Fine-pitch gearing usually has teeth of diametral pitch 20 to 200. BS 978 is a British Standard series that discusses specifications for fine pitch gears.
BS 978-1 is the first part of the BS 978 multi-series, and relates to involute spur, helical, and crossed helical gears, having diametral pitches finer than 20, in four accuracy grades. Examples of applications are:
Class A. Astronomical apparatus and scientific instruments; colour printing machinery; control systems (when multiple trains of gears are involved this grade would generally be used for low-speed components where the effect of positional accuracy is important).
Class B. Navigational instruments; high-speed components of control systems where quietness and smooth running are essential; machine tool speed control; photographic instruments.
Class C. General-purpose instruments; accounting and calculating machinery; counters; clockwork mechanisms.
Class D. Textile machinery; switch operating gear; clockwork mechanisms where accuracy is not the primary consideration.
BS 978-1 on involute spur and helical gears specification is useful for:
Users of involute spur and helical gears such as:
An involute gear has the profiles of its teeth in the shape of an involute circle. Helical gears are used increasingly often as power transmitting gears.
BS 978-1 walks you through aspects such as design details, the accuracy of gear blanks and gears, limits, and tolerances of assembly, Information given on drawings.
BS 978-1 is useful to control and assess elemental errors, and also to provide an adequate basis for accurate manufacture of the related parts.
BS 978-1 guidelines help you to follow best practices when designing and manufacturing fine pitch gears. This lets you demonstrate the efficiency and reliability of your pitch gears.