A support for a machine tool

Abstract: A support for a portable machine tool, e.g. a drill (2) is described comprising an attaching means, for attaching the drill (2) to a workpiece, the attaching means including a permanent-electro magnet unit (6) having at least one non-reversible magnetic core (14) and at least one reversible magnetic core (11) the cores being aranged so that the unit (6) can be switched to an "on" state in which the magnetic flux passes through the workpiece holding the drill (2) securely in position, and an "off" state whereby the drill (2) is released.

Description: This invention relates to a support for a machine tool, according to the pre-amble of claim 1. More particularly the invention relates to a support for portable drills of the type commonly used on construction sites, shipyards, etc. for machining of constructional elements such as rolled steel joists, boiler plates, etc. Such a support is known from document GB-A-2173427. Drill supports or drill stands of this type are well known and consist of a support which is secured to the workpiece so that the drill can be secured and positioned on the stand to effect accurate drilling or machining of the workpiece. Hitherto drill supports of this type comprise an electromagnet which is used to secure the support to the workpiece. Such electromagnets rely on an electric current which is turned on to secure the support in position and off to move the support to the correct position. The electric current has to be maintained to secure the support to the workpiece. If the electric current is interrupted either by accident or by a power failure the support will no longer be secured to the workpiece, which can be very dangerous when it occurs during machining of the workpiece. Current interruption is especially dangerous when the workpiece is vertical or upside-down. In such cases chains are sometimes provided to prevent the drill falling in the event of a power failure. However sometimes the chains are not attached due to forgetfulness or inconvenience and the consequences in the event of power failure are very dangerous particularly if the workpiece is located high above the ground, as would be the case during construction of a tall building. An aim of the support of the present invention is to avoid all these safety problems of existing drill supports by using a permanent-electro magnet instead of conventional electromagnets. Such permanent-electro magnets do not require a continuous electric current to secure the support to the workpiece because the holding power is provided by the permanent magnets. An electrical power failure will not result in any loss of magnetic holding power. The permanent-electro magnet uses an electrical current merely to switch the magnet on and off. Another aim of this invention to provide a support for a portable machine tool such as a drill which does not get hot after prolonged use so there is no risk of impairing the performance of the magnet. A further aim of this invention is to provide a support for a portable machine tool, e.g. a drill, with a magnet having a holding power which is not effected by high consumption of current from the drill. According to the present invention there is provided a support for a portable machine tool according to the pre-amble of claim 1, characterised in that the attaching means comprises a permanent-electro magnet unit which includes at least one non-reversible magnetic core and at least one reversible magnetic core, said reversible and non-reversible magnetic cores being arranged such that the permanent-electro magnet unit can be switched to an "on" state in which the magnetic flux passes through the work piece holding the machine tool securely in position, and an "off" state whereby the machine tool is released. One embodiment of the support, for a drill support, in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a side elevation of the general arrangement of a drill support in the form of a drill stand and drill; Fig. 2 is a side elevation partly in section, of the permanent-electro magnet showing the arrangement of the magnets; Fig. 3 is a bottom view of the permanent-electro magnet with the top plate removed; Fig. 4 is an end view of the permanent-electro magnet; and Fig. 5 is a schematic view of the permanent-electro magnet with a different arrangement of magnets to show the flux in the "on" and "off" positions. As shown in Fig. 1, a drill support 1 of the invention is shown connected to a drill 2 ready for use on site. The drill support has connected to its base a permanent-electro magnet unit (or PE unit) 6. The PE unit 6 can be turned on and off as required to fix the drill support in the correct place on a workpiece (not shown). The construction of the PE unit 6 is decribed in more detail below. A power supply cable 5 is attached to the drill support and is used to power the drill 2, comprising a cutting tool 3 via a further cable 4, and to control the PE unit 6. Once the PE unit 6 has been switched either to the on or off positions the electrical supply is isolated from the PE unit 6 and is only used to supply the drill 2. Thus the PE unit 6 will remain magnetised and not become detached from the work piece in the event of a power failure. The PE unit 6 will not become hot after prolonged use due to the absence of a continuous current and the holding power of the base will not be affected by high consumption of current by the drill. The drill support comprises various safety interlocks in the electrical supply circuit as follows: 1) The drill cannot be switched on until the base has been magnetised. 2) If the base is demagnetised for any reason while the drill is still running then the drill will automatically switch off. 3) If power fails and is later restored the drill will not come back on. As shown in Figs. 2 to 4, the PE unit 6 comprises a combination of reversible permanent magnets 11 and non-reversible permanent magnets 14 arranged in an alternating checkered array. The checkered arrangement is purely a matter of design choice and the invention can be achieved with any one of a large number of different arrangements of the reversible and non-reversible permanent magnets. The reversible permanent magnets 11 consist of any suitable material such as Alcomax. Each row of magnets is separted by mild steel pole pieces 15 and the whole arrangement is covered by a top plate 12 preferably made from a non-magnetic material such as aluminium. The revesible permanent magnets 11 are provided with coils 13 (see Fig. 2) which allow the polarity to be reversed when a pulse of current is passed through the coil 13. The arrangement of magnets of the unit in Fig. 5 is different to that in Figs. 2 to 4 and shows more clearly how by changing the respective polarities of the reversible permanent magnets in the PE unit 6 causes the magnetic field to change. In the on position the upper row of non-reversible permanent magnets 14 is magnetised in the same direction as the lower row of reversible permanent magnets 11. The easiest path for the magnetic flux to take is through the workpiece 16 which holds the workpiece securely in position on the surface of the magnet 6. To switch the device off, a pulse of current is passed through the coils 13 surrounding the reversible magnets 11, which remagnetises the Alcomax in the opposite direction. The upper row of non-reversible permanent magnets 14 is now magnetised in the opposite direction to the reversible magnets 11 in the lower row. The magnetic flux now forms a closed loop within the PE unit 6 and the workpiece 16 is released.

Claims: A support for a portable machine tool, said support being attached to the portable machine tool, such as a drill (2), and portable therewith, for use on a fixed workpiece (16), such as the steel framework of a building, which comprises an attaching means for attaching the portable machine tool to the fixed workpiece (16), characterised in that said attaching means comprises a permanent-electro magnet unit (6) which includes at least one non-reversible magnetic core (14) and at least one reversible magnetic core (11), said reversible and non reversible magnetic cores being arranged such that the permanent-electro magnet unit (6) can be switched to an "on" state in which the magnetic flux passes through the workpiece (16) holding the machine tool securely in position and an "off" state whereby the machine tool is released. A support for a machine tool according to claim 1, characterised in that the attaching means is fixed to the base of the support for the machine tool. A support for a machine tool, according to claim 1 or claim 2, characterised in that at least one of said reversible magnet core(s) (11) is surrounded by a coil (13). A support for a machine tool according to any one of the preceding claims, characterised in that the permanent-electro magnet unit (6) comprises at least one row of alternating reversible (11) and non-reversible magnetic cores (14). A support for a machine tool according to any one of the preceding claims, characterised in that mild steel pole pieces (15) are dispersed between the reversible (11) and non-reversible cores (14). A support for a machine tool according to any one of the preceding claims, characterised in that the attaching means only requires current when changing the state of the permanent-electro magnet (6). A support for a machine tool according to any one of the preceding claims, characterised in that if electrical power to the permanent-electro magnet unit (6) fails for any reason while the permanent-electro magnet unit is in the "on" state the magnetic flux will continue to pass through the workpiece (16) holding the machine tool securely in position.

Inventors: JOHNSON MARK, JOHNSON, MARK
Applicants: UNIVERSAL DRILLING AND CUTTING, UNIVERSAL DRILLING AND CUTTING EQUIPMENT LIMITED
Application year: 1993
Main classification: B23Q3
IPC codes: B23Q3, B23B45, B25H1