The present invention relates to a drill chuck.
A standard drill chuck has a chuck body centered on and rotatable about an axis, normally by a power-drill spindle. A plurality of jaws radially spaced about the axis are movable radially and also normally axially between outer and inner positions under the control of a mechanism normally having a screwthread connection that effects the displacement. Each jaw in turn typically has a grip edge that extends along a line that is parallel to the axis regardless of the position of the jaw and that engages the tool in line contact when the chuck is closed on the tool, typically a cylindrical shank of a drill bit. To each side of the grip edge, each jaw normally has a pair of planar flanks that slope identically away.
The apex angle of the flanks of each jaw are normally such that, when there is nothing between the jaws, they can be brought together to a position with the grip edges all touching and the flanks flatly engaging each other and extending radially of the chuck axis. Thus in a typical three-jaw chuck, the flanks extend at 120° to each other.
Whether the chuck is used for milling, drilling, or another machining process it is critical that the bit be held perfectly on center. Even the slightest off-center positioning can result in destruction of the bit and workpiece, and even create a dangerous condition for the user of the tool, especially at high rotation speeds.
A disadvantage of conventional hand-operated and also machine-operated chucks, in particular when working with bits of small diameter, is that they must be precisely precentered before clamping by the jaws. Otherwise they may be clamped off-center between the flanks of two adjacent jaws. This precise precentering is difficult to do in the field, resulting in broken bits and damaged workpieces.
It is therefore an object of the present invention to provide an improved drill chuck.
Another object is the provision of such an improved drill chuck that overcomes the above-given disadvantages, in particular that allows even a bit or tool with a small-diameter shank to be chuck without any possibility of it being chucked off-center.
A drill chuck has according to the invention a chuck body centered on and rotatable about an axis and a plurality of jaws spaced angularly about the axis, radially shiftable on the body between inner and outer positions, and each having a grip edge extending along a line substantially parallel to the axis and a pair of flanks meeting at the grip edge and extending generally radially outward therefrom. The flanks of each jaw diverging radially inward from the flanks of adjacent jaws so that a tool shank engaged between the flanks of two adjacent jaws will be pushed radially toward the axis on movement of the jaws inward from the outer positions.
Essentially, the advantage provided by the invention is that the chuck centers the tool or workpiece in a simple and economical manner solely by modification of components that are already present. For problem-free precentering of the tool shaft or the workpiece, the chuck may be opened until the distance between flanks of the jaws is less than or equal to the diameter of the workpiece or tool shaft to be clamped, or in the case of flat tool shafts, corresponds to the associated jaw span. After the tool or workpiece is introduced, the jaws may then be moved into the clamped position, thereby automatically and easily centering the tool shaft or workpiece to be clamped. In addition, it is generally possible for existing chucks to be easily and economically retrofitted with correspondingly designed jaws. Furthermore, the risk of injury to the user or nearby persons, in particular during loosening of the clamped tool or workpiece, is greatly reduced for chucks that are still rotating, since even for partially opened jaws the tool or workpiece remains clamped for a longer time between the flanks of the two jaws, and thus remains de facto for a longer time in the chuck.
Within the scope of the invention it is very particularly preferred for the chuck to have three jaws. This design has the advantage that tools or also workpieces may be centered in a very satisfactory manner, and the design of the chuck may be kept simple.
It is further particularly preferred for each of the flanks to have a concave design. This has the advantage that the grip edges define a smaller acute angle, thereby facilitating penetration of the grip edge into the tool shaft or workpiece, and allowing a greatly enhanced rotational connection between the jaw and the tool shaft or workpiece.
For further enhancing torque transmission between the jaws and the clamped tool shaft or workpiece, it is very particularly preferred for each jaw to have two grip edges that are parallel to one another and to the chuck axis. This provides the additional advantage that the maximum service life of the jaw may be further increased. According to one particularly preferred embodiment, the two grip edges of each jaw may be mirror-symmetric with respect to the center jaw plane passing through the chuck axis.
For simplified positioning of the tool or workpiece in the tool or workpiece receptacle defined by the jaws, the invention further provides that in the direction of introduction of the tool or workpiece the end faces of the jaws have a plane extending from the base of the jaws at an angle with respect to the chuck axis, or a concave surface.
The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which:
As seen in
This construction works perfectly when the tool 7 is perfectly centered between the jaws 2′ so that it can be gripped in line contact by the three edges 4′ as shown in
This problem is solved according to the invention by a system where as shown in
As a result as shown in
In
The system of
Number | Date | Country | Kind |
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102006058199.7 | Dec 2006 | DE | national |