Late-model English gearbox Chipmaster in its two-tone finish.
The actual centre height was 5.75"
The 15/16" (35 mm) bore headstock spindle ran in Gamet "micro-precision" taper roller bearings (made by another company in the Colchester group) with the lower part of the speed range obtained through hardened and ground gears. Because the high-speed range was directly by belt, and the comparatively short and rigid spindle so well supported, the lathe had a well-deserved reputation for being able to produce unusually smooth surface finishes. An American-type D1-3" Camlock nose fitting was used, that allowed the lathe spindle to be safely reversed at high speed, and the spindle was sleeved with a hardened 4.5 Morse taper short sleeve bored to accept a standard No. 2 Morse taper centre (this fitting is often missing, and expensive to replace - though sometimes cheaper replacements are available). Unfortunately, chucks with an integral D1-3" mounting are pricey to manufacture and it is often cheaper (although with only a little saving) to mount a replacement chuck on a new Camlock backplate. Certain precautions are necessary 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 them - it is absolutely essential to read the maker's instructions on this point if you are unsure.
All Chipmasters were fitted with a full screwcutting gearbox that offered a greater range of threads than the Bantam. The drive to the gearbox was by changewheels for screwcutting or, for extra-fine feeds, via a V-belt on early lathes and a toothed belt (for a more positive drive) on later models. A lever on front of the headstock - annotated with a belt and gear symbols - selected the appropriate drive. For many years only an Imperial (inch pitches) gearbox was offered, with conversion gears to cut metric threads. However, from the end of 1970 onwards a version with a dedicated metric gearbox was offered. At extra cost the box could be provided with inch-pitch conversion gears, the set comprising: 20t, 24t, 28t, 30t, 36t, 42t, 44t, 46t, 52t, 56t, 57t, 60t, 65t, 69t and 70t. The Imperial box can be recognised by its sliding lever control with indent positions (outboard of the box to the right) whilst the metric box was similar to the unit as used on the Bantam with a joy-stick control in addition to levers. At the end of 1970 an "all-metric" version of the Chipmaster became available and carried the identification "Continental". Fitted with the appropriate translation changewheels English to metric and metric to English screwcutting conversions were possible.
Identical to that used on the Colchester Bantam, the tailstock spindle was equipped with a zeroing micrometer dial and has been found engraved with inches, mm and dual inch/metric markings. Listed as having a No. 3 Morse taper (and all examples seen by the writer have been on the size) some reports indicate that a slightly large size was used, though it's specification remains, for the moment, unknown.
Once in private hands, after hard industrial service, the Chipmaster could suffer problems connected with the drive system; the variator has always been enormously expensive to overhaul and, if it started to produce any untoward noises, they would rapidly assume the volume made by a tumble-drier filled with bell bearings - and if you didn't stop using the lathe, that's more or less what the variator turned itself into. If you are thinking of buying a Chipmaster it's absolutely essential to hear it run - if the seller cannot arrange this or has "disconnected the electrics" assume that the variator is finished and value the machine accordingly - no matter how smart the paint may look. However, if the variator on the lathe you are inspecting appears to be faulty, don't worry, you don't really need it. Dump it into the scrap bin (take it apart first and have a look, just in case) and couple the 3-phase drive motor to a 1-phase to 3-phase inverter. Inverters, unlike simple capacitor-based "converters", provide a variable-output frequency (giving variable-speed drive) and hence obviate the need for any mechanical speed-changing device. They are also inherently reliable - and prices keep falling. The clutch fitted a standard to all Chipmasters not only makes the machine much more pleasant to use but also gives any 1-phase conversion (or electronic control, system) a much easier time.
Some few years ago a friend bought a new, still-crated Chipmaster which had lain forgotten in a store (that's another story). He removed the variator and arranged for the spindle to be driven directly from the electric motor through a 3-phase to 3-phase variable-speed electronic controller. He over-rated it, to give a top speed of over 4000 rpm, and rigged the DC injection braking to make it stop it in a couple of rpm or so (the first time he tried it the motor stopped dead, but the inertia of the rotating parts stripped the drive belt of its teeth.). This machine ran reliably for years, turning out thousands of critically-dimensioned and beautifully-finished aero-space components. For some export markets the Chipmaster was marketed wearing Harrison badges as the Model 10-AA.
Although it took Colchester a little time to get the drive system right, the rest of the lathe (apart from the drive system) remained essentially unchanged throughout its production life - proof that the original design was well thought out and the concept - a machine that could be marketed as a lathe suitable for toolroom, production and general workshop duties - was absolutely right. Although the main mechanical parts of the lathe stayed the same the variator did not - this going through several undocumented changes with which the handbooks issued did not, sadly keep pace. The main difficulty appears to be getting the oil level correct and its absolutely essential to put in only the amount stated on the body of the unit (if so marked) or 1 pint if the data is missing. Completely filling the unit will cause damage, as will the incorrect oil. The numbers assigned to the correct oils have changed over the years, as follows, the last named being the oil to use):
Headstock: Shell Tellus 15 = Morlina 10 = Morlina S2 BL 10
Gearbox: Shell Tellus 33 = Tellus 68 = Tellus S2 M 68
Variator: Shell Vitrea 21 = Vitrea 22 = Process Oil PB 33 = Morlina S2 BL 10
From this it can be seen that headstock and variator oils are now the same - and consistent with recommendations from Allspeed UK say the manufacturers of Kopp variator (and Kopp variator oil)..