Manufactured by a company little known outside its native France - Socomo of 25 Rue Emile-Duclaux in Suresnes - the TU lathe was built in two versions, the TU350 and TU400 - each differing from the other only in respect of their centre height: the former being 175 mm (6.9 inches) and the latter 200 mm (7.9 inches). As an aid to the turning of larger jobs on the faceplate, the swing by the headstock was increased to 15.375 inches (390 mm) on the TU350 and 17.3 inches (440 mm) on the TU400. A number of between-centres capacities was offered including, for the TU350 only, 21.6 inches and 29.5 (750 mm) inches and 39.4 inches (1000 mm) for both versions.
Designed as a general purpose lathe, this was a well made machine tool with a wide and especially deep bed well braced by cross ribbing between the walls; high quality construction and detailing was reflected by the use of inserted V and flat ways in hardened and ground steel although it is not known if these were, as a result, replaceable when worn.
Constructed from cast iron, the heavy cabinet stand held a 6 h.p. motor together with its flange-mounted speed-change gearbox on a hinged plate - the drive passing up to the spindle by the use of four V-belts with the two control levers arranged concentrically on a boss that protruded through the stand's front face below the headstock. This type of arrangement, which removed all but the low-speed gears from within the headstock, was intended both to simply the design and also reduce marks on finely finished surfaces caused by gear thrash induced vibrations. A range of twelve spindle speeds was available that spanned 65 to 2800 r.p.m. on the TU350 and (given its size and increased work-holding capacity) a slight but sensible reduction to 55 to 2400 r.p.m. on the TU400. Electrical control of the motor - start, stop and reverse - was by a "third-rod" system with a control lever pivoting from the right-hand face of the apron. As both a safety feature and to save time waiting for a heavy job to come to a standstill, a brake was fitted to the gearbox output pulley operated by a full-length, foot-operated bar on the front of the stand.
Made from a high-quality steel forging, hardened and ground, the 1.6-inch (40.5 mm) bore, No. 5 Morse taper spindle had an American A1 nose and ran in a high-precision taper roller bearing at the front and a cylindrical roller bearing at the rear - this commonly-used arrangement allowing for safe expansion of the spindle as it reached its operating temperature. Internal headstock reduction gears were also hardened and ground, as were the ball-bearing supported spline shafts on which they ran.
Fully enclosed and operated by levers, the screwcutting and feeds gearbox could produce, without changing or demounting any changewheels, thirty-three Whitworth pitches from 2 to 56 t.p.i., twenty-six metric from 0.6 to 20 mm, fifteen Diametral from 16 to 72 and nine MOD from 0.5 to 2.5.
Power sliding feeds were set at 1/10th of the leadscrew rate with power cross feed further reduced (by gears within the apron) to one third of those values. A pump, operated by a cam on one of the gearbox shafts, provided a positive flow of oil around the box and also to the headstock.
Doubled walled, completely sealed and with an oil sump in its base, the apron contained (in addition to the usual worm-and-wheel assembly to pick up drive from the power-shaft), smooth-running helical gears. Operated each time the feed was engaged, a one-shot pump distributed oil to the bed and cross slide ways - the apron's internals being lubricated by splash.
Cross and top-slide micrometer dials (they could be had with inch or metric divisions) were suitably large, finished in satin-chrome and provided with face locks that did not disturb the reading when operated.
Of conventional design with a cam-operated bed clamp and a split-barrel spindle lock, the tailstock was fitted with a micrometer dial, ruler graduations in either mm or inches and an unexpectedly large No. 4 Morse taper socket.
Weights varied from 2170 lbs (985 kg) for the shortest bed TU-360 to 2500 lbs (1135 kg) for the longest bed version of the TU-400.
Supplied with the lathe was a single toolpost, complete electrical equipment ready to run, hardened and ground headstock and tailstock centres, a chip pan, thread-dial indicator, a set of spanners and an operator's instruction book. Accessories included the usual fixed and travelling steadies, 4-way and quick-set toolposts, a taper-turning
If you have a Socomo lathe the writer would be interested to hear from you..