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 transmission 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 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 an 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, 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 forms. 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 interchangeable 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 3, being nearer to the forward open end of the socket.
The handle has a partition wall 4 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 of 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 14 received in the bore. The rear cylindrical portion of the blade is a tight fit in the rear portion of the shaft bore and extends through the partition wall 4 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. 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 teethof 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 is generally similar to that of Figures 1 and 2 except that a separate pin 17 is fitted 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 modification, 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.