US 3604305 A
Description (OCR text may contain errors)
United States Patent Primary Examiner-Edward C. Allen Attorney-Charles M. Kaplan ABSTRACT: A screw having a recess formed in the head thereof centered on and symmetrical with respect to the screw axis, the recess presenting in plan 8 symmetrically disposed comers in 45 spaced relation with any four alternate comers proceeding around the recess lying on the comers of a square and defining a recess portion adapted to receive a square cross section driving tool, the remaining four alternate corners of the recess also lying on the corners of a square in 45 angular relation to the first square and also defining a recess portion adapted to receive a square cross section driving tool.
PATENTEDSEPI 4m: $604,305
sum 1 UP 2 INVIL'N'I (1R.
GEOFFREY DREGER BY QWJW PATENTED SEPI 41971 sum 2 OF 2 GEOFFREY RECESSED SCREW FIELD OF INVENTION This invention relates to improvements in screws or the like and more particularly to an improved recess formation for screws or similar fasteners.
RELATED INVENTIONS Related inventions comprise a punch to produce the improved recess formation of this invention and a driver bit for driving screws provided with the improved recess formation of this invention.
BACKGROUND OF INVENTION The unsurpassed driving characteristics, the elimination of tool slip off during driving, the resultant extension of driver life and the ability to cling to the driver bit to facilitate driving in awkward locations has afiorded the square recess screw such as disclosed in U.S. Pat. No. 2,914,984 with important technical advantages over all other types of recessed screws presently available.
The advantageous driving characteristics of the square recess screw stem from the fact that the corners of the square are defined between right angularly meeting wall portions of appreciable depth which are substantially vertical and there are no fine sections in the recess formation to fracture or ream out and no fine sections in either the punch or driver bit to break off. The mating driver bit which is of corresponding square cross section imparts torque positively to the screw through such right angularly disposed essentially vertical recess wall portions, the torque being transferred essentially at or adjacent to the corners of the recess although the additional wall area is, of course, available to resist reaming. The essentially vertical walls preclude any appreciable upward camming force tending to eject the driver so that full torque transfer is effected without requiring any excessive or even appreciable downward pressure on the driver thus reducing operator fatigue while essentially eliminating tool slippage. Moreover, this verticality of the walls provides a clinging action between the surfaces of the recess and opposite sides of the driver bit which enables the screw to be placed on and carried firmly by the driver bit to the point of application.
Despite the significant advantages of the square recess, there are nevertheless some problems involved in the production of the square recess screw and in certain applications of the screw. In the punching of the square recess into the round screwhead it is difficult to maintain the desired accurately circular shape of the head while maintaining the square of the recess and there is a tendency to distort the head out of true circular form and to create nonuniform stresses in the head. This problem is compounded where the metal of the screw is difficult to work with, for example, stainless steel and it is difficult to produce a proper square socket recess stainless steel screw.
Apart from the technical problems there is also some resistance to the appearance of a simple square opening in the screwhead when the screw is exposed on a finished surface, particularly when the head is not precisely circular.
The square configuration of the socket also involves the concentration of wear on the forming punch at a limited number of critical points particularly at the four corners of the recess so that while punch life is acceptable it would be highly advantageous to enable punch life to be extended.
In one particular application where it is desired to drive a series of positioned screws with a high-speed gun or driver while maintaining the gun speed in moving from screw to screw, it is difficult to effect entry of the driver bit into the square recess and it would be highly desirable to facilitate such entry.
SUMMARY OF THE INVENTION It is one of the objects of the present invention to provide a screw which will match and even surpass the technically superior driving characteristics of the present square recess screw, yet will eliminate the difficulty of maintaining the round head shape and will essentially eliminate crystallized or high-stressed areas in the head enabling for example the production of high quality stainless steel or other hard to work with metal screws.
It is another important object to provide a recessed screw as aforesaid whose recess in itself will have an esthetic appearance so that the screw will constitute a highly desirable fastener in all applications where its head is to be exposed.
Another important object is to provide a recessed screw which will not only accept the present square recess bit in proper driving fit but will accept such bit while moving at high speed as the driving gun is continued to be operated in moving from screw to screw where for example, a series of screws are preoriented for driving in rapid succession.
Again it is an important object to provide a recess formation having the characteristics as aforesaid yet which will enable the useful punch life to be extended.
According to the present invention the improved recess formation comprises a symmetrical readily formed recess having eight corners or points disposed in 45 angularly spaced relation around the recess and defined by right angularly disposed downwardly extending adjoining recess wall portions, the recess presenting two sets of four alternate corners defined by eight recess wall portions with each such set of comers and wall portions outlining a square whereby the recess is adapted to receive a square-driving bit in two 45 angularly displaced positions of fit.
By the provision of the eight corners or points it has been found that the problem of head distortion out of circular form and area of high stress concentration has been eliminated and tool entrance greatly enhanced without forfeiting any of the beneficial driving characteristic of the square recess.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a broken away elevational view of a punch for forming a recess according to the invention in a flat head screw.
FIG. 2 is a mid vertical sectional view of the head of a screw in which the recess formation of the invention has been punched by the punch of FIG. 1.
FIG. 3 is a top plan view of the screw of FIG. 1.
FIG, 4 is a view similar to FIG. 1 but showing a punch for forming a recess according to the invention and for the same time providing a heading operation to produce a roundheaded screw.
FIG. 5 is a midvertical sectional view of the head-of a screw produced by the punch of FIG. 4.
FIG. 6 is a top plan view of the screw of FIG. 5.
FIG. 7 is an enlarged schematic view showing the outline in top plan view of the recess formation according to the invention and illustrating in horizontal section one position of fit for a square driver bit received in the recess and in dotted line the alternative 45 displaced position of driver bit fit.
FIG. 8 is an enlarged part plan, part diagrammatic view comparing the displacement of the metal of the screwhead to provide a recess according in the present invention and the displacement of the metal of a screwhead to provide a square recess.
FIG. 9 is an enlarged part vertical sectional view of a screwhead embodying a recess according to the invention.
DETAILED DESCRIPTION OF THE INVENTION Referring first to FIG. 3 it will be seen that the recess formation of the present invention is formed to present eight symmetrically disposed points or comers 1 each defined by right angularly disposed adjoining wall portions 2 and 3 which define an internal angle x of 90 at each of the corners. With reference to FIGS. 7 and 8 the points or corners 1 starting from the top and moving clockwise are designated ia, 1b 1c, 1d, 1e, 1f, lg and lit and the defining wall portions are designated 21: 3a, 2b 3b, 20 3c, 2d 3d, 223e, 2f 3f, 2g 3g, 2h 3h. It will be seen that the corners la, 1c, 1e, and 13 in conjunction with wall portions 2a 3a, 2c 30, 2e 3 e, and 2g 3g define one square adapted to receive a square-driving bit or tool 4. The alternative sequence of corners and wall portions lb, 1d, 1 f and lb and 2b 3b, 2d 3d, 2}" 3f and 2k 311 also define a square and similarly are adapted to receive the square bit 4.
Adjoining wall portions such as 2a and 3h meet to define an included angle y of 135 and an internal angle of 225.
As seen in FIG. 9 the wall portions 2 and 3, all of which are identical in shape and area preferably deviate slightly from the vertical and incline inwardly at an angle of from 3 to 3 towards the bottom wall 5 of the recess which preferably is of conical form having an angle from 50 to 56 to the horizontal. The entrance 6 to the recess is also preferably bevelled at an angle of 45. The juncture of the conical bottom wall 5 and the sidewalls 2 and 3 are defined by arcuate juncture lines 7 and 28. This preferred recess construction with the above taper and the appropriate depth and conical bottom wall are selected to conform the recess to receive in accurate fit the existing drivers now employed with recesses of the square configuration of U.S. Pat. No. 2,914,984 in either of the two positions illustrated in FIG. 7 so that the screw may be driven by existing drivers.
As will be seen from FIG. 8, the eight pointed or eight cornered recess of the present invention provides an increased area of entrance to the screw over the present square recess socket. The inner circle 8 represents the area available for entrance of the driving bit 4 into a square recess. The second inner circle 9 represents the area available for entrance of the bit 4 into the recess of the present invention. The area between the two circles 8 and 9 represents increased area for entrance, i.e., the increased ease of entrance.
In addition it will be appreciated that when a rotating driver bit 4 is advanced towards a square recess and fails to enter in one position of angular orientation it must rotate through an angle up to 90 before it is oriented to seat in the next possible of acceptance whereas in the case of the present recess the maximum angle the bit must rotate is 45.
In this connection it will be noted that the junction of the sidewall portions such as 2a and 3h meet at a blunt point 11 (included angle 135) and if the rotating square bit is brought into contact with the blunt point it readily falls off such point into the immediately adjacent wider entrance square opening presented. Thus, it has been found that entrance of a bit rotating at high speed can readily be accomplished whereas such entrance was difficult with a square recess.
ln forming a recess formation in a screwhead the distortion to which the head is subjected has been found to very almost directly proportional to the degree the recess formation deviates from a-circle. Thus, as seen with reference to FlG. 8 a square recess involves the displacement out of circular form of four times the mass of metal lying between the inner circle 8 and the outer circle between say corner la and corner 1c and represented by the shaded areas l2, l3, 14. In the case of the recess of the present invention the amount of metal displaced out of circular form is represented only by four times the shaded areas 12 and 14 and all of this mass lies between the second inner circle 9 and the outer circle 10. As a result according to the present invention it has been found that the eight pointed recess can be formed in the screwhead while accurately maintaining the round configuration of the head not heretofore possible with recesses formed square to receive a square-driving bit.
A highly important advantage flowing from the precisely circular configuration of the head is the uniformity of stress distribution in the head essentially eliminating weakened or crystallized areas which might fracture under high torque stress. Because of the uniformity of the stressing it has been found that a socket formation according to the present invention can readily be formed in stainless steel or other hard to work with metals without splitting, fracturing or weakening the screwhead.
Further this ability to maintain perfectly round screwheads while forming the recess coupled with the esthetic appearance of the eight point recess renders the screw of the present invention a highly desirable screw for use on exposed surfaces where the appearance of the screwhead is of importance.
The recess of the present invention is formed for example by the punch 15 of FIG. 1 which is used to produce the flat head screw 16 of FIG. 2. One of the critical points of wear in a punch occurs at a corner such as the corners I7 which form the points or corners l of the recess. This wear is particularly concentrated at the juncture points 18 with the bottom wall formation 19. In the case of the square recess the impact blow of the punch is absorbed at only four corners and when these corners wear the recess will not be sufficiently accurate to allow the driving bit to seat firmly and properly in the recess. This problem is compounded when the sidewalls of the recess are tapered because of the mismatch of the driver bit taper with the recess taper if the bit cannot seat fully home.
In the case of the recess of the present invention eight corner juncture impact absorbing points 18 are provided with the result that the wear per corner is substantially reduced. This fact coupled with the ease of entrance of the more nearly circular form of the punch 15 in comparison with a square punch life so that each punch can produce a substantially greater number of recessed screws before replacement.
Despite the provision of the eight corners and the eight junctures 11 in the recess there are no corners or junctures less than and therefore no thin punch sections are required which would tend to fracture and there are correspondingly no thin recess sections which would tend to ream out under high torque.
FIG. 4 illustrates a modified form of punch 20 used to produce the screw 21. This punch includes a recessed block 22 having a recess 23 which is adapted to shape the rounded head 24 of the screw at the same time that it forms the screw recess. The recess forming portion 25 of the punch is identical with the punch 15.
Thus it will be seen that the cumulative effect of the advantages flowing from the recess of the present invention without in anyway detracting from advantageous technical driving characteristics of square recess screw provides an important advance in the art.
It will be understood that screws provided with a recess formation according to the invention may be hardened, plated, or otherwise treated with the same facility as present square recess screws.
While it is highly desirable to maintain the taper of the recess from 3 to 3 k for purposes of enabling the recess ac curate fit existing driver bits used with the existing square recess screws as disclosed in U.S. Pat. N 0. 2,914,984 this taper is not critical for purposes of providing an improved recess for use with a screw driver bit of eight cornered cross section corresponding to the cross section of the punches 15 or 20 as disclosed in copending application Ser. No. 835,431, filed June 23, 1969.
In this connection because the displacement of metal out of circular form in producing screws according to the present invention is less than in the case of producing square recess screws the fall away of metal from the punch during forming is less and more vertical recess sidewalls 2 and 3 may be obtained. On the other hand when the screws are to be driven by an eight cornered driver bit as referred to above an appropriate cling between the bit and recess walls can be achieved when the recess walls have a greater slope than 3 5%".
Thus the preferred recess construction has been illustrated it will be understood that variations in the taper, and bottom wall formation and other such details may be made without departing from the spirit of the invention or scope of the appended claims.
1. A threaded fastener having a shank and an enlarged head meeting at a first line of juncture, and enclosing a substantially circular area centered on the longitudinal axis of the fastener, said head having a tool-engaging socket extending into its upper end, said socket being centered on and symmetrical relative to the longitudinal axis of the fastener and presenting in plan eight symmetrically disposed comers, each corner being defined by a pair of identical downwardly extending sidewall portions which intersect at a right angle, any series of four alternate corners and their defining sidewall portions outlining a square, the remaining series of four alternate corners and their defining sidewall portions outlining a second square in 45 angular relation to said first-mentioned square, each sidewall portion defining a part of an included angle of 135 with a sidewall portion defining a part of the next adjacent comer along an intersection equally spaced from such corners to provide a total of 16 identical sidewall portions, each of said sidewall portions being inclined inwardly significantly with respect to said axis of said fastener, said intersections defined by said included angles being inclined to said axis of said fastener at an angle greater than the angle of inclination of said sidewall portions, and the lines of intersection at said corners being inclined to said axis of said fastener at an angle greater than the angle of inclination defined by said included angles, a bottom wall of said socket being inclined inwardly with respect to said longitudinal axis at a greater angle than said sidewalls, and said bottom wall intersecting said sidewalls at a second line of juncture located above said first line of juncture and enclosing an area smaller than and lying within an axial projection of said circular area, so as to provide a substantial volume of material around said socket to resist shear stress when said fastener is driven.
P0405? UNITED STATES PATENT OFFICE (5/69) CERTIFICATE OF CORRECTION Patent No. 3, 604, 305 Dated September 14, 1971 Inventor(s) GEOFFREY DREGER It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
Column 2, line 37, change "area" to --areas-- Column 3, line 42, after "possible" insert -position-- Column 4, line 28, after "punch" insert --to produce the square recess provides a substantially increased punch-- f' igneri and sealed this 15th day of February 1972.
HDWRW M.FF,-FJTCHEH ,Jil T'EUBITJFL'I GOTTSCHALK Attesting Officer Commissionerof Pa tents