Patent Publication Number: US-3875984-A

Title: Chipping apparatus

Description:
United States Patent 1 1 Plough 1 1 CHIPPING APPARATUS [75] Inventor: Irving L. Plough, Everett, Wash.  
 173] Assignee: The Black Clawson Company,  
 Middletown, Ohio 22 Filed: Nov. 30, 1973 2 1] Appl. No.: 420,534  
 [52] US. Cl 144/162 R; 83/700; 144/176; 144/218; 144/220&#39;, 144/236; 241/92; 241/93;  
 - 241/222; 241/297 [51] Int. Cl. B27c H08 [58] Field of Search 144/162 R, 163, 172, 173, 144/174, 175, 176, 218, 220, 316 A-326 D,  
 1 1 Apr. 8, 1975 Nilsson H 144/176 Lindquist H 83/700 X [57] ABSTRACT Chipping apparatus, for use in the production of wood chips for the preparation of paper making pulp, includes a rotor carrying multiple knives arranged in a right angled step pattern and a stationary anvil having a complementary stepped periphery. The rotor is of special construction incorporating land segments associated with the respective knives and of such spiral configuration with respect to the direction of feeding movement of the wood as to minimize the gaps between the rotor and anvil as each knife passes the anvil and also to serve as a means for limiting the extent of projection of the feed beyond the anvil and hence the maximum length of each chip to be cut. This chipping apparatus is accordingly especially suit able for use as a rechipper of oversized chips and for the chipping of waste wood of all types.  
 8 Claims, 20 Drawing Figures [56] References Cited UNITED STATES PATENTS 864,552 8/1907 Perkins et a1. 83/700 X 2,322,922 6/1943 Chase 241/93 3,308,862 3/1967 Traben 144/162 R 3,407,854 10/1968 Lindherg et a1. 241/92 X 3,477,483 11/1969 Lapointe 144/175 X PATENTEDAPR 1915 3,875,984  
 Sl&#39;iLZT 1 [if 4 PATENTEDAPR 8i875 FIG FIG-6 FIG-5 CHlPPlNG APPARATUS BACKGROUND OF THE INVENTION This invention relates to apparatus for producing wood chips for use in the pulp and paper industry.  
  There are two primary sources for such chips. one of which comprises whole trees and portions thereof reduced to log form. and the other of which comprises waste wood material such, for example. as scrap lumber, butts and trim ends left over from the production of lumber and the fabrication of wood products such as furniture. and pieces of veneer which contain defects rendering them unsuitable for a corporation in plywood and other veneer products The prior art conventionally has differentiated betweeen chippers intended to handle whole logs and chippers for waste wood material. Both types of chipper tend to produce a certain amount of oversized chips and wood fragments which would interfere with digestion of the properly sized chips with which they are initially mixed, although the proportion is substantially larger from waste wood.  
  These oversize fragments vary in size and form. Some are pencil size splinters. some are crescent shaped pieces from around knots, some are board-like pieces several inches wide by a foot or more long, and some are clusters of chips which have not separated from each other. All of these forms of overs are randomly&#39; mixed, and with their grain direction randomly oriented, as they leave the screen where they are separated from the properly sized chips. The machine used to reduce this material to acceptable size is commonly known as a rechipper. To be effective, the rechipper must be able to accept all forms of oversize material oriented randomly with respect to the infeed direction, and to reduce them to chips of acceptable size in a single pass through the machine.  
  The conventional construction of both waste wood chippers and rechippers includes a rotor equiped with multiple chipping knives, and an anvil across which the charge is fed to the rotor, the chipping action being to cut off such portions of the feed as project across the slot which extends between the edge of the anvil and the rotor face, and which is commonly of a width equal to the projection of the knife beyond the rotor from face plus the working clearance between the knife and anvil. Pieces of wood which approach the rotor with the grain direction parallel or approximately parallel to the knife line are therefore routinely reduced to overlength sticks. The dimensions of these sticks are approximately equal to the thickness of the unchipped material multiplied by its length and by the projection of the knives. For this reason, conventional chippers are basically unsuited for chipping small and randomly oriented material such as trim ends and oversized chips rejected by a chip screen.  
  This difficulty with conventional chippers is also accentuated by the fact that as each knife passes the anvil, and thereby opens the slot between the rotor face and the anvil, the motion of the knife produces a pressure drop immediately behind it which will have the effect of inducing movement of oversized sticks and splinters through the slot. This tendency is increased by the fact that the air currents and pressure drop created by passage of the knife promote upending of undesired thin pieces of wood for more ready passage through the slot. Further, the similarity in construction of conventional waste wood chippers and rechippers is such that elongated and other oversized fragments produced in preliminary chipping operations. and particularly in waste wood chippers, tend to follow the same course through a rechipper which resulted in their initial pro duction, namely to pass through the slot between the anvil and the rotor behind the knife and ahead of the next knife. and thereby to escape the desired reduction in size.  
 SUMMARY OF THE lNVENTlON The present invention was conceived with the purpose of providing a rechipper which would overcome the disadvantages of past rechippers. and which could be relied upon for high efficiency in the production of chips of proper size from oversized chips and other reject wood pieces from a chip screen. In the course of its development, however, it was found that the inven tion exceeded that initial objective and resulted in chipping apparatus which is substantially equally successful both for rechipping and for initial chipping operations on waste wood materials, and which is also adaptable to the chipping of whole logs.  
  The chippers of the invention are further character ized by an anvil having a stepped periphery which is substantially complementary to the profile of the rotor face, and this anvil is supported with its periphery matching the rotor profile and closely spaced therefrom to provide working clearance for the knife means. Thus the knife edges cooperate with the anvil to cut from wood material on the anvil a series of chips of essentially right angled section, with each pair of adjacent cutting edges making a cutting stroke along a corresponding pair of right angled edge surfaces ofthe anvil.  
  A further characteristic of chippers in accordance with the invention lies in the provision of lands on the rotor which are composed ofa plurality ofsegments al tcrnating symmetrically with openings in which knife means are mounted. In addition, each of these land seg&#39; ments has a spiral configuration in the direction of the feeding movement of the wood, and this spiral configuration is proportioned and arranged to provide minimum clearance between the landing end of each segment and the corresponding step portion of the angle and maximum such clearance between the trailing end of the segment and the step portion of the anvil.  
  This arrangement has three major results. One is to minimize the space which exists between the land and the anvil during the interval immediately following the cutting stroke of each knife, and thereby to minimize the possibility of passage between the land and the anvil of unchipped and other undesirable fractions. Another is to establish the space between the trailing end of each land segment and the corresponding step portion of the wood as the controlling dimension of length of the chips produced by the apparatus. The third is to provide a rigid backing for each knife, which extends right up to the heel of the ground edge of the knife.  
  The invention is capable of embodiment in chippers incorporating rotors of a variety of designs, including disk, hollow cone, and drum type rotors. The preferred embodiment described hereinafter incorporates a rotor of the \/-drum or double frusto-conical type, which has proved to be especially efficient in the practice of the invention.  
 BRIEF DESCRIII ION ()F &#39;IHli DRAWINGS FIG. 1 is a side elevation of a chipper constructed in accordance with the invention.  
  FIG. 2 is an elevation looking right to left in H ll. 1 and showing the side which the wood material is sup plied to the chipper.  
  FIG. 3 is a partial side elevation of the rotor In the chipper of FIGS. I 2 looking from left to right in FIG. 4;  
  FM]. 4 is a fragmentary section on the line l--I ol FIG 3:  
  FIG. 5 is a detail elevation of the outside olonc oi the left hand face plates incorporated in the rotor oi&#34; FIGS 34.  
  FiG. (i is an elevation looking as indicated h III; line (h b of FIG. 5;  
  FIG. 7 is an elevation looking as indicated by the line 77 of FIG. 5.  
  FIG. 8 is an enlarged fragmentary section on the line 8-8 of FIG. 4;  
  FIG. 9 is an enlarged fragmentary section on the line 99 of FIG. 4;  
  FIG. II is a detailed view shouing one of the knives mounted .ni the rotor of FIGS. 3-41 FIG. 11 is a lragmentarv section on the line II-1I of HG.  
  FIG. 12 is a view similar to FIG. 5 and showing one of the righthand face plates;  
  FIG. 13 is an elevation looking as indicated by the line III--13 of FIG. 12:  
  FIG. 14 is an elevation looking indicated by the line I- l 14 of FIG. 12;  
  FIG. 15 is a fragmentary and somewhat diagranr matic view. taken as indicated by the line 15 15 of In, and showing the anvil assembly and its COOtDEILilIW? re lation with the rotor;  
  FIG. 16 is a plan view of the anvil assembly of FIG. 15;  
  FIG. 17 is a plan View of the knife set-tin gauge shown in broken lines in FIG 15:  
  FIG. 18 is an enlz rgcd diagrammatic view shorting a fragment of the anvil of FIGS. 15-16 and one rotor knife assenibl to illustrate the chipping action of the knife;  
  FIG. 1) is a diagrammatic view of fragment. oi the anvil and rotor urther illustrating the chipping action; and  
  FIG. 20 is a diagrammatic view illustrating the appli cation of the invention to a rotor ofthe disk 1.33pm  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIGS 1 2. the base structure it or the chipper includes legs 11 and supports a housing 12 cu closing the rotor 13 mounted lor rotation by the shaft 15. which is supported by bearing 16 and carries a driving sheave 17. The housing includes walls defining a feeding chute l9 liar ing a bottom tornictl by an anvil 21) o\ er \vhich wood is fed to the rotor I} for chipping. The preferred arrangement for -.lischarpe ofchips cont prises a pair ofchutes Z1 coniergln upn .nrllv from [in back ofthe housing 12 to attraction 11 lo] L&#39;UFIDLC IHIE to a suitable conduit. FIG. 1 albt shows an ilhcrnate i rangement of discharge chute 23 e1. nning l&#39;olllgtilifiilli forward from the top of the housing i1.  
 iii  
  shown in Fit 4. the rotor 13 has an essentially hourglass configuration. or more technically speaking. it has a doable lrnstoconicnl outline with its portion of minimum radius located intermediate the ends thereof. lla: rotor I3 12-. an assembly including a pair of outer end spiders 25 and Zn of complementary construction. the left liznnl spider comprising a hub 251:, an outer ring Zilland three angularl spaced spokes 2350 connecting the ring; 25h with the hub 25a. The spider 26 sirnilar&#39;iv comprises huh Erin. ring 26!) and spokes 260. Fan blalcs 27 are mounted by bolts 28 in spaced rela tion around the PMJI&#39;IPIICI. ofcach of spiders Z5 and 26 for propelling the chips through the discharge chutes.  
  The other major structural components of the rotor 13 are three left hand face plates 30 and three complenrentarr riglst hand fate plates 31, which are shown in detail in FIGS. 4 44. Each of the face plates 30 is a segment of 12% in angular extent so that in assembled relation secured to the spider 25 by bolts 28 and 27, they form a dish shaped irsl; which is continuous except for ripening; 33 provided by a cut-out along the trailing edge of each of the lace plates it). The right hand face plates 31., which are the m rror complements of the left hand face plates. are sirrrilarly secured to the spider 26 hr bolts 23 and 34 and are prmidcd with similar open lngs $5 axially aligned with the openings 33.  
  Referring, to &#34;FIGS. 5&#39;7, one of the major features of she in cnlioi&#39;i derives from the fact that the Working accof rotor I3 is composed of multiple arcuatelv con ed lands 4t! and 41 on tits: face plates 3t? and 31 respcctivclv which are arranged symmetrically about the axis of the rotor in stepped relation defining a profile composed of subsiantiali right angled steps, the reference characters 45 and 4; new used for general designation purposes, and the releience characters 40a, 401) being used to identify specific such lands. More specall each of the iLiIIIIS 4G is composed of a segment .rf a cylinder which extends between a pair of adjacent openings 33. and which has its axis parallel with but offset from the axis 44 of shaft 15.  
  Each face plate 36 shown as having six lands 40 which are designated separately as lands 40a-40f. The surfaces between adiaccnt lauds 40. which define planes est-ending radially of shaft 15, are similarly designated. ill-it&#39;ll The right hand face plates 31 differ from that: pi; i lmtil in that they are mirror com l iclt&#39;lcllt and also in that they have only five land seg incnts -siu-l1v but the sarnc number of radial portions l-51! 41H.  
  As ltcr l shew-m in lit 5, the relation between each II the .and stgrncnts it? and the axis 44 of the rotor shaft lf is cstairhshcd h}; the ocation ofthe center 45 of tlllvlilllil. of the lands 41!, which is offset from the oils 41&#39; &#34;the estent and tiiFC&#39;&#34;iIL)tl of this offset is predeicr ruin-ii o prmi he desired difference in the radial llll ril\itlllli i rrlo shaft asis 44 to the leading and trail- IiILliL 4%. It is this dimensional invention to establish actor run length i; I&#39; lire L&#39;Iligfin cut In. the apparatus. nglh of s inch. this dimensional differ- H I I&#34;. liixjli and v ce versa, and thc offset i with r-cspcct to axis 44 is calculated ac li cntls ii&#39; cach l&#39; shown in detail in FIGS. 9-11, the reference character 50 being used for general designation purposes, and the reference characters 50a being used to identify specific such knives. The knife 50 is a piece of steel of uniform thickness comprising two wings 51 and 52 connected at an included angle of approximately l by a curved center line portion. each of the wings 51 and &#39;32 having a bevelled cutting edge 53 and 54 respectively at one end. A slot 55 receives a mounting bolt 56 for adjustable mounting purposes as described hereinafter.  
  Each of the left hand face plates has six knives 50 mounted thereon. but only two are shown in FIGS. 3-4 for simplification of illustration. The mounting is such that each edge 53 is aligned with the associated land segment 40, and the other edge 54 is aligned with the adjacent radial surface 42 on the radially inner side of the land. In other words, the edge 53 of one blade 50a will be aligned with the land a, and its other edge 54 will be aligned with the radial surface 420, and so forth. The edge 54 of the innermost blade, however. has no associated surface 53 and takes no part in the chipping action.  
  The arrangement of blades on each face plate 31 is complementary to that on the face plates 30. That is, there are five blades 50, rather than six. mounted on each face plate 31, and it is the edge 54 which is aligned with the adjacent land 41, while the edge 53 is aligned with the adjacent radial surface 43. For simplicity, only one blade is shown in FIG. 4.  
  The way in which the individual knives 50 are mounted on each face plate 30 is illustrated in detail in FIGS. 8-9. Referring first to FIG. 8, the leading edge portion of each face plate 30 is thicker than the adjacent portion of the face plate and is bevelled to form a series of six trough-like seats 60, the sides of which are at the appropriate angle (e.g.l l0&#34;) to receive the back of a knife 50. The bottom of this seat is grooved at 61 for improved seating action of the knife therein, and a hole 62 is drilled through this groove and tapped to receive a mounting bolt 56.  
  Each knife 50 is mounted in the appropriate seat 60 by means of a bolt 56 and a clamp 65 which is proportioned to seat in the concave side of the knife as shown in FIG. 9, and which includes a bevelled face 66 (FIG. 4) on its exposed end nearest the knife edges 53-54. The proportions and configurations of these portions are so calculated that when the knives are mounted in operative position, the edge 53 of each knife in a face plate 30 will be parallel with the adjacent leading end of its associated land 40 and will project radially beyond the land surface by the small distance e.g. l/32 inch. The other edge 54 of the blade will then be simi larly aligned with and will project slightly beyond the associated radial surface 42. As viewed in FIG. 3, each of the knives will have its cutting edges defining a plane parallel with the leading edge surface of the associated face plate 30, and similarly parallel with the plane of the surface of the sheet in FIG. 4.  
  The construction of each of the face plates 31 and the arrangement thereon of the knives 50 correspond in mirror fashion to the face plates 30. Referring to FIGS. 12-14, each of the land segments 41 has a generally spiral configuration with respect to the rotary axis of the rotor, which is established by locating the center of curvature of each land in offset relation from the axis 44 of rotor shaft 15. The extent and direction of this offset corresponds to the similar location of the center 45 of curvature of the lands 40 on each face plate 30 so that when the rotor is fully assembled. each land 41 will define a segment of the same cylinder as a corresponding land 40.  
  The provision for mounting knives 51 on each face plate 31 is also the mirror counterpart of that for the face plates 30. More specifically. the leading edge portion of each face plate 31 is bevelled in the opposite direction from the face plates 30 so that the knives 50 which are mounted thereon are arranged in converging relation with the axially aligned knives on the face plates 31). Otherwise. the details are essentially the same on both sets of face plates.  
  For the preferred application of the invention to rechipping, namely to the processing of miscellaneous pieces of wood. oversized chips and the like rather than whole logs. the apparatus is provided with an anvil 20 of special configuration complementary to that of the rotor 13 as shown in detail in FIGS. 15 and 16. The anvil 20 comprises a base plate 70 which is welded to the base 10 at opposite sides of the feeding chute l9. and which includes a depending lug 71 at the middle at its outer end and a centerly located keyway 72 in its upper surface.  
  The anvil base 75 is a plate having a depending flange 76 on its outer end and having its inner end provided with a stepped periphery substantially matching the stepped pattern of rotor 13 defined by the lands 40-41 and radial surfaces 42-43 of face plates 30-31. The anvil base 75 has keys 77 welded to its under surfaces which fit within the keyway 72 to assure accurate align ment of the anvil assembly with the rotor 13. The anvil base 75 can be adjusted for initial set-up purposes by sliding movement of the keys 77 in keyway 72, with the aid of a positioning bolt 78 threaded in a tapped base in lug 71 and its locknut 79, the head of the bolt 78 being adapted to engage the inner surface of the flange &#39;76 on anvil base 75. The anvil base 75 is clamped in ad justed position by bolts 80 extending through oversized bores 81 in base plate 70.  
  The top of the anvil assembly comprises eleven wear plates 85 mounted by screws 84 and dowels 86 around the stepped periphery of anvil base 75. For convenience of reference the center wear plate is designated 85f. the outermost pairs are designated 85a, and soforth. The space on the anvil base between and outwardly of the wear plates 85 is covered by a filler plate 88 secured to anvil base 75 by screws 89. The knives 50 are adjusted in rotor 13 to establish a running radial ciearance between their cutting edges and the exposed ends of the corresponding wear plates 85, e.g. GINO-0.027 inch, and the parts are proportioned to provide a similar axial clearance between the knife edges and the exposed sides of wear plate 85.  
  Understanding of the operation of the apparatus, which is illustrated in FIG. 18, is facilitated by noting first that the anvil assembly is proportioned and mounted to locate the upper surfaces of the wear plates 85 and filler plate 88 tangent to the circular path of the knife edges, represented by the path 90 in FIG. 15 of the edge 53 of the innermost knife 50f. at a level substantially below a horizontal plane through the axis of rotor 15. Referring to FIG. 18, if it is assumed for purposes of illustration that the feed material is a board 99 of the same width as the filler plate 88 which has an initially square end. the first chips will be removed by the knives Stlu on face plates and the corresponding outermost knives on face plates 31. FIG. 18 illustrates the operation after sufficient chips have been removed from board 99 for the board to reach the end of the center ear plate 85f and therefore to have acquired the same periphery in plan as the anvil assembly itself.  
  FIG. 18 shows the center knife 50f in the act of re moving a chip 100. As that chip is cut from board 99. it will pass along the trough portion of the knife. over the bevelled surface 66 ofthe associated clamp 65. and through the adjacent opening 33 to the space in the housing at the end of the rotor. This same course is followed by all chips cut by the knives on face plates 30, while chips cut by the knives on face plates 31 pass through the openings 35 into the space in the housing at the other end of the rotor.  
  As previously noted. the knives SOfdiffer in opera tion from all of the other knives in that only the edge 52 of each of these centrally located knives takes part in the cutting action, whereas both edges of each other knife are used. Thus the knives 5011 are parallel with the ends of the wear plates 85a and parallel with the exposed side edges of the adjacent wear plates 85b. Similarly the knives 50c will cut along the ends of the wear plates 85c and the sides of wear plates 85f. The knives 50f have therefore no where to cut except along the end ofthe wear plates 85f, but the net results of the operations of all of the knives are the same. namely the production of essentially rectangular chips of uniform width (axially of the rotor) and length.  
  Note particularly in FIG. 18 that the leading end of the board 99 is in substantial contact with the trailing end of the land f where there is maximum spacing between the land surface and the adjacent knife edge 53. which establishes the corresponding dimension (length) of chip 100 as explained above. Immediately behind knife edge 53, in its direction of rotation. is the leading end of the next land 40f where there is minimum spacing between the knife edge and the surface of the land. and therefore minimum clearance between the land surface and the adjacent edge of the corresponding wear plate 85. This clearance, however, increases to a maximum during the next approximately 120 rotation of the rotor to reestablish maximum clearance conditions just in advance of the next knife f.  
  Four important advantages flow from these structural and operating conditions. The first is provided by the stepped arrangement of the wearplates 85 and the cor&#39; responding steps on the face plates 30. Because the in tersection of each land 40 with the inwardly adjacent radial surface 42 forms a corner which overlaps the corner of the corresponding anvil wear plate 85, the open space between the rotor face and the anvil consists of a chain of rectangular openings each having dimensions equal to the nominal chip length and width. For this reason. a piece of wood approaching the rotor will bridge across one or more of these openings and will not pass through them until it is cut to length and width by the knives 50. Because of the stepped anvil and face plate configuration, the wood will be cut to acceptable fiber length regardless of the orientation of the grain with respect to the infeed direction.  
  The point discussed in the preceding paragraph is illustrated diagrammatically in FIG. 19, which shows a fragment of a face plate 30 and a fragment of the anvil including wear plates 85b and 850. The dot and dash lines 53 and 54 represent the cutting edges of the knives 50b and 500, and the dash lines 40/) and 400 indicate the relative positions of the trailing ends of the lands 40b and 40c in passing the anvil. FIG. I9 thus shows two of the series of rectangular openings I25 which in operation define the cross section of each chip. and it also shows that these openings are essentially closed immediately following passage of each knife past the anvil and increase in size as the following land segments move past the anvil and the wood feeds forward against them.  
  In contrast with the invention, in conventional chippers. the space between the rotor disk and the anvil is a slot equal to the length of the anvil. Whenever a piece of wood approaches the rotor on these chippers with the grain direction essentially parallel to the disk, it is cut to overlength splinters by the knives. Small splinters approaching the rotor in similar manner pass through the slot uncut.  
  The second advantage of the invention is that the ten dency for the wood being chipped to up-end is substan tially reduced. In conventional chippers. it is common for short pieces to pivot about the edge of the anvil and up-end against the face of the rotor. With the wood in this position. control of chip length is lost and addi tional overlength material is produced. The present invention has a stepped anvil and. therefore, has no straight anvil edge about which a piece of wood can pivot under the action of the knives.  
  The third important advantage is related to the first. and is the control of chip length which is provided by the spacing betweenthe trailing edge of each land 404l and the adjacent knife edge 53 or 54, and which assures maximum uniformity of chip length. The sec ond is the very small clearance between the leading end of each land 4041 and the adjacent end of the complementary wear plate 85. This close clearance assures that oversized sticks and splinters lying on the anvil. such as frequently occur in the feed to any rechipper, cannot drop through this clearance as would be the case in a conventional chipper.  
  The importance of this advantage becomes apparent upon consideration of the fact that on conventional chippers. there is commonly a slot opening between the anvil and the rotor face which is equal in width to the projection of the knife beyond the adjacent face portion of the rotor. It is a periodic opening of this slot which is in large measure responsible for the production of overlength sticks and other oversized fragments. Further, this tendency is increased by the fact that the air currents and pressure drops created by the passage of each knife past the anvil promote upending of unde sired elongated pieces of wood for more ready passage through the slot. In contrast, theh spiral configuration of the land 40-41 effectively close the slot between the rotor and the anvil for a long enough interval to permit the suction effect ofthe passage of the knife to be dissipated.  
  This construction in accordance with the invention also provides a material contribution to the strength of the apparatus. particularly in that the spiral arrangement of the successive land segments provides a solid back&#39;up section on both sides of the groove 61 for supporting the back of each knife up to the heel of its ground edge, as is clearly shown at 101 in FIGS. 8 and 9. This makes it practical to use relatively thinner and less expensive material in the knives than on a conventional rotor, and also makes effective clamping of the knives easier to accomplish. These advantages also contribute to the ease and practicability of regrinding the knives for a long service life. since the trough-like seats 60 for the respective knives and their mounting slots 55 provide for quick replacement as well as repeated regrinding.  
  Because of the close clearance with which the apparatus of the invention operates. provision is made for accurate setting of the knives independently of the anvil assembly. Referring to FIGS. I and 17, the base 10 includes a bracket 110 located on the opposite side of center from the anvil assembly and comprising a shelf parallel with and slightly below a horizontal plan through the rotor axis. This bracket serves as the support for a knife setting gauge III which can be readily clamped thereon by the clamp bolt mechanism 112. The gauge I 11 is so proportioned that in mounted position, it is radially aligned with the rotor axis, and it includes a stepped periphery 115 of such dimensions that when all of the blades 50 are clamped into position with their cutting edges engaging corresponding steps in the gauge, they will have the proper working clearances with respect to the corresponding wear plates 85. The guage III is utilized only for maintainance purposes and is removed during operation of the apparatus.  
  As already noted, while this apparatus is especially effective as a rechipper for handling oversized chips and other fragments screened from the output of whole log and waste wood chippers, it has also proved to be highly effective as a waste wood chipper without any modification, and the chips which it produces from waste wood have been found to be of especially uniform size and free of oversized fragments of the type commonly produced by conventional waste wood chippers. The principles of the invention are also applicable to whole log chippers. In fact, no modification is necessary of the apparatus shown in FIGS. 1-17 to adjust it to handle whole logs, but it may be desirable to add centering guide means, defining a broad V-groove, at the entry to the anvil assembly for maintaining a whole log against rotation after the knives begin chipping action thereon.  
  Irrespective of the material being chipped, the chippers ofthe invention will operate with any conventional supply conveyor or chute, preferably with the chipper simply tilted from the position shown in FIG. I to raise the front sufficiently for gravity-induced movement of wood across the anvil assembly to the rotor. This feeding movement is of course supplemented by the action of the knives in that with their cutting strokes being executed primarily during movement from 3 o&#39;clock toward 6 oclock as viewed in FIG. 1, they have a continuing tendency to draw the work material toward the rotor.  
  The principles of the invention are not limited to a rotor of the hourglass design and can be built into other more or less conventional rotor shapes. This is illustrated by FIG. 20, wherein a disk-like rotor 125 is mounted for rotation on axis 126, and its working face is composed of a series of concentric lands 130 alter mating with concentric land surfaces 131 to define a profile composed of substantially right angled steps. The surfaces 130 and 131, however, are angled in alternately opposite directions with respect to the axis 126. It will be understood that each of these lands 130 in fact is composed of a plurality of land segments having a spiral configuration with respect to the basic conical segment they define and alternate with openings in which the knives are mounted and through which the chips pass. The surfaces 13], however are true conic sections.  
  In, FIG. 20. the rotor is assumed to be rotating clockwise as viewed looking toward the front of its working surface. The anvil I35, which has a stepped periphery matching that of the rotor, is accordingly located to the right of and below the rotor axis and defines the path of feeding movement for wood which extends substantially horizontally in the same relation to the working surface of the rotor as in the form of the invention already described.  
  While the forms of apparatus herein described constitutes preferred embodiments of the invention. it is to be understood that the invention is not limited to these precise forms of apparatus, and that changes may be made therein without departing from the scope of the invention.  
 What is claimed is:  
  1. Apparatus for chipping wood which comprises base structure including a housing, a rotor mounted for rotation in said housing on an axis, and guide means establishing a predetermined path of feeding movement of wood to said rotor, and which is characterized by:  
 a. said rotor having a working face composed of multiple arcuately curved land segments arranged symmetrically about said axis in stepped relation defin ing a profile composed of substantially right angled steps,  
 b. said rotor having openings therethrough in symmetrically alternating relation with said land segments,  
 c. knife means associated with each said opening and secured to said rotor with the cutting end thereof projecting through said associated opening adjacent the trailing edge of said opening,  
 (I. said knife means including a cutting edge arranged effectively parallel with each said land segment and another cutting edge arranged effectively parallel with the surface connecting said land segment with an adjacent land segment, and  
 e. each of said land segments having a generally spiral configuration in the direction of said wood feeding path providing minimum spacing in said direction between the leading end of said segment and the adjacent said knife edge and maximum spacing in said direction between the trailing end of said segment and the following said opening and knife edge.  
  2. Chipping apparatus as defined in claim I wherein said knife means comprises multiple knives each having a pair of angularly related cutting edges, and means forming an ajustable mounting for each said knife on said rotor to provide for adjustment of said edges thereof to positions of predetermined projection outwardly of the associated said opening.  
  3. Chipping apparatus as defined in claim 1 wherein said guide means comprises an anvil having a stepped periphery substantially complementary to said rotor face profile, and means supporting said anvil with said periphery matching said rotor profile and in predetermined spaced relation therewith providing minimum clearance between the leading end of each said land segment and the end of the corresponding step portion of said anvil for passage of said knife edge parallel with said land segment, maximum clearance between the trailing end of said segment and said step portion of said anvil, and working clearance between the side edge of said step portion and the adjacent other said knife edge.  
  4. Chipping apparatus as defined in claim 3 wherein said knife means comprises multiple knives each having a pair of angularly related cutting edges and means forming an adjustable mounting for each said knife on said rotor to provide for adjustment of said edges thereof arranged to execute a cutting stroke substantially parallel to and in closely spaced relation with the corresponding step portions of said anvil.  
  5. Apparatus for chipping wood which comprises base structure including a housing a rotor mounted for rotation in said housing. and guide means in said housing for establishing a predetermined path for feeding movement of wood to said rotor. and which is characterized by:  
 a. said rotor having a double frustoconical outline with its portion of minimum radius intermediate the ends thereof.  
 b. said rotor having a working face composed of multiple arcuately curved lands defining cylindrical segments parallel with said axis and of different radii providing a profile composed of substantially right angled steps,  
 c. each of said lands being composed of a plurality of segments alternating with an opening extending through said face to the adjacent end of said rotor,  
 d. knife means associated with each said opening and secured to said rotor with the cutting end thereof projecting through said predetermined opening adjacent the trailing edge of said opening,  
 e. said knife means including a cutting edge arranged effectively parallel with each land and a cutting edge arranged effectively parallel with the surface connecting each said land and an adjacent land.  
  and f. each of said land segments having a spiral configuration radially of said rotor axis providing the maxi mum dimension of said segment radially of said 5 axis at the leading end thereof and the minimum dimension of said segment radially of said axis at the trailing edge thereof. 6. Chipping apparatus as defined in claim 5 wherein said knife means comprises multiple knives each having a pair of angularly related cutting edges. and means securing each said knife to said rotor with one of said edges thereof extending substantially parallel with said rotor axis and the other of said edges lying in a plane substantially normal to said axis. 7. Chipping apparatus as defined in claim 5 wherein said path is substantially normal to a plane through the rotational axis of said rotor, and said guide means comprises an anvil having a stepped periphery substantially complementary to said rotor face profile, and means supporting said anvil with said periphery matching said rotor profile and in predetermined spaced relation therewith providing minimum clearance between the leading end of each said land segment and the end of the corresponding step portion of said anvil for passage of said knife edge parallel with said land segment, maxi mum clearance between the trailing end of said seg ment and said step portion of said anvil, and working clearance between the side edge of said step portion and the adjacent other said knife edge.  
  8. Chipping apparatus as defined in claim 7 wherein said knife means comprise multiple knives each having a pair of angularly related cutting edges, and means securing each said knife to said rotor with each of said 3 edges thereof arranged to execute a cutting stroke substantially parallel to and in closely spaced relation with the edges of corresponding step portions of said anvil. l