During the middle years of the 20th century the largest lathes in the Essbeco range were the 12-inch and 14-inch (310 mm and 360 mm) centre height models SA310 and SA630. Identical in all respects except for their centre height, the two machines were of conventional but robust construction having a very deep and strong bed with flat and 45 degree angle V-ways and closely-spaced U beams bracing the front and back wall. Both non-gap and gap bed models were available and designated with an addition B in the model description, as in SA 310-B-SS for a gap-bed version of the 310 mm centre height machine.
Mounted on the rear of the headstock end stand, a 10 h.p. motor was drove by multiple V-belts to a 9-speed, oil-immersed, ball-bearing gearbox mounted inside the cabinet leg. The headstock spindle had its drive pulley carried in its own ball races, the design intended to eliminate from the shaft any effects due to the tension of the belts. Spindle speed changes were controlled by two handwheels just to the right of the screwcutting gearbox with a third (and a stop/start lever) mounted on the apron. A further headstock-mounted high-low gear selector, operating a sump-lubricated, helical-gear "backgear" assembly, gave a total of 18 spindle speeds arranged so that the slower range spanned 8.8 to 63 r.p.m. and the higher 70 to 500 r.p.m. On the faster range the 76 mm (3") bore headstock spindle was driven directly and smoothly by V-belts, so isolating it from any vibrations or gear chatter coming from the remote speed-change box.
Hardened and ground, headstock spindle ran in large diameter phosphor-bronze bearings lubricated by thrower chains that dipped into an oil tank in the base of the headstock casting. Axial spindle thrust was taken out by large diameter, adjustable ball race.
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Drive to the screwcutting gearbox and 22-diameter (50 mm) 1/2" pitch leadscrew was through sliding gears, arranged to generate both left and right-hand threads, and contained within and lubricated from the headstock oil supply. The drive went initially to a simple, three-speed gearbox and then into the gearbox proper where a further choice of 11 speeds gave a total range of 66 feeds and threads without any changes being made to the drive gears. On English-specification lathes threads from 3/4 to 60 t.p.i. were available with an additional 27 metric from 0.5 to 26 pitch; standard longitudinal feed rates spanned 0.0016" to 0.12365" (0.04 mm to 3.14 mm) per revolution of the spindle.
Of the heavy-duty, double-wall pattern, the apron had well supported shafts and gears; the power from the feed shaft was engaged by a drop-in worm that allowed instantaneous starting and stopping of the feeds without any binding or reluctance under heavy cutting loads. A single lever selected either power sliding or surfacing, with a separate control to reverse the feeds; in addition, the carriage also carried a mechanism whereby the longitudinal feed could be automatically disengaged, when moving in either direction, at a pre-set point. An unusual and very useful fitment was an apron-mounted handwheel that, when turned though one complete revolution, changed the headstock spindle speed. A lever pivoting from the right-hand face of the apron (and duplicated at the headstock-end of the feed shaft) controlled the electrical stop, start and reverse of the spindle. A simple addition to the lathe, and one that gave protection against inadvertent use (and denied the operator an easy excuse to the foreman when he engaged the wrong lever and smashed the machine) was a set of labels on the apron that indicated the function of each control.
Of conventional design, the compound slide assembly was fitted with tapered gib strips and a 360-degree swivelling top slide that carried, as standard, just a single-tool toolpost.
A robust, very heavy affair, the tailstock was equipped with a rack feed to assist its considerable weight up down the bed; it was clamped down by four bolts that, while effective, need a loose spanner to operate..