Colchester Student & Master Mk. 1 (see below for Mk. 2)
Drive System and Spindle Speeds
Although the option of fitting the Master (but not Student) to old-fashioned cast-iron plinths (and rigged for drive to overhead line shafts) remained until as late as 1960, the vast majority were mounted on the same type of full cabinet stand employed as standard for the Student. Both models used a 1425 r.p.m 3 h.p. 3-phase motor mounted on a large adjustable plate inside the headstock end of the stand, with drive to the headstock pulley by either a wide flat belt or double V-belts. Although efficient, the twin V-belt drive can cause problems and, should the geared headstock on any V-belt drive Colchester make a knocking, rattling or rumbling sound, the cause may not be worn gears or bearings but unequal-length drive belts "fighting" each other. To check, try running on one belt to see if the headstock runs more smoothly; if it does, fit a second belt, run a chalk line across the two, start the machine for a few seconds and check that the belts are still in line; it's almost certain that they will not. Should it prove impossible to buy a pair of genuine "matched" belts, either buy a dozen standard ones (and find the two closest in length) or, even better, use a modern T-link belts. A further point on V-belt drives (and relevant to all applications) is the effect of belts with sections worn thin: as the worn sections fall into the pulleys and the thicker sections ride up them this effectively varies the gear ratio and causes the drive to speed up and slow down. The end result is vibration, with detrimental effects on the longevity of the machine and often a poor surface finish on workpieces. Fitting new V-belts can often make a significant different to how smoothly a machine tool runs.
The range of spindle speeds differed slightly according to the year of manufacture. Machines produced immediately prior to the 1950s Student and Master usually had a rather slow range, from 20 to 550 r.p.m., with the new models much faster at 52 to 1000 r.p.m. and later further improved to 54 -1200 r.p.m., both with eight speeds. Two-speed motors were a costly and hence infrequently fitted option, but gave sixteen speeds from 34 to 1500 rpm or even, on some very rare, special-order models, 17 to 750 rpm.
Another (rarely-encountered drive configuration) drive used a two-speed Brook Compton motor and an electrically-actuated disc brake. On this model the normal "plug-in" electrical control panel on the front of the stand was replaced by a line of four switches and a stop button immediately beneath the front edge of the chip tray. This version also had a "third-shaft" control rod fitted below the powershaft and operated by a lever attached to the right-hand end of the apron - an arrangement not unlike that employed on a Mk. 1 Bantam. At the right-hand end of the rod was a box, containing a cam that operated the special Klockner Moeller reversing switchgear. On some of the Klockner-equipped lathes an unusual (and presumably heavier-duty) main spindle arrangement has been found where, instead of the components being located by a single key a much heavier fully splined shaft was used with the sliding components engaged by dog clutches. If you have one of these models the writer would be interested to hear about it.
As standard, both Student and Master were fitted with a spindle brake, operated by a horizontal lever (on the headstock's front face) that also acted as a motor switch. To start the lathe the lever had first to be pulled out against a safety spring (designed to prevent accidental engagement then lifted up (this mechanism was later more fully developed with a proper external gate and called "Safti-lok" by the makers). The lathe was stopped by returning the lever to its central position and then pressed down further to operate what was, when the lathe was new, a powerful drum brake built into the headstock input pulley - though Colchester's assertion that this stopped the spindle "instantaneously" revealed that the handbook writer had either not used the lathe - or a dictionary. However, the brake was very useful, especially to those being paid on "piece-work" who would otherwise have had to watch the seconds tick away as 120 lbs of cast iron came slowly to rest from top speed. It's worth knowing that, after many years of neglect, the headstock brake first becomes ineffective and then (usually following ham-fisted attempts to improve it) may start to interfere with the free running of the spindle. If your Colchester shows signs of slowing down or even "seizing up" after a few minutes running, the brake assembly is the first place to look. If shoe linings are badly worn most industrial areas have a friction-materials specialist who can bond on new material. Unfortunately, unlike the competitor English Harrison lathes, a combined clutch and brake was not fitted as standard but a multi-plate clutch manufactured by "Matrix" used instead. This was a very well designed, easily adjusted and reliable device - and one that should still be working perfectly when any lathe fitted with it is otherwise worn out. Although a 3-phase motor is very robust, and will put up with a good deal of abuse, its 1-phase cousin is a relatively delicate thing and best run near its rated capacity all the time (i.e. worked nearly flat out); if such a motor is switched on and off frequently against "no load" the windings will be damaged and, if run through a cycle where it is started, worked briefly, stopped and started again, the capacitor will fail prematurely. To prevent this happening on 1-phase (and DC) equipped lathes Colchester fitted a Matrix clutch as standard - even though it meant sacrificing the benefits of a brake. On clutch-equipped lathes the stop/start handle was adapted to open and close the plates with a separate electrical switch on the front control panel. In normal use, once started, the motor was left running for as long as possible, the spindle being controlled by the clutch. If you come across one it is worth knowing that on early clutch-equipped lathes the safety-spring loading on the start handle was not fitted - and accidentally brushing against it can start the lathe running. If needed, a clutch can be retrofitted to a used machine - but make sure you acquire all the operating linkages as well. An electrical reversing switch was (at first) an optional extra and, if chosen, was neatly built onto the hub of the stop/start lever and worked concentrically with it.
The 1.5" bore No. 3 Morse-taper headstock spindle (bushed down to No. 3 Morse from something close to, but not actually, a No. 5 Morse) carried an American Type L (long-taper) nose - this, for the benefit of readers unfamiliar with the world's first widely-adopted safety spindle fitting, consists of a large screwed ring (held captive on the spindle's tapered and keyed nose), with a matching thread taper in the chuck backplate. Unfortunately, the various sizes of this fitting are easily confused by the inexperienced; the Student and Master both used the L0 (L-zero) size, while larger models used an L1 or L2, (etc.) - and smaller machines the L00. If you have a sample with which to make ca omparison, all is well, but it is very easy to believe that the fitting either side of the one you need is correct. If you look carefully the size is (usually) stamped somewhere on the backplate; failing this - do your homework, and use a ruler. The 8-inch 3-jaw chucks commonly fitted to these lathes when new were high-quality ones, with an integral backplate, made by in the UK by Burnerd. Today these special chucks are no longer available, but new standard ones can be fitted to a separate backplate - however, don't be tempted to use a cheap, unbranded import; the stresses encountered on top speed when holding large job are considerable. Instead, you are welcome to email for details of quality replacements that we can recommend.
The forged, high-tensile steel 1.5-inch (38 mm) bore spindle ran in Gamet "One-micron Precision" bearings - Gamet being a separate company within the controlling 600 Group who also supplied many other machine-tool makers. A small pre-load was applied to the bearings by spring pressure - that immediately behind the spindle nose being a double-row type with a single-row at the rear. Gamet claimed that the "unique design ... ensures minimum temperature rise and accurate running of the spindle throughout the speed range"
All the gears were hardened and honed with the 8 spindle speeds changed by two levers on top of the headstock and one, for high and low speed ranges, on the front. Unfortunately the gears of the Mk. 1 were never entirely silent, even when new (though individual examples did vary widely with some even being relatively "quiet"), and a "noisy" headstock can almost be expected on these machines. The Mk. 2, with gears cut on newly-installed German machinery, were much better but even so, prolonged use inevitably leads to a noisy headstock - the worst offender usually being that speed immediately below the highest. In an attempt to quieten the headstock some owners have mistakenly resorted to using a thick oil instead of the thin hydraulic lubricant that should be used; the heavier oil will defeat the spiral oil-return grove (built into the bearing cover plate on the left-hand end of the spindle) and appear to be almost 'sucked out' as the machine runs. Small oil leaks from the headstock are almost a feature of these lathes and, providing the oil is kept topped up, should result in no harm; the time to worry is when the oil stops coming out - the reservoir will be empty. If the rest of the machine is serviceable, but the headstock gears are in very poor or damaged condition, it might be worth removing the headstock cover and arranging a V-belt drive direct to the middle or end of the spindle from a variable-speed, inverter-controlled 3-phase motor; although a crude solution this has been known to extract another decade's life from some machines. On Student and Master lathes the headstock pivots on a dowel, fitted to the back corner nearer the tailstock and can, as a consequence, be adjusted. At the left-hand end of the headstock, sitting between the bedways is a block with pointed-end Allen screws that can be used, by slackening one and tightening the other, to swing the headstock slightly. Before doing this the holding down bolts, which have a little clearance round their holes, should be slackened but not loosened completely. An accurate test bar will needed (it fits directly into the headstock spindle), together with a high-quality DTI used to assess the alignment. Alternatively, test cuts can be taken between minute amounts of adjustment with the holding-down bolts fully tightened, of course.