Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to an annular cutter
for forming holes in workpieces.
One of the common problems associated with
annular cutkers is wear and chipping of the radially
innermost edges of the cut-ter teeth. It is believed
that this problem arises from the fact that during a
cutting operation metal chips frequently become lodg-
ed between the inner periphery of the cutter teeth
and the outer periphery of the central slug in the
workpiece that is produced by the cutter. These chips
huild up and become welded to the inner periphery of
the cutter adjacent the leading edge thereof. The
build up of metal at the inner periphexy of the cutter
teeth creates considerable Eriction and incxeases the
torque required to rotate the cutter. It also results
in the creation of additional heat and produces excess
wear which hastens failure of the cutter by chipping
and breakageO
I-t is the object of this invention to over-
come the problem of wear, chipping and breakage ofannular cutters resulting from build up of chips
around the inner periphery of the cutter.
1.
More specifically, it is the object of this
invention to form an annular cutter so that the inner
periphery of the cutter body have a minimum surface
contact with the center slug being formed by the cutter.
Other objects, features and advantages of the
present invention will become apparent from the follow-
ing description and accompanying drawing, in which:
FIGURE 1 is a side elevational view of a
cutter according to the present invention;
FIGURE 2 is a fragmentary plan view of the
lower end of the cutter; and
FIGURE 3 is a sectional view along the line
3-3 in FIG. 1.
The cutter of the present invention is gener-
ally designated 10 and is formed with a shank 12 at its
upper end from which an annular side wall 14 depends.
The lower end of side wall 14 is formed with a plural-
ity of circumferentially spaced cutting teeth 16. Be-
tween the successive teeth 16 the wall 14 is form~d
with upwardly extending helical flutes 18 which have a
radial depth equal approximately to one-half the thick-
ness of wall 14. Thus, each flute 18 is radially jux-
taposed ~o a web 20. In the preferred form of cutter
according to the present invention each tooth 16 is
formed with three radially and circumferentially
~.
staggered cutting edges; nam~ly, an inner cutting edge
22, an intermediate cutting edge 24, and an outer cutting
edge 26. Cutting edges 22,24 are formed at the lower
end of webs 20 and/ to accommodate the chips formed
thereby, the adjacent portion of the webs is formed
with an inner gullet 28 and an outer gullet 30. Cutting
edge 22 is defined by-the lower end of the trailing
face 27 of gullet 28 and cutting edge 24 is defined by
the lower end of the trailing face 29 of gullet 30.
Cutting edge 26 is defined by the lower end of the
trailing face 31 of flute 18.
Cutting edges 22,24 are interconnected by a
circumferential shouldex 32 and cutting edges 24,26
are connected by a radius 34. These three cutting
edges are vertically.staggered by reason of the fact
that each tooth is formed with a pa:ir of hack-off faces
36 r 38 which extend circumferentially rearwardly f~om
these cutting edges in an upwardly inclined direction,
for example, at an angle of about 8 to 10. In addi-
tion, back~off face 36 inclined radially inwardly andaxially upwardly and back-off face 38 inclines radial-
ly outwardly and axially upwardly. These two back-off
faces intersect in a crest 40. If the cutter is to be
subjected to a heavy chip load, back-off face 36 pre-
ferably inclines radially at an angle of +10 to ~3to the horizontal and back-off face 38 preferably .in-
clines radially at an angle of about 20 to 25.
3.
When each of the cutting edges 22, 24, 26 is
vertically staggered a distance in excess of the depth
of cut per each revolution of the cutter, each of these
cutting edges will cut a separate chip. By reason of
the radial inclination of cutting edges 22, 24, the
chips cut by these edges will be directed upwardly
through their respective gullets and into flute 18.
Likewise, the chip cut by the outer cutting edge 26
will be directed upwardly through the adjacent flute
18 so that all of the chips are discharged smoothly
and readily upwardly through the inclined flutes 18
As shown in Fig. 2, the inner periphery
of wall 14 is relieved radially outwardly to form a
clearance space 42 so as to leave a narrow margin
a extending circumferentially
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~9V~L9
rearwardly a~d upwardly from the inner cutting edge
22 of each tooth. The clearance 42 ls preferably
formed by removing metal from the inner periphery of
the cutter wall by means of a cylindrical cutter in
which case the rel.ieved portion is defined by a seg-
ment of a circumferential arc 44. The m~i ~tl~ radial
depth of the r~].ieved portion 42 is between .005 and
.025 inches, preferably in the range of about .010
and .015 inches. In order to provide an escape path
for any chip that might become lodged within the clear-
ance space 42, the relieved portion should extend rear-
wardly into the inner gullet 28 of the next successive
tooth so as to form an escape passage as indicated at
46 in FIG. 2. The margin a should have a cirGumferen-
tial width of between .010 and .060 inches, preferably
about .015 inches~ When the relieved portion 42 is
formed wi~h a cyl.indrical cutter so that it becomes
proyressively narrower in a direction toward the
cutting edge 22, the margin a preferably has a width
on the order of ~010-inches. However, when the reliev-
ed portion 42 is machined as a groove of substantially
unifsrm radial depth, then, in order to avoid suhstan-
tial weakening of the tooth~ the margin a should have
a width greater than .010 inches depending upon the
radial depth of the clearance yroove.
5.
The trailing face 27 of each gullet 28 is in~
.clined rearwardly and upwardly at an angle of about 60
to the horizontal. As pointed out previously, the low-
er end of this trailing face cooperates with the back-
off face 35 to define the cutting edge 22. It is pre-
ferred to form the margin a so that it has a substan-
tially uniform width in a direction parallel to the
trailing face of gullet 28 so that, as the cutter
teeth are sharpened by grinding the back-off faces 36,
38, the margin a will .remain of substantially constant
width. The uniform width of the margin can be obtained
by orienting the cutting tool which forms the relieved
portion 42 so that its axis is inclined to the central
axis of the cutter in a direction generally parallel to
the trailing face of guIlet 2~ which in turn forrns the
front rake face of cuttiny edge 22. In FIG. 3 the
broken line 48 depicts in a horizontal plane the out-
line of a tilted cutter tha-t produces the circular arc
44 o~ clearance space 42~ The relieved portion 42 can
extend upwardly the full height of wall 14. However the
desired results are obtained when the margin a has a
- - height which corresp~ds generally to the vertical a -
mension of the teeth 16. ~or exarnple, as shown in FIG.
3, the clearance space 42 provided by the relieved por~
tion extends upwardly slightly beyvr.d the upper end of
the outer gullet 30~
~ , .
As p~inted out previously, one of the problems
involved in u~ing annular cutters of the general typP
described herein is the lodging of chips between the
inner p~riphery of the cutter wall and the outer per-
iphery of the central slug formed by the annular cutter.The provision of the narrow margin a substantially
eliminates this problem. If a chip becomes wedged
between the inner periphery of the cutter and the
central slug, the high unit pressure exerted thereon by
the narrow margin _ results in ~racture of the chip or
at least wearing down of the chip sufficiently so that
it will be discharged into the clearance space 42 and
then radially outwardly through the escape pas sage 46
into the next successive gu]let 28. ~hus, the narrow
margin a prevents build up of chips between -the inner
periphery of the cwtter and the outer periphery of the
slug and the problems resulting from such build up are
thus avoided.
7.
