Cutoff tool

A groove cutter (1) has a groove cutting edge (3) that is inclined at a lead angle (.kappa.). The groove cutting edge (3) has a hollowed-out center region (11) between end regions (9, 10) on both sides, and connection cutting edges (15, 16) provide transitions between the center region (11) and the end regions (9, 10). The connection cutting edges (15, 16) have different lengths and are disposed with respect to one another at a flank angle (.delta.). The groove cutter (1) also has a cutting edge corner (7) that leads in a groove cutting direction (5), along with a cutting edge corner (8) that trails in the groove cutting direction (5). One of the connection cutting edges (15) is disposed adjacent to the leading cutting edge corner (7) and forms an inclination angle (.alpha.) with respect to an adjacent end region cutting edge (12). This angle of inclination (.alpha.) is greater than an oppositely directed inclination angle (.beta.) between the other connection cutting edge (16) and another end region cutting edge (13), which trails in the groove cutting direction.

BACKGROUND OF THE INVENTION 
The invention relates to a cutoff tool, and more particularly to a cutter 
of the type having a flank and a cutting face which are adjacent a groove 
cutting edge, with the flank being disposed at an angle near 90.degree. 
with respect to the vertical longitudinal center plane of the cutter and 
providing a lead angle (.kappa.) in the plane of the cutting face. A 
cutter of this type is made of hard cutting material and is intended to be 
releasably fixed in a holder in such a manner that the vertical 
longitudinal center plane of the cutter extends in a groove cutting feed 
direction. Such cutters may be employed, for example, as cutting tools or 
milling cutters. In their configuration according to the invention they 
serve primarily to cut off the ends of workpieces. 
Cutoff tools should ensure the flattest possible surface at the end of the 
cut-off component or workpiece from which a piece has been cut off. The 
lead angle .kappa. of the cutting edge serves to prevent remainders of the 
material, for example, in the form of a remaining hump at an end face 
formed by the groove cutting movement. The lead angle .kappa., however, 
generates a deflecting pressure F.sub.p which acts on the groove cutting 
edge and on the cutoff tool. This pressure urges the tool out of its 
centered position, approximately in the longitudinal direction of the 
groove cutting edge. This may lead to a rather spherical or hollowed-out 
surface configuration instead of the desired planar end face. 
It is already known to compensate for the deflecting pressures acting on 
the leading corner of the groove cutting edge by configuring the groove 
cutting edge so that it ascends in the direction toward the trailing 
cutting edge corner. This generates a pressure component F.sub.p ' which 
acts in the direction toward the cutting edge corner that trails during 
the groove cutting process. 
SUMMARY OF THE INVENTION 
It is an object of the invention to create a cutoff tool of the 
above-mentioned type which, on the one hand, compensates for the 
deflecting pressure resulting from the lead angle (.kappa.) of the groove 
cutting edge but, on the other hand, also enhances chip formation in the 
cut groove in the sense of easy and reliable chip removal. This can be 
accomplished by providing a cutter of the above-mentioned type which is 
characterized in that the groove cutting edge includes a hallowed-out 
center region between two end regions, the end regions having end region 
cutting edges and the center region having a central region cutting edge 
that is essentially parallel to the end region cutting edges; in that the 
groove cutting edge also has connecting cutting edges between the central 
region cutting edge and the end region cutting edges, the connecting 
cutting edges being disposed at a flank angle (.delta.) with respect to 
one another; and in that one of the end region outting edges leads in a 
groove cutting feed direction and the other end cutting edge trails in the 
groove cutting feed direction, one of the connection cutting edges being 
disposed adjacent the leading end region cutting edge and forming an angle 
of inclination (.alpha.) with respect to it, the other connection cutting 
edge being disposed adjacent the trailing end region cutting edge and 
forming angle of inclination (.beta.) with respect to it, the angle of 
inclination (.alpha.) being larger than the angle of inclination (.beta.) 
and being oppositely directed to the angle of inclination (.beta.). The 
angle of inclination (.alpha.) preferably has a magnitude such that an 
outgoing chip remains essentially out of contact with a flank cutting face 
that is inclined at the angle of inclination (.alpha.), while the angle of 
inclination (.beta.) is dimensioned so that the outgoing chip remains in 
contact with a flank cutting face that is inclined at an angle of 
inclination (.beta.). 
The concept of the invention is that, in contrast to prior art cutoff tools 
of the above-mentioned type, no continuous, straight cutting edge exists, 
and also that the cutting edge does not ascend toward the cutting corner 
trailing in the groove cutting direction. Instead, the cutting edge has an 
essentially horizontal position which, for a cutoff tool, lies 
approximately in the horizontal plane defined by the workpiece axis. A 
compensatory pressure that counteracts the deflecting pressure acting in 
the direction toward the leading cutting edge corner is generated since 
the outgoing chip essentially contacts only the flank cutting face 
adjacent the trailing cutting corner and thus provides a compensation 
pressure F.sub.p ' which counteracts the deflecting pressure F.sub.p. 
The compensation pressure F.sub.p ' counteracting the deflecting pressure 
F.sub.p may also be supported by configuring the cutter so that it has a 
cutting edge corner that leads in the groove cutting feed direction and a 
cutting edge corner that trails in the groove cutting feed direction the 
leading cutting edge corner having a corner radius that is greater than 
the corner radius of the trailing cutting edge corner. 
The groove cutting edge of the tool according to the invention is 
distinguished by a positive rake angle. As customary, the groove cutting 
edge may be chamfered over its entire length.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
A cutter 1 in accordance with the invention has a flank 2 and a groove 
cutting edge that is marked 3 as a whole. A cutting face 4 is disposed 
adjacent groove cutting edge 3. In order to form a lead angle .kappa. in 
the plane of the cutting face 4, the flank 2 encloses an angle .gamma. of 
almost 90.degree. with respect to the vertical longitudinal center tool 
plane 6. Plane 6 extends in a groove cutting feed direction 5. 
Cutter 1 also has a cutting edge corner 7 that leads in groove cutting feed 
direction 5 and a cutting edge corner 8 that trails in the groove cutting 
feed direction. Groove cutting edge 3 has an end region 9 adjacent cutting 
edge corner 7, an end region 10 adjacent cutting edge corner 8, and a 
hollowed-out center region 11 with a center region cutting edge 14 which 
is essentially parallel to two end region cutting edges 12 and 13. 
Connection cutting edges 15 and 16 are provided between the center region 
cutting edge 14 and the end region cutting edges 12 and 13. The connection 
cutting edges 15 and 16 form a flank angle .delta. that closes toward 
center region cutting edge 14. The connection cutting edge 15 forms an 
angle of inclination .alpha. with the adjacent end region cutting edge 12. 
This angle is greater than the oppositely directed inclination angle 
.beta. between the other connection cutting edge 16 and the end region 
cutting edge 13. The inclination angle .alpha. is dimensioned so that the 
outgoing chip 17 (FIG. 4) remains essentially without contact with the 
flank cutting face 18 (which is inclined at inclination angle .alpha.), 
while the oppositely directed inclination angle .beta. (FIG. 2) is 
dimensioned so that the outgoing chip 17 remains in contact with the 
mating flank cutting face 19. 
The flank angle .delta. between the two connection cutting edges 15 and 16 
is an obtuse angle. The difference between inclination angle .alpha. and 
oppositely directed inclination angle .beta. is about 
7.degree.-13.degree., and preferably about 10.degree.. The inclination 
angle .alpha. is about 40.degree. and the oppositely directed inclination 
angle .beta. is about 30.degree.. The two end region cutting edges 12 and 
13 each amount to about 15%-30% of the cutting width, and preferably about 
18%-21%. 
The cross-sectional shape of the entire cutting face 4 essentially 
coincides with the shape of groove cutting edge 3. In practice, this means 
that the shape of groove cutting edge 3 continues in the chip discharge 
direction, that is, the direction opposite to groove cutting feed 
direction 5, over the entire cutting face 4. In the chip discharge 
direction, cutting face 4 changes into a chip breaker groove 20. The 
transition from cutting face 4 to chip breaker groove 20 extends upwardly 
approximately in the shape of an arc segment. The two end region cutting 
edges 12, 13 and the center region cutting edge 14 together form more than 
50%, preferably more than 70%, of the cutting width. 
The corner radius R.sub.a of the cutting edge corner 7, which leads in 
groove cutting feed direction 5, is greater than the radius R.sub.b of the 
opposite corner at the trailing cutting edge corner 8 (FIG. 3). 
The rake angle between cutting face 4 and flank face 2 is an acute angle. 
Groove cutting edge 3 and its individual components (that is, end region 
cutting edges 12 and 13; center region cutting edge 14; and connection 
cutting edges 15 and 16) are rounded and the transitions between them are 
filleted. The depth dimension 21 of center region cutting edge 14 relative 
to end region cutting edges 12 and 13 is between about 6% and 9% of the 
groove cutting width, with 9% being associated with the smallest groove 
cutting width and 6% with the largest. The groove cutting widths generally 
lie between about 2 and about 6 mm. The lead angle .kappa. may lie between 
1.degree. and 15.degree.. In the embodiment discussed, a lead angle of 
about 6.degree. has been selected and the remaining dimensions are based 
on this.