email: tony@lathes.co.uk
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Colchester Student & Master
Mk.1 & Mk.2 Lathes

& Colchester Dominion Lathes

Screwcutting and Power Feeds
High quality Handbooks & Parts Manuals are available for the Mk. 1 & Mk. 2 Models
Headstock & Gearbox Pages  Carriage Pages
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   Magnum   Serial Numbers    Outline of Colchester Range as Text Only   Factory 
Testing  Catalogue Covers  Early Drive System  Colchester 1909/14  Colchester 1919



Continued from this page:
Screwcutting and Power Feeds
Both Student and Master were available with either screwcutting by changewheels or (and by far the most common specification) a dual inch/metric screwcutting gearbox. However, detailed differences in the screwcutting were noticeable over the years, with the first Student models listed with either a gap or straight bed and with either changewheel or screwcutting gearboxes in inch or dual inch/metric versions. The range was arranged as follows: "Cub", "Penny", "Colt" and "Dime" The Cub was a gap-bed lathe with screwcutting by changewheels (and a 2-speed gear on the leadscrew); the Penny (later called the Dominion) was a straight-bed model also with changewheels; the Colt had a gap bed and a dual inch/metric quick-change screwcutting gearbox with 36 inch pitches from 4 to 60 t.p.i. and 11 metric from 0.5 to 6 mm. A special feedbox was available for the Colt (at extra cost) that had no metric capability and incorporated pitches of 5.75, 11.5, 23, and 46 threads per inch, but at the expense of omitting the 7.5 15, 30 and 60 pitches. The Dime was another straight-bed lathe with a screwcutting gearbox having 36 inch pitches - though at extra cost the dual metric/inch box from the Colt could also be fitted.
Later versions of the Student, and all models of the Triumph, had screwcutting gearboxes able to generate 45-inch pitches from 4 to 120 t.p.i. and sliding 45 feeds from 0.0025" to 0.068" with cross feeds set at exactly half those rates. 12 metric pitches could also be obtained (by just lifting a small lever on the face of the gearbox) of 0.25 to 6 mm pitch.
Just to confuse matters, the straight-bed, plain saddle model was also known as the  "Dominion" and was listed in some catalogues as either a 6" x 24" or 6.5" x 36" model. Although at extra cost it could be fitted the dual inch/metric gearbox it was fitted as standard with either changewheels or an English-only screwcutting gearbox with two extra pitches of 11.5 and 23 t.p.i. By the mid 1960s a rare "Continental" all-metric model was also listed, a machine easily recognised by a distinctly different gearbox fitted with a Bantam-like joy-stick control lever on its front face. Both the Dominion and Continental boxes could be persuaded (at some expense) to generate metric and English threads respectively by means of translation changewheels.
Unlike their Harrison competitors, the changewheel models had no convenient and easily-operated 3-speed gearbox to allow a quick change in the rate of power feeds, instead a double gear on the feed shaft could be slid by hand 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 changewheels were guarded by a cast-aluminium cover secured, not by a hinge, but on studs; although this arrangement was perfectly satisfactory for use on the gearbox-equipped models on the changewheel version, where access to the gears was required for every change of thread, the design was a considerable inconvenience.
All Mk. 1 and Mk. 2 Students and Masters had a 6 t.p.i. Leadscrew (with no metric alternative) that was used only for thread cutting and not power feeds - normally it was left disengaged by positioning the inch/metric thread-selector handle in its middle position. Power sliding and surfacing (along the bed and across) was provided by a separate power rod and fitted to all models with, on the Mk. 1, both selection and engagement by a single lever that was slid along the lower edge of the apron and lifted (and locked) into one of two slots. Releasing the feeds merely required the lever to be pressed downwards; unfortunately, the heavier the cutting load the greater the effort required to disengage it, but at least it was a positive in-out action and did not require (as on so many older lathes) a knob to be unscrewed to release a clutch.
The apron was double walled but open at the bottom, so precluding any chance of the gears being run in oil and requiring the operator to periodically supply lubricant. Unfortunately, in many cases, this simple task was ignored and allowed such severe wear to take place on the inside of the worm-wheel carrier that the whole assembly dropped so low that engagement became impossible.
A few Mk. 1 lathes had a ball-bearing "clutch" incorporated in the feed-shaft to protect the apron against overload damage - a mechanism that could be used to advantage in combination with bed stops to provide a reliable, automatic means of turning repeated shoulder lengths in production work. All models had a shear pin incorporated in the top gear of the screwcutting drive; when the leadscrew and power shaft refuse to rotate, this is the first place to look; if the pin has broken replace it with one made from aluminium, not steel. All versions were provided as standard with a thread-dial indicator built into a rather perfunctory cast-iron leadscrew guard.
Just before the introduction of the proper Mk. 2 the Mk. 1 was updated (as the jokingly-called  "mark-one-and-a-half") with a completely redesigned and far safer apron. For the first time the bottom of the assembly was enclosed, allowing the gears to run in an oil bath, though oddly not all models had the sight-glass level indicator showing this feature was fitted. The function of selection and engagement of feeds was separated with a push-pull knob, protruding from the middle of the aprons face, selecting the feed and with engagement by flicking up and down a lever at the bottom of the apron - in the long-established Harrison manner. However, inside the apron the Colchester mechanism was quite different, and incorporated an important safety feature: an automatic feed knock-off for when cutting forces become too high. This was achieved by mounting the engagement mechanism on a separate carrier that transmitted drive to the carriage through a spring-loaded ball-bearing running up a ramp. To adjust the spring pressure (and so the release point) the engagement lever was given a threaded barrel (often found jammed tight) that the operator could screw in or out. By using a combination of a correctly-adjusted lever together with a bed stop a useful automatic-disengage could be set up by which means repeated runs could be made up to a shoulder.
Continued below:



Continued:
Saddle and Compound Slide Rest
On gap-bed lathes the saddle carried T-slotted wings (a "boring" saddle) and the straight-bed models wings with plain, ground tops; the main castings were all pre-drilled and tapped to accept such things as hydraulic-copying, taper-turning and other attachments but (surprisingly), until as late as 1959, felt bed wipers were an extra-cost option. The compound slide was entirely conventional, but well made, with stiff gib blocks screwed into the roof of the full-length cross slide with adjustment by screws through the sidewall. These side and top screws are time-consuming to adjust but, once set, the slide remains play-free for hundreds of hours. One potential weakness concerns the circular T-slot, machined into the cross slide, and on which the top slide rotates. The two T bolts securing the slide are small, and easily overlooked, but they must be kept tight for, if the cutting tool digs in heavily and the top slide is loose, the bolts may well smash the slot and wreck the (very expensive) slide.
Most lathes had either single inch or Metric zeroing micrometer dials but all could be fitted, at extra cost, with finely engraved dual inch-metric units each with a rather fragile cast-aluminium sliding cover. Both inch and metric feed screws and nuts were fitted, the type used on a particular lathe being denoted by the graduations of the outer ring. The cross-feed nut was adjustable to reduce backlash and it appears that both early and late types were used. The early was in three parts and held to the slide by a large exterior nut with an oil nipple in its centre; two of the nut's sections were threaded, with cotter pins passing through that engaged against a wedge to press them apart. The later version, which can be recognised by three Allen screws arranged in a line, was also in two parts but with the inner faces formed at an angle with a wedge between them. With the front screw fixed, that at the back could be slackened to allow the middle screw to be tightened onto the wedge and the two halves moved slightly apart and backlash eliminated.
Tailstock
The tailstock on early versions of the Student and Master had a barrel locked (by that pet hate of the writer) a slit in the casting closed down by the action of a screw thread. Fortunately, later machines were fitted with a barrel increased in size to take a No. 3 rather than the original No. 2 Morse taper and with a proper "split-clamp" that acted directly on the barrel at a point just before it emerged from the casting - a system that always works no matter how worn the components become. The bore of the casting was honed and the barrel (marked with both inch and mm graduations) ground to get as good a fit as possible and ensure a long and accurate life. The top of the unit could be offset on the sole plate for simple taper turning.
Student and Master Mk. 1 and Mk. 2 - Essential Differences
The most important differences between the Mk. 1 and Mk. 2 machines, apart from the apron, are found in the headstock where new German-manufactured gear-cutting machinery allowed the use of much quieter and smoother running gears. The obvious recognition points of a Mk. 2 are its angular styling and distinctive, flat, ribbed, aluminium headstock cover - a handy place to hold spanners, tools and small jobs in progress. Another safety feature of the MK. 2 was the "gate" on the high-low speed selector handle on the front face of the headstock. Before the lever could be moved it had to be pulled out and could not be accidentally knocked into neutral.
There was also an interim model (jokingly referred to as the "Mark one-and-a-half" with round headstock but the safety apron
The Student is around 61 inches long, 30 inches wide and weighs approximately 1372 lbs. (625 kg). The Master is just one foot longer and weighs approximately 1400 lbs. (635 kg).
Clausing-Colchester
A version of the lathe was sold in the USA and Canada as the "Clausing-Colchester 13-inch" this lathe had an English-threads-only gearbox but a hardened bed as standard, straight or gap, with a choice of 24" or 36" inches between centres and, on the Mk. 2 versions, an improved version of the single-lever "Safety" apron that was modified to include an oil bath in its base..



Handbooks & Parts Manuals are available for the Mk. 1 & Mk. 2 Models
Headstock & Gearbox Pages  Carriage Pages

Colchester Student & Master
Mk.1 & Mk.2 Lathes

& Colchester Dominion Lathes

Screwcutting and Power Feeds

COLCHESTER HOME   Bantams Original   Bantams 800, 1600 & 2000 Modern   
Chipmaster   Student 1800   Mascot 1600  Student/Master Mk. 1 & Mk. 2   
Student 3100   Master Original 1930s/40s  Master 2500   Colchester 1920s
   Triumph Mk. 1 & Mk. 2   Triumph 2000   Mascot - 1950s   Mascot 1914-18  Mastiff 1400   
   Magnum   Serial Numbers    Outline of Colchester Range as Text Only   Factory 
Testing  Catalogue Covers  Early Drive System  Colchester 1909/14  Colchester 1919

email:tony@lathes.co.uk
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