ROTARY HAND TOOLS

Abstract: A rotary hand tool, such as a screwdriver comprises a handle (1) formed with a socket to receive a tool bit carrying shaft (7) with some limited axial movement. A spring (6) urges the shaft forwardly of the handle, but yields under manual pressure to permit engagement of respective rows of internal clutch teeth (2) and (3) with corresponding external clutch teeth (8) and (9) formed on the shaft. With the rows of teeth interengaged the handle and shaft are clutched together for rotation in unison. To disengage the teeth and thereby free the parts for relative rotation, axial pressure is reduced to allow the spring (6) to restore the parts to their original "rest" positions.

Description: Rotary Hand Tools. This invention relates to rotary hand tools, such as screw drivers of the form known, for example in ratchet screw drivers, comprising a handle part and a driven shaft part adapted to carry the screw driver blade, or other tool-bit, one part being received in a socket in the other, and clutch means which are engaged to couple the parts together for rotation in unison, and which are disengaged to permit relative rotation between the parts. Good quality ratchet screwdrivers, that is to say which operate reliably and with good torque -trans¬ mission properties are relatively complex and expensive to manufacture and assemble, and the user is required to select by means of a manual control,often in the form of a slider the direction i.e. clockwise, counterclockwise or both β -2- in which torque is transmitted from the handle to the shaft. The present invention provides a screwdriver or like rotary hand tool in which these complications are substantially reduced, and is characterised in that the parts are capable of limited axial movement relative to each other and that spring means- are provided which normally urge the parts into relative axial positions in which the clutch means are disengaged, the clutch means being engaged by axial movement of the handle part against the action of the spring means, relative to the shaft part. With this arrangement construction of the tool may be greatly simplified and in use, the user merely has to exert axial pressure on the handle to engage the clutch means for rotation of the shaft part and tool bit in either direction. Relaxation of the pressure automatically disengages the parts to permit the handle to be turned back through an arc in readiness for the cycle to be repeated. As will be understood from the following description and accompanying drawings, the tool can be of very rugged, but simple construction, with a minimum number of components. Two forms of rotary hand tool in accordance with the invention will now be described by way of example, with reference to the accompanying drawings in which: Figure 1 is an axial cross-section of one form of the rotary tool; Figure 2 is an enlarged section on the line II-II in Figure 1; and Figure 3 is a -π. axial cross section of a second form of the rotary tool. In the drawings, the invention is illustrated as a screwdriver, having a simple screwdriver blade, but it will be appreciated that the tool bit could take a variety of forms to adapt it for use with cross-head screws s hexagon screws or other socket head screws, alternatively, the tool bit could be formed with a socket to run nuts or bolts of various head orms. Furthermore, the tools may have permanently attached, " single purpose tool bits, but it will be understood that with minor modification the tool could be adapted to receive a range of interchangea tool bits, in well known manner. The screwdriver shown in Figures 1 and 2 comprises a handle part 1, preferably of the "pistol grip" form, of hollow construction and formed at its forward end with a stepped socket formed with two axially spaced rows of internal teeth in the form of axially extending, Vee-shaped serrations 2 and 3 of different diameters, with the larger diameter row 3j being nearer to the forward open end of the socket. The handle has a partition wall with a central aperture and a leaf spring 6 is housed in the handle behind the partition. Telescopically received in the socket of the handle is a driven shaft 7 of generally circular cross-section, the rear, inner end of which is stepped and is formed with two axially spaced rows 8 and 9 external teeth formed as Vee-shaped serrations to co-operate with the respective rows 2 and 3 o- * -" the handle. At its outer, forward end beyond the end of the handle, the shaft is formed with an external collar formed by teeth or serrations 11 to facilitate finger tip rotation of the shaft. The shaft is hollow, having a progressively stepped through bore the intermediate portion 12 of which is slotted to receive radial vanes 13 formed on a screwdriver blade l-i received in the bore. The rear cylindrical portion of the blade is a tight fit in the rear portion of the sha t bore and extends through the partition wall . where it is held captive by a retaining clip 16. The inner end of the blade engages and stresses the free arm of spring 6 t which normally holds the parts in their illustrated positions, wherein the handle and shaft are free to rotate relative to each other. If the blade is now engaged with a screw to be tightened or released, a relatively light forward pressure on the handle causes the handle to move axially forward, against the action of the spring, so that the rows of teeth 2,8; and 3*9 respectively interengage and clutch the handle and shaft together for rotation in unison when the handle is rotated. By relaxing the axial pressure the user allows the teeth to disengage, under the action of spring 6, so that he can rotate the handle back to a comfortable position prior to continuing rotation. By providing a plurality of pairs of rows of clutch teeth, the requisite torque capacity of the tool can be increased without the need to provide for a longer axial displacement between the engaged and disengaged positions, as would be the case if a single row of teeth- of equal strength were to be employed, since torque transmission capacity, is a function of tooth root area. Engagement of the teeth is facilitated by bevelling their confronting end edges. Of course, for some light duty applications a single pair of co-operating rows of clutch teeth would be sufficient, and if necessary for very heavy duty applications, , three or more pairs of rows could be provided. The screwdriver shown in Figure 3 ≤ generally similar to that of Figures 1 and 2 except that a separate pin 17 is fit * ted in the rear end of the- shaft part, the forward part of which is dimensioned to grip the tool bit (not shown) and has radial vanes 18 for keying engagement with the tool bit, which in this case can be interchangeable. In a further modi ication, not illustrated. the pin 17 may be formed as an integral extension of the shaft. The handle and shaft in the illustrated embodiments are conveniently formed as mouldings of plastics material. OMPI

Claims: (received by the International Bureau on 26 January 1982 (26.01.82)) 1. A rotary hand tool, such as a srrewrlriver, comprising a handle part and a driven shaft part adapted to hold a rotary tool bit, one said part being received in a socket in the other said part, and clutch means comprising interengageable rows of teeth which are engageable to couple the parts for rotation in unison and disenageable to permit relative rotation of the parts, and wherein in that the parts are capable of limited axial movement relative to each other and spring means are provided which normally urge the parts into a relative axial positions in which the clutch means are disengaged, the clutch means being engaged by axial movement of the handle part against the action of the spring means, relative to the shaft part, characterised in that the clutch means comprises a row of internal axially extending teeth in the socket part and row of external axially extending teeth on the other said part. 2 A tool according to claim 1, wherein the teeth take the orm, as seen in **xial section, of Vee-shpped serrations. 3- A tool according to claim 1 or 2, ^herein each said part has a plurality of axially spaced rows of teeth of different effective diameters, for simultanteous engagement with corresponding respective rows of teeth on the other part. . A tool according to any preceding claim wherein the said socket is formed in the handle part, and the driven shaft part is received in the socket. 5. A tool according to claim k - wherein the shaft part is provided, externally of the handle part, with an external collar for the purpose of facilitating rotation of the shaft part by hand. STATEMENTUNDERARTICLE 19 The claims have been amended to ta e account of the prior art cited in the international Search Report, of which the most pertinent is believed to he U.S. 3^ 7^71, in which the clutch means comprise teeth extending essentially radially but with at a slight angle to the main axis. This arrangement has three main disadvantages relative to the invention as now claimed. First the teeth have a camming action tending to force them apart under operating torque. Secondly, the zig-zag gap left at the externε.1 circumference presents a danger to the finger of the user. Thirdly, the possibility is excluded of further rows of teeth for additional strength without a substantial increase in overall diameter.

Inventors: MUMFORD M
Applicants: MUMFORD M
Application year: 1981
Main classification: B25B15
IPC codes: B25B15