US 3913647 A
A screw driver having intersecting blade portions each of which includes a foot portion on the lower extremity thereof for increasing the effectiveness of the blade in gripping the sidewalls of intersecting slots in a screw head.
Claims available in
Description (OCR text may contain errors)
United States Patent [191 Arnn 1451 Oct. 21, '1975 SCREW DRIVER  Inventor: Edward T. Arnn, 505 Country Lane, Louisville, Ky. 40207  Filed: July 8, 1974 21 Appl. No.: 486,487
Related US. Application Data  Continuation of Ser. No. 473,840, May 28, 1974.
 US. Cl 145/50 A  Int. Cl. B25B 15/02  Field of Search 145/50 R, 50 A  References Cited UNITED STATES PATENTS 1,055,031 3/1913 Groos 145/50 A 2,369,853 2/1945 Purtell 145/50 A 2,402,342 6/1946 Phillips 145/50 A UX 2,764,197 9/1956 Torresen 145/50 A 2,859,782 ll/l958 Cummoro 145/50 A 3,419,135 12/1968 Millner 145/50 A X FOREIGN PATENTS OR APPLICATIONS 400,465 11/1966 Australia 145/50 A Primary Examiner Al Lawrence Smith Assistant ExaminerMarc R. Davidson  ABSTRACT A screw driver having intersecting blade portions each of which includes a foot portion on the lower extremity thereof for increasing the effectiveness of the blade in gripping the sidewalls of intersecting slots in a screw head.
2 Claims, 3 Drawing Figures U.S. Patent Oct. 21, 1975 SCREW DRIVER CROSS REFERENCE TO RELATED APPLICATION This application is a continuation in part of U.S. Pat. application Ser. No. 473,840 filed May 28, 1974.
BACKGROUND OF THE INVENTION result arising from the present day screw driver blade geometry.
Many attempts have been made to modify screw driver blades to make them perform better when in use on difficult-to-turn screws. Representative of these attempts are U.S. Pat. Nos. 3,236,275, 2,684,094 and 370,255. Generally, these attempts have included m'odifying the screw head as well as the screw driver blades. However, modification of the screw head is impractical since screws currently in use do not have modified heads and industry acceptance of any modification is a major obstacle. This is particularly true in the automobile industry where screws having cross slotted blades are predominantly used.
Other attempts include modifying the screw driver blade by providing ribs which project downwardly on each side of the screw head as in U.S. Pat. No. 697,836. Such an approach is particularly inappropriate for cross slotted screw heads since the slots of such heads may not run to the outer circumference thereof.
The invention of this application is a rugged, inexpensive, readily constructed and easily employed screw driver for use with screws having cross slotted heads. The screw driver overcomes all of the defects of prior art screw drivers.
SUMMARY OF THE INVENTION The present invention relates to a screw driver for use with screws having cross slotted heads, including a plurality of blades, each terminating in a lower foot portion which protrudes outwardly from its respective blade faces to provide a gripping means. The gripping means imbeds itself into the sidewalls of the slot in a screw head to prevent the screw driver from slipping out of driving engagement with the screw head.
More specifically, the invention includes a screw driver comprising a shank portion terminating in a plurality of blades integral therewith each of the blades extending generally downwardly along an extension of the longitudinal axis of the shank and each having a lower foot engageable with the bottom portion of a slot of a cross slotted screw head, each of the lower foot portions being generally isosceles trapezoidal in transverse cross section with its widest base portion being most remote from the extension of the longitudinal axis of the shank. Preferably, the base portion lies in an arcuate plane extending from the periphery of the shank to the extension of the longitudinal axis of the shank portion. Also, each of the blades converge generally to a point and taper diminishing in thickness as they extend downwardly along an extension of the longitudinal axis of the shank. Each foot is defined by the trapezoidal sidewalls and the base, the intersections of which form wedge-like bites which cut grooves in the parallel sidewalls of the intersecting screw slots upon application of a torque to the screw driver shank.
The screw driver of this invention has been found to be capable of transmitting a torque to a screw head having crossed slots therein which is many times the torque that can be transmitted by a conventional screw driver. Also, the screw driver of this invention has been found to be resistant to being dislodged once inserted into a cross slotted screw head and subjected to a torque. In addition, the screw driver of this invention can engage a cross slotted screw head from an angle other than straight on and still provide its superior torque transmitting qualities, and, lastly, the screw driver of this invention allows the user to position a screw thereon with the bites engaging the parallel sidewalls of the cross slotted head, whereupon the screw is removably held by the combined efforts of each of the individual foot portions and is easily positioned in a hole not otherwise accessible to a screw.
DESCRIPTION OF THE DRAWING FIG. 1 is an isometric view of the screw driver of this invention;
FIG. 2 is a front view of the shank and blades of the screw driver of this invention; and,
FIG. 3 is a sectional view taken along lines 3-3 of FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a screw driver 10 having a handle 12, a shank 14 and four blades 16 intersecting at about angles with respect to each other. Collectively, the blades converge to form a pointed end portion 18 at the free end of shank 14. Each blade includes faces 22 which are located in opposed relationship to one another on opposite sides of the blade. Each blade 16 terminates in a foot portion 28 which includes wedge-like bites 30 on either side thereof. Each such foot portion 28 is generally isosceles trapezoidal in cross section, when viewed in a plane generally perpendicular to the longitudinal axis of the shank. Also, each foot portion diverges outwardly away from faces 22 of its respective blade and terminates at a generally arcuate base 32. Each foot portion 28 further converges to a point coincident with the point below the shank 14 which is formed by converging blades 16. It should be noted that advantageously as shown in FIG. 2, the arcuate bases of each of the respective foot portions are engageable with the bottom of a screw slot when the screw driver is being used. Further, each base advantageously lies in an arcuate three dimensional plane which extends from the outer periphery of the shank to the pointed end portion. The bases of each of the foot portions may, in the alternative, lie each in a flat plane at an angle to the longitudinal axis of the shank 14 to form portions engageable with the respective bottom portions of the slots of a cross slotted screwhead, each plane extending from the periphery of said shank portion toward an extension of the longitudinal axis of said shank portion 8-8.
In using the screw driver of this invention, one simply inserts the blade into the slots of a cross slotted screw head with each base of each foot portion extending downwardly thereinto. The screw driver shank is then twisted either manually with the aid of a handle, or by mechanical means such as an electric motor arrangement, for example, a power drill and chuck.
It should be noted that the screw driver of this invention need not be inserted in the screw head so that the longitudinal axis of the shank is in line with the longitudinal axis of the screw since each blade has a foot portion which extends along the entire length of the blade that would contact a screw slot. Thus, the axis of the shank may be slightly angled with respect to the axis of the screw since, in essence, the bites run the entire length of each foot portion 28 and may thus cut into the screw slot sidewalls at any angle. This feature is particularly advantageous when one considers the number of times screw heads are encountered where the head is not accessible from a straight on position, yet considerable torque is needed.
The material of construction of the screw driver can vary widely; however, a high quality steel is preferred. One such steel is designated as AISI No. A3150 and is a high carbon steel having about 0.48-0.53% carbon, 0.70O.90% manganese, l.1()-l .40% nickel and 0.70O.90% chromium contained therein among its principal additives.
It should be recognized that although the drawing depicts a round shank and a round handle for the screw driver shown therein, any suitable configuration can be employed in the practice of this invention.
Having thus described the invention, what is claimed l. A screw driver comprising a shank portion terminating in four blades integral therewith, each of said blades tapering, diminishing in thickness, as it extends downwardly to form a point at an extension of the longitudinal axis of said shank portion and each terminating in a lower foot engageable with the bottom portion of a slot of a cross slotted screw head, each of said feet portions protruding outwardly from its respective blade faces to provide a gripping means engageable with opposed sides of a screw slot to removably hold a screw thereon and also to cut a groove in the parallel sidewalls of a screw-head slot upon application of a torque to said shank, said feet portions each defining the lower most portion of its respective blade and being generally isosceles trapezoidal in transverse cross section with its base being most remote from said extension of said longitudinal axis of said shank and lying in an outwardly bowed arcuate plane which extends from the periphery of said shank portion toward an extension of the longi: tudinal axis of said shank portion, each of said feet portions intersecting with the other feet portions to form a point and each having its inwardly tapered sidewalls extending along the entire length of its respective blade to be engageable with the parallel sidewalls of a screw