Cutting tool

A cutting tool, such as a turning tool, includes a clamping holder on which a clamping shoe is secured. The clamping shoe has a curved surface projecting member adjacent one end for securing a cutting bit in a recess in a first surface on the clamping holder. The projecting member seats within a shaped recess in the cutting bit. Guide cams are located adjacent the opposite end of the clamping shoe and contact a second surface on the clamping holder inclined relative to the first surface. A clamping bolt located between the projecting member and the guide cams secures the clamping shoe to the clamping holder. A spring encircling the bolt biases the clamping shoe outwardly from the clamping holder. A pin member is mounted in the second surface of the clamping holder and engages between the guide cams as protection against turning the clamping shoe about the axis of the clamping bolt.

SUMMARY OF THE INVENTION 
The present invention is directed to a cutting tool, such as a turning tool 
or lathe, made up of a clamping holder with a recess in one surface for 
receiving a cutting bit. The cutting bit has a depression into which a 
projecting member on a clamping shoe seats and the clamping shoe is 
secured to the clamping holder by a clamping bolt. 
A cutting tool of this general type is disclosed in Federal Republic of 
Germany Offenlegungsschrift No. 26 20 201. The tool includes a cutting 
plate or bit with a depression or recess on its upwardly facing side and 
the depression extends substantially parallel to the underside of the 
clamping shoe and the projecting member on the shoe presses against the 
cutting plate in the depression so that there is a flat support of the 
clamping shoe in the depression. The pressure exerted by the clamping shoe 
extends parallel to the axis of the clamping bolt which tightens the shoe 
against the clamping holder. Due to such construction, no draw cuts can be 
performed with the tool under a high load if large chip cross-sections are 
to be removed, since the cutting plate becomes displaced in the holder 
recess. Moreover, it cannot be assured that the cutting bit always 
maintains the same seat when it is replaced, since the user must exercise 
case to assure that it is inserted accurately into the holder recess. 
Where cutting bits are exposed to small loads, and where such small loads 
may be mechanical or thermal loads, it is usual to provide the cutting bit 
with a through-hole, generally conically shaped in which a threaded pin 
engages, with the pin having a frusto-conically shaped head. By tightening 
the pin, the cutting bit is pressed against stop faces on the holder and 
is fixed in position against any displacement. Such an arrangement is 
disclosed in U.S. Pat. No. 3,341,923. Such through-holes or openings, 
however, generally weaken the cutting bits so that large chip 
cross-sections cannot be worked at high temperatures or with strong 
pressures, since such conditions would tend to break the cutting bit. 
Therefore, it is the primary object of the present invention to prevent 
breakage of the cutting bit. 
Another problem in conventional clamping holders is that difficulties are 
experienced in inserting and adjusting the cutting bits during overhead 
rotation. When the clamping shoe is removed it adjusts itself and presses 
against another point on the cutting bit so that it is not possible to 
assure an optimum clamping effect, moreover, the cutting tool operator 
usually does not know with absolute certainty whether he has inserted the 
cutting bit correctly. Therefore, frequently it is the practice to replace 
the entire clamping holder when a clamping bit is worn out. 
Therefore, it is a primary object of the present invention to provide a 
cutting tool having an exchangeable cutting bit or insert in which the 
cutting bit is held during a draw cut and is automatically brought into 
its fixed position during overhead cuts as well as when the cutting bit is 
replaced. 
The objects of the present invention are achieved in a cutting tool 
embodying the following characterizing features: 
a. A projecting member on the clamping shoe engages within a depression in 
the cutting bit. 
b. The clamping shoe and/or the clamping holder has a countersunk recess in 
which a lifting spring is positioned. 
c. The clamping shoe has guide cams in engagement with a sloping surface on 
the clamping holder. 
d. The clamping holder includes a member engageable between the guide cams 
on the clamping shoe to protect against any tendency of the clamping shoe 
to rotate. 
Since the projecting member on the clamping shoe engages in the depression 
in the cutting bit, the bit can be removed by displacing the clamping 
shoe. At a location spaced from the projecting member, the clamping shoe 
has guide cams which engage a surface on the clamping holder which slopes 
relative to the surface in which the cutting bit is seated. When the 
clamping shoe is tightened onto the clamping holder, the guide cams slide 
along the sloping surface of the holder and the cutting bit and the 
clamping shoe along with it move into the recess in the surface of the 
clamping holder where they are properly positioned. Due to the sloping 
surface of the clamping holder on which the guide cams slide, the required 
positions of the cutting bit and of the clamping shoe are achieved. When 
the clamping shoe is released, it moves outwardly from the clamping holder 
due to the biasing action of the lifting spring. As a result, the guide 
cams are positioned outwardly from the sloping surface of the clamping 
holder, though the projecting member on the clamping shoe is still in 
engagement with the depression in the cutting bit. In this position, the 
member secured to the clamping holder extending between the guide cams on 
the clamping shoe prevents any turning or rotation of the clamping shoe 
about its connection to the clamping holder. In this position it is 
possible to tilt the clamping shoe and move its projecting member out of 
the depression in the surface of the cutting bit. With the cutting bit 
released by the clamping shoe, it can be removed manually from the 
clamping holder and replaced with another bit, although it will be still 
be held by the clamping shoe in the overhead position even after the 
clamping bolt is loosened. Since the cutting bit adjusts itself when the 
clamping bolt is tightened, this arrangement is especially suited for 
positions where it is difficult to gain access and where an extension of 
the clamping holder was necessary in the past. 
In a preferred embodiment of the invention, the projecting member of the 
clamping shoe is in the form of a half barrel to ensure a punctiform 
contact of the projecting member in the depression in the cutting bit. It 
is even more advantageous if the projecting member on the clamping shoe is 
in the form of a half cylinder. In each case it is a prerequisite that the 
depression in the cutting bit is substantially spherically shaped. With 
this particular configuration of the depression in the cutting bit, it is 
possible to use oxide ceramic materials, such as aluminum oxide or 
zirconium oxide, as the material for the cutting bit with the depression 
being formed such that it does not cause any weakening and result in any 
breakage of the cutting bit. For a considerable period of time oxide 
ceramic materials have been compressed into cutting bits and subsequently 
sintered. In the past, however, it has not been possible to provide such 
cutting bits with recesses or depressions which enable a centering contact 
when the bits are exposed to high loads. When the depression in the 
cutting bit is spherically formed, no sharp edges are present and the 
oxide ceramic powder forming the bit flows more easily during the pressing 
process. Accordingly, the cutting bit is uniformly compressed, that is, a 
uniform pressure is applied during the pressing operation and this leads 
to a uniform density over the entire cross-section of the cutting bit. As 
a result, the cutting bit is more resistant to breakage and, at the same 
time, the spherical form of its depression ensures that a centering 
engagement of the bit by the clamping shoulder can be effected. 
In a preferred embodiment, the invention provides that the projecting 
member of the clamping shoe is in punctiform contact with a surface 
defined by the shape of the depression in the bit. The surface of the 
depression in the bit is formed as straight or convex lines when a 
half-barrel shaped projection member is used and as concave lines when a 
half-cylinder shape of the projecting member is employed. 
As a result, the clamping shoe does not contact the cutting bit in a flat 
manner, such as shown in Federal Republic of Germany Offenlegungsschrift 
No. 26 20 201 nor in the linear form as in U.S. Pat. No. 3,341,923. 
Instead, a punctiform contact is afforded. As is shown, oxide ceramic 
materials withstand great pressure strains so that large forces can be 
transmitted through a punctiform area without any negative effects on the 
cutting bit. In contrast, such materials are more susceptible to bending 
stresses and to tensile stresses, and this factor must be taken into 
account. 
The application of punctiform pressure results, from the construction of 
the clamping shoe and the shaped configuration of the depression in the 
cutting bit. After the cutting bit is inserted into the recess of the 
clamping holder, the projecting member on it engages in the depression in 
the bit when the clamping holder is tightened so that the projecting 
member is in punctiform contact with the surface of the depression. By 
further tightening the clamping shoe against the clamping holder, pressure 
is exerted. The contact point within the depression in the cutting bit 
shifts further downwardly. At the same time, the guide cams slide on the 
sloping surface of the clamping holder in the downward direction. A 
laterally acting force develops and displaces the cutting bit in the 
direction of the border of the recess in the clamping holder so that the 
cutting bit is adjusted. By further tightening the clamping bolt on the 
clamping shoe, the cutting insert is firmly secured in the adjusted 
position. 
In an advantageous embodiment of the invention, the depth of the depression 
in the cutting bit is defined by a radius which is greater than the depth. 
As a result, a relatively flat recess, rounded on all sides, is provided 
which, as mentioned above, is very advantageous in the production of the 
cutting bits, does not affect the strength of the cutting bit and, at the 
same time, enables the centering support of the bit. 
Another advantageous feature of the invention is that the width of the 
projecting member on the clamping shoe is equal to or less than the 
distance between the convexly curved end portions of the depression in the 
bit. In accordance with the invention it is possible to permit higher 
tolerances in the construction of the clamping holder and the clamping 
shoe. In the clamping holder, due to this construction, the opening or 
borehole which receives the clamping bolt for the clamping shoe need not 
be related to the recess in the clamping holder with absolute accuracy. By 
providing a point-support for the projecting member on the clamping shoe 
in connection with the larger dimensioning of the depression, the 
possibility results that the projecting member has sufficient play to 
adjust itself at the center of pressure, even if it engages in the 
depression at a varied angle because of manufacturing tolerances. 
Another preferred feature of the invention is that the maximum radius of 
the half-barrel shaped or half-cylinder shaped projecting member on the 
clamping shoe is in the range of 60 to 80% of the dimension of the radius 
of the surfaces in the depression in the cutting bit. In accordance with 
the invention, the machining accuracy in the production of the clamping 
holder and of the clamping shoe can be reduced. Further, it is possible to 
form the clamping shoe in a casting process. 
The various features of novelty which characterize the invention are 
pointed out with particularity in the claims annexed to and forming a part 
of this disclosure. For a better understanding of the invention, its 
operating advantages and specific objects attained by its use, reference 
should be had to the accompanying drawings and descriptive matter in which 
there are illustrated and described preferred embodiments of the invention 
.

DETAIL DESCRIPTION OF THE INVENTION 
In FIGS. 1 and 15, a clamping holder 1 is illustrated. The clamping holder 
1 has a recess 2 in one of its surfaces and a cutting bit 3 is positioned 
in the recess. A centering recess or depression 4 is formed in the cutting 
bit 3 and a projecting member 5 on the clamping shoe 6 seats in punctiform 
contact within the depression. The clamping shoe 6 is connected by a 
clamping bolt 7 to the clamping holder 1. In the various embodiments of 
the cutting bit 3 shown in FIGS. 2-12, the same reference numerals are 
used and convexly curved lines 12 define the opposite ends of the 
depressions 4. At the transition point 19, the convex lines 12 change over 
to concave lines 13, note FIG. 2. The maximum depth 14 of the depressions 
4 is formed by a radius 15 having its center point located outside of the 
cutting bit 3 so that the maximum depth 14 is less than the radius 15. 
Because of the formation of the bottom of the depression 4 as a radius 
surface 16 the bottom has an arched configuration. The distance 18 is the 
dimension between the transition points 19. 
As shown in FIG. 15, the projecting member 5 extending downwardly from the 
clamping shoe 6 has a width or dimension 17 equal to or less than the 
dimension 18 extending between the transition points 19 of the convex 
lines 12 located at the opposite ends of the depression 4. 
The clamping shoe is secured to the clamping holder 1 by the clamping bolt 
7 which extends downwardly through the clamping shoe into a threaded hole 
in the clamping holder. In the facing surfaces of the clamping holder 1 
and the clamping shoe 6 through which the clamping bolt 7 extends, there 
are countersunk recesses 21 each providing an annular space around the 
clamping bolt with the bottom of the countersunk recess forming a 
shoulder. A lifting spring 22 encircles the clamping bolt 7 and extends 
between the two countersunk recesses 21 so that the spring bears against 
the bottom of each of the recesses. The lifting spring 22 biases the 
clamping shoe outwardly from the clamping holder. While the projecting 
member 5 is located at one end of the clamping shoe 6, at the other end 
and also directed toward the clamping holder 1 are a pair of guide cams 23 
spaced laterally apart forming a channel 26 between them. As shown in FIG. 
1, the guide cams 23 are in bearing contact with a surface 24 sloping or 
inclined relative to the surface of the clamping holder in which the 
recess 2 for the clamping bit 3 is formed. At the lower end of the sloping 
surface 24 a horizontally extending shaft 27 of the clamping holder 1 
extends outwardly away from the cutting bit. A blind bore extends 
downwardly from the inclined surface 24 into the clamping holder 1 in 
generally parallel relation with the clamping bolt 7. A cylindrical pin 25 
is inserted in closely fitting contact with the blind bore so that an 
axially extending part of the pin projects upwardly from the surface 24 
between the guide cams 23. The diameter of the cylindrical pin 25 
corresponds to the width of the channel 26 formed between the facing 
surfaces of the guide cam 23. The cylindrical pin 25 prevents the clamping 
shoe from turning or rotating about the axis of the clamping bolt 7 while 
permitting sliding movement of the guide cams 23 relative to the 
cylindrical pin. When the clamping bolt 7 is backed out of the threaded 
hole in the clamping holder 1, the lifting spring 22 displaces the 
clamping shoe so that the guide cams are moved upwardly out of contact 
with the sloping surface 24 while the projecting member 5 remains in 
engagement with the depression 4. As shown in FIGS. 1, 13 and 14, the hole 
28 in the clamping shoe 6 through which the clamping bolt 7 extends has a 
larger diameter than the clamping bolt so that the clamping shoe in its 
released or lifted position can be tipped or tilted with the projecting 
member 5 moved out of the depression 4 so that the cutting bit 3 can be 
removed and replaced. When the clamping shoe is lifted the cylindrical pin 
25 prevents it from turning about the clamping bolt 7. 
While specific embodiments of the invention have been shown and described 
in detail to illustrate the application of the inventive principles, it 
will be understood that the invention may be embodied otherwise without 
departing from such principles.