Method for forming pilot holes and cutting tool for electromagnetic drill

Abstract

A method for forming a pilot hole that allows easy formation of the pilot hole and a cutting tool for an electromagnetic drill that is suitable for use in the method are provided. [Solution] With the outer ring 73B of the radial bearing 73 of the cutting tool 7 fitted into the small hole SH formed in the connecting plate IB1 so that it moves in the axial direction of the shaft 6 but does not rotate within the small hole SH, the shaft of the electromagnetic drill is rotated to form an annular guide recess GS [Fig. 4(B)] with a diameter larger than the small hole SH in one connecting plate IB1 using the annular cutting tool 71. A pilot hole PH is formed using an electromagnetic drill equipped with a drill cutting tool DC whose tip fits into the annular guide recess GS and whose outer diameter is equal to the diameter of the annular guide recess GS.

Description

[Technical Field]

[0001] The present invention relates to a method for forming pilot holes in the preliminary assembly process of a steel bridge, and to a cutting tool for an electromagnetic drill suitable for use in the method. [Background technology]

[0002] As described in Japanese Patent Laid-Open Publication No. 2008-45371 (Patent Document 1), when a steel bridge structure is formed by assembling multiple assembly members, the individual assembly members are formed in a factory, and then transported to the installation site of the steel bridge and assembled. Typically, individual assembly members contain slight dimensional errors, geometric distortions, etc., and when these assembly members are assembled at the installation site of the steel bridge, the dimensional errors and geometric distortions of the individual assembly members accumulate, resulting in large dimensional errors and distortions overall. Therefore, to avoid the occurrence of large dimensional errors and distortions, so-called pre-assembly work is performed in the factory and inspections are carried out. Through this pre-assembly work, the dimensional errors and geometric distortions of each assembly member are inspected and adjusted so that they fall within the allowable range.

[0003] The assembly members assembled in the temporary assembly work are disassembled after the temporary assembly work, and then transported individually to the erection site and reassembled. If the assembly members are not assembled in the same manner as in the temporary assembly work, installation errors may occur, resulting in dimensional errors and distortion of the shape of the bridge, making it impossible to reproduce the adjustments made in the temporary assembly work. Therefore, in the temporary assembly work, a predetermined assembly member and other assembly members are temporarily fixed using a connecting plate with pilot holes formed therein, and at the erection site, drift pins are driven into the pilot holes of the same connecting plate to fix the positions of the predetermined assembly member and other assembly members, thereby aligning the predetermined assembly member and other assembly members in the same manner as in the temporary assembly work. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-45371 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the past, during the temporary assembly process of steel bridges, the connected parts of two assembly members used in the steel bridge were sandwiched between two connecting plates made of steel plates, and the two assembly members and two connecting plates were temporarily fixed using multiple bolts.When forming pilot holes that pass through the two connecting plates and the connected parts of the assembly members, it took time to adjust the position of the holes in each steel plate.

[0006] An object of the present invention is to provide a method for easily forming a pilot hole and a cutting tool for an electromagnetic drill suitable for use in said method. [Means for solving the problem]

[0007] The electromagnetic drill tool jig suitable for forming a pilot hole of the present invention is an electromagnetic drill tool jig that includes a base incorporating an electromagnet for fixing to a workpiece, a drilling machine mounted so as to be movable up and down relative to the base, and an annular cutting tool attached to the tip of the shaft of the drilling machine. The electromagnetic drill tool jig of the present invention includes a jig body fixed within the internal space of the annular cutting tool and having an exposed end exposed from the tip of the annular cutting tool, and a radial bearing attached to the exposed end of the jig body. The outer diameter of the outer ring of the radial bearing is smaller than the outer diameter of the annular cutting tool.

[0008] When the electromagnetic drill tool jig of the present invention is attached to an electromagnetic drill, a guide recess suitable for drilling through holes can be formed in the steel plates when drilling pilot holes, for example, when the workpiece is a stack of steel plates with pre-formed small holes that are connected to each other. This is because, if a radial bearing with an outer diameter of its outer ring is used that fits into a small hole formed in the outermost steel plate to which the electromagnetic drill is directly attached, simply by rotating the shaft of the electromagnetic drill, the center of the annular recess formed by the annular tool coincides with the center of the small hole in the outermost steel plate. When the annular tool of the electromagnetic drill, with the jig body removed, is inserted into this recess (annular guide recess) and the electromagnetic drill is rotated, through holes whose inner diameters coincide with the outer diameters of the annular tool can be formed in the steel plates with pre-formed small holes with minimal cutting. The through holes are suitable as pilot holes that pass through the two connecting plates and the connected portions of the assembly members when the two assembly members and the two connecting plates are temporarily fixed together.

[0009] A jig body can be used in which a female thread extending in the axial direction of the shaft is formed in the center of the jig body, and a reduced diameter portion is formed at the exposed end of the jig body into which the inner ring of the radial bearing is fitted. In this case, if a structure is used in which, with the inner ring of the radial bearing fitted into the reduced diameter portion of the jig body, the inner ring of the radial bearing is pressed in the axial direction by a bolt member with a male thread that screws into the female thread portion, then the radial bearing can be easily attached and removed.

[0010] By using an electromagnetic drill equipped with the electromagnetic drill tool jig of the present invention, pilot holes can be easily formed through the two connecting plates and the connecting portions of two assembly members used in a steel bridge during the temporary assembly process, with the connected portions of the two connecting plates sandwiched between two steel connecting plates and the two assembly members temporarily fastened together using multiple bolts. In the method of the present invention, before or during the temporary assembly, multiple small holes with diameters smaller than the outer diameter of the annular cutting tool are formed in the two connecting plates and the assembly members so that they communicate with each other during the temporary assembly process. Then, with the two assembly members and the two connecting plates temporarily fastened together using multiple bolts to connect the multiple small holes, the electromagnetic drill is fixed to one of the two connecting plates selected. Next, the outer ring of the radial bearing of the tool jig is fitted into the small hole formed in one of the connecting plates so that it moves axially within the small hole but does not rotate. Then, the shaft of the electromagnetic drill is rotated, and an annular cutting tool is used to form an annular guide recess in one of the connecting plates, the diameter of which is larger than the small hole. If the outer ring of the radial bearing does not rotate within the small hole, rotating the shaft rotates only the inner ring of the radial bearing and the annular cutting tool, smoothly forming the annular guide recess. Furthermore, the outer ring of the radial bearing does not wear. Then, a pilot hole is formed using an electromagnetic drill equipped with a drilling tool whose tip fits into the annular guide recess and whose outer diameter is equal to the diameter of the annular guide recess. In this way, simply by fitting the tip of the drilling tool into the annular guide recess and driving the electromagnetic drill, a pilot hole whose center coincides with the center of the small hole in one of the connecting plates can be reliably formed without any special adjustment work. Therefore, the method of the present invention significantly simplifies the process of forming pilot holes in the pre-assembly process. Note that multiple pilot holes are formed. When the actual assembly is carried out at the installation site of the steel bridge, drift pins are driven into the pilot holes to fix the positions of the specified assembly members with the other assembly members, thereby aligning the specified assembly members with the other assembly members in the same way as in the temporary assembly work.

[0011] The electromagnetic drill equipped with a drill bit may be a dedicated one for drilling the pilot hole, or an electromagnetic drill equipped with a tool jig prepared for forming the annular guide recess may be used. In this case, the radial bearing attached to the exposed end of the jig body may be removed, and the annular tool may be used as the drill bit. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a perspective view of an example of an embodiment of a cutting tool for an electromagnetic drill according to the present invention; [Figure 2] FIG. [Figure 3] FIG. 10 is a diagram illustrating the use of a pilot hole to combine two assembly members used in a steel bridge structure. [Figure 4] 1A to 1C are diagrams used to explain an embodiment of the method of the present invention. [Figure 5] 1 is a diagram used to explain an overview of an electromagnetic drill and a cutting tool used in an embodiment of the method for forming a pilot hole of the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0013] An example of an embodiment of the present invention will be described in detail below with reference to the drawings. Fig. 5 is a diagram used to explain the outline of an electromagnetic drill and a cutting tool jig used in an embodiment of a method for forming a pilot hole of the present invention. The electromagnetic drill 1 has a base 2 incorporating an electromagnet for fixing it to a workpiece W, and a drilling machine 3 that is movable up and down relative to the base 2. The drilling machine 3 can be moved up and down by operating a handle 4. A shaft 6 of the drilling machine 3 is rotatably supported by a support part 5 provided on the base 2, and a cutting tool jig 7 of this embodiment, equipped with an annular cutting tool, is attached to the tip of the shaft 6.

[0014] [Cutting tool] Fig. 1 is a perspective view of an example of an embodiment of a cutting tool jig 7 for an electromagnetic drill of the present invention, and Fig. 2 is an exploded perspective view of the cutting tool jig 7. In Figs. 1 and 2, the cutting tool jig 7 includes a jig body 72 that is fixed within the internal space of an annular cutting tool 71 and has an exposed end that is exposed from the tip of the annular cutting tool 71, and a radial bearing 73 that is attached to the exposed end of the jig body 72.

[0015] The annular cutting tool 71 is particularly suited to drilling holes in multiple stacked plate-like workpieces, and has a structure such as that shown in Japanese Patent Laid-Open Publication No. 8-252708, sold by Nitto Kohki Co., Ltd. under the name Jet Broach (registered trademark). The annular cutting tool 71 has a cylindrical main body 71A at one end with multiple cutting blades 71B arranged circumferentially around the main body 71A, and flutes 71C for removing chips are formed spirally on the outer surface of the main body 71A toward the other end of the main body 71A. A through-hole 71D is formed at the other end of the main body 71A, into which a screw 74 for fixing a jig body 72 is inserted.

[0016] The jig body 72 is integrally formed from the same metal material as the annular cutter 71. The jig body 72 is fitted inside the main cylindrical body 71A of the annular cutter 71. Although not shown, six grooves are formed on the outer periphery of the main body 72A of the jig body 72 inside the main cylindrical body 71A of the annular cutter 71, into which six circumferentially equally spaced protrusions 72B are fitted. A screw hole 72D is formed in the center of the jig body 72 and has a female screw portion 72C extending in the axial direction of the shaft 6. The female screw portion 72C is formed on the inner surface of the screw hole 72D that penetrates the jig body 72 in the longitudinal direction, and a male screw portion 74A of a screw 74 inserted into the through hole 71D of the annular cutter 71 is screwed into the female screw portion 72C. By this screwing, the jig body 72 is fixed in a state where it is fitted inside the main cylindrical body 71A of the annular cutting tool 71.

[0017] When the main body 72A of the jig body 72 is fitted into the main cylindrical body 71A of the annular cutter 71, a reduced-diameter portion 72E into which an inner ring 73A of a radial bearing 73 is fitted is formed at the exposed end of the jig body 72 that is exposed from the end of the annular cutter 71. The outer diameter of the outer ring 73B of the radial bearing 73 is smaller than the outer diameter of the annular cutter 71. When the inner ring 73A of the radial bearing 73 is fitted into the reduced-diameter portion 72E of the jig body 72, the inner ring 73A of the radial bearing 73 is pressed against the main body 72A of the jig body 72 by a bolt member 75 having a male thread portion 75A that screws into the female thread portion 72C. The outer diameter of the outer ring 73B of the radial bearing 73 is substantially the same as the diameter of a small hole SH for forming a pilot hole PH, which will be described later. In other words, the outer ring 73B of the radial bearing 73 has an outer diameter dimension that allows it to slide in the axial direction of the shaft 6 when fitted in the small hole SH, but not to rotate together with the shaft 6. As a result, the annular blade 71 moves in the axial direction while rotating, with the center of the small hole SH and the center of the shaft 6 aligned.

[0018] In this way, in the cutting tool of this embodiment, the dimensions of the outer ring of the radial bearing 73 are selected according to the pilot hole to be formed.

[0019] [How to form a pilot hole] 3 and 4 are diagrams used to explain an embodiment of the method of the present invention, in which a pilot hole PH is formed using the cutting tool 7 of the above-described embodiment. FIG. 3 is a diagram illustrating the use of a pilot hole to assemble two assembly members AB1 and AB2 used in a steel bridge structure. When individual assembly members AB1 and AB2 are formed in a factory and then transported to the steel bridge installation site for assembly, each assembly member AB1 and AB2 contains slight dimensional errors and geometric distortions. Therefore, when the assembly members are assembled at the steel bridge installation site, the dimensional errors and geometric distortions of the individual assembly members accumulate, resulting in large overall dimensional errors and distortions. Therefore, to avoid large dimensional errors and distortions, a so-called pre-assembly process is performed in the factory to perform a preliminary inspection. Through this pre-assembly process, the dimensional errors and geometric distortions of each assembly member are inspected and adjusted to fall within the allowable range.

[0020] The assembly members AB1 and AB2 assembled during the temporary assembly work are disassembled after the temporary assembly work and then transported individually to the erection site and reassembled. If the assembly members are not assembled in the same manner as in the temporary assembly work, installation errors may occur, resulting in dimensional errors and distortion of the bridge shape, making it impossible to reproduce the adjustments made during the temporary assembly work. Therefore, as shown in Figure 3, during the temporary assembly work, a specific assembly member AB1 and another assembly member AB2 are connected using connecting plates IB1 and IB2 with pilot holes PH. At the erection site, drift pins DP are driven into the pilot holes PH of the same connecting plates to fix the positions of the specific assembly member and the other assembly members. In this way, the specific assembly member AB1 and the other assembly member AB2 are aligned in the same manner as in the temporary assembly work.

[0021] In the method of forming a pilot hole in this embodiment, an electromagnetic drill 1 equipped with an electromagnetic drill cutting tool jig 7 shown in Figures 1 and 2 is used in a temporary assembly process, where the connected portions of two assembly members AB1 and AB2 used in a steel bridge are sandwiched between two connecting plates IB1 and IB2 made of steel plates, and pilot holes PH are formed that pass through the two connecting plates IB1 and IB2 and the connected portions of the assembly members, with the connected portions of the two assembly members AB1 and AB2 and the two connecting plates IB1 and IB2 temporarily fixed using multiple bolts B.

[0022] In the method of this embodiment, before or during pre-assembly, small holes SH (diameter 22.5 mm) having a diameter smaller than the outer diameter of the annular cutting tool 71 are formed in the two connecting plates IB1 and IB2 and the assembly members AB1 and AB2 so as to communicate with each other during the pre-assembly process, as shown in Fig. 4. The bolt holes for inserting the bolts B also have the same diameter as the small holes SH (diameter 22.5 mm).

[0023] As shown in Figure 4(A), when the two connecting plates IB1 and IB2 and the assembly member AB1 (AB2) are stacked in the temporary assembly process, the centers of the small holes SH formed in each are not aligned due to variations in processing accuracy.

[0024] In the method of this embodiment, as shown in Figure 4(A), two assembly members AB1 and AB2 and two connecting plates IB1 and IB2 are temporarily fixed using bolts B to connect the multiple small holes SH, and then an electromagnetic drill 1 (Figure 5) is fixed on one connecting plate IB1.

[0025] In this embodiment, the radial bearing 73 has an outer diameter substantially equal to the diameter (22.5 mm) of the small hole SH formed first to form the pilot hole PH. As shown in FIG. 4(A), the outer ring 73B of the radial bearing 73 of the cutting tool 7 is fitted into the small hole SH formed in one connecting plate IB1 so that it moves in the axial direction of the shaft 6 (FIG. 5) but does not rotate within the small hole SH. Then, the shaft of the electromagnetic drill is rotated, and the annular cutting tool 71 forms an annular guide recess GS (FIG. 4(B)) in the connecting plate IB1. The diameter (24.5 mm) is larger than the diameter (22.5 mm) of the small hole SH. When the outer ring 73B of the radial bearing 73 does not rotate within the small hole SH, rotating the shaft 6 (FIG. 5) rotates only the inner ring 73A of the radial bearing 73 and the annular cutting tool 71, smoothly forming the annular guide recess GS. Furthermore, the outer ring 73B of the radial bearing 73 will not wear out.

[0026] Next, as shown in Figure 4(B), a pilot hole PH is formed using an electromagnetic drill equipped with a drill bit DC whose tip fits into the annular guide recess GS and whose outer diameter is equal to the diameter of the annular guide recess GS (22.5 mm). In this way, simply by fitting the tip of the drill bit DC into the annular guide recess GS and driving the electromagnetic drill, a pilot hole PH whose center coincides with the center of the small hole SH in one of the connecting plates IB1 can be reliably formed without the need for special adjustment work. By forming the pilot hole PH in this manner, when actually assembling the steel bridge at the installation site, a drift pin DP is driven into the pilot hole PH to fix the position of a specific assembly member AB1 with another assembly member AB2, allowing the specific assembly member AB1 and another assembly member AB2 to be aligned in the same manner as in the temporary assembly work.

[0027] The electromagnetic drill equipped with the drill bit DC may be dedicated solely for drilling the pilot hole, but an electromagnetic drill equipped with the cutting tool jig 7 prepared for forming the annular guide recess GS may also be used. In this case, the radial bearing 73 attached to the exposed end of the jig body 72 may be removed, and the annular cutting tool 71 may be used as the drill bit DC. [Industrial Applicability]

[0028] When the electromagnetic drill tool jig of the present invention is attached to an electromagnetic drill, for example, when the workpiece is a stack of steel plates with pre-formed small holes, each of which is connected to the other, a guide recess suitable for drilling through holes in the steel plates can be formed. Then, simply by fitting the tip of the drill tool into the annular guide recess and operating the electromagnetic drill, pilot holes can be reliably formed with centers aligned with the centers of the small holes in one of the connecting plates, without requiring any special adjustment work. Therefore, the method of the present invention significantly simplifies the process of forming pilot holes in the pre-assembly process. [Explanation of symbols]

[0029] 1 Electromagnetic drill 2 pedestal 3 Drilling machine 4 Handle 5 Support part 6 shafts 7 Cutting tool jig 71 Circular blade 71A Main barrel 72 Jig body 72C female thread 72D screw hole 72E Reduced diameter part 73 Radial bearing 73A Inner ring 73B outer ring PH Pilot Hall SH small hole AB1,AB2 assembly parts IB1,IB2 connection plate

Claims

1. An electromagnetic drill tool jig including a base incorporating an electromagnet for fixing to a workpiece, a drilling machine provided so as to be movable up and down relative to the base, and an annular cutting tool attached to the tip of a shaft of the drilling machine, a jig body fixed within the internal space of the annular blade and having an exposed end exposed from the tip of the annular blade; a radial bearing mounted on the exposed end of the jig body; The cutting tool jig for an electromagnetic drill is characterized in that the outer diameter of the outer ring of the radial bearing is smaller than the outer diameter of the annular cutting tool.

2. a female screw portion extending in the axial direction of the shaft is formed in the center of the jig body, and a reduced diameter portion into which an inner ring of the radial bearing is fitted is formed in the exposed end portion of the jig body; 2. An electromagnetic drill cutting tool jig as described in claim 1, wherein, with the inner ring of the radial bearing fitted into the reduced diameter portion of the jig body, the inner ring of the radial bearing is pressed in the axial direction toward the main body portion of the jig body by a bolt member having a male threaded portion that is screwed into the female threaded portion.

3. A method for forming pilot holes that penetrate the two connecting plates and the connected portions of the assembly members, respectively, in a temporary assembly process of a steel bridge using an electromagnetic drill equipped with the cutting tool jig for the electromagnetic drill according to claim 1, in a state in which the connected portions of two assembly members used in the steel bridge are sandwiched between two connecting plates made of steel plates and the two assembly members and the two connecting plates are temporarily fixed using a plurality of bolts, Before or during the temporary assembly, a plurality of small holes having a diameter smaller than the outer diameter of the annular cutting tool are formed in the two connecting plates and the assembly member, respectively, so as to communicate with each other during the temporary assembly process, The two assembly members and the two connecting plates are temporarily fixed using the plurality of bolts to communicate the plurality of small holes, and the electromagnetic drill is fixed to one connecting plate selected from the two connecting plates; The outer ring of the radial bearing of the cutting tool jig is fitted into the small hole formed in the one connecting plate so that it moves in the axial direction of the shaft but does not rotate within the small hole, and the shaft of the electromagnetic drill is rotated to form an annular guide recess in the one connecting plate with the annular cutting tool, the diameter of which is larger than that of the small hole; A method for forming a pilot hole, characterized in that the pilot hole is then formed using an electromagnetic drill equipped with a drill bit whose tip fits into the annular guide recess and whose outer diameter is equal to the diameter dimension of the annular guide recess.

4. The method for forming a pilot hole according to claim 3, wherein the electromagnetic drill equipped with the drill bit removes the radial bearing attached to the exposed end of the jig body and uses the annular bit as the drill bit.

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