Gerbruder Thiel GmbH was based, originally, in Ruhla a small town in the Thüringen area of Germany and had begun as makers of pocket, wrist and toy watches and general metal products. The development of their famous machine tools began in the early 1900s, the initial aim being simply to supply their own factory with more efficient methods of production. Although the new products included a series of unique and long-lived filing and sawing machines, together with a specially developed metal cutting bandsaw, it was for their range of superb, very high quality universal millers that they were to best known. The earliest such type, built in 1906, was intended for the manufacture of punches but by 1914 had developed into the much more useful and ingenious "Duplex" (the term indicating that the cutter spindle could be arranged anywhere from vertical to horizontal and the machine used for a variety of tasks). However, Thiel were not the only makers of such a model and in the United States Van Norman manufactured their own uncannily similar type, also called a "Duplex". Van Norman were handled in Germany by the well-known agents Schuchardt & Schütte, numerous examples appearing in their catalogues from 1899 to 1914. Hence, Thiel would have had the chance to see early examples of the type and either copied it, or were inspired by the design to make their own version. In addition, from the late 1800s onwards America had taken the world lead in outright production numbers and innovation in the machine-tool field - surely further circumstantial evidence that the German design sprang from an American drawing board.
By the early 1930s the very fine "Duplex 58" was in production - in which form the arrangement of its various components and controls provided such versatility that the success of the type was finally guaranteed.  At the end of WW2, in 1945, Thüringen fell under Russian control and the works directors, the designers and many workers fled to West Germany where a factory was established at Leinfelden, near Stuttgart, In Ruhla the remaining workers restarted production (with some modifications) of the pre-war Duplex 58 - while in the West a new machine, the 158 was designed and built. It is also reported (but not confirmed) that Junghans, a firm of watch makers in the Black Forest, also built the Duplex 158. After some years the East German factory was renamed "VEB Ruhla" and a new model, the 59 introduced.
Illustrated on this page is the Ruhla Duplex 58 with a 25" x 8.5" table having three power feeds - longitudinally, in traverse and vertically - whilst power backwards and forwards was also fitted to the head. On some versions of the miller, fitted with a clutch, spindle speeds could be changed, or reversed, without stopping the cutter spindle. The head gearbox had three levers: that at the lower left gave forward - neutral - reverse whilst the other two levers were for speed changes by moving gears within the gearbox. The clutch engaging lever had three positions: left for high range - centre for disengaged - right for low range. Typically, with the LHS gear lever in its the central position, the RHS gear lever to its right-hand position and clutch in low range would give 105 r.p.m.--or 210 r.p.m. in the high-range setting.
A range of accessories was available including a dividing attachment, supplementary horizontal  swivelling table, power down-feed to the spindle, slotting attachment, self-contained high-speed (5000 rpm) vertical head attachment, and the usual range of vices and precision setting and measuring  equipment. The whole machine was remarkably similar to, but much larger than, the much copied Deckel** universal miller - and, because of their unique features and superb quality of construction many examples of both types are still to be found doing  experimental and development work, nowadays often in the hands of highly skilled, self-employed engineers.
After WW2, Thiel was split into two parts with one based in the Allied-controlled Federal Republic of Germany and the other in the communist-controlled German Democratic Republic. In the West, Junghans, a firm of Watch Makers in the Black Forest, built the Duplex 158 and 159 using the Thiel brand name whilst in Ruhla, Thüringen, in the East the same machine labelled as the Duplex 58 was produced by VEB Ruhla under the long-established WMW brand name.
A truly amazing machine, the  Ruhla followed typical Deckel, and Maho design ideas but in its later versions must have been built without regard to cost - a situation explained by its manufacturer being in communist-controlled East Germany where a desperation for Western currency ensured that numerous machine-tool (and other) bargains were to be had.  Built in early and late versions (the earlier almost identical to the Thiel 58 original), not only was the standard of construction very high, but the specification outstanding with the incorporation (on late versions) of pre-selector gearboxes for both feeds and spindle drive, a spindle brake and "rapids" on each travel of head and table. On the first models a single motor was flange mounted against the rear of the column with the drive passing through a chain to a speed-change gearbox and then, via a second chain, to the upper, geared-together spindles. On later models two motors were employed, each held within the column and driving to a pair of pre-selector gearboxes with feed through multi-disc clutches. Each box had 24 speeds with selection of speed by a central dial on the face of the box and engagement by a separate lever.
Locked in all directions by electromagnetic brakes, the standard-fit table was bolted to the usual vertical surface and could be rotated along its Y axis. Split into upper and lower sections, with each able to be moved independently but geared together, the spindle inside the lower overarm was used for horizontal milling while the upper was fitted with a vertical head, the quill-feed of which was under the control of a fine-feed handwheel. Travel in and out was through 250 mm with, on early single-motor models, horizontal spindle speeds of 67, 95, 134, 184, 290, 430, 555 and 825 r.p.m. and on the vertical head of 102, 144, 205, 280, 440, 653, 845 and 1250 r.p.m.
By the time the last versions were being assembled, electrical arrangements were thorough and controlled by a 4-foot by 1.5-foot panel packed with 20 internal fuses, 400V, 230V, 35V DC, 20V and 6V wiring circuits, two triple mercury-filled time relays and thermo-switches, etc.
As they are rare in the UK, the writer has a limited amount of information about these machines and, should you have one, he would be pleased if you could make contact.