US3540342A - Self-aligning high torque screw slot - Google Patents

Description

United States Patent 72] Inventor Rudolph Marlon Vaughn 2172 Salt Air Drive, Santa Ana, California 92705 [2]] Appl. No. 818,546 [22] Filed April 23, 1969 [45] Patented Nov. 17, 1970 [54] SELF-ALIGNING HIGH TORQUE SCREW SLOT 2 Claims, 4 Drawing Figs.

Primary Examiner-Marion Parsons, Jr. Attorney- Pastoriza and Kelly ABSTRACT: A high-torque screw head having a transverse slot with an arcuate bottom for use with a high-torque driving screw driver similarly being provided with an arcuate blade is modified to aid in guiding the driver blade into proper position for reception in the slot. This modification takes the form ofa circular recess of diameter greater than the width of the slot formed on the top surface of the screw head in a position coaxial with the longitudinal axis of the screw. The radius of curvature of the recess is less than the radius of curvature of the arcuate end of the driver blade so that only two point contact resultswhen the blade engages the recess, rotation of the blade being guided by the recess to maintain proper positioning of the driver turning axis with respect to the longitudinal axis of the screw so that the driver blade will drop into the screw head slot when it is aligned with the slot.

521 u.s.c| 85/45 511 lnt.Cl ..F16b23/00 [50] FieldofSearch 1 85/45; 145/501 [56] References Cited UNlTED STATES PATENTS 2,182,568 12/1939 Olson 85/45 2,322,509 6/1943 De Vellier 85/45 2,677,985 5/1954 Vaughn. 85/45 2,808,087 10/1957 Vaughn 85/45 Patented Nov. 17, 1970 3,540,342

INVENTOR RUDOLPH MARION VAUGHN 8) F5 6- 4 W a n ATTORNEYS SELF-ALIGNING HIGH TORQUE SCREW SLOT This invention relates to screws and more particularly to an improved high-torque screw slot structure which functions to facilitate reception ofa driving tool within the slot.

BACKGROUND OF THE INVENTION In my US. Pat. No. 2.677985, issued May II, 1954, there is described in detail a novel high-torque screw headslot structure and in my divisional US. Pat. No. 2,808,087, issued Oct. 1, I957. there is set forth a driver for use with the hightorque slot. The high-torque screws as described have been extremely successful both in commercial and military applications. The driving tool or screwdriver is normally of a power actuated type in order to speed up torquing ofa large number ofthe screws.

In utilizing these power drivers, there can be encountered difficulties in positioning the driving blade in the high-torque slot. Thus, from the above noted patents one of the unique featurcs constitutes the provision of an arcuate bottom for the slot and similarly an areuatc tip end for the driver blade. Because of this rounded configuration of the blade of the driver, should the tip not be received directly in the slot but rather on some other top surface portion of the screw head, operation of the power driver will result in the blade walking" over the surface of the screw head with a result that the head can be damaged or weakened and actual driving of the screw itself will not take place. In other words, unless the turning axis of the power driver is positioned substantially over the longitudinal axis of the screw, initial contact of the end or tip of the driver blade with at least a portion ofthe slot will not necessarily take place.

BRIEF SUMMARY OF THE INVENTION With the above in mind. the present invention contemplates a modification of the screw slot structure of the high-torque type screws such as described in my referred to U.S. Pat. No. 2,677,985 in such a manner as to aid in initial positioning ofa driving blade for reception in the slot. In its broader aspects, this modification takes the form ofa circular recess formed in the screw head. of diameter greater than the slot width, and positioned coaxially with the longitudinal axis ofthe screw. By means of this recess. the central slot area in the screw head is enlarged to thereby facilitate sceking ofthe slot by the arcuate tip ofthe driving blade.

BRIEF DESCRIPTION OF THE DRAWINGS A better understanding of the invention will now be had by referring to the accompanying drawings, in which:

FIG. I is a fragmentary view of a screw head incorporating the novel slot ofthis invention and a fragmentary portion ofa DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. I there is shown a screw I having a head II and transverse slot I2. The longitudinal axis of the screw is indicated at A. The slot 12 extends along a transverse axis 8 perpendicular to the longitudinal axis across the top of the head.

A driving tool 13 is shown disposed above the screw head II. This tool includes a driving blade 14 having an arcuate bottom or tip of radius ofcurvature R and a tip thickness of I.

The slot 12in the screw head I I is precisely as described in my heretofore referred to US. Pat. No. 2,677,985 with the exception that there is provided a circular recess IS in the cen tral portion of the slot. The axis of this circular recess corresponds with the longitudinal axis A of the screw 10. The recess in question may be formed by a counterboring opera tion or simply a punching operation.

With particular reference to the plan view of FIG. 2. the diameter ofthe circular recess 15 is designated (1 and is greater than the width m of the slot I2 at the portions of the slot ad jaccnt to the recess. In the particular embodiment illustrated, it'will be noted that this circular recess defines a portion of a concave spherical surface. It is important that the radius of this spherical surfaccbc less than the radius ofcurvature R for the driver blade described in FIG. I.

The spherical configuration will be evident from the cross section of FIG. 3 wherein the radius ofcurvature thereof is indicatcd at r. The radius of curvature of the slot bottom is indicated at R and corresponds to the radius ofcurvature R of the driving blade I4. It will be clear that r is less than R. It will also be noted in FIG. 3 that the driver has been rotated from the position in FIG. I to a position in which its driving blade is in alignment with the slot.

Except for the modification of the circular recess, the screw head slot 12 shown in FIGS. 2 and 3 and as mentioned heretofore, is precisely the same as that described in my US. Pat. No. 2,677,985. Thus, there are provided opposite undercut side walls 16 and 17 to the right of the recess diverging from each other in a direction towards the periphery ofthe head II. The wall surfaces themselves are defined by nonplaner conical surfaces of revolution. The pair of opposite sidewalls l8 and 19 to the left of the central portion of the slot are similarly designed.

Prior to modification of the slot by means of providing the circular recess 15, the slot would have straight line portions at its central area. These straight line portions would form the tops of inverted triangles when viewed from the side. these triangles being flat planer surfaces parallel to each other at the central area of the slot. As described in my mentioned patent. these portions of the slot do not contribute towards turning torque but rather it is the undercut nonplaner conical surfaces of revolution which effect full surface contact with the par tieular driving blade. Therefore, the provision of the circular recess does not remove material in the screw head which is es sential or actually utilized to any extent in enabling proper torquing to take place.

FIG. 4 illustrates the position of the driving blade 14 as it might initially engage the top of the screw head. Because of the relatively increased area of recess portions on the head afforded by the circular recess 15, and because of the arcuate bottom ofthe driving blade 14, initial engagement ofthe blade with the top surface of the screw will invariably result in a self seeking of the arcuate bottom with the circular recess 15 even though the alignment of the driving blade may be different from the alignment of the screw slot. Thus. the circular recess in cooperation with the arcuate bottom itself of the driver serves the function of positioning the axis of the driver, re gardless of its turned position at least over or in a position to intersect the longitudinal axis of the screw. Such initial contact is indicated at the points a and h in FIG. 4. Since the radius of curvature r is less than R as described, the contact will only he at two points.

Once the turnittg axis of the driving bit has been positioned over the longitudinal axis of the screw, rotation of the driver will then result in the driving blade being guided by the two point contact until it is aligned with the slot at which position it will fall in the slot.

OPERATION The operation of this invention will be evident from the foregoing description. Considering the situation wherein the conventional known type of high-torque driving tool is employed such as described in my referred to U.S. Pat. No. 2,808,087; that is, where the end of the driving bit is arcuate, an initial center positioning will be effected by the modified slot structure in the form of the circular recess 15. As described in conjunction with FIG. 4, should the plane of the driving surfaces be at an angle to the direction of the slot. the arcuate bottom will engage the periphery of the circular recess 15 or at least better seek this periphery in view of the enlarged recessed central area on the screw head, so that the risk of walking" of the blade tip over the screw head surface is minimized. ln a sense, the cooperation of the circular recess periphery with the arcuate bottom ofthe driving blade effects a self-seeking positioning of the blade over the longitudinal axis ofthe screw even though the turning axis ofthc blade may be at an angle to the longitudinal axis ofthe screw.

After the initial centering afforded by the circular recess is achieved, turning of the driver will result in the blade itself falling within the slot structure In actual embodiments of the invention, the diameter 1/ of the recess [5 was between [.5 m and 4 m, where m is the narrowest cross dimension of the slot as shown in FIG. 2. This dimension In is only slightly more than the dimension In for the driver blade to permit entry of the driver when aligned. Where the recess is a concave spherical surface, the radius of the sphere must be less than the radius ofthe arcuate bottom ofthe driver blade R to assure only a two point contact. However, it will be evident that the recess need not be spherical in shape but need only constitute a circular cavity or depression so shaped that its side walls extend downwardly and inwardly to terminate at a depth less than the depth of the central portion of the slot measured along the longitudinal axis of the screw, all surface areas of said sidewalls being spaced outside of a theoretical sidewall geometry for the recess defined by a concave spherical surface portion of radius of curvature less than the radius ofcurvature of said arcuate bottom of said slot such that only its upper circular peripheral edge at the top surface of said screw head will be engaged by the driver blade. In other words, the walls of the cavity must extend away from the upper peripheral edge at an angle greater than the angle defined by a tangent to the arcuate driver blade tip at its point of contact with the peripheral edge. Moreover, the depth of the recess must be greater than the distance between a cord drawn between the driver blade contact points and its lowest end portion so that no portion of the driver blade will engage the slot structure except at the two initial contact points in the plane of the top surface of the screw head. By this arrangement, there is avoided any n alking" ofthc extreme tip ofthc driver blade on the bottom surfaces ofthe recess on either side of the central portion of the slot.

The particularcombination of the recess in a screw head slot of the type described in my U.S. Pat. No. 2,677,985 results in unique and surprising advantages. It will be noted, for example in FIG. 2, that the peripheral edge ofthc recess 15 intersects the upper edges of the undercut sidewalls l6, l7, l8, and 19 of the slot at the points designated 0, g, e, and f respectively. Because of the divergence of these sidewall edges as they progress from the central towards the peripheral areas of the screw head, the distance between the points 0, g and the distance between the points e,fwill be greater than the narrowest slot width distance In. These greater distances or widths are indicated at m" and 111".

Visualizing now a driving blade positioned over the head of the screw as shown in H0. 2 with its plane oriented such that an initial two point contact as indicated at a and bin FIG. 4 occurs, upon rotation or turning of the blade in a clockwise direction, the trailing edges ofthc arcuate bottom of the blade will pass over and be free of the recess at the points 0 andfof H6. 2 before the leading edges of the arcuate bottom of the blade reach the points g and e. This is because the distances In" and m are greater than the distance m which in turn is only slightly greater than the thickness of the arcuate end of the blade as shown at m in FIG. 1. Therefore, there is greater assurance that the blade will drop into the slot at its first ap proach towards alignment than would be the case were t e slot of uniform width equal to m entirely along its extent.

Great reliability in actual seating of the blade in the slot is accordingly realized, particularly when power drivers are used wherein rotation or turning of the blade is at a relatively high speed.

From the foregoing description, it will thus be evident that the present invention has provided an improved high-torque screw slot wherein alignment difficulties encountered heretofore are avoided.

lclaini; l. A self-aligning high-torque screw for use with a driving blade having an arcuate bottom of given radius of curvature, said screw including: a screw head having a top surface, a low gitudinal screw axis and a slot extending along a transverse axis perpendicular to said longitudinal axis across said top surface ofsaid head.

a. said slot having an arcuate bottom of radius of curvature equal to said given radius of curvature and having a center of curvature on said longitudinal axis at a point above said top of said screw head; b. the central portion of said slot having a circular recess coaxial with said longitudinal axis, said recess having an upper circular peripheral edge at said top surface of said head lying in a plane perpendicular to said longitudinal axis and of dimension as measured across the slot of between L5 and 4 times the width of said slot at its central portion; said recess having sidewalls extending downwardly and inwardly to terminate at a depth less than the depth of the central-portion of said slot measured along said longitudinal axis, all surface areas of said sidewalls being spaced outside of atheoretical sidewall geometry for said recess defined by a concave spherical surface portion of radius ofcurvature less than the radius ofcurvature ofsaid arcuate bottom ofsaid slot such that the bottom of said driving blade engages said recess at solely two points on said upper peripheral edge in the said top surface of said head to thereby position the turning axis of said driving blade substantially over said longitudinal axis of said screw head; d. said slot having opposite undercut sidewalls which diverge frotn each other in the direction of the periphery of said screw head and which are defined by nonplaner conical surfaces of revolution, said upper peripheral edge of said circular recess at the said top surface of said screw head intersecting said conical surfaces of revolution at given points spaced further apart across said slot than the center width ofsaid slot, whereby said blade is guided into a position of alignement with said slot for reception therein by said two points of contact upon turning ofsaid driver about its axis, and

whereby said driving blade is more readily receivable in said slot as it becomes aligned therewith than is the case were said slot of uniform width throughout its extent.

2. The subject matter ofclaim l, in which said top surface of said screw head is substantially flat and said sidewalls of said circular recess define a'concave spherical surface portion of radius ofcurvature less than the radius ofcurvature of said arctlatc bottom of said slot.

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