Field of the Invention
The present invention relates to a high speed planer head,
such as for use in commercial manufacturing of construction lumber and finished
The finish on construction lumber, such as cut from logs
into 2 X 4, 2 X 6, 2 X 12, and 4 X 4 nominal dimensions, has become increasingly
important as a result of the trend for such construction lumber to be sold in retail
outlets, such as the large home improvement chain stores, to "do-it-yourself" (DIY)
consumers. While construction lumber is typically covered with sheet rock or gypsum
board and so is not visible in finished construction, DIY consumers often select
and purchase construction lumber primarily on the basis of surface-finish. Accordingly,
well finished construction lumber can command a premium price, and construction
lumber that is not well finished may be difficult to sell.
Commercial planer heads include a plurality of elongate
knives spaced circumferentially on a cylindrical hub rotating at high speed. The
elongate axes of the knives are typically, but not necessarily, aligned with the
axis of rotation. The wood travels relative to the head in a direction perpendicular
to the axis of rotation of the hub, the knives cutting a surface on the wood. The
resulting surface finish is affected by a number of factors, e.g., the extent to
which the planer head is in balance, the density of knives on the planer head, the
speed of rotation, the speed of travel of the wood, and the ability of the apparatus
to efficiently keep chips away from the cutting surface as it is being cut.
Standard practice provides for statically balancing the
knives and knife assemblies carried by the hub as well as dynamically balancing
the hub and the shaft to which the hub is attached (or with which the hub is integrally
formed). The speed of rotation of the head is set as high as practical, and the
speed of travel of the wood is set as high as possible while still providing acceptable
surface finish, to increase the speed of production. Some "chip marks" occur as
a result of chips remaining on the cutting surface as the wood is being cut and
have been accepted in the prior art.
With a given degree of balancing and speed of rotation
of the planer head, increasing the speed of wood travel to obtain further efficiency
increases will decrease the quality of the surface finish, and it would be advantageous
either to be able to increase the speed while maintaining the quality of surface
finish, or maintain the speed and improve the quality of the surface finish.
One means for increasing the surface quality given the
limitations noted above is to increase the frequency of cutting by increasing the
density of knives on the planer head. Particularly, the parallel and circumferentially
distributed cutting edges of the knives should be spaced as close together as possible.
However, each knife must be removable so that the knife can be sharpened or replaced.
The knives are typically clamped in knife assemblies by screws. The screws may bear
on a block of metal called a "gib" that it turn bears on the knife, the end of the
screw may bear directly on the knife, or the screw may extend into a collar that
wedges against the knife. In all cases, the construction methodology places limits
on the potential for increasing the density of the knives.
Typically, prior art knives have a straight cutting edge
and one or two radiused or semi-circularly curved cutting edges at respective ends
of the straight cutting edge. Where only one curved cutting edge is employed; the
knives are alternated in upside-down and right-side-up position so that two knives
together cut respective opposite corners of the wood and each knife cuts the straight
face of the wood so that the straight face of the wood is twice cut. In either case,
a straight cutting edge is physically merged with a curved cutting edge. In a process
known as "jointing," used for sharpening the knives as the knives are installed
in the planer head and as the head is rotating, wherein a fixed stone is introduced
against the rotating knives, what is known in the art as "relief" is lost for the
outer portions of the curved cutting edges. This lack of relief results in hammering
the wood at the corners, degrading surface finish.
Another problem in the prior art is adjusting the planer
head between cutting an article of wood from green wood stock to cutting an article
of the same nominal size from dry wood stock, and vice-versa. This has required
replacing the complete planer head, which is costly.
There is a need, therefore, for a high speed planer head
provided according to the present invention that solves the aforementioned problems
and provides additional features and advantages.
Summary of the Invention
The invention disclosed herein is a high speed planer head.
According to one aspect of the invention a hub and a threaded member are provided.
The hub is axially disposed for rotation about an axis and has a pocket for receiving
a first knife against a supporting wall of the pocket. The threaded member has a
frustoconical ramping portion for producing a wedging force against the knife when
the threaded member is threaded into a threaded hole in the hub.
According to another aspect of the invention, a second
hub for carrying a second knife is provided, the second hub preferably being bolted
to the first hub to that the hubs can be disassembled. The first knife preferably
has two linear cutting edges and the second knife preferably has at least two curvilinear
The second knife preferably has two linear cutting edges
and the second knife preferably has at least two curvilinear cutting edges and more
preferably has four concave, semi-circular cutting edges that are spaced apart from
one another with 90 degree rotational symmetry.
Brief Description of the Drawings
Detailed Description of a Preferred Embodiment
- Figure 1A is side elevation of a prior art planing apparatus.
- Figure 1B is a top view of the planing apparatus of Figure 1A.
- Figure 2 is an end view of a prior art planer head for use in the apparatus
of Figures 1A and 1B.
- Figure 3 is more detailed end view of the planer head of Figure 2.
- Figure 4A is a pictorial view of an alternative prior art planer head.
- Figure 4B is a pictorial view of two collars used in the planer head of Figure
- Figure 5 is an end view of a face-cutting planer head according to the present
- Figure 6 is more detailed end view of the planer head of Figure 5.
- Figure 7 is a pictorial view of a preferred knife for use in the planer head
of Figure 5.
- Figure 8A is a cross-sectional view of an unfinished article of lumber.
- Figure 8B is a cross-sectional view of the article of lumber of Figure 8A in
a finished condition.
- Figure 9A is a pictorial view of side-cutting planer head according to the present
- Figure 9B is a side elevation of the planer head of Figure 8A.
- Figure 10 is an exploded view of a preferred configuration of the planer head
of Figure 8A.
- Figure 11 is an end view of a comer-cutting planer head according to the present
- Figure 12A is a pictorial view of a front side of a corner-cutting knife according
to the present invention for use in end portions of the planer head of Figure 9A.
- Figure 12B is a pictorial view of a back side of the knife of Figure 12A.
- Figure 13A is a cross-sectional schematic view of an article of lumber being
cut with a comer-cutting knife having a full 1/4 round cutting edge in perfect alignment.
- Figure 13B is a cross-sectional schematic view of the article of lumber of Figure
12A cut with the knife of Figure 13A in imperfect alignment.
- Figure 14A is a plan view of two knives according to the present invention,
comparing dimensions thereof for cutting an article of lumber from dry and green
- Figure 14B is an end view of an article of lumber shown with finished corners
produced by the two knives of Figure 14A.
- Figure 14C is a plan view of a positioning, according to the present invention,
of the two knives of Figure 14A for finishing the article of lumber as shown in
- Figure 15A is a schematic view of the knife of Figures 12A and 12B showing geometric
constructions useful for defining the configuration of the knife according to the
- Figure 15B is a schematic view of a prior art knife corresponding to the schematic
view of Figure 15A.
- Figure 16A is a pictorial view of the knife shown in Figures 12A and 12B showing
line segments used to describe the shape of a beveled surface of the knife according
to the present invention.
- Figure 16B is a partially cut-away cross-sectional view of the knife of Figure
16A taken along a line 16B-16B thereof.
- Figure 16C is a partially cut-away cross-sectional view of the knife of Figure
16A taken along a line 16C-16C thereof.
- Figure 16D is a partially cut-away cross-sectional view of the knife of Figure
16A taken along a line 16D-16D thereof.
- Figure 17A is a schematic view of a face-cutting knife cutting an article of
lumber showing an attack relief angle according to the prior art.
- Figure 17B is a schematic view of a comer-cutting knife according to the present
invention shown relative to the article of lumber of Figure 17A.
Figures 1A and 1B show two orthographic views (side and
top, respectively) of a high speed planing apparatus 10. The apparatus 10 has a
table 12 for supporting an article of wood 14 that travels horizontally on the table.
At least four planer heads 16 are provided: one (16a) above the article of wood
(hereinafter "top"), one (16b) below the article of wood (hereinafter "bottom"),
one (16c) to one side of the article of wood and one (16d) to the other side of
the article of wood (hereinafter "side"). Each planer head rotates about a respective
axis of rotation "Ra," "Rb," "Rc," and Rd." As a result of this rotation, in conjunction
with travel of the wood 14 relative to the planer heads, each planer head cuts a
corresponding surface on the article of wood, so that a top surface, a bottom surface,
and two opposing side surfaces are cut. An object of this process is to produce
a surface having a high surface quality; however, it is not essential that the planing
apparatus be used to produce a finished surface.
Figure 2 shows an end view of one (17a) of the planer heads
16. The head 17a has an axis of rotation "R." A hub 18 of the head 17a carries a
plurality of circumferentially spaced apart knives 20 and associated gibs 22 in
corresponding pockets 19 of the hub. Figure 3 shows one of the pockets 19a in more
detail. A knife 20a and its associated gib 22a are disposed in the pocket 19a. A
screw 24 is threadably received through a hole in the hub 18 and a terminating end
24a thereof extends outside the hub and bears against the gib 22a which, in turn,
bears against the knife 20a. This clamping force clamps the knife against a supporting
wall 19as of the pocket 19a. A minimum circumferential spacing "S" is required between
adjacent knives to provide space for accessing and removing the screw 24a in the
direction of the arrow "A."
Figure 4a is a pictorial view of an alternative prior art
planer head 17b, showing a knife 20b removed therefrom. The knife 20b is clamped
in a pocket 19b in the head 17b by an axially directed screw 242 extending
through an upper collar 25a and into a corresponding lower collar 25b. Referring
in addition to Figure 4B, the collars 25 include corresponding ramped planar portions
25ap (not visible in Figure 4A) and 25bp for mating with corresponding ramped planar
portions 22b-upper and 22b-lower of a gib portion 22b of the knife 20b that functions
analogously to the gib 22a of the knife 20a. Rather than bearing against the knife
as does the gib 22a, the gib portion 22b is integrally attached to the knife and
supports the knife, which is cantilevered therefrom. Therefore, the gib portion
22b must be particularly large and robust to withstand the required forces, as compared
to the gib 22a.
One of the collars (25a) is adapted to receive the head
of the screw 242 and the other collar (25b) includes threads "Th" adapted
to receive the threads of the screw. Inserting the screw through the collar 25a
and tightening the screw into the collar 25b forces the collars together, wedging
the collars against the ramped planar portions of the knife and thereby forcing
the knife against a back surface 19bs of the pocket 19b, to clamp the
knife to the planer head. This construction provides an advantage over the planer
head 17a described immediately above in providing the capability to move the knives
closer to one another and therefore achieve denser knife spacing. However, this
density is limited by the dimensions of the collars and the gib portions 22b, all
of which must be robustly sized in order to withstand the required forces.
Turning to Figure 5, an end view of a face-cutting planer
head 26 according to the present invention is shown. A hub 28 of the head 26 carries
a plurality of circumferentially spaced apart knives 30. Each knife 30 is disposed
in an associated pocket 31 and has an associated gib 32. As best seen in Figure
6, showing a portion of the periphery of the hub 28 in greater detail, a screw 34
has a threaded portion for threading into a hole 35 in the hub. The threaded portion
terminates in a terminating end 34a that is, preferably, contained within the hub
and, in any event, is not used to exert a force on either the gib or the knife.
Rather, the screw 34 according to the present invention has a ramping shoulder portion
34b which in a preferred embodiment of the invention is of frustoconical shape.
The ramping portion 34b exerts increasing wedging force (in the direction indicated
by the arrow "b") against the gib 32 as the screw is tightened, the gib in turn
transmitting this wedging force against the knife, to clamp the knife in place against
a supporting wall 31c of the pocket 31, and against the gib, to force the gib against
a front side 40 of the knife and a bottom 31b of the pocket 31. The screw 34 is
shown with a male tightening member 34c; however, a female tightening member may
also be used. Moreover, a female tightening member has been determined not to become
loaded with wood waste during operation and the female configuration provides for
greater clearance and so may, therefore, be preferable.
An angle &THgr; defines the ramp angle of the of the ramping
portion 34b of the screw 34; This ramp angle provides a mechanical advantage in
translating a tightening force applied to thread the screw into the hole 35 into
a clamping force bearing against the gib and, in turn, the knife. A small ramp angle
&THgr; increases the advantage; however, if the ramp angle &THgr; is too small,
too little range of movement of the gib will be provided to accommodate manufacturing
tolerances between the screw, gib and knife, along with the additional elastic compression
of the parts necessary to exert the required clamping force. It has been found that
the ramp angle &THgr; is preferably in the range of about 10 - 25 degrees.
The combination of the screw 34 and gib 32 clamp each knife
30 in the planer head 26. The gib 32 need be no more robust than the gib 22a described
above in connection with the head 17a. The screw 34 in essentially incorporating
the function of the collars 25 of the head 17b can be of smaller overall dimensions
than the corresponding screw and collar combination, and the gib 32 need not be
as strong and therefore may be smaller and, particularly, thinner than the corresponding
gib portion 22b. Thence, the screw and gib according to the present invention provide
minimum sized components for clamping knives in a planar head, providing for maximum
density of spacing of the knives and, therefore, a maximum degree or quality of
Referring to Figure 7, the knives 30 are preferably provided
with dual, opposed, cutting edges 36a and 36b and corresponding deflector ridges
38a and 38b such as described in Schmatjen, U.S. Patent No. 5,819,826 that project
from the front side 40 of the knife and extend parallel to an elongate axis "L"
of the knife. The deflector ridges define a channel 42 having a channel surface
42a. The channel 42 is effectively a recess in the front side of the knife, which
may be provided in other configurations, such as a keyway. The knives 30 also have
a back surface 44 that is received against the supporting wall 31c of the pocket
The recess provided, in the preferred embodiment, by the
deflector ridges 38 and the associated channel 42 define an interlocking feature
adapted for interlocking with the gib 32, providing a double-sided, indexable knife
system that securely and positively holds the knife in the associated pocket. Particularly,
as seen in Figure 6, for use with the preferred knife 30, the gib is adapted so
that one of the deflector ridges 38a is disposed outside a toe 39 of the gib at
one end of the toe, the other end of the toe being defined by a recess 41 shaped
to receive the other deflector ridge 38b. The channel 42 as bounded by the deflector
ridges defines a recess that, along with the relatively projecting toe of the gib
32, provide interlocking means which cooperate to index and further securely hold
the knife 30 in position against the gib 32.
Referring back to Figure 7, the knife 30 has an elongate
axis "L" and, a line perpendicular to the elongate axis "L" and passing through
the cutting edges 36 of the knife defines a transverse axis "TA" of the knife. Now
referring back to Figure 5, the gib 32 associated with the pocket wall 31c defines
an orientation of the axis "TA" for the knife as installed in the hub 28. This orientation
can be specified as an angle &thgr;1 relative to a radial line "RL"
extending through the axis of rotation "R" of the head. The angle &thgr;1
establishes the axis "TA." The angle &thgr;1 is optimized to provide
a desired angle of attack for the knife and is preferably in the range of 10 - 30
The hole 35 for receiving the threaded portion of the screw
34 has an elongate axis "EA" that makes an angle &thgr;2 relative to
the radial line "RL." The angle &thgr;2 is optimized to direct the clamping
force against the knife. The angle &thgr;2 is preferably in the range
of 10 - 20 degrees and is determined without regard to the angle &thgr;1,
i.e., the axes "EA" and "TA" rotate together as the angle &thgr;1 is
The planer head 26 provides several outstanding advantages.
One advantage is that the manner described above for clamping each knife 30 provides
for much denser spacing of the knives as compared to the prior art. The screw 34
may be accessed and removed from essentially a radial direction rather than a circumferential
direction, so that the spacing between the knives need not provide space for screw
access or removal as was required in the prior art. This denser spacing of the knives,
by itself, improves surface finish. Moreover, this improved surface finish can be
traded off, to any extent desired, to achieve higher production throughput by increasing
the speed of travel of the wood being cut.
The mechanical advantage provided by the screw 34 has been
found to decrease the number of screws required to achieve a given clamping force.
This provides for less machine downtime, since fewer screws need to be loosened
or removed in order to remove a knife for replacement or repair. This mechanical
advantage also makes the screw less prone to loosening, so that clamping is made
It is also recognized by the present inventor that each
of the knives 30 may be made very thin (dimension "t" in Figure 7), so that, from
material considerations, it becomes economical to dispose of the knives rather than
repair them. For example, for a typical knife that is 7/8" wide (dimension "w" in
Figure 7) and arbitrarily long (e.g., anywhere from 1" to 48"), a representative
dimension "t" is only 0.082". Employing disposable knives further reduces machine
downtime as well as the cost of providing and operating machines used for knife
repair. The ability to make the knives thin is due, at least in part, to the security
of the clamping force provided by the screw 34 as well as the indexing provided
by the deflector ridges.
The knives 30 and the gibs 32 need not extend the entire
(axial) length of the hub 28. For example, two knives 30 and/or two associated gibs
32, axially butted against one another, are preferably used in each pocket 31, each
pair of a knife and associated gib extending about half the axial length "1" of
the hub. Two axially disposed knives and/or two axially disposed gibs, or more than
two axially disposed knives and/or more than two axially disposed gibs may be provided
in each pocket without departing from the principles of the invention.
The just described planer head 26 corresponds to two of
the four planer heads 16a - 16d of Figures 1A and 1B. Turning to Figure 8A, a generalized
cross-section of a length of unfinished construction lumber 45UF is shown.
Two of the planer heads 26 are arranged in correspondence to the heads 16a and 16b
of Figures 1A and 1B and cut, respectively, top and bottom faces Ft and
Fb of the lumber 45UF. After this cutting the lumber has a
finished thickness "tF," and an unfinished width "wuf."
Figure 8B shows a cross-section of the article of lumber
shown in Figure 7A in a finished condition 45F as a result of cutting
two side faces Fs, along with four respective radiused corners "r," with
planer heads corresponding to 16c and 16d of Figures 1A and 1B. Accordingly, each
of the side-cutting planer heads has comer-cutting adaptations for cutting two radiused
corners "r" in addition to an adaptation for face-cutting a flat side face Fs.
Turning to Figures 9A and 9B, a side-cutting planer head
46 is shown having the corner and face-cutting adaptations just indicated. Particularly,
the side-cutting planer head 46 has a face-cutting center portion 47 and two comer-cutting
end portions 49a and 49b, on either side of the center portion 47, for cutting respective
radiused corners "r." The portions may be attached to a shaft for rotating the portions
as is known in the art or may be formed integrally with the shaft.
Turning to Figure 10, the face-cutting center portion,47
includes a hub 48 carrying a plurality of circumferentially spaced apart knives
50. Each knife 50 is disposed in an associated pocket 51 and has an associated gib
52. A screw 54 is threadably received through the hub 48. The screw 54 preferably
has the same features as the screw 34 for wedging against the gib 52, and in turn
for wedging the knife against a supporting wall 51 c of the pocket 51. As the center
portion 47 is used to cut a flat face like the planer head 26 described above, the
center portion is preferably provided with all of the features of the planer head
With reference to Figures 10 and 11, each comer-cutting
end portion 49 includes a hub 58 (58a, 58b in Figure 10) carrying a plurality of
circumferentially spaced apart knives 60. Each knife 60 is disposed in an associated
pocket 61 and has an associated gib 62. A screw 64 is threadably received through
the hub. The screw 64 preferably has a ramping shoulder portion 64b that is the
same as or similar to the ramping shoulder portion 34b of the screw 34, for wedging
against the gib 62, and in turn for wedging the knife against a supporting wall
61 c of the pocket 61. The screw 64 is shown with a female tightening member 64c;
however, as mentioned above, either female or male tightening member may be used.
As best seen in Figure 9B, the comer-cutting end portions
49 are adapted to cut two of the radiused corners "r"shown in Figure 8B. Turning
to Figures 12A and 12B, showing the knife 60 in more detail, the knife has at least
one comer-cutting edge "CE1" for this purpose. It is advantageous, however,
to provide the knife 60 with four comer-cutting edges "CE1," "CE2,"
"CE3," and "CE4," so that the knife carries a multitude of
replacement edges and so that a symmetry is provided in the knife so that the knife
is suitable for use in either end portion 49. However, any number of comer-cutting
edges (or cutting edges) may be provided. Preferably, the four comer-cutting edges
are disposed with respect to one another with 90 degree rotational symmetry as shown;
generally, it is preferable to provide "n" cutting edges with 360/n degree rotational
The knife 60 has a front side 60a (Figure 12A) and a back
side 60b (Figure 12B). Taking the end portion 49a for example and with reference
to Figure 9, to expose the comer-cutting edge "CE1," the knife is indexed
to the pocket 61 by seating a first outer edge "OE1" against a bottom
supporting wall 61b in the hub 58a. A second outer edge "OE2" is index
to a sidewall 53a (see also Figures 9A and 9B) of a pocket 53 in the adjacent hub
48 of the center portion 47. Similar considerations apply in mirror image for the
end portion 49b.
With particular reference to Figure 12B, the cutting edge
"CE" is a portion of a concavely circular arc for cutting a round (radiused) corner
"r," though other shapes could be used for forming corners having different configurations.
A full 90 degree arc, necessary for cutting a complete 1/4 round corner "r,"is shown
superimposed on the cutting edge "CE1" in dotted line. The 90 degree
arc terminates at end-points P3 (corresponding to P1) and
P4 (corresponding to P2). Tangent lines "LT3" and
"LT4" that are tangent to the end-points P3 and P4
are spaced apart 90 degrees.
By contrast, the cutting edge "CE1" is preferably
less than a full 90 degree arc and terminates at end-points P1 and P2.
Tangent lines "LT1" and "LT2" that are tangent to the end-points
P1 and P2 are spaced apart greater than 90 degrees. Particularly,
respective alignment relief areas "RA1" and "RA2" are defined
between the respective tangent lines "LT1" and "LT2" and the
corresponding respective tangent lines "LT3" and "LT4." These
alignment relief areas (or "alignment reliefs") are preferably formed by employing,
preferably though not necessarily, straight outer perimeter sections "OP" flanking,
on each side, the cutting edge "CE1." An alignment relief angle &thgr;3
corresponding to the alignment relief area "RA1" and an alignment relief
angle &thgr;4 corresponding to the alignment relief area "RA2"
are preferably equal to each other and are preferably about 20 degrees; however,
the angles can vary depending on need according to the following considerations.
The alignment reliefs are provided to ensure that the knife
does not extend into space in which it is not desired as a result of misalignment
of the knives. Even if the knives are originally perfectly aligned, such misalignment
can subsequently occur, for example, as a result of the process known in the art
as "jointing," which is used to sharpen the knives in a planer head with a stone,
while the knives remain clamped to the apparatus. Referring to Figures 9A and 9B
for context, the stone (not shown) contacts the cutting edges of the knife 50 of
the center portion 47 and the cutting edges of the knives 60 of the end portions
49 at the same time, and it is highly desirable that the stone be applied to the
same thickness of metal for all cutting edges, to provide for even sharpening. However,
if the outer perimeter sections of the knives 60 extended along the lines "LT3"
and "LT4," and if the knives 60 were not perfectly aligned or oriented
with respect to the knives 50, portions of the knives 60 would project into space
adjacent to that occupied by portions of the knives 50, "doubling-up" on the amount
of metal confronted by the stone at such locations.
As another consideration, the alignment reliefs prevent
potential interference between the comer-cutting knife 60 and an adjacent face-cutting
knife. An example is shown in Figures 13A and 13B. Figure 13A shows a corner portion
(in cross-section) of an article of lumber 45c. A top face "FT" is cut
with a face-cutting planer head (not shown) such as the planer head 26, while a
side face "FS" is cut with the face-cutting center portion 47 of planer
head (also not shown) adapted for corner cutting such as the planer head 46. A corner-cutting
end-portion 49 (also not shown) of the planer head carries a knife 60 having a cutting
edge "CE." As shown, the cutting edge "CE" is a full 1/4 round and is perfectly
aligned with respect to the top face "FT;" however, this is not a practical
Turning to Figure 13B, if the knife 60 is misaligned by
any angle &thgr; that is greater than zero, the cutting edge CE will cut into the
top face "FT" regardless of whether the top face is cut before or after
the side face "FS." If the knife is misaligned in the opposite direction,
a similar interference will occur with the side face "FS."
The knives 50 and screws 54 of the center portion 47 of
the planer head 46 are preferably oriented as shown in Figure 10. The gib 62 associated
with the pocket wall 61 c defines an orientation of an axis "TAa" in
the plane of the back surface 60a (Figure 12A) of the knife 60 as installed in the
hub 58. This orientation can be specified as an angle &thgr;1a relative
to a radial line "RLa" extending through the axis of rotation "R" of
the head. The angle &thgr;1a establishes the axis "TAa."
The angle &thgr;1a is optimized to provide a desired angle of attack
for the knife and is preferably in the range of 10- 30 degrees.
A hole 65 for receiving the threaded portion of the screw
34 has an elongate axis "EAa" that makes an angle &thgr;2a
relative to the radial line "RLa." The angle &thgr;2a is
optimized to direct the clamping force against the knife. The angle &thgr;2a
is preferably in the range of 0 - 20 degrees and is determined without regard to
the angle &thgr;1a, i.e., the axes "EAa"and "TAa"
rotate together as the angle &thgr;1a is varied.
The prior art typically provided a single knife having
a straight cutting edge integrally formed with one (or two) curved cutting edges,
to cut both the side face Fs and one (or two) of the corners r of the
article of lumber 45F in Figure 8B. The novel construction of the present
invention provides a number of outstanding advantages over the prior art. For example,
to change the radius of the finished lumber, all that is required according to the
invention is to change the relatively small and inexpensive comer-cutting knives
60, while in the prior art, the entire cutting surface needed to be changed.
Moreover, the prior art planer head was adapted for a particular
knife. Turning back to Figure 10, the center and end portions according to the present
invention are preferably provided as separate units that are bolted together as
shown. Although this feature is not essential and the end portions may be manufactured
integrally, the feature provides for changing the width of the finished lumber simply
by changing out the center portion 47, while in the prior art, the entire planer
head would need to be changed.
According to another aspect of the invention, and taking
advantage of the preferred "bolt-together" construction of the planer head 46 shown
in Figure 10, the planer head can be adjusted from being adapted to cut dry lumber
to being adapted to cut green lumber, and the reverse, simply by changing the knives
60 and the end portions 49.
Figure 14A shows the outline of a representative knife
60DRY, corresponding to the configuration shown in Figure 12A, for cutting
an article of lumber of nominal size from stock that has been kiln dried. The cutting
edges CEDRY have respective radii RDRY. Shown in dotted line
is the outline of a corresponding knife 60GREEN having larger respective
radii RGREEN adapted for cutting the same article of lumber from green
Figure 14B shows an of a finished 2 X 4 70DRY
finished from dry stock, corresponding to the outline shown for the article 45F
in Figure 9B, along with the corresponding outline of a 2 X 4 70GREEN
finished from green stock shown in dotted line. The widths of the two articles differ
slightly, typically by the dimensions indicated, and the radii of the respective
corners RDRY and RGREEN differ as shown Figure 14A.
With additional reference to Figure 10, it is recognized
that to leave the outer edges OE (Figure 14A) of the knives 60 available for indexing
to the center portion 47 (particularly, the sidewall 53a) as described above, the
end portions 49 the knives 60DRY
and 60GREEN can be shifted relative to one another as shown in Figure
14C (compare with Figure 14A). Outer edges OE of both knives remain positioned to
contact the sidewall 53a (Figure 10) of the center portion 47, so that the same
center portion can be used. Outer edges OEDRY and OEGREEN
are shifted relative to one another, and this shift can be accommodated by modification
of the end portions 49.
For example, to cut 2 X 4's from dry stock, the knife 60DRY
has the position shown in Figure 14C: A cutting edge CEDRY merges or
aligns with the face side Fs of the 2 X 4; the knife 60DRY
is indexed to the sidewall 53a of the center portion 47 at the outer edge OEC
; the knife 60DRY is indexed to the bottom supporting wall 61b of the
pocket 61 of the end portion 49 (49a in Figures 9B and 10) at the outer edge OEDRY.
Similarly, to cut 2 X 4's from green stock, the knife 60GREEN has the
position shown in Figure 14C. A cutting edge CEGREEN merges or aligns
with the face side Fs of the 2 X 4, the knife 60GREEN is indexed
to the sidewall 53a at the outer edge OEC, and is indexed to the bottom
supporting wall 61b at the outer edge OEGREEN' The outer edges OEDRY
and OEGREEN are displaced an amount &Dgr; from one another that is
equal to S the difference in the widths shown in Figure 14B, and the respective
depths of the pockets 61 of end portions 49 corresponding to the two knives are
Preferably, the pockets 61 are identical for end portions
adapted for the two types of wood stock, and the depths of the pockets are adjusted
simply by changing the outer diameter "D" of the end portion (see Figure 10), though
this is not essential. In any event, to change from cutting green lumber to dry
lumber or the reverse, or to change the width of the article of lumber a small amount
for any other reason, only the knives 60 and the end portions 49 need to be changed;
the more expensive center portion 47 may be used for either purpose and therefore
may remain in the cutting apparatus.
Turning to Figure 15A, the knife 60 has a distinct configuration
that can be defined with reference to lines "BL" that bisect the cutting edges CE
of the knife. Each cutting edge CE is preferably semi-circular as described above
and, therefore, has a radius of curvature Rc that is constant. The radii of curvature
extend from respective focal points Pf that lie on the lines BL. The lines BL intersect
the cutting edges at respective points PI, and vectors extending along the lines
BL in the direction from the points PI to the points Pf diverge from another as
shown, i.e., they do not cross one another. Figure 15B provides a comparison with
a prior art knife having two curvilinear cutting edges. The same principles can
apply to distinguish knives 60 having more complex curvilinear shapes for the cutting
Figures 16A - 16C illustrate another aspect of the knife
60 according to the present invention. As seen in Figure 16A, a number of line segments
"LS" are shown on a beveled face "Fb" that includes the cutting edge CE4
shown in Figure 12B. The line segments "LS" are lines perpendicular to both an outer
peripheral contour "OCa" that defines a periphery of the front surface 60a of the
knife (not visible in Figure 16A-see Figure 12A) that includes the cutting edge
"CE4" and a corresponding, parallel outer peripheral contour "OCb" that
defines a periphery of the back surface 60b of the knife. The line segments "LS"
are therefore of minimum length for connecting the two outer contours. As the line
segments "LS" are geometric constructions rather than distinct physical features,
there are an infinite number of the line segments "LS" defining the beveled face
Figures 16B - 16D are cross-sections of the knife 60. Each
cross-section is taken in a plane perpendicular to (a) the front surface 60a, (b)
the parallel back surface 60b, and ©) the respective outer contours "OCa" and
"OCb," and includes one of the line segments "LS." Particularly, Figure 16B illustrates
the cross-section indicated in Figure 16A that includes the line segment "LS15B,"
Figure 16C illustrates the cross-section indicated in Figure 16A that includes the
line segment "LS15C," and Figure 16D illustrates the cross-section indicated
in Figure 16A that includes the line segment "LS15D."
Each of these line segments are angled, as are all of the
line segments "LS," with respect to the plane of the front side 60a of the knife,
by a substantially fixed angle &ggr; that is preferably in the range of 25 - 40
degrees. The angle &ggr; is referred to herein as an "attack relief angle" to
distinguish it from the alignment relief angle described earlier. The attack relief
angle is often referred to in the art simply as "relief."
The attack relief angle can be better understood with reference
to Figures 17A and 17B. Referring to Figure 17A, a schematic drawing of an elongate
article of lumber 45 is shown being cut or chipped by a knife 75 rotating in the
direction indicated and defining a cutting arc "Rc." The knife 75 corresponds to
the face-cutting knife 50 of the center portion 47 of the planer head 46 shown in
Figure 10. The article 45 extends along an elongate axis "BALUMBER."
An attack relief angle &ggr;L with respect to the elongate axis having
some nonzero magnitude must be provided to avoid hammering the wood with an undersurface
"US" of the knife 75. Such hammering deleteriously affects the surface finish provided
by the knife.
Figure 17B views the article of wood shown in Figure 17A
from a direction perpendicular to the axis "EALUMBER." The knife 75 is
omitted, but a comer-cutting knife 77 according to the present invention is shown.
The knife 77 has a front side 60a and two outer contours OCa and OCb as described
above. The line segment "LSL "in Figure 17B corresponds to the line segment
"LS16B" in Figure 16B and, therefore, provides an attack relief angle
&ggr; as shown in Figure 16B. Thence, attack relief in the longitudinal direction,
i.e.,. the direction of "EALUMBER." is provided by the knife 77.
An outstanding advantage of the knife 77 is that the knife
77 also provides attack relief in the transverse direction "TLUMBER."
Particularly, the line segment "LST" shown in Figure 17B corresponds
to the line segment "LS16D" in Figure 16D and, therefore, provides an
attack relief angle &ggr; as shown in Figure 16D. Moreover, according to the present
invention, the knife 77 provides an attack relief angle of &ggr; in every and
all intermediate directions. In the preferred embodiment of the invention the attack
relief angle is constant over the surface "Fb" (Figure 16A) as mentioned above;
however, this is not essential.
The curvilinear knife 77 according to the present invention
is provided independent of the corresponding face-cutting, linear knife and it is
therefore relatively easy to provide an optimally configured surface Fb. For example,
it is relatively easy to manufacture the knife 77 with a constant attack angle of
relief over the entire surface Fb. Moreover, because the curvilinear knives are
staggered with respect to the corresponding face-cutting knives so that their cutting
surfaces overlap, jointing the knives does not increase the width of the cut or
cause surface imperfections such as lines at the apparent points of joinder of the
respective cutting surfaces.
It is to be recognized that, while a particular high speed
planer head has been shown and described as preferred, other configurations and
methods could be utilized, in addition to those 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 will be appreciated that the invention includes within
its scope (and for the avoidance of all doubt the same is asserted) a wood cutting
apparatus for receiving a knife and comprising a hub axially disposed for rotation
about an axis and having therein a pocket for receiving a knife against a supporting
wall of said pocket, said hub further having therein a threaded bore, the apparatus
including a threaded member having a frustoconical ramping portion cooperative in
use with a surface of a member of the apparatus to produce a wedging force against
said knife when said threaded member is threadedly received into said threaded bore.
In embodiments of the invention concerned with the wood
cutting apparatus, it is a preferred feature that in apparatus having plural knives
at least the second (conveniently both the second and the third) should have two
or more curvilinear cutting edges and preferably four (or perhaps more) such cutting
edges, said curvilinear cutting edges being preferably concave and semi-circular
and especially in such case it being additionally preferred that the cutting edges
are spaced apart from one another with 90 degree rotational symmetry. The preferred
specific feature just mentioned is especially preferred in the context of the embodiments
referred to above wherein the second knife (or the second and third knives) have
four curvilinear cutting edges. A particular embodiment may therefore comprise second
and third knives each with four curvilinear cutting edges of concave and semi-circular
form with or without the cutting edges spaced apart from one another with 90 degree