Built with both 4.5 and 5-inch centre heights the VSL was later listed as the Model 500 VSL. Introduced as a 4.5-inch centre height machine in January 1966 (from Serial No. 18970) both are very desirable machines - but, unfortunately, difficult to find. Apart from a very rare, non-screwcutting, capstan-equipped export version with a "Harrison" label, the VSL was made only in Model AUD form with an under-drive stand, screwcutting gearbox and power cross feed. On early versions only the drive system was altered, to a mechanical variable-speed type, with the rest of the lathe mechanically identical to the AUD. However, on later models, an effort was made to significantly upgrade the machine and it was equipped with a larger 1.375" bore headstock spindle with a hardened and ground American Standard size L00 taper nose and a 5-Morse taper complete with both a short reduction sleeve (to take it down to 2-Morse) and an adaptor to accept direct-fitting C5 draw-bar operated collets. Instead of cast-iron gears the backgears were made in induction-hardened steel and, to improve their reliability, the tumble-reverse gears equipped with needle roller bearings. On all VSL models the electric motor, positioned inside the left-hand side of the cabinet stand, had a wide "expanding-and-contracting" V pulley mounted directly on its shaft. Pulley movement was controlled by a cable and rod driven from a handwheel on the front of the stand. The upper drive pulley, which reacted to the movement of the motor pulley by opening and closing automatically, was carried in bearing hangers from which a second (conventional) link-type V-belt took the drive up to the headstock spindle. The speed range was typically 50 to 2000 rpm and, because the drive was infinitely variable, either an electric or mechanical rev. counter was fitted to show the operator what was going on. If the tachometer is broken or missing businesses specialising in vintage car and motorcycle restoration can often help with replacement or repair. Some early 4.5" centre-height VSLs were fitted with a motor with an extended left-hand shaft on which was mounted a very expensive electro-mechanical disc brake, controlled by a switch fitted to the left-hand face of the motor-control panel. Nearly all VSL lathes were supplied when new with 3-phase motors - 930 r.p.m./1-h.p. on the screwed-spindle nose models and 930 rpm/1.5-h.p. for the L00 version. Unfortunately, because the drive mechanism fitted to them has to be accurately aligned to work properly the VSL is difficult to change to single phase operation. In addition, because the coolant pump, light unit and safety-interlock transformers are also 440 volt 3-phase, rather than attempt to completely re-engineer the peripheral controls, it is much easier to leave everything in place and run the lathe from a phase converter or inverter. If this is done it is worth bearing in mind that, whilst the main motor can be easily altered from "Star" 440 volt to "Delta" 240 volt working, many of these machines were fitted with both a push-button safety starter of the front panel and another "automatic" contactor unit at the rear. Because the coils in the contactors are 440 volt they usually refuse to work when supplied with the 220/240 volts put out by the inverter. Coupling the inverter (as is usually recommended by their makers) directly to the motor and bypassing the built-in controls has been known to produce a far more effective conversion. Of course, doing this means that the safety-interlocks on doors and backgear are lost and other arrangements have to be made to power the coolant pump and light unit*.
Fitted to a distinctly different stand, and with a 5-inch centre height, the final version of the VSL was known as the Model "500 VSL". An interesting point concerns VSL models fitted with the LOO spindle: on these lathes a screwcutting gearbox was standard but with changed internal ratios and the availability of "compact" English/metric and metric/English conversions gears. Instead of the older "full-size" 127/110t (inch to metric) and 135/127t (metric to inch) gears the LOO versions were, respectively: 64/54t and 76/65t.