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Publication numberUS3748949 A
Publication typeGrant
Publication dateJul 31, 1973
Filing dateOct 19, 1971
Priority dateOct 19, 1971
Also published asCA1017979A1, DE2251115A1
Publication numberUS 3748949 A, US 3748949A, US-A-3748949, US3748949 A, US3748949A
InventorsG Dreger
Original AssigneeRobertson Manuf Co Ltd
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Thread system
US 3748949 A
Abstract
A threaded member capable of being driven into low density materials has a sharp thread with its leading angle substantially larger than its trailing angle.
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Claims  available in
Description  (OCR text may contain errors)

United States Patent 11 1 Dreger 1451 July 31,1973

1 1 THREAD SYSTEM [75] lnventor: Geoffrey Dreger, Oakville, Ontario,

Canada [73] Assignee: P. L. Robertson Manufacturing Company, Limited, Milton, Ontario, Canada [22] Filed: Oct. 19, 1971 [21] Appl. No.: 190,506

[52] 11.8. C1. 85/46 [51] Int. C1. F161) 25/00 [58] Field of Search 85/41, 46

[56] 1 7 References Cited UNITED STATES PATENTS 1,294,268 2/1919 Holmes 85/41 2,350,346 6 1944 065x611 85/46 2,330,724 7/1945 Crooks 85/46 2,742,074 4/1956 Rosan 85/46 FOREIGN PATENTS OR APPLICATIONS 1,150,769 4 1969 Great Britain 85/46 Primary ExaminerEdward C. Allen Attorney-Charles M. Kaplan [57] ABSTRACT A threaded member capable of being driven into low density materials has a sharp thread with its leading angle substantially larger than its trailing angle.

1 Claim, 4 Drawing Figures BACKGROUND OF THE INVENTION This invention relates to threaded members and more particularly to screw threaded fasteners for use in low density materials.

The expression low density materials is intended to include materials having a density below about 40 pounds per cubic foot and penetratable by a threaded member. Widespread use of some low density materials as a substitute for natural wood has been hindered by the inability of conventional wood screws to penetrate and hold in such materials. For example, conventional wood screws cause low density particle board materials to crumble between the screw threads and thus prevent the screw from penetrating the material properly. Some low density particle board materials such as Novaply permit conventional wood screws to be driven thereinto, but such screws do not hold well enough in that they loosen or are pulled out under too low a load to make their use practical. When an attempt is made to drive conventional wood screws into laminated materials such as natural wood veneer bonded to a thicker core of polyurethane foam of 20 pounds per cubic foot density, the screws lift the veneer from the core. The result has been that relatively expensive fasteners, or fasteners that are difficult to use, have had to be used instead of screws. Also, when an item is made from materials having vastly different densities, several different kinds of fasteners must be stocked by its manufacturer.

SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to provide a threaded fastener capable of being screwed into and capable of holding well in low density materials.

Another object is to provide a threaded fastener usable in materials having a wide range of densities.

Another object is to provide a threaded fastener that can be driven without requiring a pre-drilled pilot hole.

Another object is to provide a threaded fastener that can be made in a single pass by rolling a blank between dies.

Another object is to provide a threaded fastener that does not crumble low density particle board between its threads.

Another object is to provide an easily manufactured, relatively inexpensive fastener that is rugged and durable.

Still other objects and advantages of the invention will be revealed in the specification and claims, and the scope of the invention will be set forth in the claims.

Briefly stated, in accordance with one aspect of the invention a screw threaded member has sharp-edged, asymmetrical threads of increased surface area and spacing that penetrate and hold the member in materials having a wide range of densities.

DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1 is a side view of a threaded member in accord with this invention.

FIG. 2 is an enlarged side view of a portion of the thread from the member shown in FIG. 1.

FIG. 3 is an enlarged side view of a portion of the member shown in FIG. 1.

FIG. 4 is a plan view taken along the line 4-4 in FIG. 3.

DESCRIPTION OF A PREFERRED EMBODIMENT FIG. 1 shows how this invention would be applied to a wood screw 1 having a conventional round head 2 with a slot 3 facilitating driving of same, it being understood that this thread system can be used to anchor essentially any type of threaded member, such as a hearing rod having a threaded end. Thread portion 4 is a single, continuous, sharp-edged, asymmetrical screw thread spiraling down the root portion 5 of fastener l and terminating at sharp pointed tip 6.

As shown in FIG. 2, the thread leading angle is 30 and the trailing angle is 15. This results in an included angle at sharp edge 7 of 45 that permits thread portion 4 to bite into and hold well in materials having densities in the range of about 15 to about pounds per cubic foot. The threads do not crumble or damage low density materials, and it is not necessary under most circumstances to pre-drill a pilot hole for member 1 before driving. These thread angles are critical, and the advantages of this invention will not be attained if there is any significant deviation therefrom.

FIG. 3 shows the relationship between the depth T of thread portion 4 and the diameter R of root 5. Thread depth T must always be at least 30 percent of the root diameter R and preferably is between 30 and 40 percent. Thus, the thread system of this invention provides substantially more thread depth than the prior art. This results in a greater thread bearing surface area which reduces crumbling and other damage to low density materials while member 1 is being driven, as well as increasing its holding power thereafter. One factor in achieving this desirable resultis that relatively less material is displaced when screw 1 is driven.

FIG. 4 shows the relationship between thread surface area and root area for this thread system. This thread system has substantially greater thread surface area than do comparable prior art systems, and this greatly increases the ability of this system to hold in low density materials. This greater thread surface area results from the above relationship between threaddepth T and root diameter R, and from the specific values specified for the leading and trailing angles.

In FIG. 1 the distance between threads is designated D. For threaded members in accord with this invention to perform properly, it is necessary that the thread spacing D be at least double the thread depth T, and

preferably 2.2 to 3 times the thread depth. This results in fewer threads per inch, and contributes to substantial elimination of the crumbling that occurs when prior art threads are driven into low density particle board.

Tests have been run to demonstrate the greater holding power of screws in accord with this invention. Size 10 gauge screws in accord herewith driven one-half inch into 18-20 pound per cubic foot urethane foam required a pull-out force averaging 215 pounds, while conventional type A screws of the same-size resisted an average of only 158 pounds before being pulled out of the same material. This is an improvement of about 36 percent. The same test showed these screws to be about 20 percent more resistant to pull-out from particle board materials. The same test in other materials revealed that screws in accord herewith always resisted a larger average pull-out force than did conventional types of wood screws. This shows that the holding power of fasteners with threads in accord with this invention in low density materials is substantially greater than Conventional wood screws of the same size. The tests also revealed increased holding power in materials with densities up to about 60 pounds per cubic foot. Furthermore, conventional screws showed a much greater deviation in pull-out resistance values than did the screws of the instant inventions.

It has thus been shown that screw threaded members in accord with this invention are easily driven into low density materials without damaging such materials and also have substantially increased holding power when compared to conventional structures. Threaded members as disclosed herein are also readily usable in high density materials, and this means that industrial users can reduce their fastener inventories. Also, these threaded members are especially suited for use in mass production operations where they are driven by power rotated tools (as contrasted with hand rotated tools). The threaded members of this invention can be economically manufactured in a single pass between dies in a conventional rolling operation because the metal flows easily and fills out the sharp crested thread when the leading angle is 30 and the trailing angle is 15".

While the present invention has been described with reference to a particular embodiment, it is not intended to illustrate or describe herein all the equivalent forms and ramifications thereof. Also, the words used are words of description rather than limitations, and various changes may be made without departing from the spirit or scope of the invention disclosed herein. it is intended that the appended claims cover all such changes as fall within the true spirit and scope of the invention.

What is claimed is:

l. A screw threaded member for use with materials having a density in the range from about 15 to about pounds per cubic foot comprising a root portion of predetermined diameter, a single continuous external sharp-edged thread portion having a leading angle of 30 and a trailing angle of 15', the depth of. said thread portion being from 30 to 40 percent of the diameter of said root portion, and the spacing between threads being from 2.2 to 3 times as greatas said thread depth.

i I II t l l l

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US1294268 *Aug 26, 1915Feb 11, 1919Edward C HolmesScrew-spike.
US2350346 *Apr 14, 1943Jun 6, 1944Clifford R GaskellSelf-tapping screw
US2380724 *Jan 12, 1944Jul 31, 1945Lestershire Spool And Mfg CompWood screw
US2742074 *Mar 9, 1951Apr 17, 1956Rosan JosephInsert and reduced diameter locking ring therefor
GB1150769A * Title not available
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3965793 *Oct 18, 1973Jun 29, 1976Keystone Consolidated Industries, Inc.Particleboard screw
US4439077 *Feb 11, 1982Mar 27, 1984Godsted Kent BConcrete screw anchor
US4527932 *Mar 3, 1983Jul 9, 1985Richard Bergner Gmbh & Co.Self-tapping screw
US4536117 *Jun 18, 1984Aug 20, 1985Mid-Continent Screw Products CompanyScrew fastener
US4653486 *Apr 12, 1984Mar 31, 1987Coker Tom PFastener, particularly suited for orthopedic use
US4842467 *Nov 9, 1987Jun 27, 1989Yamashina Seiko-Sho, Ltd.Concrete screw
US4861206 *Nov 23, 1987Aug 29, 1989Tox-Dubel-Werk Richard M. Heckhausen GmbH & Co. KGStraddling plug
US5061135 *Aug 28, 1990Oct 29, 1991Research Engineering & Manufacturing, Inc.Thread tapping screw
US5114278 *Oct 4, 1991May 19, 1992F. M. Locotos Equipment & Design Co.Mining bolt apparatus and method
US5304024 *Aug 19, 1992Apr 19, 1994Adolf Wurth Gmbh & Co. KgScrew, method and rolling die for the production thereof
US6113331 *Jul 28, 1998Sep 5, 2000Ejot Verbindungstechnik Gmbh & Co. KgSelf tapping screw for screwing into thermoplastics and the like
US6394726 *May 31, 2000May 28, 2002Illinois Tool Works Inc.Threaded fastener
US6575061Feb 5, 2001Jun 10, 2003John B. WagnerDriver, fastener and forming tool
US6702537 *Jan 12, 2001Mar 9, 2004Illinois Tool Works Inc.High profile thread forming screw
US6994502 *Aug 13, 2003Feb 7, 2006Lifetime Products, Inc.Pole joint screw for a basketball goal system
US8360702 *Mar 28, 2011Jan 29, 2013Yu su-lanScrew
US20120096701 *Jun 4, 2009Apr 26, 2012Stefan SchachnerAttachment means for connecting plane material combinations in dry construction
US20120251268 *Mar 28, 2011Oct 4, 2012Yu su-lanScrew
US20120257945 *Sep 30, 2011Oct 11, 2012Infastech Intellectual Properties Pte. Ltd.Threaded fastener
US20130039720 *Aug 11, 2011Feb 14, 2013Sheng-Tsai SHIHScrew
EP0060441A1 *Mar 3, 1982Sep 22, 1982Häfele KGConnection device for a pair of wood panels, chip boards or the like, one being perpendicular to the other
WO1998051933A1 *May 13, 1998Nov 19, 1998Europ Ind Services LimitedThreaded fastener, method of making a threaded fastener and rolling dies for making a threaded fastener
Classifications
U.S. Classification411/411
International ClassificationF16B25/00, F16B25/04
Cooperative ClassificationF16B25/0015, F16B25/00, F16B25/0047
European ClassificationF16B25/00C1, F16B25/00G1A, F16B25/00