite ends of the cylinder, and a manually operable control means for selectively directing said forcing of liquid into opposite ends of the cylinder either upon reversing the direction of movement of the work carrying table or upon reversing the direction of movement of the grinding wheel carriage.

2. A construction as defined in claim 1, and hydraulic means for moving said grinding wheel carrying carriage comprising, a hydraulic piston cylinder structure, means for alternately forcing liquid under pressure into opposite ends or the cylinder and against opposite ends of the piston therewithin, connections for carrying liquid under pressure from the supply of liquid delivered to said last mentioned cylinder, said manually operable control means being disposed between said connections and the first mentioned hydraulic cylinder, and a manual operable valve included in said control means for providing communication between said connections and said second mentioned cylinder, combined with automatic means associated with said control means for directing liquid under pressure into the 0pposite ends of the first mentioned hydraulic cylinder upon change of the direction of said liquid under pressure to alternate ends of the cylinder of the second piston cylinder apparatus.

3. In a grinding machine having a horizontal reciprocable work carrying table, a vertically adjustable head and a grinding wheel carriage reciprocable on'said head in a direction transverse to the direction of the work carrying table, means for raising and lowering the head including a rotatable shaft, a hydraulic cylinder mounted adjacent said shaft, a piston within said cylinder, means for supplying liquid under pressure alternately to opposite ends of the cylinder at the end of reciprocatory movements. in one'direction of the table and the beginning in the opposite direction, means for rendering said. last mentioned means inoperative and for rendering operative means for supplying liquid under pressure alternately to opposite ends of the cylinder at the ends of the transverse reciprocatory movements of the grinding wheel carriage and the beginning of such movements in the other direction, and means interposed between the piston and said shaft for turning the shaft in amounts corresponding to the movement of said piston to move said head downwardly a predetermined distance selectively between said reciprocatory movements of said work carrying table, or change in direction of the reciprocatory movements of the grinding wheel carriage.

4. In a grinding machine having a work carrying table mounted for horizontal reciprocatory movements and having a head located above the table, and a carriage mounted on said head for horizontal reciprocatory movements in a direction transverse to the movements of the table,

means for raising and lowering said head in' alinement with the piston at one end, a bell crank lever pivotally mounted at its end on and to one side of said support having an arm extending laterally and outwardly therefrom and a second arm extending substantially at right angles to the first arm, a link connecting said first arm to the bell crank lever and the pawl carrying arm, toggle links pivotally connected together at their meeting ends, one of said links having a pivotal connection at its opposite end to said support and the other link a pivotal connection to the other arm of the bell crank lever, and a link connecting the pivot rod with said toggle links at their pivotal connection.

5. In a grinding machine having a work carrying table'mounted for horizontal reciprocatory movements and having a head located above the table and a carriage mounted on said head for horizontal reciprocatory movements in a direction transverse to the movements of the table, means for raising and lowering said head including, a shaft to be turned, a ratchet wheel on the shaft, a vertical hydraulic cylinder with closed ends, a piston in said cylinder, means for alternately forcing liquid under compression into opposite ends of the cylinder and exhausting liquid at an end opposite to where the pressure is applied, an arm mounted at one end on said shaft extending alongside of and beyond the edge of the ratchet wheel, a pawl carried by said arm normally engaging with the teeth of the ratchet wheel, a piston rod connected with said piston, said piston rod extending beyond both ends of the piston, a tubular fixture into which the other end portion of the rod extends, said fixture having oppositely disposed longitudinal slots therein, a pin extending through said piston rod and through said slots, said fixture being exteriorly threaded, and two nuts on said fixture spaced from each other and between which said pin passing through the rod is located, the position of the nuts on said fixture governing the extent of movement of the piston within the cylinder, and means connecting one end of the piston rod with said arm for lifting the arm and pawl and for drawing said arm and pawl downwardly upon reciprocation of said piston to turn the shaft in a direction to lower the head.

6. In a grinding machin having a horizontal reciprocable work carrying table adapted to be reversed in its movements at preselected times and having a cross-head carrying a grinding wheel, means for raising and lowering said head including, a shaft the turning of which in opporeciprocable work carrying table adapted tobe reversed in its movements at preselected times, and having a cross-head carrying a grinding wheel, means for raising and lowering said head including a shaft, the turning of which in opposite directions will raise and lower the head, hydraulic means including a hydraulic cylinder closed at both ends, a piston rod extending through the cylinder, a piston within the cylinder, means for alternately forcing liquid under pressure into opposite ends of the cylinder upon reversing the direction of movement of the work carrying table, a toothed ratchet on said shaft, a movable pawl to engage with the ratchet teeth to turn the shaft when moved in one direcion and pass over said teeth when moved in the opposite direction, connections between one end of said piston rod and pawl have effecting said movements upon movement of the piston within said cylinder, means connected with said cylinder and associated with the opposite end of the piston rod for adjustably limiting and controlling the extent of movement of the piston within said cylinder, said means between the first mentioned end of the rod and said pawl including a support, a bell crank lever-pivotally mounted within its end at one side of said support, two toggle links pivotally connected at their meeting ends, one of said links bein pivotally connected at its other end to said support and the other link to one arm of the bell crank lever, an arm mounted at one end on said shaft to rock thereabout on which said pawl is carried, a link connecting the other arm of the bell crank lever with said pawl carrying arm, and link connections between the piston rod and the pivotal connections of said toggle links, the extent of movement of the piston within the cylinder controlling the'extent of movement of said toggle links, whereby when thelinks are moved across their dead center line, the pawl is both lifted and lowered with respect to the ratchet wheel.

8. Operating means for raisin-g and lowering the grinding wheel carrying head of a surface grinding machine with respect to work carried site directions will raise and lower the head, hy-

draulic means including a hydraulic cylinder closed at both ends, a piston rod extending through the cylinder, a piston within the cylinder, means for alternately forcing liquid under pressure into opposite ends of the cylinder upon reversing the direction of movement of the work carrying table, a toothed ratchetwheel on said shaft, a movable pawl to engage with the teeth of the ratchet wheel to turn the shaft when moved in one direction and pass over said teeth when moved in the opposite direction, connections between one end of the piston rod and pawl for eifecting said movements upon movement of the piston within said cylinder, and means connected with the cylinder in association with the other end of the piston rod for selectively controlling the extent of movement within the cylinder.

7. In a grinding machine having a horizontal on the work table of said grinding machine in cluding a shaft, means between said shaft and said head for raising and lowering the head on turning the shaft in opposite directions, a ratchet wheel on said shaft having consecutive ratchet teeth at its periphery, an arm loosely mounted on said shaft extending upon the edge of said wheel, a pawl carried by the arm to engage said ratchet teeth, a hydraulic cylinder, a piston within the cylinder, means for alternately forcing liquid under pressure into opposite ends of the cylinder, a piston rod connected with said piston and extending at both ends beyond the cylinder, means connecting one end of said piston rod with said arm for swinging said arm back and forth about the shaft on which it is mounted upon movements of said piston, combined with means associated with the other end of said piston rod for limiting the extent of movement of said piston in said cylinder, said means connecting the first end of said rod with said arm including, linkage which upon the piston being moved less than a preselected distance in one direction will move the arm in one direction only, but upon adjustment per mitting movement of the piston in one direction a greater distance than such preselected distance will swing the arm in one direction and back in the opposit direction.

MARTIN DE YOUNG.

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