US1933373A - Grinding and lapping machine - Google Patents

Description

Oct 31, 1933. w FRASER 1,933,373

GRINDING AND LAPPING MACHINE Filed Sept. 7, 1928 4 Sheets-Sheet l n N l2 G I gwumtoz Qrm y WARRENEFRAsER L 35% Qg m Oct. 31, 1933. w FRASER 1,933,373

GRINDING AND LAPPING MACHINE Filed Sept. 7, 1928 4 Sheets-Sheet 2 25 h II- V l0 \IIIIII I||| Mun u "'H" 4 \5 nu l7 v y/ m 3mm WW F g-Z MEEEN f." FRASER Oct. 31, 1933. 1 w. F. FRASER 7 GRINDING AND LAPPING MACHINE Filed Sept. '7, 1928 4 Sheets-Sheet 3 F nia gvwemloz F198 WARREN fIFfi-AsEri' 61cm wag (M. 31, 1933. w E FRASER GRINDING AND LAPPING MACHINE Patented Oct. 31, 1933 UNITED STATES PATENT OFFICE GRINDING AND LAPPING MACHINE Application September 7, 1928. Serial No. 304,467

8 Claim.

This inventionrelates to grinding and lapping machines and more particularly to machines of that type in which the wheel and the work support are relatively moved into and out of proximate engagement with each other.

In the operation of grinding machines of this type, it is desirable that the feed mechanism be so constructed that it will bring the grinding wheel and the work rapidly into close proximity, and thereafter relatively feed the wheel and the work slowly during the grinding operation and then stop the feeding movement to permit the wheel to grind itself out, and finally rapidly separate the wheel and the finished work.

One object of the present invention is to produce a grinding machine in which some or all of these movements may be obtained automatically and with the required degree of a curacy.

Another object of the present inventi n is to 20 simplify and improve the mechanism for relatively feeding the grinding wheel and the support rapidly to bring the wheel into close proxscale, of the feed, controlling mechanism;

imity to the work and for relatively feeding the grinding wheel and the support slowly to cause the wheel to grind the work.

This feature of the invention contemplates the provision in a grinding machine having a work support, a grinding wheel and fluid pressure mechanism for relatively feeding the wheel and the support to bring the wheeland the work into close proximity and for relatively feeding the wheel and the support to cause the wheel to grind the work, of means independent of the fluid pressure for automatically controlling the second I named feeding movement.

Broadly considered, the means independent of the fluid pressure for controiling the relative feeding movement of the grinding wheel and the support to cause the wheel to grind the work may take any form considered desirable or convenient. As herein shown, therapid and slow relative feeding movements of the wheel and the support are obtained by fluid pressure mechanism and it is preferred to resist the force of the fluid pressure during the slow relative feeding movement of the wheel and support by a train of mechanism which is connected to a source of power different from the fluid pressure mechanism.

Further features of the invention contemplate the provision of means for producing a uniformly slow relative feeding movement of the wheel and the support to cause the wheel to grind the work. for controlling the rate of this slow feed, for controlling the extent of the'slow feed which may the work and spark out, for relatively moving be varied by varying the rate duration of the slow feed, for stopping the slow feed to permit the wheel to continue to rotate in engagement with the wheel and the support to separate the wheel and the ground work, and for varying the interval of time between the stopping of the slow feed and the starting of the separating movement to vary the sparking out period or dwell, and in certain 1 devices, combinations and arrangementsof parts tending to improve and simplify the operation of grinding machines and enable them to operate with precision and without liability of wear, lost motion or breakage of parts.

These and other features of the invention will be best understood and appreciated from the following description of a preferred embodiment thereof, selected for purposes of illustration and shown in the accompanying drawings, in which Fig. 1 is a view in side elevation of the machine;

Fig. 2 is a similar view, partly in section;

Fig. 3 is a view in elevation, on an enlarged Fig. 4 is a viewin horizontal section on the s invention may beembodied with equal advantage in cylindrical grinding machines, lapping machines or grinding machines of any yp wherein it is necessary or desirable to secure the relative feeding movements of the grindingelement and the work which have been outlined above.

In the illustrated grinding machine the work support, comprising a magnetic chuck 10, is mounted upon the upper end of a vertical shaft 11 journaled in the lower portion of. the frame 12.

. The shaft 11 is rotated by a belt 13 which is passed around one of a series'of change speed pulleys 14 on the shaft 11 and around one of a series of driving pulleys 15 on a vertical shaft 16. The shaft 16 is driven by a vertical motor 17 bolted to the machine frame 12. The upper end of the shaft 16 is journaled in a bearing 18 carail) . and 55 secured to the frame 12.

ried by a bracket 19 which is bolted to the upper part of the frame 12.

An annular grinding wheel 20 is secured to the lower end of a vertical shaft 21 (Fig. 2) which is journaled in suitable bearings in a head 22 having vertical ways 23 by which it' is slidably mounted on the frame 12. The shaft 21 is rotated in the head 22 by a belt 24 which passes around a pulley 25 on the upper end of the shaft 16 and around a drum pulley 26 slidably keyed upon the upper end of the shaft 21. The weight of the shaft 21 and the parts carried thereby is more than counterbalanced by a spring 27 coiled about the upper end of the shaft 21 and interposed between the hub of the pulley 26 and an adjustable nut secured to the threaded upper end of the shaft 21. The result is that the shaft 21 will always be pressed upwardly against the thrust bearing 28 which is located between a shoulder on the shaft 21 and the lower end of the head 22.

In order to reciprocate the grinding wheel into and out of engagement with the work supported on the work support, the head 22 is provided with a bracket 29 (Fig. 2) which is connected to the lower end of a piston rod 30. The upper end of the rod 30 is connected to a piston 31 arranged to slide within a stationary cylinder 32 depending from a head 33 secured to the machine frame 12. The rod 30 enters the cylinder 32 through a suitable gland 35 secured to a cover plate 36 comprising the lower head of the cylinder 32.

The cylinder 32 is provided at each end with ports 3'7 and 38 which are connected respectively with pipes 39 and 40 (Figs. 2 and 8) leading to the ports 41 and 42 respectively in a valve casing 43 carried by the frame 12. The valve casing 43 is also provided with an intake port 44 and two exhaust ports 45 and 46. The inlet port 44 is connected by a pipe 47 to an oil pump 48 (Fig. 1) secured to the frame 12. The oil pump 48 may be of any commercial type provided with a relief valve and a by-pass so that the maximum pressure developed in the oil will be uniformly maintained at the desired point. The pump is driven by a belt 49 which passes over a pulley 50 on the oil pump shaft 51 and over a pulley 52 on a horizontal shaft 53 journaled in brackets 54 The shaft 53 is driven from a worm 56 on the shaft 16 which meshes with a worm wheel 57 on the shaft 53. The exhaust ports 45 and 46 communicatewith an-exhaustpipe 58 (Fig. 1,) which discharges the support.

'oil' into a reservoirtank .59 on theframe 12 from which the oilisdrawn for use by thepump 48 through a supply pipe 60.

. Mounted to slide within. the are casing 43 is a balanced piston valve 61 having a stem 62 whichv passes out of the valve casing 43 through a gland packing 63 held in place by a gland 64 47, flows out through the port 41 into the pipe 39 which cinducts the oil through the port 3'? into the cylinder 32, thus forcing the piston 31 downwardly to move the grinding wheel downwardly from its position of clearance towards the work During this movement, the oil below the piston 32 is discharged through the pipe 40,

oeaava port 42 and exhaust port 46 into the exhaust pipe 58.

When the piston valve 61 is displaced toward "the left, as seen in Fig. 8, oil under pressure flows through the port 42 into the pipe 40 which conducts the oil through the port 38, thus forcing the piston 32 upwardly to return the grinding wheel to its original position of clearance, which position is above that shown in Figs. 1 and 2. During this movement of the piston, the oil above it passes out of the cylinder into the pipe 39 and into the tank 59 by way of the port 41 and the exhaust port 45.

In the third or intermediate position of the piston valve it is moved but very slightly from the last named position and enough to close both the ports 41 and l2, thus allowing the fluid pressure to hold the grinding wheel elevated in its position of clearance, which also is the extreme upper position of piston 31 in cylinder 32. This movement of the valve 61 from the second to third named position is incidental to other movements or functions of other parts to be hereinafter described and is of no significance in the functioning of the valve 61.

As has been stated, it is desired that the grinding wheel in its downward movement be brought rapidly into close proximity to the work on the work support and then be fed slowly into the work during the grinding operation. In the illustrated machine, the rapid feed of the grinding wheel towards the work is effected by the fluid pressure feeding mechanism which moves the grinding wheel rapidly until the wheel is in close proximity to the work, at which time a micrometer screw 66 (Fig. 1), which is adjustably mounted on a bracket 67 secured to the head 22, engages a stop 68 which is supported from the machine frame 12 in a manner to be hereinafter described. The slow feed of the grinding wheel into the work isobtained by retracting the stop 68 while engaged by the micrometer screw 66 and followed up by the grinding wheel head under the influence of the fluid pressure mechanism. With this construction, the fluid pressure mechanism actuates the grinding wheel rapidly from its position of clearance to a position in close proximity to the work and then slowly from said last named position into the work to its final position. The rate and duration and, therefore, the extent of the feed of the grinding wheel into the work by the fluid pressure mechanism is controlled entirely by the movements imparted to the stop 68.

- The upper end of the stop 68 is provided with a collar 69 (Fig. 5) having a recess '70 therein which embraces a stationary pin 71 and thuspreventing rotation of the stop 68. The pin 71 projects from the cover 72 of a control box 73 secured to the frame 12. The lower end of the stop 68 is threaded into a nut or .sleeve 74 which is mounted to rotate upon and wihin a sleeve 75 carried by the control box 73. To reduce friction and insure easy rotation of sleeve 74 without undesired rotation of sleeve '75, the members of a ball race 76 are interposed between lateral faces formed on the sleeves 74 and 75. In order to control the downward movement of the stop 68 both at a'predetermined uniform rate and for a predetermined time or, stated in another way, to control the rate of the feed of the grinding wheel into the work to a predetermined extent, the sleeve 74 is provided with a gear "77 which forms one element of a train of mechanism (Ill) driven from a source of power different from the fluid pressure mechanism.

Broadly considered, the rotatable sleeve 74 alone may control the movement of the stop 68 as it recedes before the advancing head 22. But in order to stop the advance of the head after a predetermined interval of feed and hold the grinding wheel in engagement with the work to permit it to grind itself out, the sleeve is provided with external threads which engage similar threads formed in a nut 78 rigidly secured to the control box 73, said threads being of a the same pitch and lead as the threads on stop 68 and sleeve 74 if it is desired to obtain a complete dwell or rest of the slow feed between wheel and work. If, however, a very .slow feed is desired instead of a complete dwell or rest, then the said threads may be of a slightly less lead but in same direction as the threads on stop 68 and sleeve 74.. With this construction, the rotation of the sleeve 74 alone in a counter clock-wise direction, as viewed in Fig. 5, controls the fluid pressure feed of the grinding wheel into the work but provision is made, at the end of the feeding movement, for rotating both the sleeve 74 and 75 in the same direction to rotate the'sleeve 74 on the threads of the part 68 and sleeve 75 on the threads of part 78 and thus stop the further advance of the wheel into the work.

To this end, the sleeve .74 is provided with a collar 79 having a pin 80 (Figs. 5 and 6) thereon arranged to be rotated with the sleeve 74, during the feed of the wheel in'o the work, in a counter clockwise direction between a fixed stop 81 and an adjustable stop 82, both'stops being carried by a collar 83 rigidly secured to the sleeve 75. Normally, the pin 80 engages the stop 81. The distance the pin 80 moves before it engages the adjustable stop 82 determines the extent of the slow feeding movement, as this movement is stopped as soon as the pin 80 engages the stop 82 and starts the rotation of the sleeve 75 with the sleeve 74. When the sleeves rotate together, the threaded engagement of parts '75 and 78 raises the sleeves '75 and 74 at the same rate that rotation of the sleeve 75 alone would lower the stop 68, thus exactly neutralizing the receding action of the stop 68 and feeding of wheel into the work and causing a dwell or rest. ever, the thread on the sleeve 75 and-the part 78 is of slightly less lead than the thread on the stop 68 and the sleeve 75, then instead of a dwell or rest there will be a further very flnefeed of the wheel into the work controlled by the further recession of the stop 68 at a rate determined by the difference in lead or pitch of the threads on the sleeve 75 and the part '78 and the sleeve 74 and the stop 68. In order to aid the operator in adjusting the stop 82 to obtainthe proper length of the slow feeding movement of the grinding wheel under the influence of the fluid pressure mechanism as controlled by the stop 68, the peripheries of the collar 83 and the stop 82 are graduated, as shown in'Fig. 3.

The gear 77 is driven by a pinion 84 (Figs. 4 and 5) formed on the hub of a worm -wheel 85 whichis rotatably mounted on a stud 86 carried by the control box 73. The worm wheel 85 is driven by a worm 8'7 on a horizontal shaft 88, journaled in bearings 89 and 90 (Fig. 4) carried by the control box 73, and is held against end- If, hOW- I Rotatably mounted on the shaft 88 is a second sleeve 96 having a friction clutch face 97 integral therewith and having a pinion 98 secured thereto. The gear meshes with an idler pinion 99 which meshes with a pinion '100 secured to a horizontal shaft 101 journaled in extensions 102 and 103 from the control box 73. The shaft 101 may be rotated at diiTerent speeds as it is provided with change speed pulleys 104 any one of which may be driven by a belt 105 (Fig. 1) from a reversely arranged set of driving pulleys 106 on the shaft 53. The pinion 98 is driven in the opposite direction from that of the gear 95 and at a much greater speed by a large gear 107 on the shaft 101.

In order to clutch the sleeve 93 to the shaft 88, thus to rotate the sleeve 74 in a direction to allow the stop 68 to recede at a uniform rate before the advancing movement of the micrometer screw 66, the shaft 88 is provided with a clutch member 108 splined thereto. On one end face the clutch member 108 is provided with clutch teeth 94 to engage the clutch teeth 109 on the sleeve 93. The other end face of the friction face 110 to engage thetfriction face 97 .on' the sleeve 96. When the clutch teeth 94 and 109 are engaged, the shaft 88 is positively ro-. tated in a direction to cause the stop 68 to be retracted by the sleeve 74. When the friction faces 97 and 110 are engaged, the sleeve 74 is rotated in a-reverse direction and at high speed to return the stop 68 and the sleeves 74 and 75 to their original elevated positions.-

The clutch member 108 is shifted to rotate the sleeve 74 in one direction or the other by a yoke 111 having pivoted members thereon adapt ed to embrace a peripheral groove 112 formed in the clutch member 108. I The yoke 111 projects laterally from the-upper end of a vertical shaft 113 mounted to oscillate in the control box 73. The lower end of the shaft 113 (Fig. 8) is pro vided with an arm 114 which carries a pivot pin 115 for one end of a short link 116, the free end of which is pivoted on a pivot pin 117 secured to one arm 118 of a three-armed lever-119. The lever 119 is pivoted on a stud 120 depending from the control box 73., and is provided with an arm 121 whichis secured to the valve stem 62 by a link 122. The third arm of the lever 119 is provided with an operating handle 123. The link 117 and the arm 118 form a toggle which is normally held in its broken position by a spring 124, one end of which is connected to a pin 125 on the arm 114 and the other end of which is connected to a pin 126 depending from the control box 73'.

When the handle 123 is moved by the operative into the full line position of Fig. 8, the

toggle, comprising the link'117 and the arm 118,

through the link 122 opens the port 41, thus i starting the fluid pressure mechanism to feed the grinding wheel rapidly towards the work and also, through the vertical shaft 113and sliding clutch member 108, clutches the sleevev 93 to the shaft 88, thus starting the rotation ofthe sleeve 74 in a counter clockwise direction and slowly moving the stop -68 downwardly.

When the micrometer screw 66 strikes the moving stop 68, the fast feed of the grinding wheel under the influence of the fluid pressure mechanism is slowed down to the rate determined by the recession of the stop 68 under the control of the rotating sleeve 74 to allow the grinding wheel to feed slowly into the work. This slow feed of the grinding Wheel continues until the pin 80 engages the adjustable stop 82 on the collar 83, whereupon the pin 80 rotates the sleeve 75 at the same rate as the sleeve 74, thus stopping the further recession of the stop 68 and theslow feed of the grinding wheel into the work. This permits the grinding wheel to remain in the work and bottom or grind itself out.

The grinding out rotation of the grinding wheel continues until a tail 128 (Fig; 8) on the lever 119 is engaged by a stop 129carried by a ring 130 adjustably mounted, beneath a cover plate 131, on the bottom of the collar 79. When the tail 128 is engaged by the stop 129, further rotation of the sleeve 74 breaks the toggle, comprising the link 116 and the arm 118, thus restoring the lever 119 to the influence of the spring 124. The lever 119 is then thrown into the extreme dotted line position of Fig. 8 to move the valve piston to the left therein and to move the clutch member 108 to the right (Fig. 1). The movement of the valve to the left opens the port 42 to the oil pressure from port 44 and opens the port 41 to the exhaust port 45. The fluid pressure is thus exerted against the bottom of the piston 31 to elevate the grinding wheel and separate it from the ground work. The movement of the clutch member 108 to the right unclutches the sleeve 93 from the'shaft 88 and clutches the sleeve 96 thereto, thus rotating the sleeve 74 in a reverse direction and at a high speed to restore the sleeves '74 and 75 and the stop 68 to their original inoperative positions. The length of the dwell between the stopping of the slow feed of the grinding wheel into the Work and the starting of the separating movement of the grinding wheel from the ground work may be varied by shifting the position of the ring 130 on the collar 79 thus to adjust the position of the pin 129 relatively to the tail 128 of the lever 119. The operative is aided in making this adjustment by graduations formed on the peripheries of the collar 79 and the ring 130 (Fig. 3).

During the reverse rotation of the sleeve 74, the pin 80 moves away from the stop 82 but near the end of the reverse movement the pin 80 contacts with the fixed stop 81 and rotates the sleeve 75 back to its initial position Moreover, the re erse rotation of the sleeve '78 brings a pin 132 ecured to the cover plate 131 into contact with the tail 128, thus swinging the lever 119 and shifting the clutch member 108 out of operative engagement with clutch member 97. These members are so designed that a small movement of lever 119 accomplishes this result so that the accompanying incidental movement of the valve 61 is of no consequence as it makes no change in fluid pressure connections to the cylinder 32.

Prior to the commencement of the cycle of operations of the vertical spindle rotary surface grinding machine herein shown, all the working parts are stationary. The valve 61 is in its posltion for return of grinding wheel to its normal elevated position which is called, for convenience, the clearance position. The clutch member 108 also is in a neutral position out of engagement with either the clutch teeth 94 on the sleeve 93 or the friction face 97 on the sleeve 96. After the work has been engaged with the magnetic the lever 119 into the full line position thereof, 89

which movement produces simultaneously three results. It straightens the toggle, comprising the link 117 and the arm 118, which is held in made position by the pin 127 against the tension of the spring 124. It shifts the valve 61 from its initial 85 position to uncover the port 41 to the oil flowing under pressure from the inlet port 44, thereby admitting oil to the upper end of the cylinder to force the piston 31 downwardly and thus start the rotating grinding wheel away from its clear- 98) ance position. The described movement of the lever 119 also shifts the clutch member 108 on the shaft 88 into engagement with the clutch teeth 94 on the sleeve 93, thus clutching it to the shaft 88 to start the rotation of the sleeve 74 in a counter 95 clockwise direction. The grinding wheel moves downwardly rapidly until it comes into close proximity to the work, whereupon the micrometer screw 66 strikes the stop 68. This position of the grinding wheel is called the initial grinding feed 1108 position and may be varied and controlled by changing the position of the micrometer screw 66 on the head 22.

At the time the screw 66 strikes the stop 68, the sleeve 74 is being rotated by the train of mechanism connected to the power shaft 88 to cause the stop .68 to recede before the advancing grinding wheel head 22 uniformly, positively and at a slow rate of speed thus to control the further movement of the grinding wheel into the work 119 under the influence of the fluid pressure mechanism. This uniform rate of recession of the stop 68 under the control of the sleeve '14 may be varied by shifting the belt 105 on the change speed pulleys 104 and 106. The extent the grinding wheel 5 is fed slowly into the work or into the finish grinding feed position, is determined by the position of the stop 82 on the collar 88 on the sleeve 75. If the pin 80 travelling with the rotating sleeve 74 contacts with the stop 82 early in the 120 rotation of the sleeve 74, the extent of the slow feed of the grinding wheel into the work is less than when the pin 80 contacts with the stop 82 late in the rotation of the sleeve 78. During the rotation of the sleeve '74, it is held from moving 5 longitudinal by its weight and its engagement with the stationary sleeve 75. Consequently, its rotation functions solely to cause the stop 88 to recede downwardly When, however, the pin 89 engages. the stop 82 the sleeve 74 rotates the sleeve 75 in its nut 78, thus producing an upward movement of the sleeve '74. This movement of the sleeve '74 under the control of the sleeve 79 stops the retraction of the stop 68 and the slow feed of the grinding wheel in the finish grinding feed position. The grinding wheel is maintained in this position for a predetermined time in order to allow the wheel to bottom in the work or spark out, as it is called in the grinding art. This predetermined time or dwell may be regulated by a variation of the position of the ring on the collar '79.

The ring 130 carries the pin 129 which early or late in the combined rotation of the sleeves 7a and 75, depending upon the adjustment of the ,5 ring 130, engages the tail 128 of the lever 119 and breaks thetoggle, thus permitting the spring 128 to shift the valve 61 into position to operate the fluid pressure mechanism to return the grinding wheel to its original clearance position and also to shift the clutch member 108 into position to clutch the sleeve 96 to the shaft 88 to reverse the direction of rotation of the sleeve 74. The speed of this reverse rotation of the sleeve 74 is fast in order to return the sleeves '74 and 75 and the stop 68 to their original positions in the minimum amount of time. When this occurs, the stop 132' has engaged the tail 128 of the lever 119 and has shifted the lever into its original inoperative position, in which position the clutch member 108 is in its neutral position and grinding wheel in its clearance position.

It isapparent that in this machine, while the cycle of operations is initiated by the operator, the operations proceed automatically to feed the grinding wheel rapidly from the clearance position to the initial grinding feed position, to feed the grinding wheel slowly from the initial grinding feed position to the finish grinding feed position to cause the wheel to grind the work, to stop the advance of the grinding wheel into the work after the wheel has reached the finish grinding feed position to allow the grinding wheel to spark out, and finally to separate the grinding wheel and the groundwork and return the grinding wheel to its original clearance position where the parts contributing to the described automatic movements are automatically stopped in readiness for the operator to restart them.

Having thus described my invention, what I claim as new anddesire to secure by Letters Patent is:

11 In a grinding machine, the combination-with a base, of a work support, and a carrier for a grinding wheel mounted thereon, means for. rapidly moving the carrier from an initial position of clearance toward the work support, a stop in the path ofsaid carrier movable at slow rate simultaneously with the carrier to a predetermined extreme position, said carrier moving means there- 'upon acting to return the carrier rapidly to initial position, and means for returning said stop to its initial position at a slower rate of speed.

2. A grinding machine having, in combination, a work support, a grinding wheel, fluid pressure mechanism for relatively feeding the wheel and the support to cause the wheel to grind the work, automatic mechanism actuated independently of the fluid pressure mechanism for retarding the feeding movement when the wheel has reached a predetermined position, and a single controlling device for throwing both mechanismssimultaneously into action.

3. A grinding machine comprising a work sup-- port, a grinding wheel and carrier therefor movable :towards and from the work support, fluid pressure mechanism for rapidly feeding the wheel and carrier to a predetermined position in, close proximity to the work, a movable stop cooperable with the carrier to retard said rapid feed at a predetermined position and thereafter provide a continuous slow finish grinding feed, and automatic means independent of the fluid pressure mechanism to cause the stop to move continuously during the grinding feed and control the rate thereof;

41A grinding machine having, in combination, a grinding wheel carrier, a work support, a

grinding wheel, fluid'pressure actuated mechanism for moving the carrier and applyingpressure tending to move the same rapidly towards and from the work, a movable stop in the path of and engageable by said carrier, automatically actuated mechanism independent of the fluid pressure mechanism for positively and continuously retracting said stop at a slow, measured rate, thereby controlling the grinding feed irrespective of any pressure variations in the fluid pressure mechanism, means for stopping the wheel feed to cause a dwell before the separating movement of the wheel from the work, and means for independently adjusting said automatic mechanism to vary the dwell and the rate and duration of the feeding movement.

5. A grinding machine having, in combination, a work support, a grinding wheel carriage movable toward and from the support, means operating to urge the carriage toward the support,

'towards and from the work, a retractable stop enagageable with the grinding wheel support, means to cause said stop to recede at a relatively slow and constant rate and thereby control the feed of the grinding wheel support after engagement therewith, a manually operable lever for simultaneously operatingthe fluid pressure mechanism and the movable stop, mounted to be rocked by the operator to one position to move the wheel into the work and to be rocked in the opposite direction to rapidly withdraw the wheel from the work and return the stop member to its initial position, and automatically operated means to shift the lever in said opposite direction upon completion of the grinding operation.

7. A grinding machine having a yieldingly actuated wheel carrier, a mechanically operated stop therefor having a threaded portion, a nut for moving said stop, and a threaded holder for the nut arranged to be turned by the nut itself to reducethe effect of the nut upon the stop.

8. A grinding-machine comprising a base, a grinding wheel carrier, a work support, fluid pressure actuated mechanism for moving the carrier and applying pressure tending to move the same rapidly and continuously toward the work, a movable stop in the path of and engageable by said carrier located initially out of engagement therewith, and means independent of the fluid pressure mechanism for positively and continuously retracting the stop at a measured rate and thereby controlling the grinding feed after the carrier has overtaken and contacted with the stop, irrespective of any pressure changes in the fluid pressure mechanism.

WARREN F. FRASER.

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