A later Model EE with the rectangular screwcutting chart on the face of the headstock.
By 1945 the swing had increased a little to 12.5 inches and a longer bed was listed (which, surprisingly, did not prove popular) admitting 30 inches between centres. Modifications to the screwcutting gearbox resulted in an improvement to 50 feeds (from 0.0005" to 0.016") with the threading range extended to cover 60 threads from 3 to 184 t.p.i. In 1970 further mechanical modifications were made including the fitting of a combined English/Metric screwcutting gearbox and beautifully finished dual English/metric compound-feed dials. The English/metric gearbox could generate 60 English pitches from 3 to 184 t.p.i and 50 metric from 0.25 mm to 11 mm.
With a standard spindle run-out of less than 40 millionths, and 30 millionths being an option (denoted by a headstock badge) the 113/32" bore headstock spindle runs in super-precision angular contact ABEC5 hand-matched, 60 mm ID bearings with the front being a non-standard and very expensive type fitted with a flange. The spindle is sleeved with an adaptor bush from its standard No. 12 Jarno to a No. 2 Morse taper and carries a 3"-D-1 Camlock nose with, as one useful option, an adapter unit containing an indexing gear and graduations to assist in the cutting of 2, 3, 4, 6, and 8 multi-start threads. Fitted with a substantial mechanical lock to ease the removal of chucks, the spindle is also provided with two safety devices: an electrical interlock to prevent it from running if accidentally engaged and a "Hi-lock" to prevent the engagement of backgear above 250 r.p.m. However, these features were only fitted on 'square-dial' machines, the 'round dial' having neither. Although the motor could be "plug reversed", that is, instantly changed from one direction of rotation to the other, this was also limited to no more than 250 r.p.m., a relay in the DC control box (called the anti-plug relay) pulling in and refusing reverse until the spindle stops.
Spindle-speed ranges have varied over the years with the option, on earlier lathes, of either 25 to 2000 rpm, 40 to 4000 rpm and another with a maximum speed of 3500 r.p.m. (though just the higher set was available on later machines). There were no mechanical changes to the models, the only differences between them being the use of different diameter belt sheaves (pulleys) and recalibrated tachometers. All versions of the lathe have been fitted with the 5 : 1 reduction gearing that, on later lathes, gives 8 to 800 rpm; because the gearbox is mounted on the motor (in the cabinet base) the headstock spindle is completely isolated from whatever vibration effects the drive might create. On early lathes the headstock-mounted tachometer was mechanically driven by a gear on the spindle (the only gear in contact with it) and could read in forwards rotation only. Later models were given an improved electrical counter able to read with the spindle running backwards.
As a point of interest it is not recommended to increase the top speed on 'round dial' machines. These have a headstock divided into three compartments: one each for the front and rear bearings and one for the gearbox. The bearings are lubricated by the simple expedient of letting them sit, partially submerged, in a oil bath - a system adequate for slower running, but not for continuously high r.p.m.. Later revisions saw the headstock opened up into one cavity and a splash system, together with pipes, used to carry oil direct to the bearings. The leadscrew and its drive gears are used only for screwcutting - the power for sliding and surfacing feeds being fed from the headstock to the gearbox by a flat, endless belt, driven from the end of the headstock spindle and tensioned by a jockey pulley. In standard form (and bearing in mind the differences between the older and newer models) 60 English threads are available of: 3, 3.25, 3.5, 3.75, 4, 4.5, 5, 5.5, 5.75, 6, 6.5, 6.75, 7, 7.5, 8, 9, 10,11, 11.5, 12, 13, 13.5, 14, 15, 16, 18, 20, 22, 23, 24, 26, 27, 28, 30, 32, 36, 40, 44, 46, 48, 52, 54, 56, 60, 64, 72, 80, 88, 92, 96, 104, 108, 112, 120, 144, 160, 176 and 184 t.p.i. Carriage feed rates vary through fifty changes from 0.0005" to 0.016" per revolution of the headstock spindle. A combined English-metric gearbox was also built and offered as an optional extra. It is possible to cut metric threads on the ordinary lathe, but only by unbolting the cover over the automatically-lubricated gear train and substituting the appropriate translation gears.
Some lathes have been found fitted with an ELSR (Electronic Leadscrew Reverse) threading system. These versions are easily recognised by a long rod running parallel to the top edge of the bed and their distinctly-different rectangular-form threading selector box on the front face of the headstock - this having, instead of just a dial selector on its front, a chrome-plated, left-to-right travel lever fitted on top. However, the ELSR was misleadingly named, for it did not actually reverse the leadscrew, its function was to provide a repeatable method of stopping the spindle at some chosen point for operations such as threading to a shoulder, or into the bottom of a blind hole, without the risk of over-running.
Instead of a headstock-mounted drum switch, a control rod was arranged to run from the threading selector housing through the top of the apron and from there to a support bracket fixed to the tailstock end of the bed. Keyed to the rod was a sliding motor-control lever, locked in place by a thumb-screw this acted as an adjustable stop. At the tailstock end the rod had a helical gear that turned on a white-metal bearing inside the support housing: moving the lever up and down caused the rod to slide left and right. At the headstock end the control rod had several grooves machined so as to form a circular rack, these engaging with a drum sporting two square cams off-set at 45° degrees to each other that operated, via a sliding rocker, forward and reverse micro-switches. There was also a small plunger fitted to the lower left of the threading control switch housing used as a safety device to lock the control rod in neutral and so avoid unexpected starts when working on the set-up. On top of the housing was a 3-position mechanical switch that slid the rocker (between the two square cams) to select left or right turning, or neutral, in which latter case neither cam was engaged and the spindle would not start. For normal turning and right-hand threading, the switch would be set to RIGHT. Pressing the control lever down caused the spindle to turn forwards and the carriage to move towards the headstock until it pushed on the lever and opened the contactor of the DC motor. The effect of opening the contactor was to bring into operation an electrical brake and this provided - if the same spindle speed was kept for all cuts- a repeatable stop. At low speed the system became even more effective and would give repeatability to within a fraction of a turn.