US2874517A

US2874517A - Grinding machine

Info

Publication number: US2874517A
Application number: US505423A
Authority: US
Inventors: Markle Adolf
Original assignee: MONTANWERKE WALTER AG FA
Current assignee: MONTANWERKE WALTER AG FA; MONTANWERKE WALTER AG Firma
Priority date: 1954-06-24
Filing date: 1955-05-02
Publication date: 1959-02-24
Anticipated expiration: 1976-02-24

Description

Feb. 24, 1959 Filed May 2, 1955 A. MARKLE GRINDING MACHINE 5 Sheets-Sheet l f Mair rr/e 57:

0mm 5. sm/rm A. MARKLE 2,874,517

GRINDING MACHINE 3 Sheets-Sheet 3 E Q Q mm Q 7 $2 8 .5 9 .Q R \X km 5. 1 l I l Imv v@ R 7 \w Q9 mm mm Q Q E a mm mqwm E E. Q 56 Feb. 24, 1959 Filed May 2, 1955 United. States Patent 2,874,517 GRINDING MACHINE Adolf Miirkle, Tubingen, Germany, assignor to Firma Montanwerke Walter Aktiengesellschaft, Tuebingen, Germany 7 Application May 2, 1955, Serial No. 505,423 Claims priority, application Germany June 24, 1954 10 Claims. (CI. 51-34) The present invention relates to grinding machines, and more particularly to a control device arranged in a grinding machine for grinding cutter heads having angularly spaced cutters.

It is known to provide in grinding machines turnable supporting means for a cutter head and to angularly shift the supporting means in accordance with the angular spacing of the cutters by means of a dividing head 2,874,517 Patented Feb. .24, 19595 ICC reversing the same, actuating means for operating the It is the object of the present invention to overcome the disadvantages of the known arrangements for grind ing a series of cutters arranged in a cutter head, and to provide means for automatically placing each cutter in proper grinding position.

It is another object of the present invention to provide motor means for turning the cutter head in opposite directions, and control means controlling the operation of the motor means so that the cutter head is' first turned into a position in which a cutter is located beyond a stop means and then rotated in the opposite direction until the cutter engages the stop means.

It is a further objectof the present invention to provide hydraulic motor means for rotating the support of the cutter head so that the ground cutter can be urged by the rotating motor into engagement with a stop member.

It is a still further object of the present invention to provide a pivoted control lever which is pivoted by a cutter moving into grinding position, and to reverse the motor by actuating means actuated by the pivotal movement of the control lever.

With these objects in view the present invention mainly consists in a grinding machine for grinding cutters on a cutter'head and comprises, in combination, turnable supporting means for supporting a cutter head having a plurality of cutters arranged spaced from each other a predetermined angle, drive means for turning the turnable supporting means, actuating means for actuating the drive means to turn the turnable supporting means from an initial position in one direction, control means for reversing the drive means for turning the turnable supporting means in opposite direction when the turnable supporting means have turned in the one direction an angular distance exceeding the predetermined angle, and stop means for stopping rotation of the turnable supporting means in the opposite direction in a final position spaced from the initial position an angular distance equal to the predetermined angle between adjacent cutters on the cutter head.

. According to a preferred embodiment of the present reversing valve means to actuate the hydraulic motor means to turn the turnable supporting means from an initial position in one direction, the supporting means being adapted to support in the initial positionthereof the cutter head with one of the. cutters in a grinding position, and a control device including a pivoted con-f trol lever-means movable between an arresting position and an actuating position and being connected to the reversingvalve means andadapted to be pivoted into the actuating position by the next following cutter during turning of the supporting means in the one direction for operating the reversing valve means to reverse the hydraulic motor means for turning the turnable supporting means in opposite direction when the turnable supporting means have turned in the one direction an angular distance exceeding the predetermined angle, the control lever means tending to assume the arresting position for being engaged by the next following cutter during rotation of the turnable supporting means in the opposite direction for stopping rotation of the turnable supporting means in the opposite direction in a final position spaced from the initial position an angular distance equal to the predetermined angle between adjacent cutters on the cutter head. a

In the arrangenientaccording to the present invention it is possible to accurately place the cutter in grinding position even if the angular spacing between the cutters on the cutter head is not exactly the same. Moreover, the hydraulic motor means can be regulated to different degrees in the two directions of rotation so'that the movement of the cutter toward the stop can be adjusted to obtain a slow engagement. Furthermore, the arrangement according to the present invention assures that the grinding operation can only be started after the cutter has engaged the stop means-in grinding position.

According to a preferred embodiment of the present invention electromagnetic means are provided for actuating the reversing valve means of the hydraulic motor and for operating the control valve of a hydraulic motor which reciprocates the grinding means.

The novel .features which are considered as characteristic forthe invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof,

will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which: a

Fig. l is an isometric view illustrating a grinding machine according to the present invention;

Fig. 2 is a schematic view including a diagram showing the electrical connections between, the various parts of the machine according tothe present invention;

Fig. 3 is a schematic sectional view showing an opera tional position of a control valve means;

Fig; 4 is a longitudinal sectional view of a preferred embodiment of a control device according to the present invention;-

Fig. 5 is a fragmentary sectional view on line 5--5 in Fig. 4; and

Fig. 6 is Referring now to the drawings, and more particularly to Fig. 1, the base Aof a grinding machine according to the. present invention carriesan upright supporting post B; A face plate C is turnably mounted on the post B and carries a projecting bracket D on which the grinding head E is reciprocably mounted. The grinding means F is mounted on the grinding head E. A support I on the base A supports a control device K which is illustrated in detail in Figs. 4 to 6.

A carriage is slidable on the base A and carries a turnable supporting means H which is rotated by a hydraulic motor 34 indicated inbro ken lines in Fig. l and carries a cutter head G. Fig. 1 illustrates the hydraulic motor coaxial with the turnable supporting means H, but it is also contemplated to arrange'the hydraulic motor adjacent the turnable supporting means and to connect it with the same by a suitable transmission.

-Fig., 2 diagrammatically illustrates the elements of a preferred embodiment of the present invention as applied in the grinding machine illustiatediil Pig- A hydfsulie engine includes a cylinder '10 and a reciprocable piston member 11. A piston rod 12 is fixedly connected to the reeiprocable piston member 11 and passes through the front walls of the cylinder 10. The ends of the rod' 12 arefixedly connected to the U-shaped reciprocablemen ber 13 which supports the grinding head E. Conduits '14 and 15 lead from the two chambers defined by the piston 11 in the cylinder 10 to a switching valve 16' whose movable valve member carries an arm 17 cooperating with the adjustable lugs 18 and '19 on the U-shaped member 13. Conduits 2t and 7 connect the switching valve 16 with a control valve means 21. Another conduit 22 con; meets the control valve means 21 with the cylinder chamber located on the right side of cylinder as viewed in Fig. 2. The control valve means 21 is connected to a pump 23 which supplies pressure fluid and includes a slide '24" which is urged by spring 26 in one direction out of the position illustrated in Fig. 2 and into the position illustrated in Fig. 3. Electromagnetic operating meansare provided for shifting the control slide 24 into the position illustrated in Fig. 2. A discharge conduit 76 permits discharge of operating fluid from the control valve means 21.

End contact means 30 including a pair of fined contacts 28 and a movable contact 31 are arranged adjacent he ep re ip s e m mber 13- The m able. contact 3 s op y m m e 1.3 as will be de ribed e i t in. mor d ail- The c t heed G s mou ted on the t rn ble supp ing me n H, s d cr d it r fe nce to g- 1; and rotates with the same when the supporting means -l-I are o t y h yd u ic motor 34- ,Hyd e otor 4 is connected to a reversing valve means 37 by supply nd dis ha e cond it and 6- Th r rs val e meens nc ud a piston em e hi m a l in a cylinder means 39 against the action of spring 43 or pri il e r m n t e mean 42 a e on ec d 8 he i te m mber 8 o h r v rsin valve me ns 37 nd'inelude ve w nd ng and 4. A. p mp 45 sun plies perat ng fl d. o th ev r ng valve means 37- A control apparatus, generally indicated with the refer ence numeral 46, includes a housing 47 in which a control device 48 is arranged, The control device 48 includes an actuating member 49 having an abutment flange cooperating with shoulders in housing 47 to. he shiftable in' housing 47 between an advanced position and a retracted p s n- A pr n 50 e mem er to he e t n F 2 into the advanced position, A control lever means ineludin e ntr l a m and a stop a m 56 is p otauy meun ed t 5 en. t e actuat g member 49. The stop means 56 is engaged by a cutter 58 when the same is in r ding-p sit n A contact means 52 is arranged adjacent the housing 47 and includes a movable contact member 51 which is connected to the actuating member 49 and operated bythe' the contacts 54 which are connected into the circuit 65 of a time-delay relay 66 operating a switch 67 in themain circuit 33 which will be described in greater detail hereinafter.

The control lever means is urged by the spring 59 into the illustrated position. A contact device 61 is operated by the control arm 57 of the control lever means. The contact device 61 includes a first pair of contacts 63 connected into a first circuit 71, and a second pair of conreacts-6 4 connected into a second circuit 70. The movable contact means 62 is connected by a connecting member 60 to the control arm 57. Spring means 62a urge the movable contact 62 into engagement with the first pair of contacts 63.

The first pair of contacts 63 is arran ed in a first circuit means 71 which includes the winding 40, a source of electric current 72, a time relay 175, and a pair of contacts 28. The second pair of contacts 64 is connected into a second circuit 70 which includes a source of electric current 74, a time relay 176, and the winding 41.

The switch 67 which is operated by the time-delay relay 66 is arranged in the main circuit 33 which also includes a source of electric current 69, a main switch 68 and a winding 25 of the electromagnetic means by which the control valve slide 24 of the control valve 21 is operated.

The apparatns according to the present invention operes is the f l ow n ma ne A cutter head Ci having a plurality of radially extending cutters 58 which are equally spaced from each other a predetermined angle, is placed on the turnable supporting means H. Fig. 2 illustrates a position in which motor 34 rotates in the direction of arrow S so that acutter 58.

engages the stop arm 56 of the control means. 48. In this position the cutter 58 is ground by the grinding means F.

At the beginning of the next following operation the time delay relay switch 67 in the main circuit 33 is closed, so that when the main switch 68 is closed, the electromagnetic means 25 is connected to the source of current 69 and the control slide 24 is moved into the position illustrated in Fig. 2 against the action of the spring 26. In this position of the control valve means 21, pressure fluid passes from the pump 23 into the conduit 20, and from there through the switching valve 16 and the conduit 14 into the left chamber of the hydraulic engine 10, 11 so that the piston 11, and the reciprocable member 13 are moved to the right in Fig. 2.- The fiuid passes from the right chamber in cylinder 10 through conduit into the control valve means 21 and is discharged through conduit 76. The reciprocable.

member 13 travels to the right in Fig. 2 until the lug 18. engages the control arm 17 of the switching. valve 16 and switches the valve 16 into a position in which ti Pr ssu e fluid passes through conduit 15 into the chamber located on the right in Fig. 2 in cylinder 11)- rupts the main circuit 33.

The lug 18 is so arranged that the piston 11 and reciprocable member 13 are reversed before the movable contact 31 is actuated since the member 13 is still spaced from the actuating portion 32 when the piston 11 arrives in its left dead-center position as viewed in Fig. 2

When he time-delay. relay 66 opens the switch 67, the electromagnetic means 25 become ineffective, and the spring 26 urges the control slide 24 into the position illustrated in Fig. 3. The pressure fluid passes in this position through conduit 22 into the cylinder chamber located on the right side in Fig. 2 and urges the piston member 11 and the reciprocable member 13 into an extreme position located beyond the dead-center position of the piston 11; In this position the reciprocable'member 13 engagesmember 32 and closes the contacts 28. Consequently, the first circuit means 71 are closed since the contacts 63 are still closed by the contact means 62. The winding 40 is supplied with current from the source of current 72, and the electromagnetic .means 42 shifts the valve member 38 of the reversing valve 37against the action of the spring 43, for instance to'theleft in Fig. 2. i

In this position the hydraulic motor 34 is supplied with pressure fluid from the pump 45 through the conduit 36 and starts rotation in counter-clockwise direction in the direction of the arrow R. The supporting means H and the cutter head G turn with the drive means 34, and the cutter 58 moves away from the stop means 56 so that the spring 50 urges the actuating member 49 into its advanced position. r

When 'thedrive means 34 turn the turnable supporting means H of the cutter head G in the direction of the arrow, R, the next following cutter 73 turns from the position illustrated in Fig. 2 in counter-clockwise direction, and engages the stop arm 56 of the control lever means, from below and pivots th'e same' in clockwisedirection in Fig. 2 until the control arm 57 shifts the movable contact means 62 of the contact means 61'into a position in which the second pair of contacts 64 is closed.

When the contacts 64 are closed, the source of current' 74 in the second circuit 70 is connected to the second winding 41, and .the reversing valve means 37 are shifted into a'position. in which pressure fluid is supplied to the hydraulic motor 34 through the conduit 35.

In this position of the reversing valve means 37, the

hydraulic mot0r-34 ,tends to turn in opposite direction in the direction of the arrow S. The actual reversal of rotation of the turnable supporting means H and of the cutter head G takes place a little later since the movable supporting means H and the cutter head G continue their rotation in the direction of the arrow R due to inertia. The arrangement is adjusted in such manner that the turnable supporting means H and the cutter head G turn through an angular distance exceeding the angle between cutters 58 and 73 into a position in which the next following cutter 73 is located on the left of the free end of the stop means 56 so that the control lever means can return to the position illustrated in Fig. 2 under the action of the spring 59 and of the first pair of contacts 63, which tend to close under the action of the spring loaded contact 62. Thecontacts 63 close, but the circuit 71 is not closed since the time relay 175, schematically shown in Fig. 2, is actuated so that the circuit 71 is closed after a predetermined time. At the time the circuit 71 is closed by the time relay 175,the switch 30 is already closed by member 13 due to the movement of the grinding head E, and the grinding head E has started its reciprocating motion. When the

arms

56 and 57 move back into the position shown in Fig. 2, the pair of contacts 64 is opened. Since at this time the motor 34 still continues its rotation in the clockwise direction of arrow S, a time relay 176. is provided in "the circuit 70 which keeps this circuit closed a predetermined time. Due to this arrangement energizing of the

windings

40, 41 is prevented before the next following cutter is in grinding position.

As described above, the drive means 34, 37 tend to rotate the supporting means and the cutter head in the direction of the arrow S and overcome the inertia of the turning members so that the cutter 73 moves from the position in which it was located on the left of the stop means 56.to a position in which it engages the stop means 56 so that the actuating member 49 is pushed back into its retracted position to the right in Fig. 2. The contacts 54 are closed and the time-delay relay 66 is energized and closes the switch 67 and thereby the main circuit 33. This position isillustratedin Fig. 2.

However, the cutter 73 is now in the position of the cutter 58 and ready for the next grinding operation.

During the entire grinding operation on each cutter, the hydraulic motor 34 is under pressure and tends to turn in the direction of the arrow S. The stop means 56, 49, however, prevent such turning, and the control means 48 and the actuating member 49 are held in the position illustrated in Fig. 2, in which a flange on member 49 engages thehousing 47.

From the above description it will be apparent that the grinding machine according to the present invention comprises a 'turnable supporting means H for supporting a cutter head, drive means 34, 37 for turning the supporting means, actuating means 40 for actuating the drive means to turn the supporting means from an initial position shown in Fig. 2 in the direction of the arrow R, control means 41, 48 for reversing the drive means to turn the supporting means in the direction of the arrow S when the supporting means have turned in the direction of the arrow R an angular distance exceeding the angle between two adjacent cutters, and stop means 49, 56 for stopping rotation of the cutter head in the direction of the arrow S in a final position in which cutter 73 has assumed the position of the cutter 58 illustrated in Fig. 2.

Figs. 4 to 6 illustrate a preferred embodiment of the control device which is indicated by the reference numeral 46 in Fig. 2.

Referring now to Figs. 4-6, in a tubular casing 80,

an inner tubular member 81 is arranged and threadedly' connected to the casing so that it can be adjusted by turning the hand wheel 82. The hand wheel 82 is mounted on the tubular casing so that the hand wheel may rotate relative to the tubular casing. For this purpose the hub of the hand wheel 82 is provided adjacent one end thereof with an annular groove into which inwardly bent end portions of a split collar 80a extend so that the hand wheel 82 may rotate with respect to the tubular casing 80 without being able to shift in longitudinal di rection thereof. The two halves of the split collar 80a are, respectively, fastened to the tubular casingSO by screws or in any other convenient manner.

A sleeve 83 is mounted in the tubular inner member 81 and is longitudinally slidable on ball-bearings 84 and 85, while a key 110 prevents relative turning between the inner tubular member 81 and the sleeve 83. A spring 86 abutting against a ring 87 which is fixedly connected to the tubular inner member 81, exerts pressure against the ring 88 which is fixedly connected to the sleeve 83 so that the ring 88 abuts against the right end (as viewed in Fig. 4) of a sleeve under the action of the spring 86.

The other end of the sleeve abuts against a shoulder 81' of the inner tubular member 81.

A housing 90 fixedly connected to the ring 87 supports a switch 91 corresponding to switch 52 in Fig. 2 whose operating member 92 engages the end face of the sleeve 83. The electrical conductors connected to switch I 91 are not illustrated.

A connecting member 93 is threaded into the sleeve 83 andis provided with a passage 94 adapted to house electrical conductors. The connecting member 93 is rigidly connected to a housing 95, and this housing 95 is movable together with the connecting member 93 and the sleeve 83 relative to the outer casing 80 against the action of the spring 86 a distance a.- A sealing means 96 is provided between the outer casing 80 and the housing 95.

A holding means 97 is fixedly connected to the housing 95 and provided on its outer surface with an abutment portion 98. The holding means 97 turnably support on a pin 99 which is attached to a fork-shaped member 100. Pin 99 projects with one end portion thereof into a bore in the fork-shaped member 100 and is secured thereto at the other end thereof by means of a bushing 101. A small pin 99 connects the pin 99 with a bushing 101 and with the fork-shaped member 100.

Two recesses 102 are provided'in the fork-shaped member 100 into which a holder 103 can be inserted. The holder 103 carries a stop means 104 and is secured in the respective recess bymeans' of a screw 105.

A lever 106 is screwed into the pin 99 and is urged by a spring 107 to turn in clockwise direction as viewed in Fig. 4. A

double arm lever

108, 109 engages with one arm 108 thereof the right end of lever 106, while the other arm 109 thereof engages the actuating portion 114 of a tumbler switch 113. The end portion of arm 109 is formed with a lateral projection as best seen in Fig.5.

Two stop screws 111 and 112 are arranged on the forkshaped member 100 and abut against the abutment portion 98 when the fork-shaped member turns. The angle through which the fork-shaped member 100 turns may be adjusted by adjusting the stop screws 111 and 112, whereby the angle through which the stop means 104 turnsis also adjusted.

The control device illustrated in Figs. 46 is a preferred embodiment of the control device 46 illustrated in Fig. 2. It will be understood that the stop means 104 corresponds to the stop arm 56, the lever 106 corresponds to the control lever 57, the tumbler switch 113 corresponds to the contact means 61, the sleeve 83 corresponds to the actuating member 49, and the switch 91 corresponds to the switch 52 in Fig. 2. The operation of the control device illustrated in Figs. 4-6 corresponds to the operation of the control device 46 illustrated in Fig.2.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of grinding machines for cutter heads dilfering from the types described above.

While the invention has been illustrated and described as embodied in grinding machine including a control device for reversing a motor turning a cutter head, it is not intended to be limited to the details. shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can byapplying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims. 1

What is claimed as new and desired to be secured by Letters Patent is:

1. In a grinding machine for grinding cutters on a cutter head, in combination, turnable supporting means for supporting a cutter head having a plurality of cutters arranged spaced from each other substantially equal angles; drive means for turning said turnable supporting means; actuating means for actuating said drive means to turn said turnable supporting means from an initial operative position in one direction, said supporting means being adapted to support in said initial operative position thereof the cutter head with one of said cutters in a grinding position; control means adapted to be actuated by the next following cuttersupported on said turnable supporting means during turning thereof in said one direction for reversing said drive means for turning said turnable supporting means in opposite direction when said turnable supporting means have turned in said one direction an angular distance exceeding the angle between said one cutter and said next following cutter; and stop means adapted to be engaged by the next following cutter during. turning of said supporting means and of said cutter head in said opposite direction for stopping rotation of said turnable supporting means in said opposite direction in another operative position spaced from said initial operative position an angular distance equal to the angle between said one cutter and said next following cutter so that said next following cutter is in said other operative position of said supporting means in exactly the same grinding position as said one cutter in said initial operative position.

2. In a grinding machine for grinding cutters on a cutter head, in combination, turnable supporting means for supporting a cutter head having a plurality of cutters arranged spaced from each other substantially equal angles; drive means for turning'said turnable supporting means; actuating means for actuating said drive means to turn said turnable supporting means from an initial operative position in one direction, said supporting means being adapted to support in said initial operative position thereof the cutter head with one of said cutters in a grinding position; and a control device including a pivoted control lever means movable between an arresting position and an actuating position and being connected to said drive means, said control lever means being adapted to be pivoted into said actuating position by the next following cutter during turning of said supporting means in said one direction for reversing said drive means for turning said turnable supporting means in opposite direction when the same have turned in said one direction and angular distance exceeding the angle between said one cutter and said next following cutter; and spring means urging said control lever to assume said arresting position for stopping rotation of said turnable supporting means in said opposite direction in another operative. position spaced from said initial position an angular distance equal to the angle between said one cutter and said next following cutter so that said next following cutter is in said other operative position of said supporting means in exactly the same grinding positionas said one cutter in said initial operative position.

3. An arrangement as claimed in claim 2 wherein said control device includes a stationary support; an actuating member mounted in said support for movement between a retracted position and an advanced position, said actuating member supporting said control lever means for pivotal movement; spring means urging said actuating member with said control lever means into said advanced position, said control lever means in said arresting position being adapted to urge said actuating member into said retracted position when engaged by said next following cutter during turning movement of said supporting means in said opposite direction in said arresting position of said control lever means; and stop means on said stationary support engaging said actuating member in said retracted position.

4. In a grinding machine for grinding cutters on a cutter head, in combination, turnable supporting means for supporting a cutter head having a plurality of cutters arranged spaced from each other substantially equal angles; hydraulic motor means for rotating said turnable supporting means; reversing valve means operatively connected to said hydraulic motor means for reversing the same; actuating means for operating said reversing valve means to actuate said hydraulic motor means to turn said turnable supporting means from an initial operative position in one direction, said supporting means being adapted to support in said initial operative position thereof the cutter head with one of said cutters in a grinding position; and a control device including control means connected to said reversing valve means and adapted to be actuated by the next following cutter during turning said supporting means in said one direction for operating said reversing valve means to reverse said bydraulic motor means for turning said turnable supporting means in opposite direction when said turnable supporting, means have turned in said one direction an angular distance exceeding the angle between said one cutter and said next following cutter, said control device including. stopmeans adapted to be engaged by the next following cutter during rotation of said turnable supporting means in said opposite direction for stopping rotation of said turnable supporting means in said opposite direction in another operative position spaced from said initial operative position an angular distance equal to the angle between said one cutter and said next follow ing cutter so that said next following cutter is in said other operative position of said supporting means in exactly the same grinding position as said one cutter in said initial operative position.

5. In a grinding machine for grinding cutters on a cutter head, in combination, turnable supporting means for supporting a cutter head having a plurality of cutters arranged spaced from each other substantially equal angles; hydraulic motor means for rotating said turnable supporting means; reversing valve means operatively connected to said hydraulic motor means for reversing the same; actuating means for operating said reversing valve means to actuate said hydraulic motor means to turn said turnable supporting means from an initial operative position in one direction, said supporting means being adapted to support in said initial operative position thereof the cutter head with one of said cutters in a grinding position; and a control device including a pivoted control lever means movable between an arresting position and an actuating position and being connected to said reversing valve means and adapted to be pivoted into said actuating position by the next following cutter during turning of said supporting means in said one direction for operating said reversing valve means to reverse said hydraulic motor means for turning said turnable supporting means 'in opposite direction when said turnablesupporting means have turned in said one direction an angular distance exceeding the angle between said one cutter and said next following cutter, said control lever means tending to assume said arresting position for being engaged by said next following cutter during rotation of said turnable supporting means in said opposite direction for stopping rotation of said turnable supporting means in said opposite direction in another operative position spaced from said initial position an angular distance equal to the angle between said one cutter and said next following cutter so that said next following cutter is in said other operative position of said supporting means in exactly the same grinding position as said one cutter in said initial operative position. I

6. An arrangement as claimed in claim and comprising electromagnetic means connected to said reversing valve means for operating the same and including first and second windings for shifting said reversing valve means between two reversing positions; first circuit means connected to said first windings and including a first pair of contacts; second circuit means connected to said second winding and including a second pair of contacts; a movable contact means movable between a first position connecting said first pair of contacts for energizing said first winding and a second position connecting said second pair .of contacts for energizing said second winding, said movable contact means being connected to said control lever means and being in said first position when said control lever means is in said arresting position and in said second position when said control lever means is in said actuating position; and means for urging said contact means into said first position, and said control lever means into said arresting position, respectively.

7. An arrangement as claimed in claim 5 and comprising an actuating member movable between an advanced and retracted position and tending to assume said advanced position, said actuating member pivotally supporting said control lever means and adapted to be moved to said retracted position when during rotation of said supporting means in opposite direction said control lever means in said arresting position is engaged by a cutter; contact means connected to said actuating member and being closed by the same when the same moves to said retracted position; a time-delay relay connected to said contact means and operated by the same; a main circuit including a switch connected to said time-delay relay and operated by the same; a grinding device for grinding the cutters; and operating means for operating said grinding device and including electromagnetically operated means connected into said main circuit.

8. An arrangement as claimed in claim 7 and including electromagnetic means connected to said reversing valve means for operating the same and including first and second windings for shifting said reversing valve means between two reversing positions; first circuit means connected to said first windings and including a first pair of contacts; second circuit means connected to said second winding and including a second pair of contacts; a movable contact means movable between a first position connecting said first pair ofv contacts for energizing said first winding and a second position connecting said second pair of contacts for energizing said second winding, said movable contact means being connected to said control lever means and being in said first position when said control lever means is in said arresting position and in said second position when said control lever means is in said actuating position; and means for urging said contact means into said first position, and said control lever means into said arresting position, respectively.

9. An arrangement as claimed in claim 8 wherein said grinding device includes a grinding means, and a hydraulic engine having a reciprocable member connected to said grinding means for reciprocating the same; control valve means hydraulically connected to said hydraulic engine and being movable between an operating position in which said reciprocable member reciprocates between two dead center positions and a control position in which said reciprocable member moves to an end position located beyond one of said dead center positions; end contact means connected into said first circuit means and being closed by said reciprocable member in said end position of the same; and electromagnetic operating means for shifting said control valve means between said operating and control positions, said electromagnetic operating means being connected into said main circuit.

10. An arrangement as claimed in claim 9 and including another adjustable time-delay relay connected into said one of said first and second circuit means.

References Cited in the file of this patent UNITED STATES PATENTS