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Thought to have been first produced during WW2, when supplies of German machines by makers such as Lorch and G.Boley were unobtainable, the B.T.M. was a beautifully-made English watchmaker's lathe with a centre height of 50 mm and 165 mm available between centres - both the straight and gap beds some 254 mm long being available. However, the lathe must have been but a minor distraction for its makers, the British Tabulating Machine Company Limited, for this was a large organisation, long familiar with precision production methods, who may have made the machine at the behest of a government department.
B.T.M. were later to become ICT and then, in the 1970s, the well-known and very successful computer firm ICL. During the 1930s the company was based in Icknield Way, Letchworth in North Hertfordshire and licensed by the Tabulating Machine Company (TMC) of America (later IBM) to produce punched-card machines. However, in connection with the same products, they had also independently developed a particularly successful mechanism, the ingenious Rolling-total Tabulator, a device that was to be further developed by B.T.M. (and adopted by IBM) and play an important part in scientific and commercial calculations during the 1940s and 1950s. Of even greater interest is that their background in complex machines gave B.T.M. the experience and skills necessary to undertake the development and manufacture of the 210 massive and ingenious mechanical "Bombe" mechanisms (known internally by the company as the 6/6502 or CANTAB) used at Bletchley Park from 1940 to 1945 as part of the programme to decoded enemy signals during World War Two. The "Bombe"s were not a form of electronic computer, but entirely mechanical, and designed to rapidly mirror the operation of a German Enigma code machine.
Built along lines of the original light Swiss 'Geneva' pattern watchmakers' lathe - as distinct from the heavier American Webster Whitcombe (WW) models - the B.T.M. watchmakers' lathe had a round bed with the flat element at the top rather than at the (more usual) back. It was intended for, and widely used by, precision industries and the armed services for the manufacture and repair of mechanical instruments. The numbers built must have been considerable for the model continued to be available - in boxes marked "Manufactured by ROF" and in a black crackle finish - until the early 1950s with sales handled by, amongst others, the well known machinery dealer E. H. Jones of Edgware Road, The Hyde, London N.W.9.
With a headstock that looks to have been an exact copy of that used on the 1920s and 1930s G.Boley watchmakers' lathe, the lathe had a maximum through-collet capacity of 4.8 mm (and partial of 5.4 mm), with the 8 mm bore headstock spindle running in plain bronze bearings with a stated running clearance of 0.00025". A spring-loaded pin was fitted as standard to engage in a ring of indexing holes in the front face of the headstock pulley. The lathe was supplied in a lockable wooden box complete with a very generous level of equipment that enabled it to be pressed into service immediately. Items included: a straight bed, bed with gap, compound screw-feed slide rest, headstock with hollow spindle and 3-step pulley, two tailstocks - one with a securing lug and one without; a T-rest holder with wide and narrow Tees, bell chuck, self-centring 3-jaw scroll chuck, 5 step "chucks", set of plain collets to take 1.5, 2.1, 3.2, 3.6, 4.0, 4.2, 4.4, 4.8, 5.2 and 5.4 mm diameters, set of cone collets to take 0.8, 1.0, 1.2, 1.8, 2.4, 2.6 2.8 and 3.0 mm diameters, driving chuck with carrier, pulleys runner for tailstock with two pulleys, two plain and six hollow centres and two carriers, centre ejector with vulcanite knob and a driving belt. Available as extras were an electric motor with a drive pulley, a round foot-stand for bench mounting and a lever-action tailstock.
Apart from the crackle-black mounting post, the lathe was finished in nickel plate or polished steel. According to reports by contemporary users, many of these lathes were returned from reserve stores after the war (together with masses of other unused high-precision equipment) and sold off cheaply - but are now comparatively rare..
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