Core drill

Abstract: A core drill characterised in that it is provided with a base 1 which has a shank 2 and a core body mounting part 3 formed in it; hook-shaped locking grooves 5 which are formed in the peripheral surface of the core body mounting part; a cylindrically shaped core body 6 which is provided with hole-cutting blades 9a and 9b around the peripheral edges of both end openings; a coupling ring 13 from the inner surface of which project locking protrusions 8 that lock with said locking grooves 5, and which is selectively fit into a designated position on the inner surface of the end of the two openings in the core body 6; and stopper balls 19 which are arranged inside the said core body mounting part and which are supported by springs 21 so that they move in and out of the locking grooves 5 and hold the locking protrusions 8 at the locking end points inside the locking grooves.

Description: This invention relates to a core drill having the features of the preamble of claim 1 (see US-A-3 162 067). Such a core drill first uses a center drill to drill a center hole and then uses a core body which is combined in a single unit with the center drill to cut a large-diameter hole in a concentric circle around the center drill. Up until now a wide variety of drills have been developed and marketed for use in the cutting of large-diameter holes. Core drills, which combine a cylindrically shaped core body provided with hole-cutting blades around the peripheral edge of its opening in a single unit with a center drill, and which first uses the center drill to drill a center hole and then uses the core body to cut a large-diameter hole, have been widely used in order to smoothly execute the work of cutting large-diameter holes. Figure 4 is an exploded perspective view of a core drill showing one example of a core drill (see US-A-3 162 067). In the drawing, a base 1 has a shank 2 supported by the chuck of a drive shaft at the center of its top surface, and a core body mounting part 3 provided with a shoulder part 4 is formed in the peripheral surface of the base 1. Locking grooves are formed at two locations at equal intervals on the peripheral surface of the core body mounting part 3, and each of these locking grooves 5 is comprised of a vertical groove 5a formed in the generating-line direction from the bottom edge of the core body mounting part 3 and a horizontal groove 5b formed so that it continues from the vertical groove 5a in the peripheral direction in the shape of a hook. A core body 6 is coupled to the base 1, and a tapered mounting tube 7 into which the core body mounting part 3 is fitted is provided at the top of this core body. Locking protrusions 8 project from the inside surface at the top of this mounting tube 7 so that they engage and release in and out of the locking grooves 5, and cutting blades 9 comprised of cemented carbide bits are provided at the bottom edge of the core body 6. A center drill 10 is mounted to the base 1, and the base of the drill is inserted into a mounting hole 11 provided in the center of the bottom surface of the base 1 and secured in such a manner that it is freely mountable and removable by a securing screw 12 screwed in from the side with respect to the mounting hole 11. The groove surface of the horizontal groove 5b of the locking grooves 5 is formed so that, as it approaches the end, it slants gently upward and at the same time gradually becomes shallower. After fitting the core body mounting part 3 into the mounting tube 7 so that the locking protrusions 8 enter the vertical grooves 5a of the locking grooves 5, by turning the base 1 and the core body 6 relative to each other so that the locking protrusions 8 move toward the ends of the horizontal grooves 5b, as the locking protrusions 8 move inside the horizontal grooves 5b, they are guided by the gently upward slanting groove surfaces, thus causing the core body 6 to be drawn upward. In addition to strengthening the contact relationship between the top edge of the mounting tube and the shoulder part 4, the locking protrusions 8 reach the gradually shallower ends of the horizontal grooves 5b and press against the groove surfaces, thus eliminating any looseness or play between the base 1 and the core body 6 and providing a secure coupling. With the core drill having the composition described above, although the base and the core body can be coupled and separated easily by a one-touch operation, thus providing convenient handling, because the composition is designed so that the hole-cutting blades of the core body are provided at the peripheral edge of the opening at one end of the core body and the opening at the other end is used for coupling with the base, as a core drill used in applications such as a rotary hammer drill, in which breakage of the hole-cutting blades occurs easily, if hole-cutting becomes impossible as the result of breakage of the hole-cutting blades or for some other reason, it is necessary to replace the core body, and it is desirable to separately prepare spare core bodies. In addition, because the hole-cutting blades of the core drill are fabricated in accordance with the characteristics of the material in which the hole is going to be cut, in order to cut holes in materials having different physical properties, it is also necessary to prepare separate core bodies on which the hole-cutting blades are different, even if the diameters of the holes being cut are the same. Furthermore, because breakage of the hole-cutting blades is a fatal problem, the disposal of the core body is also a considerable economic loss. US-A-3 360 025 discloses a cylindrically shaped core body fixed to a shaft by means of a compressed resilient block. In consideration of the problems described above, the objective of this invention is to propose a core drill in which hole-cutting blades are provided on the peripheral edges of both end openings of the core body, thus achieving both convenient handling and excellent economy. The essential point of this invention in order to achieve the objective stated above is that it is a core drill provided with a base which has a shank in the center of its top surface and a core body mounting part formed in its peripheral surface; hook-shaped locking grooves which are each comprised of a vertical groove followed by a horizontal groove and which are formed in multiple locations on the peripheral surface of the core body mounting part; characterised in that it is provided with a cylindrically shaped core body which is provided with hole-cutting blades around the peripheral edges of both end openings; a coupling ring from the inner surface of which project locking protrusions that lock with said locking grooves, and which is selectively fit into a designated position on the inner surface of the end of the two openings in the core body; and stopper balls which are arranged inside the said core body mounting part and which are supported by springs so that they move in and out of the locking grooves and hold the locking protrusions at the locking end points inside the locking grooves. Because a coupling ring is fit into the inner surface of the end of the openings in the core body on the end opposite the hole-cutting blades which are being used and the base and the core body are coupled together via this coupling ring, it is possible to use both of the sets of hole-cutting blades provided at the peripheral edges of the two end openings of the core body, thus improving work efficiency. In the coupling together of the base and the core body, because the locking protrusions inside the locking grooves are held in place at the locking end points by stopper balls which project into the locking grooves under the force of springs, there is no looseness or play in the coupling relationship between the base and the core body during the cutting of a hole using the core drill, thus providing high stability. The following is a detailed explanation of an embodiment of this invention with reference to the accompanying drawings, in which:- Figure 1 is a vertical cross-sectional view of the core drill embodying this invention. Figure 2 is a cross-sectional view along the plane A-A in Figure 1. Figure 3 is a partial cross-sectional view showing the condition of the insertion of the coupling ring into the core body. Figure 4 is an exploded perspective view of a core drill of the prior art. In the following explanation, parts of which are common or equivalent to those in Figure 4 are indicated by the same identification numbers. In the embodiment of this invention, a core body 6 having a straight diameter is used, and cutting blades 9a and 9b are provided at the peripheral edges of both end openings of the core body 6. These cutting blades 9a and 9b can either both be of the same type, or of different types for different types of materials to be cut. In order to couple together the base 1 and the core body 6, a coupling ring 13 is fit into a designated position on the inner surface of the end of the opening in the core body. This coupling ring 13 is comprised of a resilient plate designed to fit closely and elastically against the inner surface of the core body 6, and on its inner surface are provided multiple locking protrusions 8 corresponding to the locking grooves 5. In addition, multiple locking protrusions 14 are provided at equal intervals on the outer surface of the coupling ring 13 at positions different from those of the locking protrusions 8, and, when the coupling ring 13 is fit into the core body 6, these locking protrusions 14 are locked from the inside into locking holes 15 formed in the core body 6, thus making it impossible for the position of the coupling ring 13 to shift. In particular, in order to prevent the movement of the coupling ring 13 in the axial direction with respect to the core body 6, a groove 16 which locks the outer periphery of the coupling ring 13 is provided around the inner surface of the core body 6. In order to mount and remove the coupling ring 13 onto and off of the core body 6, the two ends of the coupling ring 13 are bent inward so as to provide tabs 17. When removing the coupling ring 13 from the core body 6, the two tabs 17 are squeezed together against the elastic force of the coupling ring 13. If the elastic force of the coupling ring 13 is strong, although not shown in the drawings, a screw member or something similar can be provided bridging the space between the two tabs 17 in order to employ a screw method for changing the distance between the tabs 17. A notch 18 is provided in the core body mounting part 3 so that the tabs 17 do not become an obstruction when fitting the core body mounting part 3 into the coupling ring 13 during the coupling together of the base 1 and the core body 6. Stopper balls 19 are provided so that they move freely in and out of the horizontal grooves 5b of the locking grooves 5 from inside the core body mounting part 3, and they are housed together with springs 21 inside housing holes 20 provided facing the horizontal grooves 5b of the locking grooves 5 from the bottom edge surface of the core body mounting part 3. A part of the stopper balls 19 protrudes under the force of the springs 21. When the base 1 and the core body 6 are coupled together, the core body mounting part 3 is fit into the coupling ring 13 so that the locking protrusions 8 enter the vertical grooves 5a of the locking grooves 5, and then the two parts are turned relative to each other so that the locking protrusions 8 move toward the ends of the horizontal groove 5b. This action causes the locking protrusions 8 to move past the stopper balls 19 and reach the locking end points and, unless the base 1 and the core body 6 are intentionally turned in the loosening direction, the locking protrusions 8 are held at the locking end points and the coupled relationship between the base 1 and the core body 6 is securely maintained. It should be noted that, in the drawings, 22 is a cover member which is attached to the base 1 end and which covers the cutting edges of the cutting blades 9 of the core body 6, and it is made of a rubber material or something similar. With the core drill embodying this invention having the composition described above, because the core body has hole-cutting blades provided at the peripheral edges of both openings and either of the core body's sets of hole-cutting blades can be used simply by changing the coupling ring to the inner surface of the other core body opening, it is possible to quickly deal with breakage of the hole-cutting blades when the core drill is used in applications such as a rotary hammer drill, thus improving work efficiency. In addition, the core body can be used for a longer length of time, thus making it advantageous from the viewpoint of the effective use of materials. Furthermore, unless the base and the core body are intentionally turned in the loosening direction, the coupled relationship between the base and the core body is maintained unchanged and there is no looseness or play during use, thus providing consistently reliable hole cutting.

Claims: A core drill provided with a base (1) which has a shank (2) in the center of its top surface and a core body mounting part (3) formed in its peripheral surface; hook-shaped locking grooves (5) which are each comprised of a vertical groove followed by a horizontal groove and which are formed in multiple locations on the peripheral surface of the core body mounting part; is characterised in that it is provided with a cylindrically shaped core body (6) which is provided with hole-cutting blades (9a, 9b) around the peripheral edges of both end openings; a coupling ring (13) from the inner surface of which project locking protrusions (8) that lock with said locking grooves (5), and which is selectively fit into a designated position on the inner surface of the end of the two openings in the core body (6); and stopper balls (19) which are arranged inside the said core body (6) mounting part (3) and which are supported by springs (21) so that they move in and out of the locking grooves (5) and hold the locking protrusions (8) at the locking end points inside the locking grooves (5).

Inventors: MIYANAGA MASAAKI, MIYANAGA, MASAAKI
Applicants: MIYANAGA KK, KABUSHIKI KAISHA MIYANAGA
Application year: 1992
Main classification: B23B31
IPC codes: B23B51, B23B31