When introduced, the 500 was the largest machine to join the original line up of M250, M300 and M400/M450 and was designed to meet the international ISO standards R1708 and BS4656 for general-purpose lathes (suitable for both production use and in maintenance and repair shops); it was also subjected to lengthy testing by the Machine Tool Industry Research Association. The actual swing was 530 mm with a choice of three between-centres' capacities of 1000, 1500 and 2000 mm (40", 60" and 80"). A detachable gap in the induction-hardened bed was optional and when fitted allowed the lathe to turn a piece of metal 730 mm (28.75") in diameter and up to 200 mm (7.875") deep. The bed was identical in size and weight to that used on the M400 and M450 lathes with a maximum depth beneath the headstock of 380 mm (15") and a width of 360 mm (14.125"); heavy cross ribs braced the front and back faces and left clear vertical spaces for swarf to fall through. The stand, whilst adequately strong and supplied with a splash-back had neither any form of storage, nor a slide out chip tray - both cost-cutting measures that would have been certain to annoy the unfortunate operator, if not the purchasing company's bean counters.
Of massive construction, the headstock held hardened and 'Reishauer' ground gears fitted to shafts rotating in Gamet precision bearings - a double row at the front and a single row at the rear; the gears and bearings were supplied with oil from a belt-driven pump attached to a separate tank held within the cabinet base. The spindle was bored to pass 80 mm (3.125") and was fitted with a hardened No. 8 D1 Camlock nose and a bush to sleeve it down to a No. 5 Morse taper.
18 spindle speeds were provided from 31 to 1600 rpm from (an easily-changed) 9.2 kW (12.5 hp) motor fastened to an adjustable plate bolted to the back of the bed immediately below the headstock. Five V belts transmitted the power to the geared headstock - the input shaft was fitted with separate clutches, manufactured by the Matrix Company, for forward and reverse operation and the main spindle also carried (as standard) a powerful Warner electro-magnetic brake mounted on its outer end. Two concentrically mounted, rotary selectors that had unambiguous markings and positive indents selected the spindle speeds.
Oil-splash lubricated, the screwcutting and feeds gearbox (with induction-hardened gears) was controlled by three smooth levers - awkward to operate with oily hands - and a single rotary selector. Without changing or rearranging any of the end gears (changewheels) 54 metric pitches from 0.2 to 14 mm pitch, 51 English threads from 2 to 84 t.p.i., 18 Module pitches from 0.2 to 3.5 MOD and 27 Diametral from 8 to 72 DP. The feed to the leadscrew (but not the powershaft) incorporated a torque-limiting mechanism and power feeds ranged from 0.04 to 2.84 mm per revolution of the headstock spindle (0.0016" to 0.112") with power cross feed set to be one half of the longitudinal rate.
With a double-wall, oil-sump apron the carriage was of a type developed in the 1980s where twin bevel gears, which incorporated dog clutches, powered the sliding and surfacing feeds; this feature enabled the operator to instantly reverse either without having to stop the headstock spindle. The engagement lever for the feeds worked through a simple safety gate and merely had to be lifted to selected power surfacing (cross feed) or lowered for sliding (longitudinal feed) - returning the lever to its central position, which could be done under load from the heaviest cut, stopped the feed. On gap-bed machines the carriage-traverse handle (which could be disengaged when using power feeds) was positioned on the right-hand side of the apron, whilst on straight-bed models it was on the left. The makers described the leadscrew nut as being of the "floating" type, used to ensure "maximum threading accuracy". On the right-hand side of the apron, immediately below the standard-fit dial thread indicator was a gated spindle-control lever that provided electrical stop/start and forward/reverse functions. In the middle of the apron was a single gear (moving through a vertical gate in a manner first used on Kerry lathes of the early 1950s) that both selected and engaged power feeds; a separate rotary control was used to set the point at which the power-feeds would be automatically disengaged if overloaded.
Of the full-length type, the cross slide and the top slide (the latter able to be swivelled through 360 degrees) were both fitted with taper gib strips; the handwheels were of the typical Colchester/Harrison semi-lever type with the micrometer dials (dual reading metric/English units were an optional extra) finished in non-glare satin chrome; the cross feed screw could be adjusted to eliminate backlash. When a machine is fitted with dual dials the cross feed screw and nuts (the nut was a 2-part affair with fixed and adjustable components) and be either English or metric. To tell which is fitted look at the micrometer dials: the engravings on the outside (nearer the operator) indicate that type is fitted. i.e. if the metric graduations are on the outside the lathe has been fitted with a metric screw and nut.
Apart from its height the tailstock was identical to that on the M400 and M450 machines; it had a 73 mm diameter (2.875") spindle with 155 mm (6.125") of travel and a No. 5 Morse taper. The spindle was engraved with ruler marks in either inch, metric (or both) graduations and a rotary micrometer dial was fitted as standard.
A 1000 mm capacity machine weighed 1871 kg (4124 lbs), the 1500 mm version 2074 kg (4571 lbs) and the long-bed 2000 mm model 2277 kg (5027 lbs). Overall lengths were, approximately: 2215 mm, 2690 and 3240 mm (88", 106" and 127") respectively..