Made by the Coventry Machine Tool Works at St. George's Road, Coventry, England, today the Covmac lathe is rarely found. While the company was not a major player in the lathe market, they were well known for their specialised products connected with the manufacture of nuts and bolts including cold heading, bolt trimming, horizontal forging, thread rolling, screw nicking and "hot-sawing and milling" machines.
Details of the company's lathes are limited but it is known that during the 1930s, and possibly 1940s, just two models were offered: the "13-inch" and "17-inch" - both of almost identical design and construction save for the necessary differences in the castings to accommodate capacity and proportions, the pitch of the leadscrew and the method of drive. Whilst the 13-inch could be had with the option of either an open flat-belt drive or all-geared headstock the 17-inch could only be purchased with the latter specification. The 13-inch model had 39-inches between centres and the 17-inch 60-inches.
Unusually for an English lathe of the time the bed was of the inverted V and flat pattern with the saddle running on an outer pair of Vees and the tailstock guide by an inner Vee and flat. The catalogue listed a detachable gap bed as standard and, with the bridge section, it provided a maximum turning capacity (on a faceplate) of 28 by 7.5-inches on the 13-inch model and 28-inches by 9.5-inches on the 17-inch. The works would also supply straight bed lathes, or beds of any particular length, providing a minimum of 6 machines was ordered at once. Although the depth of the bed was reduced to the right of the gap, unlike many competing lathes on the Covmac this was not too sudden, and a decent length of full-depth casting was left to improve rigidity. On the 13-inch lathe of both types the bed was supported on simple legs at each end whilst the very much heavier 17-inch stood on a large cast-iron plinth (with a small storage compartment) at the headstock-end and a plain leg at the other.
Fitted with a "0.5 carbon steel" spindle of 1.5625-inch bore with a 3-Morse taper and a 6 t.p.i x 2-inch nose thread, the flat-belt drive headstock of the 13-inch model was fitted with plain, parallel gun-metal bearings - carefully reamed to a jig and finished, where necessary, with the scraper - with that at the front being 2.625-inches in diameter. Each bearing was secured by twin bolts caps and end thrust taken by a ball race. The spindle carried a 3-step cone pulley of considerable width with the backgear assembly incorporating a neat device whereby the spring-loaded plunger that connected the large spindle gear (the bull wheel) to the pulley would, when turned to the engage position, automatically engage itself if the spindle was revolving slowly. Tumble-gears to reverse the direction of the leadscrew were placed inside the headstock, benefiting from the oil splash and away from swarf that had worked its way out through the end of the spindle. The geared headstock of both lathes was, to all intents and purposes, of identical layout but with that for the larger machine having a very much more substantial 2.375-inch bore, 4-Morse taper spindle with a 5 t.p.i x 3.25-inch nose thread that ran in a 3.625-inch diameter front bearing with a 4-bolt front cap. Unfortunately the bearing construction (with detachable caps) meant that the headstock was completely open at the top with the casting walls having to finish no higher than the centre line of the spindle and a large bolt-on plate being required to seal the assembly. The input shaft was fitted with a single cone pulley and built into it was a toggle-lever operated clutch controlled by a long wooden rod that ran above the whole length of the bed and was thus handy for the operator no matter where he stood.
Headstock gears were all in heat-treated nickel steel with shafts that ran in bronze bearings; lubrication was by splash from a oil sump in the base of the casting. Eight speeds were available controlled by a separate high-low and 4-speed levers mounted on top of the headstock. Unlike the 13-inch, with its tumble-reverse gears on the inside face of the headstock, the geared models had their on the outside in a manner more commonly found on smaller lathes.