US3643381A

US3643381A - Knife grinder

Info

Publication number: US3643381A
Application number: US74093A
Authority: US
Inventors: George M Standal
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-09-21
Filing date: 1970-09-21
Publication date: 1972-02-22
Anticipated expiration: 1989-02-22
Also published as: CA919917A

Abstract

A knife grinder for chipping knives having plane beveled surfaces interconnected by a curved beveled corner surface. The knives are mounted on a rotatable head that carries them past a movable grinding unit. A powered grinding surface engages each knife while moving in an arcuate path about the corner axis of the knife along the line of engagement and while moving in arcuate paths about pivot axes perpendicular to the straight knife edges. The grinding unit is guided by a pivot frame and powered by a constantly turning crank. Automatic advancement of the grinding unit toward the knives is provided by a pawl and ratchet wheel engaged at the completion of each complete pass of the unit across the knife surfaces.

Description

[ lFeh. $2, 1%72 [54] KNlllFE GRINDER [72] inventor: George M. Standal, 1916 San Fernando Place, Victoria, British Columbia, Canada [22] Filed: Sept. 21, 1970 [21] Appl.No.: 74,093

Standal ..5 1/55 Primary Examiner-William R. Armstrong Att0rney-Wells, St. John & Roberts [57] ABSTRACT A knife grinder for chipping knives having plane beveled surfaces interconnected by a curved beveled comer surface. The knives are mounted on a rotatable head that carries them past a movable grinding unit. A powered grinding surface engages each knife while moving in an arcuate path about the corner axis of the knife along the line of engagement and while mov ing in arcuate paths about pivot axes perpendicular to the straight knife edges. The grinding unit is guided by a pivot frame and powered by a constantly turning crank. Automatic advancement of the grinding unit toward the knives is provided by a pawl and ratchet wheel engaged at the completion of each complete pass of the unit across the knife surfaces.

41 (Ilaims, 11 Drawing Figures PATENTEUFEB 22 1912 SHEET 3 [1F 5 FIG. 5.

INVENTOR. 65026;,5 M. dTA/VDAL O @ZQM PAIENIHJFEB22 m2 3,6A 3,38l

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66 INVENTOR. (EORCE M. QFTANDAL K.) 62 131 7 mm i 122%,

KNIFE canvass BACKGROUND OF THE INVENTION This disclosure relates to a chipper knife grinder. An example of the type of knife involved herein is shown in my U.S. Pat. No. 3,282,312, granted Nov. 1, 1966, titled Chipper linife and Apparatus." Each knife includes a continuous cutting edge formed by beveled surfaces joined by a curved beveled surface forming a comer radius.

A prior chipper knife grinder for a different form of knife is shown in my U.S. Pat. No. 2,976,649, granted Mar. 28, 1961, entitled Chipper Knife Grinder." That disclosure is concerned with the grinding of a chipper knife which requires one ground face to be in a plane and the other ground face to be curved. In that arrangement both faces were ground simultaneously by two separate grinding units.

The present apparatus is an improvement upon my earlier grinder in that a single-grinding unit is used to work upon both plane and curved beveled surfaces to form the required cutting edges on a set of chipper knives. This eliminates the necessity for maintaining more than one grinding wheel surface and minimizes the mechanical complications of operating two grinders simultaneously. It also insures even grinding contact across the entire knife, since the same grinding surface is used on all surfaces.

SUMMARY OF THE INVENTION The invention disclosed herein basically comprises a supporting framework that rotatably carries a knife-mounting head for releasably fixing each knife radially outward from a rotational axis with the knife beveled surfaces exposed and facing outwardly. A motor is connected to the head for rotating it and the knives about the axis to thereby move the knife surfaces about a circular path. A knife-grinding unit is located tangential to the circular path of the knives for engaging the beveled surfaces. The knife-grinding unit includes a grinding surface pivotally mounted about a fixed axis coincident with the knife corner axis at the line of grinding engagement and further includes means for selectively arresting such pivotal motion and moving the grinding surface along the respective straight beveled surfaces. A common drive element controls the knife-grinding unit to successively grind the plane beveled surfaces and the intermediate curved beveled surface of each knife.

One object of this invention is to reduce the complexity required in prior knife-grinding machines by utilizing a singleknife grinding unit to engage both plane and curved beveled surfaces along knife-cutting edges.

Another object of the invention is to provide a knife-grinding apparatus which is adaptable to various sizes and shapes of knives.

Another object of the invention is to provide such an apparatus with automatic control of grinding depth, such control being constant across the entire knife. These and further objects and advantages of the invention will appear from the following description and accompanying drawings which illustrate a preferred form of the apparatus.

DESCRIPTION OF THE DRAWINGS FIG. l is a front elevation view of the apparatus;

FIG. 2 is a fragmentary horizontal sectional view taken along line 22 in FIG. 1;

FIG. 3 is a top view of the apparatus as illustrated in FIG. ll;

FIG. A is a fragmentary top view of the apparatus showing the grinding unit at its opposite extreme position;

FIG. 5 is a side elevation view of the apparatus taken from the left in FIG. ll;

FIG. 6 is a view similar to FIG. 2, showing the grinding unit at its opposite extreme position;

FIG. 7 is a side elevation view of the apparatus taken from the right in FIG. 3;

FIG. 8 is a schematic view illustrating the manner by which the knife surfaces are engaged by the grinding wheel;

FIG. 9 is a fragmentary enlarged side elevation view similar to FIG. 7, showing the manner by which the grinding unit pedestal is angularly tilted for grinding the knife plane beveled surfaces;

FIG. MI is an enlarged fragmentary sectional view through the grinding unit as seen along line lltl-lllll in FIG. l; and

FIG. Jill is a sectional view of the grinding unit as seen along line lll-ll in FIG. Ml.

DESCRIPTION OF THE PREFERRED EMBODIMENT The grinding apparatus is mounted on a stationary reference framework 10. The knives are clamped to a knifemounting device in the form of a cylindrical head llll supported on framework by means of a drive shaft 112 and bearings 13. The center of head If is coaxial with the horizon tal rotational axis of shaft 12. Shaft 12 and head II are rotated about the axis of shaft 12 by a motor I5 and speed reducer l6 drivingly connected to shaft 12 by a conventional drive chain The chipping knife and an example of an apparatus in which it is employed are described in detail in my U.S. Pat. No. 3,282,312. Each knife 20 consists of a rectangular side cutting blade 21 to which is joined a rectangular face cutting blade 22. The

blades

21 and 22 are joined along abutting edges and define an included obtuse angle, shown as l35 in the illustrated example. A common edge extending across both

blades

21, 22 is beveled along the outer knife surfaces, the bevel angle illustrated being approximately 34. The

corner joining blades

21, 22 is beveled about a corner axis that lies between the

blades

21, 22. Referring to FIG. 8, which schematically illustrates the grinding operation, the plane beveled surface along the side cutting blade 21 is designated at 2A, the plane beveled surface along the face cutting blade 22 is designated at 25, and the connecting curved beveled surface is designated at 26. The corner axis of curved beveled surface as is indicated at 27.

The head lll carries a plurality of mounting blocks l7 that clamp the individual knives 20. A spring-loaded clamp 18 holds each knife 20 on an individual mounting block 17. Any desired number of knives 20 may be mounted on head llll, which is preferably designed to hold one or two complete sets of knives for a chipping apparatus. The block 117 may be arranged to hold a plurality of knives facing in opposite directions or a plurality of knives all facing in a common direction about the periphery of head Ill, depending upon the requirements of the particular chipping apparatus. For purposes of illustration, only a single-knife block I7 is illustrated in the overall assembly views (FIGS. l, 3, 41, 5 and 7) but it is to be understood that identical blocks 17 are arranged about the complete periphery of head Ill and are angularly spaced so as to balance the weight of the assembly about the axis of shaft 112.

The knives 2.0 are arranged about the periphery of head If in a circular pattern with the

beveled surfaces

2A, 25 and 26 facing outwardly in a common radial orientation. In the example illustrated, the plane beveled surface 25 of the face cutting blade 22 in each knife is arranged in a radial plane across head ll perpendicular to the axis of shaft 112. The plane beveled surface 24 of the rectangular side cutting blade 21 of each knife is arranged in a concial path that is intercepted by the plane of surfaces 25 to form a frustrum of a cone about head 111. It is not essential that the knives 20 be so oriented, so long as the corresponding beveled surfaces thereof are mounted in a common radial orientation relative to the axis of shaft l2 and head Ill, with one beveled surface in a first circular path of movement relative to the axis of shaft l2, and the second beveled surface in an intercepting path.

The knife-grinding unit 28 comprises a grinding wheel Sill positioned so as to tangentially engage the

beveled surfaces

24, 25 and 26 during rotation of head If. The line of engagement along surfaces 26 is a radial line in a horizontal plane including the axis of head llll.

The general manner by which the knives 20 are ground by the wheel 30 can be seen in FIG. 8. Wheel 30 includes a conical grinding surface 31 which traverses the respective plane beveled surfaces 24, 25 and which pivots about an axis coincident with the corner axis 27 to engage the intermediate curved beveled surfaces 26. The mechanism by which such movement is attained by a single-grinding unit 28 is discussed below.

The grinding unit 28 is pivotally mounted to framework by means of an upright post 32 rotatably joumaled by a base bearing 33. Post 32 provides a first frame element for grinding unit 28. Offset slightly to one side of the upper end of upright post 32 is a horizontal pivot shaft 34 fixed to post 32 by a radially projecting support bracket 35. Shaft 34 thereby turns in unison with post 32 about the pivot axis extending vertically through the center of post 32.

The frame for grinding unit 28 also includes a base 36 pivotally mounted to shaft 34 by depending bearings 37. Bearings 37 support base 36 for pivotal movement about the horizontal axis of pivot shaft 34.

The base 36 of the frame for grinding unit 28 carries an upwardly extending pedestal 38 which supports the grinding unit 28 at its upper end. The details of the grinding unit 28 will be found below. I

The base 36, which is partially supported by the upright post 32, is also carried by a pair of arcuately aligned rollers 40 which are rotatably mounted at its underside. The rollers 40 are supported along the upper surfaces of three

guide plates

41, 42 and 43. The guide plate 41, at the center of the guide plate assembly, is stationary and rigidly fastened to framework 10 by an integral bracket 44. The guide plate 42, shown to the left in FIGS. 1, 4 and 6, is hinged to the abutting end of plate 41 about a hinged axis designated at 45. The axis 45 is perpendicular to the path of the plane beveled surfaces 25 of knives 20. Likewise, the remaining guide plate 43 is connected to the opposite end of plate 41 by a hinge having an axis 46 which is perpendicular to the path of the plane beveled surfaces 24 of knives 20.

The

plates

42 and 43 are each urged upwardly to positions coplanar with the center plate 41 by compression springs 47 interposed between their lower surfaces and the base of framework 10. Normal horizontal alignment of the plates 41-43 is achieved by abutment of their adjacent edges above the respective hinge axes 45, 46.

The angular extent of movement permitted the grinding unit 28 about the vertical axis of post 32 is limited by

upstanding stops

48, 50, which are selectively engaged by the sides of pivot shaft 34. These limits can be seen in FIGS. 2 and 6, which illustrate the respective positions of base 36 on the

plates

41, 42 and 43 while the plates are maintained in a common horizontal orientation.

The base 36 is designed with lateral side edges 51, 52 arranged immediately above

plates

42, 43 respectively. At the respective limits of angular movement of base 36 about post 32, the

edges

51, 52 will respectively be aligned at the outer edges of

plates

42 and 43. At this position, they contact an upstanding ear 53 of a spring-loaded trigger 54 which is normally received through a slot 55 at the respective end of

plate

42 or 43. The outward movement of a trigger 54 due to contact of

edge

51 and 52 frees the guide plate for downward pivotal movement about

axis

45 or 46 in response to pressure exerted on

plates

42 or 43 by the rollers 40. Triggers 54 are spring biased to a vertical position so as to be automatically reengaged within the slots 55 upon release of such pressure.

The design of base 36 is such that the axis of pivot shaft 34 is aligned immediately above the

hinge axis

45 or 46, when pivotal motion about post 32 is arrested by

stop

48 or 50, so that the base 36 can then pivot about the axis of shaft 34 while supported on the released guide plate 42 or 43 (see FIG. 7).

Movement of the grinding unit 28 is achieved by a powerdriven crank 56 on vertical shaft 57. Shaft 57 is driven by a motor unit shown generally at 60. This may be an independent motor or a unit driven from a common power source such as motor 15. An outwardly extending crank arm 58 is connected to crank 56 by a universal joint 61, its remaining end being connected to an upper plate 62 by a similar universal joint.

The rotational movement of crank 56 is transmitted to the pedestal 38 and its supporting frame through crank arm 58. It results in pivotal movement of the frame base 36 between the limits defined by

stop

48, 50. Following release of triggers 54 and arrest of frame movement about post 32, crank 56 causes pivotal movement of the grinding unit about the horizontal axis of shaft 34 while pivot shaft 34 has its axis perpendicular to either the plane beveled surfaces 24 (FIG. 3) or the plane beveled surfaces 25 (FIG. 4).

The grinding wheel 30 is fixed to the axis of a motor 63 which is slidably mounted on plate 62 for endwise movement parallel to the motor axis. This is accomplished by a shaft 64 journaled on plate 62 at its ends. Shaft 64 has a threaded portion 65 that is threadably engaged in a depending boss on the motor base 66. A handwheel 67 is fixed to the shaft 64 and has peripheral gear teeth which mesh with a pinion 70. Pinion 70 is fixed on a shaft 71 joumaled by bearings 72 depending from plate 62. Shaft 71 in turn has a ratchet wheel 73 at its end remote from pinion 70. Turning of handwheel 67 can be done by the handle 74 or by turning ratchet wheel 73.

To accomplish automatic turning of ratchet wheel 73, a pawl 75 is pivoted on an upstanding fixed post 76. Post 76 holds the pawl in the path of ratchet wheel 73. An adjustable stop 77 is threaded into the post 76 and a leaf spring 78 fixed on the post 76 yieldably holds pawl 75 against the stop 77, but allows the pawl 75 to slip over the teeth of ratchet wheel 73 when it is moving away from the post 76.

With this construction, when the pedestal 38 is oscillated to the left from the position shown in FIG. 3, the grinding unit 28 is moved in an arc about the axis of pivot shaft 34 to cause the wheel 30 to traverse each beveled surface 25 of the face cutting blades 22 moved past it by rotation of head 11. At the finish of each stroke of the grinding unit 28, the pawl 75 engages ratchet wheel 73 and turns it a fraction of a turn. This causes pinion 70 to turn the handwheel 67 which will advance the motor 63 and grinding wheel 30 toward the path of the knives 20. The grinding wheel 63 can always be brought to the work or away from it by turning handwheel 67 whenever pawl.

75 is out of engagement with the ratchet wheel 73.

It is believed that the general operation of the apparatus is clear from the description above. To grind a set of knives 20, the several knives are clamped by the individual mounting blocks 17. The grinding unit 28 is then adjusted to bring the grinding surface 31 into contact with the beveled knife surfaces, initial adjustment being accomplished by manipulation of handwheel 67. The

powered motor units

15, 60 are then activated to rotate head 1 1 and crank 56 respectively. The head 11 rotates the knives past the grinding wheel 30 at a rapid rate (50 rpm.) while the crank 56 is rotated at a relatively slow rate 1 rpm). The motor 63 for grinding wheel 30 rotates the grinding wheel at a high rate of speed common in grinding applications.

As is evident from the drawings, the grinding unit 28 is pivoted in a horizontal plane about the axis of post 32 to dress the beveled corner surface 26 of each knife as schematically shown in FIG. 8. At the completion of each pass of the grinding surface 31 across the comer surface 26, such pivotal movement is arrested by engagement of shaft 34 by one of the stationary stops 48, 50. Simultaneously, with such engagement the

edge

51 or 52 of base 36 will release the corresponding trigger 54 to permit the

plate

42 or 43 to pivot about its hinge with respect to the center plate 41. Such pivotal movement will be accomplished due to continued movement imparted to the grinding unit 28 by the crank arm 58, thereby overcoming the upward pressure of springs 47. The angular movement of the grinding unit 28 about the axis of pivot shaft 34 continues until the grinding surface 31 traverses the full width of the straight beveled surface at the respective side of the knives 20. The successive pattern of pivotal movement of grinding unit 28 about pivot shaft 34 and upright post 32 proceeds in a repetitive fashion from one end of the beveled surfaces to the other to accomplish complete grinding of the knife-beveled surfaces by the single-grinding unit: Advancement of the grinding wheel 30 toward the work is automatically accomplished at the conclusion of each cycle by automatic engagement of pawl 'l'fi as discussed above. The operation of the apparatus is continued until the desired degree of grinding has been accomplished, at which time each knife 20 will be ground to an identical extent so as to form a matched set of knives suitable for chipping purposes.

When desired, the automatic advancement of the grinding unit 2% can be overcome by turning of handwheel 67. In some instances it might be desirable to cut steps along the corner bevel of the knives, and this can be readily accomplished by manually positioning and setting the grinding unit as it traverses the corners of knives 2ft.

Obviously, the unit illustrated has been designed specifically for grinding of a particular knife design. Modification of the apparatus to accommodate differing knife lengths or blade angles is readily accomplished by changing the pivotal axis positions on the grinding unit or by modifying the stroke of the powered crank assembly.

Various modifications might be made in this structure without deviating from the basicconcepts discussed above and the general relationship of the elements described in detail herein. Therefore, only the following claims are set out as limiting definitions of the disclosed invention.

Having thus described my invention, I claim:

1. In an apparatus for grinding bent chipping knives of the type comprising a cutting blade having a plane beveled surface terminating along a curved beveled surface:

knife-mounting means for releasably fixing a plurality of said knives at positions located radially outward from a central rotational axis with the respective knife beveled surfaces exposed and facing outwardly;

power means operatively connected to said knife-mounting means for rotating said knife-mounting means about said rotational axis to thereby move the beveled surfaces of said knives about circular paths centered about said rotational axis;

knife-grinding means including a grinding surface tangential to the rotational paths of the beveled surfaces of knives on said knife-mounting means;

said knife-grinding means comprising means for pivoting the grinding surface along a curved path tangential to the path of the curved beveled surfaces of said knives about said rotational axis;

said knife-grinding means further comprising means for selectively arresting the pivotal movement of the grinding surface about said first axis and subsequently reciprocating the grinding surface in a path tangential to the path of the plane beveled surfaces of said knives about said rotational axis.

2. In an apparatus for grinding bent chipping knives of the type comprising a side cutting blade having a first plane beveled surface, a face cutting blade having a second plane beveled surface, and a curved beveled surface joining the respective first and second plane beveled surfaces:

knife-mounting means for releasably fixing a plurality of said knives radially outward from a rotational axis with the respective beveled surfaces thereof exposed and facing outwardly in an arrangement balanced about said rotational axis;

knife-grinding means including a grinding surface located tangential to the rotational path of the beveled surfaces of knives on said knife-mounting means;

said knife-grinding means further comprising means for selectively arresting the pivotal movement of the grinding surface about said first axis and subsequently reciprocating the grinding surface in a path tangential to the path of the plane beveled surfaces of said knives about said rota tional axis.

3. in an apparatus for grinding bent chipping knives of the type comprising a side cutting blade having a first plane beveled surface, a face cutting blade having a second plane beveled surface, and a curved beveled surface joining the respective first and second plane beveled surfaces:

knife mounting means for releasably fixing a plurality of said knives radially outward from a rotational axis with the respective beveled surfaces thereof exposed and facing outwardly in an arrangement balanced about said rotational axis;

a stationary framework fixed relative to the rotational axis of said knife-mounting means;

knife-grinding means including a grinding surface for tangentially engaging the beveled knife surfaces;

a first frame member pivotally mounted to said framework about a first axis;

a second frame member supporting said knife-grinding means and pivotally mounted to said first frame member about a second axis perpendicular to said first axis;

and means on said framework operatively connected to said knife-grinding means for alternately pivoting said second frame member about said second axis while arresting pivotal movement thereof about said first axis to thereby traverse the respective rotational paths of said plane beveled surfaces of the knives about said rotational axis, or to pivot said first frame member about said first axis while arresting pivotal movement of said second frame member about said second axis to thereby traverse the rotational path of said curved beveled surfaces about said rotational axis.

l. In an apparatus for grinding bent chipping knives of the type comprising a side cutting blade having a first plane beveled surface, a face cutting blade having a plane beveled surface, and a curved beveled surface joining the respective plane beveled surfaces of said blades and centered about a corner axis between the blades:

a stationary supporting framework;

knife-mounting means on said framework for releasably fixing a plurality of said knives radially outward from a stationary horizontal rotational axis on said framework, the respective plane and curved beveled surfaces of the knives being exposed and facing outwardly in an arrangement balanced about said horizontal rotational axis;

means on said framework operatively connected to said knife mounting means for rotating said mounting means about said horizontal rotational axis to thereby move said knife-beveled surfaces about circular paths centered about said horizontal rotational axis;

knife-grinding means including a grinding surface for tan gentially engaging the beveled knife surfaces, said knife grinding means comprising:

a post centered on said framework about a vertical axis coincident with the knife corner axis in a horizontal plane containing said horizontal rotational axis;

a frame member mounted to said post about a second axis perpendicular to said vertical axis;

a powered grinder mounted to said frame member about said second axis including a grinding surface positioned at a height with respect to said framework so as to engage the curved beveled surfaces of the knives along said said knives;

and yieldable guide means on said framework in the path of said frame member about said vertical axis for permitting angular motion of said frame member relative to said post about said second axis in response to said powered means to thereby pass said grinding surface along the path of the respective plane beveled surfaces following engagement of said frame member by said motion limiting means

Claims

1. In an apparatus for grinding bent chipping knives of the type comprising a cutting blade having a plane beveled surface terminating along a curved beveled surface: knife-mounting means for releasably fixing a plurality of said knives at positions located radially outward from a central rotational axis with the respective knife beveled surfaces exposed and facing outwardly; power means operatively connected to said knife-mounting means for rotating said knife-mounting means about said rotational axis to thereby move the beveled surfaces of said knives about circular paths centered about said rotational axis; knife-grinding means including a grinding surface tangential to the rotational paths of the beveled surfaces of knives on said knife-mounting means; said knife-grinding meAns comprising means for pivoting the grinding surface along a curved path tangential to the path of the curved beveled surfaces of said knives about said rotational axis; said knife-grinding means further comprising means for selectively arresting the pivotal movement of the grinding surface about said first axis and subsequently reciprocating the grinding surface in a path tangential to the path of the plane beveled surfaces of said knives about said rotational axis.

2. In an apparatus for grinding bent chipping knives of the type comprising a side cutting blade having a first plane beveled surface, a face cutting blade having a second plane beveled surface, and a curved beveled surface joining the respective first and second plane beveled surfaces: knife-mounting means for releasably fixing a plurality of said knives radially outward from a rotational axis with the respective beveled surfaces thereof exposed and facing outwardly in an arrangement balanced about said rotational axis; power means operatively connected to said knife-mounting means for rotating said knife-mounting means about said rotational axis to thereby move the beveled surfaces of said knives about circular paths centered about said rotational axis; knife-grinding means including a grinding surface located tangential to the rotational path of the beveled surfaces of knives on said knife-mounting means; said knife-grinding means comprising means for pivoting the grinding surface along a curved path tangential to the path of the curved beveled surfaces of said knives about said rotational axis; said knife-grinding means further comprising means for selectively arresting the pivotal movement of the grinding surface about said first axis and subsequently reciprocating the grinding surface in a path tangential to the path of the plane beveled surfaces of said knives about said rotational axis.

3. In an apparatus for grinding bent chipping knives of the type comprising a side cutting blade having a first plane beveled surface, a face cutting blade having a second plane beveled surface, and a curved beveled surface joining the respective first and second plane beveled surfaces: knife mounting means for releasably fixing a plurality of said knives radially outward from a rotational axis with the respective beveled surfaces thereof exposed and facing outwardly in an arrangement balanced about said rotational axis; power means operatively connected to said knife-mounting means for rotating said knife-mounting means about said rotational axis to thereby move the beveled surfaces of said knives about circular paths centered about said rotational axis; a stationary framework fixed relative to the rotational axis of said knife-mounting means; knife-grinding means including a grinding surface for tangentially engaging the beveled knife surfaces; a first frame member pivotally mounted to said framework about a first axis; a second frame member supporting said knife-grinding means and pivotally mounted to said first frame member about a second axis perpendicular to said first axis; and means on said framework operatively connected to said knife-grinding means for alternately pivoting said second frame member about said second axis while arresting pivotal movement thereof about said first axis to thereby traverse the respective rotational paths of said plane beveled surfaces of the knives about said rotational axis, or to pivot said first frame member about said first axis while arresting pivotal movement of said second frame member about said second axis to thereby traverse the rotational path of said curved beveled surfaces about said rotational axis.

4. In an apparatus for grinding bent chipping knives of the type comprising a side cutting blade having a first plane beveled surface, a face cutting blade having a plane beveled surface, and a curved beveled surface joining the respective plane beveled surfaces of said blades and centered about a corner axIs between the blades: a stationary supporting framework; knife-mounting means on said framework for releasably fixing a plurality of said knives radially outward from a stationary horizontal rotational axis on said framework, the respective plane and curved beveled surfaces of the knives being exposed and facing outwardly in an arrangement balanced about said horizontal rotational axis; means on said framework operatively connected to said knife mounting means for rotating said mounting means about said horizontal rotational axis to thereby move said knife-beveled surfaces about circular paths centered about said horizontal rotational axis; knife-grinding means including a grinding surface for tangentially engaging the beveled knife surfaces, said knife-grinding means comprising: a post centered on said framework about a vertical axis coincident with the knife corner axis in a horizontal plane containing said horizontal rotational axis; a frame member mounted to said post about a second axis perpendicular to said vertical axis; a powered grinder mounted to said frame member about said second axis including a grinding surface positioned at a height with respect to said framework so as to engage the curved beveled surfaces of the knives along said horizontal plane containing said horizontal rotational axis; powered means on said framework for reversibly moving said frame member about said axes; motion limiting means on said framework in the path of movement of said frame member about said vertical axis for selective engagement by said frame member at angular limits of movement thereof relative to said vertical axis corresponding to a complete pass of said grinding surface across the path of the curved beveled surfaces of said knives; and yieldable guide means on said framework in the path of said frame member about said vertical axis for permitting angular motion of said frame member relative to said post about said second axis in response to said powered means to thereby pass said grinding surface along the path of the respective plane beveled surfaces following engagement of said frame member by said motion limiting means.