Abstract:
A deep hole cutting apparatus has a chip-replaceable guide pad on a cutting head section. With the deep hole cutting apparatus, finish qualities of a cut hole to be formed can be improved and the service life of the guide pad is lengthened. A guide pad ( 3 A) which is slidably brought into contact with the inner circumference of a cutting hole (H) is removably attached with an attaching screw ( 17   b ) to a pad attaching recessed section ( 18 ) which is formed on the outer circumference of a cutting head section ( 11 ). The top portion (P 1 ) of the guide pad ( 3 A) protrudes outward in the diameter direction from a cutting circumference (S) of a cutting blade (outer circumference side cutting blade ( 2 A)).

Description:
FIELD OF THE INVENTION 
       [0001]    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. 
       BACKGROUND 
       [0002]    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. 
         [0003]      FIGS. 1A to 1C  illustrate an example of a drill head in which guide pads and cutting blades are both tip-replaceable. In the drill head  1 , a cutting head portion  11  at a front side and a screw shank portion  12  at a rear side constitute a substantially cylindrical head body  10 . The screw shank portion  12  is provided with a male thread  12   a  on an outer periphery thereof. The head body  10  has a hollow interior constituting a chip discharging passage  13  which is open to a rear end. The cutting head portion  11  has a front end surface  11   a  provided with open chip discharging ports  14 ,  15  in large and small fan-shapes. The chip discharging ports  14 ,  15  are communicated with the chip discharging passage  13 . There are concavely provided three cutting blade mounting seats  16  along walls  14   a ,  15   a  of the chip discharging ports  14 ,  15 . On the cutting blade mounting seats  16 , cutting blades  2 A to  2 C composed of throw-away tips respectively are fixed via screws  17   a . Two groove-shaped pad mounting depressions  18  along a head axis direction are concavely provided in respective locations on an outer peripheral surface  11   b  of the cutting head portion  11 . Guide pads  3  in a shape of a substantially thick strip are fixed on the pad mounting depressions  18  via mounting screws  17   b , respectively. Reference numeral  19  in the drawing denotes a pair of chucking flat portions formed in the opposed positions in a radial direction on the rear side of the outer peripheral surface  11   b  of the cutting head portion  11 . 
         [0004]    As shown in  FIGS. 2 and 3 , cutting work is carried out by coupling a circular tubular tool shank (also referred to as a boring bar)  4  of a drill for deep-hole cutting to a spindle of a machine tool and the like and rotatingly driving the tool shank  4  or rotating a work material W side reversely while the drill head  1  is coupled to a distal end of the tool shank  4  by threadedly inserting the screw shank portion  12 . A tool rotational direction herein means a relative rotational direction of a tool with respect to a work material W in the work, including the cutting work by rotational driving of the latter work material W side. 
         [0005]    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  4   a  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. 
         [0006]    As shown in  FIGS. 7A and 7B , each guide pad  3  for this kind of drill head  1  conventionally has an outer surface configured with a flat portion  30  at the center thereof in the longitudinal direction and both sides configured with circular arc-shaped bulging portions  31 . A threaded hole  32  is provided in the flat portion  30 . A periphery of each bulging portion  31  is generally chamfered  33 . As shown in  FIG. 8 , each bulging portion  31  of the guide pad  3  has a left-right symmetrical cross section in a width direction (a direction along the tool rotational direction), regarding the width direction as the horizontal direction. A surface except for the chamfered  33  periphery has a smaller radius of curvature than a cutting circle S defined by an outer peripheral side cutting blade  2 A. Additionally, the surface constitutes a circular arc-shaped surface whose circular arc center Q is located on a diameter D passing the rotation center O of the drill head  1 . The surface has a top P configured at a protruding height coincident with the cutting circle S. 
         [0007]    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. 
       SUMMARY OF THE INVENTION 
       [0008]    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. 
         [0009]    In order to achieve the aforementioned object, a first aspect of the present invention, described with reference symbols in the drawings, includes guide pads  3 A,  3 B detachably attached via mounting screws  17   b  to pad mounting depressions  18  formed on an outer periphery of a cutting head portion  11 , the guide pads  3 A,  3 B slidingly contacting with an inner circumference of a cutting hole H, further the guide pads  3 A,  3 B having respective tops P 1 , P 2  protruding further outward in a radial direction than a cutting circle S defined by a cutting blade (outer peripheral side cutting blade  2 A). 
         [0010]    A second aspect of the present invention is configured such that the tops P 1 , P 2  of the guide pads  3 A,  3 B 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  3 A,  3 B along the cutting direction. 
         [0011]    A third aspect of the present invention is configured such that the tops P 1 , P 2  of the guide pads  3 A,  3 B 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  2 A). 
         [0012]    A fourth aspect of the present invention is configured such that the tops P 1 , P 2  of the guide pads  3 A,  3 B 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  2 A) in the range of 0.5 to 50 μm. 
         [0013]    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. 
         [0014]    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. 
         [0015]    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. 
         [0016]    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. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  illustrates a drill head provided with tip-replaceable guide pads and cutting blades used in a deep hole cutting apparatus to which the present invention is directed;  FIG. 1A  is a plan view,  FIG. 1B  is a side view of the whole and  FIG. 1C  is a side view of a cutting head portion. 
           [0018]      FIG. 2  is a longitudinal sectional side view showing deep-hole drilling work by the deep hole cutting apparatus. 
           [0019]      FIG. 3  is a longitudinal sectional side view showing the cutting head portion side of the deep hole cutting apparatus in an enlarged manner. 
           [0020]      FIG. 4  is an enlarged transverse sectional view showing a guide pad mounting portion of a drill head used in a deep hole cutting apparatus of a first embodiment in accordance with the present invention. 
           [0021]      FIG. 5  is an enlarged transverse sectional view showing a guide pad mounting portion of a drill head used in a deep hole cutting apparatus of a second embodiment in accordance with the present invention. 
           [0022]      FIG. 6  illustrates a guide pad used in the deep hole cutting apparatuses of the present invention;  FIG. 6A  is a perspective view of the guide pad used in the first embodiment and  FIG. 6B  is a perspective view of the guide pad used in the second embodiment. 
           [0023]      FIG. 7  illustrates a guide pad used in a conventional deep hole cutting apparatus;  FIG. 7A  is a front view and  FIG. 7B  is a side view. 
           [0024]      FIG. 8  is a plan view showing a main part of a drill head of the conventional deep hole cutting apparatus. 
       
    
    
     DESCRIPTION OF SYMBOLS 
       [0000]    
       
           1  Drill head 
           11  Cutting head portion 
           11   b  Peripheral surface (outer periphery) 
           17   b  Mounting screw 
           2 A to  2 C Cutting blades 
           3 A,  3 B Guide pads 
         H Cutting hole 
         P 1 , P 2  Tops 
         S Cutting circle 
         y Tool Rotational direction 
       
     
       DETAILED DESCRIPTION 
       [0035]    Hereinafter, embodiments of a deep hole cutting apparatus in accordance with the present invention are described in detail with reference to the drawing.  FIGS. 4 and 5  illustrate enlarged transverse sectional views of first and second embodiments respectively, each of which showing a guide pad mounting portion of a drill head  1  in the deep hole cutting apparatus.  FIGS. 6A and 6B  illustrate perspective views of guide pads  3 A,  3 B employed in the first and second embodiments. The deep hole cutting apparatus of the embodiments has exactly the same fundamental structure with the deep hole cutting apparatus already described with reference to  FIGS. 1A to 1C ,  2  and  3  except for a form of guide pads  3 . Therefore, explanations of components other than the guide pads  3  are omitted. 
         [0036]    In the deep hole cutting apparatus of the first embodiment, as shown in  FIG. 4 , guide pads  3 A composed of a hard material such as cemented carbide, cermet and the like are fixed on the pad mounting depressions  18  provided on the outer peripheral surface of the cutting head portion  11  of the drill head  1 , via the screws  17   b , respectively. The guide pads  3 A assume a substantially thick strip shape as a whole, as shown in  FIG. 6A . Each guide pad  3 A has an outer surface configured with a flat portion  30  at the center thereof in the longitudinal direction and both sides configured with circular arc-shaped bulging portions  31 . A threaded hole  32  is provided in the flat portion  30 . Surfaces of the both bulging portions  31  constitute circular arc-shaped surfaces with a smaller radius of curvature than the cutting circle S defined by the outer peripheral side cutting blade  2 A (see  FIG. 1 ). In this respect, the guide pads  3 A are the same as the guide pads  3  (see  FIG. 8 ) used in the aforementioned conventional deep hole cutting apparatus. 
         [0037]    In the guide pad  3 A, as shown in  FIG. 4 , the circular arc-shaped surface of the bulging portion  31  has the same radius of curvature as the circular arc-shaped surface of the aforementioned conventional guide pad  3  shown by the phantom line in  FIG. 4 . However, the guide pad  3 A has a circular arc center Q 1  located in a position where the circular arc center Q of the conventional guide pad  3  is displaced forward in the tool rotational direction by t 1  in the head tangential direction. The guide pad  3 A has a left-right asymmetrical cross section in a width direction (a direction along the tool rotational direction shown by an arrow y), regarding the width direction as the horizontal direction. In brief, the circular arc-shaped surface of the guide pad  3 A is displaced by t 1  toward the head tangential direction from the circular arc-shaped surface of the guide pad  3 . The guide pad  3 A has such a shape that a front side in the displacement direction protruding from the pad mounting depression  18  (phantom line a) is removed and a rear side in the displacement direction is added with a circular arc elongated portion b. 
         [0038]    Thus, a top P 1  of the bulging portion  31  of the guide pad  3 A is located on a parallel line L 1  at t 1  apart from the diameter D passing the rotation center O of the drill head  1 . The top P 1  projects slightly further outward than the cutting circle S defined by the outer peripheral side cutting blade  2 A. 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. 
         [0039]    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  FIGS. 2 and 3 ), as mentioned above. Each guide pad  3 A slidingly contacts with the inner circumference of the cutting hole H during the deep-hole drilling work, whereby cutting reaction force is received on the inner circumferential surface of the cutting hole H via the guide pad  3 A. By the burnishing action, the rotational state of the drill head  1  is maintained stable, and satisfactory working accuracy can be obtained. Additionally, unevenness produced on the inner circumference of the hole in cutting is smoothed. Since the top P 1  of the guide pad  3 A protrudes 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. Accordingly, the cutting hole H superior in smoothness of the inner circumferential surface and of high quality can be formed. 
         [0040]    In general, initial abrasion in a guide pad tends to be significant at a rear side in a tool rotational direction. However, the top P 1  of the guide pad  3 A is located further forward in the tool rotational direction than the midpoint in the width thereof, so that advance of abrasion in the top P 1  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  3 A 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  FIG. 7 ) in the conventional deep hole cutting apparatus. As a result, the guide pad  3 A can be attached to the cutting head portion in the conventional deep hole cutting apparatus by using its pad mounting depression  18  without any problem. 
         [0041]    In a deep hole cutting apparatus of a second embodiment, guide pads  3 B 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  17   b , as shown in  FIG. 5 . Each guide pad  3 B is formed into a substantially thick strip shape as a whole, as shown in  FIG. 6B . Each guide pad  3 B has an outer surface configured with a flat portion  30  at the center in the longitudinal direction thereof, the flat portion  30  provided with a threaded hole  32 , and both sides configured with circular arc-shaped bulging portions  31 . A surface of each bulging portion  31  is composed of a circular arc-shaped surface  31   a  at the front side in the tool rotational direction and an inclined plane  31   b  at the rear side in the tool rotational direction. Additionally, each bulging portion  31  is provided with chamfering  34  on both edges in the longitudinal direction and a rounded  35  on the front edge in the tool rotational direction. 
         [0042]    The guide pad  3 B has a left-right asymmetrical cross section in the width direction in the same manner as the guide pad  3 A in the foregoing first embodiment. However, the circular arc-shaped surface  31   a  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  FIG. 5 . The circular arc-shaped surface  31   a  has a circular arc center Q 2  located on a parallel line L 2  which is spaced apart by t 2  toward the front side in the tool rotational direction from the diameter D passing the rotation center O of the drill head  1 . The inclined plane  31   b  forms an inclined surface from the rear edge in the tool rotational direction of the circular arc-shaped surface  31   a  to an open edge of the pad mounting depression  18 . A top P 2  of the bulging portion  31  in the guide pad  3 B is located on the line L 2  and protrudes slightly further outward than the cutting circle S defined by the outer peripheral side cutting blade  2 A. 
         [0043]    In deep-hole drilling work by the drill head  1  provided with the guide pads  3 B thus configured, cutting reaction force is received on the inner circumferential surface of the cutting hole H via the guide pads  3 B 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 P 2  of each guide pad  3 B 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  3 A in the first embodiment, the guide pad  3 B has the top P 2  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  3 B is designed to have a bottom surface in the same dimensional shape as the guide pad  3  (see  FIG. 7 ) in the conventional deep hole cutting apparatus, the guide pad  3 B can replace the guide pad  3  to be used in the conventional deep hole cutting apparatus. 
         [0044]    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. 
         [0045]    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. 
         [0046]    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. 
         [0047]    In the embodiments, the drill head  1  provided with three cutting blades  2 A to  2 C 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  FIG. 2 . The coolant internal supply system is configured such that the drill head is connected to a double-tube tool shank, a coolant is delivered from a coolant supply passage between inner and outer cylinders of the tool shank to the outside of the drill head and then the delivered coolant is, together with chips, flown from a coolant discharging port of the drill head to a coolant discharging passage within the inner cylinder of the tool shank.