1. Field of the Invention
This invention relates to a securing arrangement for retaining a cutting tooth on a drill bit, wherein the cutting tooth has a tool head and a shaft, the shaft is accommodated in a shaft receiver of the drill bit or of a holder which is connected to the drill bit, and the cutting tooth rests on support faces of the drill bit with one or a plurality of contact faces.
2. Discussion of Related Art
A securing arrangement is known from European Patent Reference EP 0 439 821 A 1. In this case, the drill bit includes pocket-shaped notches, into which each base part is welded. The base part has a shaft receiver, which is tapered. The shaft of the cutting tooth can be inserted into the shaft receiver. To create a cone connection, the shaft has a conical outer outline. A spring cotter is used to secure the cone connection and connects the base part to the shaft.
In operation, particularly where the loads are jerky and intermittent, the cone connection can become worn. The cutting tooth is then no longer retained without play and this leads to a heavy increase in wear until the tool finally breaks.
It is one object of this invention to provide a securing arrangement of the type mentioned above but where the cutting tooth is retained on the drill bit in a secure manner.
This object is achieved with support faces and contact faces that are set to be inclined in a circumferential direction. The drill bit includes a shoulder which is offset relative to the contact faces in the direction of the axis of the drill bit and is associated with and spaced from the cutting tooth. The cutting forces occurring during the cutting operation can be absorbed mostly via the inclined support faces. This type of supporting, in interaction with the space, makes it possible for the shaft of the cutting tooth to be substantially free of the cutting forces and reduces the danger of the tool breaking. Also, the space also makes it possible for the cutting tooth to be adjusted if the support face of the drill bit and/or the contact face of the cutting tooth becoming worn.
According to a preferred embodiment of this invention, the shaft receiver is admitted partially into the shoulder face, which is formed by the shoulder and faces the cutting tooth. A particularly sturdy support of the cutting tooth is produced when the drill bit provides two contact faces for each cutting tooth, and the two contact faces are set opposite one another. When the securing arrangement is developed so that the cutting tooth includes a threaded portion, which is mounted on the shaft, a nut is screw-connectable to the threaded portion, and the cutting tooth is pressed onto the support faces via the contact faces in a pre-tensioned manner by the nut, so that the shaft can then build up an initial tensioning, which absorbs even intermittent, jerky tool loads in a secure manner without loosening of the threaded connection.
The securing arrangement is configured advantageously so that, at least over a portion of its longitudinal region, which extends in the direction of the axis of the drill bit, the shaft of the cutting tooth is surrounded around the circumference completely by the shaft receiver. At the same time, a lateral deviation of the cutting tooth is prevented in a secure manner. In this case, the shaft of the cutting tooth includes at least one calibrating receiver, which is set back relative to the inner wall of the shaft receiver. In this case, the cutting tooth can then be produced true to measurement in the region of its shaft. Superfluous material can be used in the region of the calibrating receiver.
In one embodiment of this invention, the shaft of the cutting tooth is tapered at least over a portion of its longitudinal extension in the direction of its free end. The shaft receiver is also tapered at least in a regional manner, and an outside cross-section of the shaft is smaller than the inside cross-section of the shaft receiver. This arrangement simplifies the mounting of the cutting tooth into the shaft receiver. If the tool head of the cutting tooth includes one or a plurality of radial recesses in its region directed radially inwards, then material pockets are formed on the cutting tooth. Residue material collects in the pockets and forms a layer for protection against wear.
An improved cutting performance is provided if the tool head is closed at its circumferential end region with triangular, convexly curved shaped faces. In addition, the hard material elements are admitted into a web, which is disposed in a region of the cutting tooth lying radially outwards and which extends in the direction of the axis of the drill bit and protrudes above a base part of the cutting tooth. The hard material elements protrude in a regional manner in the radial direction above the web. The hard material elements form calibrating pins, which constantly free-cut the cutting tooth in the drill hole.
To improve the cutting performance even further, at a region remote from the shaft, the tool head of the cutting tooth includes a top face, into which a hard material insert, such as a hard metal insert, is inserted.
This invention is described in detail in view of an embodiment represented in the drawings, wherein:
The disposition and development of the insertion channel 22.1 and of the opening 12 is shown in
The cutting tooth 30 is inserted with its shaft 32 into the insertion channel 22.1. In the installed state, the cutting tooth 30 rests with corresponding mating faces on the support faces 24.
The threaded portion 33 extends into the region of the opening 12, so that a nut 34 can be screw-connected. The cutting tooth 30 can be tensioned on the support faces 24 with the nut 34. As the cross-sectional geometry of the shaft 32 of the cutting tooth 30 is adapted to the outline of the insertion channel 22.1, it is retained in a non-rotatable manner. As shown in
To calibrate the drill bit 10, projections 13 are disposed on the outer face of the base body 11 and have elements 14 produced from hard metal for protection against wear.
In the region of the inner wall 17.1, the base body 11 also has projections 17.2 which extend into the interior of the drill bit 10 and optimize protection against wear at that location.
FIGS. 5 to 7 provide a more detailed representation of one embodiment of a cutting tooth 30. The cutting tooth 30 has a tool head 31, on which a shaft 32 is integrally formed via a rounding transition. The shaft 32 ends at the end remote from the tool head 31, in a threaded portion 33. The tool head 31 has an upper top face 31.1, into which a hard metal insert 35 is admitted. To form a receiver for the hard metal insert, which is in the form of a straight pin, a web 37.1, 37.2 proceeds from the top face 31.1 at both the front and the rear.
As shown in
The shaft 32 is adjacent to a base part 39 of the tool head 31. The shaft 32 has an oval cross-section, as shown in
Number | Date | Country | Kind |
---|---|---|---|
102 05 643.9 | Feb 2002 | DE | national |
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/EP02/14789 | 12/28/2002 | WO |