This invention relates to a cutting apparatus used for deep-hole drilling work, and in particular, a deep hole cutting apparatus attached with a tip-replaceable guide pad on an outer periphery of a cutting head portion.
A guide pad provided on an outer periphery of a cutting head portion in a deep hole cutting apparatus, in general, slidingly contacts with an inner circumference of a cutting hole during drilling, rendering an inner circumferential surface of the cutting hole receiving a cutting reaction force by a cutting blade. By a so-called burnishing action of keeping a physical relationship between the slidingly contacted area and the cutting blade constant all the time, the cutting head portion is maintained in a rotational state on a constant axis line without runout, thereby enhancing cutting accuracy. The guide pad also exhibits an action of crushing and smoothing unevenness on the inner circumference of the hole involved in cutting. A guide pad of this kind is sometimes integrally formed with the cutting head portion. In most cases, however, the guide pad is configured such that a tip made of a hard material such as cemented carbide, cermet and the like is brazed on or a similar tip is screwed to a pad mounting depression provided on the outer periphery of a cutting head portion made of steel. In particular, the latter screw type guide pad has an advantage of being detachably replaceable with a new one according to abrasion limits and damage. The guide pad is generally applied to a cutting head portion whose cutting blade is also a detachably replaceable throw-away tip.
As shown in
In this case, a coolant C is supplied in the manner of an external supply system. While a coolant supply jacket 41 encompassing the tool shank 4 oil-tight as shown in the figure is pressed contacted with the work material W via a seal ring 42, the coolant C is introduced from an introduction port 43 into the coolant supply jacket 41 under high pressure. The coolant C is then supplied to a distal end side of the drill head 1 through a gap T between an outer peripheral surface of the tool shank 4 and an inner circumferential surface of a cutting hole H. The coolant C flows into the chip discharging passage 13 from the chip discharging ports 14, 15 of the drill head 1 together with chips F produced in a cutting region. After that, the coolant C is discharged to the outside, passing through a chip discharging passage 4a in the tool shank 4. During the cutting work, cutting reaction force is received on the inner circumferential surface of the cutting hole by the guide pads 3 which slidingly contact with the inner circumference of the cutting hole H. Accordingly, the rotational state of the drill head 1 is maintained stable, and the inner circumference of the hole is smoothed.
As shown in
In deep-hole drilling work by the deep hole cutting apparatus as described above, however, improvement in finished quality of cutting holes to be formed has recently been demanded. Also, as for a tip-replaceable guide pad, extending its service life has been demanded in order to reduce running costs.
The present invention was made in view of the foregoing circumstances, and accordingly an object of the present invention is to provide a deep hole cutting apparatus provided with a tip-replaceable guide pad on a cutting head portion and being capable of improving finished quality of cutting holes to be formed and extending the service life of the guide pad.
In order to achieve the aforementioned object, a first aspect of the present invention, described with reference symbols in the drawings, includes guide pads 3A, 3B detachably attached via mounting screws 17b to pad mounting depressions 18 formed on an outer periphery of a cutting head portion 11, the guide pads 3A, 3B slidingly contacting with an inner circumference of a cutting hole H, further the guide pads 3A, 3B having respective tops P1, P2 protruding further outward in a radial direction than a cutting circle S defined by a cutting blade (outer peripheral side cutting blade 2A).
A second aspect of the present invention is configured such that the tops P1, P2 of the guide pads 3A, 3B in the deep hole cutting apparatus of the first aspect are located further forward in the cutting direction than a midpoint in the width of the guide pads 3A, 3B along the cutting direction.
A third aspect of the present invention is configured such that the tops P1, P2 of the guide pads 3A, 3B in the deep hole cutting apparatus of the first aspect are located on circular arc-shaped surfaces whose radius of curvature is smaller than the cutting circle S defined by the cutting blade (outer peripheral side cutting blade 2A).
A fourth aspect of the present invention is configured such that the tops P1, P2 of the guide pads 3A, 3B in any one of the deep hole cutting apparatuses of the first to third aspects have an outward protruding amount in the radial direction with respect to the cutting circle S defined by the cutting blade (outer peripheral side cutting blade 2A) in the range of 0.5 to 50 μm.
According to the deep hole cutting apparatus in accordance with the first aspect of the present invention, the top of each guide pad protrudes further outward in the radial direction than the cutting circle defined by the cutting blade, so that the guide pad slidingly contacts with the inner circumference of the cutting hole while strongly pressing the latter during the cutting work. Accordingly, unevenness produced on the inner circumference of the cutting hole in cutting is reliably crushed to be smoothed, whereby a cutting hole with a smoother inner circumferential surface and of high quality can be formed. In addition, the guide pad is increased in thickness by the protruding amount, so that abrasion resistance life of the guide pad is extended.
Initial abrasion of the guide pad generally tends to be significant at the rear side in the tool rotational direction. According to the second aspect of the present invention, however, the top of the guide pad is located further forward in the tool rotational direction than the midpoint in the width of the guide pad along the tool rotational direction, so that advance of abrasion in the top which protrudes more than the cutting circle is delayed. Accordingly, this results in extending abrasion resistance life.
According to the third aspect of the present invention, since the top of the guide pad is located on a circular arc-shaped surface with a smaller radius of curvature than the cutting circle defined by the cutting blade, the surface can be easily configured into a dimensional shape which prevents the front edge side of the guide pad in the tool rotational direction from biting into the inner circumference of the cutting hole.
According to the fourth aspect of the present invention, the top of the guide pad protrudes with respect to the cutting circle defined by the cutting blade in an appropriate range, so that effective burnishing action and smoothing action of the inner circumferential face can be exhibited without incurring any excessive increase in cutting resistance.
Hereinafter, embodiments of a deep hole cutting apparatus in accordance with the present invention are described in detail with reference to the drawing.
In the deep hole cutting apparatus of the first embodiment, as shown in
In the guide pad 3A, as shown in
Thus, a top P1 of the bulging portion 31 of the guide pad 3A is located on a parallel line L1 at t1 apart from the diameter D passing the rotation center O of the drill head 1. The top P1 projects slightly further outward than the cutting circle S defined by the outer peripheral side cutting blade 2A. Each bulging portion 31 has both edges in the longitudinal direction which are chamfered 34 and a front edge 35 in the tool rotational direction which is rounded.
The drill head 1 in the first embodiment is provided for required deep-hole drilling work as the screw shank portion 12 is threadedly inserted and coupled to the distal end of the tool shank 4 of the drill for deep-hole cutting (see
In general, initial abrasion in a guide pad tends to be significant at a rear side in a tool rotational direction. However, the top P1 of the guide pad 3A is located further forward in the tool rotational direction than the midpoint in the width thereof, so that advance of abrasion in the top P1 which protrudes further than the cutting circle S is delayed. Accordingly, abrasion resistance life as a guide pad can be extended, which contributes to a reduction in running costs. Additionally, the guide pad 3A has such a shape that the circular arc center of the surface of the bulging portion 31 which slidingly contacts with the inner circumference of the cutting hole H is merely shifted as compared with the guide pad 3 (see
In a deep hole cutting apparatus of a second embodiment, guide pads 3B made of a hard material of the same sort as the above are fixed on pad mounting depressions 18 which are provided on the outer peripheral surface of the cutting head portion 11 of the drill head 1, respectively, via mounting screws 17b, as shown in
The guide pad 3B has a left-right asymmetrical cross section in the width direction in the same manner as the guide pad 3A in the foregoing first embodiment. However, the circular arc-shaped surface 31a of the bulging portion 31 has a smaller radius of curvature than the circular arc-shaped surface of the aforementioned conventional guide pad 3 shown by the phantom line in
In deep-hole drilling work by the drill head 1 provided with the guide pads 3B thus configured, cutting reaction force is received on the inner circumferential surface of the cutting hole H via the guide pads 3B which slidingly contact with the inner circumference of the cutting hole H, in the same manner as the work by the deep hole cutting apparatus of the foregoing first embodiment. By the burnishing action, the rotational state of the drill head 1 can be maintained stable, and satisfactory working accuracy can be obtained. Since the top P2 of each guide pad 3B protrudes slightly further outward than the cutting circle S and slidingly contacts with the inner circumference of the cutting hole H while strongly pressing the latter, unevenness on the inner circumference of the cutting hole H is more strongly and reliably crushed to be smoothed. Consequently, the cutting hole H superior in smoothness of the inner circumferential surface and of high quality can be formed. In the same manner as the guide pad 3A in the first embodiment, the guide pad 3B has the top P2 located further forward in the tool rotational direction than the midpoint in the width thereof. As a result, abrasion resistance life as a guide pad can be extended, which contributes to a reduction in running costs. If the guide pad 3B is designed to have a bottom surface in the same dimensional shape as the guide pad 3 (see
In the deep hole cutting apparatus of the present invention, an outward protruding amount in the radial direction of the top of the guide pad with respect to the cutting circle defined by the cutting blade is preferably in the range of 0.5 to 50 μm in general, although an optimum range varies in accordance with a tool diameter (cutting hole diameter). If the amount is too small, effects of smoothing the inner circumference of the hole and extending the service life of the guide pad cannot be obtained sufficiently. If the amount is too large, on the contrary, slide contact resistance is increased, so that cutting efficiency is rendered lower.
As a guide pad used in the deep hole cutting apparatus of the present invention, however, it will suffice if the top of the guide pad protrudes further outward in the radial direction than the cutting circle defined by the cutting blade and more preferably the top is located further forward in the tool rotational direction than the midpoint in the width of the guide pad along the tool rotational direction. The guide pad is not limited to a substantially thick strip guide pad with a pair of bulging portions that are provided on both sides of the screwed portion and slidingly contact with the inner circumference of the cutting hole as exemplified in the foregoing embodiment, and various forms can be adopted, for example, a guide pad configured such that a strip length is shortened and a single bulging portion having a center provided with a threaded hole is provided. In addition to being composed of a hard material such as cemented carbide, cermet and the like entirely, the guide pad may be composed by using a hard material only for the surface of the bulging portion which is subjected to slide contact with the inner circumference of the cutting hole and an inexpensive material such as common steel for other parts as a base.
Additionally, the surface of the bulging portion in the guide pad may be variously configured with a variety of curved surfaces and combinations of curved surfaces and inclined surfaces. However, it is preferable that a main part including the top be a circular arc-shaped surface in terms of workability. By rendering the radius of curvature smaller than the cutting circle defined by the cutting blade, the circular arc-shaped surface including the top can be easily configured into a dimensional shape which prevents the front edge side of the guide pad in the tool rotational direction from biting into the inner circumference of the cutting hole.
In the embodiments, the drill head 1 provided with three cutting blades 2A to 2C of outer peripheral side, central and intermediate ones on the cutting head portion 11 thereof is exemplified. However, the present invention is applicable to a case where the number of cutting blades on the cutting head portion is one, two or four or more. The present invention can also be applied to a deep hole cutting apparatus in which a cutting head portion is integrally formed with a tool shank without being independent as a drill head. Furthermore, in a case where the cutting head portion constitutes an independent component as a drill head, a coolant internal supply system (double tube system) may be employed instead of the coolant external supply system (single tube system) as shown in
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/JP2008/055505 | 3/25/2008 | WO | 00 | 10/1/2009 |