Disc type wood chipper knife having positioning serrations and intermediate land therebetween

A knife assembly for a disc type wood chipper for cutting wood chips from a log, for example, comprises a pair of knife holding means between which a multi-section two-edged reversible knife and an associated counter knife are releasably clamped. One surface of the knife has two spaced apart sets of indented (female) serrations with an intermediate land between the sets which engage two spaced apart sets of protruding (male) serrations and a corresponding land on one surface of the counter knife to ensure proper knife alignment. The counter knife is adjustably positionable relative to the knife holding means.

BACKGROUND OF THE INVENTION 
1. Field of Use 
This invention relates generally to material chopping devices, such as disc 
type wood chippers. In particular, it relates to a knife assembly for use 
therein in which the knife is positionable relative to the knife holding 
means by positioning serrations and an intermediate land therebetween. 
2. Description of the Prior Art 
U.S. patent application Ser. No. 187,164 entitled KNIFE ASSEMBLY FOR 
CHOPPING APATUS filed Sept. 15, 1980, by Jack R. Haller and William M. 
Haselton, issued Sept. 28, 1982 as U.S. Pat. No. 4,351,487 and assigned to 
the same assignee as the present application discloses a knife assembly 
for use in a chopping apparatus, such as a wood chipper, of the type 
having a rotatable disc and an opening therethrough to permit passage of 
the chopped material through and away from the disc. The assembly 
comprises a pair of knife holding means including a knife seat and a knife 
clamp or cover, for engaging a reversible knife with two cutting edges. 
Means are provided to ensure proper alignment of the knife and its knife 
holding means. Thus, one of the knife holding means has a flat knife 
engaging surface for cooperatively engaging a complementary flat surface 
of the knife. The other knife holding means has either an arcuate 
protrusion for cooperatively engaging an arcuate groove in the knife, or 
an arcuate groove cooperating with the groove in the knife to define a 
space for accommodating a rod which prevents relative blade movement. 
However, this knife assembly does not permit the position of the knife 
edge to be adjusted or changed relative to the knife holding means. Such 
change in position may be necessary after a knife has been sharpened a 
sufficient number of times to significantly change its dimensions. Or, 
such change in position might be desirable to alter the size of the chips 
being cut or to accommodate the nature of the material being cut. Minor 
adjustments are also desirable to accurately align all adjoining knife 
edges in a true vertical plane of rotation for closer running clearances 
between the disc knives and the stationary anvil or base knives, thus 
producing a product of more uniform size with more cleanly sheared 
surfaces. 
U.S. Pat. No. 3,559,705 issued Feb. 2, 1971, to Louis Salzmann, Jr., for 
CHIPPER KNIFE AND KNIFE MOUNTING FOR DRUM TYPE WOOD CHIPPER discloses a 
reversible symmetrical knife for a drum type wood chipper. Such knife is 
extremely short in length, as compared to the knives used in disc type 
chippers, and the cutting edge thereof moves in a circular plane, as 
compared to the flat plane in which the knife cutting edge moves in a disc 
type chipper. Furthermore, in the structure shown in U.S. Pat. No. 
3,559,705 a holder is secured to the inner surface of a drum wall by means 
of a screw. The head of the holder has a serrated surface which engages 
the serrated surface of the knife and the knife is secured to the head by 
means of a screw. In the aforesaid structure, forces acting on the knife 
as the latter cuts are ultimately transferred as shear forces to the screw 
through the block and to the other screw through the holder. Although 
there is a direct transfer of force from the knife to the block and a 
transfer of force from the knife to the holder through the serrations, 
there is no direct face-to-face transfer of force from the block to the 
holder or from the holder to the drum wall. Such an arrangement is 
tolerable in a drum type chipper wherein the knives are very short but is 
not acceptable strengthwise in a disc type chipper wherein the knives are 
quite long and encounter greater forces for a longer time interval during 
chipping. 
U.S. patent application Ser. No. 352,246 entitled DISC TYPE WOOD CHIPPER 
KNIFE HAVING POSITION ADJUSTING SERRATIONS filed Feb. 25, 1983, by Jack R. 
Haller and Dino M. Demopoulos, issued Jan. 3, 1984 as U.S. Pat. No. 
4,423,758, and assigned to the same assignee as the present application 
discloses apparatus for chopping material, such as logs. Such apparatus 
comprises a rotatable disc and at least one radially disposed opening 
extending through the disc and a knife assembly comprising first knife 
holding means attached to the disc and adjacent the opening and second 
knife holding means mounted on the first knife holding means. The first 
knife holding means comprises a knife seat secured to the disc by screws 
and a counter knife secured to the knife seat by other screws. The counter 
knife has a first knife-engaging portion including protruding serrations 
thereon. The second knife holding means has a second knife-engaging 
portion including a flat knife-engaging surface. A reversible knife having 
two cutting edges is mounted between said first and second knife holding 
means. The knife has a complementary flat surface for cooperatively 
engaging the flat knife-engaging surface of the second knife holding 
means. The knife has indented serrations for cooperatively engaging the 
protruding serrations. Clamping engagement means are provided for 
clampingly engaging the knife between the counter knife of the first knife 
holding means and the second knife holding means. The clamping engagement 
means comprises studs with two ends. Each stud has one of the ends fixed 
to the second knife holding means and the other of said ends is threaded. 
The threaded end is threadably engaged to a nut abutting the rotatable 
disc, whereby rotation of the nut causes axial movement of the stud 
therealong and permits relative movement between the first knife holding 
means and the second knife holding means. 
The counter knife is secured to said knife seat by securement means, such 
as the aforesaid other screws, which enables the counter knife to be 
adjustably positioned relative to the knife seat. 
In one embodiment the knife has the same number of indented serrations as 
there are protruding serrations on the counter knife whereby the knife and 
the counter knife can assume only one position relative to each other and 
there is no possibility of knife position error when a knife is installed. 
In another embodiment the knife has a larger number of indented serrations 
when there are protruding serrations on the counter knife whereby the 
knife and the counter knife can assume a plurality of positions relative 
to each other to further enhance knife position adjustability. 
The serrations disclosed are triangular in cross-section but could take 
some other form. Knife position gauge means are provided on the inner most 
end of each knife seat. 
A disc type chipper in accordance with U.S. Pat. No. 4,423,758 offers 
several advantages over the prior art. For example, the configuration and 
arrangement of the components including the disc, the knife seat, the 
knife cover, the counter knife and the knife, as well as the cap screws 
and studs, provides a substantially stronger arrangement than in prior art 
chippers and provides for transfer of forces between the surfaces of 
components rather than merely through the studs and cap screws. 
Furthermore, the knife, when interlockingly engaged with the counter 
knife, is adjustably positionable in response to positioning of the 
counter knife on the knife seat, the positioning means therefor including 
cap screws and shims. In one embodiment, the arrangement of serrations on 
the knife and counter knife is such that the knife can only assume one 
position with respect to the counter knife and this arrangement provides 
for an even range of adjustments of knife positioning. The combination of 
movement of the knife on the serrations and the fine adjustment of the 
counter knife by use of shims provides an infinitely adjustable knife 
projection for very accurate alignment of all adjoining knife edges and 
subsequent closer running clearance adjustment of the disc knives and the 
stationary anvils or base knives. In addition, the counter knife serves as 
the point of maximum wear and, being a relatively small piece, is 
substantially cheaper to replace when worn than is the larger knife seat 
in some prior art apparatus. 
When the chipper of U.S. Pat. No. 4,423,758 is in operation, the average 
cutting velocity at the centerline of the knife is approximately 7,000 
feet per minute. Rim speed at the periphery of the disc can reach 10,500 
feet per minute. The total weight of the rotating mass can reach 21 tons. 
This combination of great mass plus high velocity makes it imperative that 
running clearances be maintained and all rotating parts be fastened 
securely. It is quite common to adjust the chipper so that the running 
clearance between the disc knives and the base knives is from 0.010" to 
0.030". 
Knife changing is often done at night by an operator who at best is half 
asleep and working in a poorly lighted area. Therefore, it is essential to 
provide a means for locating knives that is as foolproof as possible. 
The serrations shown in one embodiment in U.S. Pat. No. 4,423,758 can allow 
a careless operator to "cross thread" or misalign the grooves or align the 
male-female grooves in a tip-to-tip position. If the operator then 
tightens the knife cover stud nuts while the knife is in improper 
position, he may damage the serration tips and, if he is inattentive, he 
can mistakenly assume the knife is properly located. Since one can use 
3,000 pounds per linear inch as the clamping force to secure the knives, 
considerable deformation of the serrations can take place. 
In practice, a set of 2 or 3 short knives are used to make up a full knife 
length. If one of the knives in a set is misaligned, it may prevent the 
other knives in the set from being properly clamped. The same can occur if 
one of the knives does not receive its full portion of the clamping 
pressure due to the misalignment of the adjoining knife. 
A misaligned knife may eliminate the necessary running clearance, strike 
the base knives and damage may occur. This may be anything from a broken 
knife to a severely damaged chipper and injury or death to personnel. 
SUMMARY OF THE INVENTION 
In accordance with the invention there is provided improved apparatus for 
chopping material, such as logs, which overcomes the aforesaid and other 
problems. The apparatus comprises a rotatable disc and at least one 
radially disposed opening extending through the disc and a knife assembly 
comprising first knife holding means attached to the disc and adjacent the 
opening and second knife holding means mounted on the first knife holding 
means. The first knife holding means comprises a knife seat secured to the 
disc by screws and a counter knife secured to the knife seat by other 
screws. The counter knife has a first knife-engaging portion including two 
spaced apart sets of protruding serrations (one or two protrusions in each 
set) with an intermediate land therebetween. The second knife holding 
means has a second knife-engaging portion including a flat knife-engaging 
surface. A reversible knife having two cutting edges is mounted between 
said first and second knife holding means. The knife has a complementary 
flat surface for cooperatively engaging the flat knife-engaging surface of 
the second knife holding means. On its opposite surface the knife has two 
spaced apart sets of indented serrations (one or two indentations in each 
set) with an intermediate land therebetween for cooperatively engaging the 
serrations and land on the counter knife. Clamping engagement means are 
provided for clampingly engaging the knife between the counter knife of 
the first knife holding means and the second knife holding means. The 
clamping engagement means comprises studs with two ends. Each stud has one 
of the ends fixed to the second knife holding means and the other of said 
ends is threaded. The threaded end is threadably engaged to a nut abutting 
the rotatable disc, whereby rotation of the nut causes axial movement of 
the stud therealong and permits relative movement between the first knife 
holding means and the second knife holding means. 
The counter knife is secured to said knife seat by securement means, such 
as the aforesaid other screws, which enables the counter knife to be 
adjustably positioned relative to the knife seat. 
In the embodiment shown, the knife has the same number of indented 
serrations as there are protruding serrations on on the counter knife 
whereby the knife and the counter knife can assume only one position 
relative to each other and there is no possibility of knife position error 
when a knife is installed. The lands lie in the same planes as the surface 
on or in which the associated serrations are found. 
The serrations disclosed are triangular in cross-section but could take 
some other form. Knife position gauge means are provided on the inner most 
end of each knife set. 
A disc type chipper in accordance with the invention offers several 
advantages over the prior art. For example, the arrangement of sets of 
serrations with a land therebetween on the knife and counter knife is such 
that the knife can only assume one position with respect to the counter 
knife and this ensures that the knife is always in proper position on the 
disc, assuming, of course, that the counter knife is properly positioned. 
With the intermediate land between the serrations a wider support is 
provided in the serration area as the female serrations of the knife are 
slid across the male serrations of the counter knife when the knife is 
being inserted. Since it creates an irregular pattern as compared to the 
regular pattern of a series of serrations there is a greatly reduced 
possibility of the operator getting a false "feel" of the knife being in 
the proper position. Since the intermediate land provides a wider positive 
locating means when mated into the wider groove of the counter knife, the 
operator has a much greater feel as the knife literally jumps into 
position as its slides across the serrations of the counter knife. This is 
verified in actual comparisons in the factory and field between. 
The knives and counter knives in accordance with the invention are also 
easier and less expensive to manufacture. The series of serrations was 
originally made by machining the serrations in the knife and counter knife 
prior to hardening by heat treatment. It was discovered that the heat 
treatment distorted the parts to such a degree that the serrations would 
interfere before proper clamping could occur. This necessitated hand 
lapping each piece before it could be used. To overcome this, the 
serrations were then ground into the hardened parts. Grinding is a much 
slower and more costly process. Redressing the grinding wheel as the 
grinding surfaces broke down was both tedious and expensive since the 
accurancy of the grooves in the wheel impart the accurancy of the 
serrations in the parts. Reducing the number of grooves alone reduced 
grinding wheel initial cost and maintenance. Two serrations on each side 
of the land allows two two-groove wheels to be mounted on a single spindle 
with reduced initial and maintenance costs. This invention also lends 
itself to purchasing rolled sections with the serrations rolled into the 
steel bar from which the roughly shaped knives are cut. This is 
particularly true if the number of grooves on each side of the land is 
reduced to one. A rolled section greatly reduces the manufacturing costs 
of the knives. 
Other objects and advantages of the invention will hereinafter appear.

DESCRIPTION OF PREFERRED EMBODIMENTS 
The knife assembly 22 described herein is typically for use in a chopping 
disc of a disc type wood or log chipper, as shown in FIGS. 1 and 2. The 
disc 10 is rotatable by a shaft 12 powered by power means (not shown). The 
materials to be chopped, such as logs, are fed to the disc 10 through a 
spout 14 angularly disposed to the axis of the disc, as defined by the 
shaft 12. After the wood is chopped into small pieces or chips, those 
chips pass through radially disposed openings 16, the details of which 
will be explained later, and are then swept by a plurality of paddles 18 
attached to the radial ends of the disc 10 through a spout or discharge 
opening 20 for transfer to a remote location. 
As an alternate, the chips can drop through an opening in the bottom of the 
chipper enclosure on to a conveyor beneath the chipper. 
The knife assembly 22 includes an elongated knife seat 24 on which is 
mounted, by means of cap screws 19, a counter knife 21 which constitutes a 
first knife holding means. The assembly 22 also includes an elongated 
knife cover or clamp 26 which constitutes a second knife holding means, a 
plurality of disc knives 28A, 28B, 28C which constitute reversible knives, 
and means 30 for clampingly engaging the knives 28A, 28B, 28C between the 
first knife holding means 21, 24 and the second knife holding means 26. 
The knife seat 24 is attached to the disc 10 and rotates therewith, and is 
also adjacent the radial opening 16 by which the chopped material passes 
through and away from the disc 10 after being chopped by the knife 
assembly. The second knife holding means or clamp 26 is mounted on the 
knife seat 24, as may be seen in FIG. 4, where a surface 32 at the upper 
end of the knife cover 26 rests against an elongated support 30 of knife 
seat 24. 
The support 30 for clampingly engaging the knife 28 between the knife seat 
24 and counter knife 21 and the knife holding means 26 includes threaded 
studs 38, each having one end threadably engaged in the second knife 
holding means 26, which permits easy replacement of second knife holding 
means 26 when it is worn or damaged. The other end of stud 38 is threaded, 
and is threadably engaged to a nut 40, which abuts the disc 10 through a 
special washer 42. As shown in FIG. 4, the surface 32 of second knife 
holding means 26 is tightly abutting the adjacent support 30 of first 
knife holding means 24, such that no rightward movement of second knife 
holding means 26, with respect to first knife holding means 24 is 
possible, and the knife 28 and counter knife 21 are firmly engaged 
therebetween. Stud 38, which passes through the knife holding means 24 and 
into 26 and also extends through disc 10, permits relative clamping 
movement of knife holding means 24 and 26. Assuming right-hand threads, 
counterclockwise rotation of nut 40 about the threaded end to which it is 
engaged results in space between nut 40 and washer 42 or between washer 42 
and the disc face 44 abutting that washer. This space permits leftward 
movement of stud 38, which in turn permits leftward movement of second 
knife holding means 26 relative to first knife holding means 24. Knife 28 
and counter knife 21 will then no longer be tightly engaged between means 
24 and 26, and thus may be readily removed to facilitate adjustment or 
reversal or replacement of the knife. 
The counter knife 21 has a first knife-engaging portion including two 
spaced apart sets of protruding (male) serrations 46 (one protrusion in 
each set) with an intermediate land 46A between the two sets. The knife 
holding means or cover 26 has a second knife-engaging portion including a 
flat knife-engaging surface 48. In the embodiment described herein, the 
counter knife 21 has the protruding serrations and the second knife 
holding means 26 has the flat knife-engaging surface. 
Each elongated knife seat 24 has attached thereto the counter knife 21 with 
which knife 28 is associated, which knife may be of one-piece or 
multiple-piece construction. A three-piece knife, each piece designated 
28A, 28B or 28C being identical, is shown mounted beneath the elongated 
knife cover 26 of FIG. 1. Knife 28 chops material as it rotates with disc 
10 by cooperative cutting action with the base knives or anvil 58A. Each 
knife 28 has two sides, one side 51 formed so as to include two spaced 
apart sets of (female) serrations 50 (one indentation in each set) with an 
intermediate land 50A between the two sets which accept the protruding 
serrations 46 and engage the land 46A. The other side 52 of knife 28 is 
formed flat to engage the flat knife-engaging surface 48 of clamp 26. 
Each land 46A, 50A lies in the same plane as the surface of the counter 
knife 21 or knife 28, respectively, at which the associated serrations 46 
and 50, respectively, are formed. The protruding serrations 46 integrally 
formed on the counter knife 21 of the first knife holding means 24 and the 
indented serrations 50 on knife 28 are triangular in cross-section. The 
number of serrations 46 equals the number of serrations 50, one of each 
serration (protruding or indented) being shown in each set of FIGS. 3 
through 6. FIG. 7 shows an arrangement embodying two serrations per set. 
This illustrates the ability of the knife 28, when mounted as described, 
to align itself on the counter knife 21 of the second knife holding means 
26 and provide good contact thereagainst. Thus, knife 28 can be placed in 
only one position relative to counter knife 21. The mating serrations 46 
and 50 act as thrust elements. 
The second side of the knife 28 comprises the complementary flat surface 
52, which engages the flat knife-engaging surface 48 of second knife 
holding means 26. This flat surface 52, as explained hereinabove, 
transmits less stress per unit area to the flat knife-engaging surface 48 
than any other configuration and thus permits the second knife holding 
means 26 to be constructed of a less expensive material than would be 
possible with another configuration. 
Wear on knife edge 54 on knives 28A, 28B and 28C tends to be localized due 
to the peculiar cutting action of the chopper. Thus, any of the plurality 
of knives in each knife assembly may experience more wear in one area of 
its edge making it undesirable to keep that edge in its present position. 
However, the unworn portion of the knife may allow it to function 
satisfactorily in another position relative to the other knives in the 
knife assembly. Therefore, the knives may be shifted within the set 
relative to one another. This is done by separating the knife holding 
means 24 and 26 as described above and the knives are repositioned 
relative to one another. When edge 54 is worn out, the knife holding means 
24 and 26 are separated as described above and the knife is rotated 180 
degrees about an axis normal to the surface 91 of counter knife 21 so as 
to present edge 56 as a cutting edge. This edge may be used in different 
positions as described above until edge 56 is completely dull. When both 
edges 54 and 56 are dull the knife is removed and replaced with a new 
knife. The replacement knife may also be a resharpened knife. If the knife 
is resharpened, the counter knife 21 may be repositioned on the knife seat 
24. 
The apparatus is also provided with a plurality of replaceable disc wear 
plates 58, secured to the disc 10 with stud and nut means 60. 
As FIGS. 4 and 5 show, the knife seat 24 comprises a large base surface 61 
which bears against disc 10 and also comprises an outwardly facing groove 
which receives the counter knife 21 and is defined by the two surfaces 62 
and 64 which meet at a right angle. One or more shims 66 are disposed 
between the rear edge surface 67 of counter knife 21 and the surface 64 of 
knife seat 24. The shim thickness determines the rearwardmost position of 
knife seat 24. Knife seat 24 is provided with threaded holes 69 for 
receiving the threaded ends of the cap screws 19 which secure the counter 
knife 21 to the knife seat 24. The heads of screws 19 are received in 
countersunk recesses 70 in the surface 71 of counter knife 21 and the 
shank of screws 19 extends through elongated slots 72 in counter knife 21. 
Slots 72 enables the counter knife 21 to be positioned at different 
distances from surface 64 of knife seat 24. 
Knife position gauge means are provided to ensure that the knife 28 is 
located in correct position on the disc 10 relative to all other 
components. As is apparent, knife 28 can be held in a fixed position 
relative to counter knife 21 because of the interengaging serrations 46 
and 50. Only one fixed position is possible. However, counter knife 21 can 
be placed in many positions relative to knife seat 24 because of the 
screw-receiving slot 72 in counter knife 21. Accordingly, knife 28 can 
assume several possible positions, only one of which is correct relative 
to knife seat 24, knife position gauge means are provided to ensure 
placement of the knife in that position. As FIGS. 1 and 6 show, such means 
comprise a plate 77 which is secured as by a plurality of cap screws to 
the innermost end of knife seat 24. Plate 77 is trapezoidal in form and 
its outer point 79 defines the locus of knife edge 54. Provision of such 
gauge eliminates the need to measure blade position. It is to be 
understood that the knife position gauge means could be mounted on a 
component other than the knife seat and could take a form other than 
shown.