From Martyn Todd
Your patents column mentions the problem of stripped threads in nuts and bolts
(This Week, 1 May, p 11).
Henry Royce (the engineer of the short-lived but
famous partnership) knew that mechanics, with the best of intentions, put all
their effort into tightening nuts. The aero engines that he designed in the
1930s and 1940s had arrays of small studs and nuts to spread the load over the
whole of mating surfaces between light alloy castings. Most of these fastenings
were 2BA or 3BA.
Tired of expensive reworking of stripped threads in castings, Royce measured
the average force that a well-intentioned fitter exerted. He then used the
maximum torque allowed on the range of BA thread sizes to calculate the length
of lever that, when the average fitter force was applied, resulted in the
desired torque. The resulting set of spanners was made and issued to all
aircraft engine fitters. Compared with normal spanners they were extremely short
of shank and had only one set of jaws each.
When I was an apprentice with Rolls-Royce in 1968 there were a few fitters
who still had and prized their Royce BA spanner sets. I suppose a full set today
would be worth a small fortune.
Lisburn, Northern Ireland
