US2378903A

US2378903A - Grinding machine

Info

Publication number: US2378903A
Application number: US411529A
Authority: US
Inventors: William G Baldenhofer
Original assignee: Thompson Grinder Co
Current assignee: Thompson Grinder Co
Priority date: 1941-09-19
Filing date: 1941-09-19
Publication date: 1945-06-26
Anticipated expiration: 1962-06-26

Description

June 26, 1 w. e. BALDENHOFER GRINDING MACHINE Filed Sept. 19, 1941 5 Sheets-Sheet 1 Gttornegs June 1945- W'. G. BALDENHOFER GRINDING MACHINE June 1945- w. s. BALDENHOFER 2,373,903

GRINDING MACHINE lnvcntor y- ML.-

(Ittorucgs J1me 1945- w. e. BALDENHOFER 7 GRINDING MACHINE Filed Sept. 19. 1941 5 Sheets-Sheet 4 Inventor flii? v 0 1M, (Iltornegs June 26, 1945.

w. G. BALDENHOFER GRINDING MACHINE Filed s t. 19. 1941 5 Sheets-Sheet 5 m d p Snnegtor attorney Patented June 26, 1945 UNITED STATES PATENT OFFICE GRINDING MACHINE William G. Baldenholer, Springfield, Ohio, as= signor to The Thompson Grinder Company, Springfield, Ohio, a corporation of Ohio Application September 19, 1941, Serial No. 411,529

22 Claims.

This invention relates to improvements in surface grinding machines, it more particularly relating to improving a grinding machine of the type shown and described in my Patent No.

reversing dogs. After re-loading, the workholder must again be manually returned to the vicinity of the grinding wheel and the control elements readjusted for the normal grinding 2,068,529, dated January 19, 1937, having a toolstroke. head slidably mounted on a vertically disposed In the machine of the present application decolumn, the tool-head carrying a grinding wheel vices are provided by means of which the aboveand being capable of making successive intermitmentioned steps are carried out automatically. tent traversing feeding movements across a work- The new machine may, therefore, be considered piece carried on a reciprocating work-holder, in as extending the convenience and advantages which machine in grinding the tool-head i lowof the machine of the patent referred to. ered manually to grind stock from the work- One of the objects of the present invention is piece, whereby certain manual operations oi that to provide that in the automatic grinding cy patent are automatically performed. when started the grinding wheel is automatically In the present application, a machine such as lowered in what is known as the down-feeding that of said patent may be considered as one portion of the cy The total amount of down" form of a construction to which the invention in feeding is variable by adjustment to suit difl'erany or all of its parts may be added to the end ent working conditions, with a provision for adthat the convenience and advantages in operaj t y securing Variation in the Extent of an tlon of the machine of that patent are augindividual down-feeding increment. The downmented. The invention tends toward a much feeding is maintained at these set regular incregreater ease of operation in that the grinding ments until the desired low point the tool-head is ycle is practically automatic in character, to reach is attained, when further down-feeding whereby acceptable work is produced by operais arrestedtors of limited experience. The fore part of the 95 Another object is the provision of mechanism following specifications up to the point of brlngwhereby a part of the automatic grinding cycle ing in the new added elements is similar to the known as the smoothing or "spark-out period description found in the patent mentioned, and follows in rotation when down-feeding is arthe reference characters employed in this fore rested. This spark-out" period is a surfacing part are, as far as possible, the same as those 80 operation continued for a regulatable length of used in the abovementioned patent for equivatime with the tool-head held at the low po t i lent elements. reached when down-feeding ceased. This ope ole Setting out the objects and advant eration is advantageous since the surfaces of the of the present invention, a brief explanation will work-pi are f n uneven. and as s usual be made oi the manner in which the machine of in surfacing machines, th d g w l f the patent is operated. With this machine, a lows the irregularities to a limited extent. In work-piece is placed in position, th height or sparking-out, the decrease in the volume of the grinding wheel is adjusted, t m- 1 sparks coming from a stationarily held wheel (so verse dogs ar adjusted, th reciprocatjon r t far as elevation is concerned) shows that only work-table and the cross-feeding of the tool-head the high P s are being around away Without are started, while th operator manually lowers proportionate increase in the depths of adiacent the grinding wheel from time to time a th lower portions. The duration of time allowed for wheel removes stock from the work-piece. When the spark-Out p i is easily varied in h p the surface is finished, the grinding wheel is mann machine y a simpl a J i-ment. lially elevated to the former height, and a new Another object is to provide means whereby work-piece is loaded in position. To lessen the when the work-holder reaches the loading posihazard to the operator, re-loading is preferably tion, the tool-head is automatically elevated to made with the work-holder removed to a point its former height, this elevation being made with remote from the grinding wheel, which is seldom a degree of exactness such that in mass producshut down once it has been started. and if artlon schedules, where the raw material is of relarangements were made in the machine of the tlvely uniform thicknesses, it is possible to start patent for a loading position. it is usually the the next grinding cycle on the next work-piece case that the work-holder is moved'to this posiwith no adjustments other than such as are nection only by the manual shifting or changing of essary to compensate for the natural wearing some of the control elements such as work-holder 66 down or the grinding wheel.

However, it should be explained that another object is to provide that with the work-holder moved onto the loading position, this member is retained in this position for the length of time the operator may desire, and that to re-start the machine on a succeeding automatic grinding cycle, the operator has only to open a push-button switch.

Anothe object is to provide means whereby, should it be preferred that the present machine be operated as the simpler type of the aforementioned patent, which may be advisable when work-pieces differing in character are routed to the machine, such operation is obtainable by the opening of a switch in the electro-hydraulic control system of the present machine.

Other objects will appear from the accompanying specification and claims.

In th accompanying drawings:

Fig. l is a front elevation of a machine embodying the improvements.

Fig. 2 is a view partly in side elevation and partly in longitudinal section, on a larger scale than Fig. 1. the sectional portions being taken on the line 1-2 of Fig. 1.

Fig. 3 is an enlarged fragmentary horizontal section on the line 3-4 of Fig. 2.

Fig. 4 is an enlarged fragmentary elevation of a portion of the invention, 1. e., a switch actuating mechanism seen in elevation in Fig. 1.

Fig. 5 is an enlarged vertical section on the line 5-5 of Fig. 2.

Fig. 6 is a fragmentary view similar to Fig. 5 but with some of the parts of that figure shown in a different working position.

Fig. 'l is a fragmentary horizontal section on the line 1-4 of Fig. 5.

Fig. 8 is a diagrammatic showing of the devices by which the novel features of the invention are obtained, together with a showing of the hydraulic and electric circuits pertaining to the invention, with some of the parts being shown in longitudinal section and other parts in elevation.

Fig. 9 is an enlarged detail showing a modification of the means for arresting the down-feed of the tool-support, the view being a front elevation of a portion of the hand wheel, partly broken away which is associated with the mechanism which operates the tool slide, and of parts associated therewith which control the extent of the down-feed of the tool-support.

Fig. 10 is a top plan of Fig. 9 with some of the parts shown in longitudinal section, some of the sectional parts being on the line Il-Ill of Fig. 9.

Fig. 11 is a detail view partly in side elevation and partly in longitudinal section showing in full and dotted lines three difl'erent positions of the switch operating lever.

Fig. 12 is a front elevation of a detail to show some of the parts in a different position than that illustrated in Fig. 9.

Fig. 13 is a atic view of the switch and its circuits and the parts which operate the switch, some of the parts being broken away.

Referring to the drawings, the base of the grinding machine is indicated at I. On this is mounted for reciprocatory motion on a V-way 2 and a fiat-way I a work-holder I to which the work W may be attached by any of the usual methods.

Reciprocatory motion is imparted to the workhoider by means of fluid pressure acting in a fluid motor. This motor comprises a cylinder I, one end of which is secured to the inside upper portion of the base I (Fig. l), a piston 8 (Fig. B) and a piston rod I, the outer end of which is secured to a downwardly-extending arm I attached to an extension of the work-holder l (Fig. 1) Fluid under pressure is admitted alternately to each end of the cylinder 5, there being a port 9 at the right, and a port II at the left of the cylinder 5 (left center Fig. 8). Communicating with these ports are conduits II and II, respectively, which lead to ports in the body portion l3 of the unitary structure housing the hydraulic valve control mechanism.

' The work-holder is reversed at the ends of a desired stroke by the reciprocatory movements of a master piston valve to which motion is imparted by means of fluid pressure under the control of a piston pilot valve, which in turn receives its motion from the work-holder itself. Due to the small size of the pilot valve and although the pilot valve operates in fluid pressure equal to those pressures which the master valve controls, the movements of the work-holder are not affected.

' The pilot valve is moved by contact of stopdogs ll and I5 (Figs. 1 and 8), adjustably positioned on the work-holder, with lugs l6 and i1 integrally attached on the forward and rear side of a reversing lever it, which is pivotally mounted, on the forward side of the base i, on the shaft it The shaft l9 extends into the interior of the base i and on its inner end there is secured a. forked lever 11, Fig. 8, which straddles the extended stem 23' of the pilot valve 23 between the collars 23" on this stem. The pilot valve 28 is a portion of the hydraulic valve control mechanism which will be described later in the speciflcations.

The abrasive wheel 24 (Figs. 1 and 2) is mounted on the end of the horizontal shaft or spindle 25 supported in bearings (not shown) carried by the tool-holder or slide 28. The tool-holder is supported in angularly disposed ways I! machined in the lower part of a projecting portion 30 of a vertical support or slide Ii. The support or slide Si is gibbed by gibs 82 to the vertically disposed ways 13' of a column ll attached to the base I, and by means of a grinding wheel elevation mechanism may be elevated or lowered so that the position of the wheel 24 with respect to the work on the work-holder 0 may be altered.

The grinding wheel elevating and lowering mechanism comprises an elevating screw 2|, Figs. 1 and 2, depending from bearings in the upper end of the column 33. The screw is threaded through a nut 20' secured to the column side of the vertical support or slide II, and at its lower end there is secured the gear 2i (Fig. 2) meshing with a pinion II. The pinion II is secured on the inner end of an elevation cross-shaft 22 rotatably carried in hearings in the base. The cross-shaft extends forwardly throuflh the forward wail of the base, and on its outer end is fixed a hand wheel 22'. On the portion of the cross-shaft 22 just outside the base there are attached certain members of the devices by which the automatic elevation and lowering of the grinding wheel is provided, the parts being contained in a housing interposed between the forward wall of the base I and the hand wheel It. A full description of these new parts will appear in a latter portion of the specification. Rotation of the hand wheel 22' and cross-shaft 22 in an anti-clock-wise direction as viewed in Fla. 1 results in a lowering of the support or slide 3| and of the holder IO and grinding wheel carried thereby, while the reverse rotation elevates the parts.

The tool-holder or slide 28 is actuated by a fluid motor similar to the motor previously described in connection with the operation of the work-holder, This fluid motor comprises a cylinder 34, one end of which is secured to the inner surface of the rear wall 35 of the vertical support or slide ll. A piston 36 (Fig. 8) on the inner end of a piston rod 31 operates within the cylinder 34, while the outer end of the piston rod 31 is connected to a vertically extending arm 38 secured to the upper portion of the tool-holder or slide 2|. Fluid under pressure is admitted in successive charges to either end of the cylinder 34 whereby the slide 28 is moved step-by-step in either direction in a horizontal plane at right angles to the direction of travel of the workholder 4.

The direction in which the intermittent movements of the tool-holder or slide 28 are made is under the control of a piston type reversing valve indicated at 34' (Fig. 8), and when a desired number of movements is made in one direction, the valve is longitudinally shifted to change the movement to the reverse direction. This valve is contained in a valve housing integrally attached to the tool-holder fluid motor cylinder 34, Fig. 8, and may be manually shifted by means of the forwardly extending stem extension 26 ending in a knob 26' outside the forward wall of the vertical support 3|. In the automatic operation of the machine, the valve is shifted by the tool-holder stroke limiting dogs Ill! and I05, the dog I09, which limits the rearward movement being shown in Figs. 1, 2 and 8, while the dog I09 which limits the forward motion of the tool-holder is shown in plan in Fig. 8. It is identical with the dog I09 except that it is in reversed-hand form.

These dogs I09 and I09 are adjustably secured to a T-slot bar I09" attached to the tool-holder or slide 28, and effect the reversal of the toolholder reverse valve through linkage which consists of a rock-shaft I ill rotatably mounted in the vertical support'3l, a down-turned lever arm H0 on the outer end of the rock shaft H0 in such position as to project in the path of the dogs I09 and Hill whereby the shaft is rocked, and an up-turned, forked lever Ill, Figs. 2 and 8, which straddles the valve extension 26 between a pair of collars 28" secured to this extension. It should 'be explained that with this type of valve reversing linkage and valve that as the valve passes over center, all fluid pressure that created the movement of the tool-holder or slide is cut oil; that is, each dog can move or shift a valve of this type but half its reversing stroke only, To complete the stroke, use is made of a wedge-cam and an over-the-center spring arrangement whereby the remaining portion of the reversing stroke is brought about by the action or a spring. The wedge-cam is secured to the valve extension 2', Figs. 2 and-8, and is indicated at H2, and the spring at H2 (Fig. 8) contained in a housing attached to the cylinder 34. The spring acts through a plunger I II on one side or the other of the wedge-cam H2, whereby the valve is shifted in a manner well known to those acquainted with this art.

Fluid is conveyed to the'cylinder 34 by means of conduit 38, the fluid being admitted to the cylinder through ports 4| and 42 respectively, in the forward and rear ends of the cylinder heads of the cylinder 34 under the control of hydraulic valve control mechanism in a manner later to be described.

The grinding wheel spindle 25 is rotated by means of an electric motor shown conventionally in Fig. 1, 44 representing the field ring and 45 representing the rotor of this motor, the rotor being secured directly to the spindle.

The fluid under pressure is supplied to the hydraulic valve control mechanism by means of a pump 46 driven by a small electric motor (not shown). A conduit 48 connected to the suction side of the pump 46 conveys fluid from a receptacle 49, the suction end of the conduit 48 being submerged below the fluid level of the fluid which is stored in the receptacle. To the discharge side of the pump is connected a pipe ill which leads to the valve control mechanism [3; interposed in this pipe is a pressure regulating and relief device shown conventionally at 5| whereby the pressure is regulated.

Valve control mechanism The manner in which the work-holder 4 is started, stopped, automatically reversed at the ends of the desired stroke follows a customary practice. The supply of fluid to either end of the work-holder fluid motor is under the direct control of a master piston valve which itself is under the control of the previously mentioned pilot valve 23 (center, Fig. 8). It is preferable to interpose a stopping, starting and throttling valve 58 between the source of supply of the fluid and the work-holder fluid motor whereby the movements and rate of speed of the work-holder may be controlled independently of the movement of the pilot valve. The advantages of this construction are that the operator may stop the work-holder at any point desired and resume operations in either direction at the same or changed rate of speed. The pilot valve 23 also controls the successive intermittent movements of the tool-head whereby when the work-holder movement is stopped no movement of the toolhead may be made except by a separate control means, there being a distinct advantage in this provision, as in case if the stopping of the workholder is for the purpose of making measurements on the work, continued motion of the toolhead at this time might be a source of danger to the operator. The master valve is given a reciprocatory movement so as to supply fluid to one end and allow the exhaust of the fluid from the other end of the work-holder fluid motor.

Referring to Fig. 8, center portion, the master valve is indicated at 53. It consists of a series of lands or piston portions integrally attached to a cylindrical rod and is closely fitted in a comparatively long bore 51 in the lower portion of the hydraulic valve control body l3. Fluid is fed to the throttle valve 58 from a port 55, thence downwardly through a port 55' which leads directly into the bore 51. The stop and throttle valve 58 of the plug type is horizontally positioned in the valve body ll, intersecting the port 55', whereby the fluid may be entirely cut of! and prevented from reaching the master valve 53. A lever 94 is attached to the cylindrical extension of the throttle valve 58 by which this valve is actuated.

Referring to Fig. 8, in the plug type valve 58 a suitable notch 59 is machined in one side of the valve body in alignment with the port 55' so that when the throttle valve 88 is rotated, in the present case through a one-quarter turn, the full capacity or the port it is presented for a flow or fluid to the master valve bore 51.

as a free piston, and is provided at its central portion with the land Bl (Fig. 8). In this view the land Bil is in position to permit a flow of fluid from the port II to the conduit l2 leading to the left-hand end of the work-holder motor cylinder 5 with the obvious result that the workholder will move to the right. As the workholder moves in this direction, the right end of the cylinder is opened to exhaust by providing that the flow of fluid is reversed through the conduit ii and is discharged to the storage tank 49 through a port 82 which will be noticed leading directly from the master valve bore into a cored exhaust passage 83 which is positioned in parallel relation to the master valve bore 51. Fluid from the exhaust port it is eventually returned through a conduit N, then through a mechanically operated hydraulic device indicated in general at 253 (right central portion, Fig. 8) designed to reduce work-holder speed as this member is approaching the loading position during the automatic grinding cycle, then through a conduit II to the tank 48. A description of the retarding device appears later.

The position of the master valve as shown in Fig. 8 is a result of fluid pressure existing at this time in the extreme left end of the master valve bore 51. This pressure acts against the land ll of the master valve and therefore moves the valve to the right end of the bore. The fluid which caused the movement is supplied under the control of the pilot valve in the following manner: Fluid pressure from the port I58 enters the pilot valve bore 85 between, at this time, the central enlarged land Ill and left-hand land I! of the pilot valve. Two ports lead from this portion of the bore; the function of one of these ports 69' being explained hereafter. The other port I2 leads to the left end of the master valve bore 51, while at ll is shown an exhaust port, at present blocked by the land II. The fluid flows into the downwardly positioned port 12 into the master valve bore 51 to move the master valve 53 to the right.

So long as the master valve is in this position, fluid will flow into the left end of the workholder fluid motor cylinder 5 and cause the workholder to move to the right. When the dog I on the work-holder strikes the lug IS, the resulting pivotal movement of the reversing lever ll moves the pilot valve to the left and as the pilot valve controls the master valve, the master valve is moved to the right, which movement reverses the work-holder movement. The manner in which the master valve is moved to the left is identical with that already described for the master valve movement to the right. In Fig. 8 the pilot valve is at its extreme right hand position, this being the result of a previous workholder reversal. 0n the movement of the pilot valve to the left, fluid pressure is diverted from the port 56 to a pair of

ports

81 and 88. One of these ports 81 corresponds to the port 68' at the left end of the pilot valve bore, its purpose appearing later. The other port Bl leads downwardly and fluid flowing therethrough flows through an external conduit 243 and eventually arrives at the extreme right end of the master valve bore but in so doing the fluid passes through an electro-hydraulic blocking device 89 (right center, Fig. 8) to be described fully later, and from the blocking device 88 through a second external conduit 2 to the right end of the master valve bore 51. Simultaneously, with the downward flow just described, the fluid at the extreme left end of the master valve bore displaced by the movement of the master valve is flowing to exhaust in reverse flow through the port 12 into the pilot valve bore. With the pilot valve at its left position as seen in the figure, the ports 68' and I! are in communication with the exhaust port II which leads to the exhaust conduit 84.

Continued movement of the work-holder l to the left follows until the dog I! strikes the lug ll of the work-holder reverse lever is. This restores the pilot valve 23 to the right-hand position as seen in Fig. 8, with the results described. This movement also connects the extreme right end of the master valve bore to exhaust, permitting fluid therefrom to flow in reverse order through the conduit 24!, the blocking device 89, conduit 2, and port 88 into the pilot valve bore 66 and thence through the downwardly extending port Bi which communicates with the previously mentioned exhaust port Bi, and thence to the main exhaust conduit 84.

Tool-holder motor The motor which operates the toolholder receives a regulated quantity of fluid at each reversal of the work-holder'and is supplied with fluid from the same source as the work-holder motor. This is accomplished by providing an admission valve for the tool-holder motor which is operated by the fluid and at a speed in proportion to the pressure of the fluid so that upon a lower pressure a longer time interval is allowed to admit the fluid to the tool-holder motor, while at a greater pressure of the fluid a shorter time interval is allowed to admit the fluid to the toolholder motor, thus insuring the admission of a substantially uniform quantity of fluid to the tool-holder motor upon each reversal of the work-holder.

The fluid necessary to move the tool-holder is taken from the common supply, i. e., from the port 58 in the valve body l3, and is delivered to the tool-holder fluid motor cylinder after passing a manually operated tool-holder throttle valve I01 and a fluid-operated admission valve III, which like the master valve 53 is in the nature of a free-piston.

The throttle valve iill is manually adjusted by means of the hand lever I01 to govern the extent of the intermittent movements by regulating the amount of fluid supplied to the tool holder cylinder 3|, while the valve I02 controls the timing of the tool-holder intermittent movements.

The valve N32 is a cylindrical reciprocating valve closely fltted in a horizontal bore ifll (Fig. 8) which intersects a port llil which conveys fluid from the port 56. The port MI is normally closed by either one of the solid portions of the valve I02, and thereby prevents movement of the tool-holder during grinding operations except at the ends of the work-holder strokes when the grinding wheel is clear of the work.

The reciprocatory movement of the valve I02 is merely a longitudinal shifting in its bore IIII under the impulse of fluid pressure admitted alternately to the ends of the bore Ill, conveyed thereto. on the one hand, from the port 80, and on the other, from the port ll. Therefore the right end of the valve ill! is exposed to pressure conveyed from the right end of the pilot valve bore 68, while the left end is acted upon by fluid conveyed from the left end of the pilot valve bore Ii. so that as the pilot valve is shifted at workholder reversals, so also is the valve I02 given a single movement from-one end to the other of its stroke for each movement of the pilot valve.

It was stated that the port IIII is normally closed by the valve I02. To allow admission of fluid through this port Ill whereby the toolholder is moved at the proper time, the valve II! is provided at its central portion with a fluid supply opening in the nature of a narrow circumierential groove Ilil. During the space of time that the groove IIM is passing the ends of the port III, a charge of fluid is permitted to pass through the port III, and after the valve passes to the opposite end of the bore Ill3, this port IflI is again closed by one of the solid portions of the valve. The quantity of fluid so admitted is small because it is necessary only to overcome the friction oi the tool-holder and to force a similar small quantity from the opposite side of the toolholder motor piston. For this reason, the groove I" is narrow, and the valve I02 admits only the fluid that is able to pass therethrough during the short space of time that elapses while the groove Ill is passing the port IIII.

In Fig. Bthe position of the tool-holder reversing valve II is such that the intermittent movement of the toolholder is being made rearwardly or to the left in the view, inasmuch as fluid pressure being delivered to the valve chamber from the supply conduit 39 is diverted by the valve is into the port ll leading to the forward end 01' the cylinder 34. Fluid displaced from the opposite and flows in reverse through the port 42 again into the valve chamber, thence into an open port 40' in communication with the toolholder exhaust conduit 40.

When the tool-holder is to be reversed so that the intermittent movements are to be made in a forward direction or to the right in the view, the reversing valve is longitudinally shifted forwardly either by contact of the Stroke-limiting dog I" with the rock-shaft lever or by manual means, whereby the fluid pressure is directed by the new position of the valve into the rear or left end of the cylinder ll by way of the port I, while the path for fluid-displaced from the forward end of the cylinder at this time is seen to be through the port II and into the exhaust conduit I. through the short port Iii". It is obvious that one or the other of the companion ports ll or ill" will be closed by the reversing valve 34 according to the position of the valve.

In the operation of the machine constructed according to the description just given which corresponds to that of the patent mentioned, the grinding wheel is preferably placed near an edge of the work-piece, and is fed intermittently across the work as the work-table is reciprocated.

When the grinding wheel has removed all of the stock at this elevation of the wheel, the wheel is lowered manually. When the work-piece is finished and removed, the operator manually elevates the grinding wheel for a start on the next piece.

Automatic control devices By the improvements to be nowdescribcd, it is provided that at each reversal of the tool-holder;

yet of the work-holder reciprocations or the accompanylng traversing intermittent movements of the tool-holder.

One purp se of allowing the machine to continue to run without down-feeding oi the toolsupport is to provide a smoothing or finishing operation on the work-piece which automatically follow the down-feeding period. The smoothing operation may be known as the spark-out time, since evidence is given by lack of sparks from the grinding wheel that the smoothing operation is completed. The length of time the finishing or smoothing operation is allowed to continue is variable at will, and it is further provided in the improved machine that at the conclusion of the spark-out time, the work-holder is caused automatically to move to a loading position. The loading position is usually located at a far point on the base at some distance from the grinding wheel in order to further insure the safety of the operator, and after the work-holder comes to a stop, the tool-support is automatically elevated to a precise predetermined height.

Mechanical features of automatic down-feed and elevation for tool-support The description that follows relates to the devices which are added to the machine constructed according to the specifications set out in the patent mentioned whereby the present improved machine is obtained.

It was previously mentioned that a housing containing certain devices pertaining to the new construction was located on the forward wall of the base I. This housing is indicated at I. The housing has a central opening through which the cross-shaft 22 of the tool-support elevating mechanism projects, on the outer end of which shaft the elevation hand-wheel 22' is secured.

On the portion of the cross-shaft I! (Fig. 2) within the housing III is secured a pair of ratchet wheels I" and I", with which pawls cooperate. In the present instance, two pawls oflset in relation to each other are used for each ratchet wheel, the pawls I45 and Ill (Figs. 5, 6 and 7) cooperating with the ratchet wheel I, while the pawls I" and I coact with the ratchet wheel I. flhe pawls I" and I" are pivotally connected with a pawl arm I, known as the down-feed pawl arm, rctata'bly carried on the hub I50 of the ratchet wheel I, while the pawls I" and I" are similarly pivotally connected with a pawl arm Iii, called the elevating pawl arm, rotatably supported on the hub I82 of the ratchet wheel I. Since the pawls are located below their respective ratchet wheels, it is preferable that the pawls are spring-pressed into engagement with the ratchet wheels, compression springs such as are indicated at I" being employed for the purpose.

The ratchet wheels and therefore the crossshaft are alternately given partial rotation by hydraulic fluid motors, liquid pressure such as oil being preferred for, among other reasons, an inherent smoothness of action. The valves for these fluid motors are electrically controlled and actuated as will be brought out in the description, use being made of certain now available accurately performing switches. It will also be made clear that but one of the ratchet wheels is actuated at a time, and that each returns to a normal position wherein no interference to manual operation can be offered.

To transmit the motion of the fluid motors to 78 the elevating mechanism the lower end of each pawl arm is provided with a. segment of gear teeth. Referring to the down-feed pawl arm I49 the gear tooth segmental portion is shown at I54, meshing with which is a hydraulic piston I55 in the upper portion of which rack teeth I55 are out. In itsinitial stage of manufacture the piston I55 is a cylindrical rod having the rack teeth machined in its upper surface as explained. As such, the piston comprises a portion 01' a fluid motor, the cylinder for which is located in the lower portion of the housing I40 and is indicated at I51, asbestseen inFigs. 5, 6 and 8.

The elevation; pawl arm I5I-ls also provided with a segment of gear teeth as shown at I58, meshing with which teeth is a second rack piston II! of another fluid motor located in the housing I. The cylinder bore of this second fluid. motor is indicated at Ill and as seen in Figs. 5 and 6 is located in a parallel position with reference to the fluid motor I51.

The hydraulic pressure by which the fluid motors perform their respective functions is derived from the main fluid pressure system through a conduit Iii, Fig. 8, being branched oil the main conduit III leading from the relief valve 5|. conduit III further branches forming a pair of conduits, one, at I62 carrying fluid pressure to a control valve indicated in general at I53, while the second of these branches I84 leads to a second control valve also indicated in general at I65.

In Fig. '1 it is seen that the rack pistons I55 and I5! are disposed in parallel relation with each other; as are also the rack arms and ratchet wheels; however, in Fig. 8 these parts are, placed side by side in order to more clearly show their functions.

The purpose of the control valves is to control the flow of fluid pressure to and from the downfeeding and elevating fluid motors. The movable parts of the valves are actuated by electrical means and the fore part of the following descrip tion will deal first with the mechanical and hydraulic features pertaining to these valves, the :18e ption of the electrical portions being made Referring to the control valve indicated at I", the movable part thereof consists of a piston type valve I" which has enlarged lands or spools at each end and a narrower land at the. central portion.

The conduit 18! delivers fluid pressure to the central portion oi the bore I61 in which the movable valve Ili is fitted, and as seen in Fig. 8. the piston valve I is positioned in the left end of its bore, whereby any fluid pressure entering passes to the right of the central land to a port I" in the opposite side of the bore. This port I" communicates by means of the conduit I69 with the right end of the bore I51 of the downfeedlng fluid motor containing the rack piston valve I55, the fluid reaching this end by passing through the internal passage I590 in the housing I48 (Figs. 5 and 8). This position of the control valve I55 is maintained ,as a normal position, the valve being returned and retained there by a compression spring I10 located at the right end of the piston valve. By this position of the piston valve, the rack piston 155 is held at the left end of its travel, which position is the normal position 01 the rack piston.

The control valve 185 is identical with the valve Just described. Its piston valve, indicated at "I, is maintained at the right end of its bore as a normal position by the compression spring I12, in which position fluid pressure flows to the left of The* the central land through the conduit I13 and internal port I15a in the housing I" (Figs. 7 and 8) to the left end of the second, or elevating fluid motor containing the rack piston I59 and at this normal position of the piston valve ill the rack piston is retained in the right end of its bore as its normal position.

The purpose of causing the control valves and rack pistons to return to these normal positions as described is to permit when desired of the manual handling of the machine at which time the tool-support may be elevated or lowered manually, whereby it is possible to change over from a machine which is operated in every respect as was the machine as described in the patent mentioned to the automatic machine of the present application with no more than the mere closing of an electric switch.

In order to permit manual elevation and lower- I ing of the tool-support, the pawls connected with the pawl arms are disengaged from contact with the ratchetwheels. The means for causing this disengagement is the use of curved pawl-withdrawing shields encompassing a part of the lower portion of the ratchet wheels. Referring to the first of these shields, there is one seen at I14 (Figs. 5, 6, 7 and 8) secured to a lug I15 on the interior wall of the housing I". The shield is cut away as shown at I18 (Fig. 7) to accommodate the oflset pawls, but each of the pair 01' pawls I45 and I48 is disengaged at the same time which occurs when the rack piston returns to its normal position.

The other shield is shown at I11 in Fig. '1. This shield is secured to the lug I18 similar to the lug I15 and the shield covers a portion of the ratchet wheel I44, whereby on the return movement of the pawl arm I5] due to the return of the control valve "I to its normal position withdraws the pawls I41 and I48 out of engagement with the elevating ratchet wheel 141. Like the shield I14, the shield I11 is cut away at I11 whereby each pawl I41 and I48 leaves the ratchet wheel I44 at the same time.

Electrical features of down-feed of tool-support The parts just described constitute the mechanical and hydraulic lowering and elevating means, the actuation of which is dependent on electric switching arrangements such as will now be described.

It will be observed that the diilerence between the ratchet wheels I45 and I44 is merely that the ratchet teeth point in opposite directions, thus, with an angular partial rotation of the pawl arm I43 from its normal position as seen in Fig. 5, the pawls I45 and I46 will slip oil the shield I14 into engagement with the ratchet teeth and turn that wheel I43 in an anti-clock-wise direction. It will be understood that since the elevating ratchet wheel I44 is also keyed to the cross-shaft I that this ratchet wheel also at this time turns in an anti-clock-wise direction, but with no eilect since the pawls I41 and I48 are kept from contact with the ratchet wheel I 44 by riding on their shield.

In the present machine, clock-wise rotation of the hand wheel I42, whether by manual or autotro-hydraulic means, the rack piston I55 is moved to the right, importing a partial rotation to the rack arm I49 in an anti-clock-wise direction.

The automatic elevation, the control for which will be fully described later, is eilected by a movement of the rack piston I", which causes the pawls H1 and ill to slip oil the disengaging shield II'I to engage the teeth of the ratchet wheel I to impart to this. ratchet wheel a partial rotation in a clock-wise direction.

As before stated, the control valve I83 controls the movement of the rack piston I". The means for actuating the control valve itself consists of electrical equipment including a solenoid to move the valve. a time relay to provide a variable time lapse and a switch to energize the time relay and with it, the solenoid.

The automatic down-feeding movement of the tool-support is timed to occur when a complete traverse of the grinding wheel across the workpiece has been made, and before the grinding wheel starts on the following traversing movement. The shifting of the tool-holder reversing valve ll when the reverse of the tool-holder is made provides a means for bringing about the energization oi. the electrical portions oi the down-feed arrangements.

In that part of Fig. 8 in which electrical circuits are shown, the circuits consist of suitable pilot current and power current circuits. The pilot The following down-feed is due to occur at the next following tool-holder reversal, during which event the cam will approach, actuate and pass by the switch. It will likely, also, be evident, however, that momentary closing of the switch III will provide an energization of the solenoid ill of such short time duration that the hydraulic mem bers oi the down-feed arrangement will have insufficient time in which to carry out the functions circuits are shown in light lines, while the heavier lines indicate power circuits. The power circuits are preferably employed incarrying current to and from the electro-magnets to be described.

On the valve stem extension 26 of the toolholder reversing valve ll there is secured a cam ill which closes a switch llil during the reversing reciprocations of the tool-holder valve. The switch "I is a single-pole, single-throw switch and as seen is only momentarily closed, the movable member of which is a spring arm so that the switch opens immediately after the passage of the cam I" thereby, and with the rod as shown. the switch I" is actuated for each movement of the valve 34' whether the valve is moved forwardly 0r rearwardly.

The closing of the switch ill results in a flow of pilot current indirectly to a down-feed electromagnet in the form in the present case of a solenoid ill (lower left portion, Fig. 8) the movable armature of which is connected to an outer extension of the down-feed control valve I", whereby the energization of this solenoid results in a shift of the valve I to the right. This movement then results in a flow of fluid pressure to the left end of the down-feed rack piston I" to bring about a down-feed of the tool-support ll, as described.

The movement of the valve I" by reason of the energization of the solenoid III is made against the compression of the valve return spring ill, therefore, when the solenoid III is deenergized, the spring I'll returns the valve and the connected solenoid armature to the normal position agithe left end of the cylinder of the valve body flow to the down-feed rack piston I" and causes it to move to its normal position at the left end of its travel. As before mentioned, at this position the pawls "I and I" are disengaged from the ratchet wheel I, so that if the operator should desire, he may manually operate the elevation mechanism without interference by the pawls.

In explanation of the statement tha the downfeed switch III is closed only momentarily, it should be made clear that the reason for this feature is that in order to be effective for the next following down-feed in automatic cycle grinding operations, the switch should be normally open.

This return of the valve reverses the fluid I for which they are intended. Consequently an electrical timer relay device is interposed between the down-feed switch I" and the solenoid I" such thatwiil prolong the energization of the solenoid Iii for a suitably long period of time.

Before the description of the timer relay is made, an explanation of another switch which acts in conjunction with the down-feed switch its will be brought in. The switch in question acts to terminate the down-feeding portion of the automatic grinding cycle, and further starts the machine on that portion of the cycle previously mentioned as the smoothing or spark-out operation.

0n the vertical slide Ii which carries the toolholder there is secured an adjustable dog having a means for obtaining the precise adjustment in keeping with the accuracy of which the machine is capable. The dog (Figs. 4 and 8) consists of a body II! which is secured to a T -slot bar i which in turn is secured to the vertical slide if,

by the use of which T-slot bar the dog is readily adjustable so as to suit different working conditions. For the more precise adjustments mentioned, there is secured to the T-slot bar I above the dog I" an anchor block I". The switch contacting dog I82 and the anchor block III are connected together by a screw I86 preferably of a micrometer type, the screw being provided with a comparatively fine thread and graduated indic'ia on an enlargement of the screw. By loosening the T-bolts I" and ill. both dog and anchor block may be shifted to any position on the T-slot bar Ill as a unit, while the precise adjustment may be made by tightening the anchor block and moving the contacting dog ill by means of the micrometer screw.

The contacting dog I82 operates the movable element I89, Fig. 8, of a single-pole, double-throw switch I mounted on the column 33, Figs. 1. 2 and 4. The movable member I89 is springpressed so as to be maintained normally closed against the stationary contact "I: that is, the

7 right side of this single-pole double throw switch is normally closed. As the vertical support 3! descends during the down-feeding portion of the automatic cycle, the contacting dog eventually makes contact-with a cam lever ll! pivotally mounted on a bracket ill secured to the column I! in such positionthat a plunger ill transmits the motion received from the dog I82 to the movable switch member I89. Should the vertical support or slide ll be lowered, as during manual operation. of the machine, below the cam lever I82. the contacting portion of the dog it! will lift and rotate partially the cam lever when the slide is again elevated, the lever returning by gravity to its normal position as seen in the diagram.

side of the switch I90 are in series, which allows that the tool-support will be intermittently lowered and the grinding wheel will remove stock from the work-piece, so long as the dog I82 is apart from the cam lever I92, for at each reversal of the tool-holder pilot current will flow to the down-feed switch I from the still closed right side of the switch I then through the conductor 200 to the timer relay indicated in general at 20I (Fig. 8 only).

The timer relay is so-called since on application of current to it by the closing of a momentarily operated switch as is the case here, its relay switch 209 may be maintained in an opened or closed condition as desired for a variable length of time, though the electrical impulse that caused the actuation of the relay switch has been cut oil by the opening of the switch I80. The means for providing the delay is on the order of a dashpot in which there is fitted a piston, the piston rod or which actuates the relay switch.

The dash-pot cylinder is indicated at 202, the piston at 209 and the preferably non-ferrous piston rod at 204. The piston is normally retained in the lower portion of the cylinder by a compression spring 205, a. boss 208 on the lower side of the piston acting as a stop to imit the downward movement 01' the piston. To raise the piston 203 by the closing of the down-feed switch I00, the pilot current flows from the conductor 200 through an electro-magnet in the form in the present case of a solenoid coil 201 surrounding the piston rod, a portion 208 of which rod is I or magnetic material such as iron serving as an armature whereby the magnetism set up by this energization of the coil will attract the armature to lift the piston 202. Although this coil 201 is known as a holding coil when speaking of relays in general, it should be understood that its energization is momentary only, and that the coil does not holdthe movable parts of the relay. The return of pilot current to the supply switch I is through the conductor 201'.

The upward movement of the piston and other movable parts occurs suddenly on the single momentary impulse delivered to the coil 201 by the closure of the down-feed switch I00, which as explained before immediately opens and the coil is also immediately de-energilted. But the energization is sufllcient to cause elevation oi the movable members of the relay which then start to descend. As soon as the upstroke is the switch by reason of the greater "strength of the dash-pot spring 205.

The upward movement of the piston carries the arm 2I2 to an elevation as shown in broken lines which is somewhat above the point were the movable member 2 of the switch will stop when it makes contact with the stationary part 2Il oi the switch, a limit for the upward movement being provided in the form of a boss on the upper side of the dash-pot piston 202.

It was stated that the upward movement of the piston and connected movable parts of the relay was made suddenly. It will be explained that a rapidly made upward movement is not essential to the proper operation of this timer relay, but is only incidental. The time lapse is measured from the time the relay switch 289 is alowed to close by relieving the pressure of the arm 2 I 2 on the switch to the time when the switch is again opened by the descending arm and to provide the time lapse, the descent is made at a relatively slow rate as desired. As is usual with dash-pot arrangements, one stroke may be made at a rapid rate, while the other may be made at a slower rate. In the present case, displacement of some medium such as air at an adjustable relatively slower rate provides for the slower descent.

On the up-stroke, the air displaced from the upper portion of the dash-pot cylinder 282 flows to the lower part of the cylinder, where at this time suction is occurring. Two passages are provided for the transfer of this displaced air, one passage being shown on the right side of the dashpot cylinder through an externally positioned non-return check valve 2, and another e shown at the left side of the cylinder as indicated at 2l5. The check valve offers little resistance to the downward flow of the displaced air, but prevents return therethrough, whereby such air must return to the upper portion of the cylinder on the down-stroke of the piston through the passage 2I5. To impart a. desired variable descent rate. a needle valve M8 is interposed in the passage 2I5, whereby the flow of diwlaced air started a relay switch 209 previously mentioned as receiving pilot current from the conductor I91 is allowed to close. This relay switch 209 is a single-pole, singlethrow switch, and although it would ordinarily be classed as a normally closed switch in view of the action of the spring 2I0 on the movable member 2" of the is subject to the restriction offered by the manner in which the needle valve is adjusted.

The closing of the relay switch 209 on the upward stroke of the relay parts allows Pilot current to flow through a conductor 2" to an electro-magnet in the form of a Power contactor 2|. (lower central part of Fig. 8) adapted. to handle the heavier power current taken from the power main 2I9 leading from the power current switch 220 (upper right portion, Fig. 8). The return of pilot current from the contactor 2I8 is shown at 22I, this conductor leading to the pilot current supply switch I95.

The energization of the power oontactor 2I8 permits power current to flow through a conductor 222 to the previously mentioned solenoid "I (left lower portion, Fig. 8) a conductor 220 forming the other part of this circuit and bei in connection with the power main switch 228.

Energization oi the solenoid III, which may be termed the down-feed solenoid, brings about a lowering or down-feed of the tool-support as mentioned before, inasmuch as the down teed control valve I88 is shifted and fluid pressure then flows to the left end of the down-feed rack-piston I55 through the conduit I89 and internal port I89b causing an anti-clockwise partial rotation of the ratchet wheel Ill.

It can be seen that momentary energization only of the down-feed solenoid III, as would be a'avacos the case had the simple switch I been employed without the added timer relay, the operation of the valve moving solenoid I8I would have been interfered with, likely to the extent that the pawls would not move so far as to engage the teeth of their ratchet wheel. With the timer relay, however, a suflicient time lapse is given to insure that the down-teed mechanism may make its full intended stroke of whatever length desired within the capacity of the mechanism, and during this time, the machine is continuing in its automatic grinding cycle.

While the timer relay 20I is maintaining energization of the down-feed solenoid III, the control valve I86 is being retained at the right end 01 its stroke against the compression of the valve spring I10. It is evident that the valve must be returned to its normal position before another down-feed stroke can be made, consequently the solenoid must be tie-energized. This is brought about when the timer relay arm 2I2 descends sufllciently to open the relay switch 209, and the needle valve 2I6 may be so set as to allow the opening of this relay switch 2I I as soon as it is certain that the down-feed rack piston I55 has made its full intended stroke. In practice, the time lapse is of less than a. minute in duration, being measured rather in seconds than otherwise. 7

Following the opening of the relay switch 2| I, de-energization of the down-feed solenoid occurs, the valve spring I10 forces the control valve I65 to the left to thereby return the rack piston I55 to the left, withdrawing the pawls from engagement with the down-feed ratchet wheel I43.

The distance the tool-support may be automatically lowered is variable, the adjustment for which is provided by a screw 225, Figs. 5 and 6. As seen in these figures in connection with Fig. 7, the screw 225 is positioned in the path of the rack arm I49 whereby the angular stroke of this member may be varied from a full stroke as offered by the full travel of the rack piston I55 to the right, in which event the screw is backed out sufilciently to permit this full stroke, to a partial stroke, such as is shown in Fig. 6, wherein the screw 225 is shown turned in to stop the rack arm I49 before the full stroke is made. It will be understood that the down-feed stroke, whatever the adjusted length may be, is always made from the normal position of the rack arm and piston I55 at the left of its travel as seen in Fig. 5 wherein the pawls are shown disengaged from the ratchet wheel.

When the tool support SI has been automatioally lowered the predetermined distance (upper right portion, Fig. 8) the dog I02 on the support makes contact with and actuates the cam lever I92 to break the circuit that controls the downi'eed devices for the support by moving the movable contact member IIQ of the switch I90 out. of contact with the member IBI.

Smoothing out 0! work The cam lever by its movement also shifts the movable member I00 of the switch I00 in contact with the stationary member 226 of the switch I00 and thereby closes anothercircuit whereby another sequence in the automatic grinding cycle is started. this being the smoothing or "sparkout" operation previously referred to. Thisis ll w d by the automatic return of the workholder to the loading position, and the elevation of the vertical slide to the proper height for a. start for automatic grinding on the next workpiece.

The closing of the left side of switch I starts a second timer relay 229 which controls, the movements of the work-holder to loading position and the elevation 01' the tool support and also by reason of a slow closing thereof allows for a smoothing out period. This relay 220 is of slightly different construction from the timer relay 20I since it is not employed for the purpose of permitting a time lapse during which a fluid motor may make a stroke, but to provide a variable time period for the smoothing or spark-out time before the reciprocation of the work-holder is ended and the work-holder moved to load position. v

When the left side of the switch I90 is closed, pilot current flows through a conductor 226' to the electromagnet in the term in the present case of a solenoid coil 22! of the second timer relay (center right portion, Fig. 8 only) indicated in general at 220 to be known as the smoothing or spark-out timer relay. The energization of this coll results in the elevation of a rod 230 having an armature portion 220' which further results in the relatively sudden lowering of the forked left side 23I of a pivoted doublearmed rocking lever 202, to which the rod is pivotally connected. This movement of the lever 232 is accomplished against the tension of the spring 200, so that when the coil 220 is deenergired, the lever and armature are returned to their normal position as seen in Fig. 8.

Through the use of the spring 223 in so retaining the lever 232, the piston rod 220 and piston 235 of this timer relay 220 are held in their normal upper position in the relay against the compression of the spring 228, this spring being preterably relatively weak as compared to the lever spring 200. At the upper end of the piston rod is a laterally projecting arm 231 in position to make contact with the relay switch indicated in general at 238. This switch has a movable, springoperated contact element 230 having a projecting extended end positioned so as to be depressed by the arm 23] when the same is lowered by the spring 238 on energization of the solenoid coil 220.

The descent of the movable portions of this timer relay, by which is meant the piston and piston rod, is made at a suitabLv slow rate such that will provide the desired time for the smoothing or spark-out operation. The duration of time allowed for the spark-out operation is that time taken up during the downward approach of the arm 201 toward the relay switch 230, and when the arm makes contact with the movable switch member 239 and forces this member in contact with the stationary element of the relay switch 230 to close this switch, this closing marks the end of the spark-out time, following which the work-holder will be removed to the loading position.

Portions oi the timer relay Just described are much like those described in connection with the explanation of the first mentioned down-feed timer relay "I, the similarity being in the manner in which the displaced air is metered in its flow from opposite ends of the dash-pot cylinder. The regulation of the rate of descent is eiiected by the adjustment or a needle valve 200 which is employed to suitably restrict the iiow or air from the lower to the upper end of the cylinder 2. A non-return check valve 202 is employed to allow tree flow of displaced air from the upper to the lower end of the cylinder and to prevent a reverse flow therethrough, forcing the displaced air to pass by the needle valve 2". The same comment as to it not being essential that the timer relay should move at a rapid rate on its idle stroke made in connection with the description of the down-feed timer relay 2" applies to this second timer relay 228.

Before going into the explanation of what follows when the relay switch 23! of the spark-out timer relay 22! is closed, it will be explained that the spark-out timer coil 228 remains energized during the spark-out time in order to delay the opening of the contacts of this relay, since, to properly carry out the smoothing or spark-out operation, it is necessary that the grinding wheel remain at the desired low point it reached when the left side of the double-throw switch I was closed. It will be further evident that during the spark-out operation, no down-feeding is to be made, and such is not made, although the down-feed switch I" is being repeatedly closed at each reversal of the tool-holder traversing movements; but, since the right side of the double-throw switch I" which is in series with the down-feed switch I was opened when the grinding wheel reached the adjusted depth, no further down-feeding is possible because the circuit which controls the power relay 2|! is now broken.

Return of work-holder to loading position At the conclusion of the spark-out operation which occurs whenthe spark-out relay switch 238 is closed, reciprocation of the work-holder is arrested and the work-holder is automatically returned to the loading position, a portion of which return stroke is made at a reduced rate of movement and also the tool support II is elevated to the upper starting point.

In reference to the description of the manner in which the work-holder is returned tc the loading position it will be pointed out that in the routine grinding operation, whether after the manner as described in connection with a machine constructed according to the patent mentioned or according to the design of the present application, that the range of reciprotions of the work-holder is normally confined to a portion of the machine by the spacing of the work-holder reversing dogs I and I5. To move the work-holder automatically to a portion of the base that may be outside the normal grinding stroke as set by these dogs means that one of the reversing dogs must be rendered temporarily ineflective to cause a work-holder reverse]. Of several methods that may be available, the following is preferred as it lends itself to automatic operation of the machine and does not involve a readjustmentof one of the reversirig dogs for this purpose.

In the present case, the loading position is at the right hand end of the base of the machine, and this means that the left hand dog II is the one which is to be made ineffective to allow the work-holder to move to the loading position. It is this dog It which indirectly will cause a shifting of the master valve 53 when the workholder is moving toward the right and the dog strikes and rocks the reverse lever It, but, to allow the work-holder to moveon by the point where it would ordinarily be reversed, the master valve is not shifted although the pilot valve 23 is shifted as usual.

By the devices to be described the master valve 53 is not shifted by the left hand dog ll at this time because the fluid pressure under control of the pilot valve 23 which ordinarily would bring about a shift is now temporarily blocked from reaching the master valve. The blocking means was previously referred to in connection with explaining the manner in which the master valve 53 is shifted under the normal control or the pilot valve 23, where it was stated that fluid pressure flowing through the passage 88 eventually to arrive at the right hand end of the master valve bore is conveyed externally through the external conduit 243 in communication with the port 88 to the blocking device indicated at I! (right central portion, Fig. 8) and from this device through the conduit 245 to the right end of th master valve bore.

The blocking device 89 is in the present case a solenoid operated hydraulic valve, the solenoid being indicated at 246. The movable part is in the form of a grooved piston valve connected to the solenoid, the valve being springreturned in order that it and the armature oi the solenoid may be restored to the normal position when the solenoid is deenergized. The

valve is shown at 241, the groove mentioned being indicated at 248, while the spring is seen at 249. The effect of the spring is to maintain the valve normally so that the circumferential groove 2 is in registry with the port openings in communication with the

external conduits

243 and 5 whereby a free flow of fluid pressure is permitted to pass to the right end of the master valve except at the time when the workholder is to be moved to the loading position.

As stated, this movement is under the control of th spark-out timer relay switch 238 which in turn is controlled by switch I90. When this switch 238 is closed as dscribed at the end of the grinding and smoothing or spark-out operations, pilot current taken from a. continuation of the conductor I91 flows through a conductor III which leads to and energizes a power contactor relay 250 (lower right portion, Fig. 8), which in turn allows power current taken from the the power main conductor 2i! through a conductor 2! to energize the blocking valve solenoid 246, the return flow conductor for the pilot current being shown at 250, and for the power current at 252. The effect of energizing the blocking solenoid 24B'is to depress the valve 2" to place the circumferential groove out of registry whereby the fluid pressure flow from the pilot valve is blocked. This obviously prevents a movement of the master valve such as ordinarily occurs when the pilot valve 23 is shifted and therefore the work-holder continues on its stroke to the right and moves to the loading position at the right.

It should be explained that the dogs II and I! are offset with relation to one another as are likewise the lugs l5 and I1 so that the lug II will stand in the path of the dog 04 and the lug ll will stand in the path of the dog l5. When the work-holder is moved to loading position the dog it striking the lug l6 will throw the lever to the right and the dog will then ride over the lug as the work-holder moves to its loading position. Upon the return movement of the work table the dog M will ride over the lug l8 and pass at one side of the lug i1 and the dog II will ride at one side of the. lug ii and strike the lug I! to again shift the pilot valve.

In the explanation of the method by which the master valve movement was blocked by the energization of the blocking solenoid 248, it must also be brought out how this solenoid is dee ergized, mention of this part the explanation being made at this point in order to make it clear that, while this blocking solenoid is energized by the closing of the switch 238, the opening of this same switch does not bring about de-energization of the solenoid 246, this being the function of another switch 254 which is manually actuated by the operator in re-starting the automatic cycle.

It will be remembered that with the master valve 53 in its right hand position as seen in Fig. 8, as long as the blocking solenoid is energized, the work-holder willcontinue to move toward the right until it stops at the loading position, which may be when the work-holder reaches the end of the base or the end of the cylinder of the work-holder fluid motor where it will be retained by reason of fluid pressure on the left side of the piston. It is also clear that should the blocking solenoid 248 be deenergized, the work-holder would immediately reverse itself and move to the left, the pilot valve 23 having already been shifted. It is one of the purposes of this construction to provide that the workholder be moved to the loading position and to be retained in that position for as long as the operator may desire. It is a further purpose that the tool-support 3| be automatically elevated when the work-holder reached the loading position, which elevation will open the left side of the double-throw switch I90. This in turn will cause deenergization oi the spark-out timer relay solenoid coil 22B whereby the Spring 233 will cause the opening of the relay switch 238, with deenergization of the blocking solenoid 246 and,

it not prevented, consequent immediate re-start of the work-holder. Obviously, this is not desirable inasmuch as the operator should have ample time in which to re-load the machine. Before the explanation is made of the manner in which the solenoid 245 is controlled jointly by two separate switches, a description will be made of the means whereby the speed of the work-holder is reduced as it approaches the loading position.

Speed retarding device for work-holder when moved to loading position The retarding device is a valve arrangement interposed in the work-holder fluid motor exhaust conduit. The device is indicated at 282 (right center, Fig. 8) and contains a grooved, spring-pressed piston valve 254 similar to the blocking valve 241. In the normal position of the retarding piston valve 254 as effected by the vlave spring 256, a free flow of exhaust fluid is aflorded by the registry oi the circumferential groove 25'! with ports in the cylinder wall which are in communication with the exhaust conduits l4 and '4'. It can be seen that depression of the retarding valve willreduce proportionately the speed of the work-holder. To bring about this speed reduction, a retarding cam 258 (left center, Fig. 8) is attached to the T-slot of the work-holder, in the present case, between the pair 01' work-holder reverse dogs l4 and IS.

The lower portion of the cam is formed with an oflset to pass the reverse lever II. When the work-holder moves sufliciently far toward the right, the lower upwardly sloping cam surface 2" makes contact 'with the retarding valve 254, this valve having an upward extension projecting through the upper portion of the valve cylinder 2. To provide that the depth to which the retarding valve is depressed may be adlustably regulated, the valve stem extension is fitted with a threaded tappet screw 280. As seen in the right central portion 01' Fig. 8, the retarding cam is shown in dot-dash lines in position to make contact with the tappet screw 260 to depress the valve stem and its valve 254 whereby the groove may be somewhat out of registry with the ports. A reduced flow will thereby be permitted, it not being the intention to cut oil entirely the flow of exhaust fluid.

The work-holder will continue to move at the reduced rate of speed toward the right, the retarding valve now being held at the desired depth or the horizontal under portion 258' or the cam 258 until the work-holder abuts against a stop, which may be of any nature, such as when the piston 6 of the work-holder fluid motor I reaches the right cylinder head of this fluid motor. This is a dead stop, and as was mentioned previously, the work-holder will be retained at this point by fluid pressure. It may be noted that with this method it is not necessary to alter the work-holdor speed control throttle 58, whereby the operator is further relieved of some responsibility in this connection.

At about the same time that the work-holder reaches the actual stop or loading position, a switch 262 (right central portion, Fig. 8) which may be known as the slide elevation switch, is closed by the upper portion 283 of the retarding earn 258. The slide elevating switch is a normally open switch and is in series with it normally closed manually operated switch 264 to be referred to later, known as the re-start switch. Pilot current is taken from a continuation of the conductor I81 on closing of the tool-support elevation switch 282 and passed through the restart switch 264 which is a normally closed switch, and through a conductor 288 to the coil 266 of an interlocking relay 261 (right central portion, Fig. 8). From this coil 266, the pilot current is returned to the conductor 22| leading to the pilot current supply switch I85.

One purpose of this interlocking relay 2" is to provide that the energization of the blocking solenoid 246 which was initiated by the closing of the left side of the double-throw switch Ill and which caused the movement of the work-holder to the loading position, is maintained by the interlocking relay, because as was explained, as soon as elevation of the tool-support II is permitted, the accompanying opening of the left side of the double-throw switch I would, without the use or the interlocking relay, have caused the deenergization of both the spark-out timer relay and the blocking valve solenoids 228 and 248, with the consequent immediate re-start of the work-holder, To put the re-starting under the manual control of the operator is the function of the interlocking relay.

When the coil 26! of the interlocking relay 261 is energized by the closing of the switch 242, two circuits are, established. One is a pilot current circuit that take over the energization of the blocking valve solenoid 246. Pilot current from the conductor IN is delivered to one or the contacts of the interlocking relay 261, and from a companion contact point of this relay through a short (in this showing) conductor 24! to a Junction with the previously mentioned conductor 218' leading to the power relay 2". Therefore, regardless of the position or the left side 01' the double-throw switch I or the spark-out relay switch 228, the blocking valve will be retalned in position to maintain the work-holder in the loading position.

Tool elevating device The other circuit closed by the elevation of the interlocking relay 261 is a power circuit whereby the tool support 3| is elevated. Power current is taken from the power main 2|! through a conductor 210 to the interlocking relay 281 and from this relay through a power conductor ill to an electro-magnet in the form, in the present case, of a solenoid 112, to be known as the tool-support elevation electro-magnet, which is connected with the previously referred to pilot control valve Hi. When the elevation solenoid 212 is energized the valve Ill is moved to the left, whereby a flow of fluid pressure through the conduit l1! to the port illb at the right end of the slide elevating rack piston I" is permitted, so that as this rack piston moves to the left the pawls H1 and H8 ride of! of the pawl shield ill (Fig. and engage the ratchet wheel i to thereby elevate the tool-support ll through the medium of the shaft 22, pinion 2|, gear 2! and screw 20. The rack piston I" remains at the left position until a manual operation of the switch 264 is made which will be explained later.

The elevation of the tool-support II is accomplished in a single movement in contrast with the successive, comparatively small down-feed,- ing movements, and the amount of elevation. is the sum of the down-feeding movements, therefore, the tool-support is returned to the same height as before. Inasmuch as the total amount of down-feeding is variable by the manner in which the down-feeding limiting dog I" is adjusted with respect to the double-throw switch I", the amount of elevation should be made equal to the total down-feed movement. This is provided for by the use of a stroke limiting screw I'll similar to the adjusting screw 22! by which, as explained before, the stroke of the down-feed pawl arm I is determined. The elevation limiting screw 213 is best seen in Fig. 5 at the left side of this view. It shouldbe made clear that the angular stroke allowed the downfeed pawl arm I" by the manner in which the stroke limiting screw 225 is adjusted does not affect the total down-feed amount; the position of the screw 225 merely provides that the total amount of down-feed is broken up into a number of comparatively small, successive down-feed movements.

Deeneroization of spark-out timer relay The automatic elevation of the tool-support obviously opens the left side of the double-throw switch I whereby the coil 22! of the spark-out timer relay is deenergized. The return spring III of this relay acts to restore the movable parts of the relay to the normal position, opening the relay switch 238. Displacement of air during the upward movement of the parts is made freely through the check-valve 242, and it will be clear as mentioned in the similar case of the downfeed relay, that it is not essential that a rapid up-stroke of these relay parts is made.

Return of blocking valve of work-holder motor to normal position Opening of the relay switch 238 does not, however. cause deenergization of the blocking device solenoid 2", but it will be evident that if either of the switches 28! or 254 is opened, that the interlocking relay 266 will be deenergized since these switches are in series with each other and with the coil 22! of the interlocking relay 281.

The urpose of the re-start switch I is then clear, for when the operator desires to again start the machine, it is necessary only to open this switch 264. By this openingthe coil 2 of the interlocking relay is deenergized and the two described circuits that were closed when the relay was energized are now broken. The deenergization of the blocking valve solenoid 246 is one result, as the relay 2" which supplies power current thereto will be deenergized, following which the blocking valve is forced upwardly by the action of its return spring 2", whereby the flow of fluid pressure from the already shifted pilot valve 23 that had been restrained is now allowed. by the registry of the groove 2 with the ports. to continue in its flow to the right end of the master valve 53. The resulting shift of the master valve 53 admits fluid pressure to the right end of the work-holder fluid motor I to start the work-holder to the left. The movement will be comparatively slow at first until the retarding cam 258 is moved off the retarding valve 255 whereupon the speed of movement of the work-holder is accelerated to its former grindin rate.

Deenerglzation of tool-holder elevation solenoid The other circuit that is interrupted by the manual opening of the re-start switch I results in'the deenergization of the elevating solenoid 212, as a. consequence of which the elevation control valve ill connected therewith is returned to its normal position toward the right by the action of its spring I12. The elevating rack-piston then also moves to the right to its normal position, since the control valve I'll is returned to the right by the spring I12, and fluid pressure is admitted to the left end of the elevating rack-piston to swing pawl arm Iii anticlock-wise. thereby withdrawing the pawls I" and I from engagement with the elevating ratchet wheel I. As might be inferred, the return to normal position of the automatic hydraulic elevating devices may be allowed to take place while the automatic grinding cycle is again in progress. Fluid that is exhausted from the elevating control valve I65 and from the downfeed valveiii as well is returned to the main exhaust fluid conduit 64' by means of the manifold ili'.

Although a dresser or wheel truing device is not shown in the present application, it is evident that it will be found necessary from time to time to true the grinding wheel. Compensation for the reduction in grinding wheel diameter by truing is had by manually lowering the tool-support ill a suitable amount. If the manual lowering is in the same amount as half the reduction of wheel diameter by truing, the lowermost portion of the grinding wheel periphery, the grinding contact surface, is again at the same elevation with respect to the surface of the workholder. However, without a certain slight readjustment of the descent limiting dog III, the next work-piece to be finished in the automatic cycle would be left too thick by the amount dressed off one side of the wheel. To compensate for this possible error, the dog in is adjusted upwardly a distance qual to the distance the tool-support was lowered manually. It so happens that at times the amount removed by truing or natural wear is comparatively slight, perhaps merely .001" or .002", whereby thepurpose of the micrometer screw I" is clear. since a precise adjustment of the dog is possible. It will be understood that the anchor block I99 is not loosened for this adjustment.

It will be explained that the machine as constructed and operated in practice is capable of such accuracy in repetition that with work-pieces of comparatively uniform thickness, that it is not necessary to make any alteration to the tool-support position as regards elevation, from the position in which it was left at the last movement of the work-holder when the latter was moving to the loading position. That is, the position of the grinding wheel as regards its relation with the forward or rear edge or center of the work-piece may have been at random when the work-holder moved to the loading position. If the re-loading of a new work-piece is not made inconvenient by this random position of the grinding wheel, there is no need to alter its position and the next grinding cycle may start at once on the new work-piece. However, if the operator desires, he may so adjust the control devices, particularly referring here to the needle valve 249 of the spark-out timer relay so as to prolong or make shorter, as he desires, the time allowed for the smoothing or spark-out operation whereby the closing of the relay switch 299 is timed to occur when, say, the grinding wheel is nearly or is fully retracted.

It should now be clear that the grinding machine of this application is similar in general design to the machine of the patent mentioned and that the devices by which the automatic grinding operations are carried out as described are to be considered as additional elements made auxiliary to the design of the machine of that patent. By the added elements, a grinding machine is made possible, the operation of which is sufllciently automatic in character as to permit that comparatively large volume of acceptable work is turned out by operators of relatively limited experience.

Further, if it is desired to operate the improved machine of the present application according to the principles as set out in the patent, it is necessary only to open the pilot current supply and power current supply switches. In so doing, all the electrical circuits shown in the diagrammatic Fig. 8 are for the time being taken out of service and the several compression or tension springs function to retain the control valves or like members in their respective normal positions. This statement more particularly relates to the springs I19 and I12 controlling the down-feed and elevating valves I69 and HI whereby the pawls are retained disengaged from the ratchet wheels.

Operation of devices Down-feed of tool-supporL-With the workholder and tool-holder reciprocating and toolsupport at its uppermost position, the tool-support is fed by step-by-step toward the work as follows: The contacts I99 and HI of the switch I99 being normally closed, pilot current is fed to the switch I99 so that at each reciprocation of the valve stem 26 of the tool-holder reversing valve 94' pilot current will be fed through the 2i and screw 29 lowers the tool-support 9| one step to the extent allowed by the adjusting screw 213. The relay 29I delays deenergization of the solenoid I9I to allow the mechanical devices time to operate. The step-by-step feed continues until the dog I92 on the tool-support contacts the cam lever I92 which through the stem I94 throws the movable contact member I99 of the switch I99 to the left which breaks the pilot circuit I99 to the switch I99 so that no further current will be supplied to the time relay 2M and therefore no further current supplied to the power relay 2I9, whereby the solenoid I9l will cease to function and the down-feed of the tool-support will be arrested.

Smoothing out of work peri0d.-The next operation is to smooth out the work before the workholder has ceased to reciprocate and is moved to loading position. Time is allowed, therefore, for the smoothing out operation by delayin the automatic return to loading position of the workholder and also for the elevation of the tool-support as follows: When the dog I92 breaks the contacts I99 and HI, it moves the contact I99 to close with contact 229 so that pilot current will flow through the circuit 229 to the solenoid coil 228 of the time relay 229, this being a relay in the pilot circuit which delays flow of pilot current to the power rela 299 through circuit I91 and 299 which when closed permits power current to flow to the solenoid 248 which operates the valve 2" to block supply of fluid to one end of the cylinder of the fluid motor that reciprocates the work-holder. The contacts of this relay 229 are slowly closed and before closing the smoothing out operation is permitted.

Return of work-holder to loading position.- When the contacts I99 and 229 of the switch I99 are closed, solenoid coil 229 of relay 229 is energized through circuit 226' and the contacts of relay 229 are closed by delayed action thereof sufficient to allow the smoothing out operation. Pilot current then flows to the power relay 299 through the conductor 299' to close the power circuit to the solenoid 299 to move the valve 241 to block fluid supply to one end of the workholder reciprocating fluid motor to allow the motor to move the work-holder to loading position. When the work-holder moves to loading position it closes the switch 292 and allows pilot current to flow through the conductor 299 to the coil 296 of an interlocking relay 291. When the contacts of the relay 261 are closed pilot current will then be supplied to the power relay 299 through the circuit I91, contacts of relay 291, and circuits 299 and 299' to maintain the blocking valve in blocking position to allow time for placing a new workpiece on the work-holder, this condition prevailing until the manually operated switch 294 is opened by the operator; one purpose of the interlocking relay 291 being to maintain the power relay 269 energized when the contacts of the time relay 229 are opened by the breaking of the circuit 229', which follows so soon as the interlocking relay 261 is energized, for the closing of the relay 261 also closes a power circuit which elevates the tool-support 9|, permitting the breaking of the contacts I99 and 229 of the switch I99 and hence the breaking of the pilot circuit 229'.

Elevation of tool-holder.-When the interlocking relay 291 is closed in the manner described a powercircuit is established through the solenoid 212 to operate the valve III to permit fluid to flow to the right end of the cylinder I99 to move the rack pinion I99 to the left so as to Modification of tool support feeding mechanism In Figs. 9 to 13 there is illustrated a modification of the electrical devices which are controlled by the tool-support feeding mechanism. Instead of having the dog I82 located on the tool slide ll in this modification the dog, indicated at I82, is secured to the periphery of the handwheel 22" by a set-screw 300. The dog in this, case carries a fixed pin 80! having a beveled upper portion which is adapted to contact, at the end of the down feed of the slide 3|. with the rounded end of a stem 30!. I'his stem is adjustably mounted in a rocking lever 303, having an extension 303' which is journalled upon a pin 304 carried by two cars 305 which are secured to a bracket 306 carried by the housing I40. The lever is normally supported for automatic operation in a horizontal plane by a boss 303" thereon (Fig. 11) which rests against the bracket 306. The stem 302 is part of a micrometer and is screwthreaded in a bushing 301 secured in the rocking lever 303, the threads between the bushin and the stem being of a rather coarse character. On the outer left hand end of this bushing there is rotatably mounted a micrometer type thimble 308, having the customary graduation such as the ones marked 1 2 7 8 9 which cooperate with the co-axial scribe Y in the upper surface of the bushing 301. The end of the stem fits in a central aperture in the thimble and is pinned to the thimble so that by turning the thlmble on the bushing the stem may be adjusted with relation to the beveled pin 30!. In order to provide triction so that endwise or axial pressure on this rather coarse pitch mike-screw stem when the dog I82 contacts therewith so that the screw stem will not be backed off, the right-hand end of the bushing is provided with an auxiliary tapered bushing 301'. One side of this auxiliary bushing is split as shown in Fig. 11, whereby as the auxiliary bushing is forced into the bushing 301 it closes in on the stem to i'rictionally hold it but not to an extent as to preclude its adjustment by rotation of the thimble.

The extension 303 of the rocking lever 803,

carries a pin 309 secured therein in any suitable manner and is adapted to cooperate with a plunger ill associated with a switch which corresponds to the switch I" previously described. The switch, indicated at ill is a panel mounted switch supported in the interior of the bracket 3", the wiring of this switch being the same as that previously described and as shown in Fig. 13, the reference characters in Fig. 13 being the same with the addition of the exponent a.

In operation, when the feeding devices for the tool support are operated in the manner before described the hand wheel 22" naturally moves with them so that when the beveled upper side of the pin lllll strikes the rounded end of the stem 30! that end of the lever 303 which carries the stem is rocked upwardly to the position shown by the dot-dash lines 303a in Fig. 11 sufficiently to press the switch plunger 3"! in to operate the switch. Further movement of the parts, and it is practically the same movement, brings the end of the dog I82 against the end of the stem 30! to positively arrest further movement of the hand wheel (Fig. 12) and hence arrest any further movement of the downward feeding movement of the tool slide II. If the machine is to be operated otherwise than as an automatic down-feed grinder the lever Ill! is swung to the dot-dash position indicated at "Sb (Fig. 11) which removes the rocking lever 303 out of the path of the dog I81.

One of the advantages is that a positive stop is provided, by reason of the contact of the dog I82 with pin Jill.

Another advantage is that when the grinding wheel must be lowered further as a result of reduction in wheel diameter by wheel wear and trulng it is convenient to provide this further lowering by backing oil the rounded-end stern 302. (See Fig. 10 in the sectional part.)

The indicia forms a convenient means for properly adjusting the stem with relation to the dog to contact the limit of the down-feed of the toolsupport.

Upon the closing of the switch contacts lila and 2260. by the rocking of the lever 30! the spark-out period follows as described in connection with the description of the other form. When the spark-out time is completed, the operation follows the previously described method; that is, the work-table moves to the loading position where it is retained until the re-start manually-operated switch 284 is opened; in such movement, the work-table closes the switch It! to thereby cause automatic elevation of the toolholder. The opening of the re-start switch 2" causes the return of the work-table to the working position. Such elevation obviously imparts a partial rotation oi the hand wheel 22" in a clock-wise direction (the down-feeding direction being antl-clock-wise) which carries the dog I82 away from the rocking lever 308, allowing this lever to be lowered to its normal position occupied during automatic operation as seen in full lines in Fig. 11. By this operation the sparkout side of the double-throw switch I as represented by the contacts 228a and "9a is opened, and the same movement of the contact "9a closing by contact with the contact iflla that side of the switch I!!! which is in series with the down-feed switch lfllla so automatic down-feeding may be resumed.

Having thus described my invention, I claim:

1. In a grinding machine, a reciprocatory work-holder, a traveling tool-supporting device, a tool carried by said device, means for feeding said tool-supporting device toward the work on said work-holder, fluid motor-operated means for reciprocating said work-holder, and electricallyoperated means automatically retarding the actuatlon of said motor-operated means in one di rection of the reciprocation of said work-holder, an electrical control circuit therefor, a circuit make and break device in said circuit operated by the travel of the tool-supporting device as it approaches the limit of its range of movement in one direction while the work-holder continues to be moved by said motor-operated means at reduced speed to a loading position beyond its normal range of reciprocation and .a. delayed action relay in said circuit for temporarily maintaining said electrically operated means in its operative condition subsequent to initiation oi return movement of the traveling tool-support.

2. In a grinding machine, a reciprocatory work-holder, a traveling tool-supporting device. a tool carried by said device, means for feeding said tool-supporting device toward the'work on said work-holder, fluid motoroperated means for asvaaoa reciprocating said work-holder comprising a cylinder, a fluid-operated piston therein, a fluid circulatory conduit communicating with the cylinder, an electrically operated cut-oil valve in the fluid circulatory conduit for reducing the circulation of fluid relative to the cylinder of said fluid motor to retard the operation of said motor operated means in one direction of the reciprocation of said work-holder, while the work-holder continues to be moved by said motor operated means to a loading position beyond its range of reciprocation an electrical control circuit for said cut-oil valve, a circuit break and make device therein operated by the travel movement of the tool-supporting device, and a timer member governing the return to normal of the cut-oil valve when operated independently of the further travel of the tool supporting device.

3. In a grinding machine, a reciprocatory work-holder, a traveling tool-supporting device, a tool carried by said device, means for feeding said tool-supporting device toward the work on said work-rholder, fluid motor-operated means for reciprocating said work-holder, electrically-operated means for retarding the actuation of said motor-operated means in one direction of the reciprocation of said work-holder while the workholder continues to be moved by said motor-operated means to a loading position beyond its normal range of reciprocation, an electrical control circuit therefor, a make and break device in the circuit operated by the travel motion of the toolsupporting device, and releasable controlled electrical means operated by said work-holder for maintaining said electrically operated means efl'ective to retain said work-holder in loading position after control of said circuit has been removed from the influence of said tool-supporting device.

4. In a grinding machine, a reciprocatory work-holder, a traveling tool-supporting device, a tool carried by said tool-supporting device, electrically controlled fluid actuating means for feeding said device toward the work on said workholder, means for reciprocating said work-holder comprising a fluid motor, and electrically oper ated means controlled by said electrically controlled fluid actuating means for feeding said tool-supporting device for preventing reversal of the reciprocatory work-holder by operation of said fluid motor whereby the fluid motor causes the work-holder to continue to move to loading position comprising a blocking valve to block fluid supply to one end of said fluid motor, an electromagnet connected with said valve, means for energizing said magnet actuated by said electrically controlled fluid actuating means for feed ing said tool-supporting device after the end of its operation upon the work including a delayed action relay, and manually controlled electrical switch devices closed by said work-holder when,

moved to loading position ,for maintaining said magnet energized to retain said work-holder in loading position after the energization thereof has been removed from the control of said toolsupportlng device.

5. In a grinding machine, an adjustable tool support, a reciprocal tool supported thereby, a reciprocatory work-holder, means to impart a feeding movement to said tool-support with relation to said work-holder, means including a fluid motor for reciprocating said work-holder, electrically operated means including an electromagnet for blocking the supply of fluid to one end of the cylinder of said motor to permit said work-holder to be moved to loading position thereby, a first switch closed by said means to impart a feeding movement to said tool-support at the end of the grinding operation of said tool upon the work. an electrically controlled retractive mechanism energized by the approach of the tool support to the limit of its range of travel for restoring said tool-support to initial position to permit opening of said flrst switch, a second switch energized by the closing of said flrst switch, including means to delay the closin thereof to permit a smoothing operation of the tool and adapted to be closed to supply current to said magnet when said first switch is closed, a third switch in series with the second switch, closed by said work-support when moved to its loading position, a fourth switch closed upon the closing of said third switch to maintain said magnet energized after said first and second switches have been opened by the restoring movement of said tool-support, and a fifth switch in series with said fourth switch manually operable todeenergize said magnet to permit said blocking means to return to normal position.

6. In a grinding machine, a reciprocatory work-holder, a fluid operated motor to reciprocate said holder, automatic reversing means for the motor operable by the work-holder as it approaches the limit of a prescribed range of movement in each direction under influence of fluid pressure supplied alternately to opposite ends of the motor, an electrical circuit including an electrically operated device for temporarily arresting the supply of fluid under pressure to one end of the motor while fluid pressure continues to be supplied to the opposite end thereof to continue the operation of the motor and movement of the work-holder in one direction beyond its normal range of reciprocatory movement into a loading position, regardless of the operation of the reversiris, means, thereby, an adjustable tool-supporting device, means to cause a relative traversing movement between said holder and device, electrically controlled means actuated by said traversing means to feed said tool-supporting device toward t e work on said work-holder, electrically controiled means actuated by said electrically-controlled means which feed said tool-supporting device to arrest thefeeding movement of said tooi-supporting device, and electrically controlled actuning means controlled by said work-holder when moved to loading position to return said tool-supporting device to initial position,

7. In a grinding machine, a reciprocatory work-holder, an adjustable tool-supportin d vice, a tool carried'by said tool-supporting device, electrically controlled fluid actuating means for feeding said device toward the work on said workholder, means for reciprocating said work-holder comprisinga fluid motor, and electrically operated means controlled by said tool-supporting device for blocking the reversal of said fluid motor while the work-holder continues to move beyond its normal range of reciprocation to loading position comprising a blocking valve to block fluid supply to one end of said fluid motor while a supply of fluid under pressure is continued to the opposite end thereof, an electromagnet connected with said valve, means for energizing said magnet actuated by said tool-supporting device after the end of its operation upon the work including a delayed action relay by which the magnet is maintained in energized condition and the blocking valve in operated position regardless of further movement of the tool supporting device,