BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front elevation of a blank for a self-drilling reaming screw to be manufactured herein;
FIG. 2 is a plan view of the blank;
FIG. 3 is a front elevation of the blank partially processed to have a reaming portion;
FIG. 4 is a side elevation of the partially processed blank;
FIG. 5 is a front elevation of the finished self-drilling reaming screw of the invention;
FIG. 6 is a front elevation of the finished screw that is being tightened in use, wherein relevant members are shown in cross section;
FIG. 7 is a front elevation of the finished screw that has been tightened in situ;
FIG. 8 is a cross section taken along the arrow line 8-8 in FIG. 7;
FIG. 9 is a front elevation of a further self-drilling reaming screw provided in another embodiment;
FIG. 10 is a front elevation of the further screw that has been tightened; and
FIG. 11 is a cross section taken along the arrow line 11-11 in FIG. 10.
THE PREFERRED EMBODIMENTS
Now some embodiments of the present invention will be described referring to the accompanying drawings.
FIGS. 1 to 5 are schemes showing a process for manufacturing a self-drilling reaming screw of the invention. As will be seen in FIGS. 1 and 2, a blank 1 for the screw is prepared using a header for processing a carbon steel rod or the like raw metallic material. The screw blank 1 has a columnar region 2 where a drill bit as well as a threaded portion (detailed below) are to be formed, and continuing from this region 2 is a non-threaded shank 3. A reaming portion (detailed below) will be formed around this non-threaded shank 3 whose upper end is shaped as a conical head 4. A recess 5 in the head 4 is for engagement with a driving tool. The non-threaded shank 3 has a diameter ‘B’ slightly or noticeably greater than diameter ‘A’ of the columnar region 2.
Next, a pair of reaming blades 6 will be formed by the pinch-pointing or the like method on the non-threaded shank 3, at its portion adjoining the columnar region 2. These blades 6 located diametrically opposite to each other do protrude in radial directions. A drill bit 7 will cooperate with a threaded portion 8 to provide a female-threaded hole 24 in a hard material 21 (see FIGS. 6 and 7). In order to enlarge this hole to give a guide hole 25 as discussed below, the circumscribed circle of a reaming portion composed of such blades 6 has a sufficient diameter ‘W’, with each blade having a sufficient thickness ‘T’.
Subsequently, the end of columnar region 2 will be pressed to give the drill bit 7 as shown in FIG. 5. Further, the threaded portion 8 is shaped by the rolling, thus providing a finished self-drilling reaming screw 10 of the invention.
The reaming portion 6 of self-drilling screw 10 has the diameter ‘W’ falling in a range from the outer diameter ‘d’ of threaded portion 8 and the outer diameter ‘D’ of head 4. The value of diameter ‘W’ is much closer to the first diameter ‘D’, and less close to the second one ‘d’. Thickness ‘T’ of the reaming blades 6 is great enough to protect them from breakage while reaming the large-diameter guide hole 25 in hard material 21. Thus, a rough hole will be bored first by the drill bit 7 piercing this material, and this hole is then tapped by the threaded portion 8 so as to provide a female-threaded hole 24. Upon enlargement of this hole 24 by means of reaming portion 6, the conical head 4 will be forced into a resultant enlarged guide hole 25 to such an extent that this head is not left projected from the surface of said material. In order to easily shape such reaming blades 6, the non-threaded shank 3 has a diameter ‘B’ greater than that ‘A’ of the columnar region 2. Also for the same purpose, a distance ‘P’ between the inner or basal ends of those blades 6 facing one another may preferably be about a half or less of the diameter ‘B’ of shank 3. This feature is advantageous in that the non-threaded shank 3 need not be made so extremely thick as compared with the columnar region 2, while ensuring desired values of ‘W’ and ‘T’. On the other hand, the screw's partial length ‘L’ from the top of its head 4 to the bottom of its reaming blades 6 is designed somewhat shorter than thickness ‘H’ of the hard material 21 being fastened (see FIGS. 6 and 7).
In an example case of the self-drilling reaming screw 10 whose threaded portion 8 has a nominal diameter of 4 mm, the diameter ‘A’ of columnar region 2 will be about 3.34 mm as the valley circle diameter of standard M4, and the diameter ‘B’ of non-threaded shank 3 will be about 3.83 mm as the valley circle diameter of standard M5. The reaming portion 6 will have a diameter ‘W’ of about 6.5 mm and a thickness ‘T’ of about 1.0 mm.
FIGS. 6 to 8 show the self-drilling reaming screw 10 in use, wherein the numeral 21 denotes a hard material such as a hardwood or a plywood board covered with a rigid surface layer. The further numeral 22 denotes a softer supporting member such as an aluminum plate or a thin steel plate to which the hard material 21 is to be fixedly attached.
In operation, the drill bit 7 of this screw 10 will pierce a rough hole 23 starting from the surface 21a of hard material 21. The threaded portion 8 will be forced towards the soft support 22 and tightened into the rough hole 23, thereby forming a female-threaded hole 24. As the reaming portion 6 subsequently expands the latter hole 24, it will become a larger-diameter guide hole 25 (of a diameter ‘W’) as shown in FIG. 6. With the drill bit 7 further advancing deeper, a rough hole 23 will be pierced also in and through the soft support 22. The threaded portion 8 will likewise be screwed into this rough hole 23 so as to tap and firmly engage with it. In such a fastened state of the screw 10, its conical head 4 is pressed in its entirety into the mouth of guide hole 25, as seen in FIG. 7. The head 4 is buried in the guide hole 25 so as not to protrude at all from the said surface 21a of hard material 21. The self-drilling reaming screw 10 thus firmly secures the hard material 21 to the soft support 22.
As illustrated in FIG. 8, the head 4 will have an acting surface (or fastening and seating surface) ‘S’ in contact with the hard material 21 when the tightening of the screw 10 is completed. This surface ‘S’ is of an annular configuration whose width depends on a difference between the diameter ‘D’ of head 4 and that ‘W’ of guide hole 25. By making the diameter ‘W’ of reaming portion 6 as large as possible and thus close to the diameter ‘D’, the contact area ‘S’ is rendered much smaller than the ordinary fastening seat of head 4. Due to this feature, the head 4 being pressed towards the interior of guide hole 25 of the hard material 21 can now be buried therein more easily. Because the distance ‘L’ between the top of head 4 and the bottom of reaming blades 6 is somewhat shorter than the thickness ‘H’ of hard material 21, these blades will stand apart from the soft support 22. The reaming portion 6 is thus inhibited from interfering with the support 22, lest the former should injure the latter.
FIGS. 9 to 11 show another embodiment of the invention, wherein a relatively thin hard material 31 is a hard plastics board. This board is reinforced with a glass fiber dispersed in a plastics matrix. The hard material 31 will be adjoined to a softer and thicker support 32 composed of the same or different plastics. A self-drilling reaming screw 30 used herein comprises a threaded portion 38, a pointed drill bit 37 and a conical head 34 continuing from said portion. The drill bit 37 is disposed at a distal end of threaded portion 38. Reaming blades 36 formed integral with a neck of the columnar body are adjacent to both the threaded portion 38 and conical head 34. These blades 36 protruding in radial directions are diametrically opposed one to another. Also in this case, diameter ‘W’ of such a reaming portion 36 is greater than diameter ‘d’ of threaded portion 38 but less than diameter ‘D’ of conical head 34. Such a large value of ‘W’ is much closer to ‘D’ and less close to ‘d’. Also similarly to the first embodiment, thickness ‘T’ of each blade 36 is made great enough not to be broken while reaming a large guide hole 35 in and through the hard material 31. However, the head 34 of this embodiment has at its annular spot-facing seat some countersinking blades 39. By virtue of this feature, the head 34 can be easily pressed into and buried in the guide hole 35.
The pointed drill bit 37 of the self-drilling screw 30 will bore a rough hole in the hard material 31, starting from its top surface 31a. The threaded portion 38 thrust towards the soft support 32 into the rough hole will deform it to a female-threaded hole. The reaming portion 36 will enlarge the latter hole to give a large-diameter guide hole (of a diameter ‘W’). With the drill bit 37 further advancing deeper, another rough hole will be pierced also in the soft support 32. The threaded portion 38 tightened into and through this hole works to fix this screw 30 to the support 32, in a manner shown in FIG. 10. The conical head 34 thus pressed into the guide hole 35 will not have its top projecting up out of the top 3 la of the hard material 31 thus firmly adjoined to said support 32. The countersinking blades 39 on the seating face of head 34 will serve to enlarge the rim of guide hole 35, to thereby facilitate the screwing of the head into this hole.
As shown in FIG. 11 and similarly to the first embodiment, the head 34 has a seating surface ‘S’ in contact with the hard material 31 when the tightening of the screw 30 is completed. This annular surface ‘S’ has a width depending on a difference between the diameter ‘D’ of head 34 and that ‘W’ of guide hole 35. By making largest possible the diameter ‘W’ of reaming portion 36, the contact area ‘S’ is rendered much smaller than the ordinary fastening seat of head 34. Thus, the head 34 being pressed into the guide hole 35 of hard material 31 can be buried therein more easily.
Patent Application
20070292235
