Tool for setting threaded bushes
BACKGROUND TO THE INVENTION 
     This invention relates to a tool for setting threaded bushes and to a method of setting threaded bushes. 
     Threaded bushes are used in many ways in all sorts of applications both in industry and in the &#34;Do-it-Yourself&#34; field. There are three basic types of threaded bush, each of which is of a generally cylindrical hollow configuration whose cylindrical internal surface is partially threaded, the non-threaded portion being expansible to anchor the bush in an aperture. This expansion is caused by screwing the bush onto a threaded mandrel and then pulling the mandrel whilst simultaneously preventing the bush from moving with the mandrel. The first type of threaded bush is intended for use with thin sheets of material such as metallic plates. Here, the unthreaded portion is designed to collapse radially outwardly so as to clench the bush tightly against the sheet. The second type is designed for apertures in thicker sheets and has a weakened portion intermediate its threaded and unthreaded portions. The end of the threaded portion is frustoconical so that it can be pulled into the unthreaded portion to expand the latter when the bush is fractured at its weakened portion. The third type of bush is intended for use in blind bores in even thicker materials, typically in such material as chip board. Here, the unthreaded portion is provided with axial slots so that this portion can expand radially outwardly in response to axial pressure. 
     Most tools for setting such threaded bores are expensive power tools and so not suitable for the &#34;do-it-yourself&#34; enthusiast. What hand tools are available suffer from the disadvantage that it is difficult to remove the mandrel from the set bush without dismantling the setting tool. 
     SUMMARY OF THE INVENTION 
     The present invention provides a tool for setting threaded bushes, the tool comprising a body portion, a mandrel puller rotatably and slidably mounted in the body portion, a mandrel fixed to the mandrel puller for rotational and sliding movement therewith, and means for sliding the mandrel relative to the body portion, the free end portion of the mandrel being screw-threaded for engagement with a threaded bush, the threaded bush being settable by sliding the mandrel puller relative to the body portion so that the threaded bush strikes the body portion, is arrested thereby, and is expanded upon further movement of the mandrel puller, and the threaded bush is releasable from the mandrel by rotation of the mandrel puller relative to the body portion. 
     Advantageously, the mandrel is fixed to the mandel puller by a screw-threaded engagement, and preferably, said screw-threaded engagement is left-handed. As the thread on the free-end portion of the mandrel is right-handed, this has the advantage that the rotational movement of the mandrel puller which releases the set bushes, tends to tighten the connection between the mandrel and its puller, thereby preventing the mandrel from working loose and dropping out of the tool. 
     The body portion may have a hollow, generally cylindrical nose into which the mandrel puller is a sliding fit, the mandrel puller also being generally cylindrical. Preferably, the nose is provided with a nose bush through which extends the free end portion of the mandrel. The nose bush may also be connected to the nose by means of a left-handed screw-threaded engagement. Again, this prevents the nose bush from being detached from the nose during release of the bushes. 
     Advantageously, a lever portion constitutes said means for sliding the mandrel puller relative to the body portion, the lever portion being pivoted to the body portion and being provided with means engaging the mandrel puller. Said means engaging the mandrel puller may be constituted by plug means which engage in an annular groove provided in the mandrel puller. 
     Preferably, both the body portion and the lever portion are provided with handles, the handles being spring biassed apart. 
     The invention also provides a method of setting threaded bushes, the method comprising the steps of screwing a threaded bush onto the screw-threaded free end portion of a mandrel which is fixed to a mandrel puller rotatably and slidably mounted in a body portion, pulling the mandrel puller so that it slides relative to the body portion whereby the threaded bush strikes the body portion, is arrested thereby, and is expanded upon further movement of the mandrel puller, and releasing the set threaded bush from the mandrel by rotating the mandrel puller relative to the body portion. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     A tool for setting threaded bushes and constructed in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 is an exploded perspective view of the tool; and 
     FIG. 2 is a perspective view of the tool. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     Referring to the drawings, the tool has a body unit 1 and a lever unit 2, both of which are made of sheet metal folded to form channel-like portions. The lower portion of the two units 1 and 2 define handles 1a and 2a and the upper portions define pairs of parallel flanges 1b and 2b. The two units 1 and 2 are pivoted together by means of a pivot pin 3 which passes through holes 1c and 2c respectively in their flanges 1b and 2b. A circlip 4 is provided to prevent the pivot pin slipping out of position. 
     A hollow nose 5 is fixed to the upper portion of the base unit 1 and a nose bush 6 having a left-hand thread 6a is screwed into a corresponding thread provided in the outer end of the nose. The cylindrical end portion 7a of a mandrel puller 7 is a sliding and rotatable fit within the inner end of the nose 5. A mandrel 8 (which may be any standard mandrel) is screwed with a left-hand thread into a correspondingly threaded axial bore in the end face of the portion 7a of the mandrel puller, the other end of the mandrel extending through the nose bush and being provided with a right-hand thread 8a corresponding to that of the bush to be set. In practice, the mandrel 8 must be screwed into position before the nose bush 6 is screwed into the nose 5. 
     The mandrel puller 7 has a portion 7b of reduced diameter and a knurled handle 7c joined to an intermediate portion 7d by a further reduced diameter portion 7e. The shoulders delimiting the portion 7b co-operate, in a manner described below, with pivot plugs 9 fixed in holes 2d in the flanges 2b of the lever unit 2. Thus, the mandrel puller 7 is held loosely within the telescoped flanges 1b and 2b in such a manner that it can rotate and in such a manner that it has a limited degree of axial play arising from the limited movement of the pivot plugs 9 as described below. 
     A spring 10 mounted on a tension pin 11 fixed in holes 2e in the flanges 2b of the lever unit 2, acts to bias the two handles 1a and 2a apart. When not in use a clamp 12 holds the handles 1a and 2a together. 
     In use, the correct mandrel 8 for the bush to be set is screwed into the threaded bore in the end face of the mandrel puller 7. The nose bush 6 (which corresponds to the chosen mandrel 8) is then screwed into the nose 5. A threaded bush (not shown) is then threaded onto the thread 8a, the handles 1a and 2a are unclamped and allowed to move into their fully open position (as shown in FIG. 2). The bush is then positioned within an aperture in which it is to be set, and the handles 1a and 2a gripped and pulled together. This causes the pivot plugs 9 to move clockwise (as seen in FIG. 2) about the pivot pin 3, the pivot plugs thus causing the mandrel puller 7 to move to the right. This pulls the mandrel 8 and bush to the right. When the end of the bush strikes the nose bush 6, further movement of the mandrel 8 to the right causes the bush to expand and grip the walls of the aperture. In some cases it may be necessary for the handles 1a and 2a to be re-opened and a second closing action to be carried out in order to set a bush in its aperture. Once set in position, the bush is released from the mandrel 8 by rotating the mandrel puller 7 so as to unthread the mandrel from the set bush. Because of the provision of left-hand threads on the nose bush 6 and beteeen the mandrel 8 and the mandrel puller 7, this action will always unthread the bush from the mandrel rather than unthreading the mandrel from the mandrel puller or the nose bush from the nose 5. 
     The tool described above can be used with any of the three standard types of threaded bush and so can be used with both thin and thick sheets as well as in blind apertures in materials such as chip board.