TECHNICAL FIELD

[0001] This application relates generally to threaded fasteners for cement board applications, and more particularly, to a multi-thread cement board screw.

BACKGROUND

[0002] A typical screw configuration includes an elongated shank that extends between a driving head of the screw and a pointed end of the screw. At least part of the shank is helically threaded. Cement board screws with a variety of configurations are known. However, improvements are continuously sought.

[0003] It would be desirable to provide a cement board screw configuration that facilitates quick and effective installation with relatively low torque requirement and a resulting high resistance to pull-out after installation.

SUMMARY

[0004] In one aspect, a cement board screw includes advantageous performance features.

[0005] In another aspect, a cement board screw includes a head end, a shank and a tapered end, the head end including a tool engaging part, the head end located at one end of the shank and the tapered end located at an opposite end of the shank. A high thread is formed along the shank, wherein the high thread begins on the tapered end, extends onto the shank and terminates at a first axial location along the shank. The high thread defines a high peripheral edge, wherein the high thread includes a leading flank and a trailing flank that meet at the high peripheral edge and together define a high thread angle that is between about thirty degrees and about fifty-five degrees. A low thread formed along the shank, wherein the low thread begins on the tapered end, extends onto the shank and terminates substantially at the first axial location along the shank such that an axial length of the low thread is substantially the same as and contiguous with an axial length of the high thread. The low thread defines a low peripheral edge, wherein the low thread includes a leading flank and a trailing flank that meet at the low peripheral edge and together define a low thread angle that is between about fifty degrees and about seventy degrees.

[0006] In another aspect, a cement board screw includes a head end, a shank and a tapered end, the head end including a tool engaging part, the head end located at one end of the shank and the tapered end located at an opposite end of the shank. A high thread is formed along the shank, wherein the high thread begins on the tapered end, extends onto the shank and terminates at a first axial location along the shank. The high thread defines a high peripheral edge, wherein the high thread includes a leading flank and a trailing flank that meet at the high peripheral edge and together define a high thread angle. The first axial location is spaced from the head end. A low thread is formed along the shank, wherein the low thread begins on the tapered end, extends onto the shank and terminates substantially at the first axial location along the shank such that an axial length of the low thread is substantially the same as and contiguous with an axial length of the high thread. The low thread defines a low peripheral edge, wherein the low thread includes a leading flank and a trailing flank that meet at the low peripheral edge and together define a low thread angle. The low thread angle is larger than the high thread angle. A set of counter threads on the shank fun from proximate the first axial location toward the head end, the counter threads having a helical direction that is opposite a helical direction of the high thread and the low thread.

[0007] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Fig. 1 shows a side elevation view of one embodiment of a cement board screw;

[0009] Figs. 2 and 3 show perspective views of the screw;

[0010] Fig. 4 shows a partial cross-section view of the screw taken along a plane in which the screw axis lies;

[0011] Figs. 5 and 6 show partial perspectives of the head end of the screw;

[0012] Fig. 7 shows a cross-section of the head end;

[0013] Figs. 8 and 9 show enlarged views of the head end;

[0014] Figs. 10 and 11 show partial perspectives of the tapered end;

[0015] Fig. 12 shows an enlarged view of the high thread;

[0016] Fig. 13 shows a view looking along the screw axis at the tapered end of the screw; and

[0017] Fig. 14 shows a partial cross-section of the screw along a plane that runs perpendicular to the center axis of the screw and that is in the region of the counter threads. DETAILED DESCRIPTION

[0018] Referring to Figs. 1-13, one embodiment of a cement board screw 10 is shown. The cement board screw includes a head end 12, a shank or core 14 and a tapered end 16. The head end 12 includes an end face 18 with a drive recess 20 (e.g., a star recess or any other suitable drive recess). The end face may include a textured surface feature as shown, such as a pattern of recesses or other texturing. As used herein the term shank refers to the elongated core or shaft of the screw, which can include threaded and unthreaded portions. The tapered end 16 is located at an opposite end of the shank 14 and terminates in a point or tip 22. By way of example, the taper angle al defining the point 22 may be between about fifteen and about twenty -five degrees (such as about eighteen to twenty -three degrees). The tapered end may also include a wedge cut 15 as shown. The wedge cut begins at the tip and extends the full axial extent of the tapered end.

[0019] A high thread 30 begins on the tapered end 16 (e.g., preferably slightly short of the tip as depicted by spacing X in Fig. 11, or at the tip), extends onto the shank 14 and terminates at an axial location 32 along the shank. The spacing X may be, for example, in the range of 0.10 to 0.90 inches (e.g., 0.030 inches to 0.070 inches, or 0.40 to 0.060 inches). The high thread 30 is a right-hand thread as shown, and has a peripheral edge 34 formed where a leading flank 36 meets a trailing flank 38, which together define a high thread angle a2 of between about thirty-five degrees and about fifty -five degrees (e.g., between forty degrees and fifty degrees). In one implementation, the high thread is asymmetric, with a leading flank angle 01 and a trailing flank angle 02 that are different.

In particular, the trailing flank angle is less than the leading flank angle. For example, the trailing flank angle may be no more than twenty degrees (e.g., between fifteen degrees and twenty degrees) and the leading flank angle may be no less than twenty-five degrees (e.g., between twenty-five degrees and thirty-five degrees). The high peripheral edge 34 may be defined with a radius of between about 0.002” and about 0.008”, where the radius joins the leading and trailing faces of the thread.

[0020] The screw 10 has a penetrating axial length LP defined between the tip 22 of the tapered end 16 and the end face 18. An axial distance DH is defined between the tip 22 of the tapered end 16 and the axial location 32. Here, the axial distance DH is at least seventy percent of the penetrating axial length LP of the screw. However, variations are possible (e.g., distance DH at least seventy-five percent of length LP or at least eighty percent). [0021] A low thread 60 begins on the tapered end 16 (e.g., preferably slightly short of the tip or at the tip), extends onto the shank 14 and terminates at an axial location 62 along the shank. Here, the axial location 62 is substantially the same as the axial location 32, and an axial length of the low thread is substantially the same as and contiguous with the axial length of the high thread. The low thread 30 is a right-hand thread as shown, and has a peripheral edge 64 formed where a leading flank 66 meets a trailing flank 68, which together define a low thread angle a4 of between about fifty degrees and about seventy degrees (e.g., between fifty-five degrees and sixty-five degrees). In one implementation, the low thread is symmetric, with a leading flank angle and a trailing flank angle that are both the same.

[0022] The pitch PH of the high thread 30 is substantially uniform along the length of the thread, as is the pitch PL of the low thread 60, and the low thread pitch PL is substantially the same as the high thread pitch PH. Each turn of the low thread 60 is located substantially at an axial mid-point between adjacent turns of the high thread 30. The substantially uniform thread pitch PH and PL may, for example, be between about 0.080 inches and about 0.140 inches (e.g., between about 0.100 inches and about 0.120 inches).

[0023] The high thread 30 includes a minor diameter Dm and a major diameter

DMH, and the low thread 60 includes the same minor diameter Dm and a major diameter DML. The height of each thread along the shank 14 is defined as the major diameter less the minor diameter. The shank 14 is substantially a right-circular cylinder along the high and low threads, and the cross-section of the tapered end 16 is circular, where the cross- section lies in any plane that is perpendicular to the screw axis 50.

[0024] The axial location 32, 62 is spaced from the head end 12 and the shank 14 includes a set of counter threads 80 on the shank, where the counter threads run from proximate the axial location 32, 62 toward the head end 12. The counter threads 80, which operate as reaming threads, have a helical direction that is opposite a helical direction of the high thread and the low thread. The counter threads 80 have a major diameter DMC that is less than the major diameter DMH of the high thread and more than the major diameter DML of the low thread. The counter threads have a minor diameter Dmc that is greater than the minor diameter Dm of both the high thread and the low thread. Here, the set of counter threads is formed by six counter threads, wherein each counter thread extends helically through no more than one-hundred and twenty circumferential degrees. However, variations with more or less counter threads are possible. For example, the set of counter threads may be formed by no more than four counter threads, wherein each counter thread extends helically through no more than one-hundred and twenty circumferential degrees. Regardless of the number of counter threads, the counter threads 80 have a substantially uniform circumferential spacing about the shank as shown.

[0025] As best seen in the end view partial cross-section of Fig. 14, in any given plane that is perpendicular to the center axis 50 of the screw and along the axial length of the counter threads, the trailing flank 80A of each counter thread 80 extends substantially radially, per line 81, and the leading flank 80B extends in a direction that is offset from radial in a direction toward the trailing flank 80A, per line 83. The angle cp4 that is enclosed by the two flanks 80A and 80B in the perpendicular plane of cross-section, is between about thirty degrees and about forty degrees (e.g., about thirty-five degrees).

[0026] The head end is formed as a countersunk head configuration with a frustoconical lower part having a plurality of nibs, including a plurality of large nibs 82 and a plurality of small nibs 84, where multiple small nibs are disposed between successive large nibs as shown. The head end includes both an outer lower part 86 and an inner lower part 88. The outer lower part 86 defines a frustoconical taper angle cpl and the inner lower part defines a frustoconical taper angle cp2, where taper angle cpl is larger than taper angle cp2. In one implementation the taper angle cp2 is at least twice the taper angle cp2. By way of example, cp2 may be in the range of sixty-five to seventy-five degrees.

[0027] The small nibs 82 are defined substantially on the outer lower part 86 (e.g., running from the head periphery to the inner lower part 88). The large nibs 82 are defined on both the outer lower part 86 and the inner lower part 88. The large nibs are defined by a first nib portion 82A on the outer lower part 86 and a second nib portion 82B on the inner lower part 88. The first portion 82A and the second nib portion 82B meet and define an interior nib angle cp3 that is between about thirty-five and about fifty degrees. The large nibs 82 have a uniform circumferential spacing. The plurality of large nibs may formed by no more than six large nibs (e.g., four large nibs spaced apart from each other by ninety degrees, or three large nibs spaced apart from each other by one-hundred twenty degrees). Each of the large nibs 82 includes a leading face 90 that joins the lower part at a radiused juncture 92 and a trailing face 96 that joins the lower part at a juncture 94 that is not radiused. [0028] Various implementations of cement board screws in accordance with the configuration depicted in Figs. 1-11 are possible. By way of example, Table 1 and Table 2 below set forth one examples of such a screw implementation, where the high thread and low thread include a minor diameter Dm, the high thread includes a major diameter DMH, the low thread includes a minor diameter DML, the high thread includes a thread pitch PH, the low thread includes a thread pitch PL, the high thread includes a high thread height HTH on the shank, the low thread includes a low thread height LTH along the shank. Typical axial penetrating lengths LP for such screws may be in the range of between about one inch and about two and one-half inches, though other variations are possible.

Table 1 - Exemplary Screw Dimensions

(All Ranges in Inches)

Table 2 - Exemplary Screw Dimensions

(All Ranges in Inches)

[0029] The subject cement board screw includes advantageous features that improve performance. In particular, the asymmetric high thread profile improves pullout resistance, inclusion of both high and low threads renders a smoother finish in harder cement boards and wood studs, the wedge cut with sharp tip penetrates well into harder cement boards and harder woods and metal studs, the counter threads crush cement board fibers and render a smoother finish, the textured screw head end face allows bonding of finishing materials, adhesives, plasters, and fillers, the larger head nibs bite into the cement board during seating reducing torque to seat and the smaller nibs help in rendering smooth finish and flush seating.