AU2002330885B2 - Knife and apparatus for clamping a knife - Google Patents

Description

KNIFE AND APPARATUS FOR CLAMPING A KNIFE This application claims the benefit of priority from United States Patent 00 Application No. 09/918,895 and 09/908,918, the disclosure of which is incorporated by 00 reference herein in its entirety.

g The present invention relates to a knife and apparatus for clamping a knife in a wood chipper, such as a disc, drum or conical head chipper for use in the commercial processing of logs.

In wood chipping apparatus used in the forest products industry, a rotating member is provided for receiving replaceable knives for cutting chips from the log.

Each knife is typically clamped to the rotating member between an outer clamping member and an inner clamping member or counterknife, wherein the knife and counterknife together form a surface against which the log is forced to remove chips from the log. The chips themselves have commercial value, and their removal shapes the log into lumber and finishes its surface. The clamping members essentially form a cassette for the knife, although the entire cassette is often referred to in the trade as a knife. Herein, the term "knife" is used to refer to the blade that is clamped between the outer and inner clamping members.

The spacing between the outer and inner clamping members is adjustable for loading the knife into the apparatus, or unloading the knife from the apparatus, such as for replacing the knife or turning the knife end-to-end to position an alterative knife edge in the chipper. A preferred mechanism for adjusting the spacing between an outer N, clamping member an inner clamping member is described in U.S. Patent No. 5,979,522, also incorporated herein by reference in its entirety.

IDAs one example of a wood chipping apparatus, a chipper disc typically spins in a vertical plane. A number of identical knives are spaced around the periphery of the disc.

00 The knives are elongate, and their elongate axes are oriented along radial lines passing 00 Mc, approximately through the center of the disc, the axis of each knife becoming horizontal at respective 9:00 and 3:00 positions of the disc. When unclamped, the knives are typically unrestrained from sliding along these radial lines, so it is preferable to unclamp the knives when they are at least approximately in one of these two level positions.

A shroud is typically provided that covers the disc to retain chips and to shield personnel, the shroud including a closeable opening in a predetermined angular position of rotation of the disc, to provide access to a knife that has become aligned therewith.

The position of the opening is selected so that the heavy and sharp knife will not slip forwardly out of the apparatus when it is unclamped; however, even so, the knife remains free to slip backwardly into the apparatus and still presents some risk of injury or damage.

Such considerations are important as well to other types of wood chippers, such as the drum and conical head chippers.

P \OPER\I)FAI Q 926 I0 FC F rc dO- 19 )21 V -3- SIn accordance with the invention, there is provided a wood chipping apparatus, Ocomprising: a knife having a back side, said back side having a first semi-cylindrical interlocking feature therein, and a front side, wherein said front and back sides co- 0r terminate in two spaced apart cutting edges lying in a plane, said front side including, in 00 correspondence with said cutting edges, a respective two spaced apart and similar projecting interlocking features that project a maximum distance from said plane, and an (Ni outer clamping member comprising a projection terminating in a second semi-cylindrical interlocking feature that is complementary in form to said first interlocking feature for engagement therewith, for clamping said knife in the wood chipping apparatus, wherein said projection extends from said outer clamping member so as to permit rotation of said knife: relative thereto prior to clamping.

Another aspect of the invention provides a wood chipping apparatus, comprising: a knife having a back side, said back side having a first semi-cylindrical interlocking feature therein, and a front side, wherein said front and back sides coterminate in two spaced apart cutting edges lying in a plane, said front side including, in correspondence with said cutting edges, a respective two spaced apart and similar projecting interlocking features that project a maximum distance from said plane, and a clamp for clamping said knife by applying a clamping force thereto, said clamp comprising a projection terminating in a second semi-cylindrical interlocking feature that is complementary in form to said first interlocking feature for engagement therewith, substantially the entirety of said clamping force being transmitted through said engagement.

A further aspect of the invention provides a wood chipping apparatus, comprising: a knife having a back side terminating in at least one cutting edge, said back side having a first semi-cylindrical interlocking feature therein; and an outer clamping member comprising a projection terminating in a second semicylindrical interlocking feature that is complementary in form to said first interlocking feature for engagement therewith, for clamping said knife in the wood chipping apparatus, said projection extending from said outer clamping member so as to permit rotation of said knif: relative thereto during said engagement.

P \OPERIDAI23 62M 16 Fc b)07 d.-19,m2,Z6)01 w-4- SA further aspect of the invention provides a wood chipping apparatus, comprising: a knife having a back side terminating in at least one cutting edge, said back side having a first semi-cylindrical interlocking feature therein; and 0 a clamp for clamping said knife by applying a clamping force thereto, said clamp 00 5 comprising a projection terminating in a second semi-cylindrical interlocking feature that Sis complementary in form to said first interlocking feature for engagement therewith, substantially the entirety of said clamping force being transmitted through said ,I engagement.

Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, as set out below.

Figure 1A is a pictorial view of a knife according to one embodiment of the present invention, showing a front side of the knife in perspective.

Figure 1B is a pictorial view of the knife of Figure 1 showing a back side of the knife in perspective.

Figure 2A is an elevation of a disc chipper including a plurality of knives such as that 3hown in Figures I A and lB.

Figure 2B is a cross-section of the disc chipper of Figure 2A, taken through a knife that is in the 3:00 position of the disc along line 2B-2B, showing the knife clamped in the disc chipper.

Figure 3A is a cross-section of the disc chipper of Figure 2B, taken through another knife: that is in the 9:00 position of the disc along line 3A-3A thereof, showing the knife unchlamped in the disc chipper.

Figure 3B is a cross-section of the disc chipper and knife of Figure 2B, showing the knife in the 3:00 position unclamped in the disc chipper.

Figure 4A is a partial cross-section, corresponding to the cross-section of Figure 3B in the 3:00 position, of a knife and outer clamping member according to one embodiment of the present invention.

Figure 4B is a partial cross-section of the knife and outer clamping member of Figure 4A, showing the knife clamped between the outer clamping member and an inner clamping member.

P\OPR\DH2398230spa2 26 Fcb07 do.26 M2/2007 C Referring to Figures 1A and 1B, a preferred knife 10 is shown modified according to one embodiment of the present invention. The knife without modification has been widely available as manufactured by the Key Knife, Inc., of Tualatin, Oregon, and is described in detail in Schmatjen, U.S. Patent No. 5,819,826, herein incorporated by 00 5 reference in its entirety. The knife 10 may be employed in any wood chipping apparatus, M c such as a disc, drum or conical head wood chipper. The knife has an elongate axis a front side 12 and a back side 14.

0The front side 12 of the knife 10 includes spaced deflector ridges 18a and 18b that project therefrom. Each of the deflector ridges is characterised by a single linear edge 13a and 13b respectively. The deflector ridges define a channel 34 having a channel surface 34a. The channel 34 is effectively a recess in the front side of the knife, which may be provided in other configurations, such as a keyway. The deflector ridges also define two lower knife-edge-joining portions 38a and 38b that terminate in respective cutting edges 16a and 16b.

The back side 14 of the knife 10 includes a clamp-facing surface portion 14a that is substantially planar and parallel to the channel surface 34a, and two upper knife-edgejoining portions 35a and 35b that slope from opposite edges of the clamp-facing surface portion to the cutting edges 16a and 16b. The knife 10 is typically provided so that the lower knife-edge-joining portion 38a lies in the same plane as the lower knife-edge-joining portion 38b (and the channel surface 34a); however, these faces can be ground or otherwise provided according to the aforementioned US Patent Application 09/918,895 or 09/908,918, so that the lower knife-edge-joining portions are not coplanar.

As mentioned previously, the above features are described in the '826 Patent.

While an embodiment of the invention is believed to provide maximum advantage when used in connection with the preferred knife, an embodiment of the invention may THE NEXT PAGE IS PAGE 7 9 i P:\OPER\MAI\I 2398230 spw.dm.2 08,04 -7provide an advantage when used with other prior art knives as well, such as knives that do not have all of the aforementioned features, or knives which include additional features.

WO 03/011541 PCT/US02/22576 Referring to Figure 2A, a disc chipper 20 is shown employing a plurality of the knives 10. While a disc chipper is used herein to illustrate use of particular embodiments of the invention, the principles of the invention apply equally to other chipping apparatus including that employing a drum or a "conical" head, and application of those principles to alternative configurations of chipping apparatus will be readily apparent to those of ordinary skill in the art.

The knives are elongate, meaning herein that they have a shape in a crosssectional plane that is maintained for some distance along an axis that is perpendicular to the plane. For use in a disc chipper, the length of the knives along the axis is typically large in comparison to the cross-sectional dimensions of the knives; however, the length of the knives may be small in comparison to these dimensions, such as where many discs are combined to form a drum in a drum chipping apparatus. In the disc chipper, the elongate axes extend radially, approximately from the center of the disc. The disc spins in a vertical plane in the direction of the arrow, with an exposed cutting edge 16a of each knife being visible.

Figure 2B shows a cross-section of the disc chipper 20 taken through a particular knife 1 Oa that is in the 3:00 position of the disc as it is shown in Figure 2A. The knife is shown clamped in the disc chipper between outer and inner clamping members 22a and 24a respectively, so that the disc is ready for use for cutting wood. The inner clamping member is often referred to as a "counterknife." WO 03/011541 PCT/US02/22576 An insert 21 is received in a corresponding pocket in the disc chipper. The insert supports the outer and inner clamping members as well as means for adjusting the spacing between the clamping members for clamping and unclamping the knife. For clamping the knife as shown, at least a portion of the channel surface 34a (Figure 1A) is abuttably received by the inner clamping member 24a, and the clamp-facing surface portion 14a of the back side 14 of the knife (Figure 1B) is at least disposed proximate to (Figure 4B) and may be abuttably received by an inner surface 23 (Figure 3A) of the outer clamping member 22a.

Preferably, the outer clamping member 22a is fixedly disposed with respect to the insert 21, and a threaded adjustment member 26a is received in a corresponding threaded aperture through the outer clamping member which permits translating the adjustment member in the directions indicated by the arrows, for adjustably pivoting the inner clamping member 24a about a bearing surface 33 that is provided as part of the insert 21.

Alternatively, the position of the inner clamping member may be fixed and the outer clamping member may be adapted to be adjustably spaced apart therefrom, and either or both clamping members may be adjustably movable by any desired means without departing from the principles of the invention.

Turning to Figure 3A, a cross-section similar to that of Figure 2B shows another knife 10b (see also Figure 2A) which is in the 9:00 position of the disc. By contrast to the knife 10a in Figure 2B, the knife 10b is unclamped in the disc chipper. The inner clamping member 24b for the knife 10b has been pivoted about the surface 33 to provide WO 03/011541 PCT/US02/22576 a spacing from the outer clamping member 22b that is sufficient for removing the knife from, or installing the same knife or a different knife, between the clamping members.

When the clamping members 22b and 24b are separated, the knife lOb in the 9:00 position rests on the inner clamping member 24b under the influence of gravity.

More particularly, one of the deflector ridges 18a is disposed outside a toe 19 of the inner clamping member 24b at one end of the toe, the other end of the toe being defined by a recess 28 shaped to receive the other of the other deflector ridge 18b. The channel 34 as bounded by the deflector ridges defines a recess that, along with the relatively projecting toe of the inner clamping member, provide interlocking means which cooperate to hold the knife 10b to the inner clamping member 24b against the influence of gravity when the knife is unclamped in the 9:00 position of the disc. Alternatively, a keyway may be provided in the knife for receiving the toe. However, if the knife is dislodged, it may fall outwardly from the disc chipper along a line of slippage posing a substantial risk of injury or damage.

Interlocking the knife to the inner clamping member also provides for locating and positioning the knife ("indexing") so that it is accurately disposed for cutting when the clamping members are adjusted to clamp the knife therebetween.

Turning to Figure 3B, a cross-section similar to that shown in Figure 2B illustrates the knife 10a unclamped in the disc chipper in the 3:00 position of the disc. The inner clamping member 24a has been pivoted about the surface 33 to provide a spacing from the outer clamping member 22a that is sufficient for removing the knife from, or WO 03/011541 PCT/US02/22576 installing the same knife or a different knife, between the clamping members. When the clamping members 22a and 24a are separated, such as by use of the adjustment mechanism 26a, the knife 10a in the 3:00 position of the disc rests on the outer clamping member 24a under the influence of gravity as shown. It may be noted that the clamping members need not be maximally separated for this result to occur, the clamping members becoming separated at the point that the clamping force they exert on the knife is reduced to zero.

The knife 10a in the 3:00 position cannot be interlocked with the inner clamping member 24, hence the safety and indexing features provided by the deflector ridges of the knife and the recess 28 of the inner clamping member are lost in this position. Thence, the unclamped knife in the 3:00 position of the disc will ordinarily slip backwardly into the apparatus along the line of slippage against interior portions of the outer and inner clamping members. While the risk of injury to personnel is much reduced as compared to that posed by slippage of the knife in the 9:00 position, such slippage may cause damage to the knife or the apparatus, and may make removal of the knife somewhat difficult. Moreover, installation of the knife is also difficult, and indexing the knife into proper position while clamping the knife is very difficult.

With additional reference to Figure 1A, to improve the safety and security of holding the unclamped knife in the 3:00 position of the disc as well as to provide for indexing of the knife, the knife and outer clamping members are provided with interlocking features to prevent slippage of the knife into or out of the apparatus along the V.

I

WO 003/011541 PCT/US02/22576 axis (Figure 3B) when the knife is unclamped, providing an outstanding advantage over the prior art.

In a preferred embodiment of the invention, the otherwise substantially planar clamp-facing surface portion 14a of the back side 14 of the knife includes a recess 30 that is particularly a groove, and the outer clamping member 22 includes a complementary elongate projection 32 adapted to fit into the groove, where persons of ordinary skill will immediately recognize the equivalence of providing the knife with a projection and the outer clamping member 22 with a complementary and corresponding groove. According to the embodiment, the interlocking features of the knife and outer clamping member may be any interlockingly cooperating male or female structures that permit removing the knife from the outer clamping member while preventing the aforementioned slippage.

Preferably, the interlocking features interlock or retain one another in the direction or plane of slippage while providing for free movement of the knife in one or both perpendicular directions. As mentioned, the recess 30 and projection 32 are preferably elongate, and at least a portion of each is preferably semi-circular as seen in a crosssection perpendicular to the elongate axis (Figure 1A), to provide surfaces that are semi-cylindrical. Most preferably and particularly as shown, the shape of the recess and the shape of a distal tip 27 (best seen in Figure 4B) of the projection in cross-section are half-circular, to provide surfaces that are half-cylindrical.

2 0 These shapes are believed to be especially advantageous for easing installation of the knife, by permitting the knife to pivot on the projection about the elongate axis of the WO 03/011541 PCT/US02/22576 knife which facilitates manipulating the knife into position, and by accommodating greater manufacturing tolerances, which further reduces the effort required to place the knife into position as well as manufacturing costs.

Referring to Figures 4A and 4B, the preferred form of the interlocking features provides that the projection 32 extends far enough from the inner surface 23 of the outer clamping member so that a "three-point" contact is provided for clamping the knife, wherein the projection 32 provides one of the points of contact. In Figure 4A, the inner clamping member 24 has been moved away from the outer clamping member 22, and the knife 10 is held loosely by the projection 32. In Figure 4B, the clamping member 24 has been pivoted to receive the front side 12 of the knife and clamp the knife to the projection 32 of the clamping member 22, wherein the projection 32 has sides 32a and 32b that are substantially perpendicular to the inner surface 23 of the clamping member 22, terminating in a tip 27 having the semicircular cross-section, and extending far enough from the surface 23 so that the knife can rotate (compare Figures 4A and 4B) about its elongate axis at the tip 27, and so that the back side of the knife is not otherwise in contact with the surface 23 when the knife is clamped (Figure 4B).

Permitting a minimal but significant ("substantial") degree of rotation of the knife on the projection facilitates installation of the knife while not defeating the purpose of the projection to interlock with the recess 30 to prevent slippage. The semi-cylindrical surface of the projection may extend over an arc that is greater or less than a half-cylindrical 180 degrees, while the semi-cylindrical surface of the recess should have an arc that is about 180 degrees or less, to prevent the recess 30 from WO 03/011541 PCT/US02/22576 pinching or capturing the projection, which would decrease the efficacy of the connection between the parts and make both removal and installation of the knife difficult.

As mentioned, providing that most of the back side of the knife does not contact the surface 23 when the knife is clamped provides for a "three-point" contact, a point of contact "Al" at the tip 27 falls between, with respect to a line two other points of contact "A2" and so that contact is not being made, and force is not being transmitted, between most of the back side of the knife 14 and the clamping member 22. This provides a means for applying the clamping force that is consistent in spite of manufacturing variations in the dimensions of the parts.

The semi-cylindrical shapes for the projection and recess 30 are also believed to decrease manufacturing cost by rendering the capability to index the knife accurately to the outer clamping member less sensitive to manufacturing tolerances in these features.

While in the preferred embodiment these features extend over the entire length of the knife (determined in the direction of the axis this is not essential, and it may provide some additional indexing capability to limit the lateral extent of the interlocking features, so that the knife is retained laterally (into and out of the plane of Figure 3A) as well as with respect to slippage in the direction or plane However, the knife may be freely moved away from the inner clamping member 22a along the perpendicular direction for changing the knife.

Preferably, the interlocking feature of the knife is located so that the knife is or remains bilaterally symmetric with respect a plane (Figure 1B) that is parallel to the elongate axis of the knife, so that the knife may be turned end-to-end in a Sperpendicular plane, rather than rotated about the elongate axis, such as is required in tValo, U.S. Patent No. 4,271,882 or Svensson, U.S. Patent No. 4,047,670, for example, IND to obtain a fresh cutting edge from the knife. In view of the sharp edges of the knives S and their great weight, it is believed that the former operation is easier to perform than 00 the latter as it can be performed without touching the cutting edges, without holding 00 Mc, both sides of the knife, and without requiring a rotation of the wrist.

It should be noted that to provide such symmetry does not require a single interlocking feature that is centered on or in the back side 14 of the knife such as shown in Figure 1B. For example, bilateral symmetry with respect to the plane "P" may be obtained by providing an interlocking feature of the knife consisting of two, or any even number of recesses 30 that are symmetrically disposed with respect to the plane, either alone or in combination with a recess 30 that is centrally disposed in the plane. This provides the option of applying clamping force to the back side of the kife offits center.

To permit the aforementioned pivoting of the knife about the projection, it is preferable that only one projection is provided that is adapted to be received in just one of the one or more recesses 30 that are provided. However, it is contemplated that providing this advantage may not be essential, and that additional projections may be provided.

It is also contemplated that forms and shapes of the interlocking features may be provided without departing from the principles of the invention. For example, the one or more projections could be formed as pins and the one or more recesses as complementary apertures, holes or cavities providing for free movement along the axis even though sliding the knife laterally is not permitted without first separating the pins from the holes by movement of the knife along the axis A similar effect is obtained, as mentioned above, by forming the preferred groove so that it does not extend the entire length of the knife.

Provision of the recesses 30 (Figure 3A) and projections 32 makes it particularly advantageous to access the knife for changing or other purposes at the 3:00 position of the disc. According to the embodiment, then, the opening in the shroud is preferably situated at this position. Moreover, providing the interlocking features of the knife and outer clamping member in combination with the interlocking features of the knife and counterknife provides for safely holding the knife in the apparatus as well as indexing the knife to the apparatus in either or both the 9:00 and 3:00 positions of the disc, resulting in outstanding flexibility.

It is to be recognized that, while a specific method and apparatus for clamping a knife has been shown and described as preferred, other configurations could be utilized, in addition to configurations already mentioned, without departing from the principles of the invention.

The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention in the use of such terms and expressions to exclude equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.

I I P;:PER\ArI\12398230 sp doc-20/05/04 16A- Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia.

Claims (29)

1. A wood chipping apparatus, comprising: a knife having a back side, said back side Shaving a first semi-cylindrical interlocking feature therein, and a front side, wherein said 00 5 front and back sides co-terminate in two spaced apart cutting edges lying in a plane, said 0 front side including, in correspondence with said cutting edges, a respective two spaced apart and similar projecting interlocking features that project a maximum distance from said plane, and an outer clamping member comprising a projection terminating in a second semi-cylindrical interlocking feature that is complementary in form to said first interlocking feature for engagement therewith, for clamping said knife in the wood chipping apparatus, wherein said projection extends from said outer clamping member so as to permit rotation of said knife relative thereto prior to clamping.

2. The apparatus of claim 1, wherein said first semi-cylindrical interlocking feature is a recess, and wherein said second semi-cylindrical interlocking feature is convex.

3. The apparatus of claim 1, wherein said projecting interlocking features include, corresponding with said cutting edges, two spaced apart deflector ridges projecting away from said front side a maximum distance from said plane.

4. The apparatus of claim 3, wherein each said deflector ridge terminates in a single linear edge disposed said maximum distance from said plane.

The apparatus of claim 3, wherein each of said deflector ridges defines an a.sociated knife-edge-joining portion providing a smoothly curving transition from a point oin the deflector ridge that is disposed from said plane said maximum distance to a corresponding point on the corresponding cutting edge.

6. The apparatus of claim 3, further comprising an inner clamping member adapted to interlockingly receive at least one of said deflector ridges during said engagement. P kOI'ERDMI 2308230 spa2 26 Feb 07 do~.2M)2J2X7 -18-

7. The apparatus of claim 6, wherein each said deflector ridge terminates in a single IND linear edge disposed said maximum distance from said plane. 0

8. The apparatus of claim 6, wherein each of said deflector ridges defines an 00 00 5 associated knife-edge-joining portion providing a smoothly curving transition from a point 0 Cc on the deflector ridge that is disposed from said plane said maximum distance to a corresponding point on the corresponding cutting edge.

9. The apparatus of claim 3, wherein said first semi-cylindrical interlocking feature is a recess, and wherein said second semi-cylindrical interlocking feature is convex.

The apparatus of claim 9, wherein each said deflector ridge terminates in a single linear edge disposed said maximum distance from said plane.

11. The apparatus of claim 9, wherein each of said deflector ridges defines an as:sociated knife-edge-joining portion providing a smoothly curving transition from a point on the deflector ridge that is disposed from said plane said maximum distance to a corresponding point on the corresponding cutting edge.

12. The apparatus of claim 1 the apparatus further comprising an inner clamping member adapted to interlockingly receive at least one of said projecting interlocking features.

13. A wood chipping apparatus, comprising: a knife having a back side, said back side having a first semi-cylindrical interlocking feature therein, and a front side, wherein said front and back sides co-terminate in two spaced apart cutting edges lying in a plane, said front side including, in correspondence with said cutting edges, a respective two spaced apart and similar projecting interlocking features that project a maximum distance from said plane, and a clamp for clamping said knife by applying a clamping force thereto, said clamp comprising a projection terminating in a second semi-cylindrical interlocking feature that is complementary in form to said first interlocking feature for engagement P \OPIR\DH 12318230 spa2 26 Fb U07 doc-261)2/20? -19- therewith, substantially the entirety of said clamping force being transmitted through said IND engagement. 0

14. The apparatus of claim 13, wherein said first semi-cylindrical interlocking feature 00 00 5 is a recess, and wherein said second semi-cylindrical interlocking feature is convex. N

15. The apparatus of claim 13, wherein said projecting interlocking features include, corresponding with said cutting edges, two spaced apart deflector ridges projecting away from said front side a maximum distance from said plane.

16. The apparatus of claim 15, wherein each said deflector ridge terminates in a single linear edge disposed said maximum distance from said plane.

17. The apparatus of claim 15, wherein each of said deflector ridges defines an associated knife-edge-joining portion providing a smoothly curving transition from a point on the deflector ridge that is disposed from said plane said maximum distance to a corresponding point on the corresponding cutting edge.

1 8. The apparatus of claim 15, further comprising an inner clamping member adapted to interlockingly receive at least one of said deflector ridges during said engagement.

19. The apparatus of claim 18, wherein each said deflector ridge terminates in a single linear edge disposed said maximum distance from said plane.

20. The apparatus of claim 18, wherein each of said deflector ridges defines an associated knife-edge-joining portion providing a smoothly curving transition from a point on the deflector ridge that is disposed from said plane said maximum distance to a corresponding point on the corresponding cutting edge. P %OFERkDHl21)8fO) SpS 2 26 Feb Ol dC2MY2I27 V

21. The apparatus of claim 15, wherein said first semi-cylindrical interlocking feature IND is a recess, and wherein said second semi-cylindrical interlocking feature is convex.

22. The apparatus of claim 21, wherein each said deflector ridge terminates in a single 00o5 linear edge disposed said maximum distance from said plane. 00 ¢€3 M

23. The apparatus of claim 21, wherein each of said deflector ridges defines an Sassociated knife-edge-joining portion providing a smoothly curving transition from a point on the deflector ridge that is disposed from said plane said maximum distance to a corresponding point on the corresponding cutting edge.

24. The apparatus of claim 13 the apparatus further comprising an inner clamping member adapted to interlockingly receive at least one of said projecting interlocking features.

A wood chipping apparatus, comprising: a knife having a back side terminating in at least one cutting edge, said back side having a first semi-cylindrical interlocking feature therein; and an outer clamping member comprising a projection terminating in a second semi- cylindrical interlocking feature that is complementary in form to said first interlocking feature for engagement therewith, for clamping said knife in the wood chipping apparatus, said projection extending from said outer clamping member so as to permit rotation of said knife relative thereto during said engagement.

26. A wood chipping apparatus, comprising: a knife having a back side terminating in at least one cutting edge, said back side having a first semi-cylindrical interlocking feature therein; and a clamp for clamping said knife by applying a clamping force thereto, said clamp comprising a projection terminating in a second semi-cylindrical interlocking feature that is complementary in form to said first interlocking feature for engagement therewith, substantially the entirety of said clamping force being transmitted through said engagement. P OFER\DHI2398211 spl2 26 Feb07 doc.26M2/20 -21- I

27. A wood chipping apparatus as claimed in claims 25 or 26, wherein the knife has a front side an the front and back sides co-terminate in two spaced apart cutting edges lying in a plane. 00 00

28. A wood chipping apparatus as claimed in claim 27, wherein the front side includes, in correspondence with said cutting edges, a respective two spaced apart and similar 0projecting interlocking features that project a maximum distance from said plane.

29. A wood chipping apparatus, substantially as described with reference to the drawings and/or examples.