Constructed in the style of the already established and very successful 7.5-inch centre height Triumph 2000 and 8.5-inch Mascot 1600 models, the 6.5-inch (165 mm) centre height Student 3100 (together with its close cousins the Student 1800 and Master 2500), continued Colchester's traditional use of two names that had been synonymous with lathes of an almost perfect design and capacity for both training and professional workshop use since the early 1950s. As with older Student and Master model the two lathes shared the vast majority of their components and had only small but nevertheless significant differences in their specifications - all of which, in the case of the newer machines, centred on the headstock and drive system. The expensive Student 3100 was intended to fill the niche vacated by the long-serving 3000 rpm variable-speed "Chipmaster", a machine that proved so popular its production was continued until 1983. Unfortunately, the appeal of the tough little Chipmaster had always been restricted by its limited capacity: a centre height of 5.5 inches and a capacity between centres of just 20 inches made it suitable only for the smaller tasks in a commercial workshop. The "3100" was designed to overcome these limitations and was not only much larger but fitted with an improved and more reliable variable-speed drive system that employed three "geared" speed ranges; these  ranges allowed seamless bands of speeds to be selected between 20 to 120 rpm, 90 to 540 r.p.m. and 500 to 3100 r.p.m. and also ensured that a great amount of torque was available at the slower revolutions. Claimed by the makers to be "maintenance-free" a pair of expanding and contracting pulleys generated the variable-speed changes while a simple gear set within the headstock delivered the fixed speed ranges. The speeds were caused to change by push buttons that activated (limit-switch protected) motors driving threaded rods that caused the pulleys to be moved closer together or further apart - with the "geared ranges" engaged by a single handle integral with a large dial on the face of the headstock. A digital speed display was fitted to the headstock. Because of the high top speed, and the lathe's ability to mount very large jobs, the makers warned against the use of other than the dynamically balanced, ductile-iron chucks with hardened scrolls that had been specially commissioned from Burnerd; if a new chuck is required on these lathes it would be unwise to fit anything other than one recommended by a reputable Western manufacturer. You are welcome to email for details of quality replacements that we can recommend. Once the motor had been switched on by a headstock-mounted push-button starter the starting and stopping of the spindle was by a single lever pivoted from the right-hand apron wall and working through a 'third shaft' (parallel and below the feed shaft and leadscrew) and connected by links to a cross shaft that passed through the bed just in front of the headstock.
Although the lathe was capable of rotating heavy jobs at high speed it was not possible, because of the variable-speed drive system, to fit the same sort of powerful spindle brake that was used on the otherwise very similar Student 1800 and Master 2500 Models. The lathe was, however, fitted with an automatic "fail safe" brake that had a manual release button. Also included was a headstock-mounted emergency-stop button that operated through the obligatory "no-volt" release (to prevent the motor restarting after a power cut) and a motor-run warning light to alert the hard-of-hearing, or those working in a noisy environment, that things were "active" and the controls should not be played with casually.
The rest of the machine was identical to the ordinary Student 1800 and all the accessories for that lathe, and the Master 2500, were identical.
9.5-inch (230mm) wide, the bed was induction hardened and ground-finished as standard; it was of the usual Colchester V-and-flat type with separate pairs of ways for the carriage and tailstock. It was available in two lengths that gave either 25 or 40 inches (635 mm and 1000 mm) between centres but wisely could not, because of its size and very high top speed, be ordered with a gap. The headstock gears were lubricated by oil splash, from a supply within the base, with the system improved by the fitting of a "distributor tray" in the roof of the headstock that collected the flung up oil and fed it though pipes to ensure that it reached the right places; the same oil was fed, unfiltered, to the "Gamet Super Precision", pre-loaded and self-adjusting taper roller bearings. The 1.625" (40 mm) bore, 4-in D1 Cam Lock nose spindle was especially rigid and had been designed in conjunction with the British Machine Tool Industry Research Association.
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The oil-bath dual Metric/English screwcutting gearbox was totally enclosed and fitted with hardened and ground gears throughout. Three conventional levers, and one that moved through an unusual, 8-position vertical gate, swapped the ratios. The box was able to generate a wide range of pitches without dismounting or changing any of the changewheels the range comprised: 39 Metric from 0.2 mm to 14.0 mm; 18 Module from 0.3 to 3.5m; 45 English from 2 to 72 t.p.i. and 21 Diametral from 8 to 44 D.P.  The range of sliding feeds varied from 0.001" to 0.040" (0.03 mm to 1.0 mm) and surfacing feeds (at half the sliding rate) from 0.0005" to 0.020" (0.015 mm to 0.5 mm) - all per revolution of the spindle. Both the leadscrew and the powershaft were protected by special shear pins, the specification of which was outlined in the manual with strict instructions not to vary the material used.
The apron was doubled-walled, with all the shafts supported on bearings at both ends and the base closed off to form an oil bath. Although not fitted as standard, or even on the Options List, some Student 1800s have been found fitted with an apron-mounted, hand-plunger-operated pump (as fitted to the master 2500) that fed lubricant to the bed, cross slide and cross slide feed screw.
The power feeds were selected by a push/pull button and positively engaged by a lever that allowed the feed to be instantly stopped regardless of how deep the cut was. A thread-dial indicator was fitted as standard to the right-hand apron wall. The carriage traverse handwheel could be pulled out to disengage it when power feeds were being used - though it is unclear if this was a standard fitting during all the years of production.
Machined all over, the compound slide rest was fitted with taper gib strips that allowed a very precise fit to be obtained while giving far superior support in comparison with the cheaper "loose-strip" type. The 8.25-inch travel cross slide was especially wide and fitted with a cross-feed screw that could be adjusted to reduce backlash; although the slide was devoid of T slots and tapped holes - and so appeared, at a glance, to be incapable of mounting any accessories - the edges of the slide were machines to accept slide-on T-slotted and plain blocks that could hold a variety of items including hydraulic profiling units, and parting-off and other special tools. Although the top slide could be rotated through 360 degrees the standard toolpost was, unfortunately, a barely-adequate and very simple slotted block able to hold just one tool.
With a No. 3 Morse taper socket, the (set-over) tailstock barrel was hardened and engraved with metric and inch graduations; unfortunately there was no micrometer collar on the feed screw.
The stand was constructed around two cast-iron plinths with a slide-out chip tray between them. Surprisingly, the stand offered no storage at all, in either plinths or under the centre section, even though this would not have been difficult to engineer and would have made life a lot easier for the operator..

The speeds were varied by push buttons, that activated motors driving threaded rods that caused the pulleys to be moved closer together or further apart, whilst the set geared ranges were engaged by a single handle integral with a large dial on the face of the headstock.

Besides the expanding and contracting pulleys the variable-speed drive system employed three "geared" speed ranges that allowed seamless bands of speeds to be selected between 20 to 120 rpm, 90 to 540 rpm and 500 to 3100 rpm and ensured that maximum torque was available at the slower revolutions.