South Bend "Light Ten 10-K Model A" rear-drive bench lathe.
The "Light Ten" series of lathes were introduced in 1950 and followed the normal South-Bend nomenclature of A for lathes fitted with a screwcutting gearbox and power cross feed; B for machines which retained power cross feed but screwcutting with changewheels and C for the standard, non-power cross feed changewheel models.  The machine was South Bend's cheapest ten-inch lathe and originally specified with either a 12-speed flat-belt drive that gave spindle speeds of approximately 48 to 1435 rpm. or, as an option, a sixteen speed V-belt drive. Whilst the latter offered a better spacing of speeds, the upper and lower limits were almost identical; however, such was South Bend's attachment to flat-belt drive that they relegated the 16-speed model to an almost casual mention in the back of the Light Ten sales brochure (though featured equally in the General catalog) - and even pointed out to prospective customers the disadvantage that, when the V belt needed changing, the headstock and countershaft would have to dismantled first - hardly a ringing endorsement for a system probably forced on them by market preferences. Spindle speeds with flat-belt drive were: 48, 80, 96, 137, 165 and 276 r.p.m. in backgear and 244, 415, 502, 706, 844 and 1435 r.p.m. in direct drive. With V-belt drive the speeds became approximately: 52, 72, 95, 112, 130, 150, 195 and 265 r.p.m. in backgear and 285, 370, 495, 570, 670, 1010 and 1365 in open gear. Besides the  bench models a version of the 10-K was also available fitted to a very compact, twelve-speed, underdrive, sheet-metal cabinet stand as first used for the 9" "Workshop" model in the 1940s. During 1966 and 1967 a small number of these underdrive lathes were fitted with an infinitely variable-speed drive system that gave, from a 0.75 h.p. motor, a range from 65 to 360 r.p.m. in backgear and 325 to 1800 r.p.m. in direct drive. Interestingly, the drive unit, made Hi-Lo Manufacturing of Minneapolis,  Minnesota, is still in production and, far from being confined to machine tools, has been applied over many years to countless other types of industrial machinery. A full spares service is available with parts stocked by run-of-the-mill belt and pulley dealers.
The Light Ten was, in effect, an upgrade of the classic 1930s original with a modified headstock spindle (still running in bronze bearings fed by capillary oilers) modified to accept direct fitting collets of the 6K type that allowed an increase in through bore from the 1/2" or the previous 3C type to a useful 5/8". The centre height was increased to 5 inches and numerous detailed changes made to the specification - including a spring-plunger arrangement instead of a bolt to locate the tumble reverse gears and a conveniently positioned "knob" on the face of the headstock to release the belt tension. However, the main elements of the lathe, the complete carriage assembly (with the exception of the thicker top-slide base) the screwcutting gearbox , bed and many of the accessories could be interchanged with the original pre-war design.
In line with standard South-Bend practice a "toolroom" version of the lathe was also available; this was no more accurate than the ordinary machine but was fitted, as standard, with a "precision" leadscrew, taper-turning unit, draw-in collet attachment, collet rack for attachment to the tailstock end of the bed (but no collets), dial thread indicator, thread cutting stop, large faceplate and a micrometer stop.
Four between-centre capacities of 16", 22", 28" and 34" were offered across the range of different models and included, like the contemporary 9-inch range, versions with a gap bed - though these are very rare and seldom found.

South Bend Light Ten circa 1950 fitted with the 12-speed flat-belt drive countershaft unit.
Although by 1950 greater consideration  was being given to safety matters (and the lathe was certainly well-guarded compared to earlier models) the changewheel gear-guard cover was still not fitted with a catch.

Sold as Catalog No. CL222 the rare South Bend 10-K "Light Ten" lathe with infinitely variable-speed drive. With its extra-large micrometer dials and taper-turning unit this lathe was particularly well specified.
The lathe was offered only during 1966 and 1967, with the South Bend variable-speed unit being very similar to those adapted for use on Rockwell-Delta and Sheldon lathes. The unit used expanding and contracting pulleys side-by-side on a common, overhung shaft and was of a type known in the UK as the "Ainsworth", after its Victorian inventor. Many similar devices have been offered over the decades by such as Browning, Gerbing, Lewellen, Lovejoy, Maurey, Reeves, Speed Selector and T.B. Woods - and are still available today as a Google search will confirm.
The South Bend assembly was a self-contained unit, very heavily built and carried on a cast-iron frame bolted into a sheet-steel cabinet. A handwheel on the front of the stand controlled the mechanism through a universally-joined shaft and screwed rod that moved the vari-speed pulley assembly up and down a pair of vertical bars positioned between a fixed motor and fixed final-drive shaft. Forcing the unit in either direction caused the tension of the two belts to simultaneously open and close their pulleys and so vary the drive ratio. From the expanding and contracting pulleys the drive passed up to a shaft, mounted in bearings on a swinging plate, that carried a single pulley from which the headstock spindle was driven by an enormously wide flat belt. Tension of the final drive belt could be adjusted independently by a right-and-left-hand-threaded turnbuckle.
To save the expensive of a electric revolution counter the long handwheel boss was provided with a sliding pointer to indicate spindle r.p.m and is possible that, like those used on Delta-Rockwell lathes, a mechanism could have been incorporated to limit maximum speed when the lathe was used for training apprentices - and especially in schools.