Thread-Cutting Chuck Using a Minimum Amount of Lubrication

The present invention relates to a thread-cutting chuck which operates with minimum amounts of lubrication having an axially central lubricant channel for connecting an insert sleeve for the collet chuck, particularly a quick-change insert, which accommodates a screw tap that is provided with a longitudinal borehole, with a minimum lubrication source on a machine side, from which the lubricant is passed as an aerosol to the longitudinal borehole of the screw tap, and wherein the lubricant channel, in the junction region leading into the insert sleeve, comprises an axially displaceable coolant pipe which brings about a direct connection with the longitudinal borehole of the screw tap.

Known thread-cutting chucks in which an aerosol of the cooling lubricant, which is dispersed finely in the compressed air, serves to cool the thread-cutting site, as well as to lubricate the thread-cutting tap in the threaded borehole that is to be cut, are presently on the market in various embodiments. With such a thread-cutting chuck, the difficulty exists that screw taps of different sizes must be used, which protrude inwardly in each case to a different extent. This results in chambers of undefined size behind the screw tap. In these chambers, the danger exists that, due to turbulence, the aerosol will demix from the transporting compressed air. The droplets of cooling lubricant, which are required to be very finely dispersed, can ball together into large drops, in which case the cooling and lubricating effects are no longer provided to the degree desired.

German patent DE 42 18 237 A1 discloses a thread-cutting chuck of the type described above, in which, by providing a coolant pipe, a direct connection to the longitudinal borehole of the screw tap is possible without having to form a chamber between the pipe end and the screw tap. The sealing connection is accomplished in the disclosed thread-cutting chuck by way of a displaceable connecting piece which is at the end of the coolant pipe and can lie elastically against the screw tap. This known arrangement is, however, not suitable for aerosol lubrication since the coolant pipe protrudes at the inner end into a chamber, in which demixing of the aerosol would inevitably take place. In addition, such demixing would likely also occur at the connecting piece because of the differently expanding diameters present. Moreover, this type of sealing arrangement for the coolant at the end of the screw tap is suitable only for a particular axial position of the screw tap and not for a thread-cutting chuck with quick-change exchangeable inserts, for which the end surface of the screw tap is positioned axially at very different positions for drills of different thicknesses. The slight contact pressure springiness in the case of the aforementioned thread-cutting chuck disclosed in DE 42 18 237 A1 is neither intended for nor suitable for such axial positional displacements of the end of the screw tap.

It is therefore an object of the invention to provide a thread-cutting chuck of the above mentioned type having a suitable configuration such that when different quick-change inserts with axially different positioning of the ends of the screw tap are used, turbulence with the attendant danger of demixing of the aerosol is reliably prevented.

In accordance with these and other objects of the invention, a thread-cutting chuck is provided in which a coolant pipe extends as one piece continuously from a screw tap up to a lubricant supplying channel formed in a chuck shaft. The coolant pipe is mounted displaceably in an insert sleeve for a collet chuck, provided particularly in the form of a quick-change insert. Due to the pressure of the aerosol acting on the inner end surface of the coolant pipe, the coolant pipe is pressed, independently of the axial position of the screw tap, into an engagement position in which an end portion of the coolant pipe engages an end portion of the screw tap with the coolant pipe in communication with the longitudinal borehole of the screw tap.

In some cases, especially when the coolant pipe has only a very slight wall thickness, as would be suitable for the actual turbulence-free transport, the advancing force, which can be applied over the small end surface of the coolant pipe, is so slight, that it is not even able to overcome internal frictions. For this reason, it has proven to be advantageous to prestress, i.e. bias, the coolant pipe towards the outside by means of a spring.

In this regard, a development has turned out to be particularly simple and advantageous, in accordance with which a spirally coiled compression spring surrounding the coolant pipe is supported at one end at a rear guiding bearing bushing and, on the other, at a ring wheel which is fastened to the coolant pipe.

This construction, moreover, has the additional advantage that the ring wheel, together with a front guiding bearing bushing, forms a pull-out limit for the coolant pipe. When the quick-change chuck is not used, the coolant pipe, with a screw tap, is pressed forward by the spring into its maximum pull-out position. When the quick-change insert is used with a screw tap, the coolant pipe, depending on the axial position of the screw tap, is forced more or less inward, but always maintains a direct connection with the longitudinal borehole of the screw tap and, in this manner, avoids turbulences of the coolant lubricant that result in demixing in the chamber behind the screw tap.

The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.

FIG. 1 is a cross-sectional side view of a quick-change chuck in accordance with an embodiment of the invention shown with a screw tap of small diameter received therein; and

FIG. 2 is a cross-sectional side view of the thread-cutting chuck of FIG. 1 shown with a larger screw tap, which extends axially further towards the rear, received therein.

Referring now to FIGS. 1 and 2, a thread cutting chuck includes a chuck shaft 1 within which a coolant and lubricant channel 2 is formed, and which serves for the connection to a minimum lubrication source located on a machine side (not shown). The coolant and lubricant channel 2 is intended to establish a connection between the minimum lubrication source and a longitudinal borehole 3 of a screw tap 4, the screw tap 4 being shown clamped in a quick-change insert 5. An inner end edge 6 of the quick change insert 5 lies against a sealing ring 7 of an insert sleeve 8 of the quick-change insert 5. A thin-walled coolant pipe 9 is mounted axially, longitudinally displaceable within the coolant and lubricant channel 2. For this purpose, the coolant and lubricant channel 2 is partially provided with constrictions or inserts, which form guiding bearing bushings that tightly surround the coolant pipe. For example, as shown in the figures, a front guiding bearing bushing 10 and a rear guiding bearing bushing 11, formed by an insert, are provided. A ring wheel 12 is fastened on the coolant pipe 9 between the two guiding bearing bushings 10, 11, on which the front end of a spirally coiled compression spring 13 is supported. The rear end of the spirally coiled compression spring 13 is supported at the real guiding bearing bushing 11. By means of this spirally coiled compression spring 13, the coolant pipe 9 is forwardly biased, so that it is in a more or less tight engagement with the end of the screw tap 4, such that the coolant pipe 9 is in aligned communication with the longitudinal borehole 3 of the screw tap 4 and, moreover, such engagement is achieved independently of a particular axial position which the rear end of the screw tap 4 occupies. A continuous pipe connection is produced from the rear end of the chuck shaft, and with that, from the connecting pipe to the minimum lubricating source up to the threaded borehole 3 of the screw tap 4, regardless of whether a thick screw tap, as shown in FIG. 2, or a thin screw tap, as shown in FIG. 1 and which ends further forward than the thick screw tap of FIG. 2, is received in the thread-cutting chuck. Accordingly, in the space 14 of smaller or greater size behind the inner end walls of the screw tap 4, turbulences resulting in a demixing of the aerosol cannot occur. Instead, the aerosol is passed as a fine emulsion from the minimum lubricating source to the front end of the screw tap 4. The ring wheel 12, in conjunction with the front guiding bearing bushing 10, functions in this regard as a pull-out limit for the coolant pipe 9. If a quick-change insert has not been inserted into the chuck shaft, the coolant pipe 9 is in a position which is shifted furthest to the outside and in which the ring wheel 12 lies against the guiding bearing bushing 10. If a quick-change insert is used with a screw tap of any diameter, the inner end of the screw tap pushes the coolant pipe 9 a correspondingly distance to the rear, i.e., either into the position of FIG. 1 or the intermediate position of FIG. 2, or any other intermediate position.