Atlas 12" x 36" long-bed Series 3000 on the maker's underdrive stand
As the final 12-inch Atlas lathe was assembled on the 6th of March, 1981 it brought to an end a production run that started with the original 9-inch model of almost 50 years. Introduced during 1959. this final version of the lathe was designated in publicity material as both the "Late-model 12-inch Atlas" and the "Series 3000".
Although the flat-topped "English-style" bed (with 0.5-inch thick ways) still flew in the face of American preference for inverted V-ways, the rest of the machine was heavily revised and few parts were interchangeable with the earlier model. It was available in two versions, for either bench or stand mounting, with the former having a bronze-bearing countershaft (of rather agricultural construction) and integral hinged (cast-iron) motor mount that bolted to the bench behind the lathe (with a bracing arrangement to the back of the headstock). A lever-operated mechanism simultaneously slackened both headstock and motor belts. The stand-mounted lathe sat atop a neatly-constructed, 190 lb cabinet (made from 3/16" thick steel with a chip tray as standard) that held a simple but robust under-drive countershaft with its pulleys overhung on 3/4"-diameter shafts from each side of bearings contained within central plumber blocks. Both models had an almost ideally-useful range of 16 spindle speeds that ran, in backgear, from 28 through 45, 70, 83, 112, 134, 211 to 345 rpm and, in direct drive, from 164 through 266, 418, 500, 685, 805, 1270 to 2072 rpm. Neat cast-aluminium covers guarded both the headstock and motor belt runs and the changewheels.
Strangely, although the bench model had a single V-belt drive to the headstock, the underdrive model used two - a design that can often lead to trouble when worn or unmatched belts are used. If your 12-inch underdrive suffers from a noisy headstock, vibration or a poor finish on turned work, look first at the final drive to the headstock spindle and check (by putting a chalk line across them and running the lathe) that the two belts are exactly the same length. A solution - and one that saves having to dismantle the headstock and countershaft to replace the belts - is to use a modern T-link type.
While almost every 3000 Series lathes appears to have been fitted with a screwcutting gearbox, some were made with a standard changewheel set up; the sales catalogues were a little vague on this point with publications for the American market sometimes listing the gearbox as a standard fitting on both stand and bench models - but also as an extra on the bench model only. However, export editions managed to show it as standard and, simultaneously, amongst the extra-cost accessories for both versions (the lathe was heavily promoted in the UK, with full-page advertisements taken in the Model Engineer Magazine and other publications). The gears within the box were of unhardened steel with all the bushes, whether for gears or rotating shafts, of the simple bronze Oilite kind lubricated through handy, dirt-excluding flip-top oilers. The "English" box was able to generate feeds from 0.0042" to 0.520" per revolution of the spindle and 54 threads from 4 to 240 t.p.i while that fitted to the rare all-metric machines gave feeds from 0.089" to 6.0 mm and 29 threads from 0.1 to 6.0 mm pitches. In the right-hand section of the box was a safety over-load clutch that protected the drive against damage - one of the problems with earlier lathes being the tendency for the cast-in key on the ZAMAK gear that engaged with the leadscrew to shear off. The 3/4"-diameter 8 t.p.i leadscrew was slotted and carried a sliding key that drove, via a bevel-gear system within the apron, the power cross feed mechanism. End thrust in both directions was absorbed against radial need-roller bearings and, fitted at the headstock end of the shaft, was an over-load protection device designed to slip and prevent damage to the gearbox, its (steel) changewheel gears and the apron mechanism.
With a 1.5" 8 t.p.i. nose, 25/32" bore and 1/2" collet capacity the headstock spindle ran in Timken taper roller races; however, instead of being mounted to the rear of the spindle in traditional fashion the backgear assembly was built into the lower part of the headstock, rather like an early Clausing or Raglan lathe, and engaged by a convenient lever protruding through the front face of the headstock below and just to the left of the spindle nose.
While the apron and 11.25"-long saddle with its 33.75 square inches of bearing surface were strongly constructed - and the latter fitted to the bed by adjustable laminated shims - the compound slide rest could only be described as adequate for its purpose; the cross slide was of the type that, not being full length, caused wear across the central part of its movement and, to enable the cutting tool to be set at the lathe's taller centre line, the top slide base was simply "built up in the sand" to increase its depth. On the positive side the zeroing micrometer dials were clearly engraved and the mechanism to lock their rotation by positive finger screws.
In 1967 a minor change was made to the apron-mounted mechanism that engaged the (standard-fit) power cross feed with the provision of a simple, ball-ended toggle arm that slid the selector button in and out.
Provided with an adjustable gib fitting to the bed, the tailstock was held a 1.125"-diameter ground-steel ram with an No. 2 Morse taper socket and engraved ruler marks from 0 to 3" in 1/16" steps. The clamping handle was permanently attached at the rear of the casting and, because room within the back of the casting was limited, was of the type that could be swung up and round to give a ratcheting action.
The numbering system used by Atlas for this model was:
Bench Model, 24" between-centres, screwcutting gearbox (no motor) No. 3980 (later 3985)
Bench Model, 36" between-centres, screwcutting gearbox (no motor) No. 3981 (later 3986)
Bench Model, as No. 3980 but to an all-metric specification: No. 3965
Bench Model, 24" between-centres, changewheel screwcutting (no motor) No. 3982
Bench Model, 36" between-centres, changewheel screwcutting (no motor) No. 3983
Underdrive Model, 24" between centres, screwcutting gearbox (no motor): No. 3990 (later the 3995)
Underdrive Model, 36" between centres, screwcutting gearbox (no motor): No. 3991 (later the 3996)
Underdrive Stand Model, as No. 3996 but to an all-metric specification: No. 3975
Unlike earlier Atlas lathes, which were without any form of dating (apart from the headstock roller bearings), some if not all 12-inch models had the casting date on the inside of their beds: a mark such as 9-2-59 would indicate a pouring on September 2nd 1959 - providing the foundry workers had bothered to change the mould numbers, of course.
Although in 1959 a basic short-bed, 24" between centres machine with screwcutting by changewheels for bench mounting could be bought for $192 the lathe shown above (on the underdrive stand) was priced at a little over three times as much.
A bench version of the 12-inch weighed approximately 350 lbs with a gearbox and 350 lbs without; the stand-mounted lathes turned the scales at around 550 lbs..