Note: Descriptions are shown in the official language in which they were submitted.
7~ 3(i~ UI ~
ROTARY CUTTING TOOLS FOR WORKING OF WOODS OR WOOD-
BASED COMPOSITE MATERIALS
TECHNICAL FIELD
The present invention relates to rotary cutting tools
for working of woods or wood-based composite materials,
that is, a tipped saw for cutting, a drill, a finger
cutter-, and a molding cutter.
BACKGROUND ART
In recent years, making best use of woods has become
a large task from the viewpoint of protection of forests.
In particular, a lamination industry wherein small-diameter
materials, short-length materials, cut-off materials and
the like are laminated to form larger boards and materials
having a larger section has become played a more and more
important role in accomplishing the above task. In a
finger cutter which is a tool used in the production of a
laminated wood and functions to provide a finger-like joint
in the end in the longitudinal direction of the wood, the
formed joints should be always exactly fitted for attaining
the contemplated purposes. For this reason, the shape of
the finger should remain unchanged even upon re-grinding
of this tool, in order to maintain the fitting accuracy in
the joint.
This will be explained with reference to accompanying
drawings. A finger cutter is formed in such a manner that
the section thereof as viewed from a flank 5 of a
peripheral cutting edge 6 (Fig. la) having a clearance
angle ~z of a cemented carbide tip 2 brazed to a tip seat
of an edge body formed in a conformal position on a
circumference of a base metal 1 has an identical thickness
(Fig. ld). The oblique angle ~3 ( Fig. lb) is 3 to 10 ,
and the clearance angle ~2 in the flank 5 of the peripheral
cutting edge is 15 to 25 . From this relationship, the
clearance angle ~1(Fig. le) in the side cutting edge in
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the direction of rotation in a flank 4 of a side cutting
edge 7 (Fig. lc) is geometrically 5 or less. That is, the
flank 4 of the side cutting edge has a small angle.
Further, since the edge thickness of the edge section (Fig.
ld) as viewed from the flank of the peripheral cutting edge
is identical, it is apparent that, in re-grinding of the
tool, grinding of a front face 3 (Fig. la) alone suffices
for maintaining the working shape accuracy.
A tipped saw is used in various types of working
ranging from sawing of logs to secondary cutting of wood-
based boards. In this tipped saw, the edge thickness which
determines the groove width should be reduced in order to
improve the yield of the product and to reduce the cutting
power, and the thickness of the base metal body should be
as thick as possible in order to enhance the rigidity of
the saw. The upper limit of clearance angle of the side
cutting edge in the tipped saw, i.e., clearance angle in
the direction of rotation of the side cutting edge, is
generally about 5. The re-grinding of the tool is carried
out for either the rake or the flank of the peripheral
cutting edge or both the rake and the flank.
These two tools, finger cutters and tipped saws, are
representative tools having a small clearance angle in the
side cutting edge. Other cutters include a flooring cutter
for working a male tongue and a female tongue for joining
wood-based flooring materials in the longitudinal or
widthwise direction, a round bar cutter for working the
reverse and front surfaces of a plate material into a
semicircular form to form a round bar, and a moulding
cutter which mainly performs design working and cuts
various shapes including R face. For all the above tools,
since the rake is re-ground before use, a large clearance
angle cannot be provided in the side cutting edge from the
viewpoint of maintaining the accuracy of a shape created
by working. For this reason, the clearance angle of the
side cutting edge is generally about 5 .
~ ~1723~
Further, in the case of a drill for deep hole drilling
of a wood, particularly a drill for working horizontal
members and horizontal braces for use in wooden framework
houses, for example, a deep hole having a diameter of 15
mm and a depth of not less than 200 mm is created by
drilling. Therefore, direct advance of the drill is
important. In general, the side, i.e., peripheral face,
of the edge nose in the drill is formed in a completely
circular form having a clearance angle in the direction of
rotation of O or up to 5 . For a wood working drill, the
number of revolutions is generally 1000 to 5000 rpm which
is 10 to 100 times larger than that for steel working,
which is likely to cause resonance. The clearance angle
in the side of the edge nose should be small also from the
viewpoint of preventing this reproduced chatter vibration.
In a finger cutter, an accurate shape should be stably
created by working. Therefore, care consideration should
be given to the sharpness and the accuracy of the shape
created by the working. For this reason, the cutter should
be replaced after use for a short period of time, resulting
in short service life of the cutter. This adversely
affects the productivity in a mill for the production of
laminated materials. The moulding cutter also has a
drawback that the sharpness is rapidly deteriorated in a
portion having a small clearance angle in the side cutting
edge.
In order to solve the above problems and to keep the
edge nose sharp, the applicant has already proposed the
provision of a CrN covering on the flank of a side cutting
edge in a cutter with the clearance angle in the side
cutting edge being small (Japanese Patent Laid-Open No.
252501/1990). The effect attained by this proposed
technique is merely twice that where no covering is
provided, and the covering effect cannot be sufficiently
utilized, resulting in no satisfactory results.
On the other hand, for the tipped saw, reducing the
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saw thickness is an important task to be accomplished in
order to reduce the amount of saw dust produced to thereby
improve the yield of the wood. In addition, elimination
of unstable cutting derived from the reduced saw thickness
and, at the same time, prolongation of the service life are
also an important task to be accomplished. Further, the
long drill for deep hole drilling has problems of increased
cutting resistance and frequent breakage caused by oblique
advance.
"Deposition of gum" is known to be deeply involved in
the problems common to the above rotary cutting tools for
cutting of woods, such as finger cutter, moulding cutter,
tipped saw, and drill for deep hole drilling.
Specifically, when a wood or a wood-based composite
material is cut by rotary cutting, components of the wood
scattered from the cutting portion are deposited,
solidified, and accumulated on each face of the edge. This
phenomenon is usually called "deposition of gum." The
deposition of gum is observed also in tools wherein the
cutting edge is made of a cemented carbide, a tool steel,
or other high-strength materials. Fundamentally, the
deposition of gum is regardless of the sharpness of the
edge and occurs even when the edge is fresh. When the
material to be cut is of certain type, the finger cutter
and the tipped saw often become unusable in spite of no
significant abrasion of the edge. In this case, simple
removal of the gum makes it possible to continuously use
the cutter and the saw.
The gum is not in merely deposited and accumulated
state but in a densely solidified state and is considered
to be formed by hardening through polymerization of
components of the wood. The gum is strongly deposited on
the surface of the edge tool and can hardly be wiped off
by mechanical means.
At the present time, in order to remove the gum, the
tool is immersed in an alkaline solution or a commercial
~ 172365
detergent and carefully wiped off. This is a troublesome
work requiring a lot of time. Further, the deposition of
the gum re~uires frequent replacement of the tool and the
like, lowering the productivity.
Reducing the surface roughness as much as possible,
i.e., smoothing the surface, has hitherto been regarded as
effective in lowering the coefficient of friction by direct
contact between the edge and the wood to thereby solve the
problem associated with the gum. This method, however, has
no effect of preventing the scattered gum from being
deposited. Further, covering of a fluororesin (PTFE) which
has a low coefficient of friction and is less likely to
cause the deposition of gum is also known in the art. In
this case, however, the thickness of the PTFE covering
should be as large as several tens of,um to several hundred
of ~um, and the abrasion resistance of the covering is so
low that the covering in its portion very near the edge
which is strongly abutted against the material to be cut
is easily abraded. The remaining covering adversely
affects and renders the clearance of the side cutting edge
unsatisfactory. This results in increased lateral pressure
and consequently deteriorated sharpness, making it
impossible to attain the contemplated purpose.
The gum is deposited also on the rake. Since,
however, only chips having low rigidity are passed through
the rake, any adverse effect such as increase in cutting
resistance is not observed. The gum which raise a problem
is one deposited on the flank in the side cutting edge.
When the clearance angle of the side cutting edge is so
large that the clearance is satisfactory, most of the gum
scattered from the cutting portion is scattered in the air
and, hence, the deposited gum, if any, has no significant
influence on the cutting. On the other hand, when the
clearance angle in the side cutting edge is so small that
clearance is unsatisfactory, the scattered gum is deposited
and accumulated on the flank or base metal portion somewhat
` ~172~
away from the edge. The progress of the accumulation
causes the gum to be thickly spread to the vicinity of the
edge, creating friction between the accumulated gum and the
cut surface of the material to be cut. This results in
increased cutting resistance and scorch of the cut surface.
Further, in some cases, abnormal heat generation occurs in
the edge portion and the base metal, resulting in abnormal
abrasion or breaking of the edge, deformation of the base
metal and the like.
In the case of the finger cutter, since the material
is worked into a narrow and long finger form, the finger
undergoes side pressure and, consequently, is deflected,
making is impossible to carry out cutting into a
contemplated exact shape. Also in the case of working by
means of the moulding cutter, the cut surface temperature
is raised due to friction, causing scorch or burning. This
results in increased cutting resistance.
In the case of the tipped saw, the side pressure of
the saw edge becomes so large that vibration or deflection
of the saw body or an increase in cutting resistance
occurs. Also in the case of the drill for deep hole
drilling, the deposition of gum on the side face of the
edge causes an increase in side pressure and, consequently,
oblique advance even in the case of a sharp edge, making
the drill unusable. In all the above cases, it becomes
impossible to carry out cutting before the tools become
unusable due to the service life of the tools derived from
the abrasion of the edge. Further, the deposition of gum
on the base metal makes it impossible to accurately conduct
re-grinding.
The present inventors have repeated various
experiments and studies on the prevention of deposition of
the gum rather than on the removal of deposited gum. As
a result, they have found that the regulation of the
roughness of the flank in the side cutting edge followed
by covering of the flank having a regulated roughness with
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chromium or a chromium-based material enables the
deposition of gum to be reduced to such an extent as will
pose no problem for practical use.
An object of the present invention is to provide,
based on the above studies, a rotary cutting tool, for a
wood or wood-based composite material, which is less likely
to cause the deposition of gum and has a small clearance
angle in the direction of rotation.
DISCLOSURE OF INVENTION
The rotary cutting tool for working of a wood or a
wood-based composite material according to the present
invention is characterized in that it comprises a
peripheral cutting edge and a side cutting edge formed
separately from or continuously with each other, the
surface roughness Rmax is 1 to 10 ~m at least for the flank
of the side cutting edge and the outermost surface of the
flank of the side cutting edge is covered with at least one
member selected from chromium and a nitride, a carbide, and
a carbonitride of chromium.
The expression "separately from each other" used
herein refers to such a state that, like a finger cutter,
the peripheral cutting edge and the side cutting edge are
provided so as to be clearly distinguishable from each
other. On the other hand, the expression "formed
continuously with each other" used herein refers to such
a state that the peripheral cutting edge and the side
cutting edge are provided so as to be in smooth range with
and indistinguishable from each other.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. la is a side view of a finger cutter, comprising
a combination of a plurality of fingers, for forming a
finger joint, Fig. lb is a front view of an edge, Fig. lc
is a plan view of an edge, Fig. ld is a cross-sectional
view taken on line A-A of Fig. la, and Fig. le is a cross-
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sectional view taken on line B-B of Fig. la;
Fig. 2a is a front view illustrating a cutting test
method, and Fig. 2b is a side view illustrating the cutting
test method;
Fig. 3a is a diagram showing the direction of
grinding, of a flank of a side cutting edge, with a
straight grinding wheel, and Fig. 3b is a diagram showing
the direction of grinding using a straight cup grinding
wheel;
Figs. 4a to 4e are diagrams showing the results of
evaluation on the deposition of gum on the flank in a side
cutting edge in a cutting test, wherein the evaluation
grade is F for Fig. 4a, E for Fig. 4b, ~ for Fig. 4c, C for
Fig. 4d, and B for Fig. 4e;
Fig. 5 is a diagram showing the relationship between
the direction of grinding and the surface roughness
influencing the evaluation on the deposition of gum in a
cutting test;
Fig. 6 is a diagram showing the relationship between
the surface roughness Rmax of the flank in a side cutting
edge and the deposition of gum;
Fig. 7 is a diagram showing the relationship between
the direction of grinding of the flank in a side cutting
edge and the deposition of gum;
Fig. 8a is a side view of a spare edge of a finger
cutter, Fig. 8b is a front view of the spare edge, and Fig.
8c is a plan view of the spare edge;
Fig. 9 is a diagram showing the deposition of gum in
the cutting of a wood with the finger cutter shown in Fig.
8;
Fig. 10 is a diagram showing a tipped saw;
Fig. lla is a side view of a spare edge of a finger
cutter with a diamond film, synthesized in a gas phase,
laminated on a front face of the spare edge, and Fig. llb
is a plan view of the spare edge shown in Fig. lla;
Fig. 12a is a side view of a spare edge of a finger
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cutter with a polycrystalline diamond sinter bonded to a
front face of the spare edge, and Fig. 12b is a plan view
of the spare edge shown in Fig. 12a;
Fig. 13 is a diagram showing a drill for deep hole
drilling; and
Fig. 14a is a side view of a moulding cutter, Fig. 14b
is a front view of the moulding cutter, Fig. 14c is a plan
view of the moulding cutter, and Fig. 14d is a rear view
of a spare edge.
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention will now be described in more
detail with reference to the following examples.
Example l
Finger cutters which have a small clearance angle in
a side cutting edge and are likely to cause deposition of
gum were tested for deposition of gum with varied materials
for a spare edge, conditions for finishing of a side
cutting edge, surface roughness, covering layer and the
like. Testing methods, test results, and evaluation will
be described.
(1) Cutters under test
Various clamp type spare edges provided with a finger
having a size of 4 mm in width x 0.6 mm in point width x
7 in oblique angle and having a spare edge length of 11.4
mm were prepared and mounted on a rotary block to provide
cutters under test.
Conditions common to the cutters were edge nose circle
diameter~ 160 mm, rake angle 20 , clearance angle in
peripheral cutting edge 25 , clearance angle in nose of
peripheral cutting edge 10 , and clearance angle in side
cut-ting edge (inclined face cutting section) 3.6 .
As shown in Fig. 2a, in a spare edge 13 for a finger
cutter for practical use, two to four edges are disposed
in the periphery of a body of the tool 12. In the present
test, however, only one edge was used for convenience.
~7~3~
(2) Material for spare edge and covering
As shown in Table 1, high-speed tool steel SKH51
(hardness: HRC63) and cemented carbide K30 were used as the
material for the spare edge. The flank in the side cutting
edge was finished under various conditions, and a covering
was applied thereon by physical vapor deposition (PVD) or
hard chromium plating (Cr plating). For comparison, a
spare edge without any covering was also tested. For
samples Nos. 4 and 10, "surace Cr/CrN" represents that a
0.4 ~m-thick Cr was covered on a 2.3 ,um-thick CrN covering.
(3) Finishing of side cutting edge
The side cutting edge was finished by using abrasive
materials, such as CBN (borazon), WA (white alundum), and
~C (green carborundom). Regarding grinding methods, a cup
grinding wheel and a straight (flat) grinding wheel was
used. The grinding methods used are given in Table 1. The
grinding direction is defined by ~0 as shown in Fig. 3a.
In the grinding using a cup grinding wheel, a streak
created by the grinding is in a circular arc form.
Therefore, the grinding direction was expressed in terms
of the average value as shown in Fig. 3b. "Without zero
grinding" or sample N0. 26 represents that grinding was
carried out without spark out. For the other samples,
spark out was carried out. The term "spark out" used
herein is intended to mean that, at the time of completion
of infeed, grinding is continued for a while with the
infeed of the grinding sheet being zero to carry out
grinding by a clearance created by the deflection of a
workpiece or the like. Grinding derived from the recovery
from the deflection creates sparks for a while and is
terminated when the sparks are no longer observed.
(4) Surface roughness
Surface roughness Rmax was measured according to JIS
B0601. Surfcom 470A manufactured by Tokyo Seimitsu Co.,
Ltd. was used as equipment for measuring the surface
roughness.
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(5) Cutting method
As shown in Fig. 2a, cutting of one side of a cut end
lla of a wood 11 was carried out with a spare edge 13 of
a finger cutter under conditions of 0.3 mm per pass and
depth of cut 11.4 mm. A force dried material of a rubber
tree was used as a material to be cut, and cutting
conditions were number of revolutions o~ main spindle N =
3600 rpm and feed rate F = 2.5 m/min.
(6) Evaluation method
Cutting was carried out using each spare edge under
test until the cutting distance reached 700 m, and the
deposition of gum was observed by visual inspection, and
the results were reduced to the following six alphabetical
grades.
F: The whole spare edge was thickly covered with brown
gum, and deep brown gum was deposited particularly on a
portion near the edge nose (Fig. 4a).
E: Brown gum was thickly deposited on the whole spare
edge (Fig. 4b).
D: Brown gum was largely spread and deposited on the
spare edge (Fig. 4c).
C: Somewhat brownish gum was thinly deposited on the
spare edge (Fig. 4d).
B: Slightly clear gum was discontinuously deposited on
the spare edge (Fig. 4e).
A: No deposition of gum was observed.
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12
Table 1
Mate- Surface
Sam- rial Finishing of side cutting edge rough- Covering layer
p]efor ness Evalu-
No.SpareAbrasive GrainGrinding GrindingRmax ThiCkness ation Inv
edgematerial sizemethod directionGum)Material Cum)
SKH51 CBN #230 Cup +5 0.30 None - ~
2 Ditto Ditto DittoDitto Ditto Ditto CrN 2.3 D
3 Ditto Ditto DittoDitto Ditto Ditto Hard Cr 2.5 D
plating
4 Ditto Ditto DittoDitto Ditto Ditto Surface 0.4/2.3 D
Cr/CrN
5 Ditto Ditto DittoDitto Ditto Ditto TiN 2.9 E
6 Ditto Ditto DittoDitto Ditto Ditto TiC 2.7 E
7 SKH51 CBN #140Straight +25 5.12 None - E
8 Ditto Ditto DittoDitto Ditto Ditto CrN 2.3 A
9 Ditto Ditto DittoDitto Ditto Ditto Hard Cr 2.5 B
p]ating
10Ditto Ditto DittoDitto Ditto Ditto Surface 0.4/2.3 B
Cr/CrN
11Ditto Ditto DittoDitto Ditto Ditto TiN 2.9 D
12Ditto Ditto DittoDitto Ditto Ditto TiC 2.7 D
13SKH51 CBN #600Straight +25 1.52 CrN 0.6 B
14Ditto Ditto #230Ditto Ditto 3.09 Ditto Ditto A
15Ditto Ditto #140 Cup +45 2.90 Ditto Ditto B
16Ditto Ditto DittoDitto -20 Ditto Ditto Ditto A
17Ditto Ditto DittoStraight +25 5.12 Ditto Ditto A
18Ditto Ditto DittoDitto +50 Ditto Ditto Ditto B
19Ditto Ditto DittoDitto -50 Ditto Ditto Ditto B
20Ditto Ditto DittoDitto -65 Ditto Ditto Ditto C
21Ditto Ditto DittoDitto ~ 90 Ditto Ditto Ditto C
22Ditto WA #60Ditto +25 8.2 Ditto Ditto B
23Ditto Ditto DittoDitto Ditto 17.5 Ditto Ditto D
Ce-
ment-
24 ed Diamond #500 Cup +5 0.30 CrN 2.3 D
car-
bide
25Ditto Ditto #120Ditto Ditto 0.80 Ditto Ditto C
26Ditto Ditto Ditto (without zero grining)1.98 Ditto Ditto B
27Ditto Ditto #500Cup +5 0.30 None - F
28Ditto Ditto #120Ditto Ditto 0.80 None - E
29SKH51 GC #80Shot blast 5.45 CrN 2.1 B
30Ditto WA #60Ditto 7.42 Ditto Ditto B
31Ditto Ditto #46Ditto 10.42 Ditto Ditto C
~ ~1723~
13
Then, test results on sample Nos. 1 to 31 will now be
discussed.
For sample Nos. 1 to 12, SKH51 was used as the
material for the spare edge, the covering was formed with
varied covering material and thickness, and Rmax was 0.30
lum and 5.12 ~m. The test results reveal that (1) covering
has no effect when Rmax is small, (2) when Rmax is large,
gum is less likely to deposit, (3) ~ combination of hard
chromium plating or Cr and CrN by PVD with Rmax offers a
large effect of preventing the deposition of gum, and (4)
although TiN and TiC are somewhat effective, the effect
thereof is not satisfactory for practical use.
For sample Nos. 13 to 23, the grinding of SKH51 was
carried out by means of various grinding wheels with varied
Rmax and grinding direction, and CrN was relatively thinly
covered. Test results reveal that (1) the CrN covering is
effective even when the thickness is small and (2) gum is
less likely to deposit independently of the grinding
direction when Rmax is in the range o 1 to 10 ,um.
For sample No. 23, gum began to deposit in
irregularities of the surface, and the gum deposition was
then spread.
For sample Nos. 24 to 28, Rmax of the cemented carbide
was varied. Test results reveal that the relationship
between the effect of surface roughness and the effect of
covering was the same as that in the case of SKH51.
Specifically, it was found that a surface roughness Rmax
of 0.3 lum gave rise to gum deposition and had no
satisfactory effect.
For sample Nos. 29 to 31, nonoriented surface
roughness was adopted. The material was ground in the same
manner as described in connection with the spare edge of
sample Nos. 1 to 6, shot-blasted to increase the surface
roughness, and covered with CrN. Test results reveal that
blasting offers the effect of surface roughness as in
grinding.
- = ~
~7~3~
14
Fig. 5 shows the relationship, based on the test
results on CrN covering given in Table 1, between the
grinding direction and surface roughness Rmax influencing
the evaluation. ~, 0, and ~ (corresponding to
evaluations A, B, and C) were evaluated as effective.
Further, ~ and 0 were evaluated as favorable. From Fig.
5, it was judged that when Rmax is in the range of from 1
to lO,um, satisfactory effect can be attained independently
of the grinding direction and that the surface roughness
Rmax 1.5 to 8.2 ~m and grinding direction -50 to +50
(including nonoriented grinding) are preferred.
Fig. 6 shows the relationship between the surface
roughness Rmax and the deposition of gum in grinding
direction -25 to +25 (including nonoriented grinding).
Fig. 7 shows the relationship between the grinding
direction and the deposition of gum in the surface
roughness Rmax 2.9 to 5.2 ,um.
Regarding the roughness of the ground surface, the
recognition in the art was such that the surface roughness
of both two faces constituting the edge nose, that is, the
rake and the flank, is preferably as small as possible.
Regarding the side cutting edge of a finger cutter,
integrated by brazing, commonly used in the art, the edge
is subjected to rough grinding under conditions for sample
No. 25 and then finished under conditions for sample No.
24. Specifically, the material is ground with diamond ~120
grinding stone to a contemplated dimension, zero grinding
is carried out in this state until no spark is observed,
thereby lowering the surface roughness. Then, further
grinding is carried out with a #500 grinding wheel to
further lower the surface roughness. For sample No. 26,
the zero grinding was not carried out in the grinding
operation.
In cutters ranging from general cutters for domestic
use to cutters for industrial use, general recognition is
such that, as the smoothness of the ground surface
~ 21723~
increases and is closer to a specular surface, the
slipperiness improves and the sharpness of the edge nose
increases. Such finishing is commonly used also from the
viewpoint of commercial values including good appearance.
The present invention is contrary to the above conventional
common knowledge, and the present inventors have found that
proper regulation of the ground surface roughness by taking
advantage of the effect attained by a combination of the
grinding with a chromium or chromium nitride covering
enables the deposition of gum in rotary cutting of a wood
and a wood-based composite material to be prevented and,
in particular, the service life of a cutter with a flank
having a small clearance angle to be prolonged.
E~ample 2
The present inventors have already proposed the use of
an edge replacement type finger cutter for finger working
which has hitherto been carried out with a cemented
carbide-brazed cutter (Japanese Patent Laid-Open No.
122104/1994). In this example, a practical test on the
deposition o gum was carried out using the edge
replacement type finger cutter as a material under test.
The shape of a spare edge 13 used in the pract1cal
test was as shown in Fig. 8a. A clearance angle of 10 in
the nose of peripheral cutting edge was provided to
increase the point edge angle of the peripheral cutting
edge to 60 , thereby increasing the strength and enhancing
the shape retention of the point of the finger. As shown
in Fig. 9, the flank 4 in the side cutting edge of the
spare edge 13 mounted on a tool body 12 was finished under
conditions of sample Nos. 7 to 12 specified in Table 1.
The flank of the peripheral cutting edge was finally
finished under conditions of Sample Nos. 1 to 6 and covered
with CrN in a thickness of 3 ,um by PVD. Thereafter, the
rake 3 was ground to remove the covering in the rake to
prepare a spare edge sample.
Test conditions and test results were as follows.
~ ~1723~6
16
(1) Specifications of cutter
The edge was nose circle diameter~ 210 mm x 4.0 mm in
thickness x 4 in number of edges, the shape of the finger
was 4 mm in width x 0.6 mm in point width x 7 in oblique
angle x 11.4 mm in length. The edge angle was rake angle
20 , clearance angle in peripheral cutting edge 25 ,
clearance angle in nose of peripheral cutting angle 10 ,
and clearance angle in side cutting edge 3.6~ .
(2) Test conditions
The test sample was mounted on one axis among two axes
of finger cutter axes in a horizontal finger working
machine, and the conventional cemented carbide-brazed
cutter was mounted on the other one axis to compare the
durability of the two samples. In the horizontal finger
wor~ing, the number of cutters laminated varies depending
upon the thickness of the material to be cut. In the
present test, the minimum number of cutters and the maximum
number of cutters were 7 and 10, respectively.
(3) Cutting conditions
Rubber wood and beech wood were used as materials to
be cut, and cutting was carried out under conditions of
number of revolutions of main spindle 3400 rpm and material
feed rate 12 m/min.
(4) Test results
The service life of the conventional cemented carbide-
brazed cutter was 3 days on average due to increased
cutting noise, fitting failure of the finger and the like,
and the cutter was replaced for each 3 days for this
reason. Observation o the cutter replaced due to the
service life revealed that gum was thickly and widely
deposited on the side of the cemented carbide tip and
widely deposited also on the tool body.
By contrast, observation of the spare edge 13 having
a CrN covering after continuous use for 46 clear days
revealed that gum was thinly deposited on the flank 4 in
the side cutting edge in its portion in contact with the
t
~ ~7236~
tool body 12. Further, no cutting problem occurred. As
shown in Fig. 9, however, a large amount of gum was
deposited on a protrusion 12a of tapered cross section
having no covering, formed in a circumference form from the
rear of a groove for fitting of a spare edge in the tool
body 12. Further, the deposition of gum was observed also
on the peripheral flank. The deposition of gum on these
portions raised no cutting problems.
From the above test results, it was confirmed that the
service life of the tool according to the present invention
was about 15 times longer than that of the conventional
cemented carbide-brazed cutter.
It was found that, by virtue of the prolongation of
the tool according to the present invention, marked
shortening of the time taken for replacement of cutter and
adjustment accompanying the replacement, that is, the
period of suspension of working line, can be realized
resulting in significantly improved productivity in
laminated wood production line. The deposition of gum on
the spare edge and the tool body was as shown in Fig. 9.
The above effect lowers the running cost of the spare
edge, enabling the spare edge to be disposed after use,
that is, thrown away and, hence, can improve the
troublesome control of the cutters. In this connection,
it should be noted that the prevention of the deposition
of gum on the tool body is preferred because the tool body
is used repeatedly. In this case as well, the deposition
of gum can be prevented by a combination of the regulation
of the surface roughness of the protrusion 12a with the
covering of chromium or a nitride, carbide, or carbonitride
of chromium by PVD.
For hard chromium plating, homogeneous
electrodeposition is difficult, and focus of overcurrent
on a sharp edge or a protrusion occurs, which is likely to
cause the creation of the so-called "scorch plating" or
"spitting." Therefore, in the case of the edge replacement
~723~
18
type finger cutter, this plating raises a problem
associated with the precision of the groove for fitting a
spare edge and a problem associated with dimensional
accuracy in the lamination of the tool body. In order to
prevent these unfavorable phenomena, it is necessary to
dispose auxiliary negative electrodes in a complicated
manner in the plating, to minutely regulate the shape of
the tool body, to use masking, or to use other means.
These methods are unsuitable for practical use. On the
other hand, PVD has no fear of heterogeneous coating
(covering) and, hence, is suitable for use in the
prevention of the deposition of gum on the body of the
finger cutter.
Further, in order to improve the resistance to
abrasion against materials to be cut, such as laminated
wood containing an adhesive, it is also possible to cover
the internal layer with TiN with the upper layer, that is,
the outermost surface, being covered with chromium or a
nitride, carbide, or carbonitride of chromium. This
technique can be applied to all rotary cutting tools.
Example 3
A base metal surface is ground with a proper grinding
wheel so that the streak created by the grinding is -50
to +50 to the direction of rotation. Thereafter, a tip
seat is prepared by cutting, and, as shown in Fig. 10, a
cemented carbide tip 20 is brazed. Then, a side 21 of the
cemented carbide tip was ground to a surface roughness Rmax
of 1 to 10 ~um so that a streak created by the grinding is -
50 to +50 to the direction of rotation. The ground
surface is then covered with chromium or a nitride,
carbide, or carbonitride of chromium by PVD. After
brazing, the deposition of silver as a brazing filler metal
around the tip or the formation of an oxide film generally
occurs. For this reason, the bond strength of the covering
is ensured by regulating the surface roughness of the
silver braze or removing the oxide film. For this purpose,
~ ~23~
19
this portion can be shot-blasted after brazing. In this
case as well, the blasting conditions are regulated so that
the surface roughness Rmax is brought to 1 to 10 ,um.
After covering, a rake 22 and a peripheral flank 23 in
the cemented carbide tip is finished by grinding. The
covering may have a multi-layer structure, and chromium or
a nitride, carbide, or carbonitride of chromium is covered
on at least the outermost surface. The thickness of the
covering may vary depending upon the material to be cut.
For example, a covering thickness of 0.1 to 0.3 ~m suffices
for cutting of general woods, and a covering thickness of
3 to lO ~m is used for cutting of wood-based boards which
have strong abrasive action. In this case, the bond
strength between the covering and the cemented carbide tip
is unsatisfactory in the case of hard chromium plating,
making it necessary to form the covering by PVD.
Example 4
A polycrystalline diamond sinter comprising a cemented
carbide alloy as a substrate and a polycrystalline diamond
laminated and sintered thereon has been used as a tool
material having a very long service life. In recent years,
a gas phase synthesized diamond film formed by chemical
vapor deposition has also been used as a tool material.
The present invention can be provided by utilizing these
diamond materials in a tipped saw to prolong the service
life.
Specifically, in the tipped saw described in Example
3, a polycrystalline diamond sinter or gas phase
synthesized diamond film having a thickness of not more
than 0.5 mm is laminated on the surface of a rake 22 of a
cemented carbide tip to from an edge nose. In this case,
since the diamond layer is electrically insulated, the
diamond layer cannot be covered with chromium or a nitride,
carbide, or carbonitride of chromium by PVD wherein the
bond strength is ensured by the application of a negative
voltage.
,
~17236~
Since, however, gum is not deposited in a region which
comes into strong contact with the material to be cut
during cutting, that is, in a region of 0.5 mm from the
side cutting edge line in the direction of rotation, the
deposition of gum on the side of the tip does not occur
when the thickness of the diamond layer is not more than
0.5 mm.
Example 5
A substrate 15 for a spare edge 13 of a finger cutter
is made of a cemented carbide, a tool steel, such as a
high-speed tool steel or a high-chromium alloy tool steel,
or other high-strength materials, for example, a cast
stellite, a sintered stellite, or a cermet. As shown in
Fig. lla, a gas phase synthesized diamond film 16 having
a thickness of not more than 0.5 mm is as such laminated
on the surface of the substrate 15 on the rake side thereof
to form an edge nose. Alternatively, as shown in Fig. 12a,
a substrate 17 with a polycrystalline diamond sinter 18
laminated on the surface thereof is laminated to from an
edge nose. Specifically, a tip seat is formed by grinding
or cutting on a rake of the substrate 15 for a spare edge,
and the substrate 17 with a polycrystalline diamond sinter
18, having a thickness of not more than 0.5 mm, laminated
on the surface thereof is brazed thereto. In this case,
the brazing filler material is preferably used in a
previously determined minimum amount so that the brazing
filler material does not significantly flow on the side of
the substrate.
Subsequently, the diamond layer including the
substrate 17, together with the substrate 15 for a spare
edge, is finished by grinding so that the surface roughness
Rmax of the side cutting edge flank and the peripheral
cutting edge flank is 1 to 10 ~um. In the case of brazing
in the air, the oxide film on the surface in a region
heated in a brazing is removed by shot blasting. In this
case, the grain size of the shot is selected so that the
236~
surface roughness does not become large. Then, for
example, CrN is covered in a thickness of several ,um by
PVD. The rake in the diamond layer may be finished by
grinding after covering or alternatively finished by
grinding before covering. In any event, since the covering
is not strongly adhered to the diamond layer, the covering
on the rake and the side face are removed in an early stage
of cutting operation. However, CrN on the side of the
substrate for a spare edge remains unremoved and functions
to prevent the deposition of gum.
Example 6
An edge nose of a drill as shown in Fig. 13 is made of
a cemented carbide, a tool steel, such as a high-speed tool
steel or a high-chromium alloy tool steel, or other high-
strength materials. The roughness Rmax of the tool in itsperipheral surface 26 near an axial point nose 25 is
brought to 1 to 10 ,um. A hard layer of chromium or a
nitride, carbide, or carbonitride of chromium is provided
as the outermost surface. After covering of the hard
layer, the axial point edge portion is finished by
grinding. This can prevent the deposition of gum on the
peripheral surface of the drill, ensuring the straight
advance of the drill.
Example 7
Fig. 14a shows an example of a moulding cutter wherein
a stiffening plate 29 and an edge nose plate 30 in a spare
edge portion are separably put on top of the other. In the
laminated state, the stiffening plate corresponds to the
substrate for a spare edge, and the edge plate corresponds
to a nose material. The shape of the edge line in the
present example is suitable for use in inishing o the
edge of a plate material to be cut into a circular arc
form. A side cutting edge flank 31 near the maximum
cutting diameter of the edge line is in such a state that
the oblique angle is close to substantially 0 such as
found in the ~inger cutter. For this reason, the clearance
2~72366
angle ~4 in the side cutting edge should be positively
provided. Therefore, the initiation of re-grinding from
the rake results in a change in shape. The application of
the present invention to such a moulding cutter enables gum
to be less likely to be deposited on the side cutting edge
flank. Therefore, the use of the cutter in an identical
shape for a long period of time becomes possible.
Further, since the gum is less likely to be deposited,
the clearance angle in the side cutting edge may be small,
so that re-grinding gives rise to no significant change in
shape. In applications where a change in shape is
unacceptable or re-grinding is unfavorable, the cutter can
be designed so that the edge nose plate alone is
replaceable. Further, when there is no edge line portion,
that is, when the oblique angle is close to 0 , the
clearance angle in the side cutting edge can be naturally
set by providing a usual peripheral cutting edge clearance
angle ~5 over the whole edge line. Therefore, even when
the side edge clearance angle is small, the application of
the present invention can provide a cutter which has a
prolonged service life and undergoes no shape change upon
being re-ground.
