US3322110A - Dressing device for sharpening apparatus grinding wheel - Google Patents

Description

7 May 30, 1967 A. ANDERSON 4 DRESSING DEVICE FOR SHARPENING APPARATUS GRINDING WHEEL 5 sheets-Sheet 1 Filed Aug. 19, 1963 May 30, 1967 A. ANDERSON DRESSING DEVICE FOR SHARPENING APPARATUS GRINDING WHEEL 5 Sheets-Sheet 2 Filed Aug. 19, 1963 m HE DRESSING DEVICE FOR SHARPENING APPARATUS GRINDING WHEEL 5 Sheets-Sheet :3

Filed Aug. 19, 1963 y 1967 A. ANDERSON 3,322,110

DRESSING DEVICE FOR SHARPENING APPARATUS GRINDING WHEEL Filed Aug. 19, 1963 5 Sheets-Sheet 4 May 30, 1967 A, ANDERSON DRESSING DEVICE FOR SHARFENING APPARATUS GRINDING WHEEL Filed Aug. 19, 1963 m: mzhm United States Patent 3,322,110 DRESSING DEVICE FOR SHARPENING APPARATUS GRINDING WHEEL Axel Anderson, Rockford, Ill., assignor to Sundstrand Corporation, a corporation of Illinois Filed Aug. 19, 1963, Ser. No. 302,963 3 Claims. (Cl. 125-11) This invention relates in general to a grinding wheel dressing device for a sharpening apparatus.

An object of this invention is to provide a new and improved dressing means for a grinding wheel so as to dress the wheel in such a manner as to render it capable of grinding a complete tooth form.

And still another object of the invention is to integrate a wheel dressing means as described in the preceding paragraph into a unitary broach sharpening machine.

These and other objects of the invention will become more fully apparent from an examination of the following specification and drawings wherein:

FIGURE 1 is a prespective view of a broach sharpening machine embodying the principles of the present invention;

FIGURE 2 is a rear elevational view of the apparatus illustrated in FIGURE 1 with certain parts broken away for clarity;

FIGURE 3 is an enlarged view taken substantially as shown along line 3--3 of FIGURE 2;

FIGURE 4 is an enlarged front elevational view of the dressing means for the grinding wheel of the present invention;

FIGURE 5 is a view taken generally along line 55 of FIGURE 4;

FIGURE 6 is a view taken generally along line 6-6 of FIGURE 4;

FIGURE 7 is a view taken generally along line 77 of FIGURE 4;

FIGURE 8 is an enlarged view showing the grinding wheel engaging a broach tooth;

FIGURE 9 is an enlarged view taken along line 99 of FIGURE 2; and

FIGURE 10 is an enlarged view taken generally along line 1010 of FIGURE 2.

While this invention is susceptible to embodiment in many different forms, there is shown in the drawings and will herein be described in detail one specific embodiment, with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiment illustrated. The scope of the invention will be pointed out in the appended claims.

Referring now to the drawings, wherein like reference characters designate like or corresponding parts throughout the several views, the broach sharpening machine of the present invention is shown generally at 10, and includes a base 11 and a box-like housing or frame 12 affixed thereto. A slide 13 is mounted on the top of housing 12 for longitudinal reciprocating movement relative thereto, with the components for effecting such movements mounted within housing 12. A broach holding and indexing mechanism indicated generally at 14 is mounted on base 11, and a grinding wheel assembly indicated generally at 15 is mounted on slide 13 and is movable therewith into and out of grinding engagement with the broach teeth, as will hereinafter become more fully apparent. A dressing device indicated generally at 16 is provided to dress the appropriate form of the grinding wheel.

As is best seen in FIGURE 2, the means for effecting the reciprocation of slide 13 includes a motor 20 aflixed to base 11, and having a pulley 21 mounted on the output shaft thereof. A suitable switch 20a is mounted on the 3,322,110 Patented May'30, 1967 front face of housing 12 and is connected in circuit with motor 20 for manual control thereof. Suitable friction means 22 are provided on pulley 21 for driving engagement with the outer periphery of a large diameter wheel 23. Wheel 23 is mounted on a shaft 24 which is journalled in the rear wall of housing 12, and which extends into the interior thereof. A pinion 25 is fixed to the inner end of shaft 24, and drivingly engages a gear 26 which is rotatably mounted in the housing rear wall by a shaft 26a. A link 27 is pinned at one end to gear 26 and at the other end to an arm 28 that is aflixed to slide 13 to comprise a slide crank mechanism for reciprocating slide 13. Wheel 23 extends above the upper surface of slide 13, as can be seen in both FIGURE 1 and FIGURE 2, and thus is readily accessible for manual operation so that the movement of the slide 13 can be effected either automatically or manually as desired.

Grinding wheel assembly 15 includes a motor 30 (FIG- URE 2) suitably supported upon a motor support arm 31. A suitable switch 30a is connected in circuit with motor 30 for manual control thereof. A shaft 32 is rotatably mounted in the opposed end of motor support arm 31, with a pulley 33 being fixed to the rearward end of shaft 32. A grinding wheel 36, formed of a suitable abrasive material, is fixed to the forward end of shaft 32 for rotation therewith. An endless belt 35 is trained over a pulley 34 fixed to the motor output shaft to drive the pulley 33 and shaft 32.

Means are provided for adjusting the vertical elevation of grinding wheel 36, and include an adjusting arm pivotally mounted at between a pair of spaced blocks 41 and 42 which are secured to the upper surface of slide 13 by bolts or the like, not shown. A flattened portion 37 of motor support arm 31 is seated upon a planar shelf portion 42 at the forward end of adjustment arm 40, with an alignment pin 43 fixed in adjustment arm 40 and extending upward through a suitable opening in support arm 31. Movement of arm 40 about its pivot 45 is effected by a threaded member 46 that engages a correspondingly threaded hole in the end of arm 40, and bears against the upper surface of slide 13. A handle 47 is aflixed to the upper end of member 46 for manual operation thereof. Undesirable movement of grinding wheel 36 once it is in the adjusted position is resisted by a spring 48 that is biased between the upper surface of arm 40 and a washer 49a that is positioned under the head of a screw 49, which is threaded into the upper surface of slide 13.

Broach holding and indexing mechanism 14 includes a vertically extending upright 50 having a stand 51 positioned on base 11. Stand 51 includes a transversely extending upright portion 51:: terminating in a longitudinally extending upright portion 51b. A transversely extending member 52 is positioned adjacent stand 51 and includes an upraised portion 54 adjacent the rear edge 55 of base 11. An arm 56 is secured to the upper surface of upraised portion 54 and extends outwardly therefrom, as is best seen in FIGURE 2.

Broach holding and indexing mechanism 14 further includes a shaft 60 which extends toward grinding mech anism 15 from the upper portion of upright 50 at generally right angles thereto. An indexing plate 61 in the form of a segment is swingably mounted about shaft 60 by a pair of upwardly converging arms 62 and 63 which are joined at a hub 64 that is pivotally mounted on shaft 60. Indexing segment 61 is connected to arms 62 and 63 by a pair of suitable connector members 65, one of which is shown in FIGURE 2. Indexing segment 61 includes two spaced apart rows of teeth 66 and 67 with the teeth being disposed on the circumference of a circle, with the shaft 60 at the center, and with the spacing between the teeth corresponding to the spacing between the teeth on the breaching tool to be sharpened, as

'limit the swinging movement of indexing plate 61 in one direction.

A switch housing 70 is secured to upright 50, and the switch is connected into the circuit of motor 20 by cable 73. A switch operator 71 extends outwardly from upright 50 into the line of travel of a trip element 73 secured to arm 63. Thus, when indexing plate 61 reaches the end of a grinding cycle, trip element 73 will engage switch operator 71 to stop motor 20.

The means for holding the broaching tools will be best understood from a consideration of FIGURE 1 and FIGURE 3, and includes a backing plate 75 fixed to indexing plate 61. A pair of identical parallel posts 76 and 77 are mounted at spaced apart points on backing plate 75. A wedge member 78 includes a generally horizontally disposed lower surface 78a which is slida-bly mounted on posts 76 and 77, and an inclined face 79 disposed at an appropriate angle, as for example 30. A longitudinally extending slot 80 is provided in wedge 78, and is disposed in substantial parallelism with a line drawn through the centers of posts 76 and 77.

The type of broaching tool with which this invention is particularly concerned is set forth in detail in copending application, Ser. No. 142,088. A typical broaching tool is shown in broken line position at 90 in FIGURE 3 and includes a generally fiat blade shaped body with a series of teeth 91 along one edge thereof arranged to define a curved cutting profile with the specific form being shown as an arc of a circle. The body of the blade is shaped to have a rear edge 92, that is adapted to be seated upon inclined surface 79, and a side edge 93 arranged at an acute angle of approximately 60 and with the side edge 93 being generally parallel to a face 94 of a cutting tooth. The back edge 92 of the blade body is generally parallel to a tangent of the curved cutting profile intermediate its ends. As will hereinafter become more fully apparent, blades 90 are sharpened along a line that is generally parallel with edge 93 so that the blades will have the same general configuration after they are sharpened. The blade edge 93 is positioned against a post 81 which extends outwardly from backing plate 75 and serves as a stop means for the blade 90. A'locking member 82, having a knob 83, impales slot 80 and engages a suitable threaded opening in backing plate 75 to lock the wedge 78 in the appropriate adjusted position. Blade 90 is held in place against post 81 by a clamping bar 84 having locking members 85 and 86 at opposed ends thereof threadably engaging suitable openings in backing plate 75. It should be understood that while a single blade has been referred to above, the holding means are capable of accommodating a plurality of blades for simultaneous sharpening thereof.

Means are provided to vertically adjust the height of the broach mounting means, to the correct setting for the amount of stock to be taken off during the grinding cycle. To this end, a vertically elongate central opening 100 is formed inthe upper portion of upright 50, with an I-shaped block 101 mounted therein for vertical 'movement relative to upright 50. Shaft 60 is mounted in block 101 and is vertically adjustable therewith. A cap 102 is secured to the upper surface of upright 50, and a threaded member 103 extends through a clearance opening in cap 102, and into a suitably threaded opening in block 101. A knob 105'is secured to the upper end of member 103 for manual adjustment thereof. A calibrated scale 104 is provided on cap 102, so that as member 103 is adjusted by knob 105, the exact vertical elevation of shaft 60 may be determined. Means are provided to limit the total vertical adjustment of the broach mounting' means so that the final grinding cycle will take place at a fixed elevation, and as shown in FIGURE 3, comprises a bolt 99 that is threaded into the upper surface 4 of block 101 to engage cap 102 at the upper limit of travel of block 101. Volt 99 may be adjusted to vary the.

position of the stop as desired.

Means are provided for determining the position of the broach tool relative to the grinding wheel 36, and

includes a gauge arm 106 having a tubular sleeve 107 swingably mounted on shaft 60. A feeler member 108 is secured to one end of arm 106, and includes a feeler surface 109 disposed on an arc of a circle corresponding to the arc of broach teeth 91. A sleeve 110 is fixed to sleeve 107 on the opposite side of shaft 60 from feeler member 108. Sleeve 110 includes a longitudinally extending bore 111 in which a threaded release member 112 is received. Member 112 is provided with a knob 116 for manual operation thereof. A nut 113 is threaded on release member 112 and serves as a stop for one end of a compression spring 114. A threaded fitting 115 is mounted on release member 112 adjacent the end of sleeve 110 and serves as a stop means for the other end of spring 114. It will be readily apparent that the retraction of release member 112 by pulling out knob 116 will release gauge arm 106 for swinging-movement relative to '26, an upwardly inclined area 122 extending generally 90 around gear 26 and terminating in a flattened portion 123, and a downwardly inclined area 124 extending generally 90 around gear 26. A cam follower in the form of a roller 125 mounted on the end of a follower arm 126 is adapted to ride around the aforedescribed cam as gear 26 is rotated by pinion 25. Ann 126 is mounted for pivotal movement about vertically extending pin 127. A spring 128 is secured to arm 126 between follower and pivot 127, and to the adjacent housing wall, to resist clockwise movement of arm 126 as viewed in FIGURE 9. Arm 126 extends outwardly through a suitable opening 129 provided in the end wall of housing 11 and includes at the outer end thereof a suitable driver element 130-. A spring 131 is secured at one end to a vertically extending post 132, and at the other end to arm 126 adjacent driver,130 to resist counterclockwise movement of arm 126 as viewed in FIGURE 9.

A pair of side by side pawl members 135 and 136 are positioned in vertical alignment with the rows of teeth 66 and 67, respectively, of index plate 61. Pawls 135 and 136 are mounted for pivotal movement relative to the upraised portion 54 of transverse member 52 by a pin 137 which impales suitable aligned apertures in pawls 135 and 136, and which threadably engages a suitably threaded hole in upraised portion 54. As is best seen in FIGURE 3, pawls 135 and 136 extend outwardly from base 11 a Sllfli'. cient distance so as to be readily accessible for manual operation. Pawls 135 and 136 include upwardly extending tooth members 138 and 139 which engage the adjacent teeth on the index plate rows 66 and 67 respectively. Pawl 135 includes a vertically extending groove 140 that is opened toward housing 12, and is adapted to be engaged by the driving portion 130 of arm 126. Pawl 135 also includes a longitudinal slot 141 which receives pin 137, so that pawl 135 is slidably mounted relative to pawl 136. Thus, as arm 126 pivots counterclockwise as viewed in FIGURE 9, pawl 135 will be advanced to the left as viewed in FIGURE 3, and index plate 61 will be indexed one tooth length, with pawl 136 pivoting to allow the passage of the teeth on row 67 of index plate 61 to pass thereunder. When arm 126 rotates clockwise as viewed in FIGURE 9, pawl 135 will be moved to the right as viewed in FIGURE 3, with the tooth 139 on pawl 136 engaging the adjacent tooth on row 67 of index plate 61 to hold index plate 61 in position. As pawl 135 moves to the right as viewed in FIGURE 3, it will pivot around pin 137 to allow the tooth 138 to pass under the adjacent tooth on the row of teeth 66 of index plate61. As pawl 135 moves to the right as viewed in FIGURE 3, pawl 136 remains stationary with tooth 138 engaging the adjacent tooth on row 67 to hold index plate 61 in position. Arm 126 moves clockwise as viewed in FIGURE 9 when follower 125 rides from portion 123 down the inclined portion 124 and arm 126 moves in the counterclockwise direction as follower 125 rolls up incline 122, so that the index plate 61 will be indexed one tooth for each rotation of gear 26.

Referring now to FIGURE 4 through FIGURE 8, the dressing means 16 for grinding wheel 36 is set forth in detail, and includes a mounting block 150 secured to the front face of housing 12 as by bolts 151 and 152. Dowel pins are provided at 153 and 154 to accurately locate the support block 150 relative to the housing 12. A central recess 155 is provided in the forward face of block 150, and defines a vertical slideway for reception of the base 156 of the dresser assembly. Base 156 includes a pair of spaced apart vertical slots 157 and 158 which receive the shanks of bolts 159 and 160 therein respectively, with bolts 159 and 160 being received in suitably threaded horizontally aligned openings in block 150, to lock base 156 at the desired elevation. A screw 161 is threadably received in a tab 162 that extends outwardly from recess 155, with the end of screw 161 engaging the bottom surface of base 156 to provide an incremental adjusted means for the dresser assembly.

A generally cylindrically shaped member 163 is secured to the upper portion of base 156 with its axis being disposed in a horizontal plane. Member 163 has an axially extending bore 164 in which a cylindrical member 165 is rotatably mounted. A longitudinally extending bore 167 is provided in member 165, with the axis 168 of bore 167 being spaced from and parallel with the axis 166 of memher 165. A generally cylindrical member 169 is positioned in bore 167, and is rotatable about axis 168.

Member 169 extends outwardly from the left hand end of sleeve 163, as viewed in FIGURE 4 and FIGURE 6, and includes a narrowed end portion 170 having a threaded hole 171 extending transversely therethrough. A bolt 172 is threadably received in hole 171, and is provided with a diamond or other suitable dressing member 173 at one end thereof. A nut 174 is provided to hold the member 172 in the proper position on portion 170. A handle 175 is secured to the right hand end of member 169, as viewed in FIGURE 4 and FIGURE 6, as by a bolt 176. Handle 175 is bent as at 177 to provide a readily accessible gripping portion 178. A stop pin 180 is mounted on member 165, and is engageable with the upper surface 179 of handle 175. A second handle 181 is secured to the left hand end of member 165, as viewed in FIGURE 4 and FIG- URE 6, as by a bolt 182, and includes a readily accessible gripping portion 183. A stop 184 is provided on the left hand end of sleeve 163, as viewed in FIGURE 4 and FIG- URE 6, and is adapted to be engaged by the upper surface 185 of handle 181.

With particular reference to FIGURE 8, it will be noted that the grinding surface of grinding wheel 36 includes two arcuate grinding portions 360 and 36b, which function to grind the entire tooth form of a tooth 91 of the broach 90. To dress the grinding surface of wheel 36, handles 175 and 181 are gripped with the right and left hands respectively. While lightly holding handle 181, handle 175 is lifted against stop 180 overcoming the hand holding pressure on handle 181, to rotate member 165 until the upper surface 185 of handle 181 contacts stop 184. This movement swings the diamond 173 through an are slightly in excess of 180, and dresses the grinding wheel portion 36a. Handle 181 is then held firmly against stop 184, and handle 175 is swung downwardly about pivot 168. This movement causes diamond 173 to swing in an arc of approximately 180 to grind the grinding wheel portion 36b. Handle 181 is then returned to the down position illustrated in the drawings, and the dressing of the grinding wheel 36 is completed.

To operate the broach sharpening machine, the elevation of grinding wheel 36 is first fixed by the manual operation of knob 47. Dresser assembly 16 is then positioned at the proper elevation, and bolts 159 and 160 are tightened. Index plate 61 is then indexed to the position shown in FIGURE 1, with trip elements 73 having tripped switch actuator 71. The blade or blades are then positioned as shown in FIGURE 3, and wedge 78 is adjusted until feeler- 108 makes light contact with the broach teeth 91. Knobs 83, 85 and 86 are then tightened to secure wedge 78 and clamp bar 84 respectively, and gauge bar 106 is swung to the horizontal position illustrated in FIGURE 3. Slide 13 is then positioned by manual operation of wheel 23 to align a suitable pointer 190 (FIGURE 2), that is afiixed to the rear edge of slide 13, with a mark (not shown) on wheel 23 to properly position the dressing member 173 relative to the grinding Wheel 36. Switch 30a is then actuated to rotate grinding wheel 36, and the dresser assembly '16 is operated as set forth above to dress the grinding configuration of wheel 36. Index plate 61 is then lifted slightly to allow pawl teeth 138 and :139 to be manually moved out of engagement with the adjacent teeth on the indexing plate so that the indexing plate can be swung into the position shown in FIGURE 3 with arm 63 positioned in engagement with stop 68. The machine is then ready for the start of either manual or automatic grinding.

In the manually operated grinding cycle, hand wheel 23 is manually rotated to reciprocate slide 13 and index indexing plate 61 from tooth to tooth. The automatic grinding cycle is started by actuating switch 20a, and the grinding wheel 36 will sequentially pass through each tooth space on the broaching tool to be sharpened until switch actuator 71 is tripped by element 73 to complete one grinding cycle. Hand knob is then turned to raise the broaching tool to be sharpened for additional grinding. The operation is repeated until stop 99 contacts cap 102. At this position the grinding wheel 36 should be redressed for the final grinding cycle. It will be noted that during the initial grinding passes more stock is removed at the end of the blades than is removed in the center, because the swing radius of the blades is different from the final grind radius.

Since dresser assembly .16 is locked at a fixed location on housing 12, the configuration of the grinding wheel 36 is dressed in fixed relation to the base 11. Stop 99 is fixed in relation to the wheel dresser 16, and thus the finish radius of the broach teeth 191 is established by the machine and not by the operator. A suitable gauge may be provided to determine the position of diamond 173 relative to cylindrical member :169 so that the diamond may be periodically adjusted to compensate for wear thereof, and thus assure the production of the desired broach tooth form. From the foregoing it should be apparent that each of the objects of the invention have been fully achieved.

I claim:

1. A dressing device for a grinding wheel having first and second tangent arcuate portions, comprising: a sleeve having opposite ends and having an axially extending first bore; a first member pivotally mounted in said first bore and having opposite ends; a longitudinally extending axially offset second bore in said member, said member being substantially the same length as said sleeve and said second bore extending from end-to-end of said member; a second member pivotally mounted in said second bore and having opposite ends; a stop projecting outwardly from one end of said sleeve; a first handle secured to one end of said first member and movable in a plane perpendicular to the axis of said bores, said first handle having a surface engageable with said stop; an abutment projecting outwardly from the opposite end of said first member; a second handle secured to one end of said second. member and movable in a plane parallel to the plane of movement of said first handle, said second handle having a surf-ace engageable with said abutment for rotating said first member; a dressing member secured to the opposite end of said second member; said stop being located on said sleeve in a position whereby said dressing member is moved through a first are as said first member is rotated by engagement of said second handle surface with said abutment when said second handle is pivoted in one direction until said first handle surface engages said stop, and said dressing member is moved through a second arc tangent to said first arc when said second handle is pivoted in an opposite direction to pivot said second member while said first handle surf-ace is held against said stop. 7

2. A dressing device as defined in claim 1 wherein said sleeve is generally cylindrical, and said first and second members are generally cylindrical from end-to-end thereof.

8 3. A dressing device as defined in claim 1 wherein said opposite end of said second member extends outwardly of said sleeve.

References Cited UNITED STATES PATENTS 1,104,589 7/1914 Ward et a1. 51-34 1,573,153 2/1926' Garrison.

1,831,204 11/1931 Stauder 76-42 X 1,900,943 3/1933 Miller.

1,979,536 11/ 1934 Edgar 125-11 2,113,287 4/ 1938 Baldenhofer 51-56 2,301,610 11/ 1942 Brady 125-11.4 2,376,959 5/1945 Christle 125 11.4

HAROLD D. WHITEHEAD, Primary Examiner.

LESTER M. SWINGLE, ROBERT C. RIORDON,

Examiners. I. A. MATHEWS,-Assistant Examiner.

mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 322, 110 Dated May 30, 1967 Invent fl Axel Anderson It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 5, delete "Illinois" and insert -Delaware SIGNED AND SEALED MAR 101970,

o wmlm E. suuum, .m.

Attesting Officer Commissioner of Patents

Claims (1)

1. A DRESSING DEVICE FOR A GRINDING WHEEL HAVING FIRST AND SECOND TANGENT ARCUATE PORTIONS, COMPRISING: A SLEEVE HAVING OPPOSITE ENDS AND HAVING AN AXIALLY EXTENDING FIRST BORE; A FIRST MEMBER PIVOTALLY MOUNTED IN SAID FIRST BORE AND HAVING OPPOSITE ENDS; A LONGITUDINALLY EXTENDING AXIALLY OFFSET SECOND BORE IN SAID MEMBER, SAID MEMBER BEING SUBSTANTIALLY THE SAME LENGTH AS SAID SLEEVE AND SAID SECOND BORE EXTENDING FROM END-TO END OF SAID MEMBER; A SECOND MEMBER PIVOTALLY MOUNTED IN SAID SECOND BORE AND HAVING OPPOSITE ENDS; A STOP PROJECTING OUTWARDLY FROM ONE END OF SAID SLEEVE; A FIRST HANDLE SECURED TO ONE END OF SAID FIRST MEMBER AND MOVABLE IN A PLANE PERPENDICULAR TO THE AXIS OF SIAD BORES, SAID FIRST HANDLE HAVING A SURFACE ENGAGEABLE WITH SAID STOP; AN ABUTMENT PROJECTING OUTWARDLY FROM THE OPPOSITE END OF SAID FIRST MEMBER; A SECOND HANDLE SECURED TO ONE END OF SAID SECOND MEMBER AND MOVABLE IN A PLANE PARALLEL TO THE PLANE OF MOVEMENT OF SAID FIRST HANDLE, SAID SECOND HANDLE HAVING A SURFACE ENGAGEABLE WITH SAID ABUTMENT FOR ROTATING SAID FIRST MEMBER; A DRESSING MEMBER SECURED TO THE OPPOSITE END OF SAID SECOND MEMBER; SAID STOP BEING LOCATED ON SAID SLEEVE IN A POSITION WHEREBY SAID DRESSING MEMBER IS MOVED THROUGH A FIRST ARC AS SAID FIRST MEMBER IS ROTATED BY ENGAGEMENT OF SAID SECOND HANDLE SURFACE WITH SAID ABUTMENT WHEN SAID SECOND HANDLE IS PIVOTED IN ONE DIRECTION UNTIL SAID FIRST HANDLE SURFACE ENGAGES SAID STOP, AND SAID DRESSING MEMBER IS MOVED THROUGH A SECOND ARC TANGENT TO SAID FIRST ARC WHEN SAID SECOND HANDLE IS PIVOTED IN AN OPPOSITE DIRECTION TO PIVOT SAID SECOND MEMBER WHILE SAID FIRST HANDLE SURFACE IS HELD AGAINST SAID STOP.

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