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From the middle of the 19th until the early 20th century a number of American engineering companies connected with the watch, optical and metrology industries began to involve themselves in the manufacture of precision bench lathes; eventually these were to include: Stark (the originators in 1862), Levin, Bottum, American Watch Tool Company, B.C.Ames, Bottum, Hjorth, Potter, Pratt & Whitney, Rivett, Wade, Waltham Machine Works, Wade, Pratt & Whitney, Rivett, Cataract, Hardinge, Elgin, Remington, Sloan & Chace, W.H.Nichols, Crystal Lakes and (though now very rare) Frederick Pearce, Crystal Lake, Ballou & Whitcombe, Sawyer Watch Tool Co., Engineering Appliances, Fenn-Sadler, "Cosa Corporation of New York" and UND.
By the late 1940s demand for this type of machine had fallen to the extend that the only manufacturers left were Stark, Derbyshire, Hardinge and Levin, the latter a newcomer from the 1930s who built only smaller types. Although each company's lathes were still recognisably based on designs at least 50 years old, all had managed to make progress in one especially important area - the arrangement of a drive system that was compact, efficient and economical. It is fair to say that this development took some time to evolve (though Atlas had solved the problem for light amateur lathes in 1932 with their built-on, multi-V-belt countershafts and motor mounts) and it was many years before progress was made away from expensive, cumbersome and complicated systems that required the mounting of separate motors and countershafts requiring constant lubrication, adjustment and time-consuming maintenance. Early efforts by Cataract, Hardinge and Pratt & Whitney to improve on this 19th century technology involved mounting the drive system on threaded and hence adjustable cast-iron columns as part of a self-contained stand. Unfortunately, with so many tubes, bearings, hangers and pulleys involved in the construction these were very expensive and their cost often several times that of a basic lathe. By the mid 1930 all three makers had realised that the answer lay in modifying their lathes to work on simple, underdrive stands, but even these (with the exception of the Pratt & Whitney geared bench countershaft) still required the customer to buy a complete, integrated unit, it being impossible to purchase just the lathe, ready to drop on a bench and run without further ado. However, by the late 1930s even the arc traditionalist Stark had caught up and offered a confusing choice of mountings including open and enclosed stands with a base-mounted 3/4 h.p. 1725 r.p.m. motor driving though a disc clutch to an expanding-and-contracting pulley system and ball-bearing countershaft - and then by twin V-belts to the spindle. In 1940 this system was further refined and fitted to what must have been world's first precision plain-turning lathe to be equipped with a completely self-contained drive The lathe offered was company's largest, with a 9-inch swing and 20-inches between centres, and carried the traditional Stark model numbers "4" and "41/2" denoting maximum collet capacities of 3/4" and 1" respectively. However, the type was additionally described in advertising literature as both the "Pilot Shaft Type" and "Integral Drive Precision Bench Lathe" and was sufficiently different to be granted a United states under Number 20.81.641. However, other makers were also in on the act, Pratt & Whitney with their lovely Model C and Crystal Lakes, whose very rare 13-inch model used a variable-speed drive unit by "Master" together with V-belts for the final drive.
While the bed retained its traditional central T-slot and bevelled edges, the headstock-end foot was enlarged to form a box, very deep front-to-back, with a flange-mounted motor bolted to the outside of its right-hand inner face (so the motor lay parallel to the bed). Above the box was a cast-iron cube with the motor's control switchgear placed handily on top and a spindle-speed indicator needle on the front. On the inside of the main box was a self-contained variable-speed drive system (exactly as used in the underdrive-stand version) consisting of two pairs of expanding and contracting pulleys with a wide transmission belt riding between them. A handwheel on the front of the bed revolved a shaft (fitted with a bevel gear on its end to turn the drive through 90º) that caused the inner set of pulleys to open and close; as one set moved apart the belt sank nearer to the shaft while its tension forced the other set closer together and moved the belt further away - so varying the transmission ratio. Like all such systems the control only worked when the drive was running and heavy-handed attempts to alter the settings when stationary could cause damage. From the internal countershaft the drive to the headstock was by twin V-belts that, ingeniously, could be replaced without having to dismantle the headstock or drive system. Unfortunately, although the twin belts would have provided plenty of grip, and had a very long life, when replacing them it was essential (if serious vibration problems were to be avoided), that their only precision-matched pairs were used. The entire mechanism was very similar to that used on the English Raglan "Little John" lathe introduced in the late 1940s but with the added advantage of being completely enclosed within the headstock-end of the bed. As a further refinement Stark incorporated a multi-disc clutch between the motor and pulley with operation by a long lever, pivoting from a point low down on the face of the headstock; this control had the additional (very useful) function of automatically applying a spindle brake when moved to its central position.
Made to the company's standard dimensions, to accept all the older accessories, the rest of the lathe was conventional Stark with surfaces finished by hand scraping. Even the paint was carefully applied with the makers claiming that: "… for fine appearance and durability is unsurpassed in the machine tool industry." The 1.25-inch bore headstock spindle was manufactured from low-carbon steel with heavy case hardening that resulted in a tough core and very hard-wearing surface. To ensure absolute concentricity the 2" x 10 t.p.i. nose thread, collet seating and taper were all ground with the spindle mounted in its headstock bearings. The bronze spindle bearings of the Standard Model, lubricated by wicks from large oil reservoirs within the headstock walls, were of the tried-and-tested Stark pattern with, at both ends, a short 45-degree and longer 3-degree taper. In order to retain absolute alignment adjustments were made by altering the setting of just the left hand unit.
The headstock of the High Speed Model contained the finest grade of ball bearing made by the New Departure Company; these were given a degree of preloading and allowed the spindle to run at very high revolutions for extended periods. The speed range of the Standard Model ran from 170 to 2200 and the High Speed Model from 280 to 3500 r.p.m.
Like most precision bench lathes the Stark was also offered fitted out for light production work as a "screw machine" - a design known in Great Britain as a capstan lathe - and as a "second operation" lathe for the precision finishing of parts or use in an intermediate stage of production. The main additions to the standard lathe were a lever-action collet closer, a bed-mounted 6-tool automatic indexing turret and a lever-operated cut-off and forming slide..
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