Davenport engine lathes were manufactured by the Davenport Locomotive Works of Davenport, Iowa, USA. It is likely that the company offered a variety of sizes but, currently, details are available of only one type, a 22.25-inch swing (11.185-inch centre height) Extra Heavy Duty Double Backgeared Engine Lathe, as was almost certainly current during the period 1910 to 1925. The makers claimed that this particular model was an exceptionally strong machine, equal to a 24-inch model, and made extensive use of the word "liberal" - as in "liberal depth" and "liberal wearing surfaces" - throughout their sales literature.
Particularly strong, the bed had V and flat ways and was some 16-inches deep and 19-inches wide and constructed as a proper beam - without the then-common reduction in section towards the tailstock end - and heavily cross braced. With every prospect that the lathe's fate would be to tackle work of the heaviest nature, the designer had extended the front and rear bed-ways to a point half-way along the headstock, an arrangement that allowed the carriage to overlap it and, with the compound slide rest exactly on its centre line, give better-support to the tool and more even wear of the bed and saddle. A choice of bed lengths was available - 8, 10, 12 and 14-feet long - with the shortest offering 39-inches between centres. To give some indication of the fierce competition in the machine-tool trade at that time, it's worth recording that Davenport felt it necessary to mention that all the lathe's shafts and studs were in steel, all gears cut from steel blanks and that even the carriage-feed rack had machine-cut teeth - and was not therefore of the inferior type fitted as a raw casting - it even being possible at the time to buy cheap, light-duty lathes with the important headstock backgears in an "as-cast" state.
Lathes supplied with beds of 14-feet and longer were supported in the middle by an extra set of legs, no doubt as short and insubstantial-looking as those fitted to the example illustrated below - it not occurring to manufacturers for some years that long and heavy box-like cast-iron plinths could add significantly to a bed's rigidity and enable it to work commensurately harder..
The headstock was typical of its era in being fitted with cap-type bronze bearings; these were 4.75-inches in diameter and 6-inches long behind the spindle-nose - and 3.25-inches in diameter and 4.5-inches long at the other end. A 1.375-inch bore spindle of 0.35 to 0.50 carbon steel with a 3.75-inch diameter, 4 t.p.i nose thread was used and carried three suitably large cone pulleys of 10, 12 and 14-inches diameter that took a 4-inch wide belt. Spindle thrust was absorbed against hardened and ground steel washers with the clearance adjusted by nuts. The headstock carried what was known as "double backgearing", a term liable to misinterpretation by customers and abuse by manufacturers. The problem lay in the definition: some makers referred to lathes with no backgear at all as "single-geared" whilst others used a variety of terms including plain-turning, ungeared and brass-finishers'. When a genuine backgear assembly was fitted - that allowed really slow gear-driven feeds - some makers naturally adopted the term "double-geared" whilst other more honest ones referred to then as "backgeared". Larger lathes had long been available with two and even three-stage reductions on the headstock and in the case of the Davenport it appears that the makers did indeed offer a proper-two-stage reduction quoting a "slow backgearing" reduction of 12.58 : 1 and a "fast backgearing" of 3.56 : 1. The headstock bullwheel (the larger gear on the main spindle) could be locked to the cone pulley in any one of four positions. Davenport's arrangement of gearing gave a total of 9 speeds, arranged in geometric progression, and driven by the maker's "double-friction" clutched countershaft that was intended to run at 125 r.p.m. Although not stated this would have resulted in spindle speeds spanning approximately 5 to 350 rpm.
The changewheel drive from spindle to Norton-type quick-change screwcutting and feeds gearbox was through a tumble-reverse mechanism mounted on the outboard face of the headstock. The screwcutting gearbox, driving a 1.75-inch diameter, 4 t.p.i ground-finish Acme thread leadscrew, was able to generate threads with the following inch pitches: 2.25, 2.5, 2.75, 3, 3.25, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 8, 9, 10, 11, 11.5, 12, 3, 14, 16, 18 and 20. Unfortunately the rates of power sliding and surfacing feeds are unrecorded. As a cheaper alternative, instead of a full gearbox, the lathe could be equipped with a set of changewheels for screwcutting,