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Scientific instrument maker, who produced improved dividing engines
1809 'Divider of mathematical instruments' at 12 Blewit's Buildings, Fetter Lane, London
1816 Allan published a description of his method of making screws of an accuracy which he claimed was suitable for application to scientific instruments, using a relatively simple machine. In this the workpiece was located in bearings, but free to move axially, and was pressed against a curved, inclined cutter. After cutting a shallow groove with one turn of the workpiece, a follower was pressed into engagement on the opposite side to the cutter, in order to guide the workpiece for cutting the remainder of the length. The depth was progressively increased, before changing the cutter for one suitable for cutting the finished depth (the first cutter having a radius suited to the outside diameter). Allan advocated turning the workpiece round and running it through again to ensure the the angle of each flank was symmetrical. Different pitches were obtained by altering the angle of the tool.. Note that the method has some similarities to that used c.1800 by Henry Maudslay to produce master screws in a special jig in which a curved 'chisel' was pressed into the workpiece at a precisely-defined angle.