Discounting the quite different pre-WW2 flat-belt drive Bantam, the better-known and very handy later geared-head model was built in considerable numbers from 1963 until 2001. Five distinct version were constructed that we will call the Mk. 1, Mk. 2, Mk. 3, Mk. 2 Colt and the (rare) VS3500. The Mk. 1 (by far the most common encountered) was a very compact but heavily-built geared-head lathe supplied as standard with a hardened bed that provided industrial levels of strength and performance in remarkably small space; the stand, for example, was only 53" by 23", just a little bigger than the industrial cabinet used for the 3.5" Series 7 lathes. The makers labelled the machine as a 5" by 20" or 30" - but the real centre height was 5.625" - and you can squeeze a little over 23" between centres on the short-bed version and 33" on the long. Three different specifications were offered: the "Hawk", with screwcutting by changewheels, and two models with screwcutting gearboxes: the "Eagle" with English pitches and the "Condor" with metric. However, in each case, conversions sets were available to allow all types to cut both English and metric threads. The approximate weight of the standard lathe was 756 lbs (343 kg.) Non of the lathes carried Hawk or Condor badges and the "600" sticker, often found on the facia panel or bed, was not a model number but referred to the "600 Group", the owners of Colchester, Harrison, Pratt- Burned and several others machine-tool companies.
Built on very similar lines to the Mk. 1, the Mk. 2 had a new angular-style headstock and screwcutting gearbox, but with the bed, carriage and tailstock remaining virtually unchanged. A model of the Mk. 2 designated "Colt" was also manufactured in standard, long bed and Vari-Speed models whilst the Mk. 3 was an entirely different machine and, in effect, a Harrison M250 with cosmetic alterations to the controls and appropriate badges.
Mk. 1 Headstock
Running in taper roller bearing through an all-geared, oil-bath headstock, the spindle had an American type D1-3" Camlock fitting, the security of which allowed a safe, high-speed reverse. Unfortunately, chucks with this fitting are expensive to manufacture and it is often cheaper (although still not inexpensive) to mount a replacement chuck on a new Camlock backplate. Precaution is required when mounting new D1 accessories on the spindle nose - and it may be necessary, in order to achieve maximum grip, to re-set the Camlock studs within the backplate - it is essential to read the maker's instructions on this point if you are unsure of how to do it. Even on this cheapest of Colchester lathes the spindle bearings were the expensive but super-accurate "Gamet" micron-precision type used on all the company's larger lathes; as all the gears were also hardened, honed and carried on multi-spine shafts the headstock has, as a consequence, a reputation for absolute reliability and only many years of heavy use--or clumsy mishandling of the gear change--is likely to cause problems.
Mk. 1 Spindle Speeds and Drive System
Originally fitted with either a single-speed motor (and branded as the Model 800) the lathe had eight speeds from 36 to 800 rpm or, with a two-speed motor and marked Model 1600, with 16 speeds from 36 to 1600 rpm. Because the motor was mounted externally, at the rear of the headstock, it is a comparatively simple matter to change it. However, if you intend to operate lathe from (a now inexpensive and effective) 1-phase to 3-phase variable-speed drive inverter, the 2-speed motor type will require a special high-voltage inverter; if you would like more information please email for up-to-date information. On the Eagle and Hawk models the standard electrical control was by a simple push-button, direct-on-line starter but with the option of a much more sophisticated and safe system (that was standard on the Condor) of a handle, supported by a bracket on the right-hand side of the apron, rotating a "third-rod" control shaft that passed beneath the apron and connected, via a drop link, to a reversing switch mounted behind a fascia plate between the stand legs. If fitted, it is worth checking this mechanism for wear; the central, or "off" position of the handle was maintained by a bracket (fastened to the right-hand face of the apron) with a deep, spring-loaded, triangular-shaped indent; if this indent is broken, or rounded off, it is very easy for the operator to unintentionally push the handle over centre, and so cause the spindle to go into reverse. Problems with the electrical-reversing switch can sometimes be traced to play in the ball joints at each end of the vertical drop link, or rust forming on the two sliding plates on the exterior of the switch; these problems, though annoying, are easily corrected.
If the mechanical parts of the reversing mechanism are beyond repair, it is a simple matter to bypass the system and rewire the electrics to a conventional rotary-type reversing switch mounted on a bracket that allows the operator quick and easy access without moving from his normal working position. In fact, on models without the screwcutting gearbox, the electrical system was often arranged like this when new, the precise type of switchgear varying somewhat over the years.
Because they combine such a range of desirable features Bantams of all types are very sought after second-hand; if you have a machine in good condition, and maintain it carefully, it should retain its value indefinitely.
Mk. 1 Screwcutting and Power feeds
Although most Mk. 1 Bantams were fitted with a screwcutting gearbox, numbers of "Hawk" models were supplied to training workshops with cheaper imperial or metric changewheel screwcutting. On the changewheel models there was, unlike their contemporary Harrison competitors, no 3-speed leadscrew gearbox, instead a simple 2-speed gearbox was employed where a sliding double gear on the feed shaft could be moved by a lever into one of two positions to pick up a single gear on the leadscrew - and so select either a fast or a slow rate of feed (the leadscrew on Bantams is used only for cutting threads and should normally be left disengaged).
The "Eagle" screwcutting gearbox gave 29 English pitches from 3.5 to 80 t.p.i. (and 15 metric with translation gears) and the Condor 27 metric pitches from 0.2 to 6 mm (and 26 English with conversion gears). Sliding feed rates varied from 0.001" to 0.028" on the screwcutting model; from 0.001" to 0.032" on the Eagle and from 0.02 to 0.7 mm on the Condor. In every case the surfacing (cross-feed) rate was half that of the sliding. Both models were equipped as standard with a number of extra changewheels to extend the normal threading range beyond that commonly required; if these gears are missing from a used lathe, it's worthwhile asking if they have been stored separately and perhaps overlooked. Power cross and longitudinal feeds were fitted to all models - with a push-pull knob to select sliding or surfacing and with the engagement and disengagement by a flick-in-and-out lever at the bottom of the apron. To protect the power-feed mechanism against overload damage all models were fitted with a shear-pin incorporated in the topmost gear of the train to the screwcutting gearbox..
Unfortunately the maker's stand, in basic form, lacked any form of storage, although some long-bed lathes have been found with a drawer across the central section between the plinths. An interesting point concerns the four welded-on mounting points: the one at the back behind the headstock was set flush with the stand's lower edge and drilled and tapped 1-inch UNC to take a hollow, screwed stud through which passed a levelling bolt The other three points protruded below the base, with the threaded rear bolt assembly being used to set everything up level. For normal work the lathe stand could be left unsecured - or mounted on anti-vibration pads - it only being necessary to bolt it down if jobs were to involve high speeds with out-of-balance workpieces.