Fastener

BACKGROUND OF THIS INVENTION

1. Field of this invention

This invention relates to a fastener and relates particularly to a fastener allowing the head to fit flush with the workpiece to thereby ensure a perfect evenness and increase the fastening effect after the drilling operation is done.

2. Description of the Related Art

Referring to <figref idref="f0001">Figs. <b>1</b></figref> and <figref idref="f0002"><b>2</b></figref>, a conventional screw <b>1</b> includes a shank <b>12</b>, a head <b>11</b> formed at one end of the shank <b>12</b>, a drilling portion <b>13</b> formed at the other end of the shank <b>12</b>, and threads <b>14</b> spirally disposed on the shank <b>12</b>. The head <b>11</b> has a top surface <b>111</b> and a conical underside <b>112</b> extending downwards from the top surface <b>111</b>. Spaced apart ribs <b>113</b> protrude from the underside <b>112</b> and extend fully from the top surface <b>111</b> to the shank <b>12.</b> Accordingly, when the drilling portion <b>13</b> punctures a workpiece <b>2</b> with fibers and rotates the head <b>11</b> with a tool (not shown), the threads <b>14</b> keep drilling into a bore <b>21</b> and cut fibers. When the underside <b>112</b> touches the workpiece <b>2</b>, the ribs <b>113</b> cut fibers and then the head <b>11</b> engages with the workpiece <b>2.</b>

Because the workpiece <b>2</b> is formed with resilient wooden fibers, the spaced apart ribs <b>113</b> can only lift up the fibers but cannot break the fibers into chips completely. This incurs a poor cutting effect. Burrs caused by the ejected fibers may also stick out from the surface of the workpiece <b>2</b> when the head <b>11</b> is gradually cutting its way into the workpiece <b>2</b>. The screw <b>1</b> does not provide any special arrangement to overcome the accumulation of the burrs, so the head <b>11</b> cannot fit flush with the surface of the workpiece <b>2</b> after the head <b>11</b> completes the drilling operation, and the fastening effect of the screw <b>1</b> is not good. Thus, the screw still needs improvement.

SUMMARY OF THIS INVENTION

The object of this invention is to provide a fastener whose head can lie flush with the surface of the workpiece efficiently to promote the evenness after the drilling operation is done and increase the effect of fastening the fastener in position.

The fastener of this invention includes a head, a shank extending axially from the head and providing a drilling portion opposite to the head, and a threaded portion spirally disposed on the shank. The head has a top face and a conical bottom face extending from the top face to the shank. The head includes a plurality of cutting portions formed on the bottom face, a plurality of cutting ribs protruding from the bottom face, and a plurality of accommodation rooms formed between the plurality of cutting portions and the cutting ribs. Each of the cutting portions extends from the top face towards the shank and includes a projecting blade formed circumferentially of the top face at an outer edge thereof and extending in the direction of the shank, an adjoining wall and a flank wall respectively connected to the projecting blade and a cutting edge formed at a junction of the adjoining wall and the flank wall. The plurality of cutting ribs project from the bottom face and extend radially relative to the shank. Each of the cutting ribs has two rib walls protruding from the bottom face and meeting at a rib edge. Accordingly, the cutting ribs help cut unbroken fibers coming from the threaded portion, and the cutting portions continue scraping the cut material off to enhance the cutting ability and reduce the drilling resistance. The accommodation rooms receive part of the cut material to provide a firm engagement between the head and the workpiece. Burrs or a bulge produced during the drilling operation can be fully pressed down by the projecting blade and captured within a bore of the workpiece to allow the head to lie flush with the surface of the workpiece and thus attain a good evenness, thereby increasing the drilling efficiency and the fastening effect.

Preferably, in one embodiment, at least one cutting rib extends to be directed at a corresponding one of the cutting portions. In another embodiment, the cutting ribs extend respectively to be directed at part of the cutting portions so that the accommodation room can be extensively formed from the cutting portion to the shank between two adjacent cutting ribs to provide an enlarged space for receiving more chips.

Preferably, the projecting blade decreases progressively in the direction of the shank, and concurrently the adjoining wall extends from the cutting edge of one cutting portion to the flank wall of another adjacent cutting portion to allow the cutting portions to connect one after another.

Preferably, the threaded portion includes a first thread section spirally disposed on the drilling portion, a second thread section following the first thread section and formed in a wavy arrangement, and a third thread section following the second thread section. It is preferable that the second thread section has a second maximum outer diameter smaller than a third maximum outer diameter of the third thread section.

Preferably, threads of the second thread section are each provided with a plurality of notches.

Preferably, a helical portion can be formed between the threaded portion and the head to attain an anti-loosening effect.

Preferably, the rib walls of the cutting ribs are curved. It is also preferable that the adjoining wall is a curved wall to enlarge the space for receiving more chips.

BRIEF DESCRIPTION OF THE DRAWINGS

<ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">Fig. 1</figref> is a schematic view showing a conventional screw;</li><li><figref idref="f0002">Fig. 2</figref> is a bottom plan view taken on line A-A in <figref idref="f0001">Fig. 1</figref>;</li><li><figref idref="f0003">Fig. 3</figref> is a perspective view showing one variation of a first preferred embodiment of this invention;</li><li><figref idref="f0003">Fig. 4</figref> is an enlarged view showing the head of <figref idref="f0003">Fig. 3</figref>;</li><li><figref idref="f0004">Fig. 5</figref> is a bottom plan view taken on line B-B in <figref idref="f0003">Fig. 3</figref>;</li><li><figref idref="f0005">Fig. 6</figref> is a perspective view showing a further variation of the first preferred embodiment of this invention;</li><li><figref idref="f0005">Fig. 7</figref> is an enlarged view showing the head of <figref idref="f0005">Fig. 6</figref>;</li><li><figref idref="f0006">Fig. 8</figref> is a bottom plan view taken on line C-C in <figref idref="f0005">Fig. 6</figref>;</li><li><figref idref="f0007 f0008 f0009">Figs. 9 to 11</figref> are schematic views showing the fastener of this invention in use;</li><li><figref idref="f0010">Fig. 12</figref> is a front elevational view showing a second preferred embodiment of this invention;</li><li><figref idref="f0010">Fig. 12A</figref> is an enlarged view of <figref idref="f0010">Fig. 12</figref>;</li><li><figref idref="f0011">Fig. 13</figref> is a front elevational view showing a third preferred embodiment of this invention; and</li><li><figref idref="f0011">Fig. 13A</figref> is an enlarged view of <figref idref="f0011">Fig. 13</figref>.</li></ul>

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to <figref idref="f0003 f0004">Figs. <b>3</b> to <b>5</b></figref>, a fastener <b>3</b> of a first preferred embodiment of this invention includes a head <b>31</b>, a shank <b>32</b> extending axially from the head <b>31</b> and providing a drilling portion <b>33</b> opposite to the head <b>31</b>, and a threaded portion <b>34</b> spirally disposed on the shank <b>32</b>. The drilling portion <b>33</b> can be formed with a sharp point (illustrated as an example) or a drilling tip with a groove or grooves.

The head <b>31</b> has a top face <b>311</b> and a bottom face <b>312</b> extending from the top face <b>311</b> to the shank <b>32</b> and formed in a cone shape. On the bottom face <b>312</b> are formed a plurality of cutting portions <b>313</b>, a plurality of cutting ribs <b>314</b> protruding from the bottom face <b>312</b> and extending radially relative to the shank <b>32</b>, and a plurality of accommodation rooms <b>315</b> formed between the cutting portions <b>313</b> and the cutting ribs <b>314</b>. Each cutting portion <b>313</b> extends circumferentially of the top face <b>311</b> towards the shank <b>32</b>. It is preferable that the cutting portion <b>313</b> extends from the top face <b>311</b> and terminates short of the shank <b>32</b>. In addition, each cutting portion <b>313</b> includes a projecting blade <b>3131</b> formed circumferentially of the top face <b>311</b> at an outer edge thereof and extending in the direction of the shank <b>32</b>, an adjoining wall <b>3132</b> and a flank wall <b>3133</b> respectively connected to the projecting blade <b>3131</b>, and a cutting edge <b>3134</b> formed at a junction where the walls <b>3132</b>, <b>3133</b> meet. In the preferred embodiments, it is preferable that each blade <b>311</b> decreases progressively from the top face <b>311</b> and becomes tapered in the direction of the shank <b>32</b>. Concurrently, the adjoining wall <b>3132</b> extends from the cutting edge <b>3134</b> of one cutting portion <b>313</b> to the flank wall <b>3133</b> of another adjacent cutting portion <b>313</b>. For example, <figref idref="f0003">Figs. <b>4</b></figref> and <figref idref="f0004"><b>5</b></figref> show that the flank wall <b>3131</b> has a bottom edge opposite to the cutting edge <b>3134</b>, and particularly the adjoining wall <b>3132</b> can extend from the cutting edge <b>3134</b> of one cutting portion <b>313</b> to the bottom edge of another adjacent flank wall <b>3131</b>. Thus, the adjoining walls <b>3132</b> are connected one after another, namely are continuously connected. The adjoining wall <b>3132</b> may have a flat surface or a curved surface. It is adopted in the preferred embodiments that the adjoining wall <b>3132</b> is curved, preferably concavely curved as shown, and the cutting edge <b>3134</b> can also be inclined because of the curved adjoining wall <b>3132</b>.

The cutting ribs <b>314</b> are spaced from each other and extend radially relative to the shank <b>32</b>. For example, one end of the cutting rib <b>314</b> may be connected to the shank <b>32</b> (shown in <figref idref="f0003">Fig. <b>4</b></figref>) or may be close to but not exactly connected to the shank <b>32</b>. As an example in the preferred embodiments, <figref idref="f0003 f0004">Figs. <b>3</b> to <b>5</b></figref> illustrate the cutting rib <b>314</b> starting from the shank <b>32</b>. Further, each cutting rib <b>314</b> has two rib walls <b>3141</b> protruding from the bottom face <b>312</b> and meeting at a rib edge <b>3142</b>. The rib wall <b>3141</b> can be curved to benefit the cutting operation.

The cutting ribs <b>314</b> can extend in a radial direction to be directed at corresponding ones of the cutting portion <b>313</b>. For example, as shown in <figref idref="f0003">Figs. <b>3</b> and <b>4</b></figref>, one end of at least one cutting rib <b>314</b> extends from the shank <b>32</b>, and the other end thereof reaches a corresponding one cutting portion <b>313</b>. It may be possible that the other end of the cutting rib <b>314</b> stops at a point near the cutting portion <b>313</b> (not shown) . Further, the other end of the cutting rib <b>314</b> can touch any wall of the cutting portion <b>313</b>, and it is shown as an example in <figref idref="f0004">Fig. <b>5</b></figref> that each cutting rib <b>314</b> reaches each adjoining wall <b>3132</b>. Alternatively, as shown in <figref idref="f0005">Figs. <b>6</b> and <b>7</b></figref>, the cutting ribs <b>314</b> extend respectively to be directed at part of the cutting portions <b>313</b>. This shows that when one ends of the cutting ribs <b>314</b> extend radially from the shank <b>32</b>, the other ends thereof extend to or toward part of the cutting portions <b>313</b> so that between every two adjacent cutting ribs <b>314</b> is defined the accommodation room <b>315</b> extensively formed from the cutting portion <b>313</b> to the shank <b>32</b> to enlarge the space (as shown in <figref idref="f0006">Fig. <b>8</b></figref>). Likewise, the cutting ribs <b>314</b> each reach any wall of the corresponding cutting portions <b>313</b>, e.g. the adjoining wall <b>3132</b>, as shown in <figref idref="f0006">Fig. <b>8</b></figref>, or terminate short of the cutting portions <b>313</b> (not shown) . The arrangement of <figref idref="f0005">Fig. <b>6</b></figref> will be described as an example in the following operation. Furthermore, the curved shape of the adjoining wall <b>3132</b> helps enlarge the space of the accommodation room <b>315</b>.

In this preferred embodiment, a helical portion <b>35</b> can be formed on the shank <b>32</b>, preferably formed between the threaded portion <b>34</b> and the head <b>31</b>. The helical portion <b>35</b> is inclined by a leading angle different from a spiral angle of the threaded portion <b>34</b> to follow the threaded portion <b>34</b> and continue the drilling action.

Referring to <figref idref="f0007">Fig. <b>9</b></figref>, when a driving tool (not shown) is engaged with the head <b>31</b> and a driving torque is added to the fastener <b>3</b>, the drilling portion <b>33</b> and the threaded portion <b>34</b> start drilling into a workpiece <b>4</b> such as a hardwood to form a bore <b>41</b> on a surface of the workpiece <b>4</b> and concurrently cutting fibers of the workpiece 4 into chips to thereby drill the shank <b>32</b> into the workpiece <b>4</b> quickly. As the helical portion <b>35</b> follows the drilling track of the threaded portion <b>34</b> and enters the workpiece <b>4</b>, the helical portion <b>35</b> engages with an inner wall of the workpiece <b>4</b> firmly because of its leading angle different from the spiral angle of the threaded portion <b>34</b> and the elasticity of the cut materials. This arrangement allows the chips to be inwardly pressed and attains an anti-loosening effect. When head <b>31</b> advances and touches the surface of the workpiece <b>4</b>, the rib edges <b>3142</b> of the cutting ribs <b>314</b> subject the fibers left around the bore <b>41</b> to a cutting operation. In other words, the rib edges <b>3142</b> cuts and severs unbroken fibers escaping from the threaded portion <b>34</b> into small chips firstly and also enlarges the bore <b>41</b> progressively to become a countersunk hole, as shown in <figref idref="f0008">Fig. <b>10</b></figref>. The cutting edges <b>3134</b> follow the rib edges <b>3142</b> to continue cutting and shaving chips. Thus, the cutting edges <b>3134</b> cooperate with the rib edges <b>3142</b> to attain a double cutting effect. This ensures that the fibers are well cut and scraped off, prevents the head <b>31</b> from being subjected to the undue entanglement of the fibers, and prevents a drilling resistance caused by the entanglement of the fibers.

When the head <b>31</b> continues the cutting action, redundant chips run gradually along the adjoining wall <b>3132</b> and are ejected from the workpiece <b>4</b> to prevent an undue accumulation of chips from pressurizing the workpiece <b>4</b>, reduce the resistance and prevent the workpiece <b>4</b> from cracking. The enlarged space of the accommodation room <b>315</b> also receives more chips to increase the engagement between the fastener <b>3</b> and the workpiece <b>4</b>. As shown in <figref idref="f0007">Fig. <b>9</b></figref>, it is possible that when the head <b>31</b> is gradually screwed into the bore <b>41</b>, remnants such as burrs may be produced because of the fibers or chips forced out of the workpiece <b>4</b> during the rotation of the fastener <b>4</b> or at least a bulge may stick out from the surface of the workpiece <b>4</b>. The extension of the projecting blade <b>3131</b> presses the burrs and the bulge downwards to make them move down back into the bore <b>41</b> of the workpiece <b>4</b>, as arrowed in <figref idref="f0008">Fig. <b>10</b></figref>. Therefore, the top face <b>311</b> of the head <b>31</b> lies flush with the surface of the workpiece <b>4</b>, as shown in <figref idref="f0009">Fig. <b>11</b></figref>, to promote the evenness after the head <b>31</b> completes the entire drilling action and reaches its countersunk position and to increase the engagement between the fastener <b>3</b> and the workpiece <b>4</b>.

<figref idref="f0010">Fig. <b>12</b></figref> shows a second preferred embodiment of this invention whose correlated elements are the same as the first preferred embodiment. This embodiment is characterized in that the threaded portion <b>34</b> includes a first thread section <b>341</b> spirally disposed on the drilling portion <b>33</b>, a second thread section <b>342</b> following the first thread section <b>341</b>, and a third thread section <b>343</b> following the second thread section <b>342</b>. Preferably, the three thread sections can be connected in sequence to construct a single convolution, as shown. Particularly, the second thread section <b>342</b> provides a thread crest lying like waves rising and falling, as shown in <figref idref="f0010">Fig. <b>12A</b></figref>. Further, the second thread section <b>342</b> has a second maximum outer diameter <b>D2</b> smaller than a third maximum outer diameter <b>D3</b> of the third thread section <b>343</b> and larger than a first maximum outer diameter <b>D1</b> of the first thread section <b>341</b>.

The cooperation between the three thread sections with different outer diameters benefits a good drilling and fastening effect. Specifically, the first thread section <b>341</b> assists the drilling portion <b>33</b> in performing a pilot drilling operation. The second thread section <b>342</b> moves along a drilling track created by the first thread section <b>341</b> and uses its wavy crest to continue cutting. In other words, the wavy second thread section <b>342</b> increases cutting points to enhance the cutting capability and reduce resistance. The wavy arrangement also benefits removal of redundant chips and allows a certain amount of chips to stay among the second thread section <b>342</b> to thereby attain an anti-loosening effect and prevent cracks in the workpiece. The second maximum outer diameter <b>D2</b> larger than the first maximum outer diameter <b>D1</b> also helps a reaming action and allows the chips to move upwards to the third thread section <b>343</b>. When the third thread section <b>343</b> with the third maximum outer diameter <b>D3</b> is gradually drilled into the workpiece, partial chips coming from the second thread section <b>342</b> can be pressed inwards to enhance the engagement between the third thread section <b>343</b> and the workpiece (not shown in <figref idref="f0010">Fig. <b>12</b></figref>). Therefore, the threaded portion <b>34</b> with different types of thread sections <b>341</b>, <b>342</b>, <b>343</b> allows the fastener <b>3</b> to be quickly drilled into the workpiece, reduces resistance during the drilling operation, and contributes to improved forces preventing the fastener <b>3</b> from being pulled out of the workpiece. By this arrangement, an undue accumulation of chips is avoided, and the workpiece such as a hardwood does not crack easily. This also benefits the effect of fitting the head <b>31</b> level with the workpiece and helps a stable fastening effect.

<figref idref="f0011">Fig. <b>13</b></figref> shows a third preferred embodiment of this invention whose correlated elements are the same as the second preferred embodiment. This embodiment is characterized in that threads of the second thread section <b>342</b> are each provided with a plurality of notches <b>3421</b>, and the notches <b>3421</b> are formed along the wavy form of the second thread section <b>342</b> to be open in different directions. These notches 3421 can be in a continuous connection to become serrated as shown in <figref idref="f0011">Fig. <b>13A</b></figref>, or be spaced from each other. Accordingly, the notches <b>3421</b> provides multiple cutting points to increase the cutting ability of the threaded portion <b>34</b>, speed up the cutting and drilling operation and help removal of chips. The friction resistance and torque generated during the drilling operation can be greatly reduced. Cut materials like chips can also be received within the notches <b>3421</b> to enhance the engagement between the fastener <b>3</b> and the workpiece (not shown in <figref idref="f0011">Fig. <b>13</b></figref>), thereby increasing the ability of resisting the pulling-out force. This also benefits the effect of fitting the head <b>31</b> level with the workpiece and helps a stable fastening effect.

To sum up, this invention takes advantages of cutting portions and cutting ribs formed on the bottom face to subject unbroken fibers coming from the threaded portion to a continuous cutting and shaving action, thereby reducing the drilling resistance. Accommodation rooms formed between the cutting portions and the cutting ribs also receive sufficient chips to increase the engagement between the fastener and the workpiece. Remnants, burrs and the bulge sticking out from the workpiece can be fully pressed down into the bore by the projecting blade formed circumferentially of the top face when the head is cutting its way into the workpiece. After the head is completely screwed into the workpiece, the entire head lies flush with the surface of the workpiece to promote the evenness, and the fastening effect is increased.

While the embodiment of this invention is shown and described, it is understood that further variations and modifications may be made without departing from the scope of this invention.