US1911266A - Grinding machine - Google Patents

Description

May 30, 1933.

C. R. DAHLIN GRINDING MACHINE Filed May 2l, 1931 3 Sheets-Sheet 1 ...5MM hw gru/nudo@ n May 30, 1933. c. R, DAHLIN GRINDING MACHINE Filed May 21. 1931 3 Sheets-Sheet 2 C. R. DAHLIN GRINDING MACHINE May 30, 1933. 1,911,266

Filed May 21 1931 3 Sheets-Sheet 3 me/nin Patented May 30, 1933 UNITED STATES PATENT OFFICE CARL R. DAHLIN, OF WORCESTER, MASSACHUSETTS, ASSIGNOR TO THE HEALD MACHINE COMPANY, OF WORCESTER, MASSACHUSETTS, A CORPORATION 0F MASSA- CHUSETTS GRINDING MACHINE Application led May 21,

The present invention relates to grinding machines and its particular utility is in connection with internal grinding machines for grinding the internal cylindrical or conical surfaces or sleeves, gears, bushings, or like articles. f

In the patent to Heald & Hubbell No.

- 1,705,114, dated March 12, 1929, fluid actuated mechanism procures a traversing movement of a grinding wheel relative to the surface of a workpiece being ground, and, when the grinding operation is completed, procures an axial se aration of the wheel from the work to permit removal of the work from the machine. The machine is constructed so that the movement which procures the axial separation of the wheel and work occurs at a high rate of speed in order to decrease the time of each grinding operation. It is also customary, in this type of machine, to procure a separation of the wheel and work during the grinding operation nin order to obtain a dressing and truing operation on the wheel, during which operation the wheel is carried from the work to the dressing tool at the same rate of speed as the traversing movement. However, when the surface being ground and the dressing tool are'spaced a substantial distance apart, the necessarily slow movement of the wheel as itis withdrawn from the workpiece and carried past the dressing tool lengthens the time of each grinding operation and thereby reduces the efliciency of the machine. Accordingly, the principal object of the present invention is to provide a construction in which the above advantages are incorporated with none cf the disadvantages.

According to the present invention, after a predetermined amount of grinding'has occurred, during which the wheel reciprocates past the surface being ground at a slow rate of speed, the* wheel and work are axially separated at a high rate of speed to position the wheel in operative relation to a dressing tool. The movement of the wheel past said dressing tool is arranged to occur ata slow rate and the wheel is again returned, after ythe dressing operation, to operative grinding position relative to said work at a high rate of speed. When the grinding operation is 1931. Serial No. 538,973.

com leted, the lWheel and work are again axia ly separated at a high rate of speed. Other and further objects and advantages will appear from the following description taken in connection with the accompanying drawings in which-d F ig. l is a front elevational view of a grinding machine embodying the invention.

Fig. 2 is an isometric view of the reversin mechanism for the reciprocating table witg the reversing dogs thereon in normal operative position. I

Fig. 3 is a view similar to Fig. 2 with the dogs in the position they occup just prior to the location of the grinding w eel in operative relation to the dressing tool.

Fig. 4 is a view similar to Fig. 2 with the dogs in the osition they occupy at the` right hand end otp the extended movement for the dressing operation.

Fig. 5 is a diagrammatic pressure system.

Fig. 6 is a wiring diagram.

Like reference characters refer to like parts throughout the drawings.

Referring first to Fig. 1, the machine provides the usual reciprocatory table or carriage 1, which is ordinarily provided in any internal grin-ding machine. In such a machine either the grinding wheel or the work to be ground may be carried on the table 1, the reciprocation of the latter being utilized in either case to produce a relative traversing movement between the grinding wheel and the work. As here shown, the.table 1 supports and carries a wheel head 2, while the work which is to be operated upon is held in a work head 3, the latter being carried by a bridge 4, which spans the slideways provided by the machine frame for the back and forth movement of the table 1. In the machine herein illustrated, the grinding wheel view of the fluid 5 is rotated at high speed, as by a belt drive workpiece 8 is imparted in the manner dis I closed 5 mounted on the frame beneath thetable 1 and provides a piston having a piston rod 11 extending from one end of the cylinder and connected to a lug 12 on the reciprocating table. Movement of the piston to actuate the tabl(` is obtained by the introduction of fluid under pressure alternately to opposite ends of the cylinder 10.

The fluid under pressure is supplied by a pump 13, Fig. 5, driven in any suitable manner, the pressure side of which is connected by a pipe 14 to a channel l5 in a casting 16 in which the fluid control means is mounted. A rotating valve 17 is arranged to connect the channel 15 alternately to opposite ends of the cylinder by the pipes 18 and 20. With the valve in the position shown, fluid may flow through the channel 15 .and pipe 18 to the left hand end of the cylinder, whereby the piston within said cylinder and accordingly the table 1 is actuated toward the right. `In this position of the valve the pipe 20 to the right hand end of the cylinder is connected to an outlet 21, so that the actuating fluid `may exhaust from said right hand end of the cylinder. When' the valve 17 is in the opposite position, fluid under pressure flows i through the channel 15 to the pipe 20 andthe table 1 is accordingly moved toward the left since t-he pipe 18 is now connected to the outlet 21.

A throttle valve 22 is provided in the channel 15 by which to control the flow of fluid therethrough in order to regulate the speed of travel of the table 1; the position of said throttle valve is controlled by a handle 23, Fig. 1, on the front of the frame. A by-pass channel 24 is provided in the casting 16 by which fluid from the pump may flow directly to the reversing valve 17 without passing through the throttle valve 22; this permits the full flow of fluid from the pump directly to the ends of the cylinder, in order to procure movement of the table 1 at maximum s d regardless of the setting of the throtte valve. A valve 25 normally closes this by-pass 24,'said valve being held in closed position by a spring 26.

Movement of the valve 17 by which to rocure reciprocatory movement of the tab e 1 is obtained by a reversing lever 27 operatively connected to said valve; the lever in the normal operative position of the table is situated between two reversing dogs 28 and 30 on the table 1 in a position to be struck alternately by said dogs, and, by its consequent movement, rotates said valve to permit flow of the actuatingfluid under pressure alternately to opposite ends of the cylinder.

The cross-feed movement of the wheel head on the table 1, which is adapted to procure advance of the grinding wheel in cutting relation to the workpiece,is obtained b mechanism of the .type shown in the Gulld Patent 1,682,672, issued Au st 28, 1928. It is sufficient to note, for t e purposes of the present ap lication, that the wheel head 2 of the mac ine is mounted on a cross-slide, not shown, which is adapted to have an in and out movement on the reciprocatory table 1 to rocure a cross-feed movement of the in ing wheel against the workpiece. ovement of said cross-slide is secured b rotation of a screw shaft 31, Fig. 1, whichl engages an internally threaded member in the slide. Rotation of the screw shaft 31 in a clockwise direction procures inward movement of the cross-slide to urge the grinding wheel into cutting relation ywith the workpiece, and is obtained automatically in response to the reciprocatory movement ol? the table 1. As shown in Fig. 1, a ratchet wheel 32, which `is operatively connected to the screw shaft, is actuated y a pawl 33 pivotally mounted on an arm 34. As the1 table 1 reaches the left hand end of its normal working stroke, a portion of the 'arm 34 enages a cam-35 carried on a bar 36 extendin groin the bridge 4, thereby actuating sai pawl and procuring clockwise movement of the ratchet wheel. This actuation of the ratchet wheel by the pawl results in a stepby-ste cross-feed movement of the grinding wlieel against the surface of the workpiece. i

The preliminary grindin lon the workpiece is continued until the sur are of the workpiece being ground has reached a predetermined size in relation to the finished size at which time the grinding wheel is withdrawn from o rative relation to the workpiece for a dressing operation. This separation may be rocured in any suitable manner as by mec anism of the type disclosed in the above cited Guild Patent 1,682,672, in which the separation is determined by the position of the cross-slide, and occurs after a predeter` mined amountof grinding, or by mechanism of the ty e disclosed in the atent to Kem ton and allimore No.l 1,731, 19, in which t e separation is determined by gages which enter the bore of a workpiece when said workpiece reaches a predetermined size, the structure shown being similar to the structureof said Guild patent.

For the purposes of the resent application, it is sufficient to note t at a cam 37 is mounted on the ratchet wheel 32 for rotation therewith, and, during such rotation, engages successively with thumb screws 38 andv 40. Engagement of the cam with the screw 38, which occurs'prior to the final grinding operation, causes the wheel dressing instrumentalities of the machine to be brought into operation and procures axial se aration of the wheel and work to position t e grinding wheel in operative relation to the wheel dressing tool.. Engagement of the cam with the thumb screw 40, which occurs when the workpiece has been ground to the finished size, proeures axial separation of the grinding wheel and workpiece, the former being moved to extreme right hand rest position.

The dressing operation on the grinding wheel is procured when the cam 37 engages and aetuates the thumb screw 38 by the electrical connections shown in Fig. 6. Referrin to this figure, electrical current. is supplied by a direct current generator 4l which is driven continuously in any suitable manner. ()ne terminal of -this generator is grounded at 42 and the other terminal is connected by a lead 43 to a stationary plate 44 of a switch 45, which, as shown in Fig. 1, is mounted on the front lof the frame. Said switch 45 provides an oscillatory connector 46 by which said plate 44 is normally connected to a second stationary plate 47. In the other position'of the connector, the oscillatory connector 46 is swung out of contact with plate 47 whereby the electrical connection between the plates 44 and 47 is broken. The plate 47 is connected by a lead 48 to one terminal of an electromagnetO, the other terminal of said magnet being connected by a lead 51 to an electrical contact 52. The contact 52 is in a position to be engaged by a contact 53 in response to movement of the thumb screw 38 when said screw is actuated by the cam 37. With the plates 44 and 47 connected. since the contact 53 is connected to a ground 54 by a lead 55. engagement of contacts 52 and 53Kbv actuation ofv the thumb .screw 38 energizes the electromagnet 5() causing attraction of the armature member 56 pivotally mounted at 57 on the front of the frame. Movement of the armature member in response to energiz-at-ion of the magnet procures upward movement of the end of an upwardly extending leverarm 58 integral with said armature and counterclockwise rota-tion of a depending arm 60 also integral with said armature.

The dressing point 6l. Fig. 1, is moved into operative position for engagement.with the grinding wheel to procure a truing action on said grinding wheel by a mechanism fully disclosed in Patent No. 1,779,094. granted October 2l, 1930 to Heald and Guild. For the purposes ofthe present application, it is sufficient to n ot-e that the dressing point 61 is suitably supported in a pivotally mounted carrying member 62 and is swung downwardly from -t-he inoperative position of Fig. 1 into operative position, when the depending lever arm 60 attached to the 'armature 56 is actuated, by any suitable mechanism connecting said lever to the carrying member.

The upward movement of lever' arm 58, in response to engagement of cam 37`and screw 38, proeures the extended movement of the table by which the grinding wheel is moved past the dressing tool. Referring to Figs. 2, 3 and 4. the left hand table dog 28, which normally limits the ri 4ht hand movement of table 1. is carried by a lock 63, and the latter, instead of heilig secured directly to the table 1. as in the ease of the block 64 of the dog 30` is mounted for free sliding movement longitudinally of said table. When the table is making its normal reciprocations, to traverse the wheel over the surface of the workpiece, the block 63 is held in definite spaced relation to a block 65 which is held in fixed position on the table 1. The block 65 provides a latch lever 66 ivoted thereto and having its free end 6 disposed by gravity in a slot 68 formed in the block 63, thereby maintaining the spacing of blocks 63 and 65, and holding the block 63 in fixed position. Upward movement of the lever arm 58 engages and lifts said latch member to disengage the free end 67 from the slot 68, thereby breaking the normal connection between the slidable block 63 and the stationary block 65. so that on right hand movement of the table 1, the block 63 slidesalong the table and the dog 28 bears without eHect on the reversing member 27. Thus, on this particular stroke, the right hand movement of the table 1 is extended beyond its normal operative reciproeatory position, and the grinding wheel is carried out of the workpiece to a point just beyond the dressing device which is now in operative position. As the -table moves to the right on this extended movement, the block 63 carrying the dog 28 slides longitudinally of the table until an adjusting stud 69 on said block 63 engages the block 65, whereupon the solid backing thus afforded for the block 63 enables the dog 28 to shift the reversing mem` ber 27. The stud 69 is adjusted to engage the block 65,*and thus to procure reversal of the table 1, immediately after the grinding wheel has passed the dressing tool during the right hand movement of the table, and the left hand movement of said table thus inaugurated returns the grinding wheel into operative position relative to the workpiece. 'lhe block 63 is returned to the normal position in spaced relation to block 65, as the table moves to the left, by mechanism disclosed in the above identified Guild Patent 1.682,672.

The movement of the table as it is withdrawn from the workpiece for the dressing operation is arranged to occur at a high rate of speed, in order to diminish the time required for the extended dressing movement, and is obtained by a downward movement of the valve 25 against lthe pressure of the spring 26 which allows the fluid under pressure to be admitted directly to the cylinder, without passing the throttle valve. As shown in Fig. 5, the valve 25 has an elongated upwardly extending stem 70, the upper end of which is operatively connected to an arm 71 ivotally mounted at one end on the front o? the frame, in any suitable manner, as by the mechanism shown in the above cited Heald and Guild Patent No. 1,582,468. The arm 71 carries a roller 72 on the outer end thereof which is in line with and arranged to engage a longitudinal cam bar 73 mounted beneath the stationary block 64; said cam has upwardly beveled ends 74 and 75 to permit said roller to ride more readily onto the cam surface.

During the normal reciprocations of the table 1, with the grinding wheel in operative relation to the work iece, the roller 72 is not reached by the cam 3, since the table is reversed when the cam and roll are still spaced apart the cam being on the left of the roller, and the normal speed of traverse of the table as determined by the throttle valve 22 is un- `changed. However, vwhen the extended k:us

movement for the dressing o ration occurs, the cam 73 is carried to the right beyond the normal position, thereby engaging and depressing the roller 72 and the arm-71. Depression of the arm 71` opens the by-pass valve 25 causing the full fluid pressure as supplied by the fluid pump to act on the piston in the cylinder 10, thereby moving the table to the right at maximum speed. The valve 25 is held open by engagement of the roller 72 with the lower longitudinal edge of the cam 73 until the grinding wheel is directly tothe left of the dressing tool at which point the beveled end 75 of the cam allows the roller 73 to return to its normal position, whereby the by-pass valve is closed and the table is again under the control of fluid through the throttle valve. Accordingly, from this position, the table is carried at its normal slow rate of travel until the grinding wheel has passed the dressing tool in both directions of travel of the table, the table being reversed by engagement of the dog 28 with reversing lever 27, directly after the grinding wheel has passed tle dressing tool during the right hand movement of the table, as above pointed out. As soon as the wheel has been carried past the dressing tool on the left hand movement of the table on its return to grinding position, the cam 73 again engages and depresses the roller 72, thereby again opening the valve 25. The wheel is thus returned to operative engagement with the work at the maximum speed of the table. The cam 73, accordingly, is substantially equal in length to the distance between the surface a of the' workpiece and the dressing tool, sc that the maximum speed of the table is obtained only when the grinding wheel is between the workpiece and dressing tool and not in operative engagement with either.

On the am lilied right hand dressing stroke of the ta le 1, an arm 76, Fig. 6, pivoted at 77 on the block 65 and hanging by gravity in the position shown in Fig. 6, strikes an arm 78, Fig. 6, of switch member 45, rocking said oscillatory member 46 away from the bar 47, thereby breaking the circuit through the electromagnet 50 and preventing a repetition of the dressing stroke. Upon this deenergization of themagnet 50, the dressing tool is returned to its inoperative position of Fig. 1 and the lever arm 58 returns to its normal inoperative position.

After the return of the wheel to the work following the dressing operation, the crossfeed movement of the wheel a anst the work is continued until the cam 3 engages and actuates the thumb screw 40; this occurs, as above stated, directly as the workpiece is ground to predetermined finished size and procures the separation of wheel and work, the former being moved to extreme right hand rest position. Referring to the diagram of Fig. 6, movement of the thumb screw 40 makes an electrical connection between contacts 80 and 81; the contact 80 is connected to a ground 54 by a lead 82 and the contact 8l is connected by a lead 83 to one terminal of an electromagnet 84, the other terminal of said magnet being connected by a lead 85 to the lead 43 from the generator 41. Energization of ma net 84 by connection 'of the contacts.

80 an 81 causes attraction of an armature member 86 pivotally mounted on the same shaft 57 that forms the pivotal mounting for the armature member 56 on the front of the frame. An upwardly extending lever arm 87 is integrally connected to the armature 86 and attraction of the armature`86 procures upward movement of the end of said lever arm into the normal path of the reversing dog 28. Said dog 28 is pivoted on the carrying block 63 and normally rests by gravity in a position to engage with the reversing member 27. Upward movement of the lever arm 87 beneath the reversing dog 28 causes said dog to ride over the reversing member 27 without actuating it ywhereby the table is not reversed but is carried out of the workpiece to the right, and to its extreme right and position where it is brought to rest by a mechanism of the type disclosed in the above cited Heald and Guild patent No. 1,582,468.

The mechanism by which the table is brought to rest at the completion of the lgrinding operation is shown in Fig. 5 in w ich a va ve 88 is arran d to close the passage between the reversm valve 17 and the left hand end of the cyllnderlO, whereby farther right hand movement of the table is prevented. A bell crank lever 90 is pivotally mounted on the casting 16, with one of its arms extending upwardly for engagement with a portion of the table, the other end of said lever being in engagement with the upper end of the valve stem 91 of the valve 88. As the table 1 reaches its extreme right hand position the bell crank lever 90 is rocked by engagement of the upwardly extending arm with a portion of the table, thereby closing the valve 88 and discontinuing the right hand movement of the table.

The movement of the table with the grinding wheel from its operative relation with the workpiece to its rest position, as above pointed out, occurs at a high rate of speed to diminish the time required for a grinding operation. To procure this rapid movement, a cam bar 92 is mounted on the under side of the sliding block 63 in line with the cam 73. The end of the cam bar 92 adjacent the end of cam 73 is beveled to correspond with the beveled end of said cam 7 3 so that when the blocks 63 and 64 are in normal operating position, as shown in Fig. 2, the adjacent surfaces of the cams 73 and 92 are in contact, and said cams together provide a continuous under surface extending from the right hand end of cam 73 to the left hand end of cam 92. As the grinding wheel is withdrawn from the work to rest position, the roller 72 engages and is depressed by the under surface of the cam 73 and is held depressed by cam 73 and then by cam 92 for the full length of the withdrawal movement. The by-pass valve 25 is opened and held open by en agement of the cams 73 and 92 with ro ler 2, allowing the full pressure from the pump 13 to act directl on the left hand side of the piston so that tlle table is moved at a high rate of speed to its extreme right hand rest position where it is bron ht to rest, as above pointed out, by the closlng of valve 88.

After an unground workpiece has been inserted in the work-holding member and the ratchet wheel has been rotated in a counterclockwise direction to reposition the grinding wheel for engagement with said unground workpiece, the wheel is returned to the work for another grinding operation. A handle 93, Fig. 1, is operatively connected to the reversing lever 27 so that movement of said handle actuates the reversing valve to direct the fluid under pressure to the right hand end of the cylinder. thereby procuring movement of the table toward the workpiece. On this return stroke of the table 1 to workengaging position an arm 94 pivotally mounted at 77 and hanging by gravity in the position shown in Fig. 6, strikes an arm 95 of movable switch member 45, thereby rocking said switch member into the position shown in Fig. 6 in which contact between the plates 44 and 47 is made by the oscillatory member 46 to permit a dressing operation to occur during the subsequent grinding operation.

It will be apparent that the construction shown provides a machine by which the grinding wheel may be rapidly moved from operative] grinding relation with respect to the wor piece into position for a dressing operation to be performed by, means of the 'the cams 92 and 73 cooperating to cam 73 which permits the full pressure of the pump to act against the table actuating piston so that movement of the table is very rapid. Such a construction, however, permits reciprocation of the grinding wheel both in operative relation to the workpiece and in relation to the dressing tool at a slow rate of speed to procure a smooth grinding action on the workpiece and an even dressing action on the grinding wheel, the cam 92 being separated from cam 73 during the dressing operation to permit release of the roller 72 and accordingly closing of the by-pass valve 25 as the grinding wheel moves past the dressing tool, the separation of said cams 73 and 92 resulting from the sliding movement of block 63 along the table, the cam 92 being carried by said block as above pointed out. It will be further apparent that the final separation of wheel and work occurs at maximum speed and that the Wheel is returned to operative engagement with a successive workpiece at the same maximum s eed, by liold the by-pass valve 25 open, during the withdrawal and return movement of the wheel.

I claim:

1. In apparatus of the class described, a reciprocating table having a normal reciprocatory stroke and an extended stroke, means to limit the normal rate of traverse during said normal stroke and at the end of said extended stroke to procure a relatively slow rate of movement of said table, and automatic means controlled by the table movement to render said limiting means inoperative between the ends of said extended stroke to procure a relatively fast movement of said table from its normal stroke to the end of said extended stroke.

2. In apparatus of the class described, a reciprocating table actuated by fluid under pressure and having a normal reciprocatory stroke and an extended stroke, a throttle valve to control the flow of pressure fluid to limit the rate of movement of said table, and automatic means to render said valve inoperative only between the ends of said extended stroke, whereby said table is moved from its normal stroke to the end of said extended stroke at the maximum rate of speed, said table moving at the limited rate of movement at the end of the extended stroke.

3. In apparatus of the class described, a:

reciprocating table actuated by fluid under pressure and having a normal reciprocatory stroke and two extended strokes occurring in succession, means to limit the rate of movement of said table during the normal reciprocatory stroke and at the end of the first extended stroke, means to render said limiting means inoperative between the ends of said first extended stroke, and means cooperating with` said last means to render said limiting means inoperative during the entire length of the second extended stroke.

4. In apparatus of the class described, a reciprocatm table actuated by iuid under pressure an having a normal reciprocatory stroke and two extended strokes occurring in succession, a throttle valve to limit the rate of movement of said table during the normal reciprocatory stroke and at the end of the first extended stroke, means to render said valve inoperative between the ends of said first extended stroke, and means cooperating with said last means to render said valve inoperative during the entire length of the second extended stroke.

5. In a grinding machine, a grinding wheel having a normal reciprocatory traverse in operative relation to a workpiece, means to procure an extended movement of said wheel to carry said wheel past a dressing tool in operative relation thereto, means to control the rate of movement of said wheel to procure a relatively slow movement of said wheel over the surface of the workpiece and past the dressing tool, and automatic means to procure movement of said wheel during its inoperative movement from said workpiece to said dressing tool at a high rate of speed independently of said control means.

6. In a grinding machine, a grinding wheel having a normal reciprocatory stroke in operative relation to a workpiece and an extended stroke to carry said wheel past a dressing tool at the end of said stroke, means to procure said extended movement at a predetermined point during the grinding of a wor iece means to limit the rate of travel of said wheel in o erative relation to said workpiece and to said dressin tool, and automatic means to render said limiting means ino rative between the ends of said extended stro e.

7 In a grinding machine, a grinding wheel having spaced operative positions, means to procure a reciprocating movement of said wheel in One operative position and means to procure movement of said wheel to the other of said positions, means to limit the speed of movement of said wheel in the operative positions, and automatic means to procure a relativelyhigh rate of movement of said table between said operative positions independently of said limiting means.

8. In a grinding machine, a grinding wheel having spaced operative positions, fluid actuated means to rocure a reciprocating movement of said w eel in one operative position, means to procure movement of said wheel tothe other of said ositions, a throttle valve to limit the flow of uid and thereby the rate of movement of said wheel in the operative positions, and automatic means controlled by the movements of the wheel to render said valve inoperativeduring the movement of u said wheel from one position to the other whereby said movement occurs at the maximum rate of speed.

9. Ink a grinding machine, a grindin wheel, a workpiece and a dressing tool, s ai workpiece being in fixed spaced relation to said dressin tool, a reciprocating table having a normal reciprocatory stroke to procure relative movement of said grinding wheel and workpiece in operative relation, and an extended stroke to bring said inding wheel into operative relation to sai dressin tool at the end of said stroke, means to limit the rate of movement of said table during the normal reciprocato stroke and at the end of the extended stro e, and automatic means to render said limitin means inoperative between the ends of said extended stroke.

10. In a rinding machine, a grindin wheel, a workpiece and a dressing tool, sai workpiece being in fixed spaced relation to said dressing tool, a reciprocating table having a normal reciprocatory stroke to procure relative movement of said grinding wheel and workpiecein operative relation, and an extended stroke to move said inding wheel into operative relation to sairdressin tool at the end of said stroke, a throttle va ve to limit the rate of movement of said table during the normal reciprocatory stroke and at the end of said extended stroke, and means including a cam carried by said table adapted to open a by-pass around said valve to render said valve inoperative between the ends ofV said extended stroke.

1l. In apparatus of the class described a reciprocating table actuated by Huid un er pressure having a normal reciprocatory stroke and two extended strokes occurring in succession, a throttle valve to limit the rate of movement of said table during the normal reciprocatory stroke and at the end of the first extended stroke, a cam carried by said table adapted to open a by-pass around said valve to render said valve inoperative between the ends of said first extended stroke and a second cam slidably mounted on said table and adapted to be moved into cooperatin relation with said first cam to render said valve inoperative duriner the entire length of the second extended stroke.

12. In apparatus of the class described, a reciprocating table having a normal reciprocatory stroke and two extended strokes occurring in succession, means to control the rate of movement of said table during the normal reciprocatory stroke and at the end of the first extended stroke, means to render said control means ino erative between the ends of said first exten ed stroke, and other means coo erating with said last means to render sai limitin means inoperative durisitig 1the entire lengti of the second extended ro e.

13. In a machine of the class described, a

reciprocatory table having a normal reciprocating stroke in operative relation to a workpiece, and short and long extended strokes occurring in succession, means to control the rate of movement of said table to procure a relatively slow movement thereof during the normal reciprocating stroke and at the end of the shortextended stroke, means to procure movement of said table during the short stroke between the ends of said stroke at a high rate of speed independently of said control means, and other means cooperating with said last mentioned means to procure movement of the table during the long extended stroke at a relatively high rate of speed independently of the control means.

14. In a rinding machine, a grinding wheel, a wor piece, and a dressing tool, said workpiece being in fixed space relation to said dressing tool, a reciprocatory table having a normal reciprocating stroke to procure relative movement of sald grinding wheel and workpiece in operative relation, and an extended stroke to bring said grinding wheel into operative relation to said dressing tool at the end of said stroke by relative movement of said grinding wheel and dressing tool,

means to limit the rate of movement of said table during the normal reciprocatin stroke and at the end of the extended stro e, and automatic means responsive to movement of said table to render said limiting means inoperative between the ends of said extended stroke.

CARL R. DAHLIN.

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