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Drummond Round Bed "A" Type 4" x 11.5". This lathe, famous amongst generations of British model engineers taking their first tentative and usually impecunious steps into the hobby, was manufactured from 1908 to 1940. During that long production run there were, apart from three designs of headstock bearing, only minor changes in specification required. Although comparatively inexpensive, and designed to sell at the bottom end of the market, the lathe was not cheapened in any way but built to the usual honest, practical, Drummond standards; even the wheel on the end of the leadscrew had a proper horn-covered handle.
The heart of the lathe was the heavy, round, 3" diameter cast-iron bed, ground to within 1/1000" on an American Norton cylindrical grinder and formed with a bevelled slot along its base. The right-hand thread leadscrew passed through the centre of the bed (of which a 12" longer version was also available) and was engaged by a dog clutch, the operating lever of which protruded through the headstock casting below the front spindle bearing. The end of the leadscrew was fitted with a large, ungraduated wheel for hand operation (the rather-fine handle being made from horn or hardwood) but because the leadscrew had a right-hand thread, this worked in the "opposite" sense to normal; turning it clockwise resulted in the saddle being brought back towards the tailstock not moved towards the chuck; however, after a few ruined jobs, most owners quickly adapted to this idiosyncrasy.
The "saddle" assembly, with its top formed into a boring table, could be partially rotated round the bed - which had the effect of altering the height of the table in relation to the lathe centres; it was thus possible to make vertical adjustments when setting work on the boring table, setting cutting tools to height and milling, etc.
A compound slide was never available for the Round Bed, instead the single tool slide was mounted on a vertical bar that passed through an extension to the front edge of the saddle; this extension, being split and formed into a clamp, allowed the toolslide, which had a graduated base, to be both raised, lowered and swivelled. The toolpost was self-contained (which meant that no tool-holding strains were carried by the central bolt) and fitted with a round hole for boring tools as well as the usual rectangular slot.
On the first machines the top of the headstock was machined flat and the bronze bearings bolted to it. On the very earliest lathes these bearings were in two parts, with the upper and lower sections separated by adjustment shims; later models had the bearings formed in one piece with the clearance set by a slot and pinch bolt. Later still, from around 1919 (when the Serial number prefix changed from "MCHA" to "O") , the design of the headstock was modified to that shown in the picture above, the spindle running direct in the cast iron of the headstock with the bearing "nipped" into adjustment by a clamping screw acting on a slit at the rear. Other changes introduced at around the same time (although, as with the flat-bed lathes, there would inevitably have been some considerable overlap) were a reduction in the number of T slots in the cross slide from 4 to 3, a modification to the tailstock where the barrel was increased in diameter and the previous use of a white metal liner abandoned - and the adoption of push-in spring retainers on the changewheel studs instead of the previous slow-to-operate, screw-on rings.
Although very early examples appear to have had slightly different spindles to later versions with a thread 1.040" in diameter by 14 TPI (with no plain section to act as a register before the abutment face) and bored out to 0.325" rather than 0.375". The spindle was then modified to carry a 7/8"-diameter, 10 TPI thread on the nose and was given a better ground (rather than turned) finish on the bearing surfaces; as standard it was not hollow, but the 0.375" diameter hole could be ordered for a: "small extra cost". Later spindles (fitted to lathes with the headstock spindle running direct in the headstock casting) had a 3/4"-diameter by 10 t.p.i thread with a small plain register about 0.25" long before the abutment face. If your Round Bed differs from these specifications do not be surprised; many have been fitted with replacement spindles over the years and the factory did not seem averse to the occasional experimentation with different details of design. The three-step cone pulley on all models was in cast iron, rather heavily made and with diameters of 6", 4.5" and 3.5" - it was intended to be driven by a 1" wide belt.
From the start of production until 1925 a set of eight changewheels was provided as standard: 20t, 24t, 28t, 32t, 36t, 40t 44t and 64t with an extra set to generate metric pitches (at additional cost) of 25t, 35t, 45t 50t and 63T. Thereafter a set of 9 gears (which included those necessary for the metric translation) was supplied: 20t, 25t, 26t, 30t, 35t, 40t, 45t, 50t and 66t giving a threading range of: 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 16, 18, 20, 24, 26, 28, 32, 36 and 40 t.p.i. As on all small Drummond lathes the changewheels were 14 DP with a 14.5 degrees pressure angle; today, unfortunately, the standard pressure angle is 20 degrees so "off-the-shelf" gears will not match satisfactorily; if a new gears are required they have to be specially made. To connect the gears in pairs for a compound train each gear carried a pin and a pin hole; the pins are seated in tapered holes and, if driven out the wrong way, will fracture the gear. By combining extra changewheels a large number of odd pitches and metric threads could also be cut - however, one drawback with the lathe was its lack of slow speeds to help with screwcutting and large facing jobs; no backgear was fitted and the bottom speed with the maker's countershaft was approximately 120 r.p.m. To some extent this could be overcome by re-jigging the belt drive to give lower ratios or, more effectively, by resorting to various third-party accessory suppliers who offered both conventional backgears and a rather splendid epicyclic mechanism built into a slightly larger-than-standard and modified headstock pulley. At least two forms of the latter mechanism were designed: the first, by George Gentry, being published in the "Model Engineer" magazine during 1912 and the second, by A. E. Bowyer-Lowe complete with illustrations and detailed drawings in the same magazine on April 1st, 1915. Because the headstock casting assembly of the early lathes lacked the later cast-in slot to accept a stud on which to run an extra changewheel (to produce left-hand threads) a slotted bracket was provided that bolted to the left-hand face of the headstock; this positioned the extra "reversing" changewheel in a rather distinctive fashion above the others. A range of accessories was offered including a vertical slide that, when mounted on a swivelling adapter with a graduated base, could also be used to mount a neat and effective Indexing and Gear-Cutting Attachment. The swivelling adapter must have been either very popular as an accessory, or later supplied as standard, for many used machines come with one in their stock of kit.
Various drive arrangements were available, the most common being a cast-iron stand fitted a with treadle drive and 100 lb flywheel.
The Round-bed Drummond, though of simple construction, was capable of accurate work and many examples are still in use today; in standard short-bed form its overall length was 2 feet 11 inches (889 mm) and it weighed approximately 105 lbs. (48 kg)..
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