US2116775A - Screw driver - Google Patents

Description

May 10, 1938. G. P. BLACKBURN 2,116,775

SCREW DRIVER Filed March 5, 1936 Inventor,

George RBIacKbuflv.

Rafa liq-J iiy'b .ing grip of the blade on the screw; 7 1

On the other hand. if the screw withstands Patented May 10, 1938 UNITED STATES PATENT OFFICE 3 Claims.

screw, and if the screw strongly resists rotation the blade is quite apt to' damage the side walls of the slot to such an extent that it is dlfllcult and sometimes impossible to maintain a holdhard usage the flat blade unless of ample dimensions is frequently twisted out of shape in the screw-driving operation.

In my present invention I have sought to ac-- complish several objects. First, to provide a screw-driver blade having double the contacting surface of the ordinary single, fiat type. Second. to equip each of the elements comprising the blade with friction-acquiring means calculated to largely reduce the tendency of the blade to slip out of the screw slot when operating under excessive tortional strain. Third,.to supply facilities for removal of any broken or injured parts comprising the blade by a simple chuck arrange-- ment. And fourth, to so construct the device that it may serve either in the capacity of an ordinary screw-driver applicable for single, straight slotted screws, or for use with screws having cross-shape slotted heads.

Other advantages and objects will appear as the description of the invention proceeds; and for a clearer understanding of the import of my invention reference should be had to the accompanying drawing in which like reference characters are employed to identify similar parts, and in which,-

Fig. l is a perspective view of my improved screw-driver construction;

Fig. 2 is a fragmentary perspective view of the same, drawn to a greatly enlarged scale;

Fig. 3 illustrates, in perspective view, the end of the screw-driver with two of the bits retracted to form a flat, straight blade for singleslot screws;

Fig. 4 is a central longitudinal section through the parts, as indicated by lines 4-4, Fig. 2;

Fig. 5 is a side elevation, partly in section, of the collet portion of the chuck member;

Figs. 5a and 5b are end views of the smaller and larger ends, respectively, of the collet;

Fig. 6 shows the screw-driver in place in a cross-slotted screw head;

Fig. 7 is a section on line 1-1, Fig. 6;

Fig. 8 shows the ends of the bits which are housed in the handle;

Fig. 9 is a modified form of bit end:

Fig. 10 is a very simple method of constructing the screw-driver blade;

Fig. 11 shows the bits in transverse section through one of the holes aligning. with the handle-securing pin; r

Fig. 12 shows the ends of the bits slightly convexed, and v a Fig. 13 is the same as Fig. 12 with the additional feature of having the ends of the bits or blades made tapering to fit a V-shape slotted screw.

Referring to; the drawing, I is a handle having two scarfs, each cut transversely of and at right angles to the other and extending through and for a short distance along the handle from its I inner end, forming a cruciform shape slot. The handle is equipped with a ferrule '2, the outer end of the latter having a wall or head with an opening shaped like a cross to receive thefour bits or blades 3 which extend for a. distance into the body of the handle.

Extending from the screw-driving end of each bit, for a distance somewhat greater than the usual depth of the slot in a screw, are closely spaced, transversely disposed serrations 4, the serrations being cut or otherwise formed on both faces of each bit, somewhat resembling a fine cut file.

The object of this construction is to provide a greater or more positive grip on the wall of the screw slot, the serrations having a tendency to embed themselves into the sides of the slot, particularly when the screw strongly resists turning in the screw-driving operation.

In Fig. 9 the serration principle is carried out with but a single projecting ledge which contacts the wall of the slot at the extreme bottom thereof. the character 8 representing the screw, L the slot, and la the single serration.

The inner, longitudinal edges Ia of the bits I are V-shape so that when brought together they miter and form a solid center for the cross-shape structure, the apices 5 of the edges of the bit mutually meeting on the axis of the complete blade structure.

To secure the four bits together in the form of an integrated cross-shape structure I employ a compressible collet member 6, slightly tapering on its outside and having an external screwthread 6a cut over its entire length.

The collet is split for nearly its full length by four scarfs 1, one on each quarter of its circumference. The smaller diameter end 6b of the collet is perforated by a cross-shape opening 8 similar in contour to that of the cross-sectional shape of the assembled bits I. It will be observed.

'tiidinally-on the collet toward the screw-driving by reference to Fig. 5d, that the scarfs 'I are located abreast, respectively, of the ends of the cross in the opening 8.

Operating over the collet 6 is a closing sleeve 9 internally screw-threaded to fit the external thread on the coliet member.

By rotating the sleeve 9 so that it moves longiend of the blade, the parts are loosened sufficiently to permit free movement of the bits through the opening I in the collet. This makes it possible to secure the collet, which together with the sleeve provides a very simple chuck structure, in various positions along the screw-driver blade. The peripheral surface of the sleeve is knurled so that it can be wrung on to the collet with greater facility, but in case hand-gripping of the sleeve does not procure sufilcient pressure to bind the bits, there is provided a hole 9a in the sleeve for use with a spanner wrench.

The bits are made of hardened steel, and while constructed to withstand ordinary wear and tear they are, like all other tools of this class susceptible of breakage should they be subjected to excessive torsional strain in the screw-driving operation. With the construction as herein outlined it is an easy matter to replace a broken or injured bit with a new one.

In the operation of replacing a broken bit the collet sleeve 9 is first loosened, then the pin In, which passes through the ferrule 2, handle I, and notches in the inner edges of all four of the bits, is withdrawn. The injured bit or bits may now be removed and one or more new ones inserted in their place.

It will be observed by reference to Fig. 8 that there are two holes I I through the bits, longitudinally spaced, relatively, and that these holes are drilled diagonally, or at such an angle as will permit the pin ll to contact all four bits, as is more clearly illustrated in Fig. 11. Thatportion of the bit assembly in which are the two holes II is housed within the handle of the screw-driver.

The present invention contemplates, primarily, a screw-driver applicable for use with cross slotted screws. As constructed, however, I am able to convert this type of driver into one adapted for operating with screws having a single, straight slot; and in Fig. 3 I have illustrated the parts so arranged that they will accomplish this object.

All that is required to make the change is to reposition two oppositely disposed bits in the four-bit assembly.

The same preliminary operation as is performed in the replacement of a broken bit is gone through with, namely, the sleeve 9 is loosened and the pin l0 withdrawn. Then two oppositelydisposed bits 3 are forced further into the handle until half portions of the two original holes ll align, as clearly illustrated in Fig. 3

This leaves the driving end of the blade with two aligning bits, adapted to serve in driving screws having a single, straight slot in their heads.

The ability to re-arrangethe bits so that the screw-driving end embodies either a straight or a cross-way blade gives the screw-driver a more or less universal character, in that screws of at least two varying types of slotted heads may be used in connection with it.

A simple, cheaply constructed form of crosswise blade is shown in Fig. 10, in which the bits are made integral and of the same width and of the same thickness throughout their lengths.

with the serrations 4 cut or otherwise formed on the faces of each branch of the cross.

The serrations perform a very important function in screw-driving operations as a hold on the screw by the driver can be obta'inedwhere. frequently a smooth blade will not be effective.

What I claim is:

1. A screw-driver comprising a handle, a ferrule secured on said handle and having in its outer end an opening made in the form of a cross, four fiat, straight bits adapted to be assembled in the shape of a cross, and in this form insertable in said handle through the cross-shape opening in said ferrule, the inner edges of said bits being bevelled two ways, providing a miterjoint construction when said bits are brought together on the axis line of said handle, coincident with the intersecting point of the central lines cutting the cross openings in said ferrule, means to secure said bits in said handle, and a chuck mechanism, including a collet and sleeve, mounted on said bits adjacent the screw-driving ends thereof.

2. A screw-driver comprising a handle having a transversely disposed hole adjacent one end thereof, two scarfs, each one cut transversely of and, through the other, extending from the extreme inner end of said handle toward the outer end, a ferrule on the inner end of said handle having therein a transversely disposed hole aligning with the hole in said handle, said ferrule further having an aperture in its outer end of crossshape contour, four fiat, straight bits having V- shape inner edges arranged in the form of a cross and meeting at the axis line of said handle, the cross-sectional contour of said bits when thus arranged conforming to the contour of the aperture in said ferrule and the lines defining the. two

scarfs in said handle. means to secure said bits in said handle in either one of two different arrangementaone with the extreme outer ends of all bits flush, and the other with two of said bits positioned in advance of the other two, and a plurality of serrations on both faces of said bits extending from the screw-driving ends thereof toward the said handle.

3. A screw-driver comprising a handle having a cross-slotted end portion and a ferrule-securing hole therethrough, a ferrule mounted on said cross-slotted end portion of the handle and having a transverse hole registering with the ferrule-securing hole in the handle, the outer end of said ferrule having a cross-shape opening aligning. longitudinally, with the slotted end of said handle, four bits, each having a V-shape inner edge, adapted when assembled with their V-shape edges mutually engag to form a cross insertable in said handle and fitting the crossshape opening in said ferrule, said bits when as sembled with their outer ends flush having two longitudinally spaced holes passing diagonally through notches in the inner edges of all of said bits, a split collet, having a tapering screw thread on its periphery and an opening in one end conforming to the contour of the assembled bits, mounted on and adjacent the screw-driving end of said bits, and a closer sleeve having an internal thread fitting the external thread on said collet, and operable thereover, for the purpose of bringing said bits into strong mutual engagement.

GEORGE P. BLACKBURN.

Images