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The Millionaire - The setting mechanism

The setting mechanism on the early Millionaires used a series of horizontal sliders. Although simple and direct in operation, the slider mechanism was rather tedious to set accurately. Later machines with a keyboard setting mechanism offered quick and accurate setting, but with a considerable increase in complexity. This page describes both arrangements.

The slider mechanism (25kb) The slider mechanism.

The slider mechanism is built on a 2.5mm brass panel that measures 205 x 133mm. The sliders are 20mm apart, and move through 9 steps of 7.5mm (the same as the cross-shaft and rack spacings). The sliders are held in the set position by flat detent springs which engage with grooves cut into the underside of the plate.

The brass selector forks straddle the cross-shaft pinion in two directions, holding the selector arm vertical and allowing the pinion to be moved into engagement with any of the ten racks.

The numeral wheels along the front of the plate provide a straight-line readout of the slider setting. Each wheel is driven by a perforated steel band which loops between a toothed pulley at the front and an idler at the rear of the panel. The band is only 0.1mm thick, and is attached to the upper end of the selector arm.

The completed slider setting mechanism weighs 1.3kg.

The Keyboard (34kb) The keyboard.

The keyboard assembly uses the same panel space and mounting points as the slider mechanism. The body of the keyboard measures 187 x 133 x 25mm, and sits above the level of the top panels of the machine.

The 8 key columns are still on 20mm centres, but the keys within each column are spread out to 13mm centres to occupy all of the space available. The keys are numbered from back to front to correspond with the layout of the racks. There are no zero keys, but a clearing button at the front of each column performs the same function. There is a larger master clearing button at the front left-hand side. The motorised control mechanism can lock and clear the keyboard via two internal controls mounted under the left-hand end.

The completed keyboard assembly weighs 2.33kg, not including the selector mechanism (described below).

Keyboard internals (29kb) Keyboard construction.

The keyboard is built up in stages on two C-section channels at the front and rear. The top and bottom plates are separate strips of 2.5mm brass, mostly 20 x 133mm. There are thin brass cover plates on the ends and back of the assembly.

The identical brass keystems measure 46 x 6 x 2mm. Moulded and filled buttons are attached with screws at the tops, with steel pins to drive the selector mechanism rivetted to the bottoms.

The keystems are set into rectangular slots in the top and bottom plates, and pass through the ramped slots in the clearing bars behind. The clearing bars are milled from 5mm square-section steel, and are held forward by flat leaf springs behind the rear C-channel. The projection on the right-hand side of the keystem catches under the clearing bar to hold the key down.

The master clearing control operates a rocking bar inside the rear C-channel to operate all the clearing bars simultaneously. The master clear can be set to operate automatically at the end of each machine cycle (eg, during addition) by a control on the multiplier lever panel.

The keyboard is locked during the machine cycle by a sliding bar inside the front C-channel (not visible). The bar blocks the movement of the clearing bars, and so prevents the keys moving up or down.

Selector forks (27kb) The selector forks.

The selector forks transfer the movements of the keystems to the cross-shaft pinions below.

The five fork assemblies (all different) are cut away and overlapped along a 5mm steel shaft.

The forks engage with the cross-shaft pinions from alternate sides.

Selector forks installed (37kb) The selector forks installed.

The selector shafts are supported on two brass bearing plates. The front plate is attached to the two central pillars, while the rear plate is mounted on the rear cross-shaft bearing plate.

The tops of the selector assemblies are level with the tops of the central pillars and the under-side of the top cover plates.

Keyboard and selectors (37kb) The keyboard installed.

The keyboard mechanism mounts on the four main pillars at the centre rear of the machine.

The tabs on the tops of the selectors are restrained between the keystems and a strip of 2.5mm brass on the underside of the keyboard, so as to prevent the selector forks rotating on their shafts and becoming disengaged from the pinions.

With no keys pressed, the tabs are held securely between the pins on the adjacent keystems, with the pinions centred in the gaps between the corresponding racks.

When a key is pressed (eg key 4 as shown), the pin will press down on the ramp below. The selector will travel 3.5mm to engage the pinion with the corresponding rack. When the key is released, the pin will act on the upper ramp to pull the selector back to its home position.

Note that the energy to restore the selector comes only from the light spring on the keystem. Friction on the selector or pinion shafts may lead to problems with sticking keys.

The rear selector is slightly different because there are no zero keys. The back of the selector assembly is cut away (see the "Selector fork" illustration above) and is normally hard against the rear mounting plate. The selector can only move forward to engage with Rack 1. The zero rack is still present, but does not engage with the pinions on the key-set machine.

Keyboard underneath (33kb) The keyboard from underneath.

This underneath view shows the keystems set into the individual plates of 2.5mm brass, which are screwed and dowelled onto the front and rear channels.

The brass strips rivetted to the plates provide the lateral restraint for the selector assemblies, as described above.

The pin at the top left operates the keyboard locking mechanism inside the front channel. A similar control in the rear channel operates the master clearing mechanism.

Original text and images Copyright © John Wolff 2006.
Page created: 17 June 2006.

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