Stima AMC Model Élan/500
The No. 5 Morse taper headstock spindle, bored to clear a 1.57-inch diameter bar and with an A1-6" size American nose, was in a nickel-chrome steel, hardened, rectified and ground. At the front it ran in a pair of pre-set opposed conical roller bearings of the "Machine -tool Type 0" - a specification that guaranteed radial play of less than 0.000016 inches. The spindle assembly was dynamically balanced and the whole assembly lubricated by a pressure pump with oil throwers to limit leakage.
The drive system and its operating controls, as befitted a machine intended for arduous, long-term duty, were well thought out and solidly engineered. Electrical push-button contactors ran at 24 volts for safety and all circuits were protected by a combination of thermal relays and fuses. The motor, 6 h.p. as standard but also optionally of 4 or 8 h.p., was mounted in the cabinet base and flanged directly to an 11-speed (Raynard range) gearbox with a built-in Type MG3 SIGMA double clutch unit. Running in the same splash oil-bath as the gearbox, the clutch was arranged to give instantaneous forward or reverse at any speed whilst a mechanical brake, automatically synchronised with the clutch control, brought the spindle to a halt at the moment of declutching. This feature not only allowed the time between work-piece changes to be kept to a minimum but also encouraged the operator to select the right speed for the job - the time wasted in stopping and starting the spindle being negligible. The clutch and brake assembly was operated by a lever pivoting from (and moving with) the right hand face of the apron and connected to a long control rod below and parallel to the leadscrew. However, even on the longest-bed versions, the control lever was not (probably because the carriage ran right up to the outer face of the screwcutting gearbox), duplicated at the headstock end as it was on most other makes. If the customer so desired, the automatic application of the brake could be disconnected and a foot-operated brake-bar supplied instead. Drive to the spindle was by 7 V-belts, the pulley at the spindle end being independently mounted and so allowing the belts to be changed without the need for dismantling. A long boss, extending from the side of the gearbox and passing through the front of the stand, ended in two conveniently positioned (if rather long) gate-change levers by which means the spindle speeds were changed. A useful and well-spaced 22 speeds were provided: 11 from the gearbox and the others by engaging a headstock-mounted backgear. For the 9.5-inch lathe the full speed range was, in backgear: 31, 40, 50, 63, 80, 100, 125, 155, 190, 250 and 310 r.p.m. and, in direct drive: 250, 310, 390, 500, 630, 780, 990, 1250, 1520, 1530 1960 and 2500 r.p.m. Alternatively, a slower range of speeds could be specified: in backgear: 20, 25, 31, 40, 50, 63, 80, 100, 125, 157 and 200 r.p.m. and in direct drive: 157, 200, 255, 320, 400, 500, 630, 800, 990, 1260 and 1600 r.p.m.
On the 7.5-inch model the available speeds were adjusted slightly to give a standard range the same as the slower alternative on the 9-inch (20 to 1600 r.p.m.) or, by paying a supplement, to be the same as that lathe's standard set (31 to 2500 r.p.m.).