Patent Description:
Fasteners, particularly screw type fasteners drive through and/or into two objects, securing them to one another. In certain applications, it is sometimes necessary to use fasteners with counter-sunk heads for clearances or aesthetics. Typically, holes for such fasteners need to have a countersunk opening drilled to accommodate the countersunk head, and various countersinking tools are known to separately countersinking the opening or to simultaneously countersink the opening as the hole is drilled. One issue here is that an extra countersinking step is required to install otherwise self-drilling screws.

Fasteners with a countersunk head that include a radially extending cutting edge that extends to the circumferential edge of the screw head to countersink the surface as the screw is installed are also known. These may be used successfully in certain applications, such as in wood or laminate surfaces; however, attempting to use such self-countersinking heads in a sheet metal surface or a sandwich panel with a sheet metal skin has not proven successful due to the creation of burrs that are not only sharp and dangerous, but may compromise the integrity of the screw attachment and the sheet metal itself. Additionally, there can be overcutting of the countersink, resulting in a knife edge of the sheet metal acting on the shaft rather than a more desired cylindrical portion of the hole. Finally, the cutting edge can severally mar the panel surface at the periphery of the head.

Document <CIT> describes a screw of said kind with a shaft and a head, wherein the lower portion of the head exhibits a cone-like, tapered transition between shaft and head. The outermost portion of the bottom of the head exhibits an annular ring shape with a plurality of inclined protrusions. Further, a plurality of knife sheets is formed on said cone, said knife sheets extending from the annular ring to the shaft. The direction of the knife sheet(s) is inclined to an axis of the lower portion of the head.

It would be desirable to provide a self-drilling, self-countersinking screw that addresses the issues of the Prior Art.

A self- drilling, self-countersinking fastener according to claim <NUM> is provided in order to address one or more of the drawbacks noted above. This fastener includes a shaft, a countersunk head located at a first end of the shaft, and a tapered point located at an opposite end of the shaft. A thread integrally extends from the shaft and extends along at least a portion of a length of the shaft. The countersunk head includes a frustoconical region having a first, smaller diameter in a shaft connection region and a second, larger diameter at a second end defining an edge area of the head, a plurality of radially extending ribs located on the frustoconical region that extend from an area of the first, smaller diameter to a respective radially outer rib end spaced radially inwardly by a distance X from the edge area of the head. A respective cutting edge is located on each of the ribs.

The ribs are formed to have a helical shape and a reverse taper at the rib end. The cutting edge is changing from a positive angle of attack at the shaft connection region to a negative angle of attack at the outer rib end along a length of the ribs as they extend radially outwardly from an area of the first, smaller diameter in the shaft connection region.

Preferably, each of the ribs has a maximum height from the frustoconical region, and the distance X is greater than or equal to one half of the maximum height. This maximum height of each of the ribs is preferably located at the radially outer rib end. However, it could also be located further inwardly, depending on the particular application.

In a further arrangement, the shaft has an axis and the countersunk head preferably has an end surface that extends perpendicular to the axis, and the outer rib end extends at an angle of <NUM>° to <NUM>° to the end surface, so that it tapers radially inwardly progressing toward the tapered point of the fastener.

The helical ribs are preferably curved as they extend radially outwardly in an advancing direction of the fastener based on a direction of the thread. In order to achieve optimum cutting, an odd number of ribs is chosen.

In an alternative arrangement (not claimed embodiment), the ribs are straight.

In both cases, the ribs may change in height along a length thereof. The ribs may extend from a minimum height Hi in an area of the first, smaller diameter in the shaft connection region to a maximum height HM at the radially outer rib end (not claimed embodiment).

Preferably, the fastener is self-drilling and includes a hole cutting edge on the tapered point. The cutting edge may be adapted for drilling a hole in steel or aluminum.

In another (not claimed) embodiment, the frustoconical region has a first, inner area and a second, outer area that is radially outward of the first, inner area, and the cutting edges of the ribs have a different angle of attack in the first, inner area from the second, outer area.

For all of the arrangements contemplated, a tool engagement recess is located in the head, and can be, for example, a cross-slot, a Phillips® or Torx® drive, or any other suitable tool engagement recess.

The foregoing summary as well as the following detailed description will be best understood when read in conjunction with the appended drawings. In the drawings:.

Certain terminology is used in the following description for convenience only and is not limiting. The words "inwardly" and "outwardly" refer to directions toward and away from the parts referenced in the drawings. "Axially" refers to a direction along the axis of a shaft. A reference to a list of items that are cited as "at least one of a, b, or c" (where a, b, and c represent the items being listed) means any single one of the items a, b, or c, or combinations thereof. The terminology includes the words specifically noted above, derivatives thereof and words of similar import.

Referring to <FIG>, a first embodiment of a self-drilling, self-countersinking fastener <NUM> is shown in detail. The self-drilling, self-countersinking fastener <NUM> includes a shaft <NUM> with a countersunk head <NUM> located at a first end <NUM> of the shaft <NUM> and a tapered point <NUM> located at an opposite end of the shaft <NUM>. Preferably, a hole-cutting edge <NUM> is provided at or along the tapered point <NUM> in order to form the self-drilling portion of the fastener <NUM>. Additionally, preferably a tool engagement recess <NUM>, such as illustrated in <FIG>, is located in the head <NUM>. This can be, for example, a cross recess, a slot, a TORX®, a Phillips®, or any other suitable type of drive. A thread <NUM> integrally extends from the shaft <NUM> and extends along at least a portion of a length of the fastener <NUM>.

In order to address the issues in the known prior art countersunk heads to minimize the creation of burrs or sharp or dangerous edges, improve the final surface appearance, and reduce any chatter marks in the component being joined in which the head is countersunk, the countersunk head <NUM> includes a frustoconical region <NUM> on the underside having a first, smaller diameter D<NUM> in a shaft connection region <NUM> and a second, larger diameter D<NUM> at a second end <NUM> defining an edge area <NUM> of the head <NUM>. The edge area <NUM> can also have a depth that leads to the end surface <NUM> of the countersunk head <NUM> which extends perpendicular to an axis <NUM> of the fastener. A plurality of radially extending ribs <NUM> are located on the frustoconical region <NUM> and extend from an area of the first, smaller diameter D<NUM> to a respective radially outer rib end <NUM>, shown in detail in <FIG>, that is spaced radially inwardly by a distance X from the edge area <NUM> of the head. This distance X is indicated as extending along the frustoconical region <NUM> in <FIG>. A respective cutting edge <NUM> is located on each of the ribs <NUM>.

In the preferred embodiment, each of the ribs <NUM> has a maximum height Hm from the frustoconical region <NUM> and the distance X is greater than or equal to one-half of the maximum height Hm. As shown in <FIG>, the maximum height Hm of each of the ribs <NUM> is preferably located at the radially outer end <NUM> of the rib. This offset distance X allows for a sufficient cutting of the countersink beneath the head <NUM> without having burrs or ragged edges extending beyond the peripheral edge of the countersunk head <NUM> at the edge area <NUM>.

As shown in <FIG>, the countersunk head <NUM> preferably includes the end surface <NUM> that extends perpendicular to the axis <NUM> of the fastener <NUM> the radially outer rib end <NUM> extends generally parallel to the axis <NUM>. More preferably, the outer rib end <NUM> extends at angle Θ shown in <FIG> of <NUM>° to <NUM>° to the end surface <NUM>. More preferably, the angle Θ is in the range of <NUM>° to <NUM>°.

As shown in detail in <FIG>, the ribs <NUM> in the first embodiment of the fastener <NUM> are helical. These helical ribs <NUM> have a reverse taper at the rib end <NUM>. This results in an angle of attack of the cutting edge <NUM> that changes along a length of the ribs <NUM> as they extend radially outwardly from an area of the first smaller diameter D<NUM> in the shaft connection region <NUM> to the rib end <NUM>. As shown in <FIG>, at the shaft connection region <NUM>, the angle of attack α1 is a positive angle of attack at the cutting edge <NUM> in this area. As the cutting edge <NUM> extends radially outwardly to a medial region in the area of angle α2, the angle of attack of the cutting edge <NUM> is becomes negative, as indicated at α2 in that it is tilted away from the direction of advancing rotation of the screw as it is installed. Finally, at the radially outer rib end <NUM>, the angle of attack of the cutting edge <NUM> is a greater negative angle α3 as shown. In each of these instances, the angle of attack is shown with reference to a line R extending as a normal from the frustoconical region <NUM> through the cutting edge <NUM>. In the first embodiment of the fastener <NUM>, this frustoconical region <NUM> is preferably a straight taper.

As can be seen from <FIG>, the fastener <NUM> has a conventional clockwise thread <NUM> and the helical ribs <NUM> are curved as they extend radially outward in an advancing direction of the fastener <NUM> based on a direction of the thread <NUM>.

In the first embodiment of the fastener <NUM>, preferably there are an odd number of ribs <NUM>. This reduces chatter and enhances the ability to install the screw without chatter. In the preferred embodiment shown in <FIG>, there are seven ribs, shown in detail in <FIG>, although this number could be varied depending upon the size of the fastener <NUM> and the particular application.

Referring now to <FIG>, a second embodiment of the fastener <NUM>' is shown. The fastener <NUM>' is similar to the fastener <NUM> and like elements have been indicated with the same reference number with a prime. In this case, the frustoconical region <NUM>' is formed of a first, inner area <NUM>'A and a second, outer area <NUM>'B that is radially outward of the first inner area <NUM>'a. The cutting edge is <NUM>' of the ribs <NUM> have a different angle of attack in the first, inner area <NUM>'A from the second outer area <NUM>'B. Preferably, the cutting edge <NUM>' extend at least partially beyond the first, inner area <NUM>'A and into the second, outer area <NUM>'b. The other aspects of the fastener <NUM>' not specifically noted are the same as the first embodiment <NUM>.

Referring now to <FIG>, a third (not claimed) embodiment of the fastener <NUM>" is shown. The third embodiment of the fastener <NUM>" includes the shaft <NUM>" along with the countersunk head <NUM>" and the first end <NUM>" having a tapered point <NUM>". In this case, the frustoconical region <NUM>" of the countersunk head <NUM>" which extends from the shaft connection region <NUM>" to the second end <NUM>" in order to define the countersinking area includes straight ribs <NUM>" having the respective radially outer rib ends <NUM>" that are spaced radially inwardly by a distance X (which would be the same as shown in <FIG>, from the outer edge area <NUM>". Here the cutting edges <NUM>" are also formed straight, although the ribs <NUM>" may change in height along a length thereof and the angle of attack of the cutting edge <NUM>" can also change from a more aggressive angle in the shaft connection region <NUM>" to a reverse taper at the radially outer rib ends <NUM>". While this is preferred in some embodiments, those skilled in the art will recognize that the angle of attack of the cutting edge could remain constant with a positive or negative angle of attack, depending upon the particular application for the fastener <NUM>, <NUM>', <NUM>".

Additionally, although the helical ribs <NUM> of the first embodiment of the fastener <NUM> are preferably formed for a more aggressive cutting action with the curvature extending in an advancing direction of the fastener based on the direction of the thread <NUM>, a retreating helical rib could also be provided as well.

Using the fasteners <NUM>, <NUM>', and <NUM>" according to the embodiments above, the issues with the prior known countersunk heads are addressed in that a smooth cutting action for the countersink is provided as the fastener <NUM>, <NUM>', <NUM>" is installed. This has specific advantages in connection with sheet metal surfaces or a sandwich panel with a sheet metal skin in that burrs are not created that extend out from underneath the head, and chatter and vibration are reduced allowing for a clean finished look of the installed fastener in the surface into which it was countersunk. Additionally, slight dimpling of a sheet metal surface can also be achieved in a region of the edge area <NUM> to the extent that it has a height and the frustoconical region <NUM> does not end directly at the end surface <NUM> of the head in which the tool engagement recess <NUM> is provided.

Claim 1:
A fastener (<NUM>) comprising:
a shaft (<NUM>), a countersunk head (<NUM>) located at a first end (<NUM>) of the shaft (<NUM>), and a tapered point (<NUM>) located at an opposite end of the shaft (<NUM>);
a thread (<NUM>) integrally extending from the shaft (<NUM>) and extending along a portion of a length thereof;
the countersunk head (<NUM>) including a frustoconical region (<NUM>) having a first, smaller diameter in a shaft connection region (<NUM>) and a second, larger diameter at a second end (<NUM>) defining an edge area (<NUM>) of the head (<NUM>), a plurality of radially extending, helical ribs (<NUM>) located on the frustoconical region (<NUM>) that extend from an area of the first, smaller diameter to a respective radially outer rib end (<NUM>) spaced away inwardly by a distance X from the edge area (<NUM>) of the head, and a respective cutting edge (<NUM>) is located on each of the ribs (<NUM>);
characterized in that the helical ribs have a reverse taper at the rib end (<NUM>);
and the cutting edge (<NUM>) is changing from a positive angle of attack at the shaft connection region (<NUM>) to a negative angle of attack at the outer rib end (<NUM>) along a length of the ribs (<NUM>) as they extend radially outwardly from an area of the first, smaller diameter in the shaft connection region (<NUM>).