US1903562A - Grinding machine - Google Patents

Description

April 11, 1933. R N LD ET AL 1,903,562

7 GRINDING MACHINE Filed Nov. 14, 1929 8 Sheets-Shea: 1

gwuwntozs Roger N. Keuld Edward M-Tl )or April 11, 1933. R. N. HEALD ET AL 1,903,562

GRINDING MACHINE Filed Nov. 14, 1929 8 Sheets-Sheet 2 gwuewtocs Roger N. Healcl ;%wqrd flTu lor April 11, 1933.. I R, N. HEALD ET AL GRINDING MACHINE Filed Nov. 14, 1929- 8 Sheets-Sheet 5 Rog I Edwa er N. Heald rd (1T1;

April 11, 1933- R. N. HEALD ET AL 1,903,562

GRINDING MACHINE Filed Nov. 14, 1829 8 Sheets-Sheet 4 Roger N- Heald Edward (O-Tailor R. N. HEALD El A L GRINDING MACHINE April 11, 1933.

Filed Nov. 14, 1929 8 Sheets-Sheet 5 0 k gmento Roger N. Heuld Edward MITERP Y m I 4% %Mg Ap R. N. HEALD ET AL GRINDING MACHINE 8 Sheets-Sheet 6 Filed Nov. 14, 1929 gnaw/"tows R er N. Hecdd Emurd 1.17:

Ap 1933 R. N. HEALD El AL GRINDING MACHINE Filed Nov. 14, 1929 8 Sheets-Sheet 8 gnvenl'o'cs Roger N. Heuld.

Edward MTG lor 61 zngq dressed and trued just Patented Apr. 11, 1933 UNITED STATES PATENT OFFICE.

ROGER N. HEALD AND EDWARD M. TAYLOR, OF WORCESTER, MASSACHUSETTS, AS-

SIGNORS TO THE HBALD MACHINE COMPANY, OF WORCESTER, MASSACHUSETTS, A

CORPORATION OF MASSACHUSETTS eamnme macnrrm Application filed November 14, 1929. Serial 1T0.v 407,243.

' workpiece (or on a plurality of workpieces) to predetermined sizes or dimensions, the grinding operation being automaticall terminated as soon as, but not before, eac surface being ground has arrived at the finished size. The present invention, therefore, in-

volves some of the features set forth a co- Rianding application, Serial No. 276,381, filed ay 9, 1928 by Waldo J. Guild, now Patent No. 1,856,185, granted May 3, 1932, but the machine of the present invention is more particularly adapted to grind taper bores, or tapered surfaces. Particularly the machine of the present invention is adapted to grind successive workpieces, each having a pair of tapered surfaces 1n close relation to each other b simultaneous movement of a pair of rin ing wheels-in respect to said surfaces.

11 order to grind these workpieces to precision dimensions, the inding wheels are efore the final and finishing cuts that bring the workpiece to size are taken as set forth in U. S. Letters Patent No. 1,731,719 to Kempton and Gallimore, granted October 15, 1929. To that end the normal reciprocatory grinding traverses of the wheels are arranged to be automatically amplified, in order to subject each of said wheels to a dressin operation. In plural surface grinding as a ve described, however, there is considerable difficulty in'keeping the two grindin wheels from interfering with each other, an in order to overcome this difliculty the grinding wheels are positively and mechanically controlled in their working positions. Also, in grinding tapered surfaces very close together, the wheels must move in the same direction if they are to be kept from touching each other. One object of the invention, therefore, is to provide a positive mechanical control of reciprocating grinding wheels moving in the same direction,and to permit withdrawal of the wheels through the dressing position without disturbing the aforesaid mechanism.

The problem is further complicated by the necessity in tap'er grinding of havin the grinding wheels reciprocate at an ang e to each other, and of making this angular relationship adjustable. It is desirable that the adjustment of the angular relationship of the grinding wheels shall not require any resetting of the mechanical reciprocating mechanism ;therefore another object of the present invention is to fulfill the above requirements, and the invention is carried out in this respect by fluid pressure actuation of the grinding wheel carriages, and by using mechanical reciprocating means located about the center of angular adjustment of the carriages. The fluid pressure mechanism is used to urge the carriages against the devices for positively controlling the reciprocations, which devices in the present illustrative embodiment of the invention, take form of the eccentrics or cams.

In order that the fluid pressure and mechanical actuating mechanism for the carriages may work in harmony, the invention provides throttling means to prevent the momentum of the carriages the mechanical reciprocating means, and this is another important feature of the invention.

The machine of the invention contemplates the bringing to size of workpiece surfaces 1) a definite predetermined amount of gun ing, following the subjection of each wheel to a dressing operation, as above describedupon completion of this predetermined amount of finish grinding, the wheels are automatically withdrawn from contact with the work. Since this withdrawal involves the movements of the wheels in oppos te d1- rections away from the workpiece, the invention contemplates lateral separation of the wheels and workpiece when the workpiece has been brought to the desired size, so that neither surface will receive any more finish grinding than the other Slll'ftLCGq Such lateral separating means, or back-off mechanism, as it is called, is not per-se new, but peranism operated by fluid pressure means, a 100 from disrupting 3 manual control by which the machine may be started or stopped at will and other improvements which will appear from the following detailed description, taken in connection with the accompanying drawings, in which i Fig. 1 is a front elevation of a grinding machine embodying the invention.

Fig. 2 is a rear elevation of said machine.

Fig. 3 is a sectional plan view taken on the line 3-3 of Fig. 2.

Fig. 4 is a fragmentary View, partially in rear elevation and partially in section, shOW- ing the operating valve for the wheel-dressin device. i

ig. 5" is a fragmentary end elevation of the parts shown in Fig. 4.

Fig. 6 is. a front elevation of the cross feed and compensating mechanism and actuating devices therefor.

Fig. 7 is a fragmentary view taken from the section line 7-7 of Fig. 6.

Fig. 8 is a front elevation of the left hand carriage showing the actuating valve for the cross feed and compensating mechanism.

Fig. 9 is a fragmentary plan View of the parts shown in Fig. 8.

Fig. 10 is an enlarged sectional view of so the valve shown in Fig. 8.

Fig. 11 is a sectional view on the line 11--11 of Fig. 10.

Fig. 12 is an enlarged sectional view of the mechanical devices for actuating the carriages, taken on the line 1212 of Fig. 3.

Fig. 13 is an isometric view of one of the controls for the machine.

' Fig. 14 is a fragmentary elevation of a certain switch and its actuating mechanism.

Fig. 15 is a fluid pressure diagram.

Fig. 16 is a wiring diagram.

Fig. 17 is a large scale view, illustrating the operation of two grinding Wheels, according to the invention, on oppositely tapered surfaces of a workpiece.

Fig. 18 is an isometric view taken from the rear of the machine, showing the speed control mechanism and the operating. mechanism of the dressing-device. r

Like reference characters refer to like parts throughout the drawings.

Referring to Fig) 1, the machine is mounted upon a suitable base 1 upon which is carried a pair of sub-bases 2 and 3. The sub-bases 2 and 3 may be adjusted angularly with respect to each other and with respect to the workpiece being ground, so as to produce taper bores of any desired angle To this end the sub-bases 2 and 3 are mounted for horizontal angular adjustment upon. the base 1 by means of vertical pivots which Wlli be hereinafter described, the pivot points being at the inner I ends of the sub-bases 2 and 3, and the subbases being fastened in the desired positions of angular adjustment by means of bolts 4, 4 and '5, 5.

tables.

6 and 7, the latter having mounted thereon the J wheel heads 8 and 9 respectively and their Wheel driving motors 10 and 11. J ournaled in the wheel heads are spindles 12 and 13 which carry grinding wheels 14 and 15 for grinding the interior surfaces of successive workpieces that,in the present instance, are

held in a rotatable chuck that is open at both ends, said chuck being mounted in a centrally located workhead 16 between said The grinding wheels are rotated in any suitable manner, as by the motors 10 and 11 and the belt drives sufiiciently illustrated in Figs. 1 and 2. The workpiece, which is mountedin the chuck provided by the workhead 16, is also rotated, such rotation being imparted by a motor 17 mounted on the back of the machine frame. As shown in Fig. 2, a belt 18 passes around the chuck, which is suitably 'journaled in the workhead 16 on either side of said belt, said belt passing through a slot 19 and through another slot,

not shown, and downwardly to a driving pulley 20, rotatably mounted on a horizontal drive shaft 21 that is rotated by the motor 17. A spring actuated belt tensioning device 22 removes whatever slack there may be in the belt and allows of limited motion of the workhead 16 transverse to the direction of reci rocation of the tables or carriages 6 and 2, said transverse motion serving tofeed wheels and workpieces in cutting relation as hereinafter described. a

The machine of the present invention, as well as the machine shown and described in the above mentioned Guild patent, contemplates the withdrawal of both grinding wheels 14 and 15 from the bore of the workpiece being ground for the purpose of dressing and truing said Wheels, this interruption of the grinding being followed by the final and finishing cuts which bring the workpiece to the desired size. Also the machine of the i present invention contemplates the withdrawal of fihegrinding wheels 14 and 15 from however, which produces the grinding traverse between workpieces and wheels to secure a smooth surface on said workplece, and to prevent the formation of lines therein, is, according to thepresent invention, a positively controlled reciprocation, and comprises simultaneous movement of the grinding wheels in the same general direction, as shown in Fig. 17, (i. e. when one grinding wheel is moving towards the center of the workpiece, the other grinding wheel' is moving out from said center although the lines of motion may be and generally are not in the same line or parallel), in contradistinction to the reciprocatory motion of the carriages and wheels described in the aforesaid Guild patent, in which the reciprocation is always equal and oppositeand controlled by fluid pressure.

The reason the motion of the wheels must be in the same direction, so that one is approaching the center of the work while the other is leaving it, is to enable the machine to grind workpieces of the type shown in Fig. 17, each of said workpieces (1 having taper bores 12 and c separated by a very narrow strip d, which may sometimes even be nothing but a geometric circle. It is very apparent that if the grinding wheels moved to wards each other they would strike, while c5 or eccentrics, preferably of the peripheral even when moving in the same direction they must be accurately timed in order to prevent interference. Also the extent of the re ciprocation must not be great if hell -mouthing of the work is to be avoided, it being ell known in the art that to avoid bell-mouthing the area of grinding contact must never be reduced below a certain minimum.

To that end, t he sub-bases 2 and 3 have suitably attached thereto cylinders 24 and respectively, (see Fig. 15), said cylinders providing pistons therein which are attached to iston' rods 26 and 27, the outer ends of which are fastened to the tables 6 and 7 reends of the cylinders 24 and 25 will urge the carriages outwardly, while admission of fluid to the outer ends of said cylinders will urge the carriages inwardly. As will be hereinafter described, for the movement of the carriages to carry the wheels through the dressing position, and to carry them to the rest or idleaposition, the fluid is admitted to the inside ends of the several cylinders 24 and 25. For the return of the carriages to carry the grinding wheel into the workpiece, the fluid is admitted to the outside end of the cylinders, and the fluid pressure is maintained on the outer sides of the pistons during the normal working stroke of the grinding wheels, both during preliminary or rough grinding and during fine or finish grinding after the'dressing operation, the carriages.

being reciprocated-by means of rotating cams contact type, and the pressure of the fluid causing abutments carried by the carriages to maintain engagement with the cam surfaces. The pressure fluid may be taken from any suitable source of sufply, such as a pump 28 which is shown iagrammatically in Fig. 15 and also as actually provided on the machine in Fi 2, while in order that the fluid may back up in the piping,- .and have some outlet when the carriages are being moved by the cam means against the pressure of the fluid, a relief valve 29 is provided.

Before describing the fluid pressure valve and the controls therefor, the mechanical component of the means for producin" the normal reciprocatory working stroke will be described.

Suitably fastened to the power shaft 21 is a sprocket 30. A horizontal shaft 31 is journaled in bearings 32 as best shown in Fig. 3, and attached to this shaft 31 is a sprocket 33. A sprocket chain 34 connects the sprockets and 33 and thus rotates the shaft 31. A pair of helical gears 35 are mounted upon the ends of the shaft 31 and these helical gears mesh with helical gears 36 fastened to vertical shafts 37, (see Fig. 12) Referring now to Fig. 12, which illustrates the drive for the shaft 31 and one of the mechanical units for centrics or cam members 39. Dust 09. s 40 may be provided to keep dirt out of the arings.

The sub-bases 2 and 3, as aforesaid, each have a pivotal connection to the base 1. The upper end .of the general cylindrical member 38 constitutes in each instance the bearing surface of this pivotal connection, the subbases 2 and 3 having internal c lindrical surfaces 41, which, as shown in t e case of the sub-base 2 in Fig. 12, closely engage the said cylindrical surfaces of the members 38. In

this manner, no matter what the angular position of adjustment of the sub-bases 2 and 3, rolls 42 carried thereby which constitute the abutments engaging the peripheral surfaces of the cams 39 will always be moved through the same range of reciprocation for any given cam 39. It wi l thus be seen that rotation of the cams 39 produces reciprocation of the carriages always assuming that the fluid pressure mechanismis urging the rolls 42 into engagement with said cams or eccentrics 39.

Referring now to the fluid pressure diagram of Fig. 15, and referring also to the plan view of Fig. 3, the machine provides a pair of reversing valves controlling the pressure fluid to the cylinders 24 and 25 respectively, which reversing valves are shown as located in suitable casin s 44 and '45. Casings 44- and 45 provide flui entrance passages 46 and 47 respectively, exhaust passages 48 and 49 respectively, and ports 50, 51,

52 and 53'. Of the latter, port 50, in the easing 44, connects by means of a pipe 54 with the right hand end of the cylinder 24, while the port 52yofthe. casing 45 connects by means :-of a pipe 55 with the left hand end ofthefcyl-inder 25.- Conversely, port 51 of casing"44"connects by means of piping 56 withth left hand'end of the cylinder 24, and port 53 connects by piping 57 with the right hand-end of. cylinder 25. Each casing contains a movable reversing valve member of the same construction, said members being designated by. the-numerals 58 and 59 .for the valve casings 44 and 45 respectively.

Each of the-said reversing valve members 58 and '59 comprises a cylindrical member having tWo reduced portions alternating with threeportions of full diameter. When the member 58 is placed in its right hand position, and themember 59 in its left hand position, or stated in another way, when these reversing valve members are moved towards each other, the fluid is directed to the left hand end of cylinder 24 and right hand end of cylinder 25, by way of the piping 56 and 57 respectively; Such action obviously r 62 and 63 on the front of the machine.

tends to cause the carriages to approach each .bthei and to bring the grinding wheels into engagement with the workpiece or workpieces .in'the workhead. When the reversing-valve members 58 and 59 are placed in that position in which they are farthest apart, the fluid is directed through the pipes 54'; and 55, which urges the carriages outwardly to carry the grinding wheels away from the workhead. It will be seen, from an examination of Fig. 15, that each exhaust passage 48 and 49, by way of its port 48a or 49a, as the case may be, is adapted to convey the 'fiuid away from that side of the cylinders 24 and 25 opposite the sides to which the fluid is being admitted. The passages 46 and 47 are provided with throttle valves 60 and 61 respectively, which may be manually controlled by means of hand levers The connections between the supply pump 28 and the entrance ports46 and 47 will be hereinafter described in connection with the mechanism for slowing down the speed of movement of the carriages for the dressing operation. r

The workhead 16 is carried by a cross slide 16a which is mounted on ways 64 provided by the base 1 of the machine, for the movement of said workhead laterally with respect to the grinding wheels 14 and 15. Referring now to Fig. 6, a transverse feeding ele ment for said cross slide is here indicated by the numeral 65. Rotation of this shaft in a clockwise direction (in this particular embodiment of the invention) is adapted to draw the workhead to cause a workpiece or workpieces therein to move in cutting relation to the grinding wheels 14 and 15. Said screw shaft 65 is adapted to be rotated manually by means of a hand wheel 66 and mechanicallyfrom a ratchet, wheel 67, the latter being automatically given a 'ste -by-step movement as will presently be escribed. The ratchet wheel 67 is not fastened directly to the screw shaft 65, but together with another ratchet wheel 68, located directly behind it, is'connected to'said screw shaft through the system of gearing fully described and illustrated in U. S. patent to Taylor N 0. 1,682,673 granted August 28, 1928. (In Fig. 6, the ratchet 67 is to be considered as broken away on the right hand side to show the ratchet 68). Since ratchet 67 ratchet 68, and screw shaft 65 are three elements differentially connected, andsince ratchet 68 is normall held stationary by a lock device 69, it fol ows that intermittent rotation of the ratchet wheel 67 produces intermittent rotation of the screw shaft 65.

Referring now to Figs. 1, 6 and 16, the hand wheel 66 and ratchet 67, which are fastened together, adjustably support a cam 72. ,As shown in Fig. 6, the machine provides a pair of rock levers 7.3 and 74, which are mounted on suitable pivots not indicated, and each rock lever provides an adjustment screw said screws being numbered 75 and 76 respectively, the ends of the screws being in the path of the cam 72.

When the rock lever 73 has moved by engagement of the cam 72 with its screw 75, an electric circuit is completed which causes the carriages to move outwardly, passing the 1 grinding wheels in front of dressing devices so that the surfaces of said wheels may be dressed and trued. When the cam 72 engages the adjustable screw 76 and thus rocks the lever 74, another circuit is closed which tions to carry the two grinding wheels out i of the work, thus definitely terminating the grinding operation. Thus to a large extent the machine is automatically controlled by the mechanism which produces the cutting feed between the wheels and the work.

It is not necessary to describe herein the exact construction of the contact making mechanism, particularly that which permits the cam 72 to ride by the adjustable screw 7 5 after the contact is made, since this mechanism is fully described in the aforesaid patent to Taylor. Fig. 16 illustrates diagrammatically the rock levers 73 and 74, and the electric circuits for the automatic operation of the machine, which will be hereinafter rectly through fluid pressure means. That is to say, at. each reciprocatory movement of one of the tables, viz. the table or carria e 6, a certain valve is actuated, which causes uid under pressure to be admitted to a cylinder, moving a piston and thus, actuating a pawl 77 which then actuates the ratchet wheel- 67.

As shown in Figs. 1 and 8, a bracket 78 is adjustably mounted on the table or carriage 6, and this bracket holds an adjustable screw 79. The front'of said screw is adapted, when the grinding wheel 14 is in the work iece, and near the right hand end of its stroke, to engage a projecting head 80 of a valve device, which is suitably located in a casing 81, and illustrated in detail in Figs. 10 and 15.

The valve mechanism in the casing-81 comprises a shaft 82 which is turned down 'at various portions along its len th, so as to leave portions 83 and 84 of all diameter which are separated by five portions of alternating reduced and full diameter 85, 86, 87, 88 and 89. The portions 83 and 84, as well as the portions 86 and 88 of full diameter have a close sliding fit within a sleeve 90, and the- portions 83 and 84 block the ends of said sleeve so as to form an inclosed chamber at all times. The portions 86 and 88 are adjacent holes 91 and 92 in the sleeve, said portions 86 and '88 being, when the valve member 82 is not acted upon, just inside of sa d holes. The reduced portion 87 is always in communication with a hole 93.

The hole 93 through the sleeve 90 is in communication with a port or passage -94 which, as shown in Fig. 15, is connected b pip ng 95 to the main supply piping 96 lea ing from the pump 28. Thus the port 94, and

consequently the space around the reduced portion 87 is always filled with fluid under pressure. By resilient means, the valve member 82 has a tendency to remain in the position shown in Fig. 10, and in this position both the holes 91 and 92 are separated from the active flu d under pressure by the portions 86 and 88. At the same time, the holes 91 and 92 through the sleeve 90, and the space around the reduced portions 85 and 89, are in communication with anotherhole 99 that is, O in communication with an exhaust passage 100 adapted to lead any fluid back to the sump in the base of the machine. This connection, in the case of the hole 92, s a direct one comprising the space around the reduced portion 89, as will be plainly seen in Fig. 10,

while in the case of the hole 91 through the.

sleeve 90. the connection is by way of an axial passage 101 in the shaft 82. and lateral bores 102 and 103 respectively leading into said passage. -The sa d passage 101 is blocked at the left hand end by means of the head 80.

The hole 91 communicates with a passage 104 which is adapted to'lead fluid to andfrom a cylinder which actuates the compensating mechanism that will be described hereinafter.

ing this reduced portion 108 is a sprin 109 most of which is contained in a sli able sleeve 110 which slides in a bore 111 provided in the casing 81. The left hand end. of-

the spring 109 engages'a shoulder 112 provided by the sleeve, while the right hand end of said spring engages a loose collar 113 which also slidably fits within the bore 111. The

collar 113 1s also slidably mounted on the reduced portion 108, and engages the shoulder formed b the juncture of the reduced portion 108 with the enlarged portion 83. It will be apparent that the head prevents the sleeve 110 from moving off the end of the shaft, while another outwardly facing radial shoulder 114 provided by the sleeve 110 en- 'gages a stationary collar 115 fastened to the casing, and prevents the sleeve 110 from leaving the bore 111.

It will now be apparent, that if the shaft 82 is urged to the right, the spring 109 Will be compressed, allowing said shaft to move, the enlarged ortion 114 of the sleeve 110 sliding in the bore 111 until it contacts with the collar 113. It will further be apparent that if the shaft 82 is urged to the left, the collar 113 will move in the bore 111, the sleeve 110 being at this time held stationary by the collar 115, and the limit of movement will be the same and the spring 109 will be likesume its neutral position when the external force is removed. At each right hand movement of the carriage 6, the adjustable screw 79 provided thereby engages the head 80 and shifts the ment 117 carried by 9. depending arm 118 which is fastened to a shaft119. On the rear ofthe shaft 1191is a two armed member 120,

ment with a lever 122 pivoted at 123. The lever 122 is connected by means of a link 124 with a pawl carrying arm 125 which is pivoted at 126. The pawl 77 is pivotally mounted at 127 to'said arm 125. Without further description it will be seen that movement of the piston 116 to the right causes the pawl 77 to engage the ratchet wheel 67 thus to procure across feed movement between the grinding wheels and the workpiece. The next leftward movement of the carriage 6, relieves the pressure against the 'head 80 of the shaft 82, and the portion 88 moves to the other side of the port 92. This connects the cylinder 107 to the exhaust, and piston 116 is moved back into the cylinder 107 by means of a coil spring, not shown, surrounding the pivot shaft 126 and having one end fastened to a stationary part of the machine and the other end fastened to a pin 128 on the arm 125. Thus reciprocation of the left hand table or carriage 6 causes, through the mechanism described, oscillations of the pawl 77. The angular distance through which the ratchet 67 is moved by each oscillation of the pawl 77, is adjustable by means of a cam surface 130 which is adapted to engage a cam surface 131 on the pawl, the latter tending to take the position shown in Fig. 6 by reason of a spring and detent 132 inside the pawl member, and the coaction of these cam surfaces, when the pawl is moved upwardly, forcing the tooth of the pawl into engagement with the rachet. The cam surface 130 is adjustable in position by means of a screw 130a which bears against a stationary member, not shown, a spring 133 being employed to draw the member 134 on which said cam surface is formed in a counterclockwise direction.

This automatic step-by-step movement of the ratchet 67 in response to actuation by pawl 7 7 moves the cam member 72 gradually in a clockwise direction. The front projecting portions of the rock levers 73 and 74 lie in the path of the cam projection 72, and consequently they are actuated in the sequence named.

Referring now to Fig. 16, electric current may be supplied by a generator G driven continuously by any suitable means and located in any convenient portion ofthe machine frame. One terminal of this generator is grounded as shown at 135, and the other terminal is connected to a main supply lead 136 which is adapted to convey electric current to one terminal of a plurality of electromagnets which control the various operations of the machine, and which are energized when and as their opposite terminals are connected to ground in a manner which will be set forth. 'Specifically, a connecting lead 137 connects the supply line 136 to an electromagnet 138, which, when energized, sets in operation fluid pressure means to cause the two V ation.

The rock lever 73 provides a contact termi .nal'143 and adjacent tothisterminal is a terminal 144, and when these terminals are brought together, the electromagnets 138, 141 and 142 are, energized-in order to subject the grinding wheels to' thedressing operation.

The terminal 143 is uninsu'lated from the rock lever 73 and is therefore -grounded,'as diagrammatically indicated at 145. Insomuch as the cam 72, once it has engaged the screw 75, will hold the terminals'143 and 144 together for some considerablemtime as measured by several oscillations of thezpa-wl 7 7, the circuits through thesethree magnets138, 141 and 142'are. completed by means-of a switch generally designated by the numeral 146, and mechanism is'provided by themachine, which will be hereinafter described, for actuating this switch coincident with the amplified movement of the carriages-6 and 7 ,so as to break the'circuit and prevent hat-Infill repetitionof the dressing stroke; To that end the magnet 138 is connected by a lead 147 to a terminal 148 of said switch 146,and the terminal 144 is connected by a lead 149 to a terminal 150 of said switch. A movablem'em'ber 151 of the switch is connected by a branching lead 152 to both the electromagnets 141 and 142. During the preliminary grinding of the work, the switch member 151 is disposed in the position shown in Fig. 16, connecting the terminals 148 and 150, and connecting, by way of the branching lead 152, the electromagnets 141 and 142 to the terminal 150. It will be seen that, with the switch member in the position shown in Fig. 16, when the ter'mlnals 143 and 144 are brought together the magnets 1'38, 141 and 142 will be simultaneously energized. Referring now to Figs. 2 and 15, the electromagnet; 138 is located on the back of'the machine, and in front of it is a slidable plunger valve member 154 which is made of magnetic material and so acts as an armature. The valve member 154 is located in a suitable casing 155, which casing provides a pair of bores through it for the reception of the valve 154 and another valve which performs a different function that will hereinafter be described. The valve member 154 is located in one of these bores 156 and is adapted, when drawnto the right, under the influence of the electromagnet 138, to admit fluid under pressure to a cylinder to operate the dressing diamonds. As shown in Fig. 15, the man supply pipe 96 has a branch 157 leading to a pressure chamber 158 in the casing 155. The valve member 154 provides two portions 159 and 160 of full diameter separated by a reduced portion 161. The portions 159 and 160 block the ends of the bore 156, and in addition, when the valve is in the position shown in Figs. 2 and 15, the portion 159 blocks that end of the pressure chamber '158 associated with the bore 156. At the same t'me,'the space around the reduced portion is in connection with an exhaust passage 162. When, however, the valve 154 is drawn to the right, the portion 159 of full diameter opens up the chamber 158 to the interior of the bore 156, and the portion 160 closes the exhaust passage 162. Insomuch as a port 163 is always in communication with the space around the reduced portion 161, the fluid at that time is admitted to a pipe 164 which leads to the diamond operating cylinder. v

Referring now to Figs. 15 and 18, the piping 164 connects to a cylinder 165 which together with the diamond operating mecha- 3 nism is mounted on the cross slide 16. In cylinder 165 is a piston 166, and when fluid is admitted tothe cylinder the piston is moved rearwardly of the machine and this, in a manner which will presently be described, causes both diamonds to be ultimately lowered into the path of the grinding wheels.

The dressing devices or diamonds 170 and 171 for the grinding wheels .14 and 15 'respectively, are embedded in metal plugs or nibs which are held by oscillatory members mounted in antifriction bearin and delicately ad ust-able in their operative positions by means of knobs 172 and 173 respectively.

The construction and mounting ofthe oscillatory members which hold the diamonds, the stops which locate them at a definite plane when moved into the paths of the grindingwheels 14. and 15, and all other details ofthe supports for said diamonds, form no part of the present invention, these details being fully described in U. S. Letters Patent No. 1,655,903 granted January 10, 1928, to Guild'and Grimshaw. Suffice it to say, for the purpose of the present invention, that two mechanisms of the type shown in the aforesaid Guild and Grimshaw patent are provided by the present machine, these being designated general- 1y by the numerals 174 and 175 respectively. These mechanisms are symmetric, that is to say, identical in construction, but having similar parts located on opposite sides.

. Referring now to Figs. 2 and 18, the aforesaid oscillatory members referred to and fully described in said Guild and Grimshaw patent, 6 are each connected to a pair of links 17 6, 176,

in the case' of the mechanism 17 4, and to a pair of links 177, 17 7 in the case of mechanism 17 and rearward motion of said links causes the diamonds to be moved from the position shown in Figs. 1 and 2 into the paths of the grinding wheels 14 and 15.

Referring now to Fig. 18, the piston 166 within-the cylinder165 provides a rearwardly projecting pin 166a which is inengagement with the front face of a short arm 178, said arm being fastened to a horizontal shaft 17 9 suitably mounted in bearings 180 and 181 provided by the cross slide 16a or some part connected thereto. On the ends of the shaft 179 are fastened arms 182 and 183. The arms 182 and 183 have ball and socket connections with cross bars 184 and 185, movement of said arms being thus adapted to move said cross bars yet allowing the latter to adjust themselves angularly. Each cross bar has a hole in each end throiigh which the links 176 and 177 extend, and generally -U-sh-aped brackets 186, 186 in the case of the cross bars 184, and similar brackets 187, 187 in the case of the crossbar 185, are located on the link rods 17 6 and 177 respectively and constitute stops to transmit the motion of the cross bars 184 and 185 to said links, compression springs 188, 188 and 189, 189 being placed on the rods between one end of the brackets and the cross bars in order that the downward movement of the diamonds 170 and 171 may be cushioned. From the foregoing description, it will be apparent that rearward movement of the pis ton 166 results in counterclockwise turning of the shaft 179, Fig. 18, which moves the cross bars 184 and 185 rearwardly of the machine and thus draws the links 17 6 and 177 in the same direction to move the diamonds 17 0 and 171, mounted on oscillatory members, as described in the aforesaid Guild and Grimshaw patent, into the paths of the grinding wheels 14 and 15.

1 Notwithstanding the fact that as soon as the contact points 143 and 144 are brought 'uo together, the valve 154 is actuated to admit fluid to the cylinder'165, the piston therein does not immediately move to lower the diamonds, but is restrained from moving by mechanical means connected to the moving tables or carriages, so that the diamonds will be lowered only when the spindle bearings provided by the wheel heads 8 and 9 have moved out of the way. "That is to say, the making of the electric, circuit as described immediately actuates the valve, and fluid is then active in the cylinder to cause thediamonds to be lowered, but their position at any moment is dependent upon the cam means associated with the moving carriages, so that the diamonds .will follow the path of the ,cam, which .in turn is connected to a carriage, in order that in any given'position of the carriages, the diamonds will be at a given position. Furthermore, this mechanism, which is about to be described, constitutes positive means to return the diamonds to their original-positions after the dressing operation.

Referring now to Figs. 2 and 13, the table or carriage 7 provides a rack 190 on the back thereof, which rack is in mesh'with a gear 192 that is fastened to the upper end of a vertical shaft 193. The shaft 193 is rotatably mounted in a vertical bearing member 194 that is suitably fastened to the sub-base 3, said bearing member having attached thereto a horizontal bearing member 195. A bevel gear 196 is fastened to the lower end of the shaft 193 and this gear meshes with a'complementary gear 197 mounted on the end of a shaft 198 that is partially supported by the bearing 195. The other end of said shaft 198 is supported by a bearing 199 which is connected by 'a right angle bracket 200 to a bearing 201 mounted on a vertical shaft 202. The bearing 201 permits the entire unit 199,

200 and 201 to move angularly with respect to the machine frame, which is necessary since the rack 190 is attached to the table 7, which is in turn carried by the sub-base 3 that is angularly adjustable upon the frame, while the shaft 201 is held in positon by a forked bearing support 203 attached to a plate 204 on the back of the machine, which is therefore always in a fixed position.

That end of the shaft 198 opposite the bevel gear 197 has fastened thereto another bevel gear 205, which meshes with the upper of a pair of integrally connected bevel gears 206 and 207 that are rotatably mounted upon the vertical shaft 201. The lower gear 207 meshes with a bevel gear 208 that is fastened to a shaft 209 extending through the plate 204 and supported in a suitable bearing boss 210 formed thereon. Upon the front of the shaft 209 is fastened a pair of cams 211 and 212 respectively.

It will readily be seen that the cam 211 partakes of angular motion which corresponds to rectilinear motion of the carriage 7. The motion of this cam is used to control the position of the diamonds in the following manner.

A stud or shaft 213 is suitably attached to the plate 204, and upon this shaft is mounted a lever 214. The lever 214 provides a roller 215 that is in engagement with the cam 211. Referring again to Fig. 18, the right hand end of the lever 214 is connected by means of a ball and socket connection 216 to a link rod 217, the upper end of which is connected by another ball and socket connection 218 to an arm 219, attached to a horizontal shaft 220, that is journaled at 221 and 222 to the machine frame. See Fig.2. The shaft has an arm 223 fastened thereon, which arm is opposite an arm 224 fastened to the shaft 179. These arms are connected by'a link 225, and it will therefore be seen that the diamond operating mechanism can only move when of mechanism just described. The downward position of the diamonds is regulated by adjustable stop mechanisms incorporated in the devices 174 and 175, and when the carriages 6 and 7 are in the position to allow the diamonds to come down, the roller 215 is just clear of the cam 211. The diamonds are forced up again as the wheels 14 and 15 reenter the workpiece by the cam 211, but since the exact upward position of the diamonds 17 0 and 171'is a matter of no moment, the slight variation in this position, due to the fact that the cross slide 16a carries with it the shaft 179, while the shaft 220 is mounted in a stationary part of the machine, in nowise affects the operation of the machine.

It has already been stated that the coming together of contacts 143 and 144 causes the grinding wheels 13 and 14 to withdraw from the workpiece so that they may pass back and forth in contact with the, dressing diamonds, and that this takes place through energization of the elec'tromagnets 141 and 142. As shown in Fig. 3, and as indicated in Fig. 15, the electromagnets 141 and 142 are located on the outside ends of the casings 44 and 45 respectively, and adjacent the outside ends of the reversing valve members 58 and 59 which are made'of magnetic material. Energization of the magnets 141 and 142, which is effected simultaneously, draws the reversing valve members 58 and 59 from the positions shown in Fig. 15, to the left and the right respectively, cutting off the fluid under pressure from the outside ends of the cylinders 24 and 25, and making it active at the inside ends of said cylinders. Since previously the fluid pressure mechanism was the only the table rolleis 42 against the rotating eocentrics 39, and since this .mechanism now urges the carriages in the opposite directions, the carriages 6 and 7 move away from each other, carrying the grinding wheels 14 and 15 out of the workpiece. As the carriages move outwardly, the diamonds 170 and 171 move downwardly as already described, into the paths of the wheels 14 and 15, whereby the latter are dressed and trued. This outward motion of the carriages 6 and 7 takes place at a slow rate of speed, so that grooves will not be cut in the wheels by the diamonds. This outward motion of the carriages 6 and .7 shifts the oscillatory thing holding switch member 151 to prevent further dresstions will now be set forth in the order named. 3 i

As shown in Fig. 2, the lever 214 has a short arm 226 depending from the hub thereof. This short arm 226 is in engagement with a projection 227 formed on the side of a lever 228, which, as shown in Figs. 13 and 18, is mounted on the same pivot shaft 213 that supports the lever 214. The bottom of the lever 228 (see Figs. 2 and 18) has a link connection 229 with a threaded rod 230, the latter passing through a'pair of swivelled blocks, as indicated at 231 and 232, carried by the ends of short arms 233 and 234, respectively. Four adjustment nuts 235, 235 upon the rod 230 are provided for adjusting this mechanism.

The arms 233 and 234 are fastened to valve shafts 237 and 238, and referring to Fig. 15, these shafts have integrally formed thereon a pair of speed control valves 239 and 240. A spring 229a is adapted to reposition the valves.

The main fluid supply pipe 96 leads from the pump 28 to a casing 241 in which the said speed control valves 239 and 240 are located. The fluid passes first through a stop and start valve which has an entrance port 242 and an exit port 243 in a chamber 244 closed by full diameter portions 245 and 246 of a valve member, of magnetic material, 247. The actuation of this valve will be described hereinafter; suflice it for the moment to say that during the normal grinding operation of the machine, fluid is allowed to pass unimpeded through this valve, whence, emerging fromthe exit port 243, it goes through a branching passage 248 to the two valves 239 and 240.

The valve 239 connects by way of piping 249 to the port 46 of the valve unit 44 controlling the left hand table or carriage, while the valve 240 is connected in series by piping 250 with the entrance port 47 of the other valve mechanism for the right hand table or carriage 7. The valves 60 and 239, both of which are speed control valves, are in series, and therefore the setting of the one which most restricts the fluid, determines the rate of table travel. I That is to say, the left hand carriage is always under the influence of the throttle lever 62, and can indeed be stopped by turning said throttle lever to an extreme position, and at the same time the carriage can be slowed down by turning of the valve 239, but never can the carriage be caused to move faster by the turning of one of these two valves than the setting of the other one will permit. It should be borne in mind. that the carriage speed. so far as the fluid pressure actuation thereof is concerned, during the grinding operation, is great enough to cause the roller 42 to follow the cam 39; but during the dressing operation, the carriage is travelling by fluid pressure actuation alone, and at that time, and also hereinafter described when the carriages are about to impinge the rollers 42 onto the cam members 39, the valves 60 and 239 are so disposed that the carriages will be allowed to move only very slowly. It is obvious that everything said about the valves 60 and 239 in connection with the table or carriage 6 applies equally well to the valves 61 and 240 in relation to the carriage 7.

It will now be seen that as the diamonds 17 0 and 171 are lowered, which can not happen until the roll 215 is allowed to move toward the cam 211, the downwardly projecting arm 226 operates on the lug 227 to shift the lever 228 and through the link 229 to rock the arms 233 and 234 to turn the valves 239 and 240 to restrict the flow of fluid leading to the cylinders that actuate the tables or carriages, so that while the dressing diamonds are down, the carriages can only move at avery slow speed. The outward movement of the carriages is only a limited movement, to pass the wheels 14 and 15 across the dressing diamonds, and then the electrical circuit that has produced the shifting of the valves 58 and 59 is broken, whereupon the valves are automatically shifted to the position of Fig.v 15 to return the carriages as will now be set forth.

Referring to Figs. 2, 13, and 14, the cams 211 and 212 provide slots 251 and 252 through which pass bolts 253 and 254, which permits the relative adjustment of these cams, one of them being keyed to the shaft 209. The bolts have large heads 255 and 256 which project rearwardly of the rear face of the rear cam 211, and these bolt heads constitute means for actuating the oscillatory switch member 151. Said oscillatory switch member is shown in diagrammatic form only in Fig. 16 ;.its true shape is illustrated'in Fi s. 13 and 14. The contact terminals 148 an 150 comprise a clip whose opposite sides or blades are insulated from each other, and

a knife edge 257 of the oscillatory switch member 151 is adapted to fit between them and connect them electrically. O posite the terminals 148 and 150 is a sing e terminal 258 also in the form of a clip, the parts of which, however, constitute but a single terminal. The oscillatory switch member 151 is mounted on a pivot stud 259 and said oscillatory switch member provides a pair of rearwardly projecting studs 260 and 261. Between the studs 260 and 261, is a depending arm 262 which is journaled on the pivot shaft 259, and the lower end of this arm 262 is in the path of rotation of the bolt heads 255 and 256. The outward travel of the tables 6 and 7 for the dressing operation is sufiicient to cause the bolt head 255 to engage the arm 262, and as this arm is then in engagement with the stud 261, the motion carries the blade 257 away from the terminal outward travel of the carriages, the bolt head ,255 and possibly also the bolt head 256 will pass completely by the arm 262, so that on the return motion of said carriages, duringa subsequent grinding operation, these heads, moving in the opposite directions, re-

set the member 151 of switch 146 to the position shown in Figs. 13 and 14.

Following the movement of the oscillatory switch member 151 as just described, the direction of travel of the carriages is reversed 'bythe following mechanism. Referring to Figs. 1, 8 and 16, the carriages 6 and 7 each. provide metal projections 263 and 264 respectively, and the sub-bases 2 and 3 have adjustably mounted thereon a pair of projections 265 and 266 which lie toward the center of the machine, and another pair of projections 267 and 268 which lie outside of the first named pair. These projections 265 to 268 inclusive, are insulated and mounted with springs underneath them, so that they will give down wardly, and are supported in blocks 269, 27 Q, 271 and 272 respectively, which are adjustable along the machine frame as clearly shown. i

Referring now to Fig. 16, the projections 263 and 264 are grounded as shown at 271 and 272, being actually simply uninsulated from the table castings. The projections 265.

and 266 are electrically connected together and connected to a conductor 273. The'conductor 273 leads to a terminal 274 of a certain switch mechanism which will be hereinafter described. Suflice it to say that, until after the grinding operation, the terminal 274 is in engagement with a terminal 275 adjacent it, and this terminal 275 is connected by a lead 276 to a lead 277 having three branches as clearly shown in Fig. 16, one of which goes to.one end of an electromagnet 278, the sec--' ond of which leads to an electromagnet 279, and the third of which leads to an electromagnet 280. The function of the electromagnet 280 will be hereinafter set forth, but the electromagnets 278 and 279 are the return magnets, and are located on the inside ends of the casings 44 and 45, adjacent the ends of the valve members 58, and when energized attract said valve members 58 and 59 and move them again to the positions shown in Fig. 15. It will readily lee-apparent that this reverses the direction of flow of the fluid, and causes the carriages 6 and 7 to carry the grinding wheels back again into the workpieces. The magnets 278 and 279 are connected by leads 281 and 282 to the main supply lead 136, and they are energized when either of the projections 265 or 266 are engaged by the projections 263 or 264re'spectively, the coming together of the contacts 263 and 265 or 266 and 264 thus determining the length of the outward stroke o-f-the wheels. It is obvious that one set of these contacts is sufiicient, and that the provision of duplicate sets is unnecessary and constitutes merely a safety precaution.

The outward travel of the carriages 6 and 7 also resets the valve member 154, so as to .relieve the fluid pressure from the diamond operating cylinder 165, and to connect said cylinder to the exhaust port 162, and this takes place in the following manner. The valve member 154 has connected thereto a three armed lever 283 whose depending arm is connected to said valve member at 284. The lever 283 provides a horizontal arm 285 having a roller 286 in engagement with the cam 211. This cam, as already described, rotates when the carriage 7 moves, and it is so formed as not to interfere with the move ment of the valve 154 upon energization of the magnet 138, but upon the outward limit of the dressing stroke of the table 7, the cam contacts the roller 286 and positively resets the valve. A spring 287 is attached to the third arm of the three armed lever 283 in order to balance the weight of the horizontal arm 285.

As the carriages travel inwardly, they carry the grinding wheels 14 and 15 back into the workpiece a, in consequence of which the rollers 42 re-engage the eccentrics 39, and the carriage is then reciprocated by the opposed actuation of the ositive mechanical means,

rection, and finally engages the adjustable screw 76 carried by the rock lever 74. The rocking of this lever 74 brings together a pair of contact terminals 288 and 289, the former being part of the 'rock lever, and

therefore grounded, and the latter being con-- nected by a lead'290 to the terminal 258 of the switch 146. A lead 291 is shunted into the lead 290 and this lead 291 goes to one terminal of an electromagnet 292, the other terminal of said electromagnet being connected by a lead 293 to the main conductor 136.

From the wiring diagram of Fig 16, it will readily be seen, that insomuch as the oscillatory switch member 151 is, subsequent to the. dressing operation, in the position where it no longer contacts with the terminals 148 and 150, but instead contacts with the terminal 258, therefore the magnets 1 41 and 142, as Well as themagnet 292 will be pendicular to the surface.

preventing the grinding wheels from leaving the work gradually, with a gradual diminution of their contact areas therewith. Instead, the contact between-work and wheels is terminated at once over its entire area, by

. a withdrawal movement substantially per- This so-called back-01f movement, prevents the formation of lines or grooves in the highly polished finished, workpiece; the mechanism for effecting it is as follows Referring to Figs. 2, 4, 5 and 15, the magnet 292 is located directly behind the magnet 138, and is adapted to control a valve member 294 which has precisely the same shape as the valve member 154. The valve member is located in a bore 295 of the casing 155, which bore has communicating with ,it the same supply chamber 158 that supplies fluid under pressure to the other valve in said casing. Likewise said bore has communicating with it the exhaust passage 162 and a port 296 which is adapted to lead fluid by means of piping 297 to a cylinder 298.

The cylinder 298 is located on the back of the machine, as best seen in Fig. 2, and contains a piston 299 therein, which piston is connected to a lever 300, a spring 301 being employed to return the piston when the fluid pressure is relieved. The arm 300 is connected to a generally cylindrical member 302, which surrounds the rear end of the feed screw shaft 65, is externally threaded, and is received in an externally threaded portion of the machine frame. The screw shaft 65 is rotatably mounted in the member 302, but is held from axial movement in relation thereto, and therefore it will be seen that angular movement of this member 302 will cause a lateral displacement of the entire cross slide on its ways 64, without in the least disturbing the setting or adjustment of the screw shaft 65 or any of its operating mechanism. Such means for automatically backing off the grinding wheels in relation to a workpiece is per se not claimed in the present application, the said means being fully described in the above noted Guild Patent No. 1,856,185.

Behind the lever 283, and mounted on the same pivot 303 as the lever 283 was mounted, is a lever 304 which is best shown in Fig. 5. This lever 304 has a connection 305 with the slidable valve member-.294 already described. When the said member 294 is moved to the right, Fig. 15, to cause fluid pressure actuation of the back-off mechanism, the lever 304 is moved in a counter-clockwise direction. This lever 304 holds the contact terminal 27 4 adjacent which is the contact terminal 275, and movement of the lever breaks the connection between these terminals, and opens the circuit between conductors 273 and 276. The

outward movement of the carriages 6 and 7,

which started with energization of magnets 141 and 142 coincidently with the energization of the magnet 292, carries the projections 263 and 264 into engagement with the projections 265 and 266, such engagement representing the termination of the previous dress- I ing stroke, but owing to the fact that the circuithas been opened at 274 and-27 5, the magnets 278 and 279 arenot energized, and the carriages 6 and 7 continue to move outwardly unaffected by the coming together of the projections 263 and 265 on the one hand, or the projections 264 and 266 on the other hand. The carriages are thus caused to continue outwardly until the projection 265 on the carriage 6, or the projection 266 on the carriage 7, engages the projection 267 or 268 as the case may be. This causes both the carriages to be stopped, as will now be shown.

As shown in Fig. 16, an electromagnet 306 is connected by a conductor 307 to the main supply conductor 136. The other terminal of said electromagnet 306 is connected by a conductor 308 to a contact 309, the latter be- -ing normally connected to a companion contact 311 by means of a resilient bridging connector 310, that is carried by a certain switch lever, to be hereinafter described. The con-' tact 311 is connected by a branching conductor 312 to both the projections 267 and 268. When, therefore, either of these is engaged by the projection 265 or 266, the conductor 312 is connected to ground 271 or 272, and the magnet 306 is therefore energized and this stops both carriages in the following manner.

The magnet 306 is directly in front of the member 247, which as already stated is a valve member and made of magnetic material. The portion of full diameter 245 is, before the attraction of this member by the magnet 306, clear of the port 243 through which all fluid that actuates the tables must pass. Attraction of the member 247 by electromagnet 306 draws said member to the right and causes the portion 245 to cover the port 243, and this effectively prevents fluid from passing to actuate either of the tables, and as the fluid used is a non-compressible fluid, the tables therefore come to an abrupt stop. This allows the ground workpiece a in the workhead 16 to be removed from the machine, and an unground workpiece to be causesthe rotating chuck inside the workhead 16 to be stopped, and also reengages the terminals 274 and 275 by causingthe lever 304 to be repositioned, and this likewise repositions the valve 294, thus cutting off the pressure fluid from the back-off mechanism and allowing the spring means 301 to reposition the cross slide 16a on its way. These functions will now be described in the order named.

As indicated in Figs. 2 and 4, a lever 313 is pivoted at 314 to the machine frame, and this lever provides a roller 315 thereon. This roller 315 is in the same plane as the cam 211, and the cam is so formed that when the carriages have moved past the dressing position on their way to rest or idle position, the said cam 211 engages the roller 315 and moves the lever 313 in a counterclockwise direction, Fig. 2. Attached to the top of the lever 313 is a long bar or .rod 316. To the right hand end of the long bar 316 is attached a short bell crank lever 317 which is pivotally mount ed at 318 on the machine frame, and whose other end is connected to a link 319. The link 319 is connected to an arm 320 which is associated with a clutch mechanism generally designated by the numeral 321, which is adapted to clutch and unclutch the pulley 20 from the shaft 21. The details of. this clutch will not be described, since it could be of'any desired form, but it may be noted that it contains within itself a spring which tends to cause the parts to be clutched together, which therefore will reengage the clutch and reposition the lever 313 after'the cam 211 relieves the roller 315 on the subsequent inward motion of the carriages 6. and 7.

The lever 313 has attached to the lower part thereof a lug 322 which is adapted to engage a lug 323 on the lever 304. Movement of the lever 313 causes the lug 322 to engage the lug 323 and to reset the lever 304 to its original position, thus reen aging the terminals 274 and 275, so as to ma e the machine ready for the next grinding operation, and resettingthe valve-294 for the same purpose. I I

Outward motion of the carriages 6 and 7 also compensates the machine for previous dressing of the and wear thereo .That is to say, the machine makes use of the invention of Waldo J. Guild described in U. S. Letters Patent No. 1,682,672, wherein precision grinding is automatically attained by dressing the grinding wheels by a diamond having a fixed relation to the. finished surface locus of the workpiece, and causing a definite limited subsequent cutting advance between the workpiece and the grinding wheel. That invention presupposes that the dressing operation 'will take place each time with theaxis of the wheel slightly nearer the dressing diamond, so that there will be some material gr'nding wheels 14 and 15 '73. To that end the carriage 6 provides a block 324, which holds a pivotally mounted arm 325 on a stud 326. When the carriages are traveling outwardly, the left hand end of said arm 325 presents a rigid surface, because the arm 325 is backed up by a shoulder 327 on the block 324 as shown in Fig. 8. Under these conditions, the lower end of arm 325 strikes a lever 328 pivoted at 329 to the subbase 2, which arm provides a roller or other I abutment 330 adapted to engage the right hand end of the valve member 82. The lever 328 is normally held in adjusted position by a spring 331 which draws the roller 330 against a stop 3.32. On the outward travel of the carriage 6, the arm 325- engages the lever 328, as shown in Fig. 1, and this forces the roller 330 against the valve 82,.- This action shifts the portion of full diameter 86 of the valve member82 to the left of the port or passage 91 in the sleeve 90, and thus admits fluid pressure to the passage 104.

95 Referring to Fig. 15, the passage 104 communicates with piping 333 which leads to a cylinder 334 on .the front of thema chine. The cylinder 334 may be seen in Fig. 6, and it provides a piston 335 which is disposed to the right of the roller 117 carried by the arm 118. It will be remembered that the arm 118 is fastened to the shaft 119, to which is also fastened the two armed lever 120 whose left hand arm actuated the reciprocatory pawl 77. The right hand arm 336 provides an adjustable screw 337 which is in engagement with a portion 338 of an arm 339 pivoted on the shaft 119. The right hand end of the arm 339 is connected to a link 340, and the 'upper end of the link .340 is connected to another arm 341 which is fastened to a shaft 342. Oscillation of the shaft 342 releases the lock 69 holding the ratchet 68, and causes a pawl 343 to actuate said ratchet 68. The details of the pawl actuating mechanism" and the compensating gearing will not herein be descnbed, since they are substantially the same as disclosed in PatentNo. 1,682,673 to Edward M. Taylor already referred to, the

shaft 342 herein corresponding with the shaft

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