US 3302672 A
Description (OCR text may contain errors)
Feb, 1 19%? Filed July 12, 1965 M. WALTON 3,32,672
S CREW DR IVING TOOL INVENTOR.
Marvin Walfon United States Patent 3,302,672 SCREW DRIVING TOOL Marvin Walton, 134 Tuscaloosa Ave, Atherton, Calif. 94025 Filed .Iuly 12, 1965, Ser. No. 471,152 6 Claims. (Cl. 14550) The present invention relates to screw driving tools. More particularly, the present invention relates to driving tools for screws of the type known as one-way screws or irretrievable screws.
The present invention relates particularly to drive tools for round-headed one-way screws that are provided with indentations or excisions along diametrically opposite circumferential areas of their rounded heads which end in abutment surfaces that are located in a common plane containing the axis of the screw. To effectively engage and drive such screws into position, the driving tool must have drive elements capable of bearing against both said abutment surfaces. In a direction opposite to the direction in which the screw is to be driven into position, the floors and/or side walls of the circumferential indentations or excisions are shaped in such a manner that upon reversal in the operation of the drive tool, the tool is cammed out of said indentations or excisions and cannot effectively engage the screw head. A particularly effective one-way screw designed for operation with high speed power tools is described in my copending U.S. patent application Serial Number 458,604, filed May 25, 1965.
It is an object of my invention to provide an effective screw driving tool that is particularly suitable for high speed operation with one-way screws of the type referred to and which may be smoothly and effectively engaged with such screw heads and may be smoothly disengaged from the screw heads, upon reversal in its operation.
More particularly, it is an object of the invention to provide a drive tool for screws of the type described, that may be engaged with, or disengaged from, the screw heads without chattering, and without jarring the operators hand, and which is not likely to mar the screw head and/or the objects into which screws are driven by its operation.
Still another object of the invention is to provide a screw driving tool of the type referred to, that lends itself readily to mass production methods.
These and other objects of the present invention will be apparent from the following description of the accompanying drawings which illustrate a preferred embodiment thereof and wherein FIGURE 1 is a perspective of a screw driving bit em bodying my invention and shows below said bit a fragmentary perspective of a one-way screw of the type which it is intended to drive;
FIGURE 2 is a side elevation, partly in section, of the screw driving bit shown in FIGURE 1;
FIGURE 3 is a bottom plan view of the end surface of the screw driving bit; and
FIGURES 4 and 5 are schematic perspectives of a sphere and of two radially displaced hemispheres thereof, illustrating the geometrical parameters of the surfaces that define the conformation of the concavity in the end surface of the screw driving bit of the invention.
The screw driving bit of my invention comprises a cylindrical head portion mounted upon the end of a shank or stem 12 by means of which it may be coupled to the socket of a rotary drive tool. The fiat end surface 14 of said head contains a shallow rounded recess or concavity 15 of a diameter to fit over the head 16 of the screw 18 for which it is designed (FIGURE 1). Geometrically, the conformation of said recess is established by the top segments 2th,, and 20 of two complementary hemispheres 22,, and 22 (FIGURE 4) whose ice center points C and C lie below the end surface 14 of the head Ill and are dis-placed from each other in a plane P containing the center axis x of the screw driver, along a common diameter d to opposite sides of said axis (FIGURE 5). FIGURE 4 shows the sphere 22 before its halves 22 and 22 are displaced relative to each other in the manner explained above. In addition to the vertical piane P in which the displacement occurs, said figure indicates the horizontal section plane H that separates the segments from the sphere 22 and which coincides with the plane defined by the end surface 14 of the screw driving bit. The radii R and R of the base circle of said segments are somewhat smaller than the radius of the cylindrical head 10 of the screw driver and are about equal to the radius of the intersection line 'L between the ramp 24 of an excision or indentation 26 in the head 16 of the one-way screw and the side wall 28 of said indentation or excision (FIGURE 1); and the degree of diametrical displacement of the center points C, and C of the hemispheres 22 and 22 is about equal to, or slightly larger than, the radial depth of the floor or ramp 24 of an excision or indentation in the head of the screw adjacent the abutment surface 30 thereof.
When the concavity in the end face of the screw driver bit is of a conformation as defined hereinbefore, the two relatively displaced, juxtaposed sphere segments 20, and 20,, form inwardly directed circumferential ledges 32 and 32 that increase gradually in depth in a direction radially of the concavity and terminate in fiat end surfaces 34,, and 34 respectively, that lie within the plane P in which the hemispheres are displaced. Said end surfaces are of horn-shape, as best shown in FIG- URE l, and are the driver surfaces of the tool. In the preferred embodiment of the invention illustrated in the accompanying drawings the inner edges of said ribs 34,, and 34 are beveled as best shown at 36 in FIGURES 1 and 2; and especially the inwardly directed end corners 38 of said ribs are preferably chamfered as likewise shown in FIGURE 1 and as also shown in FIGURE 3.
In the preferred embodiment of the invention illustrated in the accompanying drawings, the driving head is provided with a centering boss 40 which may be of truncoconical conformation and which rises from the bottom of the concavity 15 coaxially with the drive head 10 preferably to a level slightly beyond the end surface 14 of the head, as best shown in FIGURE 2. Such a centering boss facilitates proper coaxial engagement of the screw driver with the screw. Accordingly, the heads of oneway screws of the type described and illustrated in FIG- URE 1 are usually provided with axially located centering bores or holes 42 of inverted conical or trunco-conical shape.
A screw driver having a head formed as described above and illustrated in the accompanying drawings, may easily be brought into proper coaxial engagement with the head of a one-way screw of the type exemplified in FIGURE 1. Its driver surfaces 34,, and 34 will effectively engage the abutment surfaces 32 in the head of the screw 18 without chattering or jarring, even though the tool may be in rotation. Due to the smoothly rounded nature of the concavity 15, of its ribs 32, and 32 and of the corners 38 of its driver surfaces 34 and 34 the tool will not mar the screw head or the article into which the screw is to be driven, and it may readily be disengaged from the screw; and the screw driver will not cause chattering nor jar the operators hand, even when its operation may he accidentally reversed, but will smoothly disengage itself from the screw head. Moreover, the construction of the screw driver bit of my invention is such that it may be easily manufactured with great accuracy by mass production methods. It is therefore as economical in manufacture as it is dependable, effective and trouble-free in operation.
1. A screw driving tool comprising a cylindrical head having an end surface, said end surface containing a concavity defined by adjacent segments of two complementary hemispheres, said segments being displaced to opposite sides of the center axis of said head upon said end surface to form with said end surface a pair of oppositely located, inwardly projecting ribs terminating in driver surfaces located at either side of said center axis in a common plane containing said axis.
2. A screw driving tool according to claim 1, wherein the inwardly pointing corners of said ribs are chamfered.
3. A screw driving tool according to claim 1, wherein the inner edges of said ribs are beveled.
4. A screw driving tool according to claim 1, including a centering boss rising coaxially with the center axis of said head from the bottom of said concavity.
5. A screw driving tool according to claim 1, including a trunco-conical centering boss rising coaxially with the center axis of said head from the bottom of said concavity to a level beyond the end surface of said head exteriorly of said concavity.
6. A screw driving tool for high speed power operation of one-way screws of the type described comprising a cylindrical head having a fiat end surface, said end surface containing a concavity defined by juxtaposed segments of two complementary hemispheres of equal radii whose geometrical center points are displaced along a common diameter of the cylindrical surface defined by said head to opposite sides of the center aXis of said head, said spherical segments defining with said end surface a pair of oppositely located, inwardly projecting circumferential ribs of gradually increasing radial depth terminating in horn-shaped driving surfaces located at either side of said center axis in a common plane containing said center axis.
References Cited by the Examiner UNITED STATES PATENTS 1,956,963 5/1934 Salmen 14550 2,180,633 11/1939 Holt 145-50 3,134,292 5/1964 Walton 145-50 WILLIAM FELDMAN, Primary Examiner.
R. V. PARKER, JR., Assistant Examiner.