Note: Descriptions are shown in the official language in which they were submitted.
l~"S76
This invention relates to a method of kerfless
cutting wood.
It has already been proposed in U.S. Patent No.
3,916,966, dated November 4, 1975, "Method of Xerfless
Cutting Wood", J. S. Johnston and ~. St-Laurent to reduce
the splitting ahead of a knife by compressively stressing
the wood to at least 25~ of its yield strength by applying
clamping pressure to the entire surfaces of two opposed
sides of the wood, and then cutting the wood along a path
between the opposed sides. Whilb this process has proved
to be useful, it is not attractive economically to cut long
lengths of lumber by this method of, for example, at least
eight feet (2.4 m).
U.S. Patent No. 3,494,396, dated February 10, 1970,
"Apparatus for Kerfless Cutting of Wood", E. H. Collins has
: proposed a wood cutting apparatus whereby the wood is fed
against a reciprocating knife or pair of opposed knives
while a force is exerted on the wood in a plane perpendi-
cular to the cut at a position adjacent the knife blade
1 20 leading edge to control in part the wedging and splitting
!' forces exerted on the wood by the knife blade. While this
- proposal is undoubtedly useful for cutting reasonably long
lengths of lumber, it is still possible for the wooa to
split ahead of the knife to some extent. In one embodi-
ment in the Collins patent, two opposed, V-shaped, reci- -
-~ procating knife blades are used having inclined leading
edges in the cutting direction and with this embodiment
there is a further problem in that the reciprocating knife
blades are free to deflect laterally from the cutting direc-
~ 30 tion and become misaligned.
:~ According to the present invention, there is
~ provided a method of kerfless cutting wood, comprising,
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causing relative movement between the wood, generally in
the grain direction, and a wood cutting and compressive
stressing assembly, wherein the wood cutting and compres-
sive stressing assembly:
i) progressively cuts the wood from one end by
a non-reciprocating, substantially rigid knife blade, an
intermediate portion of which enters and is totally sur-
rounded by the wood, with the knife blade forward cutting
edge inclined to the cutting direction, and
ii) progressively stresses lengthwise portions
of the wood in a compressive manner against sides of the
knife blade to at least 25% of the yield strength of the
wood, from the said one end, by compressive forces applied
only to substantially the whole lengthwise portion of the
wood through which the knife blade is passing.
Preferably the forward cutting is inclined at an
angle of at least 20, better still at least 30, to the
cutting direction.
In some embodiments of the present invention, the
~ 20: forward cutting edge is inclined rearwardly in the cutting
; direction from both ends of the cutting edge towards a cen-
tral portion thereof.
The rearward end portion of the knife blade is
preferably tapered to reduce in thickness rearwardly to
~ the cutting direction, and the rearward end portion of the
-~ knife blade is preferably either triangular in cross-
section or rounded for this purpose.
~ In some embodiments of the present invention,
`~ the knife blade is supported on both sides of the wood
to impart rigidity to the knife blade.
In the accompanying drawings which illustrate,
by way of example, embodiments of the present invention,
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Figure 1 is a perspective view of a test appara-
tus for }erfless cutting wood to investigate the effect of
different blade angles,
Figure 2 is a graph of the lateral deviation of
the cut for tes~s carried out using the apparatus shown in
Fiyure l and for various angles of inclination of the blade
cutting edge to the cutting direction,
Figure 3 is a perspective view of a different
apparatus to that shown in Figure 1,
Figure 4 is a perspective view of the cutting
blade of the apparatus shown in Figure 3,
Figure 5 is a perspective view of a different
apparatus to that shown in Figure 3, and
Figure 6 is a perspective view of yet a further
different apparatus to that shown in Figure 3.
Referring now to Figure 1, there is shown an
experimental wood cutting and compressive stressing assem-
bly, generally designated 1, comprising a non-reciprocating,
~. substantially rigid knife blade 2 which has a forward cut-
ting edge 4 that is inclined at an an~le of ~ to the cut-
. ting direction X. The knife blade 2 is mounted by spacerrods 6 to 9 in a substantially rigid and non-reciprocating
. manner between two dis~-shaped wood compressive stressing
side plates lO and 12 which have inner bevelled edges 14
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and 16 respectively.
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~ In this embodiment, a rearward end 18 of a portion ~:
of the knife blade 2 that will be totally surrounded by wood ~ -
`~ during cutting is shaped, in this embodiment by chamfers 20
and 22, to reduce in thickness rearwardly from both sides
, 30 24 and 26 respectively, of the knife blade 2.
i The wood cutting assembly l was mounted for ex-
. perimental purposes by means (not shown) whereby the side
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plates 10 and 12 could be rotated and then securely clamped
agaillst rotation and any other movement so that the angle ~
could be varied for the experiments. During the experiments,
a hydraulic ram (not shown) was used to push wood specimens,
such as wood specimen 28 progressively between the side ~ ;
plates 10 and 12 in the direction of arrow X until the wood
was cut so that the side plates progressively stressed
lengthwise portions of the wood in a compressive manner
against sides of the knife blade to at least 25~ of the
yield strength of the wood.
I~ actual tests, 48 mm square x 45 cm long spe-
cimens of saturated white spruce were used. From the pub-
lished yield strength of saturated white spruce, it was
determined that a gap between the side plates 10 and 12
of 46 mm would compress the sample therebetween to within
at least 25% of the yield strength of the wood.
Figure 2 is a graph of average results of the
tests of a number of such saturated spruce wood samples
using the apparatus shown in Figure 1 and using diferent
angles of the knife blade 2.
In Figure 2, the average lateral deviation "D mm"
of the cut from a straight line is plotted against the
angle "a"-that forward cutting edge of the knife blade is
inclined to the cutting direction X. The values, O are
for knife blades cutting radially and ~ for knife blades
cutting tangentially with respect to the wood annual rings
It will be seen from Figure 2 that an angle a of
at least 20 is preferred, better still at least 30, be-
cause lower average lateral deviation D mm occurs in these
3Q ranges.
Similar tests were carried out with similar satu--
rated white spruce samples but planed down to 47 mm and 47.5 mm
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s~uare, which were also compressed to within at least 25%
of the yield streng-th of the wood in a 46 mm gap between
the side plates 10 and 12 and these tests gave similar re-
sults to those shown in Figure 2.
Thus the present invention provides a method of
kerfless cutting wood 28 ~Figure 1), comprising, causing
relative movement between the wood 28, generally in the
grain direction which is direction X and a wood cutting and
~ compressive stressing assembly 1, wherein the wood cutting
- 10 and compressive stressing assembly:
i) progressively cuts the wood 28 from one end 30
by a non-reciprocating, substantially rigid knife blade 2,
an intermediate portion of which enters and is totally sur-
:' rounded by the wood, with the knife blade forward cutting .-
edge 4 inclined to the cutting direction X, and
ii) progressively stresses lengthwise portions
of the wood in a compressive manner against sides of the
knife blade 2 to at least 25% of the yield strength of the i-wood 28, from the said one end 30, by compressive forces
~, 20 applied, by the side plates 10 and 12~ only to 5ubstantialLy
. the whole lengthwise portion of the wood 28 through w~ich ~ :
the knife blade 2 is passing.
The present invention controls the direction of - -
" the cut by preventing splitting occurring in the wood 28 :~
ahead of the leading cutting edge 4 of the knife blade 2
by compressing the wood 28 sufficiently against the whole -
~i side of the knife blade 2 so that splaying of the wood 28
:. does not occur behind the rearward end 18, which can stress
the wood 28 sufficiently to influence the direction of the
cut and can cause the cut wood portions to assume permanent
curvatures in the splaying directions.
The shaping of the rearward end portion 18 to
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reduce in thickness from both sides 24 and 26 of the knife
blade 2 also assis~s in avoiding stressing the wood 28
sufficiently to reduce damage to the wood after cutting
because the wood 28 is not stressed by being pressed against
a sharp corner as it leaves the sides 24 and 26 of the knife .
blade 2.
In Figures 3 and 4 there is shown a wood cutting
and compressiv~ stressing assembly 32 mounted on a bed 34
together with a hydraulic ram assembly 36.
The wood cutting and compressive stressing assem-
bly 32 comprises a knife blade 38, mounted by pivots 40 and
42 between the bed 34 and a U-shaped bracket 44, and side
. plates 46 and 48.
i
The knife blade 38 has a forward cutting edge 50
which is inclined rearwardly in the cutting direction X
(Figure 4) from both ends 52 and 54 of the cutting edge 50
i~ towards a central portion 56 thereof. A rearward end por-
.. tion 58 of the knife blade 38 is rounded on both sides of
;, the knife blade 38.
;! 20 The side plates 46 and 48 are bevelled at both
ends and are of an appropriate thickness to progressively
stress lengthwise portions of a wood specimen 60 to at
least 25% of the yield strength. -
In operation, the wood specimen 60 is placed on
the bed 34 and is pushed by the hydraulic ram assembly 36
hetween the side plates 46 and 48 as shown in Figure 3 to
be cut by the knife blade 38 in a similar manner to that
described with reference to Figure 1.
Tests have shown that the knife blade 38 having
a forward cutting edge 50 which is inclined in the,cutting
direction X (Figure 4) from both ends 52 and 54 is better
` than a knife blade having a cutting edge as shown in
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Figure 1 because the cutting edge of the '~ni~e blade shown
in Figure 1 is twice as long and so more flexible. Further-
more, the cutting edge 50 (Figure 4), being inclined in the
cutting direction X from both ends 52 and 54, causes the
vertical components of the reaction to the cutting force -~
to counter one another and tension the knife blade 38
thereby imparting rigidity to it.
In Figures 5 and 6, similar parts to those shown
in Figures 3 and 4 are designated by the same reference nu-
merals and the previous description is relied upon to des-
cribe them.
In Figures 5 and 6, cutting knives 38 are mounted
on a base 62 by members, one of which is shown and desig-
i
nated 64, and pivots 40. Axles 66 and 68 have tires 70
and 72 respectively pivotally mounted thereon. The tires
70 and 72 are preferably pressurized by a fluid but may be
solid or foam filled. The spacing between the tires 70 and
.
72 is chosen, together with the prsssure applied thereby,
to compress a wood specimen 74 in the same manner as th~
side plates of the previous embodiments. ~;
In Figure 5, the wood specimen 74 is pushed by
,~ a hydraulic ram assembly tnot shown) between guide rolls
76 to 79 and then between the tires 70 and 72 to be cut
into three parts by the knife blades 38 in the same man-
ner as that described with reference to Figures 3 and 4.
If desired, one or more of the tires 70 and 72
and/or guide rolls 76 to 79 may be driven to draw the wood
specimen 74 therebetween instead of the wood specimen 74
being pushed by a hydraulic ram assembly.
In Figure 6, a wood specimen 80 is placed on a
, chain guide 82 and the wood specimen 80 is moved between
`1 the tires 70 and 72 by a chain 84 passing around sprockets
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86 and 88, one of which is driven by means not shown, and
along the chain guide 82. In this manner the wood specimen
80 is moved between the tires 70 and 72 for the wood spe-
cimen 80 to be cut by the knife blades 38 in the same
manner as that described with reference to Figure 5.
The present invention is particularly useful for
kerfless cutting wood substantially in the "green" condition.
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