Patent Description:
<FIG> illustrates an existing screw <NUM>. The screw <NUM> includes a head <NUM>, a shank <NUM> extending from the head <NUM>, a thread <NUM> extending helically around the shank <NUM>, and a tip end <NUM> extending from an end of the shank <NUM> opposite to the head <NUM>. To reduce the risk of cracks during drilling a wooden workpiece, the tip end <NUM> is formed with a V-shaped chip discharge groove <NUM> with a right-angled corner. The chip discharge groove <NUM> occupies one quarter of a cross sectional area of the screw <NUM> transverse to a central line (A) of the screw <NUM>.

During screwing the screw <NUM> into the wooden workpiece, through a torsional force applied to the head <NUM>, the tip end <NUM> is rotated to drill the wooden workpiece. However, the hollow space of the chip discharge groove <NUM> is too small to discharge cut chips efficiently. Thus, the thread <NUM> and the shank <NUM> driven by a high torsional force can impose excessive compression pressure to the wooden workpiece through the cut chips accumulated around the screw <NUM>, thereby cracking or damaging the wooden workpiece. In addition, the torsional force that is increased to drive the screw <NUM> can cause a hand injury to a user.

Therefore, one object of the disclosure is to provide a screw that can alleviate at least one of the drawbacks of the prior art.

The invention is a screw with the features of claim <NUM>.

Other features and advantages of the disclosure will become apparent in the following detailed description of the embodiments with reference to the accompanying drawings, of which:.

Only <FIG> shows an embodiment of the invention.

<FIG> illustrates a screw according to a first embodiment of the disclosure. The screw includes a head <NUM>, a shank <NUM>, a thread <NUM> and two chip discharge grooves <NUM>.

The shank <NUM> defines an axis (Z). The thread <NUM> helically extends around the shank <NUM>. In this embodiment, the shank <NUM> includes a main body <NUM> connecting the head <NUM> and a tip portion <NUM> connecting an end of the main body <NUM> opposite to the head <NUM>. The tip portion <NUM> is tapered. When the shank <NUM> is rotated by rotating the head <NUM>, the tip portion <NUM> and the thread <NUM> cooperate with each other to effect drilling and tapping.

As shown in <FIG>, the chip discharge grooves <NUM> are indented into the shank <NUM>. Each discharge groove <NUM> is inclined at an inclination angle (α) of between <NUM> and <NUM> degrees relative to the axis (Z). A depth of each chip discharge groove <NUM> is half an outer diameter of the thread <NUM>. At least one of the chip discharge grooves <NUM> extends in the tip portion <NUM> of the shank <NUM>. An upper one of the chip discharge grooves <NUM> has a width <NUM> to <NUM> times a width of a lower one of the chip discharge grooves <NUM> proximate to the tip portion <NUM> of the shank <NUM>. A distance between the chip discharge grooves <NUM> is greater than <NUM>. Orthogonal projections of the chip discharge grooves <NUM>, which are projected onto a plane extending along the axis (Z), overlap each other as shown by an overlapping region between two phantom lines in <FIG>. The distance between the two chip discharge groves <NUM> is designed depending on the inclination angle (α) and the outer diameter of the shank <NUM>. While two of the chip discharge grooves <NUM> are exemplified in this embodiment, the number of the chip discharge grooves <NUM> can be equal to or greater than <NUM>. When the number of the chip discharge grooves <NUM> is greater than <NUM>, at least two of the chip discharge grooves <NUM> are parallel with each other and are disposed on a same side relative to the axis (Z) of the shank <NUM>.

Noteworthily, when the depth of each chip discharge groove <NUM> is greater than half the outer diameter of the thread <NUM>, though the amount of chips discharged from the chip discharge grooves can be increased, the shank <NUM> is overcut and becomes thinned. This can affect the structural strength of the shank <NUM>. Even though the structural strength of the shank <NUM> may be enhanced by heat treatment in a post-processing procedure, the hardness of the shank <NUM> after the heat treatment will become excessive and thus increases the risk of brittle breakage. If the chip discharge groove <NUM> proximate to the tip portion <NUM> of the shank <NUM> has a depth smaller than half the outer diameter of the thread <NUM>, though the structural strength of the shank <NUM> is increased, the effect of discharging and receiving chips can be unsatisfactory.

Table <NUM> illustrates test results that compares the first embodiment with Controls <NUM> and <NUM>. Two chip discharge grooves in Control <NUM> are parallel with each other and inclined at an inclination angle smaller than <NUM> degrees; two chip discharge grooves in Control <NUM> are parallel with each other and inclined at an inclination angle greater than <NUM> degrees.

The test results in Table <NUM> reveals that, by optimizing the inclination angles of the chip discharge grooves, torsional forces required to screw in the screws of the disclosure are less than those required by Controls <NUM> and <NUM>. This is because the resistance against the screwing of the screw of the disclosure is reduced due to effective discharge of cut chips. In order to match with various sizes of screws and various types of wooden workpieces used in different fields, the width of the chip discharge grooves <NUM> may be adjusted to be cooperative with the inclination angle (α) that is optimized according to the disclosure. For example, when the thread <NUM> has the outer diameter of <NUM>, one of the chip discharge grooves <NUM> proximate to the tip portion <NUM> may have the width of between <NUM> and <NUM>. In general, a suitable width of the lower chip discharge groove <NUM> proximate to the tip portion <NUM> is half the outer diameter of the thread <NUM>. The width of the upper chip discharge groove <NUM> is designed to depend on the width of the lower chip discharge groove <NUM>. During drilling operation, because the torsional force required to drive the screw of the disclosure into a wooden workpiece is reduced, the risk of cracking or damaging the wooden workpiece is reduced.

<FIG> illustrates a screw according to a second embodiment of the disclosure, which has a structure generally similar to that of the first embodiment. However, in this embodiment, the screw further includes multiple sets of ribs <NUM>. Each set of the ribs <NUM> is disposed between two adjacent thread pitches of the thread <NUM>. As shown in <FIG>, the chip discharge grooves <NUM> cross some of the ribs <NUM> proximate to the tip portion <NUM> of the shank <NUM>. Adding multiple ribs <NUM> between the thread pitches in this embodiment optimizes the effect of enlarging hole, which can help reduction of the screwing resistance. Each rib <NUM> can be inclined relative to or parallel with the axis (Z) of the shank <NUM>. Further, each rib <NUM> can extend in a direction similar or opposite to that of the chip discharge grooves <NUM>. The direction of each rib <NUM> is not limited only to those shown in <FIG> and <FIG>. <FIG> illustrates that additional ribs <NUM> are disposed proximately to the head <NUM> so that the hole enlarging effect can be optimized further.

<FIG> illustrates a variant of the screw of the second embodiment. In this variant, each chip discharge groove <NUM> extends in a direction different from that of each chip discharge groove <NUM> shown in <FIG>. In addition, the ribs <NUM> extend in a direction opposite to that of the chip discharge grooves <NUM>.

<FIG> illustrates a screw according to a third embodiment of the disclosure, which has a structure generally similar to that of the first embodiment. However, in this embodiment, the tip portion <NUM> has two cutting faces <NUM> respectively disposed on two opposite sides of the axis (Z) of the shank <NUM>. The cutting faces <NUM> can function similarly to the chip discharge grooves <NUM> for reducing the torsional force. As shown in <FIG>, orthogonal projections of the chip discharge grooves <NUM>, which are projected onto a plane extending along the axis (Z), overlap each other (see the region between two upper phantom lines). In addition, one of the chip discharge grooves <NUM> proximate to the cutting face <NUM> has an orthogonal projection which is projected onto a plane extending along the axis (Z) and which overlaps an orthogonal projection of the cutting face <NUM> onto the same plane (see the region between two lower phantom lines). As shown in <FIG>, <FIG>, each cutting face <NUM> can have a configuration selected from a right angled configuration, a chamfered corner configuration, an oblique-angled configuration, and a rounded corner configuration. The cutting of each cutting face <NUM> begins from the main body <NUM> and extends to the tip portion <NUM> so that each cutting face <NUM> has one end directly connected to the main body <NUM>. <FIG> illustrate variants in that each cutting face <NUM> is completely formed in the tip portion <NUM>. In <FIG>, <FIG>and <FIG>, the orthogonal projections of the two chip discharge grooves <NUM> overlap each other. It is noted that the two chip discharge grooves <NUM> exemplified in each of <FIG>, <FIG> are processed at the same time using two cutters with different outer diameters. However, the two chip discharge grooves <NUM> may be varied in position and may be processed using identical cutters.

<FIG> illustrates a screw according to a fourth embodiment of the disclosure, which has a structure generally similar to that of the first embodiment. However, in this embodiment, the tip portion <NUM> has two cutting faces <NUM> respectively disposed on two opposite sides of the axis (Z) of the shank <NUM>; the chip discharge grooves <NUM> are disposed at two opposite sides of the shank <NUM> and respectively connect the cutting faces <NUM>. As shown in <FIG>, each cutting face <NUM> has a configuration selected from a right angled configuration, a chamfered corner configuration, an oblique-angled configuration, and a rounded corner configuration. Each cutting face <NUM> has one end directly connected to the main body <NUM>. In particular, <FIG> illustrates that the orthogonal projections of the two chip discharge grooves <NUM> overlap each other. Besides, one of the cutting faces <NUM> and one of the chip discharging grooves <NUM> respectively have orthogonal projections that are projected onto a plane extending along the axis (Z) and that overlap each other.

In addition, <FIG> illustrate that the cutting faces <NUM> are completely formed in the tip portion <NUM>. Noteworthily, the chip discharge grooves <NUM> disposed at two opposite sides of the shank <NUM> can be parallel or nonparallel.

<FIG> illustrates a screw according to a fifth embodiment of the disclosure. In this embodiment, the chip discharge grooves <NUM> are formed parallel in the main body <NUM> to facilitate processing and to reduce fabrication cost. Further, the tip portion <NUM> has a single cutting face <NUM>, and one of the chip discharge grooves <NUM> is directly connected to the cutting face <NUM>. As shown in <FIG>, <FIG>, the cutting face <NUM> and one of the chip discharge grooves <NUM> respectively have orthogonal projections that are projected onto a plane extending along the axis (Z) and that overlap each other.

<FIG> illustrates a screw according to a sixth embodiment of the disclosure, which has a structure generally similar to that of the third embodiment. However, in this embodiment, one of the chip discharge grooves <NUM> extends helically around the shank <NUM> and is connected to the cutting face <NUM>. As shown in <FIG>and <FIG>, because one of the chip discharge groove <NUM> extends helically around the main body <NUM>, it has a relatively long length and therefore can receive and discharge more chips. <FIG> and <FIG> illustrate that the two chip discharge grooves <NUM> extend helically around the main body <NUM>. <FIG> and <FIG> illustrate that the two chip discharge grooves <NUM> extend helically in opposite directions around the main body <NUM>.

<FIG> illustrates a screw according to a seventh embodiment of the disclosure, which has a structure generally similar to that of the first embodiment. However, one of the chip discharge grooves <NUM> is inclined at <NUM> degrees to the axis (Z), and the other one of the chip discharge grooves <NUM> is inclined at <NUM> degrees to the axis (Z). While the discharge grooves <NUM> are disposed on the same side relative to the axis (Z) of the shank <NUM> in this embodiment, they can be disposed opposite to each other with respect to the axis (Z).

Table <NUM> shows the results of tests that compares the seventh embodiment with Controls <NUM> and <NUM>. The tests demonstrate that the torsional forces required to screw in the screw of the seventh embodiment are much less than those of Controls <NUM> and <NUM>, and that the seventh embodiment has an excellent chip discharging ability. Noteworthily, although the chip discharge grooves <NUM> are nonparallel, as the inclination angles thereof fall between <NUM> and <NUM> degrees, the screw of the disclosure can still have satisfactory chip discharge performance.

<FIG> illustrate some cross sectional configurations of the chip discharge grooves <NUM>, which are a right angled configuration, a chamfered corner configuration, and an oblique-angled configuration.

Claim 1:
A screw comprising:
a head (<NUM>);
a shank (<NUM>) defining an axis (Z) and including a main body (<NUM>) connecting said head (<NUM>) and a tip portion (<NUM>) connecting an end of said main body (<NUM>) opposite to said head (<NUM>);
a thread (<NUM>) helically extending around said shank (<NUM>) to said tip portion (<NUM>);
characterized by
two chip discharge grooves (<NUM>) indented into said shank (<NUM>), said chip discharge grooves (<NUM>) being nonparallel and each inclined at an angle of between <NUM> and <NUM> degrees relative to the axis (Z);
wherein orthogonal projections of said chip discharge grooves (<NUM>), which are projected onto a plane extending along the axis (Z), overlap each other;
wherein said thread (<NUM>) and said chip discharge grooves (<NUM>) are inclined upward toward a same side of said shank (<NUM>);
wherein said two chip discharge grooves (<NUM>) are disposed on a same side relative to the axis (Z) of said shank (<NUM>); and
wherein one of said two of said chip discharge grooves (<NUM>) is inclined at an angle of <NUM> degrees, and the other one of said two chip discharge grooves (<NUM>) is inclined at an angle of <NUM> degrees.