JP2011117472A - Prepared hole for fastening screw - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a prepared hole for fastening a screw in a shape capable of reducing the occurrence of female screw forming chips brought about when a tapping screw is screwed in the prepared hole, and easily correcting the inclination of the tapping screw relative to the prepared hole. <P>SOLUTION: In the prepared hole 10 of a workpiece 8 for fastening a screw, an inlet part 11 with an inner diameter slightly larger than the outer diameter of the tapping screw 1 is formed on an inlet side, a female screw part 12, in which a screw thread 5 is screwed while forming a female screw, is arranged at the back thereof, and moreover, a guide hole part 13 is formed between the inlet part 11 and the female screw part 12. Therefore, the need for forming a prepared hole inclined bottom surface with an inclined angle equivalent to a lead angle of the tapping screw is eliminated, and the overall costs of forming the prepared hole are reduced. Moreover, the inclination can be easily corrected even when the screw is fastened by an automatic screw fastening machine, and the axes of the prepared hole and the screw become substantially the same, therefore, the occurrence of a screw floating condition is reduced. Furthermore, the occurrence of breaking of excess thickness is prevented when the female screw is formed, and the occurrence of the female screw forming chips is also reduced. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention minimizes the generation of internal thread forming scraps such as peeling due to friction and breakage due to crushed surplus when screwing while forming a female thread with a tapping screw in the pilot hole of the work, and tapping with respect to the shaft center of the pilot hole The present invention relates to a screw tightening pilot hole that makes it possible to correct the inclination of a screw.

  When a tapping screw is screwed into a prepared pilot hole and tightened to the workpiece while forming a female screw, a 90 ° chamfer is usually formed on the inlet side of the prepared hole so that the tip of the tapping screw can be easily fitted. Thus, the tip of the tapping screw is positioned at the screw tightening point. When a tapping screw is tightened in this prepared hole, it is generally as shown in FIGS. 6 and 7, and the tapping screw 101 whose tip is fitted in the chamfered portion 111 on the inlet side of the prepared hole 110 is: When screw tightening is started, the screw thread 105 is screwed into the pilot hole 110 while forming a female screw. At this time, the chamfered portion 111 into which the screw thread 105 first bites rises while the surplus thickness 114 is deformed, but this is relatively thin due to the relationship between the chamfering angle and the thread angle at the initial stage of chamfering, It is gradually broken and peeled off from the surface of the prepared hole to form a female thread forming waste.

  In addition, the tapping screw is aligned with the axis of the pilot hole of the workpiece and is substantially on the same line, for example, as shown in FIG. 7, a vertical line extending from the top of the thread so as to be orthogonal to the leg ( When the follow-up side and advance side flank angle (α) of the screw thread 105 with respect to b) are equal and screwed in the same axial center state with respect to the prepared hole, the rising angle (A) of the surplus material 114 to be retreated is almost equal. The pilot hole 110 is continuously deformed along the flank surfaces 106 and 107 of the screw thread 105 to form a female screw thread, and a uniform female screw is formed. Due to the rise of this surplus, there is relatively little generation of molding waste in the pilot hole.

  On the other hand, as shown in FIG. 8, the tip of the tapping screw 101 fits into the chamfered portion 111 when the chamfered portion 110 is provided with a general chamfering, that is, a 90 ° chamfered portion 111. The leg 103 is wobbled at the beginning of screwing, and the center line of the tapping screw 101 is often inclined with respect to the center line of the pilot hole 110 of the work 108. For this reason, the screw 101 will bite into the pilot hole 110 in the inclined state in the initial stage of screwing in with respect to the pilot hole 110 of the workpiece 108. For example, as shown in FIG. In the case of the equiangular thread 105 having the same flank angle (α), the vertical line (A) extending from the apex of the thread 105 so as to be orthogonal to the axis of the pilot hole 110 and the follower side and advancing side flank surfaces 107, 106. The angles formed by the two are (β) and (γ), respectively, and the rising of the surplus 114 when the pilot hole is formed by the leading flank surface 106 is the rising angle (B). On the other hand, A> B, and the surplus 114 is easily collapsed and easily peeled off. In addition, when screwed in an inclined state, molding scraps are likely to be generated, and even if the screw reaches a predetermined screw tightening torque, it is often not screwed completely and becomes a screw floating state.

  In order to solve such problems, many solutions have been considered recently, and for example, those disclosed in Japanese Patent Application Laid-Open No. 2007-187305 are being used. As shown in FIG. 10, the inclination of the tapping screw 201 with respect to the shaft center of the pilot hole 210 is suppressed to a small level, and an abnormal increase in screwing torque when screwed in an inclined state, or the pilot hole 210 is pushed wide. And the occurrence of cracks in the boss 208 can be prevented, and even if the tapping screw 201 is repeatedly screwed, the screwing start position does not always change, and the female screw portion formed in the pilot hole 210 is destroyed. A pilot hole shape that does not occur is obtained. For this purpose, the pilot hole-shaped inlet portion 211 is formed to have a large diameter at the height of one pitch of the thread 205 of the tapping screw 201, the bottom surface of the large diameter portion is spirally inclined, and the inclination angle of the spiral inclined surface is increased. Is formed in a shape equal to the inclination angle (corresponding to the lead angle) of the thread 205 of the tapping screw 201.

JP 2007-187305 A

  In a pilot hole having such a shape, the inlet portion of the pilot hole is inclined at an angle equal to the inclination angle of the screw thread, so that the screw thread of the tapping screw at the time of screwing moves along the axis of the pilot hole. However, it is necessary to incline the bottom surface of the entrance of the workpiece into the pilot hole by the inclination angle of the thread as described above. For this reason, the processing has become complicated and the cost has increased. Also, when using screws with different tapping screw pitches, the angle of inclination of the screw thread also changes, so the shape of the pilot hole must be changed to match this angle, and each time the angle of inclination is adjusted to match the tapping screw. Need to change. Furthermore, by forming the bottom surface of the large-diameter portion on the inclined surface of the pilot hole entrance that matches the lead angle of the screw in this way, the cost increases and it is not suitable for use in an inexpensive product. On the other hand, in order to reduce the cost of the product, the conventional pilot hole, that is, the configuration in which the chamfer at 90 ° is chamfered at the inlet of the pilot hole, the screw so that the tapping screw becomes the same axis with respect to the axis of the pilot hole at the beginning of screwing Therefore, it is necessary to provide auxiliary means such as arranging an inclination correction means in the initial stage of screw tightening, and there is still a problem that equipment such as an automatic screw tightener is still expensive.

  The object of the present invention is to eliminate such problems, reduce the generation of internal thread forming scraps when screwed into the prepared hole of the tapping screw, and make it possible to easily correct the inclination of the tapping screw with respect to the prepared hole. It is to obtain a pilot hole for screw tightening.

  An object of the present invention is a pilot hole 10 to be screwed in while a female screw is formed by the tapping screw 1, and a straight having an inner diameter slightly larger than the outer diameter of the tapping screw 1 screwed into the inlet side. An inlet portion 11 having a shape is formed, and a female screw portion 12 that is smaller than the outer diameter of the screw thread of the tapping screw 1 and is threaded while the screw thread 5 of the tapping screw 1 forms a female screw is provided behind the inlet portion 11. A screw tightening pilot hole in which a tapered hole-shaped guide hole portion 13 having an angle corresponding to the taper angle (θ) of the tip thread 5 of the tapping screw 1 is formed between the inlet portion 11 and the female screw portion 12. Achieved by providing.

  In the screw tightening pilot hole, the entrance portion has a length corresponding to one pitch of the screw 1 into which the screw is screwed or less, and in this way, at the initial stage of screw tightening, Even if the leg part enters the pilot hole with an inclination, the inclination is corrected at the entrance part, so that it is possible to easily correct the inclination of the initial tapping screw by simply operating the driver bit. .

  According to the present invention, there is no need to form an inclined bottom surface with an inclination angle corresponding to the lead angle of the thread of the leg portion of the tapping screw, and man-hours necessary for forming the inclined bottom surface of the prepared hole are not required. The overall cost of preparing the pilot hole is reduced. Further, complicated machining for forming such an inclined bottom surface is not required, and the pilot hole machining can be easily performed. Further, even if the pitch of the tapping screw is changed, this pilot hole is not related to the pitch of the screw, so that it is not necessary to consider the pitch of the tapping screw used as the pilot hole setting condition. In addition, since it is not necessary to consider the pilot hole setting conditions, it can be used for any product, and the present invention is adopted in place of the conventional chamfering of the pilot hole to be chamfered by 90 °. It is easy to adopt without any restrictions. On the other hand, by adopting the present invention, the inclination of the tapping screw at the initial stage of screwing can be easily corrected as compared with the conventional chamfered pilot hole shape. The inclination can be corrected, and no special means for correcting the inclination is required. Therefore, the cost required for equipment machines such as automatic screwing machines is also reduced.

  In addition, since the tip tapered portion of the tapping screw and the guide hole portion of the pilot hole have substantially the same inclination angle, when the tapping screw is fitted into the pilot hole, the pilot hole and the screw have substantially the same axis. There is no longer any screwing in which the screw is inclined with respect to the pilot hole, and this reduces the occurrence of screw floating when the screw tightening is completed. Furthermore, since the rising angle of the surplus resulting from the formation of the female thread in the initial stage of screwing is increased, the surplus thickness is not easily broken, and therefore, there is a specific effect such as the reduction of the generation of internal thread molding waste. can get.

It is a principal part sectional front view showing an embodiment of the invention. It is a front view of the tapping screw screwed into the present invention. It is principal part sectional drawing which shows the time of the screwing start of a tapping screw. FIG. 4 is a cross-sectional view of an enlarged main part of FIG. It is an expanded principal part sectional view which shows the fitting state of the pilot hole of this invention, and a tapping screw. It is principal part sectional drawing which shows the screwing start state of the prior art example of this invention. It is an expanded principal part sectional drawing of FIG. It is an expanded principal part sectional view which shows the fitting state of the pilot hole of a prior art example, and a tapping screw. It is an expanded principal part sectional view which shows the diagonal tightening state of a prior art example. It is a partial cross section front view which shows another prior art example.

  The best mode for carrying out the present invention will be described below with reference to FIGS. In FIG. 2, 1 is a tapping screw comprising a head 2 and a leg 3 formed integrally therewith. The head 2 of the screw 1 is formed with a cross hole-shaped drive hole 4 that engages with a driver bit (not shown) when the screw is tightened. The screw thread 5 is formed in a spiral shape. The tip end side of the leg portion of the tapping screw 1 has a shape in which the screw thread height gradually decreases as it reaches the tip end, that is, the leg so that it can be easily fitted into the prepared hole 10 formed in the workpiece 8. The appearance of the tip of the portion 3 is a tapered shape that is inclined by an angle (θ).

  In this embodiment, the thread 5 of the leg 3 is formed by a leading flank angle formed between a perpendicular line (a) from the axis of the screw 1 and each of the leading flank surface 6 and the trailing flank surface 7. The follower side flank angle is an equal angle (α), and if the axial center is not inclined with respect to the pilot hole 10 to be screwed in while the female screw is formed by the tapping screw 1, the female screw formed at the time of screwing is also the same. It is formed in a square mountain shape.

  On the other hand, the pilot hole 10 formed in the workpiece 8 has a shape as shown in FIG. 1, and the diameter of the outer diameter of the leg portion of the tappin screw 1 is larger on the inlet side of the pilot hole 10 into which the tappin screw 1 is screwed. A straight inlet portion 11 having a large hole diameter is formed. The inlet portion 11 has an inner diameter slightly larger than the outer diameter of the tapping screw 1 screwed into the pilot hole 10. For example, the outer diameter of the tapping screw 1 is a numerical value obtained by subtracting the effective diameter from the outer diameter of the tapping screw 1. A larger inner diameter may be used. Specifically, the inner diameter is about 0.1 to 0.2 mm larger than the outer diameter of the thread. In addition, the depth of the inlet portion 11 is normally set to a length corresponding to one pitch of the screw 1 screwed into the pilot hole 10 or a length less than this. The inclination of the screw 1 generated when the leg portion 3 is fitted in the prepared hole 10 is reduced. That is, even if the leg portion 3 of the screw 1 enters the pilot hole 10 at an angle, the amount of inclination is suppressed at the inlet portion 11, so that the inclination of the tapping screw 1 at the initial stage of screw tightening can be easily performed only by operating the driver bit. Can be corrected.

  Further, a female screw portion 12 having a diameter smaller than the outer diameter of the screw thread of the tapping screw 1 and screwed into the screw thread 5 of the tapping screw 1 while forming a female screw is provided behind the inlet portion 11. A guide hole portion 13 having a tapered hole shape is formed between the portion 12 and the tip screw thread 5 of the tapping screw 1 so as to be inclined at an angle corresponding to the tapered angle (θ). Yes. This angle (θ) is generally between 10 ° and 40 °. As described above, the pilot hole 10 according to the embodiment of the present invention includes the inlet portion 11, the guide hole portion 13, and the female screw portion 12. However, the inlet portion 11 in this configuration is not necessarily required, and a tapping screw is used. By aligning the tip of 1 with the guide hole 13, the axial center of the pilot hole 10 and the axial center of the screw 1 can be sufficiently matched without the entrance 11.

  When the tapping screw 1 is fitted into the workpiece 8 after the prepared screw hole 10 for screw tightening is formed in advance in the workpiece 8, the tip of the leg portion 3 of the tapping screw 1 as shown in FIGS. Enters until it contacts the guide hole 13 of the pilot hole 10. When the tip portion comes into contact with the guide hole portion 13, the tapping screw 1 is substantially on the same axis as the pilot hole 10, and subsequently, a screw is driven by a driver bit (not shown) so that the screw 1 is a female screw. And is screwed into the pilot hole 10. At this time, the screw thread 5 starts to bite into the guide hole portion 13 and the surplus meat 14 starts to rise. Since the taper angle of the guide hole portion 13 is slight, the bulge is larger than the conventional surplus thickness and close to an obtuse angle, and the thickness is large, so that the surplus thickness 14 is peeled off or cut during the screwing operation. This phenomenon is reduced. Thereby, generation | occurrence | production of internal thread shaping waste reduces.

  In this embodiment, the leading flank angle (α) and the trailing flank angle (α) are equal isometric mountains, but the leading flank angle is large and the trailing flank angle is small. Even in the case of the thread 3 of the screw 1, the leading flank angle to which a large pressure is applied during screwing is the same size as the equiangular mountain. The same action as that of the equiangular thread 5 can be obtained.

  Further, as shown by the solid line in FIG. 5, when the tapping screw 1 is inclined at a predetermined angle (ワ ー ク) with respect to the axis of the pilot hole 10 of the workpiece 8, the tapping screw 1 is tapped into the guide hole 13. The operator can operate the driver bit in a state where the tip of the screw 1 is in contact and the tip of the screw 1 is engaged with the drive hole 4 of the head 2 of the screw 1, so that the screw 1 in the inclined state is connected to the two-dot chain line in FIG. That is, it can correct | amend along the axial center of the pilot hole 10, and the diagonal fastening of the screw 1 is eliminated.

  The present invention is suitable for eliminating the occurrence of oblique tightening in a screw tightening operation in which a female screw is formed with a tapping screw 1 in a pilot hole 10 formed in the work 8, and is not caused by poor screw tightening to the work 8. By improving the reduction of non-defective products, it can be applied to improve product quality.

DESCRIPTION OF SYMBOLS 1 Tapping screw 2 Head 3 Leg 4 Drive hole 5 Thread 6 Advance side flank surface 7 Follow-up side flank surface 8 Workpiece 10 Pilot hole 11 Inlet part 12 Female thread part 13 Guide hole part 14 Extra space

Claims (2)

  Straight hole (10) of a work (8) to be screwed in while a female screw is being formed by the tapping screw (1), and having an inner diameter slightly larger than the outer diameter of the tapping screw to be screwed into the inlet side And a female screw portion (12) into which the screw thread (5) of the tapping screw is screwed while forming a female screw having a diameter smaller than the outer diameter of the screw thread of the tapping screw. Moreover, a screw having a tapered hole-shaped guide hole portion (13) having an angle corresponding to the taper angle (θ) of the tip thread of the tapping screw formed between the inlet portion and the female screw portion. Pilot hole for tightening.   2. The screw tightening pilot hole according to claim 1, wherein the depth of the inlet portion is equal to or less than a length corresponding to one pitch of a screw to be screwed.

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