US3789896A

US3789896A - Screwdrivers and like tools

Info

Publication number: US3789896A
Application number: US00262446A
Authority: US
Inventors: Yarborough E Cooke
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-06-22
Filing date: 1972-06-14
Publication date: 1974-02-05
Anticipated expiration: 1991-02-05
Also published as: GB1338139A

Abstract

A screwdriver or like tool incorporating a rotatable shaft which is driven by axially movable members mounted therein, and having helical drive connection therewith, is provided with two helical grooves of different pitch associated with corresponding drive means, whereby the shaft is driven at comparatively high speed when encountering comparatively low resistance torque, and is thereafter driven at lower speed but with greater applied torque when the resistance increases. The shaft may be fitted with a hollow, axially movable handle, having pin and helical groove connection therewith, to form said higher-torque driving means. Spring means may be provided to prevent relative axial movement of handle and shaft until the resistance torque on the shaft exceeds a prearranged value.

Description

United States Patent [191 Cooke-Yarborough Feb. 5, 1974 SCREWDRIVERS AND LIKE TOOLS Primary Examiner-James L Jones, Jr. [76] Inventor: Eustace Cooke-Yarborough, 49a Asssmm "'M Blcks Maresfield Gardens, Hampstead, Attorney, Agent, or Fzrm-Young & Thompson London NW 3, England [22] Filed: June 14, 1972 [57] ABSTRACT 1 1 pp 262,446 A screwdriver or like tool incorporating a rotatable shaft which is driven by axially movable members [30] Foreign Application Priority Data mounted therein, and having helical drive connection J 22 1971 Or at Britain 29 136/71 therewith, IS provided with two helical grooves of difune e ferent pitch associated with corresponding drive means, whereby the shaft is driven at comparatively ((31.1 145/54, 74/89]; high Speed when encountering comparatively low 58] Field 3 37 3 sistance torque, and is thereafter driven at lower speed "145/5 73 L but with greater applied torque when the resistance increases. The shaft may be fitted with a hollow, axially movable handle, having pin and helical groove [56] References C'ted connection therewith, to form said higher-torque driv- UNITED STATES PATENTS ing means. Spring means may be provided to prevent 1,531,086 3/1925 Fegley 145/54 relative axial movement of handle and shaft until the 959,157 5/1910 Noyles 145/53 resistance torque on the shaft exceeds a prearranged value.

6 Claims, 6 Drawing Figures PATENTED FEB 51974 SHEET 2 BF 2 SCREWDRIVERS AND LIKE TOOLS This invention relates to screw-drivers and like tools, and more especially to known tools of this character incorporating a shaft or spindle caused to rotate about its own axis by an axial thrust applied to a member (which may be the handle of the tool) having screwthreaded engagement with the shaft or spindle.

In known tools of this kind the spindle and its driving nut-like member are engaged and co-operate by means of a helical screw thread, and the pitch of the thread determines the rate of rotation of, and the torque offered by, the shaft or spindle. A pitch suitable for a rapid primary or run-up stage of an operation, e.g. initial insertion of a screw, is usually too fine to be effective in the final tightening stage of the operation, and vice versa, and the effectiveness of known tools of this kind is thus restricted.

The object of the present invention is to provide a tool in which the aforesaid limitation of known tools is mainly or wholly eliminated, and with this end in view the invention consists in a screwdriver or like tool comprising a spindle or shaft driven in rotation about its own axis by axially movable means having screw threaded engagement with it, wherein there are provided a plurality of helical screw threads of different pitches with which axially movable means cooperate to provide different torques, and rates of rotation, of the spindle or shaft.

The differently pitched screw threads may be arranged to function in series, so that as long as small resistance to drive is experienced a low-torque highspeed thread may be used, whereas as soon as higher resistance is encountered the higher-torque, lower speed thread comes into action. Latch means may be provided to keep the latter thread out of operation until prearranged conditions of resistance are encountered.

This invention will be clearly understood from the following description of forms (given, however, merely by way of example) which it may assume, and this description will be more readily followed by reference to the accompanying drawings wherein FIG. I represents a screwdriver or like too] in accordance with the invention in side elevation, partially in section:

FIG. 2 represents a view in the direction of the arrow A in FIG. 1 with the outer casing partially removed:

FIG. 3 represents a sectional view, similar to that of FIG. 2 showing an alternative construction of part of the tool:

FIG. 4 represents a sectional view of an alternative handle fitted for a tool similar to that shown in FIG. 1:

FIG. 5 represents in exploded view parts of another form of tool in accordance with the invention: and

FIG. 6 represents a sectional view of a part shown in FIG. 5. In carrying the invention into effect in one convenient manner, as shown in FIGS. 1 and 2 of the aforesaid drawings, a hand tool, such as a screwdriver, comprises a helically-grooved spindle l on which is slidably fitted an internally grooved or threaded nut 2 with a handle shaft 3 by which the nut 2 can be forced axially along the spindle 1, thereby causing the spindle to rotate. Such an arrangement is known, and as illustrated the spindle may be provided with crossed helical grooves of opposite hand, and the nut may be fitted with a switch 4 to throw internal engaging parts into one or other position in order to drive the spindle in clockwise or counter-clockwise sense, by axial movement of the nut, as desired. The handle shaft 3 is hollow and when the handle is forced down to move the nut 2 the inner end of the spindle 1 telescopes into the handle shaft, compressing a spring 5, which restores the spindle to an outer position when the thrust on the handie is relieved. In known tools the handle 6 is rigidly secured to the shaft 3.

In the known tool the speed at which the spindle can be rotated, and the torque which can be applied to the spindle, are determined by the pitch of the helical grooves on the spindle 1, and remain substantially constant. For example when applied to a screwdriver, if a fine pitch of groove is provided a lightly turning screw can be rapidly engaged in a hole, but insufficient torque is available for final tightening. The torque available can be increased by providing a groove of coarser pitch, but speed of operation is then reduced.

In one form of tool according to the invention providing alternative speeds and torques for use under different conditions, as shown in FIGS. 1 and 2, the handle 6 is hollow to fit slidably over a ring 7 pinned externally to the hollow shaft 3. The pin 8 serves as a seating for the upper end of the spring 5. A flanged collar 9 on the shaft 3 closes the lower end of the handle 6. The part 10 of the shaft 3 between the ring 7 and collar 9 has a step or rib ll surrounding it, and detent springs 12 secured to the collar 9 engage this step or rib to hold the handle in the extended position illustrated. A helical groove 13 of comparatively coarse pitch is provided on the outer face of the shaft 3 and is engaged by an internal finger or projection 14 (FIG. 2) inside the handle.

When using the arrangement shown in FIG. 1, applied for example, to a screwdriver, a bit at the end of the spindle l is applied to a screw and the handle 6 forced down axially to move the nut 2 in known manner. The springs 12 are of such strength as to retain the handle in the extended position shown until, as the screw approaches its final position the reaction torque makes it necessary for the operator to increase the thrust. When a prearranged load is reached the springs 12 yield to release the handle which then moves axially forwards along the shaft 3. The finger l4 acting in the helical groove 13 thereupon provides an increased torque sufficient to fianlly tighten the screw. A restoring spring 15 in the handle, seated on the ring 7 lifts the handle to its extended position, and re-engages the springs 12 in the rib 11 when the operation is completed.

Alternative details of construction which may be incorporated in a tool such as shown in FIG. 1 are illustrated in FIGS. 3 and 4.

In FIG. 3 a latch device to replace the springs 12 and rib 11 comprises a magnet 16 mounted in the lower end of the handle 6 and a cooperating magnet 17 with a cover 18 surrounding the upper end of the shaft 3. The magnets are of such strength that they are held together by mutual attraction until a prearranged value of thrust is applied to the handle (corresponding to the occasion when the torque provided by the nut 2 on the spindle 1 is unable to dirve a screw further). When the thrust is then increased beyond the prearranged value the magnets separate, and the handle advances along the shaft 3, rotating the shaft by engagement of its finger 14 with the slot 13 of the shaft 3.

In the arrangement shown in FIG. 4 as an alternative to the groove 13 on the shaft 3 there is provided a like groove 19 inside the handle 6, and this is engaged by a side projection 20 of a head 21 on the shaft 3. The handle 6 is held extended by suitable latch means (e.g. as described above) until a prearranged thrust is applied to the handle, whereupon the handle telescopes on to the shaft 3 and rotates it by co-operation of the projection 21 and groove 19.

A simplified form of tool according to the invention is shown in FIGS. and 6. A helically threaded spindle 3 carries a threaded nut 22 mounted in a sleeve 23, a pin 24 on the nut projecting through a helical groove 25 in the sleeve. A collar 26 loosely mounted externally on the sleeve 23 is urged against a lower stop ring 27 by a coiled spring bearing against an upper stop 28. Teh collar 26 has a notch 29 engaging the pin 24. The upper end of the sleeve 23 fits in the lower open end of the handle 6 and a cover 30 encasing the sleeve fits externally on the lower end of the handle, and has a central aperture in its base for the spindle. Inside the lower end of the handle is fitted a ratchet ring 31, and the upper edge of the sleeve 23 has a pawl 32 to cooperate therewith. The spindle 3 is urged downwards by a coiled spring 33 in the handle, (FIG. 5), bearing on a base or platform 35 of a block 34.

The tool shown in FIGS. 5 and 6 operates substantially as previously described. A screwdriver bit fitted to the end of the spindle 3 is applied to a screw, and the handle 6 thrust down to force the nut 22 along the spindle, causing the latter to rotate and screw down the screw. The nut 22 reaches a final position where the torque increases and cannot be overcome by the nut 22. The operator increases the thrust on the handle 6, and the sleeve 23 slides down over the nut 22. The ring 26 is engaged with the pin 24 by a slot 29 and the pin 24 follows the helical slot 25 which, because of its coarser pitch provides an increased torque applied by way of nut 22 and spindle 3 to the screw, which is thus screwed down firmly.

From the above description it will be seen that the invention provides a hand-tool such as a screwdriver havwithout departing from the scope of the invention, as defined in the appended claims.

What I claim is:

l. A handtool incorporating a shaft having externally a first helical groove, and a first drive means in the form of a nut on said shaft internally formed to engage said first helical groove and to rotate said shaft about its own axis when moved axially along said shaft, and wherein there are provided second drive means for rotating said shaft comprising a tubular member axially slidable in relation to said shaft and having driving engagement therewith in the form of a projection from one cooperating with a second helical groove on the other, said second helical groove being of substantially coarser pitch than the said first helical groove, and means for preventing relative sliding movement of said second drive means on said shaft until the torque resistance of said shaft to said first drive means exceeds a predetermined value.

2. A handtool according to claim 1 wherein said second drive means comprise a hollow handle slidably mounted on the end of the shaft.

3. A handtool according to claim 1 wherein said second drive means comprise a hollow handle slidably mounted on the end of the shaft, and spring means for preventing relative sliding movement of said handle and said shaft until torque resistance of said shaft to said first drive means exceeds a prearranged value.

4. A handtool according to claim 1 wherein said second helical groove is formed in said shaft, and said second drive means comprise a hollow handle slidably mounted on the end of said shaft, and having an inward projection engaged with said second helical groove.

5. A handtool according to claim 1 comprising a ho]- low handle slidably mounted on the end of said shaft, and wherein a projection from said shaft engages said helical groove formed internally of said hollow handle.

6. A handtool according to claim 1 wherein said second drive means comprise a hollow cylindrical member formed with said second helical slot in its surface, mounted coax-ially on said shaft, a hollow handle slidable in relation to said shaft, and co-operating with said hollow cylindrical member to move the latter axially in relation to said shaft, a nut on said shaft having a pinlike extension engaging said second helical slot, whereby said shaft is rotated by axial movement of said hollow cylindrical member.

Claims

1. A handtool incorporating a shaft having externally a first helical groove, and a first drive means in the form of a nut on said shaft internally formed to engage said first helical groove and to rotate said shaft about its own axis when moved axially along said shaft, and wherein there are provided second drive means for rotating said shaft comprising a tubular member axially slidable in relation to said shaft and having driving engagement therewith in the form of a projection from one cooperating with a second helical groove on the other, said second helical groove being of substantially coarser pitch than the said first helical groove, and means for preventing relative sliding movement of said second drive means on said shaft until the torque resistance of said shaft to said first drive means exceeds a predetermined value.

5. A handtool according to claim 1 comprising a hollow handle slidably mounted on the end of said shaft, and wherein a projection from said shaft engages said helical groove formed internally of said hollow handle.

6. A handtool according to claim 1 wherein said second drive means comprise a hollow cylindrical member formed with said second helical slot in its surface, mounted coaxially on said shaft, a hollow handle slidable in relation to said shaft, and co-operating with said hollow cylindrical member to move the latter axially in relation to said shaft, a nut on said shaft having a pin-like extension engaging said second helical slot, whereby said shaft is rotated by axial movement of said hollow cylindrical member.