An anchor member for friable material

Abstract: An anchor member comprising a hollow body (10) substantially in the shape of an elongate body of revolution that is open at both ends and provided with a self-cutting outside thread (12) suitable for anchoring it in a friable material. According to the invention, said hollow body is provided with means (16, 16') for securing it to a drill bit (20, 30) which includes longitudinal grooves (22, 23, 36, 37) whose sides constitute cutting edges (22a, 23a, 32a, 32b, 33a, 33b) distributed around the circumference of the hole to be made, said drill bit passing through said hollow body so that its hole-making tip (21, 31) projects forwards from said hollow body.

Description: The present invention relates in general to anchor members, commonly called "plugs", and more particularly to an anchor member designed to be inserted in friable material. Document US-A-3 911 781 discloses an anchor member for friable material which, in conventional manner, comprises a circularly cylindrical body carrying a self-cutting outside thread and provided with an axial bore open at one end to receive a fastener inserted into said member. The installation of a fastener in a friable material by means of such an anchor member generally takes place in three independent operations. Firstly a hole is drilled in the friable material by means of a hole-making tool such as drill. Thereafter the anchor member is inserted in the previously prepared hole so that its self-cutting outside thread engages in the friable material. Finally, the threaded fastener is screwed into the anchor member that has been inserted in the friable material. Another anchor member provided with a self-cutting outside thread is also known in the prior art, that anchor member being suitable for threading on a plane hole-making blade for the purpose of being installed in a friable material. In order to insert such an anchor member in a friable material, said material is drilled with the plane hole-making blade being driven in rotation and carrying said member. The tip of the hole-making blade forms a hole in the friable material in which said anchor member anchors itself. However, the hole made by that hole-making blade is not even. In addition, when the density or hardness of the friable material is slightly greater than average, the plane hole-making blade has difficulties piercing it. Furthermore document EP-A-501 201 discloses an anchor member according to the preamble of claim 1. The present invention proposes an improved, novel type of anchor member that is of simple design, and that fits on a drill bit enabling well-calibrated holes to be made in any type of friable material. More particularly, the anchor member of the invention comprises a hollow body substantially in the shape of an elongate body of revolution that is open at both ends, the body being provided with a self-cutting outside thread suitable for anchoring it to a friable material, wherein the anchor member includes anchor grooves for co-operating with longitudinally extended grooves of a drill bit when said drill bit is inserted and passes through said hollow body to enable a hole making tip of the drill bit to project from an inner end of the hollow body, wherein said anchor grooves are formed so as to extend in a substantially longitudinal direction along an inner channel of the hollow body and extend from an inlet region adjacent to an outer end of the hollow body substantially the whole length of the hollow body to the inner end of said body, characterised in that said anchor grooves comprise helical grooves for co-operating with helical grooves of a twist drill bit to ensure that the anchor member rotates together with the twist drill bit. Furthermore, the anchor member must be secured to the drill bit in such a manner as to ensure said anchor member is properly rotated, and the drill bit must be compatible with standard hole-making tools. The present invention proposes the following embodiment of an anchor member in order to resolve those technical problems. In this embodiment, said means for securing the anchor member of the invention with the drill bit comprise helical grooves formed in the inside wall of said hollow body and suitable for co-operating with the helical grooves of a twist drill bit. The following description made with reference to the accompanying drawings given as non-limiting examples, makes it clear what the invention consists in and how it can be performed. In the accompanying drawings: Figure 1a is a diagrammatic perspective view of a first embodiment of an anchor member of the invention; Figure 1b is a partially cutaway perspective view of the Figure 1a anchor member; Figure 2 is a view of the Figure 1a anchor member seen along arrow A; Figure 3 is a diagrammatic perspective of the hole-making tool used with the Figure 1a anchor-member; Figures 4a to 4e show different steps in implementing the Figure 1a anchor member to fix a fastener in a friable material; and As a preliminary point, it should be observed that from one figure to another, elements or portions that are identical or similar have been designated wherever possible by the same reference symbols, and they are not described each time. Figures 1a and 1b show an anchor member designed to be inserted in a friable material. The anchor member comprises a hollow body 10 that is elongate along an axis X-X'. The body 10 has a conical outside surface and an axial passage 11 that is substantially circularly cylindrical. The body 10 is open at both ends 13 and 15. At a first end 13, it includes in conventional manner a collar 14 which is conical in shape and extends radially from said hollow body, having a plane thrust face around the opening of said hollow body. The conical outside surface of the hollow body 10 carries a self-cutting thread 12 which extends along the major part of the length of said body. This self-cutting thread 12 comprises a pyramid-shaped thread with a sharp edge suitable for anchoring the body 10 within a friable material. In addition; the self-cutting thread 12 has gaps 12a close to the other end 15 of the hollow body 10, which gaps have surfaces that are substantially radially flat for the purpose of performing a cutting operation. On its conical outside surface, the body 10 carries a second thread 18 interposed within the self-cutting thread 12. The second thread 18 comprises a thread of rounded shape suitable for preventing rotation of the body of the anchor member when inserted in the friable material. The axial passage 11 in the body 10 has helical grooves 16 formed in the inside wall of said body 10. As can be seen in Figure 1b, the helical grooves 16 start from a certain distance d from the end 13 provided with the collar 14 and extend all the way to the other end 15 of said body such that the axial passage 11 includes a cylindrical portion of length d adjacent to the end 13 and forming an inlet 19. The inlet 19 makes it possible to centre a fastener inside said anchor member when inserted in the friable material. The helical grooves 16 are designed to co-operate with the helical grooves 22, 23 of a twist drill bit 20, whose sides 22a, 23a constitute self-cutting edges distributed around the circumference of the hole to be made, said twist drill bit 20 passing through said hollow body 10 so that its hole-making tip 21 projects forwards from said body of the anchor member. The helical grooves 16 of the anchor member serve to ensure that the anchor member rotates together with the twist drill bit 20. Figure 2 shows that at its end 13 provided with the collar 14, the body 10 of the anchor member includes a set of teeth constituted in this case by four teeth 17 regularly distributed around the opening of said body. Each of the teeth 17 extends radially from the inside wall of the hollow body towards the centre of the opening. The teeth are suitable for fixing the fastener inserted into the body of the anchor member. Implementation of the anchor member shown in Figures 1a and 1b is described below with reference to Figures 4a to 4e. In a first step, the twist drill bit 20 mounted on a drill is threaded inside the body 10 of the anchor member in such a manner that its hole-making tip 21 projects forwards from said body 10. Thus, by virtue of the helical grooves, the anchor member is constrained to rotate with said twist drill bit, with the plane face of the collar 14 bearing against the bit-support means 22 of the drill. In a second step, the hole-making tip 21 of the twist drill bit 20 is placed against a panel of friable material and the drill is rotated so as to make a hole in the friable material. When the tip 21 of the twist drill bit 20 penetrates into the panel, the self-cutting thread 12 of the anchor member begins to cut complementary tapping in the friable material so as to anchor the body 10 of the anchor member in the calibrated hole made by the twist drill bit in the panel. The single operation of making the hole and installing the anchor member is terminated once the collar 14 of the body of the anchor member comes flush with the outside surface of the panel. It will be observed that the self-cutting thread serves to hold the anchor member axially in the panel while the rounded second thread serves to lock it in place. In a subsequent step, the twist drill bit is extracted from the anchor member. Finally, the fastener 23, carrying an object to be fixed, is screwed into said anchor member. In this case the fastener is a screw adapted to the anchor member and the tip of the screw 23 projects from the body of the anchor member. The screw is held in the anchor member by the set of teeth of said member. Naturally, the present invention is not limited to the embodiments described and shown, and the person skilled in the art could devise any variant coming within the spirit of the invention, provided the invention remains as defined in claim 1.

Claims: An anchor member comprising a hollow body (10) substantially in the shape of an elongate body of revolution that is open at both ends, the body (10) being provided with a self-cutting outside thread (12) suitable for anchoring it to a friable material, wherein the anchor member includes anchor grooves (16) for co-operating with longitudinally extended grooves (22, 23) of a drill bit (20) when said drill bit is inserted and passes through said hollow body (10) to enable a hole making tip (21) of the drill bit to project from an inner end (15) of the hollow body (10), wherein said anchor grooves (16) are formed so as to extend in a substantially longitudinal direction along an inner channel (11) of the hollow body and extend from an inlet region (19) adjacent to an outer end (13) of the hollow body (10) substantially the whole length of the hollow body to the inner end (15) of said body (10), characterised in that said anchor grooves (16) comprise helical grooves (16) for co-operating with helical grooves (22, 23) of a twist drill bit (20) to ensure that the anchor member rotates together with the twist drill bit (20). An anchor member as claimed in claim 1, characterised in that said hollow body (10) includes an additional thread (18) on its outer surface interposed within the self-cutting thread (12) and suitable for preventing rotation of the anchor member when inserted in the friable material. An anchor member according to any either of the preceding claims, characterised in that said hollow body (10) includes a set of teeth (17) at one end for fixing a fastener engaged in said hollow body (10) and projecting forwards from said hollow body (10). An anchor member according to any one of the preceding claims, characterised in that the self-cutting thread (12) has gaps (12a) close to one end of the elongate hollow body (10), the gaps having surfaces that are substantially radially flat for the purpose of performing a cutting operation.

Inventors: ANQUETIN ROBERT, ANQUETIN, ROBERT
Applicants: BLACK & DECKER INC, BLACK & DECKER INC.
Application year: 1995
Main classification: F16B13
IPC codes: F16B13