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One of Mikron's smallest and most popular gear hobbing machines, so successful was the Type 79 that it remained in production from the mid-1930s until the late 1980s. Designed for smaller work in clock, instrument, typewriter, mechanical calculator and optical industries, it was able to manufacture spur gears and pinions and items requiring a precision tooth form such as ratchets, clock escape wheels and worms and knurls, etc.
When making involute gears, simple hobs were used - each able to cut all numbers of teeth of the same D.P. (diametrical pitch). For cycloidal gears, Mikron could supply hobs made individually for each number of teeth. When special tooth forms were required - such as gears of the stub or saw-tooth form and for sprockets, etc. - again the factory offered a service to make and supply these to a customer's particular requirement.
The largest gear that the Type 79 could cut was 19/16" (40 mm) in diameter with a length of 11/8" (28 mm); tooth numbers 6 to 390 could be accommodated and 28 D.P. the maximum that could be generated.
Later models of the Type 79 were also capable of running an automatic cycle, the handwheel-operated clutch previously fitted being replaced and consequently "dead time" reduced - lifting the starting lever engaged both the drive motor and feed and, at the end of the job, the hob slide returned to its initial position. Once set up, the machine could be operated by unskilled labour, there being no need to make any adjustments whatsoever as the job progressed. Feed rates and cutting speeds could be set individually by the use of chagewheels, this allowing the surface finish required to be set accurately for any particular material.
Fitted as standard was an ordinary mechanical tailstock but, as an option, a quick-acting pneumatic type could be supplied, this shortening both job mounting and removal times and available in four versions to suit from the light to heavy work: the Type 80.01.01/0 hand-actuated with clamping pressures from 15 to 75 kg/cm²; the Type 80.01.03/0 hand-actuated with clamping pressures from 50 to 120 kg/cm²; the Type 80.01.05/0 foot-operated with clamping pressures from 15 to 75 kg/cm² and the Type 80.01.07/0 foot-operated with clamping pressures from 50 to 120 kg/cm².
A further option was another pneumatic-control device (Part 20.21.00/0) that allowed all functions of the machine to be automated - a less expensive alternative being Part 20.24.00/0, a semi-automatic attachment whereby the machine was started by hand but the cutting feed engaged under pneumatic control. Although these units could be retrofitted, it was recommended that they be factory-fitted before delivery.
The hobber was always supplied complete on its own cast-iron stand that held the drive motor together with built-in switchgear. Fitted as standard was a single-speed, 0.5 h.p. 3-phase motor with, as an extra-cost option, a two-speed that allowed hob speeds of up to 3200 r.p.m. to be used - these being an advantage on small work when a particularly fine surface finish was required.
To use the machine, work-holding arbors were required, these sold by Mikron in a variety of designs including the TU-79, a boxed set of the universal type that offered the possibility of 158 different clamping combinations. Other arbors included ones to hold pinions, a spring-chuck type with a stop and work-arbor revolving portion, one for "wheels" (the clockmaker's term for gears) that were clamped through arms and one with a clamp nut and a stationary, carbide tipped centre.
Like the Company's lathes, the Type 79 was given a most remarkable and durable finish, a metallic anti-corrosion coating applied to castings that were of a particularly fine finish and very low porosity. There was no paint to chip and the finish was noted for being stable over many years of hard use.
Until the 1980s, a leading UK distributor of Mikron machine tools was Henry Turner Ltd. of 55 Upper Tooting Road, London from where, in 1979, a new Type 79 could be purchased for between £1750 and £2500, plus VAT. In 2021 Turner were still trading, from Kenley, in Surrey, but the shop in Tooting now sells cloth….
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