A magnetic switchable device (often called a magnetic base) is a magnetic fixture that uses one or more permanent magnets in a configuration that allows the external field to be turned on or off. They are used in many applications including

optics Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultrav ...

metalworking Metalworking is the process of shaping and reshaping metals to create useful objects, parts, assemblies, and large scale structures. As a term it covers a wide and diverse range of processes, skills, and tools for producing objects on every scal ...

, lifting, and robotics, to attach items to metal surfaces in a secure but temporary way. The magnetic base may have a ''V'' cut into the bottom of the base or the back. This ''V'' allows the base to be attached to a round bar such as the column of a

drill press A drill is a tool used for making round holes or driving fasteners. It is fitted with a bit, either a drill or driverchuck. Hand-operated types are dramatically decreasing in popularity and cordless battery-powered ones proliferating due to i ...

or a pipe. One type of magnetic switchable device is made from two blocks of

iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...

, with a round cavity bored through the centre. The halves are joined together with a non-

ferrous In chemistry, the adjective Ferrous indicates a compound that contains iron(II), meaning iron in its +2 oxidation state, possibly as the divalent cation Fe2+. It is opposed to " ferric" or iron(III), meaning iron in its +3 oxidation state, suc ...

material such as

brass Brass is an alloy of copper (Cu) and zinc (Zn), in proportions which can be varied to achieve different mechanical, electrical, and chemical properties. It is a substitutional alloy: atoms of the two constituents may replace each other wit ...

aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...

. A round permanent magnet is inserted into the bored hole and a handle is attached to allow rotation of the magnet. This act of rotation changes the orientation of the magnetic field. In the ''off'' position, the poles are oriented towards the non-ferrous core. The iron blocks act as keepers by bridging between both poles. In the ''on'' position, the poles are each in one iron half, which then acts as an extension. The field is effectively passing across an air gap (at the base and top). If this gap is bridged with a piece of iron, it becomes part of the magnetic circuit and will be attracted with the full strength of the magnet. A magnetic base can therefore be attached in a variety of positions to any ferrous surface, allowing the base to be positioned in the desired orientation. An alternative to the post and swiveling connectors is an arrangement whereby a series of interconnecting swivels can be set in position by tightening or loosening a central member. This member may be made from wire rope as it has to be extremely flexible yet strong in tension, the possibilities for positioning this type is probably no more than the two post type but its advantage lies in the fact that there is only one mechanism (screw) to loosen or tighten the arrangement making it easier to use.

References

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