Non-core drill

Abstract: The present invention is to facilitate the forming f a blind hole by providing a recess (14) at the tip of a diamond grinding wheel assembly (12) and attaching super-hard material piece (16) at the bottom of said recess to crush the workpiece having entered into the recess.

Description: BACKGROUND OF THE INVENTION This invention relates to a non-core drill of the kind defined by the precharacterizing features of claim 1. A diamond core drill is highly effective in drilling a through-hole in hard brittle materials such as concrete, stone and others, but can not be used for a blind hole in these materials. Conventional non-core drills of the kind in question for the latter purpose are shown in Fig. 2 and Fig. 3, and have a diamond grinding wheel assembly 2 attached to the tip of a hollow shunk 1. A jet hole 3 for water or air from a spindle opens at an eccentric position, and has a groove 4 on its side. Since the relative velocity to a workpiece is zero at the center of the tip surface 5, the tool has no cutting ability thereon. In fact, small vibrations of the drill will crush the workpiece on this spot to continue drilling, and therefore drills with diameters less than 10 mm are nearly enough to be used, however the distribution of diamond grinding particles near this center gives much irregular cutting qualities. For tools with diameter not less than 10 mm, the cutting qualities will sharply decrease, and further ones with diameter not less than 14 mm can not be used practically for work materials other than highly crushable ones. SU-A 682 379 shows a non-core drill according to the precharacterizing part of claim 1. This drill is designed to make small holes in hard and brittle materials and comprises a diamond-grinding wheel assembly, besides with a groove making a longitudinal relief. It is a disadvantage of this known drill that a concrete core may remain in the recess so that the drilling properties are worsened. From the US-A 2 731 236 a non-core drill is known comprising a head having provided at the tip thereof a recess, at the bottom of which a large and massive elongated cutting diamond is attached. A large number of diamond cutters which are smaller than the massive elongated cutting diamond are provided in the peripheral surface of the recess and at the crown of the head. For the escapement of drill water which is supplied into the recess channels are disposed around the crown and extend upwardly along the outer periphery of the bit head. There are two main drawbacks in connection with this known non-core drill. The first is concerned with the relative pure sharpness of the drill head caused by the diamond cutters defining a rough cutting surface. Therefore, this known non-core drill is not suited for boring smaller holes. The second drawback is concerned with a rather pure removing of the cuttings because the channels for the escapement of the drill water and hence for the cuttings are too small for an effective washing out of the cuttings. SUMMARY OF THE INVENTION It is the object of the invention to improve the non-core drill of the kind defined at the preamble with respect to the cutting quality thereof. This object is attained by the characterizing features of claim 1. An advantageous development of the invention is given by the subclaim. In accordance with the present invention a hole is bored while grinding concrete or the like by the diamond grinding wheel, and the material to be bored is crushed only at the central portion of the grinding wheel. This combination of grinding and crushing results in a good cutting quality which is superior to the prior art. A good cutting quality is assisted by an effective removement of crushed chips as well as larger particles which are expelled through the elongated relief. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1(a) shows a plan view of an embodiment, Fig. 1(b) a longitudinal section view, Fig. 1(c) a perspective view thereof, and Fig. 2(a) and Fig. 3(a) show plan views of conventional non-core drills, and fig. 2(b) and Fig. 3(b) longitudinal cross-sectional views of the same. DETAILED DESCRIPTION OF PREFERRED EMBODIMENT Fig. 1 shows an embodiment of a core drill in accordance with the present invention, and a recess 14 is provided at the tip surface 13 of a diamond grinding wheel assembly 12 attached to the tip of a shunk 11. This embodiment shows an example wherein a V-type relief is formed in the grinding wheel assembly 12, and a diamond piece 16 is exposed and a jet hole 17 opened at the bottom surface exposed by the relief 18 which extends the full length of the grinding wheel assembly 12. Due to the existence of the recess 14, the grinding wheel assembly 12 penetrates into the workpiece as a core drill does, and the core generated resultingly is easily crushed due to the small size of the core. Crushed chips, as larger particles, are expelled through the relief 18. An experiment where holes of depth 50 mm were drilled through concrete with compressive strength 250 kg/mm² using 10 kinds of non-core drills showed that cutting times could be reduced with the drill of the invention. Shorter cutting times required indicate better cutting qualities, and higher working efficiencies. And dressing intervals are indices for showing the sustaining power of cutting quality. In all cases, non-core drills of the present invention are superior to conventional ones as shown in Figs. 2 and 3. For the purpose of drilling a blind hole for an anchor bolt in a concrete structure, a vibrating drill has been generally used; however noises and vibrations are severe and breaking off in workpiece results. A suitable diamond drill has been highly demanded, but conventional non-core drills are not enough to satisfy practical needs because of their low performance or poor cutting quality and others, poor working efficiencies, and operabilities. The present invention can provide basic solutions for these setbacks, and is highly effective for drilling blind holes in hard brittle materials such as stone, ceramics and other as well as blind holes for anchor bolts in concrete.

Claims: Non-core drill comprising a cylindrical diamond grinding body (12) having a non-circular eccentric recess (14) extending downwards at the tip surface (13) of said body (12) and opening into a relief (18) at the circumference of said body (12), characterized in that the recess (14) extends longitudinally over the full length of said body (12), in that the recess (14) has a generally V-shaped cross section transverse to the longitudinal axis of said body (12), the vertex thereof being disposed at the longitudinal axis of said body (12), in that the walls of the recess (14) extend in parallel to the longitudinal axis of said body (12) over the full length of said body (12), and in that at least one tough large diamond particle (16) or a superhard object such as a sintered diamond tip is attached to the bottom of the recess (14) at the vertex of the V-shaped relief (18). Non-core drill according to claim 1, characterized in that two tough large diamond particles (16) are provided adjacent to one another.

Inventors: NARITA TOSHIYUKI, TANIGAWA TAKESABURO, NARITA, TOSHIYUKI, TANIGAWA, TAKESABURO
Applicants: ASAHI DIAMOND IND, NIKKEN TOOL CO LTD, ASAHI DIAMOND INDUSTRIAL CO. LTD., NIKKEN TOOL CO., LTD.
Application year: 1988
Main classification: B28D1
IPC codes: B28D1, E21B10