JPH0354811Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a holder used for attaching a rotary cutting tool such as a drill or tap to the main shaft of a machine tool.

(Prior Art) Rotary cutting tools such as drills have reduced cutting performance and increased cutting torque due to wear of their blades. Therefore, the number of drills to be machined is determined and the timing of re-sharpening is controlled, but if the workpiece material or cutting conditions change, it is difficult to manage the lifespan, and the workpiece may break during cutting, resulting in defective workpieces. There are many cases where Small-diameter drills and taps are particularly prone to breakage, and they often break easily even when chips become clogged during cutting.

A sensor that captures ultrasonic vibrations when a tool breaks is known as a means of detecting tool breakage during cutting, but what is actually required is to stop the machine before the tool breaks. , to replace the tool.

The main reason why a rotary cutting tool breaks is that the cutting torque increases due to wear of the blade or clogging of chips, as mentioned above. We thought that rotating the tool via a safety clutch would prevent the tool from breaking, and for example,
As described in the above publication, it has been considered to interpose a ball clutch that slips when a certain torque is exceeded between the spindle that holds the tool and the holder body.

(Problem to be solved by the invention) However, with conventional holders, when the cutting torque exceeds a certain value, even though the ball clutch can automatically cut off the transmission of rotational force to the tool, the rotational force in the axial direction Since the feeding continues, the tool is compressed in the axial direction, and the increased compressive stress causes the tool to break. In particular, small-diameter drills, taps, etc. may easily buckle and fail due to increased compressive stress in the axial direction. That is,
As mentioned above, simply interposing a safety clutch between the spindle that holds the tool and the holder body has not been able to reliably prevent tool breakage.

(Means for solving the problem) In order to solve the above-mentioned conventional problems, the present invention has a holder body that is attached to a machine tool.
A spindle having a tool chuck portion at the tip is supported concentrically in a state that allows rotation around the axis and movement in the axial direction within a certain range, and a ball is disposed between the holder body and the spindle. A clutch is interposed, and the ball clutch is formed on a cylindrical inner peripheral surface of the holder main body side with a ball held movably in the radial direction on the spindle side, and when the spindle is in the extended position. A rotary cutting tool holder comprising a ball locking hole into which a portion of the ball is fitted, and a spring that pushes out the ball in a centrifugal direction via a ball pressing plate and urges the spindle in an exit direction. This is what we propose.

(Operation of the invention) The tool holder is set on the main shaft of a machine tool, and a rotary cutting tool such as a drill is attached to the tool chuck to carry out cutting work. , is held in the extended position by the spring of the ball clutch, and the ball of the ball clutch fits into the ball locking hole on the holder body side by the biasing force of the spring, so that the ball is held against the holder body. Rotation is also stopped. Therefore, the strength of the spring should be set so that the ball of the ball clutch is pushed out of the ball locking hole with a rotational force slightly lower than the limit cutting torque that is balanced with the torsional breakage strength of the tool. If the cutting torque exceeds the transmission torque of the ball clutch because the blade has worn beyond the allowable limit or is clogged with chips, the balls of the ball clutch will resist the biasing force of the spring. The ball is pushed out of the locking hole, the clutch breaks, and the holder body becomes the spindle (tool).
It becomes a state where it spins idly. That is, it is possible to prevent a torsional stress exceeding the torsional breakage strength from acting on the tool due to excessive cutting torque.

As mentioned above, after the ball clutch operates and the forced rotational drive of the spindle (tool) is stopped, even if the holder body moves forward in the direction of the rotation axis due to the feed of the spindle, only the holder body will move against the spindle (tool). moves in the direction of the rotational axis against the spring of the ball clutch, thereby preventing excessive axial compressive stress exceeding the compressive breakage strength from acting on the tool. . At this time, the balls of the ball clutch move in the direction of the rotation axis while rolling on the cylindrical inner peripheral surface of the holder main body in the rotation circumferential direction.

Furthermore, even if the cutting torque does not exceed the transmission torque of the ball clutch, if an axial reaction force that exceeds the specified value is applied to the tool during cutting, the balls of the ball clutch will resist the biasing force of the spring. The ball is pushed out from the ball locking hole, and only the holder main body moves in the direction of the rotational axis against the spring of the ball clutch, resulting in excessive axial compression that exceeds the compression breakage strength. Stress can be prevented from acting on the tool. Of course, in this case, the rotational force transmission from the holder body to the spindle (tool) is also cut off.

(Effects of the invention) As described above, according to the tool holder of the invention,
Not only can it prevent the cutting torque acting on the rotary cutting tool from exceeding a certain value, but it can also prevent excessive compressive force from acting on the tool, so it can prevent twisting due to excessive cutting torque of the rotary cutting tool. This makes it possible to reliably prevent buckling and breakage due to excessive compressive force in the axial direction.

Moreover, since one ball clutch serves as both a safety clutch that operates when the cutting torque becomes excessive and a safety clutch that operates when the axial thrust becomes excessive, the number of parts is small and the structure is simple. and can be implemented at low cost.

(Example) An example of the present invention will be described below based on the attached illustrative drawings.

In Fig. 1, 1 is the holder body, and the shank part 3 serves as the attachment part to the main shaft 2 of the machine tool.
and a cylindrical main body 5 concentrically attached to the outer end of the shank portion 3 with bolts 4. A spindle 6 is supported concentrically within the cylindrical body 5 by a pair of front and rear rotary bearings 7a and 7b, and has a tool chuck 8 at its outer end protruding from the cylindrical body 5. This spindle 6
The cylindrical body 5 is rotated by the rotation bearings 7a and 7b.
In contrast, it is rotatable around the axis, and at the same time, it is movable in the axial direction due to the existence of a minute gap (fitting tolerance) between the rotary bearings 7a and 7b. Since an oil film of lubricating oil is present between the spindle 6 and the rotary bearings 7a and 7b, the spindle 6 can be supported with high accuracy in a state where it can move in the axial direction.

Reference numeral 9 designates a ball clutch, which, as shown in FIGS. 1 and 2, includes a ball support plate 10 integrally projecting from the spindle 6, and ball support grooves formed radially inside the ball support plate 10. 11. A ball 12 is partially fitted into each ball support groove 11 so as to be movable in the radial direction with respect to the spindle 6, and a ball 12 is loosely fitted in the spindle 6 inside the ball support plate 10 so as to be movable in the rotational and axial direction. Ball press plate 1
3. A compression coil spring 14 that presses the ball pressing plate 13 toward the ball supporting plate 11, and a compression coil spring 14 provided on the cylindrical inner circumferential surface 5a of the cylindrical body 5 so that a portion of each ball 12 fits therein. It is composed of a plurality of ball locking holes 15 in the circumferential direction.

The ball pressing plate 13 urged by the spring 14 presses each ball 12 with its conical pressing surface 13a. As a result, the spindle 6 is urged outward in the axial direction via the ball support plate 10, so that the spindle 6 is held at the extreme position where the ball support plate 10 abuts the rotary bearing 7a. On the other hand, the conical pressing surface 1 of the ball pressing plate 13
3a biases each ball 12 in the centrifugal direction with respect to the spindle 6, so when the spindle 6 is at the limit position as described above, a portion of each ball 12 is engaged with the ball on the cylindrical body 5 side. They fit into the stop holes 15, respectively. In other words, the clutch is engaged.

Reference numeral 16 denotes a transmission torque adjustment means, which, as shown in FIGS. 1 and 3, is loosely fitted onto the spindle 6 so as to be relatively movable in the axial direction and receives the inner end of the spring 14, and a spring receiving plate 17 which receives the inner end of the spring 14. The cylindrical main body 5 is arranged such that the two protrusions 17a protruding from the spring receiving plate 17 in the diametrical direction pass through each of the protrusions 17a.
Two elongated holes 18 that are long in the axial direction provided in the cylindrical body 5 are screwed into the threaded peripheral surface portion 19 provided on the outer peripheral surface of the cylindrical body 5, and the two protruding portions 17a are fitted into the inner peripheral surface of the cylindrical body 5. It consists of an adjustment ring 21 with a mating annular groove 20 and a lock bolt 22 of the adjustment ring 21. Note that 23 is a transmission torque display scale provided on the outer peripheral surface of the cylindrical main body 5.

The state shown in FIG. 1 is a state in which the spring receiver 17 is retracted to the maximum retraction position by the adjustment ring 21, and the initial compressive stress of the spring 14 is minimized, that is, the transmission torque of the ball clutch 9 is adjusted to the minimum. Indicates the condition. Therefore, when increasing the transmission torque of the ball clutch 9, rotate the adjustment ring 21 in the extending direction with the lock bolt 22 relaxed, and increase the torque transmitted through the protrusion 17a that is in contact with one side of the annular groove 20. The spring receiving plate 17 may be moved forward in the axial direction to compress the spring 14. That is, adjustment ring 2
1, the transmission torque of the ball clutch 9 increases, and as the adjusting ring 21 rotates and pulls back, the transmission torque of the ball clutch 9 decreases.

In use, the shank portion 3 of the holder body 1 is attached to the main shaft 2 of a machine tool in the same way as a conventional tool holder, and a required rotary cutting tool, such as a drill T, is attached to the tool chuck 8 of the spindle 6. The transmission torque of the ball clutch 9 is adjusted by the adjustment ring 21 as described above so that the rotational force or axial thrust that exceeds the breakage strength of the drill T does not act on the spindle 6.

The holder main body 1 and the spindle 6 are connected in the rotational direction and the axial direction by a ball clutch 9 in which a part of the ball 12 is fitted into the ball locking hole 15 and is in a transmitting state. 2 is rotated and fed in the axial direction, the main shaft 2, holder body 1, spindle 6, and drill T rotate together and move forward in the axial direction, and the drill T moves the workpiece. W can be cut and drilled.

During this cutting and drilling process, the cutting torque acting on the spindle 6 is transmitted to the ball clutch 9 due to clogging of chips in the cutting hole or wear of the blade of the drill T exceeding the limit. When the torque is exceeded, the force applied by the spring 14 to fit the ball 12 into the ball locking hole 15 through the ball pressing plate 13 causes the periphery of the ball locking hole 15 to tighten.
The force pushing out the spindle 6 overcomes the force pushing out the spindle 6.
The holder body 1 (cylindrical body 5) pushes out the ball 12 from the ball locking hole 15 as shown in FIG. 4 while rotating relative to the holder body 1 (cylindrical body 5) in the circumferential direction. At this time, the ball 12 rolls in the ball support groove 11 in the centripetal direction while pushing away the ball pressing plate 13 against the biasing force of the spring 14 and is released from the ball locking hole 15, so that It rolls on the columnar inner circumferential surface 5a in the rotational circumferential direction. As a result,
It is possible to prevent the cylindrical body 5, that is, the holder body 1 from rotating idly with respect to the spindle 6, and the application of excessive cutting torque that would cause twisting and breakage of the drill T.

As mentioned above, even after the rotational force transmission from the holder body 1 to the spindle 6 is cut off by the action of the ball clutch 9, the holder body 1 continues to rotate and move forward in the axial direction due to the rotation and feeding action of the main shaft 2. However, since the holder main body 1 and the spindle 6 are movable relative to each other in the axial direction with sliding between the rotary bearings 7a and 7b and the spindle 6, Main body 1
By simply compressing the spring 14 of the ball clutch 9 through the spring receiver 17 which moves forward in the axial direction while rotating, and moves forward together with the holder body 1, the drill T can be prevented from breaking due to axial compression. This eliminates the need to apply excessive axial compressive force that would cause this. In addition, at this time, the ball locking hole 1
As shown in FIG. 5, the ball 12 pushed out from the cylindrical body 5 rolls on the cylindrical inner circumferential surface 5a of the cylindrical body 5 in the rotational circumferential direction and also rolls in the rotational axis direction. Become.

The ball clutch 9 is a means for transmitting rotational force from the holder body 1 to the spindle 6 as described above, and at the same time is a means for transmitting thrust in the axial direction. Even when cutting rotational force is being transmitted, if an excessive axial reaction force acts on the spindle 6, the spring 14 will push the ball 12 through the ball pressing plate 13 in the same way as when the cutting torque becomes excessive. The force that forces the ball 12 to fit into the ball locking hole 15 is overcome by the force that pushes the ball 12 from the periphery of the ball locking hole 15, and as shown in FIG. The main body 1 (cylindrical main body 5) moves forward in the axial direction relative to the spindle 6 while compressing the spring 14. That is, it is also possible to prevent excessive axial compressive force from acting on the drill T, regardless of the cutting torque. Of course, in this case as well, since the ball clutch 9 is switched to the non-transmission operating state, the transmission of cutting torque from the holder body 1 to the spindle 6 is also cut off, and the holder body 1 rotates idly relative to the spindle 6.

In any case, when the rotation of the drill T is stopped due to the action of the ball clutch 9 as described above, while the holder main body 1 is moving forward in the axial direction relative to the spindle 6, that is, the spindle 6 is Before the holder main body 1 (cylindrical main body 5) reaches the retract limit position from the extension limit position, the feed of the main spindle 2 is stopped, and the main spindle 2 is moved backward to allow the drill T to escape from the cutting hole of the workpiece W. , take necessary measures such as replacing the drill T. When the holder body 1 is moved backward by the main shaft 2, the spindle 6 moves forward in the axial direction relative to the holder body 1 due to the biasing force of the spring 14, and reaches the limit position again, so that the ball pressing plate 13 is moved backward. Spring 1 through
Ball 12 biased in the centrifugal direction by 4
automatically fits into the ball locking hole 15 on the rotating holder main body 1 (cylindrical main body 5), and returns to the transmission operating state again.

As shown in FIGS. 6 to 8, a concave groove 24 having an appropriate depth that is the same as or slightly smaller than the diameter of the ball locking hole 15 is formed on the cylindrical inner circumferential surface 5a of the cylindrical body 5. By forming the ball locking hole 15 in an annular shape along the rotational axis direction and drilling the ball locking hole 15 so that the center of the groove 24 and the axis of the ball locking hole 15 coincide, The ball 12 is brought into contact with the ball 12 at the peripheral edge 15a of the ball locking hole 15 that is level with the cylindrical inner circumferential surface 5a of the cylindrical body 5, but in the circumferential direction of rotation, the ball locking hole The ball 12 is brought into contact with the ball 12 at the peripheral edge 15b in the concave groove 24, which is one step lower than the peripheral edge of the groove 15, thereby fitting the ball 12 into the ball locking hole 15 when viewed in the direction of the rotation axis. The fitting depth D1 can be made deeper than the fitting depth D2 of the ball 12 in the ball locking hole 15 when viewed in the rotational circumferential direction.

In other words, one spring 14 pushes the ball 15 through the ball pressing plate 13 into the ball locking hole 15.
Despite being biased to fit,
Since the acting force required to push the ball 12 out of the ball locking hole 15 with an axial thrust can be made larger than the acting force required to push the ball 12 out of the ball locking hole 15 with rotational force,
By selecting the depth of the groove 24, the ability to transmit axial thrust can be arbitrarily made larger than the ability to transmit rotational force in the ball clutch 9.

[Brief explanation of drawings]

Figure 1 is a partially vertical side view, Figures 2 and 3 are cross-sectional views of the main parts, Figures 4 and 5 are vertical side views of the main parts explaining the action of the ball clutch, and Figure 6 is a cross-sectional view of the main parts. 7 is a longitudinal sectional view of the same, and FIG. 8 is a horizontal sectional view of the same. 1...Holder body, 2...Main shaft of machine tool,
3...Shock part, 5...Cylindrical body, 6...Spindle, 7a, 7b...Rotating bearing, 8...Tool chuck, 9...Ball clutch, 10...Ball support plate, 11...Ball support Groove, 12... Ball, 13... Ball pressing plate, 14... Compression coil spring, 15... Ball locking hole, 16... Transmission torque adjustment means, 17... Spring receiver plate,
18...Long hole, 19...Thread groove processing peripheral surface part, 20
... Annular groove, 21 ... Adjustment ring, 24 ... Concave groove.

Claims (1)

[Scope of utility model registration request] A spindle with a tool chuck at the tip is concentrically supported in a holder body that is attached to a machine tool so that it can rotate around the axis and move in the axial direction within a certain range, and the holder body and a ball clutch is interposed between the spindle and the spindle.
The ball clutch includes a ball held movably in a radial direction on the spindle side and a cylindrical inner peripheral surface on the holder main body side, and when the spindle is at the extended position, a part of the ball is A rotary cutting tool holder comprising a ball locking hole that fits into the ball locking hole, and a spring that pushes out the ball in a centrifugal direction via a ball pressing plate and urges the spindle in an exit direction.